CN114400235A - Back-illuminated light detection array structure and preparation method thereof - Google Patents
Back-illuminated light detection array structure and preparation method thereof Download PDFInfo
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Abstract
The invention provides a back-illuminated optical detection array structure, which comprises: light focusing structure, substrate, light collecting structure, photodiode, and filling material. The invention also provides a preparation method of the back-illuminated light detection array structure. The invention provides a novel photoelectric tube array design, and a light focusing structure and a light collecting structure are integrated at the same time, so that the external quantum efficiency of a sensor system based on a small-size photodiode array can be effectively improved, and the integral light receiving efficiency is greatly improved; for the application scene of high-speed optical communication, only 1 or 4-8 photoelectric detectors are needed generally, the structural design of the invention can also reduce capacitance and dark current, and simultaneously ensure higher responsivity and larger alignment tolerance when coupled with optical fibers.
Description
Technical Field
The invention belongs to the technical field of photoelectric detectors, and particularly relates to a back-illuminated light detection array structure and a preparation method thereof.
Background
High density photodiode arrays have a number of applications in the sensor field, and in order to increase the sensitivity of such array sensors, it is often necessary to make the size of the photodiodes very small, e.g. a few micrometers. Although this design can effectively reduce the dark current and capacitance of the chip, it requires a complex optical design to ensure that the signal beam can be effectively collected and irradiated onto the photodiode, and the complexity of this design is especially significant for arrays having tens of thousands of photodiodes. Patent document No. 201980001248.0 discloses a germanium-based focal plane array for the short infrared spectral range, comprising: pyramid shaped silicon-based and germanium photodiodes. The technical problems of the prior art are that too many devices in the structure are limited, so that the application scene is limited and the preparation difficulty is high, for example, a silicon substrate needs to be a pyramid type, and then for example, a photodiode is prepared in the pyramid type silicon substrate, so that the photodiode can be only a PN or PIN type, and the photodiode can be prepared only by preparing the silicon substrate first, and the manufacturing difficulty is increased. In addition, the optical detection structure in the prior art also has the technical problems of poor collection effect and poor practicability.
Disclosure of Invention
In order to solve the above technical problems, the present invention provides a back-illuminated photodetector array structure and a method for manufacturing the same. The following presents a simplified summary in order to provide a basic understanding of some aspects of the disclosed embodiments. This summary is not an extensive overview and is intended to neither identify key/critical elements nor delineate the scope of such embodiments. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.
The invention adopts the following technical scheme:
in some alternative embodiments, there is provided a back-illuminated light detection array structure, comprising: the light collecting structure is used for emitting incident light through the tail end face of the light collecting structure after the incident light is reflected for multiple times in the light collecting structure; the light focusing structure is positioned on the head end surface of the light collecting structure and used for focusing external signal light into the light collecting structure; and the photodiode is positioned on the surface of the tail end face of the light collection structure and used for absorbing the light emitted by the light collection structure, and the photodiode is a germanium-silicon photodiode or a germanium-silicon avalanche photodiode.
Further, the back-illuminated light detection array structure further includes: the light collecting structure is positioned on the top surface of the substrate, and the light focusing structure is positioned on the back surface of the substrate; the light collection structure includes: the inner wall of the table top reflects incident light for multiple times and then the photodiode arranged on the tail end face of the table top absorbs emergent light; the light focusing structure includes: at least one microlens corresponding to the mesa, the microlens focusing ambient signal light into an interior of the mesa corresponding thereto.
Further, the back-illuminated light detection array structure further includes: a filling material filled between the mesas; the filling material is a polymer filling material or an SiO2 filling material, the SiO2 filling material is ground by using a CMP process, and the polymer filling material is filled by a glue homogenizing mode.
Furthermore, the outer structure of the table top is in the shape of one or more of a polygonal pyramid, a circular truncated cone, a polygonal prism and a cylinder; when the external structure is in the shape of a polygonal pyramid or a polygonal column, the bottom surface of the table top can be in the shape of a regular polygon or an irregular polygon; when the external structure is in the shape of a circular truncated cone or a cylinder, the bottom surface of the table top is in the shape of a perfect circle or an ellipse.
Furthermore, the outer wall of the table top is plated with a medium layer, and the refractive index of the medium layer is smaller than that of the filling material.
Furthermore, the dielectric layer is a metal film, and the metal film forms a reflecting mirror surface on the outer wall of the table top.
Further, the mesa is separately prepared using SiO2, SiN, or a polymer material and placed on top of the photodiode using glue or encapsulation.
Further, the micro lens is a convex lens, and the micro lens is prepared on the substrate, or is adhered or bonded on the substrate after being prepared separately by using SiO2, SiN or polymer materials.
In some alternative embodiments, the present invention further provides a method for preparing a back-illuminated photodetector array structure, comprising: preparing a photodiode array on a silicon wafer; a light collection structure is fabricated on top of the photodiode array.
Further, the preparation method of the back-illuminated light detection array structure further comprises the following steps: preparing a dielectric layer on the outer wall of the table top of the light collection structure; filling the space between the mesas with a filler material; preparing an electrode of the photodiode, a metal connecting wire and a metal end face for bonding; and preparing a micro-lens array on the back of the silicon wafer.
The invention has the following beneficial effects: the invention provides a novel photoelectric tube array design, and a light focusing structure and a light collecting structure are integrated at the same time, so that the external quantum efficiency of a sensor system based on a small-size photodiode array can be effectively improved, and the integral light receiving efficiency is greatly improved; for the application scene of high-speed optical communication, only one or 4-8 photoelectric detectors are needed generally, the structural design of the invention can also reduce capacitance and dark current, simultaneously ensure higher responsivity and have larger alignment tolerance when coupled with optical fibers.
Drawings
FIG. 1 is a schematic diagram of a back-illuminated photodetector array configuration in accordance with the present invention;
FIG. 2 is a top schematic view of a back-illuminated photodetector array configuration according to the present invention;
FIG. 3 is a schematic diagram of a first exemplary light focusing scenario for a microlens of the present invention;
FIG. 4 is a schematic diagram of a second exemplary light focusing scenario for a microlens of the present invention;
FIG. 5 is a schematic diagram of a third exemplary light focusing scenario for a microlens of the present invention;
FIG. 6 is a schematic view of the structure of a polygonal pyramid mesa of the present invention;
FIG. 7 is a schematic diagram of a structure of a polygonal prism mesa of the present invention;
FIG. 8 is a schematic diagram of the structure of a cylindrical mesa of the present invention;
FIG. 9 is a schematic view of the structure of the truncated cone table top of the present invention;
FIG. 10 is a schematic view of one of the light reflections inside the table top of the present invention;
FIG. 11 is a schematic view of another light reflection within the mesa of the present invention;
FIG. 12 is a schematic view of one of the light reflections inside the mesa having a dielectric layer of the present invention;
FIG. 13 is a schematic view of another light reflection within a mesa having a dielectric layer in accordance with the present invention;
FIG. 14 is a flow chart illustrating a method for fabricating a back-illuminated photodetector array structure according to the present invention.
Detailed Description
The following description and the drawings sufficiently illustrate specific embodiments of the invention to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical, process, and other changes. The examples merely typify possible variations. Individual components and functions are optional unless explicitly required, and the sequence of operations may vary. Portions and features of some embodiments may be included in or substituted for those of others.
In some illustrative embodiments, as shown in fig. 1-2, the present invention provides a back-illuminated light detection array structure comprising: light focusing structure, substrate 2, light collecting structure, photodiode 1, filling substance 3.
The light focusing structure is used for focusing the external signal light to the inside of the light collecting structure, and particularly, the light focusing structure comprises: at least one microlens 4, the microlens 4 functions to focus incident light, and a plurality of microlenses 4 are arranged to form an array. The light focusing structure is located on the back surface of the substrate 2, namely the micro lens 4 is attached to the back surface of the substrate 2, and the micro lens 4 focuses external signal light to the inside of the light collecting structure.
Wherein the micro lenses 4 are convex lenses, so that light outside the substrate 2 can be effectively focused into the substrate 2, and three typical light focusing situations of the micro lenses 4 are shown in fig. 3-5. The microlenses 4 are produced directly on the substrate 2, or SiO is used2SiN or a polymer material is separately prepared and then pasted or bonded on the substrate 2.
The surface of the microlens 4 may be covered with an anti-reflection layer to improve the projection efficiency of light.
Preferably, the thickness of the substrate 2 is 50 to 750 micrometers, and the light collection efficiency can be improved by designing the thickness value in this range.
The light collecting structure is used for collecting incident light, and the incident light is reflected for multiple times in the light collecting structure and then is emitted out through the tail end face of the light collecting structure. The light focusing structure is located at a leading end surface of the light collecting structure. Specifically, the light collection structure includes: at least one mesa 5, a plurality of mesas 5 arranged to form an array. The mesas 5 correspond one-to-one to the microlenses 4, i.e., each microlens 4 focuses ambient signal light into the mesa 5 located above it.
The light collection structure is located on the top surface of the substrate 2, that is, the bottom of the mesa 5 is in contact with the substrate 2, the inner wall of the mesa 5 reflects incident light for multiple times to form emergent light, the emergent light is emitted out from the top of the mesa 5 and absorbed by the photodiode 1 arranged on the top of the mesa 5, the top of the mesa 5 can also be called as the tail end surface of the mesa 5, and the tail end surface of the mesa 5 is used as the tail end surface of the light collection structure.
The mesa array may be fabricated directly on the substrate 2. The external structure shape of the table-board 5 is one or more of a polygonal pyramid, a circular truncated cone, a polygonal prism and a cylinder. The structure of the polygonal pyramid mesa 5 is shown in fig. 6, and may be, specifically, a triangular pyramid, a dodecapyramid, or the like. The structure of the polygonal prism mesa 5 is shaped as shown in fig. 7. The structural shape of the cylindrical mesa 5 is shown in fig. 8. The structure of the truncated cone surface 5 is shown in fig. 9.
When the outer structure shape of the table top 5 is a polygonal pyramid or a polygonal prism, the bottom surface shape of the table top 5 can be a regular polygon or an irregular polygon; when the external structure shape of the table top 5 is a circular truncated cone or a cylinder, the bottom surface shape of the table top 5 is a perfect circle or an ellipse. Therefore, the table-board 5 of the invention can be in various forms without being limited to one of the forms, thereby improving the practicability of the structure, being suitable for more application scenes and reducing the preparation difficulty.
The mesa 5 may be prepared by dry or wet etching. The mesa 5 is made of SiO2SiN or polymer material is separately prepared and attached to the top of the photodiode 1 by using glue, or the prepared mesa 5 is placed on the top of the photodiode 1 by using a packaging method.
The photodiode 1 is used for absorbing light emitted by the light collecting structure, and is positioned on the surface of the tail end face of the light collecting structure, namely, the surface is connected with the top face of the table-board 5. The photodiode 1 is a germanium-silicon photodiode or a germanium-silicon avalanche photodiode, so that the types of the photodiodes are more diversified, and the photodiodes are suitable for different application scenes. Each photodiode is provided with a P electrode and an N electrode, and the same electrodes among the photodiodes are connected through metal wiring.
The photodiode 1 uses silicon as a substrate, a layer of N-doped silicon as a bottom connection layer, a layer of P-doped silicon as a top connection layer, and germanium as an absorption layer. The avalanche photodiode has the following characteristics: using a layer of intrinsic silicon as a photoelectric multiplication layer; a layer of P-doped silicon is used as the charge layer.
The photodiode 1 is prepared on the top of the table top 5, and can be a PN type photodiode or a PIN type photodiode, and can also be an avalanche type photodiode, so that the photodiode 1 can be prepared firstly and then a light collection structure is prepared, and the photodiode 1 does not need to be prepared in the table top 5, thereby greatly reducing the preparation difficulty.
According to the invention, a light focusing structure is utilized to focus external signal light into the range of a light collecting structure, then the light collecting structure is utilized to enable the light to be reflected on the inner side wall of the light collecting structure for multiple times, finally the light is transmitted to the tail end of the light collecting structure, the tail end of the light collecting structure is directly provided with a photodiode 1, and the photodiode 1 absorbs the transmitted light.
The filling substance 3 is filled between the mesas 5. The invention completely fills the gap between the table-boards 5 by using the filling material 3 to planarize the front surface of the chip, thereby not only electrically isolating each single photodiode in the photodiode array, but also improving the structural strength and the surface smoothness.
The filling material 3 is polymer filling material or SiO2Filling material, SiO2The filling material is ground flat by using a CMP process, and the polymer filling material is filled and leveled in a glue evening mode, so that the preparation flexibility is improved. Spin-coating is one of the basic steps of a lithographic process, also known as spin-coatingAnd (3) coating the liquid phase photoresist material on the silicon wafer by a rotary coating method immediately after the silicon wafer is subjected to spin coating or spin coating to form a base film.
The side wall of the table-board 5 can be directly contacted with the filling material 3, or the outer wall of the table-board 5 can be contacted with the filling material 3 after being coated with the dielectric layer 6. When the filling material 3 is in direct contact with the mesa 5, reflection of light inside the mesa 5 is achieved by the difference in refractive index, thereby improving the overall collection efficiency of light. The refractive index of the dielectric layer 6 is smaller than that of the filling substance 3, thereby increasing the total reflection angle of the mesa 5 when it exits from the inside to the outside.
The dielectric layer 6 is a metal film that forms a mirror surface on the outer wall of the mesa so that any angle of light exiting from the inside of the mesa at the sidewalls can be reflected. The selected metal has extremely low absorption in the working wave band of the device, such as the wave band of 1200-1600 nm, and specifically, aluminum metal can be selected.
As shown in fig. 10-13, the light forms multiple reflections at the sidewalls of the mesa 5 against the light that is concentrated by the microlens 4, and is eventually absorbed by the photodiode 1 on the mesa 5. According to the invention, the outer wall of the table top 5 is covered with a medium layer 6 with a refractive index different from that of the table top or covered with a metal film, and then is filled with the filling material 3, so that the light collection effect is greatly improved.
When the photodiode 1, the microlens 4 and the mesa 5 are one, a single diode chip is formed. The photodiode 1, the microlens 4, and the mesa 5 may also be prepared as an array structure.
In some illustrative embodiments, as shown in fig. 1, 2 and 14, the present invention provides a method for preparing a back-illuminated light detection array structure, comprising the steps of:
101: the photodiode array is fabricated on a silicon wafer, which is the substrate 2.
102: a light collection structure is fabricated on top of the photodiode array. The light collection structure includes: the mesa 5, the mesa array, may be fabricated directly on the substrate 2, and the mesa 5 may be fabricated by dry or wet etching. The mesa 5 is made of SiO2SiN or polymer material is separately prepared and attached to the top of the photodiode 1 using glue, or usedThe encapsulation is to place the prepared mesa 5 on top of the photodiode 1.
According to the invention, the photodiode 1 is prepared firstly, and then the light collection structure is prepared, so that the photodiode does not need to be prepared in the table-board 5, and the preparation difficulty can be greatly reduced.
103: a reflective layer, i.e. a dielectric layer, is prepared on the outer wall of the mesa 5, which is an optional step. The refractive index of the dielectric layer is smaller than that of the filling material 3, so that the total reflection angle of the mesa 5 when the mesa exits from the inside to the outside is increased.
104: the space between the mesas 5 is filled up with a filling substance 3. The fill material 3 not only electrically isolates each individual photodiode in the photodiode array, but also improves structural strength and surface planarity.
The filling material 3 is polymer filling material or SiO2Filling material, SiO2The filling material is ground flat by using a CMP process, and the polymer filling material is filled and leveled in a glue evening mode, so that the preparation flexibility is improved. Spin coating or spin coating is one of the basic steps of the photolithography process, and after the base film is formed, the liquid phase photoresist material is coated on the silicon wafer by a spin coating method.
105: electrodes and metal connection traces of the photodiode 1 and metal end faces for bonding are prepared. The metal end face can be prepared into a copper column so as to facilitate the application scene of the chip reverse buckling package.
106: a microlens array is prepared on the back of the silicon wafer. The microlens array is directly prepared on the substrate 2, or is separately prepared using SiO2, SiN, or a polymer material and then pasted or bonded on the substrate 2.
107: the silicon wafer is diced to form chips.
The method has the advantages of simple flow and low preparation difficulty, and can ensure that the prepared photoelectric tube array has higher light collection efficiency, reduces capacitance and dark current, has higher responsivity and has larger alignment tolerance when being coupled with optical fibers.
Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.
Claims (10)
1. A back-illuminated light detection array structure, comprising:
the light collecting structure is used for emitting incident light through the tail end face of the light collecting structure after the incident light is reflected for multiple times in the light collecting structure;
the light focusing structure is positioned on the head end surface of the light collecting structure and used for focusing external signal light into the light collecting structure;
and the photodiode is positioned on the surface of the tail end face of the light collection structure and used for absorbing the light emitted by the light collection structure, and the photodiode is a germanium-silicon photodiode or a germanium-silicon avalanche photodiode.
2. The structure of a back-illuminated light detecting array of claim 1, further comprising: the light collecting structure is positioned on the top surface of the substrate, and the light focusing structure is positioned on the back surface of the substrate;
the light collection structure includes: the inner wall of the table top reflects incident light for multiple times and then the photodiode arranged on the tail end face of the table top absorbs emergent light;
the light focusing structure includes: at least one microlens corresponding to the mesa, the microlens focusing ambient signal light into an interior of the mesa corresponding thereto.
3. The structure of a back-illuminated light detecting array of claim 2, further comprising: a filling material filled between the mesas; the filling material is polymer filling material or SiO2Filling substance of said SiO2The filling material is ground flat by using a CMP process, and the polymer filling material is filled and leveled by a glue evening mode.
4. The back-illuminated light detection array structure of claim 3, wherein the outer structure shape of the table top is one or more of a polygonal pyramid, a circular truncated cone, a polygonal prism and a cylinder; when the external structure is in the shape of a polygonal pyramid or a polygonal column, the bottom surface of the table top can be in the shape of a regular polygon or an irregular polygon; when the external structure is in the shape of a circular truncated cone or a cylinder, the bottom surface of the table top is in the shape of a perfect circle or an ellipse.
5. The structure of claim 4, wherein the outer wall of the mesa is coated with a dielectric layer having a refractive index less than the refractive index of the filler material.
6. The structure of claim 5, wherein the dielectric layer is a metal film, and the metal film forms a mirror surface on the outer wall of the mesa.
7. The back-illuminated photodetector array structure of claim 6, wherein the mesas are formed using SiO2SiN or polymer material is separately prepared and placed on top of the photodiode using glue or encapsulation.
8. The structure of claim 7, wherein the micro-lenses are convex lenses and are fabricated on the substrate, or SiO is used2SiN or polymer materials prepared separately and then adhered or bonded theretoThe substrate is described.
9. A method for preparing a back-illuminated optical detection array structure is characterized by comprising the following steps:
preparing a photodiode array on a silicon wafer;
a light collection structure is fabricated on top of the photodiode array.
10. The method for preparing a back-illuminated photodetector array structure as claimed in claim 9, further comprising:
preparing a dielectric layer on the outer wall of the table top of the light collection structure;
filling the space between the mesas with a filler material;
preparing an electrode of the photodiode, a metal connecting wire and a metal end face for bonding;
and preparing a micro-lens array on the back of the silicon wafer.
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