JPH02234507A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To prevent a by-product made of a chlorine compound generated at dry etching for forming an electrode finger by forming a carbon film on the surface of a piezoelectric substrate and of the electrode finger. CONSTITUTION:A couple of electrode fingers 2, 2 are formed on a piezoelectric substrate 1 in a surface acoustic wave(SAW) device, which is formed by coating a carbon film 8 to the surface of the piezoelectric substrate 1 and the electrode fingers 2, 3. The carbon film 8 is used to prevent the by-product made of a chlorine compound formed on the surface of the piezoelectric substrate 1 and the electrode fingers 2, 2 from reacting with water in the dry etching process when the electrode fingers 2, 2 are formed. In the case of manufacturing the SAW device formed with the carbon film 8, after a couple of the electrode fingers 2, 2 are formed on the surface of the piezoelectric substrate 1, a gas of an organic compound including carbon and hydrogen atoms is decomposed under the environment of a high frequency to adhere the carbon film 8 easily on the surface of the piezoelectric substrate 1 and the entire face of a couple of the electrode fingers 2.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a surface acoustic wave device (hereinafter abbreviated as SAW device), which improves corrosion resistance by forming a carbon film on its surface. It has been improved.

[Prior art and its problems] By using surface acoustic waves propagating on solid surfaces,
SAW that processes signals from VHF band to UHF band
As devices, for example, those shown in FIGS. 2 and 3 are known. FIG. 2 is a perspective view of this SAW device, and FIG. 3 is a sectional view of the SAW device shown in FIG. This SAW device has L +N b
o 3 (hereinafter abbreviated as LNO) and LiTaOs (
Hereinafter, it will be abbreviated as LTO. ), a pair of comb-shaped electrode fingers 2, 2 made of an aluminum alloy such as aluminum-copper, aluminum-titanium, or aluminum are formed on a piezoelectric substrate l such as 3, 3 and output. It is formed by connecting terminals 4 and 4. Such SAW devices are shown in Figures 4 to 8.
It can be manufactured by a normal photolithography process as shown in the figure. (Electrode film forming process) First, a piezoelectric substrate l made of LNO or LTO with a smooth surface is prepared, and as shown in FIG. The electrode film 5 is formed by the following steps. This electrode film 5 becomes comb-shaped electrode fingers 2, 2 in a later etching process, and is made of aluminum or an aluminum alloy. (2) (Resist Coating Step) Next, as shown in FIG. 5, a resist film 6 is formed by coating a resist on the electrode film 5 by a conventional coating method such as a subin coating method. (at light process) Next, as shown in FIG. 6, a pattern is transferred by irradiating light onto the resist film 6 through a photomask 7 having the same pattern as the electrode fingers 2, 2 to be formed. . ■(Development process) 7th
As shown in the figure, the resist film 6 is developed. In this example, the resist is a positive type, but even if a negative type resist is used, the electrode fingers 2,
It goes without saying that 2 can be formed. (Etching process) As shown in Figure 8, the portions of the electrode film 2 not masked by the resist film 6 were removed by etching, and electrode fingers 2 were formed on the piezoelectric substrate l. After that, the resist film 6... is removed to form an SA as shown in FIG.
Get W device. Conventionally, the etching process has been performed by wet etching using an etching solution containing, for example, a mixture of phosphoric acid: acetic acid and nitric acid in a ratio of 15:3:1. However, in recent years, as the operating frequency of SAW devices has become higher, there has been a desire for finer electrode finger patterns, and processing using dry etching that allows anisotropic etching with less undercut has become necessary. This dry etching is performed, for example, on BCQ3, CQI
, SiC (!4, CCf2., etc.) is turned into plasma in a high frequency atmosphere, and the unmasked portions of the electrode film 5 are selectively etched by the generated highly chemically active Ce radicals and CR ions. It is etched on the surface.

However, if a chlorine-based gas is used as the etching gas when forming the electrode fingers 2, 2, fine etching is possible, but the piezoelectric substrate 1 and the electrode fingers 2, 2 react with Cl2 radicals and Ca ions. , piezoelectric substrate 1 and electrode finger 2
, LNO chloride, LTO chloride, etc. are produced as by-products on 2. These by-products made of chlorine compounds have the property of easily reacting with water to generate hydrogen chloride, so if the SAW device is left in the atmosphere, hydrogen chloride will be transferred to the piezoelectric substrate l and the electrode finger 2 by the moisture in the atmosphere. , occurs on 2. This hydrogen chloride corrodes the piezoelectric substrate 1 and the electrode fingers 2, 2, causing disadvantages such as a decrease in the life and characteristics of the SAW device and a disconnection failure.

The present invention was made to solve the above problems, and relates to a SAW device that has a fine electrode finger pattern and has good corrosion resistance without corrosion of the electrode fingers.

[Means for Solving the Problems] The SAW device of the present invention has a solution in that a carbon film is formed on the piezoelectric substrate and the surfaces of the electrode fingers.

In such a SAW device, since a carbon film is formed on the surface thereof, by-products consisting of chlorine compounds generated during dry etching for forming electrode fingers are prevented from coming into contact with water. Thereby, corrosion of the piezoelectric substrate and electrode fingers can be prevented, and the life and characteristics of the SAW device will not be impaired.

This invention is explained in detail below. <Explain.

FIG. 1 shows a SAW device of the present invention. The SAW device of this invention uses a piezoelectric substrate! A pair of electrode fingers 2, 2 are formed on the piezoelectric substrate 1 and the electrode fingers 2,
A carbon film 8 is formed on the surface of the cylindrical member 2.

This carbon film 8 is used to prevent by-products made of chlorine compounds generated on the surfaces of the piezoelectric substrate l and the electrode fingers 2, 2 during the dry etching process when forming the electrode fingers 2, 2 from reacting with water. belongs to.

In order to manufacture a SAW device on which such a carbon film 8 is formed, a piezoelectric substrate 1 is formed through a normal photolithography process, that is, the process shown in FIGS. After forming the pair of electrode fingers 2, 2 on the surface, an organic compound gas containing carbon atoms and hydrogen atoms is decomposed in a high frequency atmosphere to form carbon on the surface of the piezoelectric substrate 1 and the entire surface of the pair of electrode fingers 2. The coating 8 can be easily deposited. For example, following the etching process for forming the electrode fingers 2, 2 and the plasma ashing process using an oxygen-based gas for removing the resist film 6, the organic compound gas may be supplied and discharged. The carbon film 8 can be deposited by this method. For this reaction, a parallel plate reactive ion etching (RIE) device,
A plasma device such as a microwave magnetic field type plasma etching device can be used. Further, the raw material for the gas used when forming the carbon film 8 is not particularly limited as long as it can be decomposed by plasma discharge or the like to deposit a carbon film, but CH. , ctHa, CH30H. C! H
Gases of hydrocarbons such as 50H or organic compounds such as alcohols can be suitably used. In addition to supplying these raw materials singly or in combination of two or more, these raw gases can be diluted with an inert gas such as argon gas or nitrogen gas, hydrogen gas, or the like. The gas made of such raw materials is decomposed by discharging it in the etching apparatus, etc., and the carbon film 8 is made up not only of the surfaces of the piezoelectric substrate 1 and the electrode fingers 2, 2, but also of chlorine compounds generated on these surfaces. Precipitates on by-products. Since the carbon membranes 8 formed in this way all have a dense structure, it is possible to prevent by-products made of chlorine compounds from reacting with moisture in the atmosphere and generating hydrogen chloride. This makes it possible to prevent wire breakage and deterioration of the life and characteristics of the SAW device.

Furthermore, this carbon film 8 can be created at low temperatures by plasma means such as reactive ion etching (RIE) or microwave magnetic field type plasma etching.
There is no deterioration in the characteristics of the SAW device.

[Example 2] AQ2%Cu was placed on an LNO substrate with a smooth and clean surface.
The alloy was laminated to a thickness of one million people to form an electrode film. After applying a resist on this electrode film and exposing it to light, BC
After dry etching and patterning the electrode film using I23, a sputter cleaning process using CF4 gas was performed to clean the surface. Then, the resist film was removed by ashing using O2-based gas to form electrode fingers on the piezoelectric substrate. Subsequently, C*HsOH is supplied into the same reaction chamber and discharged to form a carbon film on the surfaces of the piezoelectric substrate and the electrode fingers,
The SAW device of this invention and its location.

Although the SAW device thus obtained was left in the atmosphere for one day, no corrosion of the electrode fingers was detected, and the SAW device exhibited exactly the same characteristics as the SAW device when it was produced.

From this, it was confirmed that by forming a carbon film on the surfaces of the piezoelectric substrate and the electrode fingers, it is possible to prevent disconnection defects and deterioration of the characteristics of the SAW device, and to extend the life of the SAW device.

[Effects of the Invention] As explained above, the SAW device of the present invention includes a pair of electrode fingers formed on a piezoelectric substrate, in which a carbon film is formed on the piezoelectric substrate and the surfaces of the electrodes and fingers. Therefore, it is possible to prevent by-products consisting of chlorine compounds generated during dry etching for electrode finger formation from coming into contact with water. Therefore, it is possible to prevent the generation of hydrogen chloride that corrodes the electrode fingers, so it is possible to prevent disconnection and characteristic deterioration of the electrode fingers due to corrosion, and it is possible to extend the life of the SAW device.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of the SAW device of the present invention, FIG. 2 is a schematic perspective view of a conventional SAW device, FIG. 3 is a schematic sectional view of the SAW device of FIG. 2, and FIGS.
Each figure is a schematic cross-sectional view showing each process of manufacturing a conventional SAW device. 1... Piezoelectric substrate, 2... Electrode finger, 8... Carbon coating.

Claims (1)

[Scope of Claims] A surface acoustic wave device comprising a pair of electrode fingers formed on a piezoelectric substrate, characterized in that a carbon film is formed on the surfaces of the piezoelectric substrate and the electrode fingers.