JPS61102810A - Manufacture of elastic surface wave element - Google Patents

Abstract

PURPOSE:To improve the dimensional accuracy of an electrode pattern and to obtain an elastic surface wave element which is stable characteristically and has a high reliability by adding the process for executing oxidation, so that light reflectance on the surface of a matellic coat formed on an piezoelec tric substrate can be dropped, before coating a resist member. CONSTITUTION:The metallic coat 3 is formed on the entire piezoelectric sub strate 1 by Al deposition. Then the surface of the metallic coat 3 is oxided to form an oxide film 11. This oxidation is conducted in order to reduce substan tially the reflectance on the surface of the metallic coat 3, and is executed after coloring by anode oxidation. Then the resist member 4 is coated on the oxide film 11, and a mask is covered to expose the member. At this exposure a light beam 8 transmits the resist member 4 and is reflected on the metallic coat 3. However, since the reflectance on the surface of the metallic coat 3 is significantly reduced by the oxide film 11, the exposure ratio of the resist member 11 which must not be exposed and located right under a light shielding film 7 is substantially reduced. Accordingly the exposure can be carried out with the high accuracy of a mask pattern transfer.

Description

[Detailed Description of the Invention] Mainly sit on top! The present invention relates to a method for manufacturing a surface acoustic wave device, and more particularly to a method for forming an electrode pattern that is deposited in the form of a film on a piezoelectric substrate.

Surface acoustic wave elements that utilize surface acoustic waves due to the piezoelectric effect of a piezoelectric substrate such as a string-distorted crystal substrate have recently become widely used as filter elements and SAW resonators. The basic structure of this surface acoustic wave element will be explained based on FIGS. 3 and 4 using a SAW resonator as an example. (1) is a piezoelectric substrate,
(2) is an AI! formed in a predetermined pattern on the piezoelectric substrate (1)! An electrode pattern made of a vapor-deposited film, each of which is comb-shaped and has a pair of IDT electrodes formed by interlocking comb teeth (
2a) (2b) and IDT electrode (2a) (2b)
) Grating electrodes (2c) formed on both sides of
(2d). The IDT electrodes (2a) (2b) have comb teeth at regular intervals λ.
a) When a pulse voltage is applied to (2b), distortions with mutually opposite phases occur on the substrate surface between adjacent comb-teeth electrodes due to the piezoelectric effect, and a surface wave with a wavelength λ is excited. This surface wave is divided into a reflected wave and a transmitted wave each time it reaches the grating electrodes (2c) (2d) on both sides, and the grating is arranged so that the phases of the reflected waves from the grating electrodes (2c) (2d) on both sides are aligned. ff electrode (2c) ('2d
), a standing wave of wavelength λ as shown by the broken line in FIG. 4 is excited and becomes a resonator.

By the way, since the electrode pattern (2) on the piezoelectric substrate (1) is a fine pattern, it is formed using the PR method (photoresist method) similar to the formation of electrode patterns of semiconductor elements.
This is done in the following manner as shown in (a) to (f) in the figure.

First, a metal coating (3) is deposited to a uniform thickness on the entire surface of the piezoelectric substrate (1) by At vapor deposition as shown in FIG. 5(a). Next, as shown in FIG. 5(b), As shown, a positive or negative resist material (4) is deposited to a uniform thickness on the metal film (3).

Next, a mask (5) as shown in FIG. 5(C) is placed over the resist material (4), and light (ultraviolet light) is vertically irradiated from above to expose the resist material (4). Mask (5
) is, for example, a light-shielding film (7) fixed to the lower surface of a transparent glass substrate (6) in a predetermined pattern, and a resist material (4)
If the area other than the part hidden by the shading 1m (7) receives light, it will react and change in quality. If the resist material (4) is positive type (1°), only the exposed areas will be removed in the subsequent development process, and if it is negative type, only the unexposed areas other than the exposed areas will be removed in the subsequent development process. Ru.

As a result of this exposure and development, the resist material (4°) remains only on the portion of the metal coating (3) where the electrode pattern is to be formed, as shown in (d) of Fig. 5, and the rest is as shown in (e) of Fig. 5. If the metal film (3) exposed from the resist material (4 degrees) is removed by etching as shown, and then the resist material (4 degrees) is removed, the piezoelectric substrate ( 1) A desired pattern (2) is formed on top.

By the way, the metal coating (3) formed on the entire surface of the piezoelectric substrate (1) is an AA vapor-deposited film, and its surface has minute irregularities, and the surface of the A4 vapor-deposited film is Therefore, during the exposure shown in FIG. 5(c), the light transmits through the resist material (4) and is diffusely reflected on the metal coating (3) at a high rate, causing the following problem.

That is, as shown in FIG. 6, the light shielding film (7) of the mask (5)
The light (8) incident along the edge of the resist material (4) enters the metal coating (3) perpendicularly and is reflected.
! ! Since the surface of (3) has a high reflectance and is uneven, much of the incident light is reflected diffusely, and some of it touches the resist material (4°) directly under the light-shielding film (7) that should not be exposed. Due to the above-mentioned problem, the resist material (4゛) that remained on the metal film (3) after exposure and development was positive type. In this case, as shown in FIG. 7(a), the pattern becomes a pattern that is slightly thinner than the predetermined mask pattern (7') and has a fluff-like cut (9) formed inside, and the electrode pattern (2) is formed as it is. ) is formed, and when the resist material (4°) is a negative type, it is slightly thicker than the mask pattern (7°) and has fluff-like abnormal protrusions (lO) on the outside, as shown in Figure 7 (b). This pattern sometimes forms the electrode pattern (2). Such an irregularly shaped electrode pattern (2) makes the characteristics of the surface acoustic wave element unstable and deteriorates its reliability. This was a contributing factor.

In addition, surface acoustic wave elements are assembled by bonding thin metal wires to the electrode pattern (2) from the outside, taking the electrodes out to the outside, and sealing them with metal caps. During assembly, metal scraps from metal camps etc. is the electrode pattern (
2) The product may fall onto the surface, causing a short circuit between the electrodes, which may impair the production yield of surface acoustic wave devices such as SAW resonators.

The present invention has been made in view of the above problem, and the technical means of the present invention to solve this problem is to reduce the reflectance of light on the surface of the metal coating formed on the piezoelectric substrate. This involves adding an oxidation treatment step before applying the resist material.

Last month, if you oxidize the surface of the metal coating to lower its reflectance, then apply a resist material and expose it to light using a mask, the reflectance of the surface of the metal coating will be low. As the amount of light reflected from the surface is reduced, the accuracy of transferring the mask pattern to the resist material increases accordingly, and as a result, a mask pattern that more closely resembles the electrode pattern formed on the piezoelectric substrate can be obtained. By leaving the oxide film formed by oxidation treatment on the formed electrode pattern, the problem of short-circuiting between the electrodes due to falling metal debris can be solved.

Emperor! ± The manufacturing method of the present invention will be explained below based on FIGS. 1 and 2.

First, as shown in FIG. 1(a), a metal coating (3) is formed on the entire surface of the piezoelectric substrate (1) by AI vapor deposition as in the conventional method.
Next, in the present invention, the surface of the metal covering ff (3) is oxidized to form an oxide film (1) as shown in FIG. 1 (B). This oxidation treatment is a metal coating! This is done for the purpose of greatly reducing the reflectance of the surface of (3). Specifically, since the metal coating (3) is an AJ vapor deposited film, it is dyed using the following anodic oxidation method.

For example, as shown in FIG. 2, a piezoelectric substrate (1) having a metal coating (3) and an electrode plate (12) are immersed in an electrolytic solution (13) such as a sulfuric acid solution, and a positive voltage is applied to the metal coating (3). A negative voltage is applied to the electrode plate (12) and the metal plate It! (3
) surface is anodized. The oxide film (1)) formed by this anodization is r-A1203 and is porous, so it is later treated with boiling water and superheated steam to seal the pores and improve the corrosion resistance and insulation properties of γ-A1203 and H2O. An excellent oxide film (1)) is formed, and the oxide film (1)) is dyed in a desired color such as black with low reflectance by such anodic oxidation.

Next, as in the conventional method, first oxidize 1) i! as shown in FIG. 1(c). (1)) Apply resist material (4) on top,
A mask (5) is placed over the resist material (4) as shown in (d) in Figure 1, and the resist material (4) is exposed to light. Transparent and metal coated 1) 5! (3), but the surface of the metal coating (3) is stained with oxidation 1j! Since the reflectance in (1)) has decreased significantly, there is less reflected light and the diffused reflectance decreases, so the exposure rate of the resist material (4") that should not be exposed directly under the light shielding film (7) is reduced. Therefore, exposure can be performed with high mask pattern transfer accuracy.

When the exposure is completed, remove the mask (5) and apply the resist material (4).
) is developed to leave a resist material (4°) that almost matches the mask pattern, as shown in (e) of FIG.

Next, as shown in FIG. '') is removed to obtain an electrode pattern (2') shown in (G) of FIG. This electrode pattern (2') has an oxidized PE surface! (
1)), it has excellent corrosion resistance, and even if metal debris falls, the insulating oxide film (1)) on the surface prevents short-circuit accidents between the electrodes.

In addition, for the surface acoustic wave element in which the electrode pattern (2') is formed in this way, gold II is later deposited on the electrode pattern (2').
The I wire is bonded, but for this bonding, if the oxide film (1) is made thin, the force during bonding will cause the oxidation II! (1)) is torn and it is possible to bond sufficiently well, so there is no problem. Or electrode pattern (2°)
Although not shown in the figure, since a dedicated band for bonding is formed, only the bonding pad may be placed without oxidation treatment to improve bonding of the thin metal wire.

According to the present invention, the exposure accuracy during electrode pattern formation of a surface acoustic wave device is further improved, and the dimensional accuracy of the electrode pattern is improved, resulting in a highly reliable elastic surface with stable characteristics. can be provided.

Furthermore, the oxide film on the electrode pattern makes it possible to provide a long-life surface acoustic wave element with excellent corrosion resistance, and even if metal debris adheres to the electrode pattern? I! The probability of short-circuiting between poles is low, and the yield of manufacturing SAW resonators using surface acoustic wave elements can be improved.

[Brief explanation of drawings]

(A) to (G) in FIG. 1 are partial cross-sectional views of the surface acoustic wave element at each manufacturing process for detailed explanation of the present invention, and FIG. 2 is an oxidation treatment in the step (B) in FIG. FIG. 2 is a schematic cross-sectional view of the device. 3 and 4 are a plan view and a cross-sectional view taken along the line A-A of the surface acoustic wave device, and FIGS. A partial cross-sectional view of the surface acoustic wave device in the process, Figure 6 is (c) in Figure 5.
FIGS. 7(a) and 7(b) are plan views showing two sides of the resist material bag after development in FIG. 5(d). (1)--piezoelectric substrate, (2°)-electrode pattern, (3
1-Total reflex film, (1)) -・Oxide film. Patent applicant: Kansai NEC Co., Ltd.
Rijin Gangwon Province Gojiang
Hide Hara

Claims (1)

[Claims] (1) When selectively exposing and developing a metal coating formed on a piezoelectric substrate to form a predetermined electrode pattern on the piezoelectric substrate, the surface of the metal coating on the piezoelectric substrate is exposed to light prior to exposure. A method for manufacturing a surface acoustic wave device, characterized by adding an oxidation treatment step to reduce the reflectance of the surface acoustic wave device.