JP2005223396A - Electrode forming method of piezoelectric device and mcf employing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a concentrically spreading a resist material forms a resist reservoir on the rotating external edge end surface of the concave of each electrode substrate, if a photoresist film is formed on an electrode metallic film on the entire concave surface of a crystal wafer on which a plurality of electrode substrates of inverse-mesa structure are formed, the residue of the resist material which has not been dissolved by development remains if exposure and development processing are performed, and unnecessary metallic film remains in a substrate vibrating portion when an excitation electrode is formed by etching processing. <P>SOLUTION: When electrode metallic films 2 are vapor-deposited by vapor deposition on each concave surface of a plurality of piezoelectric substrates 1 of the inverse-mesa structure formed on a piezoelectric material wafer, the electrode metallic films 2 are vapor-deposited by providing a mask 4 on a portion (rotating external edge end surface) 3 where the resist reservoir of each substrate concave on the wafer is formed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for forming an electrode of a piezoelectric device, and in particular, a photoresist material is applied by spin coating on the electrode metal film surface deposited on the concave surface side of an electrode substrate having an inverted mesa structure, and masking, exposure, and development processing are performed. The present invention relates to an electrode forming method for a piezoelectric device in which a photoresist film having an electrode pattern is formed and an electrode is formed by an etching process.

In recent years, communication equipment has been miniaturized or increased in frequency, and the resonance frequency has been increased even in oscillators and filters that are control devices of the reference frequency.
Two opposing excitation electrodes are formed at predetermined intervals on both principal surfaces of a piezoelectric substrate, for example, an AT-cut quartz crystal substrate, and the result of acoustic coupling between vibration modes excited on the two sets of electrodes 2 It is known that a band-pass filter, that is, a multi-mode crystal filter (hereinafter referred to as MCF) is configured using two vibration modes. As is well known, the resonance frequency of the MCF is inversely proportional to the thickness of the quartz substrate. For example, the thickness of the substrate for obtaining a resonance frequency on the order of 100 MHz is about 10 μm.

Since such an extremely thin substrate has a low mechanical strength, it is liable to be damaged by vibration or shock during assembly or use, and there is a problem in mass productivity and reliability.
As a countermeasure, as a quartz substrate structure having a thin vibration part and mechanical holding strength, a so-called inverted mesa structure substrate, that is, a central portion of a quartz substrate having a substrate center portion recessed in a trapezoidal shape. Excitation electrodes are formed on both surfaces of the thin-walled vibration part, and a connection electrode connected to the outside is formed on the annular annular part integrally formed to hold the periphery of the vibration part, and from the excitation electrode A method has been adopted in which a substrate structure having mechanical strength is provided by connecting the connection electrode to the connection electrode using an extended lead electrode.

2A and 2B are explanatory diagrams of a balanced MCF in which two pairs of excitation electrodes facing a quartz substrate having an inverted mesa structure are formed. FIG. 2A is a schematic electric circuit diagram, and FIG. The longitudinal cross-sectional view shown, (c) shows a distribution diagram of vibration energy on the substrate at the time of excitation.
The present MCF 20 represented by the electric circuit diagram of FIG. 6A includes two pairs of excitation electrodes 22a and 22b on both surfaces of the thin vibrating portion 21a at the center of the quartz substrate 21 having an inverted mesa structure as shown in FIG. The excitation electrodes 22a and 22b are connected by connection electrodes (not shown) formed on both surfaces of the annular surrounding portion 21b around the vibration portion 21a and lead electrodes (not shown) extending from the excitation electrodes 22a and 22b, respectively. Yes.
In the quartz substrate 21, for example, the vibration portion 21a at the center of the substrate has a thickness of about 10 μm, and the annular surrounding portion 21b has a thickness of about 80 μm.
The present MCF 20 is a band-pass filter in which vibration energy during excitation is distributed in the substrate central vibration portion 21a as shown in FIG.

In order to simplify the description of the procedure for forming the electrodes on the vibration part 21a of the quartz substrate 21 having the inverted mesa structure described above, the excitation electrodes 22a and 22b formed on the vibration part 21a on the bottom surface of the substrate recess will be described.
FIG. 3 is a basic process diagram showing an operation procedure for forming an excitation electrode of the MCF on a quartz substrate having an inverted mesa structure by metal vapor deposition. In addition, the code | symbol of drawing uses the code | symbol of FIG. 2 as it is for a common part.
As shown in the figure, the vibrating portion 21a is formed on the upper surface of the concave portion of the quartz substrate 21 (FIG. 5A) having a thin vibrating portion 21a on the bottom surface of the concave portion and a thick annular surrounding portion 21b around it. A mask 23 having an electrode pattern to be applied is applied (FIG. 2A).
After that, the electrode metal is evaporated from the vapor deposition source 24 of the vapor deposition apparatus, and the electrode metal is vapor-deposited on the vibrating portion 21a through the mask 23, thereby forming the excitation electrodes 22a and 22b (FIG. 5C).

Although not shown here, a mask having an electrode pattern is directly applied to the substrate surface on the flat surface side of the substrate having an inverted mesa structure, and an electrode metal is deposited by vapor deposition to form an electrode.
However, in the method shown in the figure, since there is a gap (8 μm in the case of FIG. 2B) between the mask 23 and the electrode forming surface (vibrating portion 21a surface), the evaporated electrode metal vapor is masked. There is a drawback that the electrode having a predetermined pattern cannot be formed by going to the power region (FIG. 3C shows this state).

FIG. 4 is a basic process diagram showing a conventional work procedure for forming electrodes on a quartz substrate having an inverted mesa structure using a photolithography technique, which is taken as a method for solving the above problem. In the same manner as described above, an operation procedure for forming the excitation electrode on the concave bottom vibration portion of the substrate having the inverted mesa structure will be described.

First, an electrode metal film 32 having a predetermined thickness is deposited on the entire surface of the concave surface of the quartz substrate 31 having the inverted mesa structure shown in FIG. Next, a photoresist film 33 is applied on the entire surface of the electrode metal film 32 ((c) in the figure), and a mask 34 for forming an electrode pattern is applied thereon. The photoresist film 32 is exposed (FIG. 4D).
Further, after removing the unnecessary photoresist by the development process ((f) in the figure), the unnecessary metal film is removed by the etching process (figure (f)), and finally the photoresist film 33a is peeled off. Then, the excitation electrodes 32a and 32b having a predetermined pattern are formed ((G) in the figure).
In the step of exposing the photoresist film 33 in FIG. 5D, even if there is a gap between the mask 34 and the electrode formation surface, the surface of the resist film 33 is exposed with an accurate pattern by the straightness of the light source light. Therefore, it is possible to form the excitation electrodes 32a and 32b having an accurate pattern by development and etching.
Japanese Patent Laid-Open No. 9-284092

The work procedure of FIG. 4 shows the procedure of electrode formation for one MCF, but in the actual manufacturing process, each of a plurality of crystal electrode substrates formed in a reverse mesa structure on a crystal wafer. On the other hand, a manufacturing method is employed in which the work process of FIG. 4 is sequentially performed, and then cut and divided to obtain individual MCFs.
The actual operation of applying the photoresist film 33 in FIG. 5C is performed as shown in the explanatory diagram of the photoresist film application operation by spin coating in FIG.
That is, as shown in FIG. 5A, in the crystal wafer 30 in which a plurality of electrode substrates 31 having a reverse mesa structure are formed in a matrix, an electrode metal film 32 having a predetermined thickness is formed by vapor deposition on the entire surface of the concave surface. Attached and placed on the turntable 36, a photoresist material 33 'is suspended at the center of rotation of the crystal wafer 30, and the turntable 36 is rotated at a predetermined speed (FIG. 1), and the entire surface is caused by centrifugal force. In general, a resist film 33 having a predetermined thickness is applied to the substrate (FIG. 5C), which is called spin coating.

However, according to this working method, the resist material 33 'spreads concentrically outward from the center of rotation to form a coating film, but as shown in FIG. Since the concavities of the electrode substrate 31 are formed, the resist material 33 ′ that spreads concentrically forms a resist pool 33 b on the end surface of the rotation edge of each electrode substrate 31.
When the resist film 33 on which such a resist pool 33b is formed is exposed and developed, as shown in the explanatory diagram of FIG. 6, the residue of the resist material that cannot be completely dissolved by development at the position of the resist pool 33b. 37 (FIGS. 6A and 6A), and when the excitation electrodes 32a and 32b are formed by etching, an unnecessary metal film 38 remains on the substrate vibrating portion 31a (FIG. 6C). (D)).

The above-described unnecessary metal film 38 remains on the substrate vibrating portion 31a, so that the vibration energy of the MCF is suppressed, and the vibration energy on the substrate vibrating portion 31a has a distribution indicated by a solid line in FIG.
For this reason, there is a problem that the electrical characteristics of the MCF, in particular, the CI value increases and the Q decreases, and a predetermined filter characteristic cannot be obtained.
The present invention has been made in order to solve the above-described problems, and when a photoresist is applied to an electrode substrate having a concave portion having a reverse mesa structure by spin coating, a photoresist pool is formed on the rotation outer edge end surface of each concave portion. It is an object of the present invention to provide an electrode forming method that prevents the generation.

In order to solve the above problems, in the invention of claim 1, in the invention of claim 1, a plurality of piezoelectric substrates formed in a reverse mesa structure on a piezoelectric material wafer are formed by vapor deposition over the entire concave surface. A photoresist material is applied to the formed electrode metal film by spin coating, a photoresist film having an electrode pattern is formed on the electrode metal film by masking, exposure and development processes, and a bottom surface of the concave portion of the piezoelectric substrate is etched. In the electrode forming method of the piezoelectric device that forms the pattern electrode in the vibration part,
When the electrode metal film is deposited on the piezoelectric substrate, the electrode metal film is masked so that the metal film is not deposited on the rotating outer edge end surface of each piezoelectric substrate recess of the piezoelectric material wafer that rotates during the spin coating of the photoresist. It is characterized by depositing a film.

According to a second aspect of the present invention, in the piezoelectric device electrode forming method according to the first aspect, the piezoelectric material is quartz.
Further, according to a third aspect of the present invention, there is provided the electrode forming method for a piezoelectric device according to the first or second aspect, wherein the piezoelectric device is a monolithic crystal filter (MCF).

The method of forming an electrode of a piezoelectric device of the present invention is the method of depositing an electrode metal film by vapor deposition on each concave surface side of a piezoelectric substrate formed with a plurality of inverted mesa structures on a piezoelectric material wafer. Since the electrode metal film is deposited by masking the rotation outer edge end face of the substrate recess, when the photoresist film is applied by spin coating after the electrode metal film is deposited, the resist is applied to the rotation outer edge face of each recess. Even if accumulation occurs, it is possible to prevent generation of an unnecessary metal film on the vibrating portion of the electrode substrate as a result of exposure, development, and etching.
Therefore, the electrode forming method of the present invention can produce an MCF having desired characteristics with a high yield, and thus can greatly contribute to providing a low-cost MCF stably.

The present invention will be described based on the embodiments shown in the drawings. FIG. 1 is a basic process diagram showing an operation procedure for forming an excitation electrode of MCF on a quartz substrate having an inverted mesa structure using a photolithography technique according to the present invention.
Similarly to the above, in the actual manufacturing process according to this method, each of the plurality of electrode substrates formed on the quartz wafer is simultaneously subjected to the following processing, and then cut and divided into individual substrates. In order to simplify the description, an operation procedure applied to one MCF electrode substrate will be shown and described.
As shown in the figure, first, an electrode metal film 2 having a predetermined thickness is deposited on the entire recess side of the quartz substrate 1 having a reverse mesa structure by vapor deposition. At this time, a photoresist is applied by spin coating in a subsequent process. Then, a mask 4 is applied so as to cover a portion where the resist pool is formed (the outer edge of the concave outer edge during rotation), and the electrode metal is evaporated from the evaporation source 5 to deposit the electrode metal film 2 (FIG. )).

After that, a photoresist film 6 having a predetermined thickness is applied to the entire surface by spin coating (FIG. 1A). Next, a mask 7 for forming an electrode pattern is applied, and the photoresist film 6 is exposed from the light source 8 through the mask 7 (FIG. 5C).
Next, after a photoresist film 6a having a predetermined pattern is formed by development processing (FIG. 5D), an unnecessary metal film is removed by etching to form a metal film in a predetermined pattern (FIG. )), And finally, the photoresist film 6a is peeled off to form the excitation electrodes 2a and (2b) having a predetermined pattern (FIG. 5F).

Even if a resist residue 6b is generated in the resist reservoir 3 by spin coating as a result of the development process in FIG. 6D, the electrode metal film 2 is not deposited on this portion, so that it is unnecessary as in the prior art. No metal film is formed on the substrate vibrating portion 1a.
Therefore, the MCF manufactured by the above-described electrode forming method does not deteriorate the vibration energy distributed in the substrate vibrating portion 1a, and thus can provide an MCF having excellent electrical characteristics.

In the figure, (K) shows the pattern of the lead electrode 9a, 9b and the connection electrodes 10a, 10b formed on the pattern of the mask 7 applied in the step (c) of the above procedure, thereby forming the crystal electrode substrate 1 FIG. 5 is a top view of an MCF in which excitation electrodes 2a and 2b and lead electrodes 9a and 9b are formed on the vibration portion 1a on the concave surface side, and connection electrodes 10a and 10b are formed on the annular surrounding portion 1b.
As can be seen from the figure, the mask 4 applied in the step (a) of the figure is formed with lead electrodes 9a and 9b extending from the excitation electrodes 2a and 2b formed on the vibrating part 1a. In other words, the connection electrodes 10a and 10b formed on each substrate electrode 1 of the inverted mesa structure of the quartz wafer and the lead electrodes 9a and 9b connected to the substrate electrodes 1 Needless to say, the electrode pattern must be designed so as to be formed on the center side of rotation during spin coating of the resist.

The basic process figure which shows the operation | movement procedure of the method of forming the excitation electrode of MCF in the quartz substrate of a reverse mesa structure using the photolithographic technique which concerns on this invention. It is explanatory drawing of the balance type | mold MCF which formed two pairs of excitation electrodes facing the quartz substrate of a reverse mesa structure, (a) is typical electric circuit diagram, (b) is a longitudinal cross-sectional view which shows the electrode structure of a board | substrate , (C) is a distribution diagram of vibration energy on the substrate during excitation. The basic process drawing which shows the operation | movement procedure which forms the excitation electrode of MCF in the quartz substrate of a reverse mesa structure by metal vapor deposition. The basic process figure which shows the conventional operation | movement procedure which forms an electrode in the quartz substrate of a reverse mesa structure using a photolithographic technique. Explanatory drawing of the photoresist film application | coating operation | work by spin coating. Explanatory drawing of the influence by the residue of the resist material produced in the position of a resist pool at the time of spin coating of a photoresist.

Explanation of symbols

1 .... Quartz substrate, 1a ... Vibrating part, 2 .... Electrode metal film,
3 .. part where resist pool is formed (end surface of recess outer edge during rotation) 4.. Mask
5 .... Vapor deposition source, 6, 6a ... Photo resist film, 7 .... Mask, 8 .... Light source,
9a, 9b ... lead electrodes, 10a, 10b ... connecting electrodes,
20 ·· MCF, 21 ·· Quartz substrate, 21a ·· vibrating portion, 21b ·· annular surrounding portion,
22a, 22b ... excitation electrode, 23 ... mask, 24 ... deposition source,
30..Quartz wafer, 31..Quartz substrate, 31a .., 32..Electrode metal film,
32a, 32b ... excitation electrodes, 33, 33a ... photoresist film,
33 '.. Photoresist material, 33b .. Resist reservoir, 34 .. Mask, 35 .. Light source,
36 .. Turntable 37.. Resist residue 38.. Unnecessary metal film

Claims (3)

A photoresist material is applied by spin coating to the electrode metal film formed by vapor deposition on the entire concave surface of each of a plurality of piezoelectric substrates formed in a reverse mesa structure on a piezoelectric material wafer, and masking, exposure and development processing are performed. In the electrode forming method of a piezoelectric device, a photoresist film having an electrode pattern is formed on the electrode metal film by, and a pattern electrode is formed on the bottom vibration portion of the recess of the piezoelectric substrate by an etching process.
When the electrode metal film is deposited on the piezoelectric substrate, the electrode metal film is masked so that the metal film is not deposited on the rotating outer edge end surface of each piezoelectric substrate recess of the piezoelectric material wafer that rotates during the spin coating of the photoresist. A method for forming an electrode of a piezoelectric device, comprising depositing a film.   The method for forming an electrode of a piezoelectric device according to claim 1, wherein the piezoelectric material is quartz. The method of forming an electrode of a piezoelectric device according to claim 1 or 2, wherein the piezoelectric device is a monolithic crystal filter (MCF).

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