JPS6271317A - Manufacture of surface acoustic wave device - Google Patents

Abstract

PURPOSE:To control and adjust the frequency of an SAW device with high accuracy by applying dry etching to a metallic thin film until the substrate is nearly exposed, applying wet etching to the metallic thin film left by the dry etching and forming an electrode while the cross section is clarified. CONSTITUTION:After a metallic thin film 2a such as Al is vapor-deposited to the substrate 1, a resist 4 is applied to the electrode forming part and the metallic thin film 2a is etched (the 1st stage etching) by applying dry etching by argon ion plasma. The etching is stopped before the background substrate 1 is exposed. Then the metallic thin film 2a left on the substrate 1 is etched by wet etching (the 2nd stage etching) for the removal. Since the wet etching is an isotropic etching, when over etching is applied by extending the etching time, up to the side face of the electrode 2 is etched. The frequency is adjusted by utilizing it and applying over-etching until the side face of the electrode 2 while checking the frequency.

Description

[Detailed Description of the Invention] The present invention is based on a surface acoustic wave device (hereinafter referred to as a SAW device).
The present invention relates to a manufacturing method, and more particularly to a method for forming an electrode.

In recent years, SAW devices that excite surface acoustic waves using piezoelectric effects and use them as resonators or filters have become known. For example, a SAW device used as a resonator can be
To explain based on the figures and FIG. 6, (1) is a piezoelectric substrate (hereinafter simply referred to as a substrate) such as a single crystal quartz or a thin film;
(2) is a comb-shaped electrode formed by a printing technique such as etching by interlocking a pair of comb-shaped electrodes separated at regular intervals (λ), and (3) is the surface excited by the comb-shaped electrode (2). It is a wave reflector, and is a diffraction grating in which vertically long protrusions made of An or the like are arranged at predetermined intervals on both sides of a comb-shaped electrode (2) so as to be orthogonal to the vibration direction of the surface wave.

In the above configuration, when a pulse voltage is applied to the comb-shaped electrode (2), a piezoelectric effect causes a distortion in opposite phases to occur on the substrate surface between adjacent electrodes, and a surface wave with a wavelength (λ) is excited. Each time this surface wave reaches each protrusion of the reflector (3), it is divided into a reflected wave and a transmitted wave. Therefore, if the intervals between the protrusions are set so that the phases of the reflected waves from each protrusion of the reflector (3) are aligned, each reflector (3) (
3) A standing wave of wavelength (λ) is excited between them and becomes a resonator.

Then, the propagation speed of the above surface wave is (V) and the wavelength is (λ)
, when the resonant frequency is (f), vxfλ holds true, and the resonant frequency (f) is given by f-V/λ. here,
The wavelength (λ) is determined by the interelectrode pitch of the comb-shaped electrode (2), and the propagation velocity (v) is determined by the material of the substrate (1), etc., but it is also determined by the comb-shaped electrode (2) formed on the substrate (1). Affected by mass effect. The mass effect mentioned above is that the propagation velocity (V) changes depending on the mass of the comb-shaped electrode (2), that is, the film thickness. For example, if the film thickness of the comb-shaped electrode (2) is increased without changing the inter-electrode pitch (λ). , the propagation velocity (V>) decreases and the resonant frequency (f) decreases. Therefore, when forming the comb-shaped electrode (2) by etching etc., in order to obtain the necessary resonant frequency (f), the comb-shaped electrode ( 2) The film thickness must be set to a predetermined thickness by controlling the pitch between the electrodes as well as the film thickness.

The comb-shaped electrode (2) is usually formed by printing technology,
As shown in Figure 7, a metal thin film such as Ai' (
2a) is vapor-deposited, and then, as shown in FIG. 8, a resist (4) equivalent to the electrode pattern is applied to the surface to which the electrode is deposited, followed by etching.

By the way, the electrode width of the comb-shaped electrode (2) is 1 to 3μ (m), so when forming the electrode, it must be chemically immersed in phosphoric acid, etc. Isotropic wet etching that melts the metal thin film (2a) is inappropriate, and anisotropic dry etching that evaporates the metal thin film (2a) with ion plasma such as argon is used. However, the metal thin film (2a
), in order to clearly show the cross section of the electrode, the thin metal Ill! is etched as shown in Figure 9. (2a)
Not only this, but also a part of the surface of the underlying substrate (1) is etched. As a result, the mass effect of the comb-shaped electrode (2) extends to the surface protrusions of the substrate (1) after etching, so that the gold B
It is necessary to control not only the thickness of the thin n (2a) film but also the etching depth of the substrate (1), making it difficult to set the electrode film thickness. In addition, since the metal thin film 1) (2a) is formed by vapor deposition and has an uneven surface, if it is etched at a uniform etching rate by dry etching, the substrate (
The unevenness of the surface of the metal thin film (2a) is also formed on the surface of 1).

According to the present invention, when manufacturing a surface acoustic wave device by depositing a metal thin film on a piezoelectric substrate and then forming a thin film comb-shaped electrode by etching, the metal thin film deposited on the piezoelectric substrate is The electrode is formed by etching the metal thin film by dry etching until just before exposure, and then etching the metal thin film remaining by dry etching by wet etching.

Production 1 - After depositing a metal thin film on a piezoelectric substrate and etching it by dry etching until just before the underlying substrate is exposed, the remaining metal thin film is etched by wet etching to form a thin comb-shaped electrode. The electrodes are formed by etching only the etching layer, and the etching does not reach the substrate.

(2) An embodiment in which the method of manufacturing a SAW device according to the present invention is applied will be described below in the order of application with reference to FIGS. 1 to 4.

The present invention is a manufacturing method commonly used for forming a thin film comb-shaped electrode (2) in a SAW device.First, as shown in FIG. After depositing 2a), resist (4) is applied to the electrode formation area.
The metal Km (2a) is etched by dry etching using argon ion plasma (first stage etching). The first stage of dry etching is anisotropic etching and is etched in the vertical direction, but as shown in Figure 2, the underlying substrate (1)
Stop before it is exposed. Next, the metal thin film (2a) remaining on the substrate (1) after the first stage etching is immersed in a mixed acid of phosphoric acid and nitric acid, and is etched by wet etching (second stage etching) to be removed. Then,...
Since the substrate (1) such as crystal is not removed by wet etching, as shown in Fig. 3, the resist (4) is applied to the predetermined area where the resist (4) is applied without etching the surrounding substrate (1). The cross section of the electrode can be clearly expressed by the film thickness. Here, since wet etching is isotropic etching, if the etching time is increased to cause overetching, the side surfaces of the electrode (2) will be etched as shown in FIG. 4. Therefore, by utilizing this and over-etching to the side surface of the electrode (2) while checking the frequency, the frequency can be adjusted.

According to the present invention, when manufacturing the SAv,r device by forming the thin film comb-shaped wire of the SAW device on the piezoelectric substrate by etching, the substrate is etched by dry etching the full-thickness thin film. After etching to the point where it is exposed, the thin metal film remaining from dry etching is etched using wet etching to make the cross section clear and form electrodes, so the thickness of the bridge can be controlled solely by the thickness of the thin metal film. Therefore, it is possible to easily control and adjust the frequency of the SAW device with high precision.

[Brief explanation of drawings]

1, 2, 3 and 4 are SAWs according to the present invention.
FIG. 5 is a perspective view of a SAW resonator, which is a specific example of a SAW device, and FIG. A
7 is a perspective view of a piezoelectric substrate on which a metal thin film has been deposited, and FIG. FIG. 9 is a partially enlarged sectional view of a thin film comb-shaped electric winding of a SAW device for explaining the conventional problems. (1)・-Piezoelectric substrate, (2m-thin film comb-shaped electrode, (2a
) - metal thin film. Patent applicant: Kansai NEC Co., Ltd. B-1゛=w
゛1 Agent: Sho Ebara ゛・-',,'-1 Engraving of the drawings (no changes to the contents) No. 3L No. 4<j Figure 7 Procedural Amendment February 25, 1986 Commissioner of the Patent Office U Ka Michibe 1, Indication of the case 1985 Patent layer No. 21) No. 674 2, Title of the invention Method of manufacturing a surface acoustic wave device 3, Relationship with the person making the amendment Case Name of patent applicant Kansai NEC Co., Ltd. 4. Address of agent: 1-15-26 Edobori, Nishi-ku, Osaka-shi, Osaka Prefecture, Osaka Sho Ebiru, Tokyo Name (645B) Patent attorney: Shogo Ehara 5. Date of amendment order: January 8, 1985 (Date of dispatch: Showa) (January 28, 1961) 6. Subject of amendment Drawing 7.? ili Correct contents Amend the drawing plan as shown in the attached sheet.

Claims (1)

[Claims] (1) After depositing a metal thin film on a piezoelectric substrate, a thin film comb-shaped electrode is formed by etching, and when manufacturing a surface acoustic wave device, the metal thin film deposited on the substrate is dried until just before the substrate is exposed. Etching with etch, then etching the remaining metal thin film with wet etch,
A method of manufacturing a surface acoustic wave device, comprising forming the above electrode.