WO2002031974A1 - Surface acoustic wave device and method of producing the same - Google Patents

Surface acoustic wave device and method of producing the same Download PDF

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Publication number
WO2002031974A1
WO2002031974A1 PCT/JP2000/007102 JP0007102W WO0231974A1 WO 2002031974 A1 WO2002031974 A1 WO 2002031974A1 JP 0007102 W JP0007102 W JP 0007102W WO 0231974 A1 WO0231974 A1 WO 0231974A1
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Prior art keywords
film
forming
acoustic wave
surface acoustic
wave device
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PCT/JP2000/007102
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French (fr)
Japanese (ja)
Inventor
Tadashi Nakatani
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Fujitsu Limited
Fujitsu Media Devices Limited
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Priority to PCT/JP2000/007102 priority Critical patent/WO2002031974A1/en
Priority to JP2002535256A priority patent/JPWO2002031974A1/en
Publication of WO2002031974A1 publication Critical patent/WO2002031974A1/en

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    • 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
    • H03H3/08—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 resonators or networks using surface acoustic waves

Definitions

  • the present invention relates to a surface acoustic wave (SAW) 'element and a method for forming the same. More specifically, the present invention relates to a method for forming an electrode on a piezoelectric substrate constituting a Saw element and the obtained Saw element.
  • SAW surface acoustic wave
  • S AW elements for example, S AW filters
  • the SAW element generally has a structure in which a comb-shaped electrode made of a conductive film is provided on the surface of a piezoelectric substrate.
  • the comb-shaped electrode converts and reverses the mechanical S AW signal and the electrical signal, thereby realizing frequency selectivity.
  • the center frequency of the SAW filter is proportional to the propagation speed of the sine wave and inversely proportional to the wavelength. Therefore, to increase the center frequency, it is necessary to use a material having a high propagation speed for the piezoelectric substrate, or to reduce the width of the fingers of the comb-shaped electrode (hereinafter, electrode fingers) to shorten the wavelength.
  • electrode fingers For example, when a SAW filter in the 5 GHz band is formed using a piezoelectric substrate made of Y-cut X-propagating lithium tantalate crystals, the propagation speed of elastic waves is about 400 OmZ seconds. As a result, the width of the electrode finger is about 0.2 m.
  • two methods are known for patterning a comb-shaped electrode.
  • One is to form a resist pattern on a conductive film formed on a piezoelectric substrate by photolithography, and then etch the conductive film. It is a way to make a day.
  • the other is to form a conductive pattern after forming a resist pattern on a piezoelectric substrate, dissolve the resist pattern and lift off the conductive film deposited on the resist panel. Is a method of patterning.
  • the above method has the following problems.
  • Aluminum is used as the material of the comb-shaped electrode because it has a low resistivity, a low specific gravity, and hardly causes reflection.
  • aluminum has the drawback that stress migration is likely to occur, and it has poor power durability under high power, making it difficult to obtain highly reliable devices.
  • a physical etching method using an inert ion such as argon can pattern such an aluminum alloy.
  • an inert ion such as argon
  • the piezoelectric substrate is scraped by the ion impact. Such substrate damage causes deterioration of the characteristics of the SAW device.
  • lift-off There is a turning method. This is because the resist pattern 12 is formed on the substrate 11 (FIG. 4 (a)), and then the conductive film 13 is formed (FIG. 4 (b)). In this method, the electrode 14 is formed by removing the conductive film 13. In this method, it is not necessary to etch the conductive film, so that it is possible to use materials that are difficult to RIE, such as aluminum alloys. Also, there is no damage to the substrate.
  • Japanese Patent Application Laid-Open No. Hei 9-166700 discloses a method in which a silicon dioxide film is provided under a resist pattern, and the silicon dioxide film is etched so as to form an undercut. After that, a manufacturing method is disclosed in which an aluminum alloy film is formed and lifted off.
  • the present invention provides a method for forming electrodes by lift-off that solves the above-mentioned problems.
  • the present invention provides a method for forming a SAW element including the method.
  • a process of forming a first film on a piezoelectric substrate, a process of forming a second film on a first film, and a resist film having a predetermined shape on a second film Forming the second film and the first film anisotropically or isotropically using the resist pattern as a mask, and subsequently, isotropically etching only the first film in an undercut shape. Removing the resist pattern; forming an electrode material layer on the entire surface; and lifting off the electrode material layer present on the second film by etching and removing the second film.
  • a method for manufacturing a first SAW element having a step of forming is provided.
  • a step of forming a third film on the piezoelectric substrate, a step of forming a resist 1 and a pattern of a predetermined shape on the third film, and forming the third film using the resist pattern as a mask A step of isotropically etching into an undercut shape, a step of forming an electrode material layer over the entire surface, and lifting off the electrode material layer present on the third film by etching away the third film.
  • a method for manufacturing a second SAW element having a step of forming a second SAW element is provided.
  • a comb-shaped electrode finger having a predetermined pattern is provided on the piezoelectric substrate, another film is provided on the piezoelectric substrate between the electrode fingers, and the mass per unit area of the electrode finger and the other film is provided.
  • a SAW element is provided which is approximately equal.
  • FIG. 1 is a schematic plan view of an example of the SAW element.
  • FIGS. 2A to 2E are schematic process cross-sectional views of a method for manufacturing a SAW device of the present invention.
  • 3A to 3C are schematic process sectional views of a method for manufacturing a SAW element according to the present invention.
  • 4 (a) to 4 (c) are schematic process sectional views of a conventional SAW device manufacturing method by a lift-off method.
  • the SAW element generally has a piezoelectric substrate.
  • the piezoelectric substrate is not particularly limited as long as it can be used for a SAW element. Specifically, L i T a 0 3, L i N b 0 3, KN b 0 3, a piezoelectric substrate such as L i 2 B 4 0 7 and the like.
  • glass, L i T a 0 3 on a substrate such as a resin, L i N b 0 3, KN B_ ⁇ 3, L i 2 B 4 ⁇ 7 also present invention the substrate which is formed into a film shape of the piezoelectric material back side that conductive film (the side that does not cause a piezoelectric effect) is capable of conducting an electrode formed on the surface side is preformed preferably (back surface side of the conductive film t of the substrate contained in the piezoelectric substrate ( The back conductive film) has a function of releasing electric charge derived from the pyroelectric effect of the piezoelectric substrate, which is generated when the electrode material layer is patterned into a predetermined shape or by a temperature change during the baking process of the resist.
  • the back conductive film is made of Mo, A, Li, K, ⁇ a, Ca, .Mg, Be, A metal film composed of T i, M n, V, N b, Zn, etc. can be used.
  • a first film is formed on the surface of the Shoden substrate.
  • the first film is not particularly limited, and any of a conductive film, an insulating film, and a semiconductor film can be used.
  • the second film be made of a material that is not easily attacked by an etchant used when the second film is lifted off as described below.
  • a film of an insulating material such as silicon dioxide / silicon nitride or a film of a semiconductor material such as silicon can be given.
  • the thickness of the first film is not particularly limited. It is preferable to set so that the mass per unit area of the extreme finger is substantially the same. As a result, the SAW speed becomes the same under the electrode finger and under the first film remaining between the electrode fingers, so that the reflection of elastic waves and the emission as bulk waves are reduced. As a result, a SAW element with low loss can be obtained. Furthermore, even if the material constituting the electrodes is stress-migrated, it is possible to prevent the first film between the electrode fingers from acting as a barrier to short-circuit the electrode fingers. As a result, a long-life element is obtained. f ⁇
  • the second film is not particularly limited as long as it is a material that is easily attacked by an etchant used for etching the first film into an undercut shape in the subsequent steps.
  • the second film is a conductive film in order to release electric charges derived from the pyroelectric effect on the piezoelectric substrate in the resist pattern forming step.
  • an insulating film such as silicon dioxide / silicon nitride
  • a metal film such as molybdenum
  • the thickness of the second film is not particularly limited and varies depending on the material constituting the second film, but may be set in consideration of the resistance to etching of the first film and the release of electric charge due to the pyroelectric effect. preferable.
  • the thickness can be in the range of 20 to 12 Onm.
  • a resist pattern having a predetermined shape is formed on the second film.
  • the method for forming the resist pattern is not particularly limited, and a known photolithography method can be used.
  • As the resist either a positive type or a negative type can be used.
  • the second film and the first film are anisotropically or isotropically etched using the resist pattern as a mask, and then only the first film isotropically etched into an undercut shape.
  • anisotropic etching which can form a finer pattern among isotropic etching and isotropic etching.
  • anisotropic dry etching such as RIE is used.
  • RIE reactive ion etching
  • the molybdenum in the second layer when cormorants lines etched by RIE, it is preferable to use a Etsuchanto like SF 6.
  • the second film is completely removed during this etching, it is preferable that the first film is not completely removed in order to prevent the piezoelectric substrate from being damaged by the etching.
  • the thickness of the first film to be left is preferably 10 to 50 nm.
  • the latter isotropic etching of the first film is performed under the condition that only the first film can be formed in an undercut shape.
  • an etchant that does not easily attack the second film.
  • a silicon dioxide film / silicon nitride film is used for the first film and a molybdenum film is used for the second film
  • a desired undercut shape can be formed in an etchant made of a hydrofluoric acid solution. It can be formed by immersing in time.
  • the undercut shape is such that, when the height of the first film is 1, the width of the edge removed from the end of the second film is in the range of 0.3 to 0.5. Preferably, it is shaped. By setting the content within this range, it is possible to prevent the electrode obtained by lifting off the subsequent electrode material layer from being burred or chipped.
  • the resist pattern is removed by a known method.
  • an electrode material layer is formed on the entire surface.
  • the electrode material layer is formed after removing the resist pattern, an electrode material layer with good film quality can be obtained without deterioration of the degree of vacuum during the formation. As a result, a highly reliable Saw element having excellent power durability can be obtained.
  • the electrode material is not particularly limited, and any known materials can be used. Can be used. Of these, it is preferable that the material be made of a material that is not easily attacked by the etchant used for lifting off. For example, aluminum or an alloy thereof is used. Examples of the alloy include an alloy of Mg, Cu, Mn and the like and A1. Among these, it is preferable to use an alloy from the viewpoint of improving the power durability.
  • the content of metals other than aluminum in the alloy is preferably 1% by weight or more, more preferably 1 to 30% by weight.
  • the thickness of the electrode material layer can be appropriately set according to the material used so that a SAW element having desired characteristics can be obtained.
  • the thickness be smaller than the thickness of the first film in order to prevent burrs and chipping from occurring in the electrode.
  • the electrode material layer existing on the second film is lifted off by etching and removing the second film to form an electrode.
  • the lift-off is preferably performed using an etch that does not easily attack the first film and the electrode material layer.
  • a silicon dioxide film / silicon nitride film is used for the first film
  • a molybdenum film is used for the second film
  • aluminum or its alloy layer is used for the conductive material layer
  • the diammonium cerium nitrate (IV) solution This can be done by immersion in another etchant for a period of time that allows the second film to be removed.
  • a third film is formed on a piezoelectric substrate.
  • the same substrate as that of the first method for manufacturing the Saw element can be used for the piezoelectric substrate. Further, it is preferable to have a back surface conductive film as in the first method for manufacturing the Saw element. Further, as the third film, the same film as the second film in the method for producing the first Saw element can be used.
  • a resist pattern having a predetermined shape is formed on the third film.
  • a pattern having the same register as that of the first method for manufacturing the Saw element can be used.
  • Q here isotropically etched by means such as Tsu bets shape, for example your IE, in order to form better controllability of the undercut shape, prior to the isotropic etch, halfway third membrane ( That is, the piezoelectric substrate is not exposed), and is preferably removed by anisotropic etching.
  • RIE can perform isotropic and anisotropic etching by controlling the atmospheric pressure, it is more preferable to use it in this step.
  • SF Q can be used as an etchant.
  • the undercut shape is such that, when the height of the third film is 1, the width etched away from the end of the resist pattern is in the range of 0.3 to 0,5. It is preferable that Within this range, it is possible to prevent burrs and chips from being generated in the electrode obtained by lifting off the subsequent electrode material layer.
  • an electrode material layer is formed on the entire surface in the same manner as in the first method for manufacturing the Saw element. '
  • the electrode material layer existing on the third film can be lifted off by removing the third film by etching to form an electrode.
  • the removal of the third film can be performed by the same method as the removal of the second film in the first method for manufacturing the Saw element.
  • the lift-off is preferably performed using an etchant that does not easily attack the electrode material layer.
  • FIG. 1 shows an example of the SAW element obtained by the manufacturing method of the present invention.
  • the Saw element in the figure has two reflective electrodes and a pair of comb-shaped excitation electrodes.
  • a and B are a pair of comb-shaped excitation electrodes
  • C and D are reflection electrodes.
  • Y represents the opening length of the electrode finger
  • ⁇ represents the period of the electrode finger.
  • SAW elements can be used in filters (eg, matched filters), resonators, delay lines, oscillators, acousto-optic devices, compolators, and the like. For example, when used in a filter, connect SAW elements in series.
  • filters eg, matched filters
  • resonators e.g., resonators
  • delay lines e.g., oscillators
  • oscillators e.g., acousto-optic devices
  • compolators e.g., compolators
  • compolators e.g., compolators, and the like.
  • a ladder-type structure formed by arranging a desired number of arms and parallel arms is exemplified.
  • any of known structures can be adopted.
  • a molybdenum film (not shown) is formed on the back surface of the lithium tantalate substrate (piezoelectric substrate) 1 to a thickness of 300 nm by a sputtering method.
  • a silicon dioxide film (first film) 2 is formed on the substrate surface to a thickness of 61 nm by plasma CVD.
  • a molybdenum layer (second film) 3 is formed to a thickness of 50 nm by a sputtering method.
  • a resist pattern 4 having an opening in the shape of a comb-shaped electrode finger having a width of 200 nm desired to be formed is formed (FIG. 2 (a)).
  • the molybdenum film 3 is vertically etched by RIE using SF 6 gas (etchant). 'Subsequently, the silicon dioxide film 2 is vertically etched by RIE using SF 6 gas. At this time, the etching is stopped at the remaining thickness of 30 nm of the silicon dioxide film 2.
  • the silicon dioxide film 2 is isotropically etched by 50 nm with a hydrofluoric acid solution. Since the molybdenum film 3 is not attacked by hydrofluoric acid, only the silicon dioxide film 2 is etched to form an undercut. At the same time, the remaining film of the silicon dioxide film 2 is removed, exposing the surface of the substrate 1 (FIG. 2 (b)).
  • FIG. 2 (c) Next, the resist pattern 4 is removed by oxygen plasma (FIG. 2 (c)). Next, an aluminum alloy film (electrode material layer) 5 containing 2% by weight of copper is formed to a thickness of 50 nm by a sputtering method (FIG. 2 (d)).
  • the substrate is immersed in a diammonium cerium (IV) nitrate aqueous solution, and the molybdenum film 3 is etched.
  • the unnecessary aluminum alloy layer 5 deposited on the molybdenum film 3 is lifted off, and lifted off to complete the electrode finger 6 for the SAW element (Fig. 2 (e)).
  • the thickness of the silicon dioxide film 2 is set according to the ratio of the density of the aluminum alloy layer 5 to the density of the silicon dioxide film 2 so that the two have the same mass. Since the density of aluminum alloy is 2.7 g / cm 3 and that of silicon dioxide is 2.'2 g / cm 3 , if the thickness of silicon dioxide film 2 is about 1.23 times that of aluminum Good.
  • the center frequency of the surface acoustic wave device manufactured by the above method was 5 GHz.
  • the molybdenum film formed on the back surface of the substrate 1 is connected to the molybdenum film 3 provided on the substrate.
  • a molybdenum film having a thickness of 300 nm is formed on the rear surface of the lithium tantalate substrate 1 by a sputtering method (not shown).
  • a molybdenum film (third film) 7 having a thickness of 70 nm is formed on the surface of the substrate 1 by a sputtering method.
  • a resist pattern 4 having an opening in the shape of a comb-shaped electrode finger having a width of 200 nm, which is desired to be formed, is formed by using an excimer laser (FIG. 3 (a)).
  • the molybdenum film 7 is vertically etched by RIE using S.F 6 gas at a pressure of 0.05 Torr. At this time, the etching is stopped when the thickness of the molybdenum film is 30 nm remaining. Subsequently, RIE is performed under the condition that the pressure of SF 6 gas is increased to 0.5 Torr, and the molybdenum film 7 is isotropically etched by 50 nm. This Undercut of 50 nm from the end of the resist pattern 4 into the ribden film 7. At the same time, the surface of the substrate 1 is exposed (FIG. 3 (b);).
  • an aluminum alloy layer 5 is formed to a thickness of 50 nm by a sputtering method (FIG. 3 (c)).
  • the substrate 1 is immersed in a diammonium cerium (IV) nitrate aqueous solution, and the molybdenum film 1.7 is etched.
  • the unnecessary aluminum alloy layer deposited on the molybdenum film 7 is lifted off, and the electrode finger 6 for the SAW element is completed (FIG. 3 (d)).
  • An electrode material layer is formed after the first film or the third film is etched in an undercut shape, and then an extra electrode material layer is lifted off. An electrode shape with no variation can be obtained.
  • the second film or the third film can be electrically connected to the back conductive film. It is possible to prevent defects from occurring in the top pattern. .
  • the SAW speed can be reduced below the electrode finger and the first film. Since it is the same below, it is possible to reduce the reflection of the singular wave and the radiation as the bulk wave. As a result, an element with low loss can be obtained. Also, even if the material constituting the electrodes is stress-migrated, the first film between the electrode fingers acts as a barrier to prevent short-circuiting between the electrode fingers. As a result, a long-life element can be obtained.
  • the conductive material layer is formed after the resist pattern is removed, so that the degree of vacuum does not deteriorate during the formation and the conductive material layer with good film quality is formed. Is obtained. As a result, A highly reliable SAW device with excellent power performance can be obtained.

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  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)

Abstract

A method of producing surface acoustic wave devices comprising the steps of forming a first film on a piezoelectric board, forming a second film on the first film, forming a resist pattern of predetermined shape on the second film, isotropically or anisotropically etching the second and first films with the resist pattern used as a mask, isotropically etching the first film alone into an undercut form, removing the resist patter, forming an electrode material layer on the entire surface, and lifting off the electrode material layer present on the second film by etching the second film for removal, thereby forming electrodes.

Description

明 細 書 弾性表面波素子及びその形成方法 技術分野  Description Surface acoustic wave device and method of forming the same
本発明は、 弾性表面波 （ S AW) '素子及びその形成方法に関す る。 更に詳しくは、 S AW素子を構成する圧電基板上への電極の 形成方法及び得られた S A W素子に関する。  The present invention relates to a surface acoustic wave (SAW) 'element and a method for forming the same. More specifically, the present invention relates to a method for forming an electrode on a piezoelectric substrate constituting a Saw element and the obtained Saw element.
背景技術 Background art
近年の携帯電話に代表される移動通信機器の急速な普及に伴い、 小型軽量化が可能である S AW素子 （例えば、 S AWフィルタ） の'需要は今後更に拡大すると予想される。  With the rapid spread of mobile communication devices represented by mobile phones in recent years, the demand for S AW elements (for example, S AW filters) that can be reduced in size and weight is expected to further increase in the future.
S AW素子は、 一般的に、 圧電基板の表面に導電膜からなる櫛 形電極が設けられた構造を有している。 櫛形電極によって、 機械 的 S AW信号と電気的信号の変換及び逆変換が行われ、 周波数選 択性が実現できる。  The SAW element generally has a structure in which a comb-shaped electrode made of a conductive film is provided on the surface of a piezoelectric substrate. The comb-shaped electrode converts and reverses the mechanical S AW signal and the electrical signal, thereby realizing frequency selectivity.
機器の更なる小型化の要求に伴って、 S A W素子は高周波化が 求められている。 例えば、 S A Wフィル夕の中心周波数は、 弹性 波の伝播速度に比例し、 波長に反比例する。 従って、 中心周波数 を高くするに 、 伝播速度の速い材料を圧電基板に用いるか、 波 長を短くするために櫛形電極の指 （以下、 電極指） の幅を細くす る必要がある。 例えば、 Yカッ ト X伝播のタンタル酸リチウム結 晶からなる圧電基板を用いて、 5 GH z帯の S AWフィル夕を形 成した場合、 弾性波の伝播速度は約 4 0 0 O mZ秒であるので、 電極指の幅は約 0. 2 mとなる。  Along with the demand for further miniaturization of equipment, Saw elements are required to have higher frequencies. For example, the center frequency of the SAW filter is proportional to the propagation speed of the sine wave and inversely proportional to the wavelength. Therefore, to increase the center frequency, it is necessary to use a material having a high propagation speed for the piezoelectric substrate, or to reduce the width of the fingers of the comb-shaped electrode (hereinafter, electrode fingers) to shorten the wavelength. For example, when a SAW filter in the 5 GHz band is formed using a piezoelectric substrate made of Y-cut X-propagating lithium tantalate crystals, the propagation speed of elastic waves is about 400 OmZ seconds. As a result, the width of the electrode finger is about 0.2 m.
一般に、 櫛形電極のパターニングには二つの方法が知られてい る。 一つほ、 圧電基板上に成膜した導電膜に、 フォ トリソグラフ ィ法により レジス トパタ一ンを形成した後、 導電膜をエツチング することでパ夕一エングする方法である。 他の一つは、 圧電基板 上にレジス トパターンを形成した後、 導電膜を成膜し、 レジス ト パターンを溶解してレジス トパ夕一ン上に堆積した導電膜をリ フ 卜オフすることでパターニングする方法である。 In general, two methods are known for patterning a comb-shaped electrode. One is to form a resist pattern on a conductive film formed on a piezoelectric substrate by photolithography, and then etch the conductive film. It is a way to make a day. The other is to form a conductive pattern after forming a resist pattern on a piezoelectric substrate, dissolve the resist pattern and lift off the conductive film deposited on the resist panel. Is a method of patterning.
上記パ夕一ニング方法には以下のような課題がある。  The above method has the following problems.
櫛形電極の材料には、 抵抗率が低く、 比重が軽くて反射を生じ にくいという理由から、 アルミニウムが用いられる。 しかしアル ミニゥムはス 卜レスマイグレーショ ンが発生しやすい欠点があり、 大電力下では耐電力性が劣り、 信頼性の高い素子を得ることが困 難である。  Aluminum is used as the material of the comb-shaped electrode because it has a low resistivity, a low specific gravity, and hardly causes reflection. However, aluminum has the drawback that stress migration is likely to occur, and it has poor power durability under high power, making it difficult to obtain highly reliable devices.
一般に、 アルミニウムに少量の銅やマグネシウムを添加したァ ルミ二ゥム合金を使用するとス トレスマイダレ一シヨ ンが抑えら れ、 耐電力性が改善できることが知られている。 しかし、，添加物 を含むアルミニウムは、 反応性イオンエッチング （ R I E ) が困 難である。 なぜなら、 アルミニウムの R I Eでは、 塩素系の反応 ガスが用いられる力^ 銅やマグネシウムと反応して形成されるそ れらの塩化物は沸点が高く、 R I E後に残渣として基板表面に残 る可能性があるからである。 このような現象は添加量が大きくな るほど顕著に起きる。 銅やマグネシウムの添加量は大きいほど耐 電力性の改善効果も大きくなる傾向にあるが、 R I Eによるパ夕 ーン形成法では上述のように残渣が多くなるので、 電極材料とし て適していない。  Generally, it is known that the use of an aluminum alloy in which a small amount of copper or magnesium is added to aluminum suppresses the stress reduction and improves the power durability. However, it is difficult to perform reactive ion etching (RIE) on aluminum containing additives. Because, in RIE of aluminum, the power of chlorine-based reaction gas is used ^ The chloride formed by reacting with copper and magnesium has a high boiling point, and may remain on the substrate surface as a residue after RIE. Because there is. Such a phenomenon occurs more remarkably as the amount of addition increases. The effect of improving power resistance tends to increase as the amount of copper or magnesium increases, but the pattern formation method using RIE is not suitable as an electrode material because the residue increases as described above.
これに対して、 アルゴンのような不活性イオンによる物理的な エッチング方法によれば、 このようなアルミニウム合金のパター ニングが可能である。 しかし、 パ夕一ニング時に圧電基板がィォ ン衝搫により削られる。. このような基板損傷は、 S A W素子の特 性の劣化原因となる。  On the other hand, a physical etching method using an inert ion such as argon can pattern such an aluminum alloy. However, at the time of power tuning, the piezoelectric substrate is scraped by the ion impact. Such substrate damage causes deterioration of the characteristics of the SAW device.
以上のような問題を回避する手段として、 リ フ トオフによ'るパ ターニング方法がある。 これは、 基板 1 1上にレジス トパターン 1 2を形成した後（図 4 ( a ) )、導電膜 1 3を形成し （図 4 ( b ) ) 、 レジス トパターン 1 2を溶解して不要な導電膜 1 3を除去するこ とで、 電極 1 4を形成する方法である。 この方法では、 導電膜を エッチングする必要がないので、 アルミニウム合金のような R I Eが困難な材料でも使用できる。 また、 基板の損傷もない。 As a means of avoiding the problems described above, lift-off There is a turning method. This is because the resist pattern 12 is formed on the substrate 11 (FIG. 4 (a)), and then the conductive film 13 is formed (FIG. 4 (b)). In this method, the electrode 14 is formed by removing the conductive film 13. In this method, it is not necessary to etch the conductive film, so that it is possible to use materials that are difficult to RIE, such as aluminum alloys. Also, there is no damage to the substrate.
しかしながら、 上記の方法では、 レジス トパターンの側壁や基 板との境界部にも導電膜が付着するため、 レジス トパターンを溶 解して不要部分をリ フ トオフした時に、 電極の端部にバリ 1 5や 欠け 1 6が生じる （図 4 ( c ) )。 このような端部の形状ばらつき は S A W素子の特性を悪化させる。  However, in the above method, since the conductive film also adheres to the side wall of the resist pattern and the boundary with the substrate, when the resist pattern is melted and unnecessary portions are lifted off, the edge of the electrode is formed. Burrs 15 and chips 16 occur (Fig. 4 (c)). Such variations in the shape of the end portions degrade the characteristics of the Saw element.
このような問題を解決する方法として、 特開平 9 一 1 6 2 6 7 0号公報には、 レジス トパターンの下に二酸化シリコン膜を設け、 二酸化シリコン膜をアンダ一カッ トが入るようにエッチングした 後、 アルミニウム合金膜を成膜し、 リフ トオフするという製造方' 法が開示されている。  As a method of solving such a problem, Japanese Patent Application Laid-Open No. Hei 9-166700 discloses a method in which a silicon dioxide film is provided under a resist pattern, and the silicon dioxide film is etched so as to form an undercut. After that, a manufacturing method is disclosed in which an aluminum alloy film is formed and lifted off.
しかしながら、 この方法では、 圧電基板の'表面が導電膜で覆わ れていない状態でレジス 1、パターンを形成するので、 レジス 卜パ ターンのベ一ク工程で圧電基板に焦電が生じ、 レジス トパターン が変質してパターン欠陥が発生するという問題が起きる。  However, in this method, since the resist 1 and the pattern are formed in a state in which the surface of the piezoelectric substrate is not covered with the conductive film, pyroelectricity is generated in the piezoelectric substrate in the resist pattern baking process, and the resist A problem arises in that the pattern is altered and pattern defects occur.
また、 アルミニウム合金の真空成膜工程においては、 蒸着粒子 のエネルギーにより基板温度が上昇し、 レジス トから大量のガス 状分子が放出されて真空度が悪化する恐れがあつた。 成膜室の真 空度の悪化はアルミニゥム合金膜の膜質の低下を引き起こし、 S A W素子特性を劣化.させる。 発明の開示  In addition, in the vacuum deposition process of the aluminum alloy, the energy of the vapor-deposited particles raises the substrate temperature, and a large amount of gaseous molecules is released from the resist, which may deteriorate the degree of vacuum. Deterioration of the vacuum in the film forming chamber causes deterioration of the film quality of the aluminum alloy film, and deteriorates the characteristics of the Saw element. Disclosure of the invention
本発明は、 上記の問題を解決するリ フ トオフによる電極の形成 方法を含む S A W素子の形成方法を提供するものである。 The present invention provides a method for forming electrodes by lift-off that solves the above-mentioned problems. The present invention provides a method for forming a SAW element including the method.
かく して本発明によれば、 '圧電基板上に第一膜を形成する工程 と、 第一膜上に第二膜を形成する工程と、 第二膜上に所定形状の レジス トパ夕一 'ンを形成する工程と、 レジス トパターンをマスク 'として第二膜及び第一膜を異方性又は等方性エッチングし、 続い て第一膜のみをアンダーカツ ト形状に等方性エツチングする工程 と、 レジス トパターンを除去する工程と、 全面に電極材料層を形 成する工程と、 第二膜上に存在する電極材料層を第二膜をエツチ ング除去することでリフ トオフして電極を形成する工程を有する 第 1の S A W素子の製造方法が提供される。  Thus, according to the present invention, a process of forming a first film on a piezoelectric substrate, a process of forming a second film on a first film, and a resist film having a predetermined shape on a second film Forming the second film and the first film anisotropically or isotropically using the resist pattern as a mask, and subsequently, isotropically etching only the first film in an undercut shape. Removing the resist pattern; forming an electrode material layer on the entire surface; and lifting off the electrode material layer present on the second film by etching and removing the second film. A method for manufacturing a first SAW element having a step of forming is provided.
また、 本発明によれば、 圧電基板上に第三膜を形成する工程と、 第三膜上に所定形状のレジス 1、パターンを形成する工程と、 レジ ス トパターンをマスクとして第三膜をアンダーカツ 卜形状に等方 性エッチングする工程と、 全面に電極材料層を形成する工程と、 第三膜上に存在する電極材料層を第三膜をエッチング除去するこ とでリフ トオフして電極を形成する工程を有する第 2の S A W素 子の製造方法が提供される。 ·  Further, according to the present invention, a step of forming a third film on the piezoelectric substrate, a step of forming a resist 1 and a pattern of a predetermined shape on the third film, and forming the third film using the resist pattern as a mask A step of isotropically etching into an undercut shape, a step of forming an electrode material layer over the entire surface, and lifting off the electrode material layer present on the third film by etching away the third film. A method for manufacturing a second SAW element having a step of forming a second SAW element is provided. ·
更に、 本発明によれば、 圧電基板上に所定パターンの櫛型電極 指を有し、 電極指間の圧電基板上に他の膜を有し、 電極指と他の 膜の単位面積あたりの質量が、 ほぼ等しい S A W素子が提供され る。 図面の簡単な説明  Further, according to the present invention, a comb-shaped electrode finger having a predetermined pattern is provided on the piezoelectric substrate, another film is provided on the piezoelectric substrate between the electrode fingers, and the mass per unit area of the electrode finger and the other film is provided. However, a SAW element is provided which is approximately equal. BRIEF DESCRIPTION OF THE FIGURES
図 1は、 S A W素子の一例の概略平面図である。  FIG. 1 is a schematic plan view of an example of the SAW element.
' 図 2 ( a ) 〜 （ e ) は、 本発明の S A W素子の製造方法の概略 工程断面図である。  FIGS. 2A to 2E are schematic process cross-sectional views of a method for manufacturing a SAW device of the present invention.
図 3 ( a ) 〜 （ cl ) は、 本発明の S A W素子の製造方法の概略 工程断面図である。 図 4 ( a ) 〜 （ c ) は、 従来のリ フ トオフ法による S AW素子 の製造方法の概略工程断面図である。 発明の実施の形態 3A to 3C are schematic process sectional views of a method for manufacturing a SAW element according to the present invention. 4 (a) to 4 (c) are schematic process sectional views of a conventional SAW device manufacturing method by a lift-off method. Embodiment of the Invention
以下、 本発明の S AW素子及びその製造方法を説明する。  Hereinafter, the SAW device of the present invention and a method of manufacturing the SAW device will be described.
まず、 第 1の S A W素子の製造方法について説明する。  First, a method for manufacturing the first Saw element will be described.
S AW素子は、 通^、 圧電基板を備えている。 ここで、 圧電'基 板としては、 S A W素子に使用することができるものであれば特 に限定されない。 具体的には、 L i T a 03、 L i N b 03、 K N b 03、 L i 2B407等の圧電基板が挙げられる。 更に'、 ガラス、 樹脂 等の基板上に L i T a 03、 L i N b 03、 KN b〇3、 L i 2B4〇7 の圧電材を膜状に形成した基板も本発明の圧電基板に含まれる t この基板の裏面側 （圧電効果を生じない側） には表面側に形成 される電極と導通しうる導電膜が予め形成されることが好ましい ( 裏面側の導電膜 （裏面導電膜） は、 電極材料層を所定の形状にパ 夕一ニングする際やレジス トのベークェ程での温度変化により生 じる圧電基板の焦電効果に由来する電荷を逃がす機能を有する。 従って、 レジス トパターンに焦電による欠陥が発生することを防 止することができる。 裏面導電膜は、 M o、 A し L i 、 K、 Ν a、 C a、 .M g、 B e、 T i 、 M n、 V、 N b、 Z n等からなる 金属膜を使用することができる。 . The SAW element generally has a piezoelectric substrate. Here, the piezoelectric substrate is not particularly limited as long as it can be used for a SAW element. Specifically, L i T a 0 3, L i N b 0 3, KN b 0 3, a piezoelectric substrate such as L i 2 B 4 0 7 and the like. Furthermore ', glass, L i T a 0 3 on a substrate such as a resin, L i N b 0 3, KN B_〇 3, L i 2 B 4 〇 7 also present invention the substrate which is formed into a film shape of the piezoelectric material back side that conductive film (the side that does not cause a piezoelectric effect) is capable of conducting an electrode formed on the surface side is preformed preferably (back surface side of the conductive film t of the substrate contained in the piezoelectric substrate ( The back conductive film) has a function of releasing electric charge derived from the pyroelectric effect of the piezoelectric substrate, which is generated when the electrode material layer is patterned into a predetermined shape or by a temperature change during the baking process of the resist. Accordingly, it is possible to prevent the occurrence of defects due to pyroelectricity in the resist pattern.The back conductive film is made of Mo, A, Li, K, Νa, Ca, .Mg, Be, A metal film composed of T i, M n, V, N b, Zn, etc. can be used.
庄電基板の表面に第一膜を形成する。 第一膜は、 特に限定され ず、 導電膜、 絶縁膜及び半導体膜のいずれも使用することができ る。 この内、 以下で説明する第二膜のリ フ トオフの際に使用され るエツチャン トに侵されにくい材料からなることが好ましい。 例 えば、 二酸化シリ コンゃ窒化シリ コンのような絶縁材料の膜、 シ リコンの^うな半導体材料の膜が挙げられる。  A first film is formed on the surface of the Shoden substrate. The first film is not particularly limited, and any of a conductive film, an insulating film, and a semiconductor film can be used. Of these, it is preferable that the second film be made of a material that is not easily attacked by an etchant used when the second film is lifted off as described below. For example, a film of an insulating material such as silicon dioxide / silicon nitride or a film of a semiconductor material such as silicon can be given.
第一膜の厚さは、 特に限定されないが、 最終的に形成される電 極指の単位面積当たりの質量とほぼ同じ質量となるように、 設定 することが好ましい。 これにより、 S A Wの速度が、 電極指の下 と、 電極指の間に残った第一膜の下で同じになるので、 弾性波の 反射やバルク波としての放射が低減される。 その結果、 損失の少 ない S A W素子が得られる。 更に、 電極を構成する材料がス トレ スマイグレーショ ンしても、 電極指間の第一膜が障壁となり電極- 指.同士が短絡するのを防ぐことができる。 その結果、 長寿命の素 子が得られる。 f · The thickness of the first film is not particularly limited. It is preferable to set so that the mass per unit area of the extreme finger is substantially the same. As a result, the SAW speed becomes the same under the electrode finger and under the first film remaining between the electrode fingers, so that the reflection of elastic waves and the emission as bulk waves are reduced. As a result, a SAW element with low loss can be obtained. Furthermore, even if the material constituting the electrodes is stress-migrated, it is possible to prevent the first film between the electrode fingers from acting as a barrier to short-circuit the electrode fingers. As a result, a long-life element is obtained. f ·
次に、 第一膜上に第二膜を形成する。 第二膜は、 以降の工程で 第一膜のアンダーカッ ト形状へめエッチングの際に使用するエツ チヤントに侵されにぐい材料であれば、 特に限定されない。特に、 レジス トパターン作製工程での圧電基板への焦電効果に由来する 電荷を逃がすために、 第二膜は導電膜であることが好ましい。 具 体的には、 第一膜に二酸化シリコンゃ窒化シリコンのような絶縁 膜を使用した場合、 第二膜にはモリブデンのような金属膜を使用 することが好ましい。 第二膜の厚さは、 特に限定されず第二膜を 構成する材料によって異なるが、 第一膜のエッチングに対する耐 性及び焦電効果に由来する電荷を逃がすことを考慮して設定する ことが好ましい。 例えば、 第二膜にモリブデン膜を使用した場合、 2 0〜 1 2 O n mの範囲とすることができる。  Next, a second film is formed on the first film. The second film is not particularly limited as long as it is a material that is easily attacked by an etchant used for etching the first film into an undercut shape in the subsequent steps. In particular, it is preferable that the second film is a conductive film in order to release electric charges derived from the pyroelectric effect on the piezoelectric substrate in the resist pattern forming step. Specifically, when an insulating film such as silicon dioxide / silicon nitride is used for the first film, it is preferable to use a metal film such as molybdenum for the second film. The thickness of the second film is not particularly limited and varies depending on the material constituting the second film, but may be set in consideration of the resistance to etching of the first film and the release of electric charge due to the pyroelectric effect. preferable. For example, when a molybdenum film is used as the second film, the thickness can be in the range of 20 to 12 Onm.
次に、 第二膜上に所定形状のレジス トパターンを形成する。 レ ジス 卜パターンの形成方法は、 特に限定されず、 公知のフォ トリ ソ'グラフィ法を使用することができる。 また、 レジス トは、 ポジ 型、 ネガ型のいずれも使用することができる。  Next, a resist pattern having a predetermined shape is formed on the second film. The method for forming the resist pattern is not particularly limited, and a known photolithography method can be used. As the resist, either a positive type or a negative type can be used.
次いで、 レジス トパターンをマスクとして第二膜及び第一膜を 異方性又は等方性エッチングし、 続いて第一膜のみをアンダー力 ッ ト形状に等方性エッチングする。  Next, the second film and the first film are anisotropically or isotropically etched using the resist pattern as a mask, and then only the first film isotropically etched into an undercut shape.
まず、 前者の第二膜及び第一膜のエッチングにおいて、 異方性 及び等方性エッチングの内、 より,微細なパターンを形成すること ができる異方性エッチングを採用することが好ましい。 具体的に は、 R I E法のような異方性のドライエッチングが挙げられる。 なお、 第二膜にモリブデンを使用し、 エッチングを R I E法で行 う場合、 S F 6のようなエツチャントを使用することが好ましい。 なお、 このエッチング時に第二膜は完全に除去されるが、 圧電基 板がエッチングによりダメージを受けることを抑制するために、 第一膜は完全に除去しないことが好ましい。 残存させる第一膜の 膜厚は、 1 0〜 5 0 n mであることが好ましい。 First, in the former etching of the second film and the first film, It is preferable to employ anisotropic etching which can form a finer pattern among isotropic etching and isotropic etching. Specifically, anisotropic dry etching such as RIE is used. Incidentally, by using the molybdenum in the second layer, when cormorants lines etched by RIE, it is preferable to use a Etsuchanto like SF 6. Although the second film is completely removed during this etching, it is preferable that the first film is not completely removed in order to prevent the piezoelectric substrate from being damaged by the etching. The thickness of the first film to be left is preferably 10 to 50 nm.
後者の第一膜の等方性エッチングは、 第一膜のみをアンダー力 ッ ト形状に形成しうる条件下で行われる。 このエッチングには、 第二膜を侵しにくいエツチャントを使用することが好ましい。 例 えば、 第一膜に二酸化シリコン膜ゃ窒化シリコン膜を使甩し、 第 二膜にモリブデン膜を使用した場合、 フッ酸溶液からなるエッチ ヤン卜に、 所望のアンダーカッ ト形状を形成しうる時間、 浸潰す ることにより形成することができる。  The latter isotropic etching of the first film is performed under the condition that only the first film can be formed in an undercut shape. For this etching, it is preferable to use an etchant that does not easily attack the second film. For example, when a silicon dioxide film / silicon nitride film is used for the first film and a molybdenum film is used for the second film, a desired undercut shape can be formed in an etchant made of a hydrofluoric acid solution. It can be formed by immersing in time.
ここで、 アンダーカツ ト形状は、 第一膜の高さを 1 とした場合、 第二膜の端部からエッチング除去される幅が 0 . 3〜 0 . 5の範 囲の割合になるような形状であることが好ましい。 この範囲にす ることで、 後の電極材料層をリフ 卜オフすることにより得られる 電極にバリや欠けが生じることを防ぐことができる。  Here, the undercut shape is such that, when the height of the first film is 1, the width of the edge removed from the end of the second film is in the range of 0.3 to 0.5. Preferably, it is shaped. By setting the content within this range, it is possible to prevent the electrode obtained by lifting off the subsequent electrode material layer from being burred or chipped.
次に、 公知の方法で、 レジス 卜パターンを除去する。  Next, the resist pattern is removed by a known method.
更に、 全面に電極材料層を形成する。 本発明の方法では、 レジ ス トパターンを除去してから電極材料層を形成するので、 形成中 の真空度の悪化がなく、 膜質のよい電極材料層を得ることができ る。 その結果、 耐電力性に優れた信頼性の高い S A W素子が得ら れる。  Further, an electrode material layer is formed on the entire surface. In the method of the present invention, since the electrode material layer is formed after removing the resist pattern, an electrode material layer with good film quality can be obtained without deterioration of the degree of vacuum during the formation. As a result, a highly reliable Saw element having excellent power durability can be obtained.
こ こで、 電極材料は、 特に限定されず、 公知の材料をいずれも 使用することができる。 この内、 リフ トオフの際に使用されるェ ッチャントに侵されにくい材料からなることが好ましい。 例えば、 アルミニゥム又はその合金が挙げられる。 合金には、 M g、 C u 、 M n等と A 1 との合金が挙げられる。 この内、 耐電力性を向上さ せる観点から、 合金からなることが好ましい。 合金中のアルミ二 ゥム以外の金属の含有割合は、 1重量％以上であるととが好まし く、 1 〜 3 0重量％であることがより好ましい。 電極材料層の厚 さは、 所望の特性の S A W素子が得られるように、 使用する材料 に応じて適宜設定することができる。 但し、 電極にバリや欠けが 生じることを防ぐために、 第一膜の厚さより薄いことが好ましい。 次いで、 第二膜上に存在する電極材料層を第二膜をエッチング 除去することでリフ トオフして電極 形成することができる。 リ フ トオフは、 第一膜及び電極材料層を侵しにくいエツチヤントを 使用して行う ことが好ましい。 例えば、 第一膜に二酸化シリコン 膜ゃ窒化シリコン膜を使用し、 第二膜にモリブデン膜を使用し、 導電材料層にアルミニウム又はその合金層を使用した場合、 硝酸 二アンモニゥムセリ ウム （ I V ) 溶液からなるエツチャントに、 ' 第二膜を除去しうる時間、 浸潰することにより行うことができる。 Here, the electrode material is not particularly limited, and any known materials can be used. Can be used. Of these, it is preferable that the material be made of a material that is not easily attacked by the etchant used for lifting off. For example, aluminum or an alloy thereof is used. Examples of the alloy include an alloy of Mg, Cu, Mn and the like and A1. Among these, it is preferable to use an alloy from the viewpoint of improving the power durability. The content of metals other than aluminum in the alloy is preferably 1% by weight or more, more preferably 1 to 30% by weight. The thickness of the electrode material layer can be appropriately set according to the material used so that a SAW element having desired characteristics can be obtained. However, it is preferable that the thickness be smaller than the thickness of the first film in order to prevent burrs and chipping from occurring in the electrode. Next, the electrode material layer existing on the second film is lifted off by etching and removing the second film to form an electrode. The lift-off is preferably performed using an etch that does not easily attack the first film and the electrode material layer. For example, if a silicon dioxide film / silicon nitride film is used for the first film, a molybdenum film is used for the second film, and aluminum or its alloy layer is used for the conductive material layer, the diammonium cerium nitrate (IV) solution This can be done by immersion in another etchant for a period of time that allows the second film to be removed.
次に、 第 2の S A W素子の製造方法について説明する。  Next, a method for manufacturing the second Saw element will be described.
まず、 圧電基板上に第三膜を形成する。 ここで、 圧電基板にほ、 第 1 の S A W素子の製造方法と同一の基板を使用することができ る。 また、 第 1 の S A W素子の製造方法と同様に、 裏面導電膜を 有していることが好ましい。 更に、 第三膜には、 第 1の S A W素 子の製造方法の第二膜と同一の膜を使用することができる。  First, a third film is formed on a piezoelectric substrate. Here, the same substrate as that of the first method for manufacturing the Saw element can be used for the piezoelectric substrate. Further, it is preferable to have a back surface conductive film as in the first method for manufacturing the Saw element. Further, as the third film, the same film as the second film in the method for producing the first Saw element can be used.
次に、 第三膜上に所定形状のレジス 卜パ夕一ンを形成する。 レ -ジス トパターンには、 第 1 の S A W素子の製造方法と同一のレジ ス トからなるパターンを使用することができる。  Next, a resist pattern having a predetermined shape is formed on the third film. As the resist pattern, a pattern having the same register as that of the first method for manufacturing the Saw element can be used.
次いで、 レジス 卜パターンをマスクとして第三膜をアンダー力 ッ ト形状に例えばお I Eのような手段で等方性エッチングする q ここで、 アンダーカッ ト形状をより制御性よく形成するために、 等方性エッチングの前に、 第三膜を途中まで （即ち、 圧電基板を 露出させない）、 異方性エッチングで除去することが好ましい。 更 に、 ' R I Eでは、 雰囲気圧力を制御することで、 等方性及び異方 性のェッチングを行うことができる' 'ので、 この工程に使用するこ とがより好ましい。 なお、 エツチャントとしては、 R I Eの場合、 例えば S F Qを使用することができる。 Next, under the third film using the resist pattern as a mask, Q here isotropically etched by means such as Tsu bets shape, for example your IE, in order to form better controllability of the undercut shape, prior to the isotropic etch, halfway third membrane ( That is, the piezoelectric substrate is not exposed), and is preferably removed by anisotropic etching. Furthermore, since RIE can perform isotropic and anisotropic etching by controlling the atmospheric pressure, it is more preferable to use it in this step. In the case of RIE, for example, SF Q can be used as an etchant.
ここで、 アンダーカッ ト形状は、 第三膜の高さを 1 とした場合、 レジス トパターンの端部からエッチング除去される幅が 0 . 3〜 0 , 5の範囲の割合になるような形状であ ことが好ましい。 こ の範囲にすることで、 後の電極材料層をリ フ トオフすることによ り得られる電極にバリや欠けが生じることを防ぐことができる。 次に、 第 1 の S A W素子の製造方法と同様にして、 全面に電極 材料層を形成する。 '  Here, the undercut shape is such that, when the height of the third film is 1, the width etched away from the end of the resist pattern is in the range of 0.3 to 0,5. It is preferable that Within this range, it is possible to prevent burrs and chips from being generated in the electrode obtained by lifting off the subsequent electrode material layer. Next, an electrode material layer is formed on the entire surface in the same manner as in the first method for manufacturing the Saw element. '
更に、 第三膜上に存在する電極材料層を第三膜をエッチング除 去することでリ フ トオフして電極を形成することができる。 第三 膜の除去は、 第 1の S A W素子の製造方法の第二膜の除去と同様 の方法で行う ことができる。 なお、 リフ トオフは、 電極材料層を 侵しにくいエツチャントを用いて行うことが好ましい。  Further, the electrode material layer existing on the third film can be lifted off by removing the third film by etching to form an electrode. The removal of the third film can be performed by the same method as the removal of the second film in the first method for manufacturing the Saw element. The lift-off is preferably performed using an etchant that does not easily attack the electrode material layer.
本発明の製造方法により得られる S A W素子の一例を図 1 (概 略平面図） に示す。 図の S A W素子は、 電極が 2つの反射電極と 1組の櫛型の励振電極とから構成される。 図中、 A及び Bは 1組 の櫛型の励振電極であり、 C及び Dは反射電極である。 Yは電極 指の開口長を、 λは電極指の周期を意味する。  FIG. 1 (schematic plan view) shows an example of the SAW element obtained by the manufacturing method of the present invention. The Saw element in the figure has two reflective electrodes and a pair of comb-shaped excitation electrodes. In the figure, A and B are a pair of comb-shaped excitation electrodes, and C and D are reflection electrodes. Y represents the opening length of the electrode finger, and λ represents the period of the electrode finger.
S A W素子は、 フィル夕 （例えば、 マッチドフィルタ）、 共振器、 遅延線、 発振器、 音響光学装置、 コンポルバ一等に使用すること ができる。 例えば、 フィル夕に使用する場合、 S A W素子を直列 腕と並列腕に所望数配置することにより形成されたラダー型の構 造が挙げられる。 この構造以外にも、 公知の構造をいずれも採用 することができる。 SAW elements can be used in filters (eg, matched filters), resonators, delay lines, oscillators, acousto-optic devices, compolators, and the like. For example, when used in a filter, connect SAW elements in series. A ladder-type structure formed by arranging a desired number of arms and parallel arms is exemplified. In addition to this structure, any of known structures can be adopted.
実施例 Example
以下、 本発明を実施例を用いて更に詳細に説明する。 但し、 本 発明はこれら実施例に限定されるものではない。  Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to these examples.
実施例 1 Example 1
図 2を用いて以下の実施例を説明する。  The following embodiment will be described with reference to FIG.
まず、 タンタル酸リチウム基板 （圧電基板） 1の裏面に、 モリ ブデン膜 （図示せず） を 3 0 0 n mの厚さでスパッ夕法により成 膜する。 ' ' 次に、 基板表面に二酸化シリコン膜 （第一膜） 2を 6 1 n mの 厚さでプラズマ C V D法で形成する。 更に、 モリブデン嘆 （第二 膜） 3を 5 0 n mの厚さでスパッ夕法で形成する。 次に、 エキシ マレーザステツパにより、 形成を所望する 2 0 0 n mの幅の櫛型 電極指状に開口を有するレジス トパターン 4を形成する （図 2 ( a ) )。  First, a molybdenum film (not shown) is formed on the back surface of the lithium tantalate substrate (piezoelectric substrate) 1 to a thickness of 300 nm by a sputtering method. '' Next, a silicon dioxide film (first film) 2 is formed on the substrate surface to a thickness of 61 nm by plasma CVD. Further, a molybdenum layer (second film) 3 is formed to a thickness of 50 nm by a sputtering method. Next, using an excimer laser stepper, a resist pattern 4 having an opening in the shape of a comb-shaped electrode finger having a width of 200 nm desired to be formed is formed (FIG. 2 (a)).
その後、 モリブデン膜 3を S F 6ガス （エツチャント） による R I Eで垂.直にエツチングする。'続いて、 二酸化シリコン膜 2を S F 6ガスによる R I Eで垂直にエッチングする。 このとき、 二酸化 シリ コン膜 2の厚さ力 、 残り 3 0 n mのところでエッチングを停 止する。 次に、 フッ酸溶液で二酸化シリコン膜 2を 5 0 n m等方 性エツチングする。 モリブデン膜 3はフッ酸に侵されないので、 二酸化シリコン膜 2のみエッチングされて、 アンダーカツ 卜状と なる。 同時に二酸化シリコン膜 2の残膜が除去されて基板 1表面 が露出す'る （図 2 ( b ) )。 After that, the molybdenum film 3 is vertically etched by RIE using SF 6 gas (etchant). 'Subsequently, the silicon dioxide film 2 is vertically etched by RIE using SF 6 gas. At this time, the etching is stopped at the remaining thickness of 30 nm of the silicon dioxide film 2. Next, the silicon dioxide film 2 is isotropically etched by 50 nm with a hydrofluoric acid solution. Since the molybdenum film 3 is not attacked by hydrofluoric acid, only the silicon dioxide film 2 is etched to form an undercut. At the same time, the remaining film of the silicon dioxide film 2 is removed, exposing the surface of the substrate 1 (FIG. 2 (b)).
次に、 レジス 卜パターン 4を酸素プラズマで除去する （図 2 ( c ) )。 次に、 銅を 2重量％含むアルミニウム合金膜 （電極材料層） 5 を 5 0 n mの厚さでスパッタ法により形成する （図 2 (d))。 Next, the resist pattern 4 is removed by oxygen plasma (FIG. 2 (c)). Next, an aluminum alloy film (electrode material layer) 5 containing 2% by weight of copper is formed to a thickness of 50 nm by a sputtering method (FIG. 2 (d)).
最後に、 硝酸二アンモニゥムセリウム （IV) 水溶液に基板を浸 し、 モリブデン膜 3 をエッチングする。 モリブデン膜 3上に堆積 した不要なアルミニウム合金層 5力 S、 リフ トオフされて S A W素 子用の電極指 6が完成する （図 2 ( e ))。  Finally, the substrate is immersed in a diammonium cerium (IV) nitrate aqueous solution, and the molybdenum film 3 is etched. The unnecessary aluminum alloy layer 5 deposited on the molybdenum film 3 is lifted off, and lifted off to complete the electrode finger 6 for the SAW element (Fig. 2 (e)).
ここで、 二酸化シリコン膜 2の厚さは、 アルミニウム合金層 5 の密度と二酸化シリコン膜 2の密度の比に応じて、 両者の質量が 同じになるように設定する。 アルミニウム合金の密度は 2. 7 g / c m3 , 二酸化シリコンのそれは 2. '2 g / c m 3であるので、 二酸化シリコン膜 2の厚さは、 アルミニウムの約 1. 2 3倍とす ればよい。 上記の方法により製造した弾性表面波素子の中心周波 数は 5 G H zであった。 Here, the thickness of the silicon dioxide film 2 is set according to the ratio of the density of the aluminum alloy layer 5 to the density of the silicon dioxide film 2 so that the two have the same mass. Since the density of aluminum alloy is 2.7 g / cm 3 and that of silicon dioxide is 2.'2 g / cm 3 , if the thickness of silicon dioxide film 2 is about 1.23 times that of aluminum Good. The center frequency of the surface acoustic wave device manufactured by the above method was 5 GHz.
なお、 図示していないが、 基板 1 の裏面に成膜したモリ ズデン 膜は、 基板上に設けたモリブデン膜 3 と接続されている。  Although not shown, the molybdenum film formed on the back surface of the substrate 1 is connected to the molybdenum film 3 provided on the substrate.
実施例 2 Example 2
図 3 ( a) 〜 （d) を用いて以下の実施例を説明する。  The following embodiments will be described with reference to FIGS. 3 (a) to 3 (d).
まず、 タンタル酸リチウム基板 1 の裏面にモリブデン膜を 3 0 0 n mの厚さでスパッ夕法により形成する （図示せず）。 次に、 基 板 1表面にモリブデン膜 （第三膜） 7を 7 0 nmの厚さでスパッ 夕法により形成する。 次に、 エキシマレー'ザステツパにより、 形 成を所望する.2 0 0 n mの幅の櫛型電極指状に開口を有するレジ ストパターン 4を形成する (図 3 ( a ))。  First, a molybdenum film having a thickness of 300 nm is formed on the rear surface of the lithium tantalate substrate 1 by a sputtering method (not shown). Next, a molybdenum film (third film) 7 having a thickness of 70 nm is formed on the surface of the substrate 1 by a sputtering method. Next, a resist pattern 4 having an opening in the shape of a comb-shaped electrode finger having a width of 200 nm, which is desired to be formed, is formed by using an excimer laser (FIG. 3 (a)).
その後、 モリブデン膜 7を圧力 0. 0 5 T o r rの S .F 6ガスに よる R I Eで、 垂直にエッチングする。 このときモリブデン膜の 厚さが残り 3 0 n mのところでエッチングを停止する。 続いて、 S F 6ガスの圧力を 0. 5 T o r rに高めた条件で R I Eを行い、 モリブデン膜 7 を 5 0 n m等方性エッチングする。 これによりモ リブデン膜 7 にレジス トパターン 4端部から 5 0 n mのアンダー カッ トが入る。 同時に基板 1表面が露出する （図 3 ( b )；)。 Thereafter, the molybdenum film 7 is vertically etched by RIE using S.F 6 gas at a pressure of 0.05 Torr. At this time, the etching is stopped when the thickness of the molybdenum film is 30 nm remaining. Subsequently, RIE is performed under the condition that the pressure of SF 6 gas is increased to 0.5 Torr, and the molybdenum film 7 is isotropically etched by 50 nm. This Undercut of 50 nm from the end of the resist pattern 4 into the ribden film 7. At the same time, the surface of the substrate 1 is exposed (FIG. 3 (b);).
次に、 アルミニウム合金層 5を 5 0 n mの厚さでスパッ夕法に より形成する (図 3 ( c ) )。  Next, an aluminum alloy layer 5 is formed to a thickness of 50 nm by a sputtering method (FIG. 3 (c)).
最後に、 硝酸二アンモニゥムセリウム （IV ) 水溶液に基板 1 を 浸し、 モリブデン膜 .7をエツチングする。 これにより、 モリブデ ン膜 7上に堆積した不要なアルミニウム合金層がリフ 卜オフされ て S A W素子用の電極指 6が完成する （図 3 ( d ) )。  Finally, the substrate 1 is immersed in a diammonium cerium (IV) nitrate aqueous solution, and the molybdenum film 1.7 is etched. As a result, the unnecessary aluminum alloy layer deposited on the molybdenum film 7 is lifted off, and the electrode finger 6 for the SAW element is completed (FIG. 3 (d)).
発明の効果 The invention's effect
第一膜又は第三膜をアンダ一カツ ト形状にエッチングしてから 電極材料層を形成し、 次いで、 余分な電極材料層をリフ トオフす るので、 電極端部にバリや欠けを生じず、 ばらつきのない電極形 状を得ることができる。 ，  An electrode material layer is formed after the first film or the third film is etched in an undercut shape, and then an extra electrode material layer is lifted off. An electrode shape with no variation can be obtained. ,
また、 圧電基板裏面に、 裏面導電膜を形成すれば、 第二膜又は 第三膜を裏面導電膜と導通させることができるので、 レジス トパ 夕一ン形成工程において圧電基板の焦電により、 レジス トパター ンに欠陥が発生することを防ぐことができる。 .  Also, if a back conductive film is formed on the back surface of the piezoelectric substrate, the second film or the third film can be electrically connected to the back conductive film. It is possible to prevent defects from occurring in the top pattern. .
更にまた、 電極指の単位面積当たりの質量と、 電極指間の第一 膜の単位面積あたりの質量をほぼ同じにすることで、 S A Wの速 度が、 電極指の下と、 第一膜の下で同じになるので、 弹性波の反 射やバルク波としての放射が低減できる。 その結果、 損失の少な い素子を得ることができる。 また、 電極を構成する材料が万一ス トレスマイグレーショ ンしても、 電極指間の第一膜が障壁となり 電極指同士が短絡するのを防ぐことができる。 その結果、 長寿命 の素子を得ることができる。  Furthermore, by making the mass per unit area of the electrode finger substantially equal to the mass per unit area of the first film between the electrode fingers, the SAW speed can be reduced below the electrode finger and the first film. Since it is the same below, it is possible to reduce the reflection of the singular wave and the radiation as the bulk wave. As a result, an element with low loss can be obtained. Also, even if the material constituting the electrodes is stress-migrated, the first film between the electrode fingers acts as a barrier to prevent short-circuiting between the electrode fingers. As a result, a long-life element can be obtained.
更に、 第 1 の S A Wの素子の製造方法によれば、 レジス 卜パ夕 ーンを除去してから導電材料層を形成するので、 形成中の真空度 の悪化がなく、 膜質のよい導電材料層が得られる。 その結果、 耐 電力性に優れた信頼性の高い S A W素子が得られる。 Further, according to the first SAW element manufacturing method, the conductive material layer is formed after the resist pattern is removed, so that the degree of vacuum does not deteriorate during the formation and the conductive material layer with good film quality is formed. Is obtained. As a result, A highly reliable SAW device with excellent power performance can be obtained.

Claims

請 求 の 範 囲 The scope of the claims
1 . 圧電基板上に第一膜を形成する工程と、 第一膜上に第二膜を 形成する工程と、 第二膜上に所定形状のレジス トパターンを形成 する工程と、 レジス トパターンをマスクとして第二膜及び第一膜 を異方性又は等方性エッチングし、 続いて第一膜のみをアンダー カッ ト形状に等方性エッチングする工程と、 レジス トパターンを 除去する工程と、 全面に電極材料層を形成する工程と、 第二膜上 に存在する電極材料層を第二膜をエッチング除去することでリ フ トオフして電極を形成する工程を有する弾性表面波素子の製造方 法。 1. a step of forming a first film on a piezoelectric substrate, a step of forming a second film on the first film, a step of forming a resist pattern having a predetermined shape on the second film, A step of anisotropically or isotropically etching the second film and the first film as a mask, and then an isotropically etching only the first film in an undercut shape; a step of removing the resist pattern; A method for manufacturing a surface acoustic wave device, comprising the steps of: forming an electrode material layer on a substrate; and removing the electrode material layer present on the second film by etching off the second film to form an electrode. .
2 . 第二膜が、 第一膜をアンダーカッ ト形状にエッチングする際 に使用されるエツチャントに対して侵されにくい材料から:なる請 求項 1 に記載の弾性表面波素子の製造方法。 . The method of manufacturing a surface acoustic wave device according to become請Motomeko 1: 2 second film, the first film from the material hardly affected against Etsuchanto used in etching to undercut shape.
3 . 第一) ί及び電極材料層が、 第二膜のリフ トオフに使用される エッチヤン卜に対して侵されにくい材料からなる請求項 1 に記載 の弾性表面波素子の製造方法。  3. The method for manufacturing a surface acoustic wave device according to claim 1, wherein the first and second layers and the electrode material layer are made of a material which is hardly attacked by an etchant used for lifting off the second film.
4 . 第一膜が、 二酸化シリコン、 シリコン又は窒化シリコンの膜 からなり、 第二膜が、 モリブデン又はクロムの膜からなり、 電極 材料層が、 アルミニウム又はアルミニウム合金の膜からなる請求 項 1〜 3のいずれかに記載の弹性表面波素子の製造方法。  4. The first film is made of a film of silicon dioxide, silicon or silicon nitride, the second film is made of a film of molybdenum or chromium, and the electrode material layer is made of a film of aluminum or an aluminum alloy. The method for producing a surface acoustic wave device according to any one of the above.
5 . 圧電基板上に第三膜を形成する工程と、 第三膜上に所定形状 のレジス 1、パターンを形成する工程と、 レジス 卜パターンをマス クとして第三膜をァンダ一力ッ ト形状に等方性エッチングするェ 程と、 全面に電極材料層を形成する工程と、 第三膜上に存在する 電極材料層を第三膜をエツチング除去することでリフ トオフして 電極を形成する工程を有する弾性表面波素子の製造方法。  5. A step of forming a third film on the piezoelectric substrate, a step of forming a resist 1 having a predetermined shape and a pattern on the third film, and a step of forming the third film into a standard shape using the resist pattern as a mask. A step of forming an electrode material layer on the entire surface, a step of lifting off the electrode material layer present on the third film by etching away the third film, and forming an electrode. A method for manufacturing a surface acoustic wave device having:
6 . 電極材料層が、 第三膜のリフ 卜オフに使用されるエッチヤ ン 卜に対して侵されにくい材料からなる請求項 5に記載の弾性表面 波素子の製造方法。 6. The electrode material layer is used for etching off the third film. 6. The method for producing a surface acoustic wave device according to claim 5, wherein the surface acoustic wave device is made of a material that is not easily eroded by a tool.
7 '. 第三膜が、 モリブデンの膜からなり、 電極材料層が、 アルミ ニゥム又はアルミニウム合金の膜からなる請求項 6に記載の弾性 表面波素子の製造方法。  7. The method for manufacturing a surface acoustic wave device according to claim 6, wherein the third film is made of a molybdenum film, and the electrode material layer is made of an aluminum or aluminum alloy film.
8 . レジス 卜パターンを形成する工程の前に、 圧電基板の裏面に 導電膜を形成する工程を有する請求項 1 〜 7 のいずれかに記載の 弹性表面波素子の製造方法。  8. The method for manufacturing a surface acoustic wave device according to any one of claims 1 to 7, further comprising a step of forming a conductive film on the back surface of the piezoelectric substrate before the step of forming the resist pattern.
9 . 圧電基板上に所定パターンの櫛型電極指を有し、 電極指間の 圧電基板上に他の膜を有し、 電極指と他の膜の単位面積あたりの 質量が、 ほぼ等しい弾性表面波素子。.  9. An elastic surface with a comb-shaped electrode finger of a predetermined pattern on the piezoelectric substrate, another film on the piezoelectric substrate between the electrode fingers, and the mass per unit area of the electrode finger and the other film approximately equal Wave element. .
1 0 . 他の膜力 、 二酸化シリコン、 シリコン、 窒化シリコンの膜 からなる請求項 9に記載の弾性表面波素子。  10. The surface acoustic wave device according to claim 9, wherein the surface acoustic wave device comprises another film, a film of silicon dioxide, silicon, or silicon nitride.
PCT/JP2000/007102 2000-10-12 2000-10-12 Surface acoustic wave device and method of producing the same WO2002031974A1 (en)

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