CN114430259A - Method for tuning resonator, method for forming cavity of resonator and filter - Google Patents

Method for tuning resonator, method for forming cavity of resonator and filter Download PDF

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CN114430259A
CN114430259A CN202210109109.3A CN202210109109A CN114430259A CN 114430259 A CN114430259 A CN 114430259A CN 202210109109 A CN202210109109 A CN 202210109109A CN 114430259 A CN114430259 A CN 114430259A
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acoustic wave
bulk acoustic
layer
sacrificial
mesa
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张家达
魏君如
翁国隆
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WIN Semiconductors Corp
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WIN Semiconductors Corp
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/15—Constructional features of resonators consisting of piezoelectric or electrostrictive material
    • H03H9/17—Constructional features of resonators consisting of piezoelectric or electrostrictive material having a single resonator
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
    • H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
    • H03H3/02—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
    • H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
    • H03H3/02—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks
    • H03H3/04—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks for obtaining desired frequency or temperature coefficient
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02007—Details of bulk acoustic wave devices
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02007—Details of bulk acoustic wave devices
    • H03H9/02086—Means for compensation or elimination of undesirable effects
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02007—Details of bulk acoustic wave devices
    • H03H9/02086—Means for compensation or elimination of undesirable effects
    • H03H9/02118—Means for compensation or elimination of undesirable effects of lateral leakage between adjacent resonators
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/125—Driving means, e.g. electrodes, coils
    • H03H9/13—Driving means, e.g. electrodes, coils for networks consisting of piezoelectric or electrostrictive materials
    • H03H9/132—Driving means, e.g. electrodes, coils for networks consisting of piezoelectric or electrostrictive materials characterized by a particular shape
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/15—Constructional features of resonators consisting of piezoelectric or electrostrictive material
    • H03H9/17—Constructional features of resonators consisting of piezoelectric or electrostrictive material having a single resonator
    • H03H9/171—Constructional features of resonators consisting of piezoelectric or electrostrictive material having a single resonator implemented with thin-film techniques, i.e. of the film bulk acoustic resonator [FBAR] type
    • H03H9/172—Means for mounting on a substrate, i.e. means constituting the material interface confining the waves to a volume
    • H03H9/173—Air-gaps
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/54—Filters comprising resonators of piezoelectric or electrostrictive material
    • H03H9/56—Monolithic crystal filters
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/54—Filters comprising resonators of piezoelectric or electrostrictive material
    • H03H9/58—Multiple crystal filters
    • H03H9/582—Multiple crystal filters implemented with thin-film techniques
    • H03H9/586—Means for mounting to a substrate, i.e. means constituting the material interface confining the waves to a volume
    • H03H9/587—Air-gaps
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/54—Filters comprising resonators of piezoelectric or electrostrictive material
    • H03H9/58—Multiple crystal filters
    • H03H9/60—Electric coupling means therefor
    • H03H9/605—Electric coupling means therefor consisting of a ladder configuration
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
    • H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
    • H03H3/02—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks
    • H03H2003/021—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks the resonators or networks being of the air-gap type
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
    • H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
    • H03H3/02—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks
    • H03H3/04—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks for obtaining desired frequency or temperature coefficient
    • H03H2003/0414—Resonance frequency
    • H03H2003/0421—Modification of the thickness of an element
    • H03H2003/0442—Modification of the thickness of an element of a non-piezoelectric layer
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H2009/02165—Tuning

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  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Piezo-Electric Or Mechanical Vibrators, Or Delay Or Filter Circuits (AREA)

Abstract

The invention relates to a method for tuning a resonator, a method for forming a cavity of the resonator and a filter, the method for forming the cavity of the bulk acoustic wave resonator comprises the following steps: forming a sacrificial epitaxial mesa on a compound semiconductor substrate; forming an insulating layer on the sacrificial epitaxial structure mesa and the compound semiconductor substrate; polishing the insulating layer by a chemical mechanical planarization process to form a polished surface; forming a bulk acoustic wave resonator structure on the polishing surface, wherein the bulk acoustic wave resonator structure is located on the sacrificial epitaxial structure mesa, comprising: forming a bottom electrode layer on the polishing surface; forming a piezoelectric layer on the bottom electrode layer; and forming a top electrode layer on the piezoelectric layer; and etching the sacrificial epitaxial structure mesa to form a cavity, wherein the cavity is located under the bulk acoustic wave resonant structure.

Description

Method for tuning resonator, method for forming cavity of resonator and filter
Technical Field
The present invention relates to a bulk acoustic wave filter and a method of tuning a bulk acoustic wave resonator of the bulk acoustic wave filter, and more particularly, to a method of having a bulk acoustic wave resonator capable of precisely tuning a bulk acoustic wave filter, a method of forming a cavity of the bulk acoustic wave resonator, and a bulk acoustic wave filter.
Background
Please refer to fig. 7A to 7D, which are schematic cross-sectional views illustrating process steps of a method for forming a bulk acoustic wave filter according to the prior art. In fig. 7A, a recess 74 and a recess 74' are etched in a top surface of a Silicon (Silicon) substrate 75. A sacrificial layer 77 is formed on the silicon substrate 75, and a Chemical Mechanical Planarization (CMP) process is performed to polish the sacrificial layer 77, so that the sacrificial layer 77 on the upper surface of the silicon substrate 75 is polished and removed, thereby forming the structure shown in fig. 7B. Wherein the recess 74 and the recess 74' are filled with the sacrificial layer 77. In fig. 7C, a first bulk acoustic wave resonant structure 70 and a second bulk acoustic wave resonant structure 70 'are formed on the upper surface of the silicon substrate 75, wherein the first bulk acoustic wave resonant structure 70 and the second bulk acoustic wave resonant structure 70' respectively have a bottom electrode 71 and a piezoelectric layer 72 with the same thickness, and wherein the first bulk acoustic wave resonant structure 70 and the second bulk acoustic wave resonant structure 70 'respectively have a top electrode 73 and a top electrode 73' with different thicknesses. Wherein the top electrode 73 and the top electrode 73' have a thickness difference 76. In fig. 7D, the sacrificial layer 77 filling the grooves 74 and 74 ' is etched, so that the grooves 74 and 74 ' become two cavities of the first bulk acoustic wave resonant structure 70 and the second bulk acoustic wave resonant structure 70 ', respectively. Since the top electrode 73 ' is relatively thick, the resonant frequency of the second bulk acoustic wave resonant structure 70 ' is lower than the resonant frequency of the first bulk acoustic wave resonant structure 70, and there is a resonant frequency difference between the first bulk acoustic wave resonant structure 70 and the second bulk acoustic wave resonant structure 70 ', which is associated with the thickness difference 76.
However, the difference 76 between the thicknesses of the top electrode 73 and the top electrode 73 ' is used to tune the resonance frequency difference between the first bulk acoustic wave resonant structure 70 and the second bulk acoustic wave resonant structure 70 ', and the tuning resonance frequency difference is achieved by the structural difference between the first bulk acoustic wave resonant structure 70 and the second bulk acoustic wave resonant structure 70 '. This not only complicates the manufacturing of the first bulk acoustic wave resonant structure 70 and the second bulk acoustic wave resonant structure 70 ', but also may affect the performance of the first bulk acoustic wave resonant structure 70 and the second bulk acoustic wave resonant structure 70'.
Accordingly, the inventors have developed a simple design that can avoid the above disadvantages and has the advantage of low cost to take account of both flexibility and economy.
Disclosure of Invention
To solve the problems of the prior art and achieve the intended effects, the present invention provides a method for forming a cavity of a bulk acoustic wave resonator, comprising the steps of: step A1: forming a sacrificial epitaxial mesa on a compound semiconductor substrate; step A2: forming an insulating layer on the sacrificial epitaxial structure mesa and the compound semiconductor substrate; step A3: polishing the insulating layer by a chemical mechanical planarization process to form a polished surface; step A4: forming a bulk acoustic wave resonant structure on the polishing surface, wherein the bulk acoustic wave resonant structure is located on the sacrificial epitaxial mesa, wherein step a4 comprises the steps of: step A41: forming a bottom electrode layer on the polishing surface; step A42: forming a piezoelectric layer on the bottom electrode layer; and step a 43: forming a top electrode layer on the piezoelectric layer; and step a 5: the sacrificial epitaxial structure mesa is etched to form a cavity, wherein the cavity is located below the bulk acoustic wave resonant structure.
In one embodiment, in step a3, the insulating layer is polished to expose the sacrificial epitaxial mesa, wherein the insulating layer between the bottom electrode layer and the sacrificial epitaxial mesa forms a frequency tuning structure, wherein the frequency tuning structure has a thickness, and the bulk acoustic wave resonator has a resonant frequency, such that the resonant frequency of the bulk acoustic wave resonator is tunable by adjusting the thickness of the frequency tuning structure.
In one embodiment, the method further comprises a step of forming an underetch stop layer on the compound semiconductor substrate, wherein the sacrificial epitaxial mesa is formed on the underetch stop layer; wherein the sacrificial epitaxial mesa comprises a sacrificial epitaxial layer.
In the embodiment, wherein (1) the compound semiconductor substrate is composed of gallium arsenide; the sacrificial epitaxial layer is composed of gallium arsenide; the bottom etching stop layer is composed of indium gallium phosphide; or (2) the compound semiconductor substrate is composed of indium phosphide; the sacrificial epitaxial layer is composed of indium gallium arsenide; the bottom etch stop layer is composed of indium phosphide.
In an embodiment, the sacrificial epitaxial layer has a thickness, and the thickness of the sacrificial epitaxial layer is between 50nm and 5000 nm; wherein the bottom etching stop layer has a thickness between 20nm and 500 nm.
Furthermore, the present invention also provides a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter, comprising the steps of: step B1: forming a plurality of sacrificial structure mesas on a substrate, wherein the plurality of sacrificial structure mesas include at least one first sacrificial structure mesa and at least one second sacrificial structure mesa, wherein a height of the at least one first sacrificial structure mesa is greater than a height of the at least one second sacrificial structure mesa, and wherein the at least one first sacrificial structure mesa and the at least one second sacrificial structure mesa have a first height difference; step B2: forming an insulating layer on the plurality of sacrificial structure mesas and the substrate; step B3: polishing the insulating layer by a chemical mechanical planarization process to form a polished surface; step B4: forming a plurality of bulk acoustic wave resonator structures on the polishing surface, wherein the plurality of bulk acoustic wave resonator structures include at least one first bulk acoustic wave resonator structure and at least one second bulk acoustic wave resonator structure, and the at least one first bulk acoustic wave resonator structure and the at least one second bulk acoustic wave resonator structure are respectively located on at least one first sacrificial structure mesa and at least one second sacrificial structure mesa, wherein step B4 includes the following steps: step B41: forming a bottom electrode layer on the polishing surface; step B42: forming a piezoelectric layer on the bottom electrode layer; and step B43: forming a top electrode layer on the piezoelectric layer; and step B5: etching the plurality of sacrificial structure mesas to form a plurality of cavities, wherein the plurality of cavities are respectively located under the plurality of bulk acoustic wave resonant structures; wherein in step B3, the insulating layer is polished to a level such that (1) at least one first sacrificial structure mesa is exposed and at least one second sacrificial structure mesa is not exposed, whereby the insulating layer under the polished surface and under the at least one second bulk acoustic wave resonant structure forms a second frequency tuning structure of the at least one second bulk acoustic wave resonant structure, wherein the second frequency tuning structure has a thickness, the thickness of the second frequency tuning structure being equal to the first height difference; or (2) at least one first sacrificial structure mesa and at least one second sacrificial structure mesa are not exposed, whereby the insulating layer located below the polishing surface and below the at least one first bulk acoustic wave resonant structure and the at least one second bulk acoustic wave resonant structure respectively forms a first frequency tuning structure of the at least one first bulk acoustic wave resonant structure and a second frequency tuning structure of the at least one second bulk acoustic wave resonant structure, wherein the first frequency tuning structure and the second frequency tuning structure have a first thickness difference, and the first thickness difference is equal to the first height difference; wherein the at least one first bulk acoustic wave resonant structure and the at least one second bulk acoustic wave resonant structure have a first resonant frequency difference associated with the first height difference, such that the first resonant frequency difference between the at least one first bulk acoustic wave resonant structure and the at least one second bulk acoustic wave resonant structure can be tuned by adjusting the first height difference.
In one embodiment, the substrate is a semiconductor substrate; wherein the material comprising the plurality of sacrificial structure mesas comprises at least one selected from the group consisting of: metals, alloys, and epitaxial structures.
In one embodiment, the substrate is a compound semiconductor substrate, wherein step B1 includes the steps of: step B11: forming a sacrificial structure on the substrate, wherein the sacrificial structure comprises a sacrificial epitaxial layer; step B12: etching the sacrificial structure to form a plurality of sacrificial structure mesas, such that the plurality of sacrificial structure mesas have the same height; and step B13: the at least one first sacrificial structure mesa and the at least one second sacrificial structure mesa are etched or the at least one second sacrificial structure mesa is etched such that the at least one first sacrificial structure mesa and the at least one second sacrificial structure mesa have a first height difference.
In an embodiment, the sacrificial structure further includes a first etching stop layer and a first fine tuning layer, wherein the sacrificial epitaxial layer is formed on the substrate, the first etching stop layer is formed on the sacrificial epitaxial layer, and the first fine tuning layer is formed on the first etching stop layer, wherein the first fine tuning layer has a thickness; in step B13, the first fine tuning layer of the at least one second sacrificial structure mesa is etched such that the at least one first sacrificial structure mesa and the at least one second sacrificial structure mesa have a first height difference, whereby the first height difference is determined by the thickness of the first fine tuning layer.
In one embodiment, the substrate (1) is composed of gallium arsenide; the sacrificial epitaxial layer is composed of gallium arsenide; the first etching stop layer is composed of aluminum arsenide or indium gallium phosphide; the first fine tuning layer is composed of gallium arsenide; or (2) the substrate is composed of indium phosphide; the sacrificial epitaxial layer is composed of indium gallium arsenide; the first etching stop layer is composed of indium phosphide; the first fine tuning layer is composed of indium gallium arsenide.
In an embodiment, the thickness of the first fine tuning layer is between 1nm and 300 nm; the first etching stop layer has a thickness between 1nm and 50 nm.
In one embodiment, the method further comprises a step of forming an underetch stop layer on the substrate, wherein the sacrificial structure is formed on the underetch stop layer; wherein the sacrificial epitaxial layer has a thickness between 50nm and 5000 nm; wherein the bottom etching stop layer has a thickness between 20nm and 500 nm; wherein (1) the substrate is composed of gallium arsenide; the sacrificial epitaxial layer is composed of gallium arsenide; the bottom etching stop layer is composed of indium gallium phosphide; or (2) the substrate is composed of indium phosphide; the sacrificial epitaxial layer is composed of indium gallium arsenide; the bottom etch stop layer is composed of indium phosphide.
Furthermore, the present invention also provides a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter, comprising the steps of: step C1: forming a plurality of sacrificial structure mesas on a substrate, wherein the plurality of sacrificial structure mesas have the same height, and the plurality of sacrificial structure mesas comprise at least one first sacrificial structure mesa and at least one second sacrificial structure mesa; step C2: forming an insulating layer on the plurality of sacrificial structure mesas and the substrate; step C3: grinding the insulating layer by a pre-chemical mechanical planarization process to form a pre-polished surface, so as to expose the plurality of sacrificial structure mesas; step C4: etching the at least one first sacrificial structure mesa and the at least one second sacrificial structure mesa or etching the at least one second sacrificial structure mesa such that the at least one first sacrificial structure mesa and the at least one second sacrificial structure mesa have a first height difference, wherein a height of the at least one first sacrificial structure mesa is greater than a height of the at least one second sacrificial structure mesa; step C5: forming a plurality of bulk acoustic wave resonant structures, wherein the plurality of bulk acoustic wave resonant structures include at least one first bulk acoustic wave resonant structure and at least one second bulk acoustic wave resonant structure, and the at least one first bulk acoustic wave resonant structure and the at least one second bulk acoustic wave resonant structure are respectively located on at least one first sacrificial structure mesa and at least one second sacrificial structure mesa, wherein (a) step C5 includes the steps of: step C51: forming a second polishing layer on the plurality of sacrificial mesas and the insulating layer, wherein the material forming the second polishing layer is an insulator; step C52: polishing the second polishing layer by a chemical mechanical planarization process to form a polished surface such that (1) at least one first sacrificial structure mesa is exposed and at least one second sacrificial structure mesa is not exposed, whereby the second polishing layer beneath the polished surface and beneath the at least one second bulk acoustic wave resonant structure forms a second frequency tuning structure of the at least one second bulk acoustic wave resonant structure, wherein the second frequency tuning structure has a thickness, the thickness of the second frequency tuning structure being equal to the first height difference; or (2) the at least one first sacrificial structure mesa and the at least one second sacrificial structure mesa are not exposed, whereby the second sub-polishing layer located below the polishing surface and respectively located below the at least one first bulk acoustic wave resonant structure and the at least one second bulk acoustic wave resonant structure forms a first frequency tuning structure of the at least one first bulk acoustic wave resonant structure and a second frequency tuning structure of the at least one second bulk acoustic wave resonant structure, respectively, wherein the first frequency tuning structure and the second frequency tuning structure have a first thickness difference, and the first thickness difference is equal to the first height difference; step C53: forming a bottom electrode layer on the polishing surface; step C54: forming a piezoelectric layer on the bottom electrode layer; and step C55: forming a top electrode layer on the piezoelectric layer; or (b) an extended plane coinciding with the pre-polished surface, wherein step C5 comprises the steps of: step C51': forming a second polishing layer on the plurality of sacrificial mesas and the insulating layer, wherein the material forming the second polishing layer comprises at least one selected from the group consisting of: metals and alloys; step C52': grinding the second grinding layer by a chemical mechanical planarization process to form a polished surface, so that the plurality of sacrificial structure mesas are not exposed; step C53': patterning the second polishing layer, wherein (1) in step C4, at least one second sacrificial mesa is etched; wherein the second sub-polishing layer located above the extension plane, below the polishing surface, and below the at least one first bulk acoustic wave resonant structure forms a bottom electrode layer of the at least one first bulk acoustic wave resonant structure; wherein the second sub-polish layer located above the extension plane, below the polishing surface, and below the at least one second bulk acoustic wave resonant structure forms a bottom electrode layer of the at least one second bulk acoustic wave resonant structure; wherein the second sub-polish layer below the extension plane and below the at least one second bulk acoustic wave resonant structure forms a second frequency tuning structure of the at least one second bulk acoustic wave resonant structure, wherein the second frequency tuning structure has a thickness, and the thickness of the second frequency tuning structure is equal to the first height difference; or (2) in step C4, at least one first sacrificial structure mesa and at least one second sacrificial structure mesa are etched; wherein the second sub-polishing layer located above the extension plane, below the polishing surface, and below the at least one first bulk acoustic wave resonant structure forms a bottom electrode layer of the at least one first bulk acoustic wave resonant structure; wherein the second sub-polishing layer located below the extension plane and below the at least one first bulk acoustic wave resonant structure forms a first frequency tuning structure of the at least one first bulk acoustic wave resonant structure; wherein the second sub-polish layer located above the extension plane, below the polishing surface, and below the at least one second bulk acoustic wave resonant structure forms a bottom electrode layer of the at least one second bulk acoustic wave resonant structure; wherein the second sub-polish layer located below the extension plane and below the at least one second bulk acoustic wave resonant structure forms a second frequency tuning structure of the at least one second bulk acoustic wave resonant structure; wherein the first frequency tuning structure and the second frequency tuning structure have a first thickness difference, the first thickness difference being equal to the first height difference; step C54': forming a piezoelectric layer on the polishing surface; and step C55': forming a top electrode layer on the piezoelectric layer; or (C) step C5 includes the steps of: step C51 ": forming a second polishing layer on the plurality of sacrificial mesas and the insulating layer, wherein the material forming the second polishing layer comprises at least one selected from the group consisting of: metals, alloys, and insulators; step C52 ": polishing the second polishing layer by a chemical mechanical planarization process to form a polished surface such that (1) at least one first sacrificial structure mesa is exposed and at least one second sacrificial structure mesa is not exposed, whereby the second polishing layer beneath the polished surface and beneath the at least one second bulk acoustic wave resonant structure forms a second frequency tuning structure of the at least one second bulk acoustic wave resonant structure, wherein the second frequency tuning structure has a thickness, the thickness of the second frequency tuning structure being equal to the first height difference; or (2) at least one first sacrificial structure mesa and at least one second sacrificial structure mesa are not exposed, whereby second sub-polishing layers located below the polishing surface and respectively located below the at least one first bulk acoustic wave resonant structure and the at least one second bulk acoustic wave resonant structure respectively form a first frequency tuning structure of the at least one first bulk acoustic wave resonant structure and a second frequency tuning structure of the at least one second bulk acoustic wave resonant structure, wherein the first frequency tuning structure and the second frequency tuning structure have a first thickness difference, and the first thickness difference is equal to the first height difference; step C53 ": patterning the second grinding layer; step C54 ": forming a bottom electrode layer on the polishing surface; step C55 ": forming a piezoelectric layer on the bottom electrode layer; and step C56 ": forming a top electrode layer on the piezoelectric layer; and step C6: etching the plurality of sacrificial structure mesas to form a plurality of cavities, wherein the plurality of cavities are respectively located under the plurality of bulk acoustic wave resonance structures; wherein the at least one first bulk acoustic wave resonant structure and the at least one second bulk acoustic wave resonant structure have a first resonant frequency difference associated with the first height difference; therefore, the first resonance frequency difference of the at least one first bulk acoustic wave resonance structure and the at least one second bulk acoustic wave resonance structure can be tuned by adjusting the first height difference.
In one embodiment, the substrate is a semiconductor substrate; wherein the material comprising the plurality of sacrificial structure mesas comprises at least one selected from the group consisting of: metals, alloys, and epitaxial structures.
In one embodiment, the substrate is a compound semiconductor substrate; wherein step C1 includes the steps of: step C11: forming a sacrificial structure on the substrate, wherein the sacrificial structure comprises a sacrificial epitaxial layer; and step C12: the sacrificial structure is etched to form a plurality of sacrificial structure mesas, wherein the plurality of sacrificial structure mesas have the same height.
In an embodiment, the sacrificial structure (1) further includes a first etching stop layer and a first fine tuning layer, wherein the sacrificial epitaxial layer is formed on the substrate, the first etching stop layer is formed on the sacrificial epitaxial layer, and the first fine tuning layer is formed on the first etching stop layer, wherein the first fine tuning layer has a thickness; wherein in step C4, the first fine tuning layer of the at least one second sacrificial structure mesa is etched such that the at least one first sacrificial structure mesa and the at least one second sacrificial structure mesa have a first height difference, whereby the first height difference is determined by the thickness of the first fine tuning layer; or (2) the sacrificial structure further comprises a first etching stop layer, a first fine tuning layer and a top etching stop layer, wherein the sacrificial epitaxial layer is formed on the substrate, the first etching stop layer is formed on the sacrificial epitaxial layer, the first fine tuning layer is formed on the first etching stop layer, the top etching stop layer is formed on the first fine tuning layer, and the first fine tuning layer has a thickness; wherein step C4 includes the steps of: step C41: etching the top etch stop layer of the at least one first sacrificial structure mesa and the at least one second sacrificial structure mesa; and step C42: the first fine tuning layer of the at least one second sacrificial structure mesa is etched such that the at least one first sacrificial structure mesa and the at least one second sacrificial structure mesa have a first height difference, whereby the first height difference is determined by a thickness of the first fine tuning layer.
In one embodiment, the substrate (1) is composed of gallium arsenide; the sacrificial epitaxial layer is composed of gallium arsenide; the first etching stop layer is composed of aluminum arsenide or indium gallium phosphide; the first fine tuning layer is composed of gallium arsenide; the top etching stop layer is composed of indium gallium phosphide; or (2) the substrate is composed of indium phosphide; the sacrificial epitaxial layer is composed of indium gallium arsenide; the first etching stop layer is composed of indium phosphide; the first fine tuning layer is composed of indium gallium arsenide; the top etch stop layer is comprised of indium phosphide.
In an embodiment, the thickness of the first fine tuning layer is between 1nm and 300 nm; wherein the first etch stop layer has a thickness between 1nm and 50 nm; wherein the top etch stop layer has a thickness between 50nm and 300 nm.
In one embodiment, the method further comprises a step of forming an underetch stop layer on the substrate, wherein the sacrificial structure is formed on the underetch stop layer; wherein the sacrificial epitaxial layer has a thickness between 50nm and 5000 nm; wherein the bottom etching stop layer has a thickness between 20nm and 500 nm; wherein (1) the substrate is composed of gallium arsenide; the sacrificial epitaxial layer is composed of gallium arsenide; the bottom etching stop layer is composed of indium gallium phosphide; or (2) the substrate is composed of indium phosphide; the sacrificial epitaxial layer is composed of indium gallium arsenide; the bottom etch stop layer is composed of indium phosphide.
In an embodiment, in step C51', the material forming the second polishing layer comprises at least one selected from the group consisting of: ruthenium, titanium, molybdenum, platinum, gold, aluminum, and tungsten.
In addition, the present invention also provides a bulk acoustic wave filter, comprising: an insulating layer, a plurality of bulk acoustic wave resonant structures, and one of the following structures A, B, and C; wherein the insulating layer is formed on a substrate, wherein the insulating layer has a plurality of cavities; wherein a plurality of bulk acoustic wave resonance structures are located respectively on a plurality of cavitys, wherein a plurality of bulk acoustic wave resonance structures include a first bulk acoustic wave resonance structure and a second bulk acoustic wave resonance structure, a plurality of cavitys include a first cavity and a second cavity, first bulk acoustic wave resonance structure and second bulk acoustic wave resonance structure correspond to first cavity and second cavity respectively, wherein first bulk acoustic wave resonance structure and second bulk acoustic wave resonance structure have a first resonance frequency difference, wherein each a plurality of bulk acoustic wave resonance structures include: a bottom electrode layer, a piezoelectric layer and a top electrode layer; wherein the bottom electrode layer is formed on an extending plane; a piezoelectric layer formed on the bottom electrode layer; a top electrode layer formed on the piezoelectric layer; wherein structure a: the insulating layer is provided with a polished upper surface, and the extension plane is coincided with the upper surface of the insulating layer; wherein the second bulk acoustic wave resonant structure has a second frequency tuning structure formed below the extension plane between the bottom electrode layer of the second bulk acoustic wave resonant structure and the second cavity, wherein the second frequency tuning structure has a thickness associated with a first resonant frequency difference of the first bulk acoustic wave resonant structure and the second bulk acoustic wave resonant structure; structure B: the insulating layer is provided with a polished upper surface, and the extension plane is coincided with the upper surface of the insulating layer; the first bulk acoustic wave resonant structure and the second bulk acoustic wave resonant structure are respectively provided with a first frequency tuning structure and a second frequency tuning structure, wherein the first frequency tuning structure is formed below the extension plane and is between the bottom electrode layer of the first bulk acoustic wave resonant structure and the first cavity, the second frequency tuning structure is formed below the extension plane and is between the bottom electrode layer of the second bulk acoustic wave resonant structure and the second cavity, the first frequency tuning structure and the second frequency tuning structure have a first thickness difference, and the first thickness difference is related to the first resonant frequency difference of the first bulk acoustic wave resonant structure and the second bulk acoustic wave resonant structure; structure C: a second polishing layer formed on the insulating layer and the plurality of cavities, wherein the second polishing layer has a polished upper surface, and the extension plane coincides with the upper surface of the second polishing layer; wherein the second polishing layer below the extension plane between the bottom electrode layer of the first bulk acoustic wave resonant structure and the first cavity forms a first frequency tuning structure of the first bulk acoustic wave resonant structure, wherein the second polishing layer below the extension plane between the bottom electrode layer of the second bulk acoustic wave resonant structure and the second cavity forms a second frequency tuning structure of the second bulk acoustic wave resonant structure, wherein the first frequency tuning structure and the second frequency tuning structure have a first thickness difference, and the first thickness difference is related to the first resonant frequency difference of the first bulk acoustic wave resonant structure and the second bulk acoustic wave resonant structure.
In one embodiment, the substrate is a semiconductor substrate.
In an embodiment, the material of which the first frequency tuning structure is made comprises at least one selected from the group consisting of: metals, alloys, and insulators; wherein the material comprising the second frequency tuning structure comprises at least one selected from the group consisting of: metals, alloys, and insulators.
In an embodiment, the bottom electrode layers of the first frequency tuning structure and the first bulk acoustic wave resonator structure are made of the same material; wherein the second frequency tuning structure and the bottom electrode layer of the second bulk acoustic wave resonant structure are made of the same material.
For further understanding of the present invention, the following preferred embodiments are provided in conjunction with the drawings and the accompanying drawings to describe the detailed construction of the present invention and its achieved effect in detail.
Drawings
Fig. 1A-1F are schematic cross-sectional views illustrating process steps of one embodiment of a method for forming a cavity of a bulk acoustic wave resonator according to the present invention.
FIGS. 1G and 1H are schematic cross-sectional views illustrating processing steps of another embodiment of a method for forming a cavity of a bulk acoustic wave resonator according to the present invention.
Fig. 1I is a schematic cross-sectional view of an epitaxial structure according to an embodiment of a method for forming a cavity of a bulk acoustic wave resonator.
FIGS. 1J and 1K are schematic cross-sectional views illustrating process steps of another embodiment of a method for forming a cavity of a bulk acoustic wave resonator according to the present invention.
Fig. 1L is a schematic cross-sectional view of another embodiment of a method of forming a cavity of a bulk acoustic wave resonator according to the present invention.
Fig. 2A-2F are schematic cross-sectional views illustrating process steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to an embodiment of the present invention.
Fig. 2G and fig. 2H are schematic cross-sectional views illustrating processing steps of another embodiment of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to the present invention.
Fig. 2I and 2J are schematic cross-sectional views of two embodiments of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to the present invention.
Fig. 2K to 2N are schematic cross-sectional views illustrating process steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention.
Fig. 3A to 3G are schematic cross-sectional views illustrating processing steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to still another embodiment of the present invention.
Fig. 3H and 3I are schematic cross-sectional views illustrating processing steps of another embodiment of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to the present invention.
Fig. 3J and 3K are schematic cross-sectional views illustrating processing steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention.
Fig. 3L is a schematic cross-sectional view of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention.
Fig. 4A-4D are schematic cross-sectional views illustrating process steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to an embodiment of the present invention.
Fig. 4E and 4F are schematic cross-sectional views illustrating processing steps of another embodiment of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to the present invention.
Fig. 4G and 4H are schematic cross-sectional views illustrating processing steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention.
Fig. 4I is a schematic cross-sectional view of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention.
Fig. 4J to 4M are schematic cross-sectional views illustrating processing steps of another embodiment of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to the present invention.
Fig. 5A-5C are schematic cross-sectional views illustrating process steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to an embodiment of the present invention.
Fig. 5D is a schematic cross-sectional view of another embodiment of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter in accordance with the present invention.
Fig. 5E-5G are schematic cross-sectional views illustrating processing steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention.
Fig. 5H-5K are schematic cross-sectional views illustrating process steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention.
Fig. 5L and 5M are schematic cross-sectional views illustrating processing steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to an embodiment of the present invention.
Fig. 5N and 5O are schematic cross-sectional views illustrating processing steps of another embodiment of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to the present invention.
Figure 5P is a schematic cross-sectional view of another embodiment of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter in accordance with the present invention.
Fig. 6A-6C are schematic cross-sectional views illustrating process steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to an embodiment of the present invention.
Fig. 6D to 6F are schematic cross-sectional views of three embodiments of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to the present invention.
Figure 6G is an enlarged partial cross-sectional view of one embodiment of a method of tuning a bulk acoustic wave resonator of a bulk acoustic wave filter in accordance with the present invention.
Figure 6H is an enlarged partial cross-sectional view of another embodiment of a method of tuning a bulk acoustic wave resonator of a bulk acoustic wave filter in accordance with the present invention.
Fig. 7A to 7D are schematic cross-sectional views illustrating the processing steps of a method for forming a bulk acoustic wave filter according to the prior art.
The reference numbers illustrate:
1 bulk acoustic wave resonator/first bulk acoustic wave resonator;
1' a second bulk acoustic wave resonator;
1' third bulk acoustic wave resonator;
10 a substrate;
11 an insulating layer;
12 etching the protective layer;
13 a compound semiconductor substrate;
20 bottom etch stop layers;
21 sacrificial structures;
22 a first etch stop layer;
23 a first fine tuning layer;
24 a second etch stop layer;
25 a second fine tuning layer;
26 top etch stop layer;
27 sacrificial epitaxial layer;
28 sacrificial epitaxial structure;
3 bulk acoustic wave resonant structure/first bulk acoustic wave resonant structure;
a 3' second bulk acoustic wave resonant structure;
3' third bulk acoustic wave resonant structure;
30 a bottom electrode layer;
31 a piezoelectric layer;
32 a top electrode layer;
40 cavity/first cavity;
40' a second cavity;
40 "third cavity;
41 polishing the surface;
42 pre-polishing the surface;
43 an extension plane;
50 frequency tuning structure/first frequency tuning structure;
50' a second frequency tuning structure;
a 50 "third frequency tuning structure;
51 a second polishing layer;
6a first sacrificial structure mesa;
6' a second sacrificial structure mesa;
6' third sacrificial structure mesa;
60 sacrificial epitaxial structure mesa;
7a first bulk acoustic wave resonator;
7' a second bulk acoustic wave resonator;
70 a first bulk acoustic wave resonant structure;
70' a second bulk acoustic wave resonant structure;
71 a bottom electrode;
72 a piezoelectric layer;
73 a top electrode;
73' a top electrode;
74 grooves;
74' grooves;
75 a silicon substrate;
76 difference in thickness;
77 a sacrificial layer;
ET1 thickness of first etch stop layer;
thickness of the FT1 first fine tuning layer;
thickness of the FT2 second fine tuning layer;
HD1 first height difference;
HD2 second height difference;
t thickness;
t2 thickness of the second frequency tuning structure;
t3 thickness of third frequency tuning structure;
TD1 first thickness difference;
TD2 second thickness difference.
Detailed Description
Fig. 1A-1F are cross-sectional views illustrating process steps of a method for forming a cavity of a bulk acoustic wave resonator according to an embodiment of the present invention. The method for forming the cavity of the bulk acoustic wave resonator comprises the following steps: step A1: forming a sacrificial epitaxial mesa 60(28) (shown in fig. 1B) on a compound semiconductor substrate 13, comprising: forming a sacrificial epitaxial structure 28 (as shown in fig. 1A) on the compound semiconductor substrate 13 and etching the sacrificial epitaxial structure 28 (as shown in fig. 1B) to form a sacrificial epitaxial mesa 60 (28); step A2: (see FIG. 1C) forming an insulating layer 11 on the sacrificial epitaxial mesa 60 and the compound semiconductor substrate 13, wherein the material forming the insulating layer 11The material comprises at least one selected from the following group: silicon Nitride (SiN)x) Silicon oxide (SiO)2) And a Polymer (Polymer); step A3: polishing the insulating layer 11 by a chemical mechanical planarization process (CMP) to form a polished surface 41 (FIG. 1D); step A4: forming a bulk acoustic wave resonant structure 3 (as shown in fig. 1E) on the polished surface 41, wherein the bulk acoustic wave resonant structure 3 is located above the sacrificial epitaxial mesa 60, wherein step a4 comprises the following steps: step A41: forming a bottom electrode layer 30 on the polishing surface 41; step A42: forming a piezoelectric layer 31 on the bottom electrode layer 30; and step a 43: forming a top electrode layer 32 on the piezoelectric layer 31; and step a 5: the sacrificial epitaxial structure mesa 60 is etched (as shown in fig. 1F) to form a cavity 40, wherein the cavity 40 is located below the bulk acoustic wave resonator structure 3. In step a3, the insulating layer 11 is polished to expose the sacrificial epitaxial mesa 60, wherein the insulating layer 11 between the bottom electrode layer 30 and the sacrificial epitaxial mesa 60 forms a frequency tuning structure 50, wherein the frequency tuning structure 50 has a thickness T, and the bulk acoustic wave resonator structure 3 has a resonant frequency F, so that the resonant frequency F of the bulk acoustic wave resonator structure 3 can be tuned by adjusting the thickness T of the frequency tuning structure 50. When the thickness T of the frequency tuning structure 50 is larger, the resonance frequency F of the bulk acoustic wave resonance structure 3 is smaller. Conversely, as the thickness T of the frequency tuning structure 50 is smaller, the resonance frequency F of the bulk acoustic wave resonance structure 3 is larger. The method for forming cavity of bulk acoustic wave resonator is characterized by using compound semiconductor substrate 13, using sacrificial epitaxial structure 28 as sacrificial layer, and polishing insulating layer 11 by chemical mechanical planarization process. This has the advantage of facilitating accurate control of the thickness T of the frequency tuning structure 50, i.e. of the magnitude of the resonance frequency F of the bulk acoustic wave resonant structure 3. If the thickness T of the frequency tuning structure 50 is too thick, the resonant film state of the bulk acoustic wave resonant structure 3 will be affected, and therefore the thickness T of the frequency tuning structure 50 needs to be less than 1000 nm. In some preferred embodiments, the thickness T of the frequency tuning structure 50 is equal to or less than 300 nm.
Please refer to fig. 1G and fig. 1H, which are schematic cross-sectional views illustrating processing steps of another embodiment of a method for forming a cavity of a bulk acoustic wave resonator according to the present invention. The main processing steps for forming the embodiment shown in fig. 1H are substantially the same as those for forming the embodiment shown in fig. 1F, wherein, in step a3, the insulating layer 11 is polished to expose the sacrificial epitaxial mesa 60 (as shown in fig. 1G); the bulk acoustic wave resonator structure 3 is then formed on the polished surface 41, and the sacrificial epitaxial mesa 60 is etched to form the cavity 40 (as shown in fig. 1H). Wherein the bulk acoustic wave resonant structure 3 does not have the frequency tuning structure 50 as shown in figure 1F.
Fig. 1I is a schematic cross-sectional view of an epitaxial structure according to an embodiment of a method for forming a cavity of a bulk acoustic wave resonator. The main structure of the epitaxial structure of the embodiment of fig. 1I is substantially the same as that of the embodiment shown in fig. 1A, but an etching protection layer 12 is formed on a lower surface of the compound semiconductor substrate 13. The etching protection layer 12 functions to protect the lower surface of the compound semiconductor substrate 13 from damage caused by etching (particularly, an etchant for wet etching) during the manufacturing process. Wherein the material constituting the etching protection layer 12 includes at least one selected from the group consisting of: silicon nitride (SiNx) and silicon oxide (SiO)2) Aluminum nitride (AlN), and Photoresist (Photoresist). A preferable material constituting the etching protection layer 12 is silicon nitride (SiNx). Typically, after step a5, the etching protection layer 12 is removed to facilitate the substrate thinning process. In all other embodiments of the present invention, whether the substrate is a semiconductor substrate or a compound semiconductor substrate, the etching protection layer 12 can be formed to protect the lower surface of the semiconductor substrate or the compound semiconductor substrate.
Please refer to fig. 1J and 1K, which are schematic cross-sectional views illustrating processing steps of another embodiment of a method for forming a cavity of a bulk acoustic wave resonator according to the present invention. The epitaxial structure of the embodiment of fig. 1J is substantially the same as the epitaxial structure of the embodiment of fig. 1A, but further includes an etch stop layer 20, wherein the etch stop layer 20 is formed on the compound semiconductor substrate 13, and the sacrificial epitaxial structure 28 is formed on the etch stop layer 20. When the sacrificial epitaxial structure 28 is etched to form the sacrificial epitaxial structure mesa 60, the sacrificial epitaxial structure 28 around the sacrificial epitaxial structure mesa 60 is etched, and the etch is terminated at the undercut stop layer 20. An etch stop layer 20 is disposed below the sacrificial epitaxial mesa 60. The embodiment of fig. 1K is a bulk acoustic wave resonator fabricated from the epitaxial structure of the embodiment of fig. 1J. The main structure of the embodiment of fig. 1K is substantially the same as that of the embodiment shown in fig. 1F, but further includes an underetch stop layer 20, wherein the underetch stop layer 20 is formed on the compound semiconductor substrate 13. In step a2, an insulating layer 11 is formed over the sacrificial epitaxial mesa 60 and the etch stop layer 20. Thus, after the sacrificial epitaxial mesa 60 is etched in step a5, the cavity 40 is also located above the etch stop layer 20. In some embodiments, the compound semiconductor substrate 13 is composed of gallium arsenide (GaAs); the sacrificial epitaxial structure 28 is composed of a sacrificial epitaxial layer composed of gallium arsenide (GaAs), wherein the sacrificial epitaxial layer has a thickness between 50nm and 5000 nm; the bottom etch stop layer 20 is made of indium gallium phosphide (InGaP), wherein the bottom etch stop layer 20 has a thickness between 20nm and 500 nm. In other embodiments, the compound semiconductor substrate 13 is composed of indium phosphide (InP); the sacrificial epitaxial structure 28 is formed of a sacrificial epitaxial layer formed of indium gallium arsenide (InGaAs), wherein the sacrificial epitaxial layer has a thickness between 50nm and 5000 nm; the bottom etch stop layer 20 is comprised of indium phosphide (InP), wherein the bottom etch stop layer 20 has a thickness between 20nm and 500 nm.
Fig. 1L is a cross-sectional view of a method for forming a cavity of a bulk acoustic wave resonator according to another embodiment of the present invention. The embodiment of fig. 1L is also a bulk acoustic wave resonator manufactured from the epitaxial structure of the embodiment of fig. 1J. The main structure of the embodiment of fig. 1L is substantially the same as that of the embodiment of fig. 1K, however, wherein in step a3, the insulating layer 11 is polished to expose the sacrificial epitaxial mesa 60; the bulk acoustic wave resonator structure 3 is then formed on the polished surface 41, and the sacrificial epitaxial mesa 60 is etched to form the cavity 40 (similar to fig. 1G and 1H), so that the bulk acoustic wave resonator structure 3 does not have the frequency tuning structure 50 as shown in fig. 1K.
Fig. 2A to 2F are schematic cross-sectional views illustrating process steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to an embodiment of the present invention. As shown in fig. 2F, the structure of this embodiment includes at least one first bulk acoustic wave resonator 1 and at least one second bulk acoustic wave resonator 1' formed on a substrate 10. In this embodiment, the at least one first bulk acoustic Resonator 1 may be a Series Resonator (Series Resonator); and the at least one second bulk acoustic Resonator 1' may be a Shunt Resonator (Shunt Resonator). Wherein the at least one first bulk acoustic wave resonator 1 comprises at least one first bulk acoustic wave resonator structure 3, a first frequency tuning structure 50, and at least one first cavity 40; the at least one second bulk acoustic resonator 1 'includes at least one second bulk acoustic resonator structure 3', a second frequency tuning structure 50 ', and at least one second cavity 40'. The invention relates to a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter, comprising the following steps: step B1: forming a plurality of sacrificial structure mesas over the substrate 10 (as shown in fig. 2B), wherein the plurality of sacrificial structure mesas includes at least one first sacrificial structure mesa 6 and at least one second sacrificial structure mesa 6 ', wherein a height of the at least one first sacrificial structure mesa 6 is greater than a height of the at least one second sacrificial structure mesa 6 ', wherein the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6 ' have a first height difference HD 1; in this embodiment, the substrate 10 may be a semiconductor substrate; the material forming the plurality of sacrificial structure mesas comprises at least one selected from the group consisting of: metals, alloys, and epitaxial structures; step B2: forming an insulating layer 11 on the plurality of sacrificial structure mesas and the substrate 10 (as shown in fig. 2C), wherein the material constituting the insulating layer 11 includes at least one selected from the following group: silicon nitride (SiNx) and silicon oxide (SiO)2) And a Polymer (Polymer); step B3: polishing the insulating layer 11 by a chemical mechanical planarization process (CMP) to form a polished surface 41 (FIG. 2D); step (ii) ofB4: (as shown in fig. 2E) forming a plurality of bulk acoustic wave resonator structures on the polishing surface 41 (in all embodiments of the bulk acoustic wave filter of the present invention, the plurality of bulk acoustic wave resonator structures are formed on an extended plane 43; in this embodiment, the extended plane 43 coincides with the polishing surface 41), wherein the plurality of bulk acoustic wave resonator structures include at least one first bulk acoustic wave resonator structure 3 and at least one second bulk acoustic wave resonator structure 3 ', and the at least one first bulk acoustic wave resonator structure 3 and the at least one second bulk acoustic wave resonator structure 3 ' are respectively located above the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6 ', wherein the step B4 includes the following steps: step B41: forming a bottom electrode layer 30 on the polishing surface 41; step B42: forming a piezoelectric layer 31 on the bottom electrode layer 30; and step B43: forming a top electrode layer 32 on the piezoelectric layer 31; and step B5: the plurality of sacrificial structure mesas are etched (as shown in fig. 2F) to form a plurality of cavities, wherein the plurality of cavities are respectively located under the plurality of bulk acoustic wave resonators, wherein the plurality of cavities includes at least one first cavity 40 and at least one second cavity 40 ', and the at least one first cavity 40 and the at least one second cavity 40 ' are respectively located under the at least one first bulk acoustic wave resonator 3 and the at least one second bulk acoustic wave resonator 3 '. In step B3, the insulating layer 11 is polished to expose the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6 ', so that the insulating layer 11 under the polishing surface 41 and under the at least one first bulk acoustic wave resonator structure 3 and under the at least one second bulk acoustic wave resonator structure 3' respectively forms a first frequency tuning structure 50 of the at least one first bulk acoustic wave resonator structure 3 and a second frequency tuning structure 50 'of the at least one second bulk acoustic wave resonator structure 3'. The first frequency tuning structure 50 and the second frequency tuning structure 50' have a first thickness difference TD1, and the first thickness difference TD1 is equal to the first height difference HD 1. Wherein the first frequency tuning structure 50 can lower the first resonant frequency F1 of the at least one first bulk acoustic wave resonant structure 3, and the second frequency tuning structure 50' can lower the second resonant frequency F of the at least one second bulk acoustic wave resonant structure 32 is decreased. However, since the thickness of the second frequency tuning structure 50 'is thicker than that of the first frequency tuning structure 50, the second resonant frequency F2 of the at least one second bulk acoustic wave resonant structure 3' is lowered to be lower than the first resonant frequency F1 of the at least one first bulk acoustic wave resonant structure 3. Therefore, the at least one first bulk acoustic wave resonator structure 3 and the at least one second bulk acoustic wave resonator structure 3 'have a first resonant frequency difference FD1, and the first resonant frequency difference FD1 is associated with the first thickness difference TD1 of the first frequency tuning structure 50 and the second frequency tuning structure 50', i.e. the first resonant frequency difference FD1 is associated with the first height difference HD1 of the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6 ', so that the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonator structure 3 and the at least one second bulk acoustic wave resonator structure 3' can be tuned by adjusting the first height difference HD 1. Since the size of the substrate 10 is much larger than that of the bulk acoustic wave resonator, when the insulating layer 11 is polished by the chemical mechanical planarization process, the insulating layer 11 near the center of the substrate 10 is often polished by an amount different from that of the insulating layer 11 far from the center of the substrate 10. However, the amount of polishing of the corresponding insulating layer 11 is almost the same for adjacent baw resonators, especially for plural baw resonators in the same baw filter. The present invention is characterized in that the first thickness difference TD1 between the first frequency tuning structure 50 and the second frequency tuning structure 50' in the same bulk acoustic wave filter does not vary with the position of the first frequency tuning structure near the center of the substrate 10 or far from the center of the substrate 10. In other words, the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonator 3 and the at least one second bulk acoustic wave resonator 3' does not vary with the position near or far from the center of the substrate 10. The first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3 ' is only related to the first thickness difference TD1 of the first frequency tuning structure 50 and the second frequency tuning structure 50 ', i.e. the first height difference HD1 of the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6 ', of courseThe type of material comprising the first frequency tuning structure 50 and the second frequency tuning structure 50' is relevant. By adjusting the first height difference HD1 or selecting the first frequency tuning structure 50 and the second frequency tuning structure 50 'of different materials, the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonator 3 and the at least one second bulk acoustic wave resonator 3' can be tuned. In addition, the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonator 3 and the at least one second bulk acoustic wave resonator 3' of the present invention does not vary with the location near or far from the center of the substrate 10, which is one of the features of the present invention and is very helpful for the Trimming (Trimming) process. Since the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonator 3 and the at least one second bulk acoustic wave resonator 3' in each region can be precisely controlled on a whole Wafer (Wafer) and will not change with the location, the time cost required for the trimming process can be greatly reduced. In some embodiments, the substrate 10 may be a compound semiconductor substrate; the material forming the plurality of sacrificial structure mesas is an epitaxial structure; and wherein the aforementioned step B1 comprises the steps of: step B11: forming a sacrificial structure 21 (as shown in fig. 2A) on the substrate 10; step B12: etching the sacrificial structure 21 to form a plurality of sacrificial structure mesas, wherein the plurality of sacrificial structure mesas include at least one first sacrificial structure mesa 6(21) and at least one second sacrificial structure mesa 6' (21) and have the same height; and step B13: the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6 ' are etched (as shown in fig. 2B) or the at least one second sacrificial structure mesa 6 ' is etched such that the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6 ' have a first height difference HD 1.
Please refer to fig. 2G and fig. 2H, which are schematic cross-sectional views illustrating processing steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention. In this embodiment, the substrate 10 may be a semiconductor substrate; the material forming the plurality of sacrificial structure mesas comprises at least one selected from the group consisting of: metals, alloys, and epitaxial structures. The main processing steps for forming the embodiment shown in fig. 2H are substantially the same as the processing steps for forming the embodiment shown in fig. 2F, however, in step B3, the insulating layer 11 is polished to expose at least one first sacrificial structure mesa 6 and to leave at least one second sacrificial structure mesa 6 'unexposed (as shown in fig. 2G), whereby the insulating layer 11 under the polished surface 41 (extension plane 43) and under the at least one second bulk acoustic wave resonator 3' forms a second frequency tuning structure 50 'of the at least one second bulk acoustic wave resonator 3'. As shown in fig. 2H, the second frequency tuning structure 50 'has a thickness T2, and the thickness T2 of the second frequency tuning structure 50' is equal to the first height difference HD 1. In this embodiment, the first frequency tuning structure 50 of the embodiment shown in fig. 2F is not present. Therefore, the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3 ' is related to the thickness T2 of the second frequency tuning structure 50 ', i.e. the first height difference HD1 of the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6 '. By adjusting the first height difference HD1, the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3' can be tuned.
Fig. 2I is a schematic cross-sectional view of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention. The embodiment of fig. 2I has substantially the same structure as the embodiment of fig. 2F, but further includes an etching stop layer 20, wherein the etching stop layer 20 is formed on the substrate 10, the insulating layer 11 is formed on the etching stop layer 20, and the at least one first cavity 40 and the at least one second cavity 40' are also located on the etching stop layer 20. The main processing steps for forming the embodiment shown in fig. 2I are substantially the same as those for forming the embodiment shown in fig. 2F, but a step of forming an underetch stop layer 20 on the substrate is further included before step B11. Wherein step B11 is to form the sacrificial structure 21 on the bottom etch stop layer. Wherein in step B2, an insulating layer 11 is formed over the plurality of sacrificial structure mesas and the bottom etch stop layer 20. In this embodiment, the substrate 10 is a compound semiconductor substrate; the material forming the plurality of sacrificial structure mesas (sacrificial structures 21) is an epitaxial structure. In some embodiments, substrate 10 is comprised of gallium arsenide; the sacrificial structure 21 is composed of a sacrificial epitaxial layer composed of gallium arsenide, wherein the sacrificial epitaxial layer has a thickness between 50nm and 5000 nm; the bottom etch stop layer 20 is formed of indium gallium phosphide, wherein the bottom etch stop layer 20 has a thickness between 20nm and 500 nm. In other embodiments, substrate 10 is composed of indium phosphide; the sacrificial structure 21 is composed of a sacrificial epitaxial layer composed of InGaAs, wherein the sacrificial epitaxial layer has a thickness between 50nm and 5000 nm; the bottom etch stop layer 20 is formed of indium phosphide, wherein the bottom etch stop layer 20 has a thickness between 20nm and 500 nm.
Fig. 2J is a schematic cross-sectional view of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention. Wherein the substrate 10 is a compound semiconductor substrate; the material forming the plurality of sacrificial mesas is an epitaxial structure. Wherein the main structure of the embodiment of fig. 2J is substantially the same as that of the embodiment shown in fig. 2I, however, in step B3, the insulating layer 11 is polished to expose at least one first sacrificial structure mesa 6 and not expose at least one second sacrificial structure mesa 6 '(similar to fig. 2G), whereby the insulating layer 11 under the polished surface 41 (extension plane 43) and under the at least one second bulk acoustic wave resonator 3' forms a second frequency tuning structure 50 'of the at least one second bulk acoustic wave resonator 3'.
Please refer to fig. 2K to fig. 2N, which are schematic cross-sectional views illustrating process steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention. Wherein in the embodiment shown in fig. 2K, the substrate 10 is a compound semiconductor substrate; the material forming the sacrificial structure 21 is an epitaxial structure. The epitaxial structure of the embodiment of fig. 2K is substantially the same as that of the embodiment of fig. 2A, however, the sacrificial structure 21 includes a sacrificial epitaxial layer 27, a first etch stop layer 22 and a first fine tuning layer 23. Wherein a sacrificial epitaxial layer 27 is formed on the substrate 10, a first etch stop layer 22 is formed on the sacrificial epitaxial layer 27, and a first fine tuning layer 23 is formed on the first etch stop layer 22. As shown in fig. 2L, the sacrificial structure 21 is etched into a plurality of sacrificial structure mesas, wherein the plurality of sacrificial structure mesas includes at least one first sacrificial structure mesa 6 and at least one second sacrificial structure mesa 6', and the plurality of sacrificial structure mesas have the same height (step B12). As shown in fig. 2M, wherein the first fine tuning layer 23 has a thickness FT 1. The first fine tuning layer 23 of the at least one second sacrificial structure mesa 6 'is etched such that the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6' have a first height difference HD1 (step B13). Fig. 2N, schematic diagram of step B2, step B3, and step B4 followed. The at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6' in fig. 2N are etched away (step B5), resulting in the embodiment shown in fig. 2F. The first height difference HD1 is determined by the thickness FT1 of the first fine tuning layer 23, which facilitates the fine adjustment of the first height difference HD1, i.e., the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonator 3 and the at least one second bulk acoustic wave resonator 3'. In some embodiments, the substrate 10 is comprised of gallium arsenide (GaAs); the sacrificial epitaxial layer 27 is made of gallium arsenide (GaAs); the first etching stop layer 22 is composed of aluminum arsenide (AlAs) or indium gallium phosphide (InGaP), wherein the first etching stop layer 22 has a thickness between 1nm and 50 nm; the first fine tuning layer 23 is made of gallium arsenide (GaAs), wherein the thickness FT1 of the first fine tuning layer 23 is between 1nm and 300 nm. In other embodiments, substrate 10 is composed of indium phosphide (InP); the sacrificial epitaxial layer 27 is made of indium gallium arsenide (InGaAs); the first etch stop layer 22 is made of indium phosphide (InP), wherein the first etch stop layer 22 has a thickness between 1nm and 50 nm; the first fine tuning layer 23 is composed of indium gallium arsenide (InGaAs), wherein the thickness FT1 of the first fine tuning layer 23 is between 1nm and 300 nm.
Please refer to fig. 3A to 3G, which are schematic cross-sectional views illustrating processing steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention. With a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to the present invention, at least one first bulk acoustic wave resonator 1 and at least one second bulk acoustic wave resonator 1' are formed (as shown in fig. 3G), comprising the steps of: step C1: forming a plurality of sacrificial structure mesas on a substrate 10, wherein the plurality of sacrificial structure mesas have the same height, wherein the plurality of sacrificial structure mesas include at least one first sacrificial structure mesa 6 and at least one second sacrificial structure mesa 6', in which the substrate 10 may be a semiconductor substrate; the material forming the plurality of sacrificial structure mesas comprises at least one selected from the group consisting of: metals, alloys, and epitaxial structures; step C2: forming an insulating layer 11 on the plurality of sacrificial mesas and the substrate 10 (as shown in FIG. 3A); step C3: polishing the insulating layer 11 by a pre-chemical mechanical planarization process (as shown in FIG. 3B) to form a pre-polished surface 42, so as to expose the plurality of sacrificial mesas; step C4: etching the at least one second sacrificial structure mesa 6 ' (shown in fig. 3C) such that the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6 ' have a first height difference HD1, wherein a height of the at least one first sacrificial structure mesa 6 is greater than a height of the at least one second sacrificial structure mesa 6 '; step C5: (as shown in fig. 3D to 3F), a plurality of bulk acoustic wave resonant structures are formed, wherein the plurality of bulk acoustic wave resonant structures include at least one first bulk acoustic wave resonant structure 3 and at least one second bulk acoustic wave resonant structure 3 ', wherein the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3 ' are respectively located above the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6 ', and the step C5 includes the following steps: step C51: forming a second polishing layer 51 on the plurality of sacrificial mesas and the insulating layer 11, wherein the material forming the second polishing layer 51 is an insulator, wherein the insulator material forming the second polishing layer 51 comprises at least one selected from the group consisting of: silicon nitride (SiNx) and silicon oxide (SiO)2) Aluminum nitride (AlN) and zinc oxide (ZnO); step C52: polishing the second polishing layer 51 by a chemical mechanical planarization process to form a polishing surface 41, such that the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6 ' are not exposed, thereby the second polishing layer 51 under the polishing surface 41 and under the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3 ' respectively forms a first frequency tuning structure 50 of the at least one first bulk acoustic wave resonant structure 3 and a second frequency tuning structure 50 ' of the at least one second bulk acoustic wave resonant structure 3 ', wherein the first frequency tuning structure 50 and the second frequency tuning structure 50 ' have a first thickness difference TD1, and the first thickness difference TD1 is equal to the first height difference HD 1; step C53: forming a bottom electrode layer 30 on the polishing surface 41 (as mentioned above, a plurality of bulk acoustic wave resonators are formed on an extended plane 43, in this embodiment, the extended plane 43 is coincident with the polishing surface 41); step C54: forming a piezoelectric layer 31 on the bottom electrode layer 30; and step C55: forming a top electrode layer 32 on the piezoelectric layer 31; and step C6: (as shown in FIG. 3G), the plurality of sacrificial structure mesas are etched to form a plurality of cavities, wherein the plurality of cavities are respectively located under the plurality of bulk acoustic wave resonators, wherein the plurality of cavities includes at least one first cavity 40 and at least one second cavity 40'. Wherein the at least one first bulk acoustic wave resonator structure 3 and the at least one second bulk acoustic wave resonator structure 3 'have a first resonant frequency difference FD1, the first resonant frequency difference FD1 is associated with the first thickness difference TD1 of the first frequency tuning structure 50 and the second frequency tuning structure 50', that is, the first height difference HD 1; thus, the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3' can be tuned by adjusting the first height difference HD 1. In some embodiments, the substrate 10 may be a compound semiconductor substrate; the material forming the plurality of sacrificial structure mesas is an epitaxial structure; and wherein the aforementioned step C1 comprises the steps of: step C11: forming a sacrificial structure 21 on the substrate 10; and step C12: the sacrificial structure 27 is etched to form a plurality of sacrificial structure mesas,wherein the plurality of sacrificial structure mesas have the same height.
Please refer to fig. 3H and fig. 3I, which are schematic cross-sectional views illustrating processing steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention. In this embodiment, the substrate 10 may be a semiconductor substrate; the material forming the plurality of sacrificial structure mesas comprises at least one selected from the group consisting of: metals, alloys, and epitaxial structures. The main processing steps for forming the embodiment shown in fig. 3I are substantially the same as the processing steps for forming the embodiment shown in fig. 3G, however, in step C52, the second polishing layer 51 is polished to expose the at least one first sacrificial structure mesa 6 and not expose the at least one second sacrificial structure mesa 6 '(as shown in fig. 3H), so that the second polishing layer 51 under the polished surface 41 (extension plane 43) and under the at least one second bulk acoustic wave resonator structure 3' forms a second frequency tuning structure 50 'of the at least one second bulk acoustic wave resonator structure 3' (as shown in fig. 3I). Wherein the second frequency tuning structure 50 'has a thickness T2, and the thickness T2 of the second frequency tuning structure 50' is equal to the first height difference HD 1. In this embodiment, the first frequency tuning structure 50 of the embodiment shown in fig. 3G is not present. Therefore, the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3 ' is related to the thickness T2 of the second frequency tuning structure 50 ', i.e. the first height difference HD1 of the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6 '. By adjusting the first height difference HD1, the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3' can be tuned. In this embodiment, the material constituting the second polishing layer 51 may include at least one selected from the following group: metals, alloys, and insulators.
Please refer to fig. 3J and 3K, which are schematic cross-sectional views illustrating processing steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention. In this embodiment, the substrate 10 may be a semiconductor substrate; the material forming the plurality of sacrificial structure mesas comprises at least one selected from the group consisting of: metals, alloys, and epitaxial structures. The main process steps for forming the embodiment shown in fig. 3K are substantially the same as the process steps for forming the embodiment shown in fig. 3G, however, in step C5, a plurality of bulk acoustic wave resonator structures are formed on an extended plane 43, wherein the extended plane 43 coincides with the pre-polished surface 42, wherein step C5 comprises the following steps: step C51': forming a second polishing layer 51 (as shown in fig. 3D) on the plurality of sacrificial mesas and the insulating layer 11, wherein the material forming the second polishing layer 51 comprises at least one selected from the group consisting of: metals and alloys; in a preferred embodiment, the material of the second polishing layer 51 comprises at least one selected from the following group: ruthenium, titanium, molybdenum, platinum, gold, aluminum, and tungsten; step C52': polishing the second polishing layer 51 by a chemical mechanical planarization process (CMP) to form a polished surface 41, such that the plurality of sacrificial mesas are not exposed (FIG. 3E); step C53': (as shown in FIG. 3J) patterning the second abrasive layer 51; step C54': forming a piezoelectric layer 31 on the polishing surface 41; and step C55': a top electrode layer 32 is formed on the piezoelectric layer 31. After etching to remove the plurality of sacrificial mesas in step C6, the embodiment shown in fig. 3K is formed. Wherein in step C4, at least one second sacrificial structure mesa 6' is etched. Wherein the second sub-polishing layer 51 located above the pre-polishing surface 42 (extension plane 43), below the polishing surface 41, and below the at least one first bulk acoustic wave resonant structure 3 forms a bottom electrode layer 30 of the at least one first bulk acoustic wave resonant structure 3; wherein the second sub-polishing layer 51 located above the pre-polishing surface 42 (extension plane 43), below the polishing surface 41, and below the at least one second bulk acoustic wave resonator 3 'forms a bottom electrode layer 30 of the at least one second bulk acoustic wave resonator 3'; wherein the second sub-polish layer 51 under the pre-polished surface 42 (extension plane 43) and under the at least one second bulk acoustic wave resonant structure 3 ' forms a second frequency tuning structure 50 ' of the at least one second bulk acoustic wave resonant structure 3 '. Wherein the second frequency tuning structure 50 'has a thickness T2, and the thickness T2 of the second frequency tuning structure 50' is equal to the first height difference HD 1. By adjusting the first height difference HD1, the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3' can be tuned.
Fig. 3L is a schematic cross-sectional view of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention. In this embodiment, the substrate 10 may be a semiconductor substrate; the material forming the plurality of sacrificial structure mesas comprises at least one selected from the group consisting of: metals, alloys, and epitaxial structures. The main processing steps for forming the embodiment shown in fig. 3L are substantially the same as the processing steps for forming the embodiment shown in fig. 3G, however, step C5 includes the following steps: step C51 ": forming a second polishing layer 51 (as shown in fig. 3D) on the plurality of sacrificial mesas and the insulating layer 11, wherein the material forming the second polishing layer 51 comprises at least one selected from the group consisting of: metals, alloys, and insulators; step C52 ": polishing the second polishing layer 51 by a chemical mechanical planarization process (cmp) to form a polished surface 41 such that the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6' are not exposed (as shown in fig. 3E); step C53 ": patterning the second abrasive layer 51 (as shown in FIG. 3J); step C54 ": forming a bottom electrode layer 30 on the polishing surface 41 (extension plane 43); step C55 ": forming a piezoelectric layer 31 on the bottom electrode layer 30; and step C56 ": a top electrode layer 32 is formed on the piezoelectric layer 31. The embodiment shown in fig. 3L is formed by the step C6, whereby the second sub-polishing layer 51 under the polishing surface 41 and under the at least one first bulk acoustic wave resonant structure 3 and under the at least one second bulk acoustic wave resonant structure 3 'respectively forms a first frequency tuning structure 50 of the at least one first bulk acoustic wave resonant structure 3 and a second frequency tuning structure 50' of the at least one second bulk acoustic wave resonant structure 3 ', respectively, wherein the first frequency tuning structure 50 and the second frequency tuning structure 50' have a first thickness difference TD1, and the first thickness difference TD1 is equal to the first height difference HD 1. By adjusting the first height difference HD1, the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3' can be tuned.
In the embodiments of fig. 3G and 3I, in step C2 (as shown in fig. 3A), a thick insulating layer 11 is formed, wherein the thickness of the insulating layer 11 must be higher than the height of the plurality of sacrificial structure mesas. In step C3 (shown in FIG. 3B), a pre-CMP process is performed to polish the insulating layer 11 to a thickness at least greater than or equal to the height of the plurality of sacrificial mesas. However, the chemical mechanical planarization process has a drawback that the uniformity of the polished surface is deteriorated when the thickness to be polished is too thick. In this embodiment, since the thickness of the desired abrasive insulating layer 11 is thick, the uniformity of the ground pre-polished surface 42 is deteriorated. However, the thickness of the second polishing layer 51 formed in the subsequent step C51 is very thin (relative to the thickness of the insulating layer 11), and is only higher than the first height difference HD 1. Therefore, the uniformity of the polished surface 41 formed after the CMP process in step C52 grinds the second polishing layer 51 is not degraded. Therefore, the formation of the bottom electrode layer 30 of the at least one first bulk acoustic resonator 1 and the at least one second bulk acoustic resonator 1 'on the polished surface 41 will contribute to improving the resonance characteristics of the at least one first bulk acoustic resonator 1 and the at least one second bulk acoustic resonator 1'. Similarly, in the embodiment of fig. 3L, so too. In the embodiment of fig. 3K, the piezoelectric layer 31 of the at least one first bulk acoustic resonator 1 and the at least one second bulk acoustic resonator 1 'is formed on the polished surface 41, which also helps to improve the resonance characteristics of the at least one first bulk acoustic resonator 1 and the at least one second bulk acoustic resonator 1'.
The embodiments shown in fig. 3G, fig. 3I, fig. 3K and fig. 3L can also be formed by an epitaxial structure similar to that shown in fig. 2K, wherein the substrate 10 is a compound semiconductor substrate, wherein the sacrificial structure 21 includes a sacrificial epitaxial layer 27, a first etching stop layer 22 and a first fine tuning layer 23, wherein the sacrificial epitaxial layer 27 is formed on the substrate 10, the first etching stop layer 22 is formed on the sacrificial epitaxial layer 27, the first fine tuning layer 23 is formed on the first etching stop layer 22, and the first fine tuning layer 23 has a thickness FT 1; in step C4, the first fine tuning layer 23 of the at least one second sacrificial structure mesa 6 ' is etched such that the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6 ' have a first height difference HD1, such that the first height difference HD1 is determined by the thickness FT1 of the first fine tuning layer 23, which facilitates the precise adjustment of the first height difference HD1, i.e., the precise adjustment of the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonator structure 3 and the at least one second bulk acoustic wave resonator structure 3 '.
Please refer to fig. 4A-4D, which are schematic cross-sectional views illustrating processing steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to an embodiment of the present invention. The main process steps for forming the embodiment shown in fig. 4D are substantially the same as those for forming the embodiment shown in fig. 3G, however, step C4 is: the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6 ' are etched (as shown in fig. 4A) such that the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6 ' have a first height difference, wherein a height of the at least one first sacrificial structure mesa 6 is greater than a height of the at least one second sacrificial structure mesa 6 '. After step C51 (shown in fig. 4B), step C52 (shown in fig. 4C), steps C53 to C55 and step C6, the embodiment shown in fig. 4D is formed, in which the material constituting the second polishing layer 51 is an insulator. In this embodiment, the substrate 10 may be a semiconductor substrate; the material forming the plurality of sacrificial structure mesas comprises at least one selected from the group consisting of: metals, alloys, and epitaxial structures.
Please refer to fig. 4E and 4F, which are schematic cross-sectional views illustrating processing steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention. In this embodiment, the substrate 10 may be a semiconductor substrate; the material forming the plurality of sacrificial structure mesas comprises at least one selected from the group consisting of: metals, alloys, and epitaxial structures. The main processing steps for forming the embodiment shown in fig. 4F are substantially the same as the processing steps for forming the embodiment shown in fig. 4D, wherein, in step C52, (shown in fig. 4E), the second polishing layer 51 is polished to at least make the polishing surface 41 (extension plane 43) coincide with the pre-polishing surface 42 or make the polishing surface 41 lower than the pre-polishing surface 42, and wherein the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6' are not exposed. In the embodiment of fig. 4F, the material constituting the second polishing layer 51 may include at least one selected from the following group: metals, alloys, and insulators.
Please refer to fig. 4G and 4H, which are schematic cross-sectional views illustrating processing steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention. In this embodiment, the substrate 10 may be a semiconductor substrate; the material forming the plurality of sacrificial structure mesas comprises at least one selected from the group consisting of: metals, alloys, and epitaxial structures. The main process steps for forming the embodiment of fig. 4H are substantially the same as those for forming the embodiment of fig. 3K, however, step C4 is: etching (as shown in fig. 4A) the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6 ' such that the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6 ' have a first height difference, wherein a height of the at least one first sacrificial structure mesa 6 is greater than a height of the at least one second sacrificial structure mesa 6 '; in step C5, a plurality of bulk acoustic wave resonators are formed on an extended plane 43, wherein the extended plane 43 coincides with the pre-polishing surface 42; after step C53': patterning the second sub-polishing layer 51 (as shown in FIG. 4G), and after the steps C54 ', C55' and C6 (as shown in FIG. 4H), wherein the second sub-polishing layer 51 on the pre-polished surface 42 (extension plane 43), under the polished surface 41 and under the at least one first bulk acoustic wave resonator 3 forms a bottom electrode layer 30 of the at least one first bulk acoustic wave resonator 3; wherein the second sub-polishing layer 51 under the pre-polished surface 42 (extended plane 43) and under the at least one first bulk acoustic wave resonant structure 3 forms a first frequency tuning structure 50 of the at least one first bulk acoustic wave resonant structure 3; wherein the second sub-polishing layer 51 located above the pre-polishing surface 42 (extension plane 43), below the polishing surface 41, and below the at least one second bulk acoustic wave resonator 3 'forms a bottom electrode layer 30 of the at least one second bulk acoustic wave resonator 3'; wherein the second sub-polishing layer 51 under the pre-polished surface 42 (extension plane 43) and under the at least one second bulk acoustic wave resonant structure 3 ' forms a second frequency tuning structure 50 ' of the at least one second bulk acoustic wave resonant structure 3 '; the first frequency tuning structure 50 and the second frequency tuning structure 50' have a first thickness difference TD1, and the first thickness difference TD1 is equal to the first height difference HD 1. By adjusting the first height difference HD1, the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3' can be tuned. Wherein the material constituting the second polishing layer 51 comprises at least one selected from the group consisting of: metals and alloys; in a preferred embodiment, the material of the second polishing layer 51 comprises at least one selected from the following group: ruthenium, titanium, molybdenum, platinum, gold, aluminum, and tungsten.
Please refer to fig. 4I, which is a schematic cross-sectional view illustrating a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention. In this embodiment, the substrate 10 may be a semiconductor substrate; the material forming the plurality of sacrificial structure mesas comprises at least one selected from the group consisting of: metals, alloys, and epitaxial structures. The main process steps for forming the embodiment shown in fig. 4I are substantially the same as the process steps for forming the embodiment shown in fig. 3L, however, step C4 is: etching (as shown in fig. 4A) the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6 ' such that the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6 ' have a first height difference, wherein a height of the at least one first sacrificial structure mesa 6 is greater than a height of the at least one second sacrificial structure mesa 6 '; and wherein in step C52 ″, the second polishing layer 51 is polished such that the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6 ' are not exposed, the second polishing layer 51 is patterned in step C53 ″ (as shown in fig. 4G), and after steps C54 ″ -step C56 ″ -and C6 (as shown in fig. 4I), whereby the second polishing layer 51, which is located below the polishing surface 41 (the extension plane 43) and below the at least one first bulk acoustic wave resonant structure 3 and below the at least one second bulk acoustic wave resonant structure 3 ', respectively forms a first frequency tuning structure 50 of the at least one first bulk acoustic wave resonant structure 3 and a second frequency tuning structure 50 ' of the at least one second bulk acoustic wave resonant structure 3 ', wherein the first frequency tuning structure 50 and the second frequency tuning structure 50 ' have a first thickness difference TD1, the first thickness difference TD1 is equal to the first height difference HD 1. By adjusting the first height difference HD1, the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3' can be tuned. In this embodiment, the material constituting the second polishing layer 51 may include at least one selected from the following group: metals, alloys, and insulators.
Please refer to fig. 4J to 4M, which are schematic cross-sectional views illustrating processing steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention. Wherein in the embodiment shown in fig. 4J, the substrate 10 is a compound semiconductor substrate; the material forming the sacrificial structure 21 is an epitaxial structure. The epitaxial structure of the embodiment of fig. 4J is substantially the same as that of the embodiment of fig. 2L, however, the sacrificial structure 21 includes a sacrificial epitaxial layer 27, a first etch stop layer 22, a first fine tuning layer 23, and a top etch stop layer 26. Wherein step C1 includes the steps of: step C11: forming a sacrificial structure 21 on the substrate 10; and step C12: the sacrificial structure 27 is etched to form a plurality of sacrificial structure mesas having the same height, wherein the plurality of sacrificial structure mesas includes at least one first sacrificial structure mesa 6 and at least one second sacrificial structure mesa 6'. Wherein a sacrificial epitaxial layer 27 is formed on the substrate 10, a first etch stop layer 22 is formed on the sacrificial epitaxial layer 27, a first fine tuning layer 23 is formed on the first etch stop layer 22, and a top etch stop layer 26 is formed on the first fine tuning layer 23. After the step C2 and the step C3, the structure shown in fig. 4K is formed. Wherein step C4 includes the steps of: step C41: etching (as shown in fig. 4L) the top etch stop layer 26 of the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6'; and step C42: the first fine tuning layer 23 of the at least one second sacrificial structure mesa 6 'is etched (as shown in fig. 4M) such that the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6' have a first height difference HD 1. The first fine tuning layer 23 has a thickness FT1, such that the first height difference HD1 is determined by the thickness FT1 of the first fine tuning layer 23, which facilitates the precise adjustment of the first height difference HD1, i.e., the first thickness difference TD1 of the first frequency tuning structure 50 and the second frequency tuning structure 50 ', i.e., the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonator structure 3 and the at least one second bulk acoustic wave resonator structure 3'. Embodiments such as those shown in fig. 4D, 4F, 4H, or 4I may be formed from fig. 4M. In forming the embodiment shown in fig. 4D, 4F, 4H or 4I using the epitaxial structure of fig. 4M, the insulating layer 11 is polished to expose the plurality of sacrificial mesas in step C3. In actual polishing, the sacrificial structure mesas near the center of the substrate 10 and the sacrificial structure mesas far from the center of the substrate 10 cannot be exposed at the same time. For example, when the sacrificial structure mesas located far from the center of the substrate 10 are exposed first, the polishing must be continued in order to expose the sacrificial structure mesas located near the center of the substrate 10. This causes the plurality of sacrificial structure mesas located away from the center of the substrate 10 to be polished over the head, and therefore the thickness of the first fine tuning layer 23 of the plurality of sacrificial structure mesas located away from the center of the substrate 10 is polished to be thinner than the thickness of the first fine tuning layer 23 of the plurality of sacrificial structure mesas located near the center of the substrate 10. To avoid the first fine tuning layer 23 of the plurality of sacrificial structure mesas located near the center of the substrate 10 from being ground to a different thickness than the first fine tuning layer 23 of the plurality of sacrificial structure mesas located away from the center of the substrate 10, the thickness of the first fine tuning layer 23 of the plurality of sacrificial structure mesas located near the center of the substrate 10 can be maintained equal to the thickness of the first fine tuning layer 23 of the plurality of sacrificial structure mesas located away from the center of the substrate 10 by the top etch stop layer 26. In some embodiments, substrate 10 is comprised of gallium arsenide; the sacrificial epitaxial layer 27 is made of gallium arsenide; the first etching stop layer 22 is composed of aluminum arsenide or indium gallium phosphide, wherein the first etching stop layer 22 has a thickness between 1nm and 50 nm; the first fine tuning layer 23 is composed of gallium arsenide, wherein the thickness FT1 of the first fine tuning layer 23 is between 1nm and 300 nm; the top etch stop layer 26 is comprised of indium gallium phosphide, and the top etch stop layer 26 has a thickness between 50nm and 300 nm. In other embodiments, substrate 10 is composed of indium phosphide; the sacrificial epitaxial layer 27 is composed of indium gallium arsenide; the first etching stop layer 22 is made of indium phosphide, wherein the first etching stop layer 22 has a thickness between 1nm and 50 nm; the first fine tuning layer 23 is composed of indium gallium arsenide, wherein the thickness FT1 of the first fine tuning layer 23 is between 1nm and 300 nm; the top etch stop layer 26 is comprised of indium phosphide, and the top etch stop layer 26 has a thickness between 50nm and 300 nm.
Embodiments of at least one first bulk acoustic wave resonator 1 and at least one second bulk acoustic wave resonator 1 'formed by a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to the present invention (such as the embodiments of fig. 2F, 2H, 2I, 2J, 3G, 3I, 3K, 3L, 4D, 4F, 4H and 4I) have a common feature, wherein the bottom electrode layer 30 of any bulk acoustic wave resonator structure (3 or 3') is formed on an extended plane 43. The common structure of these embodiments includes: an insulating layer 11 formed on a substrate 10, wherein the insulating layer 11 has a plurality of cavities; a plurality of bulk acoustic wave resonators respectively located on the plurality of cavities, wherein the plurality of bulk acoustic wave resonators include at least one first bulk acoustic wave resonator 3 and at least one second bulk acoustic wave resonator 3 ', the plurality of cavities include at least one first cavity 40 and at least one second cavity 40 ', the at least one first bulk acoustic wave resonator 3 and the at least one second bulk acoustic wave resonator 3 ' respectively correspond to the at least one first cavity 40 and the at least one second cavity 40 ', wherein the at least one first bulk acoustic wave resonator 3 and the at least one second bulk acoustic wave resonator 3 ' have a first resonant frequency difference FD1, wherein each of the plurality of bulk acoustic wave resonators includes: a bottom electrode layer 30 formed on an extension plane 43; a piezoelectric layer 31 formed on the bottom electrode layer 30; and a top electrode layer 32 formed on the piezoelectric layer 31; and a tunable frequency structure; the embodiments are different in that: (1) in the embodiments of fig. 2H, 2J, 3I, and 3K, the tunable frequency structure includes structure a: the insulating layer 11 has a polished upper surface, and the extension plane 43 coincides with the upper surface of the insulating layer 11; wherein the at least one second bulk acoustic wave resonator structure 3 ' has a second frequency tuning structure 50 ', the second frequency tuning structure 50 ' is formed below the extension plane 43 between the bottom electrode layer 30 of the at least one second bulk acoustic wave resonator structure 3 ' and the second cavity 40 ', wherein the at least one second frequency tuning structure 50 ' has a thickness T2, the thickness T2 is associated with the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonator structure 3 and the at least one second bulk acoustic wave resonator structure 3 '; (2) in the embodiments of fig. 2F, fig. 2I, fig. 4F and fig. 4H, the tunable frequency structure includes structure B: the insulating layer 11 has a polished upper surface, and the extension plane 43 coincides with the upper surface of the insulating layer 11; wherein the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3 ' respectively have a first frequency tuning structure 50 and a second frequency tuning structure 50 ', wherein the first frequency tuning structure 50 is formed below the extension plane 43 and between the bottom electrode layer 30 of the at least one first bulk acoustic wave resonant structure 3 and the first cavity 40, the second frequency tuning structure 50 ' is formed below the extension plane 43 and between the bottom electrode layer 30 of the at least one second bulk acoustic wave resonant structure 3 ' and the second cavity 40 ', wherein the first frequency tuning structure 50 and the second frequency tuning structure 50 ' have a first thickness difference TD1, the first thickness difference TD1 is associated with the first resonance frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3 '; (3) in the embodiments of fig. 3G, fig. 3L, fig. 4D and fig. 4I, the tunable frequency structure includes structure C: a second polishing layer 51 formed on the insulating layer 11 and the plurality of cavities, wherein the second polishing layer 51 has a polished upper surface, and the extension plane 43 coincides with the upper surface of the second polishing layer 51; wherein the second sub-polishing layer 51 under the extension plane 43 between the bottom electrode layer 30 of the at least one first bulk acoustic wave resonant structure 3 and the first cavity 40 forms a first frequency tuning structure 50 of the at least one first bulk acoustic wave resonant structure 3, wherein the second sub-polishing layer 51 under the extension plane 43 between the bottom electrode layer 30 of the at least one second bulk acoustic wave resonant structure 3 'and the second cavity 40' forms a second frequency tuning structure 50 'of the at least one second bulk acoustic wave resonant structure 3', wherein the first frequency tuning structure 50 and the second frequency tuning structure 50 'have a first thickness difference TD1, the first thickness difference TD1 is associated with the first resonance frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3'. Among them, in the embodiments of fig. 2F, fig. 2I, fig. 3G, fig. 3L, fig. 4D, fig. 4F, fig. 4H and fig. 4I of the present invention, it is common that: the bottom electrode layer 30 of the at least one first bulk acoustic wave resonator 3 and the bottom electrode layer 30 of the at least one second bulk acoustic wave resonator 3' are formed on the extension plane 43; the first frequency tuning structure 50 and the second frequency tuning structure 50' are formed below the extension plane 43. Among them, in the embodiments of fig. 2H, fig. 2J, fig. 3I and fig. 3K of the present invention, it is common that: the bottom electrode layer 30 of the at least one first bulk acoustic wave resonator 3 and the bottom electrode layer 30 of the at least one second bulk acoustic wave resonator 3' are formed on the extension plane 43; the second frequency tuning structures 50' are all formed below the extension plane 43.
Please refer to fig. 5A to 5C, which are schematic cross-sectional views illustrating process steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to an embodiment of the present invention. In this embodiment, the substrate 10 may be a semiconductor substrate; the material forming the plurality of sacrificial structure mesas comprises at least one selected from the group consisting of: metals, alloys, and epitaxial structures. The main process steps for forming the embodiment shown in fig. 5C are substantially the same as the process steps for forming the embodiment shown in fig. 2F, but at least one first bulk acoustic resonator 1, at least one second bulk acoustic resonator 1' and at least one third bulk acoustic resonator 1 ″ are formed on the substrate 10; wherein in step B1, the plurality of sacrificial structure mesas (as shown in fig. 5B) includes at least one first sacrificial structure mesa 6, at least one second sacrificial structure mesa 6' and at least one third sacrificial structure mesa 6 "; wherein a height of the at least one first sacrificial structure mesa 6 is greater than a height of the at least one second sacrificial structure mesa 6 ', wherein the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6' have a first height difference HD 1; wherein the height of the at least one first sacrificial structure mesa 6 is greater than a height of the at least one third sacrificial structure mesa 6 ", wherein the at least one first sacrificial structure mesa 6 and the at least one third sacrificial structure mesa 6" have a second height difference HD 2; in step B4, a plurality of bulk acoustic wave resonators are formed on the polishing surface 41 (extending plane 43), wherein the plurality of bulk acoustic wave resonators include at least one first bulk acoustic wave resonator 3, at least one second bulk acoustic wave resonator 3 ', and at least one third bulk acoustic wave resonator 3 ″, wherein the at least one first bulk acoustic wave resonator 3, the at least one second bulk acoustic wave resonator 3 ', and the at least one third bulk acoustic wave resonator 3 ″ are respectively located above the at least one first sacrificial structure mesa 6, the at least one second sacrificial structure mesa 6 ', and the at least one third sacrificial structure mesa 6 ″; in step B5, the plurality of sacrificial structure mesas are etched to form a plurality of cavities, wherein the plurality of cavities includes at least one first cavity 40, at least one second cavity 40 ', and at least one third cavity 40 ", wherein the at least one first cavity 40, the at least one second cavity 40 ', and the at least one third cavity 40" are respectively located below the at least one first bulk acoustic wave resonator 3, the at least one second bulk acoustic wave resonator 3 ', and the at least one third bulk acoustic wave resonator 3 ". In step B3, the insulating layer 11 is polished to expose the at least one first sacrificial structure mesa 6, the at least one second sacrificial structure mesa 6 'and the at least one third sacrificial structure mesa 6 ", so that the insulating layer 11 under the polishing surface 41 and under the at least one first bulk acoustic wave resonator structure 3, the at least one second bulk acoustic wave resonator structure 3' and the at least one third bulk acoustic wave resonator structure 3" respectively form a first frequency tuning structure 50 of the at least one first bulk acoustic wave resonator structure 3, a second frequency tuning structure 50 'of the at least one second bulk acoustic wave resonator structure 3' and a third frequency tuning structure 50 "of the at least one third bulk acoustic wave resonator structure 3". Wherein the first frequency tuning structure 50 and the second frequency tuning structure 50' have a first thickness difference TD1, and the first thickness difference TD1 is equal to the first height difference HD 1; and wherein the first frequency tuning structure 50 and the third frequency tuning structure 50 ″ have a second thickness difference TD2, and the second thickness difference TD2 is equal to the second height difference HD 2. By adjusting the first height difference HD1, the first resonance frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3' can be tuned. By adjusting the second height difference HD2, a second resonant frequency difference FD2 between the at least one first bulk acoustic wave resonator 3 and the at least one third bulk acoustic wave resonator 3 "can be tuned. In some embodiments, the substrate 10 may be a compound semiconductor substrate; the material forming the plurality of sacrificial structure mesas is an epitaxial structure; and wherein the aforementioned step B1 comprises the steps of: step B11: (as shown in FIG. 5A) forming a sacrificial structure 21 on the substrate 10; step B12: etching the sacrificial structure 21 to form a plurality of sacrificial structure mesas, wherein the plurality of sacrificial structure mesas include at least one first sacrificial structure mesa 6(21), at least one second sacrificial structure mesa 6 '(21), and at least one third sacrificial structure mesa 6' (21), and the plurality of sacrificial structure mesas have the same height; and step B13: the at least one first sacrificial structure mesa 6, the at least one second sacrificial structure mesa 6 ' and the at least one third sacrificial structure mesa 6 ″ are etched (as shown in fig. 5B) or the at least one second sacrificial structure mesa 6 ' and the at least one third sacrificial structure mesa 6 ″ are etched such that the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6 ' have a first height difference HD1 and the at least one first sacrificial structure mesa 6 and the at least one third sacrificial structure mesa 6 ″ have a second height difference HD 2.
Fig. 5D is a schematic cross-sectional view of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention. In this embodiment, the substrate 10 may be a semiconductor substrate; the material forming the plurality of sacrificial structure mesas comprises at least one selected from the group consisting of: metals, alloys, and epitaxial structures. The main processing steps for forming the embodiment shown in fig. 5D are substantially the same as the processing steps for forming the embodiment shown in fig. 5C, however, in step B3, the insulating layer 11 is polished to expose the at least one first sacrificial structure mesa 6, and to leave the at least one second sacrificial structure mesa 6 'and the at least one third sacrificial structure mesa 6 ″ unexposed, whereby the insulating layer 11 located below the polished surface 41 (extension plane 43) and below the at least one second bulk acoustic wave resonator structure 3' forms a second frequency tuning structure 50 'of the at least one second bulk acoustic wave resonator structure 3'; and the insulating layer 11 under the polishing surface 41 and under the at least one third bulk acoustic wave resonant structure 3 "forms a third frequency tuning structure 50" of the at least one third bulk acoustic wave resonant structure 3 ". Wherein the second frequency tuning structure 50 'has a thickness T2, the thickness T2 of the second frequency tuning structure 50' is equal to the first height difference HD 1; wherein the third frequency tuning structure 50 "has a thickness T3, and the thickness T3 of the third frequency tuning structure 50" is equal to the second height difference HD 2. In this embodiment, the first frequency tuning structure 50 of the embodiment shown in fig. 5C is not present. Therefore, the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3 ' is related to the thickness T2 of the second frequency tuning structure 50 ', i.e. to the first height difference HD1 of the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6 '; the second resonant frequency difference FD2 of the at least one first bulk acoustic wave resonant structure 3 and the at least one third bulk acoustic wave resonant structure 3 "is related to the thickness T3 of the third frequency tuning structure 50", i.e. to the second height difference HD2 of the at least one first sacrificial structure mesa 6 and the at least one third sacrificial structure mesa 6 ". Tuning a first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3' by adjusting the first height difference HD 1; by adjusting the second height difference HD2, the second resonant frequency difference FD2 of the at least one first bulk acoustic wave resonator structure 3 and the at least one third bulk acoustic wave resonator structure 3 ″ can be tuned.
Please refer to fig. 5E to 5G, which are schematic cross-sectional views illustrating processing steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention. Wherein in the embodiment shown in fig. 5E, the substrate 10 is a compound semiconductor substrate; the material forming the sacrificial structure 21 is an epitaxial structure. The epitaxial structure of the embodiment of fig. 5E-5G is substantially the same as that of the embodiment of fig. 5A-5B, but the sacrificial structure 21 includes a sacrificial epitaxial layer 27, a second etch stop layer 24, a second fine tuning layer 25, a first etch stop layer 22, and a first fine tuning layer 23. Wherein a sacrificial epitaxial layer 27 is formed on the substrate 10, a second etching stop layer 24 is formed on the sacrificial epitaxial layer 27, a second fine tuning layer 25 is formed on the second etching stop layer 24, a first etching stop layer 22 is formed on the second fine tuning layer 25, and a first fine tuning layer 23 is formed on the first etching stop layer 22. As shown in fig. 5F, the sacrificial structure 21 is etched into a plurality of sacrificial structure mesas, wherein the plurality of sacrificial structure mesas includes at least one first sacrificial structure mesa 6, at least one second sacrificial structure mesa 6' and at least one third sacrificial structure mesa 6 ″ and have the same height. As shown in FIG. 5G, the first fine tuning layer 23 has a thickness FT1, the first etch stop layer 22 has a thickness ET1, and the second fine tuning layer 25 has a thickness FT 2. Etching the first fine tuning layer 23 of the at least one second sacrificial structure mesa 6 'such that the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6' have a first height difference HD 1; the first fine tuning layer 23, the first etch stop layer 22 and the second fine tuning layer 25 of the at least one third sacrificial structure mesa 6 "are etched such that the at least one first sacrificial structure mesa 6 and the at least one third sacrificial structure mesa 6" have a second height difference HD 2. From the structure of FIG. 5G, an embodiment like that of FIG. 5C can be formed; the first height difference HD1 is determined by the thickness FT1 of the first fine tuning layer 23, which facilitates to precisely adjust the first height difference HD1, i.e. to precisely adjust the first thickness difference TD1 of the first frequency tuning structure 50 and the second frequency tuning structure 50 ', i.e. to precisely adjust the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3'. The second height difference HD2 is determined by the thickness FT1 of the first fine tuning layer 23, the thickness ET1 of the first etch stop layer 22 and the thickness FT2 of the second fine tuning layer 25, which facilitates the precise adjustment of the second height difference HD2, i.e., the precise adjustment of the second resonance frequency difference FD2 of the at least one first bulk acoustic wave resonant structure 3 and the at least one third bulk acoustic wave resonant structure 3 ". From the structure of FIG. 5G, the embodiment of FIG. 5D may also be formed; the first height difference HD1 is determined by the thickness FT1 of the first fine tuning layer 23, which facilitates fine adjustment of the first height difference HD1, i.e., the thickness T2 of the second frequency tuning structure 50 ', i.e., the first resonant frequency difference FD1 between the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3'. The second height difference HD2 is determined by the thickness FT1 of the first fine tuning layer 23, the thickness ET1 of the first etch stop layer 22, and the thickness FT2 of the second fine tuning layer 25, which facilitates to precisely adjust the second height difference HD2, i.e. the thickness T3 of the third frequency tuning structure 50 ", i.e. the second resonance frequency difference FD2 of the at least one first bulk acoustic wave resonator structure 3 and the at least one third bulk acoustic wave resonator structure 3". In some embodiments, substrate 10 is comprised of gallium arsenide; the sacrificial epitaxial layer 27 is made of gallium arsenide; the first etching stop layer 22 is composed of aluminum arsenide or indium gallium phosphide, wherein the first etching stop layer 22 has a thickness between 1nm and 50 nm; the first fine tuning layer 23 is made of gallium arsenide, wherein the thickness FT1 of the first fine tuning layer 23 is between 1nm and 300 nm; the second etching stop layer 24 is made of aluminum arsenide or indium gallium phosphide, wherein the second etching stop layer 24 has a thickness between 1nm and 50 nm; the second fine tuning layer 25 is made of gallium arsenide, wherein the thickness FT1 of the second fine tuning layer 25 is between 1nm and 300 nm. In other embodiments, substrate 10 is composed of indium phosphide; the sacrificial epitaxial layer 27 is composed of indium gallium arsenide; the first etching stop layer 22 is made of indium phosphide, wherein the first etching stop layer 22 has a thickness between 1nm and 50 nm; the first fine tuning layer 23 is composed of indium gallium arsenide, wherein the thickness FT1 of the first fine tuning layer 23 is between 1nm and 300 nm; the second etching stop layer 24 is made of indium phosphide, wherein the second etching stop layer 24 has a thickness between 1nm and 50 nm; the second fine tuning layer 25 is composed of indium gallium arsenide, wherein the thickness FT1 of the second fine tuning layer 25 is between 1nm and 300 nm.
Please refer to fig. 5H to 5K, which are schematic cross-sectional views illustrating processing steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention. In this embodiment, the substrate 10 is a compound semiconductor substrate; the sacrificial structure 21 is made of an epitaxial structure. The embodiment shown in fig. 5K is formed from the epitaxial structure shown in fig. 5E. The main process steps for forming the embodiment shown in fig. 5K are substantially the same as the process steps for forming the embodiment shown in fig. 3G, but at least one first bulk acoustic resonator 1, at least one second bulk acoustic resonator 1' and at least one third bulk acoustic resonator 1 ″ are formed on the substrate 10; wherein step C1 includes the steps of: step C11: a sacrificial structure 21 is formed over the substrate 10 (as shown in fig. 5E), wherein the sacrificial structure 21 includes a sacrificial epitaxial layer 27, a second etch stop layer 24, a second fine tuning layer 25, a first etch stop layer 22, and a first fine tuning layer 23. Wherein the sacrificial epitaxial layer 27 is formed on the substrate 10, the second etching stop layer 24 is formed on the sacrificial epitaxial layer 27, the second fine tuning layer 25 is formed on the second etching stop layer 24, the first etching stop layer 22 is formed on the second fine tuning layer 25, and the first fine tuning layer 23 is formed on the first etching stop layer 22; and step C12: the sacrificial structure 27 is etched (as shown in fig. 5F) to form a plurality of sacrificial structure mesas having the same height, wherein the plurality of sacrificial structure mesas includes at least one first sacrificial structure mesa 6, at least one second sacrificial structure mesa 6' and at least one third sacrificial structure mesa 6 ". Through steps C2 and C3, the structure shown in FIG. 5H is formed. Wherein step C4: etching the first fine tuning layer 23 of the at least one second sacrificial structure mesa 6 '(as shown in fig. 5I) such that the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6' have a first height difference HD 1; the first fine tuning layer 23, the first etch stop layer 22 and the second fine tuning layer 25 of the at least one third sacrificial structure mesa 6 "are etched such that the at least one first sacrificial structure mesa 6 and the at least one third sacrificial structure mesa 6" have a second height difference HD 2. Wherein the first fine tuning layer 23 has a thickness FT1, the first etch stop layer 22 has a thickness ET1, and the second fine tuning layer 25 has a thickness FT 2. Wherein in step C5: forming a plurality of bulk acoustic wave resonant structures, wherein the plurality of bulk acoustic wave resonant structures include at least one first bulk acoustic wave resonant structure 3, at least one second bulk acoustic wave resonant structure 3', and at least one third bulk acoustic wave resonant structure 3 "; wherein the step C5 comprises the following steps: step C51, step C52, step C53, step C54, and step C55. Through the steps C51 and C52, the structure shown in fig. 5J is formed, wherein the second polished layer 51 is polished to expose the at least one first sacrificial structure mesa 6, the at least one second sacrificial structure mesa 6 'and the at least one third sacrificial structure mesa 6 ", such that the second polished layer 51 under the polished surface 41 (extension plane 43) and under the at least one first bulk acoustic wave resonator structure 3, the at least one second bulk acoustic wave resonator structure 3' and the at least one first bulk acoustic wave resonator structure 3" respectively forms a first frequency tuning structure 50 of the at least one first bulk acoustic wave resonator structure 3, a second frequency tuning structure 50 'of the at least one second bulk acoustic wave resonator structure 3' and a third frequency tuning structure 50 "of the at least one third bulk acoustic wave resonator structure 3". The first frequency tuning structure 50 and the second frequency tuning structure 50' have a first thickness difference TD1, and the first thickness difference TD1 is equal to the first height difference HD 1. The first frequency tuning structure 50 and the third frequency tuning structure 50 ″ have a second thickness difference TD2, and the second thickness difference TD2 is equal to the second height difference HD 2. The structure shown in fig. 5K is formed through the steps C53, C54, C55 and C6, wherein the plurality of cavities includes at least one first cavity 40, at least one second cavity 40' and at least one third cavity 40 ″. Wherein the at least one first bulk acoustic wave resonator structure 3 and the at least one second bulk acoustic wave resonator structure 3 'have a first resonant frequency difference FD1, the first resonant frequency difference FD1 is associated with the first thickness difference TD1 of the first frequency tuning structure 50 and the second frequency tuning structure 50', that is, the first height difference HD 1; thus, the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3' can be tuned by adjusting the first height difference HD 1. Wherein the at least one first bulk acoustic wave resonator structure 3 and the at least one third bulk acoustic wave resonator structure 3 ″ have a second resonance frequency difference FD2, the second resonance frequency difference FD2 is associated with the second thickness difference TD2 of the first frequency tuning structure 50 and the third frequency tuning structure 50 ″, i.e., the second height difference HD 2; therefore, by adjusting the second height difference HD2, the second resonant frequency difference FD2 of the at least one first bulk acoustic wave resonant structure 3 and the at least one third bulk acoustic wave resonant structure 3 ″ can be tuned. Wherein the material constituting the second polishing layer 51 is an insulator.
Please refer to fig. 5L and 5M, which are schematic cross-sectional views illustrating processing steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to an embodiment of the present invention. In this embodiment, the substrate 10 is a compound semiconductor substrate; the sacrificial structure 21 is made of an epitaxial structure. The main processing steps for forming the embodiment shown in fig. 5M are substantially the same as the processing steps for forming the embodiment shown in fig. 5K, wherein in step C52, the second sub-polish layer 51 is polished such that at least one first sacrificial structure mesa 6 is exposed, and at least one second sacrificial structure mesa 6 'and at least one third sacrificial structure mesa 6 ″ are not exposed (as shown in fig. 5L), whereby the second sub-polish layer 51 under the polishing surface 41 (extension plane 43) and under the at least one second bulk acoustic wave resonator structure 3' forms a second frequency tuning structure 50 'of the at least one second bulk acoustic wave resonator structure 3'; the second sub-polishing layer 51 under the polishing surface 41 and under the at least one third bulk acoustic wave resonator structure 3 "forms a third frequency tuning structure 50" of the at least one third bulk acoustic wave resonator structure 3 ". As shown in fig. 5L, wherein the second frequency tuning structure 50 'has a thickness T2, the thickness T2 of the second frequency tuning structure 50' is equal to the first height difference HD 1; wherein the third frequency tuning structure 50 "has a thickness T3, and the thickness T3 of the third frequency tuning structure 50" is equal to the second height difference HD 2. In this embodiment, the first frequency tuning structure 50 of the embodiment shown in fig. 5K is not present. Therefore, the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3 ' is related to the thickness T2 of the second frequency tuning structure 50 ', i.e. the first height difference HD1 of the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6 '. Tuning a first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3' by adjusting the first height difference HD 1; and the second resonant frequency difference FD2 of the at least one first bulk acoustic wave resonant structure 3 and the at least one third bulk acoustic wave resonant structure 3 "is related to the thickness T3 of the third frequency tuning structure 50", i.e. to the second height difference HD2 of the at least one first sacrificial structure mesa 6 and the at least one third sacrificial structure mesa 6 ". By adjusting the second height difference HD2, the second resonant frequency difference FD2 of the at least one first bulk acoustic wave resonator structure 3 and the at least one third bulk acoustic wave resonator structure 3 ″ can be tuned. In this embodiment, the material constituting the second polishing layer 51 may include at least one selected from the following group: metals, alloys, and insulators.
Please refer to fig. 5N and 5O, which are schematic cross-sectional views illustrating processing steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention. In this embodiment, the substrate 10 is a compound semiconductor substrate; the material forming the sacrificial structure 21 is an epitaxial structure. The main process steps for forming the embodiment shown in fig. 5O are substantially the same as the process steps for forming the embodiment shown in fig. 5K, however, in step C5, a plurality of bulk acoustic wave resonator structures are formed on an extended plane 43, wherein the extended plane 43 coincides with the pre-polished surface 42, wherein step C5 comprises the following steps: step C51': forming a second polishing layer 51 on the plurality of sacrificial mesas and the insulating layer 11, wherein the material of the second polishing layer 51 comprises at least one selected from the group consisting of: metals and alloys; in a preferred embodiment, the material of the second polishing layer 51 comprises at least one selected from the following group: ruthenium, titanium, molybdenum, platinum, gold, aluminum, and tungsten; step C52': polishing the second polishing layer 51 by a chemical mechanical planarization process (CMP) to form a polished surface 41, such that the plurality of sacrificial mesas are not exposed (FIG. 5J); step C53': patterning the second polishing layer 51 (as shown in FIG. 5N); step C54': forming a piezoelectric layer 31 on the polishing surface 41; and step C55': a top electrode layer 32 is formed on the piezoelectric layer 31. After etching away the plurality of sacrificial structure mesas in step C6, the embodiment shown in fig. 5O is formed. Wherein in step C4, at least one second sacrificial structure mesa 6' and at least one third sacrificial structure mesa 6 ″ are etched; wherein the second sub-polishing layer 51 located above the pre-polishing surface 42 (extension plane 43), below the polishing surface 41, and below the at least one first bulk acoustic wave resonant structure 3 forms a bottom electrode layer 30 of the at least one first bulk acoustic wave resonant structure 3; wherein the second sub-polishing layer 51 located above the pre-polishing surface 42 (extension plane 43), below the polishing surface 41, and below the at least one second bulk acoustic wave resonator 3 'forms a bottom electrode layer 30 of the at least one second bulk acoustic wave resonator 3'; wherein the second sub-polishing layer 51 underlying the pre-polished surface 42 (extension plane 43) and underlying the at least one second bulk acoustic wave resonant structure 3 ' forms a second frequency tuning structure 50 ' of the at least one second bulk acoustic wave resonant structure 3 ', wherein the second frequency tuning structure 50 ' has a thickness T2, and the thickness T2 of the second frequency tuning structure 50 ' is equal to the first height difference HD 1; wherein the second sub-polishing layer 51 located above the pre-polishing surface 42 (extension plane 43), below the polishing surface 41, and below the at least one third bulk acoustic wave resonant structure 3 "forms a bottom electrode layer 30 of the at least one third bulk acoustic wave resonant structure 3"; wherein the second sub-polishing layer 51 under the pre-polished surface 42 (the extension plane 43) and under the at least one third bulk acoustic wave resonant structure 3 "forms a third frequency tuning structure 50" of the at least one third bulk acoustic wave resonant structure 3 ", wherein the third frequency tuning structure 50" has a thickness T3, and the thickness T3 of the third frequency tuning structure 50 "is equal to the second height difference HD 2. Tuning a first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3' by adjusting the first height difference HD 1; by adjusting the second height difference HD2, the second resonant frequency difference FD2 of the at least one first bulk acoustic wave resonator structure 3 and the at least one third bulk acoustic wave resonator structure 3 ″ can be tuned.
Fig. 5P is a schematic cross-sectional view of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention. The main process steps for forming the embodiment of fig. 5P are substantially the same as those for forming the embodiment of fig. 5K, however, step C5 includes the following steps: step C51 ": forming a second polishing layer 51 on the plurality of sacrificial mesas and the insulating layer 11, wherein the substrate 10 is a compound semiconductor substrate; the material forming the plurality of sacrificial structure mesas is an epitaxial structure; wherein the material constituting the second polishing layer 51 comprises at least one selected from the group consisting of: metals, alloys, and insulators; step C52 ": polishing the second polishing layer 51 by a chemical mechanical planarization process (cmp) to form a polished surface 41 such that the at least one first sacrificial structure mesa 6, the at least one second sacrificial structure mesa 6' and the at least one third sacrificial structure mesa 6 ″ are not exposed (as shown in fig. 5J); step C53 ": patterning the second polishing layer 51 (as shown in FIG. 5N); step C54 ": forming a bottom electrode layer 30 on the polishing surface 41 (extension plane 43); step C55 ": forming a piezoelectric layer 31 on the bottom electrode layer 30; and step C56 ": a top electrode layer 32 is formed on the piezoelectric layer 31. Step C6 is performed to form the embodiment shown in fig. 5P, whereby the second sub-polishing layer 51 under the polishing surface 41 and under the at least one first bulk acoustic wave resonator structure 3, the at least one second bulk acoustic wave resonator structure 3 ', and the at least one third bulk acoustic wave resonator structure 3 ″ respectively forms a first frequency tuning structure 50 of the at least one first bulk acoustic wave resonator structure 3, a second frequency tuning structure 50 ' of the at least one second bulk acoustic wave resonator structure 3 ', and a third frequency tuning structure 50 "of the at least one third bulk acoustic wave resonator structure 3"; wherein the first frequency tuning structure 50 and the second frequency tuning structure 50' have a first thickness difference TD1, the first thickness difference TD1 is equal to the first height difference HD 1; the first frequency tuning structure 50 and the third frequency tuning structure 50 ″ have a second thickness difference TD2, and the second thickness difference TD2 is equal to the second height difference HD 2. By adjusting the first height difference HD1, the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3' can be tuned. By adjusting the second height difference HD2, a second resonant frequency difference FD2 between the at least one first bulk acoustic wave resonator 3 and the at least one third bulk acoustic wave resonator 3 "can be tuned.
The embodiments of fig. 5K, 5M, 5O, and 5P may also be formed with the structure of fig. 5A (wherein the substrate 10 is a semiconductor substrate; the material forming the plurality of sacrificial mesas comprises at least one of a metal, an alloy, and an epitaxial structure).
Please refer to fig. 6A to 6C, which are schematic cross-sectional views illustrating processing steps of a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to an embodiment of the present invention. In this embodiment, the substrate 10 may be a semiconductor substrate; the material forming the plurality of sacrificial structure mesas comprises at least one selected from the group consisting of: metals, alloys, and epitaxial structures. Wherein the structure of fig. 6A is substantially the same as the structure shown in fig. 3B, but wherein the plurality of sacrificial structure mesas includes at least one first sacrificial structure mesa 6, at least one second sacrificial structure mesa 6' and at least one third sacrificial structure mesa 6 ". The main process steps for forming the embodiment shown in fig. 6C are substantially the same as the process steps for forming the embodiment shown in fig. 4D, but at least one first bulk acoustic resonator 1, at least one second bulk acoustic resonator 1', and at least one third bulk acoustic resonator 1 ″ are formed therein; in step C1, the sacrificial structure mesas include at least one first sacrificial structure mesa 6, at least one second sacrificial structure mesa 6' and at least one third sacrificial structure mesa 6 "; wherein in step C4, the at least one first sacrificial structure mesa 6, the at least one second sacrificial structure mesa 6 'and the at least one third sacrificial structure mesa 6 ″ are etched such that the at least one first sacrificial structure mesa 6 and the at least one second sacrificial structure mesa 6' have a first height difference HD1 and the at least one first sacrificial structure mesa 6 and the at least one third sacrificial structure mesa 6 ″ have a second height difference HD2 (as shown in fig. 6B); in step C5, the plurality of bulk acoustic wave resonators includes at least one first bulk acoustic wave resonator 3, at least one second bulk acoustic wave resonator 3 ', and at least one third bulk acoustic wave resonator 3 ″, where the at least one first bulk acoustic wave resonator 3, the at least one second bulk acoustic wave resonator 3 ', and the at least one third bulk acoustic wave resonator 3 ″ are respectively located on the at least one first sacrificial structure mesa 6, the at least one second sacrificial structure mesa 6 ', and the at least one third sacrificial structure mesa 6 ″; in step C52, the second polishing layer 51 is polished to expose the at least one first sacrificial structure mesa 6, the at least one second sacrificial structure mesa 6 'and the at least one third sacrificial structure mesa 6 ", so that the second polishing layer 51 under the polishing surface 41 (the extension plane 43) and under the at least one first bulk acoustic wave resonator structure 3, the at least one second bulk acoustic wave resonator structure 3' and the at least one first bulk acoustic wave resonator structure 3" respectively form a first frequency tuning structure 50 of the at least one first bulk acoustic wave resonator structure 3, a second frequency tuning structure 50 'of the at least one second bulk acoustic wave resonator structure 3' and a third frequency tuning structure 50 "of the at least one third bulk acoustic wave resonator structure 3"; wherein the first frequency tuning structure 50 and the second frequency tuning structure 50' have a first thickness difference TD1, the first thickness difference TD1 is equal to the first height difference HD 1; the first frequency tuning structure 50 and the third frequency tuning structure 50 ″ have a second thickness difference TD2, and the second thickness difference TD2 is equal to the second height difference HD 2. By adjusting the first height difference HD1, the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3' can be tuned. By adjusting the second height difference HD2, a second resonant frequency difference FD2 between the at least one first bulk acoustic wave resonator 3 and the at least one third bulk acoustic wave resonator 3 "can be tuned. Wherein the material constituting the second polishing layer 51 is an insulator.
Please refer to fig. 6D, which is a schematic cross-sectional view illustrating a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention. In this embodiment, the substrate 10 may be a semiconductor substrate; the material forming the plurality of sacrificial structure mesas comprises at least one selected from the group consisting of: metals, alloys, and epitaxial structures. The main processing steps for forming the embodiment shown in fig. 6D are substantially the same as the processing steps for forming the embodiment shown in fig. 6C, but wherein in step C52, the second polishing layer 51 is polished at least until the polishing surface 41 (extension plane 43) coincides with the pre-polishing surface 42 or the polishing surface 41 is lower than the pre-polishing surface 42, and wherein the at least one first sacrificial structure mesa 6, the at least one second sacrificial structure mesa 6' and the at least one third sacrificial structure mesa 6 ″ are not exposed. In this embodiment, the material constituting the second polishing layer 51 may include at least one selected from the following group: metals, alloys, and insulators.
Please refer to fig. 6E, which is a schematic cross-sectional view illustrating a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention. In this embodiment, the substrate 10 may be a semiconductor substrate; the material forming the plurality of sacrificial structure mesas comprises at least one selected from the group consisting of: metals, alloys, and epitaxial structures. The main processing steps for forming the embodiment shown in fig. 6E are substantially the same as the processing steps for forming the embodiment shown in fig. 6C, however, in step C5, a plurality of bulk acoustic wave resonator structures are formed on an extended plane 43, wherein the extended plane 43 coincides with the pre-polished surface 42, wherein step C5 includes the following steps: step C51': forming a second polishing layer 51 on the plurality of sacrificial mesas and the insulating layer 11, wherein the material of the second polishing layer 51 comprises at least one selected from the group consisting of: metals and alloys; in a preferred embodiment, the material of the second polishing layer 51 comprises at least one selected from the following group: ruthenium, titanium, molybdenum, platinum, gold, aluminum, and tungsten; step C52': polishing the second polishing layer 51 by a chemical mechanical planarization process to form a polishing surface 41 such that the plurality of sacrificial mesas are not exposed; step C53': patterning the second polishing layer 51; step C54': forming a piezoelectric layer 31 on the polishing surface 41; and step C55': a top electrode layer 32 is formed on the piezoelectric layer 31. After etching away the plurality of sacrificial structure mesas in step C6, the embodiment shown in fig. 6E is formed. Wherein the second sub-polishing layer 51 located above the pre-polishing surface 42 (extension plane 43), below the polishing surface 41, and below the at least one first bulk acoustic wave resonant structure 3 forms a bottom electrode layer 30 of the at least one first bulk acoustic wave resonant structure 3; wherein the second sub-polishing layer 51 under the pre-polished surface 42 (extended plane 43) and under the at least one first bulk acoustic wave resonant structure 3 forms a first frequency tuning structure 50 of the at least one first bulk acoustic wave resonant structure 3; wherein the second sub-polishing layer 51 located above the pre-polishing surface 42 (extension plane 43), below the polishing surface 41, and below the at least one second bulk acoustic wave resonator 3 'forms a bottom electrode layer 30 of the at least one second bulk acoustic wave resonator 3'; wherein the second sub-polishing layer 51 underlying the pre-polished surface 42 (extension plane 43) and underlying the at least one second bulk acoustic wave resonant structure 3 'forms a second frequency tuning structure 50' of the at least one second bulk acoustic wave resonant structure 3 ', wherein the first frequency tuning structure 50 and the second frequency tuning structure 50' have a first thickness difference TD1, the first thickness difference TD1 being equal to the first height difference HD 1; wherein the second sub-polishing layer 51 located above the pre-polishing surface 42 (extension plane 43), below the polishing surface 41, and below the at least one third bulk acoustic wave resonant structure 3 "forms a bottom electrode layer 30 of the at least one third bulk acoustic wave resonant structure 3"; wherein the second sub-polishing layer 51 under the pre-polished surface 42 (the extension plane 43) and under the at least one third bulk acoustic wave resonant structure 3 "forms a third frequency tuning structure 50" of the at least one third bulk acoustic wave resonant structure 3 ", wherein the first frequency tuning structure 50 and the third frequency tuning structure 50" have a second thickness difference TD2, and the second thickness difference TD2 is equal to the second height difference HD 2. By adjusting the first height difference HD1, the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3' can be tuned. By adjusting the second height difference HD2, a second resonant frequency difference FD2 between the at least one first bulk acoustic wave resonator 3 and the at least one third bulk acoustic wave resonator 3 "can be tuned.
Please refer to fig. 6F, which is a schematic cross-sectional view illustrating a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention. The main processing steps for forming the embodiment shown in fig. 6F are substantially the same as the processing steps for forming the embodiment shown in fig. 6C, however, step C5 includes the following steps: step C51 ": forming a second polishing layer 51 on the plurality of sacrificial mesas and the insulating layer 11, wherein the substrate 10 is a compound semiconductor substrate; the material forming the plurality of sacrificial structure mesas is an epitaxial structure; wherein the material constituting the second polishing layer 51 comprises at least one selected from the group consisting of: metals, alloys, and insulators; step C52 ": polishing the second polishing layer 51 by a chemical mechanical planarization process to form a polished surface 41 such that the at least one first sacrificial mesa 6, the at least one second sacrificial mesa 6' and the at least one third sacrificial mesa 6 ″ are not exposed; step C53 ": patterning the second polishing layer 51; step C54 ": forming a bottom electrode layer 30 on the polishing surface 41 (extension plane 43); step C55 ": forming a piezoelectric layer 31 on the bottom electrode layer 30; and step C56 ": a top electrode layer 32 is formed on the piezoelectric layer 31. Step C6 is performed to form the embodiment shown in fig. 6F, whereby the second sub-polishing layer 51 under the polishing surface 41 and under the at least one first bulk acoustic wave resonator structure 3, the at least one second bulk acoustic wave resonator structure 3 ', and the at least one third bulk acoustic wave resonator structure 3 ″ respectively forms a first frequency tuning structure 50 of the at least one first bulk acoustic wave resonator structure 3, a second frequency tuning structure 50 ' of the at least one second bulk acoustic wave resonator structure 3 ', and a third frequency tuning structure 50 "of the at least one third bulk acoustic wave resonator structure 3"; wherein the first frequency tuning structure 50 and the second frequency tuning structure 50' have a first thickness difference TD1, the first thickness difference TD1 is equal to the first height difference HD 1; the first frequency tuning structure 50 and the third frequency tuning structure 50 ″ have a second thickness difference TD2, and the second thickness difference TD2 is equal to the second height difference HD 2. By adjusting the first height difference HD1, the first resonant frequency difference FD1 of the at least one first bulk acoustic wave resonant structure 3 and the at least one second bulk acoustic wave resonant structure 3' can be tuned. By adjusting the second height difference HD2, a second resonant frequency difference FD2 between the at least one first bulk acoustic wave resonator 3 and the at least one third bulk acoustic wave resonator 3 "can be tuned.
The embodiments shown in fig. 6C, 6D, 6E, and 6F can also be formed by the epitaxial structure shown in fig. 5E, wherein the substrate 10 is a compound semiconductor substrate; the material forming the sacrificial structure 21 is an epitaxial structure.
The sacrificial structure 21 of fig. 5E may further include a top etch stop layer 26 formed on the first fine tuning layer 23 (not shown), thereby forming the embodiments of fig. 6C, 6D, 6E, and 6F. Wherein the function of this top etch stop layer 26 is the same as the function of the top etch stop layer 26 in figure 4J. To avoid the first fine tuning layer 23 of the plurality of sacrificial structure mesas located near the center of the substrate 10 from being ground to a different thickness than the first fine tuning layer 23 of the plurality of sacrificial structure mesas located away from the center of the substrate 10, the thickness of the first fine tuning layer 23 of the plurality of sacrificial structure mesas located near the center of the substrate 10 can be maintained equal to the thickness of the first fine tuning layer 23 of the plurality of sacrificial structure mesas located away from the center of the substrate 10 by the top etch stop layer 26.
In the embodiments of fig. 5C, 5K, 5P, 6C, 6D, 6E and 6F of the present invention, it is common that: the bottom electrode layer 30 of the at least one first bulk acoustic wave resonator structure 3, the bottom electrode layer 30 of the at least one second bulk acoustic wave resonator structure 3', and the bottom electrode layer 30 of the at least one first bulk acoustic wave resonator structure 3 ″ are all formed on the extension plane 43; the first frequency tuning structure 50, the second frequency tuning structure 50', and the first frequency tuning structure 50 ″ are all formed below the extension plane 43. In the embodiments of fig. 5D, 5M and 5O of the present invention, it is common that: the bottom electrode layer 30 of the at least one first bulk acoustic wave resonator structure 3, the bottom electrode layer 30 of the at least one second bulk acoustic wave resonator structure 3', and the bottom electrode layer 30 of the at least one first bulk acoustic wave resonator structure 3 ″ are all formed on the extension plane 43; the second frequency tuning structure 50' and the first frequency tuning structure 50 ″ are formed below the extension plane 43.
The embodiments of fig. 3G, fig. 3I, fig. 3K, fig. 3L, fig. 4D, fig. 4F, fig. 4H, fig. 4I, fig. 5C, fig. 5D, fig. 5K, fig. 5M, fig. 5O, fig. 5P, fig. 6C, fig. 6D, fig. 6E, and fig. 6F can be the same as the embodiments of fig. 2I or fig. 2J, and further include a bottom etching stop layer 20, wherein the bottom etching stop layer 20 is formed on the substrate 10, the insulating layer 11 is formed on the bottom etching stop layer 20, and the at least one first cavity 40 and the at least one second cavity 40' are also located on the bottom etching stop layer 20. Wherein the substrate 10 is a compound semiconductor substrate; the material forming the plurality of sacrificial structure mesas (sacrificial structures 21) is an epitaxial structure.
Please refer to fig. 6G, which is a schematic partial enlarged cross-sectional view illustrating a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to an embodiment of the present invention. Fig. 6G is a partially enlarged cross-sectional view of the embodiment of fig. 1F, 1K, 2F, 2I and 5C of the present invention. The bottom metal layer 30 of the bulk acoustic wave resonant structure 3 can be gradually thinned in a relatively smooth manner at the edge, and the piezoelectric layer 31 of the bulk acoustic wave resonant structure 3 can also be gradually thinned in a relatively smooth manner at the edge of the bottom metal layer 30, so that the crystallization of the piezoelectric layer 31 near the edge of the bottom metal layer 30 can be maintained in a relatively good state, and the phenomenon of crystal cracking or fracture is avoided. Therefore, in the structure of fig. 6G, the bottom metal layer 30 is gradually thinned at the edge in a more gradual manner, which is a preferred embodiment. In other embodiments of the present invention, the edge of the bottom metal layer 30 of the bulk acoustic wave resonant structure 3 (or the bulk acoustic wave resonant structure 3', or the bulk acoustic wave resonant structure 3 ") also has a structure similar to that of fig. 6G, and the bottom metal layer 30 is gradually thinned in a more gradual manner. Please refer to fig. 6H, which is a schematic partial enlarged cross-sectional view illustrating a method for tuning a bulk acoustic wave resonator of a bulk acoustic wave filter according to another embodiment of the present invention. Fig. 6H is a partially enlarged cross-sectional view of the embodiment of fig. 3L and 5P of the present invention. In which the second-time polishing layer 51 is gently thinned at the edge in a more gentle manner, in addition to the bottom metal layer 30 of the bulk acoustic wave resonant structure 3 being gently thinned at the edge in a more gentle manner. In the embodiments of fig. 4I and 6F of the present invention, the second polishing layer 51 may be gradually thinned at the edge in a more gradual manner.
In the embodiment of the present invention, if the thickness of the frequency tuning structure 50 (or the frequency tuning structure 50 ', or the frequency tuning structure 50 ") is too thick, the resonant film state of the bulk acoustic wave resonant structure 3 (or the bulk acoustic wave resonant structure 3 ', or the bulk acoustic wave resonant structure 3") is affected, and therefore the thickness of the frequency tuning structure 50 (or the frequency tuning structure 50 ', or the frequency tuning structure 50 ") needs to be less than 1000 nm. In some preferred embodiments, the thickness of the frequency tuning structure 50 (or the frequency tuning structure 50', or the frequency tuning structure 50 ") is equal to or less than 300 nm.
While the invention has been described in connection with specific embodiments and implementations, many modifications and variations are possible in light of the above teaching or may be acquired from practice of the invention, and it is intended that all such modifications and variations be considered as within the spirit and scope of the invention.
In summary, the present invention can achieve the intended purpose of the invention and provide a price-point system with industrial application, which is applied for patent.

Claims (10)

1. A method of forming a cavity of a bulk acoustic wave resonator, comprising the steps of:
step A1: forming a sacrificial epitaxial structure mesa on the compound semiconductor substrate;
step A2: forming an insulating layer over the sacrificial epitaxial mesa and the compound semiconductor substrate, wherein the insulating layer includes a raised region raised by being formed over the sacrificial epitaxial mesa and a non-raised peripheral region outside the raised region, an upper surface of the non-raised peripheral region being higher than an upper surface of the sacrificial epitaxial mesa, and a bottom of the non-raised peripheral region being lower than the upper surface of the sacrificial epitaxial mesa;
step A3: grinding the insulating layer by a chemical mechanical planarization process to form a polished surface;
step A4: forming a bulk acoustic wave resonant structure over the polished surface, wherein the bulk acoustic wave resonant structure is located over the sacrificial epitaxial structure mesa, wherein the step a4 comprises the steps of:
step A41: forming a bottom electrode layer over the polishing surface;
step A42: forming a piezoelectric layer on the bottom electrode layer; and
step A43: forming a top electrode layer on the piezoelectric layer; and
step A5: etching the sacrificial epitaxial structure mesa to form a cavity, wherein the cavity is located below the bulk acoustic wave resonant structure.
2. A method of forming a cavity of a body acoustic wave resonator as claimed in claim 1, wherein a thickness of said insulating layer is greater than a height of said sacrificial epitaxial structure mesa.
3. A method of forming a cavity of a bulk acoustic wave resonator as claimed in claim 1 or 2, wherein in said step a3, said insulating layer is ground such that said sacrificial epitaxial structure mesa is not exposed, wherein said insulating layer between said bottom electrode layer and said sacrificial epitaxial structure mesa forms a frequency tuning structure, wherein said frequency tuning structure has a thickness, said bulk acoustic wave resonant structure has a resonant frequency, such that said resonant frequency of said bulk acoustic wave resonant structure can be tuned by adjusting said thickness of said frequency tuning structure.
4. A method of forming a cavity of a bulk acoustic wave resonator as claimed in claim 1 or 2, further comprising the step of forming an underetch stop layer over said compound semiconductor substrate, wherein said sacrificial epitaxial structure mesa is formed over said underetch stop layer; wherein the sacrificial epitaxial structure mesa comprises a sacrificial epitaxial layer.
5. The method of forming a cavity of a bulk acoustic wave resonator as claimed in claim 4, wherein (1) the compound semiconductor substrate is composed of gallium arsenide; the sacrificial epitaxial layer is composed of gallium arsenide; the bottom etching stop layer is composed of indium gallium phosphide; or (2) the compound semiconductor substrate is composed of indium phosphide; the sacrificial epitaxial layer is composed of indium gallium arsenide; the bottom etch stop layer is composed of indium phosphide.
6. The method of claim 4 wherein said sacrificial epitaxial layer has a thickness, said thickness of said sacrificial epitaxial layer being between 50nm and 5000 nm; wherein the bottom etch stop layer has a thickness, the thickness of the bottom etch stop layer being between 20nm and 500 nm.
7. The method of forming a cavity of a bulk acoustic wave resonator as claimed in claim 1 or 2, wherein a material constituting the insulating layer comprises at least one selected from the group consisting of: silicon nitride, silicon oxide, and polymers.
8. The method of forming a cavity of a bulk acoustic wave resonator as set forth in claim 1 or 2, wherein said step a1 comprises the steps of:
forming a sacrificial epitaxial structure on the compound semiconductor substrate; and
etching the sacrificial epitaxial structure to form the sacrificial epitaxial structure mesa.
9. A method according to claim 8, further comprising forming an etch protection layer on a lower surface of said compound semiconductor substrate before etching said sacrificial epitaxial structure to form said sacrificial epitaxial structure mesa.
10. The method of forming a cavity of a bulk acoustic wave resonator as claimed in claim 9, wherein a material constituting the etching protection layer comprises at least one selected from the group consisting of: silicon nitride, silicon oxide, aluminum nitride, and photoresist.
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