JP3196265B2 - Method of forming electrodes of surface acoustic wave device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an electrode on a base material, and more particularly to a method for forming an electrode using a vapor deposition method.

[0002]

2. Description of the Related Art For example, various methods such as vapor deposition, sputtering, and CVD are used to form electrodes of a surface acoustic wave device.

[0003]

In such a surface acoustic wave device, it is said that as the thickness of the electrode becomes thinner, the specific resistance becomes higher and the characteristics are deteriorated.
In the case of the surface acoustic wave device up to 300 MHz, even if the thickness of the electrode is relatively large and the specific resistance of the electrode is large, there is no problem in characteristics.

However, if the surface acoustic wave device is to be used in a frequency band exceeding 1 GHz, the thickness of the electrode becomes 1000
Å, and the magnitude of the specific resistance of the electrode cannot be ignored due to the characteristics of the surface acoustic wave device.

[0005] The above-mentioned problem is not limited to the electrodes of the surface acoustic wave device, but may be encountered, for example, in the field of semiconductors even for electrodes for obtaining electrical continuity.

Therefore, an object of the present invention is to provide a method for forming an electrode which can solve the above-mentioned problems.

[0007]

SUMMARY OF THE INVENTION The present invention is directed to a method for forming electrodes of a surface acoustic wave device on a piezoelectric substrate by a vapor deposition method, and solves the above-mentioned technical problems. Therefore, only in the initial stage of film formation, the inert gas is positively irradiated to the piezoelectric substrate.

The vapor phase film forming method used in the present invention includes, for example, sputtering, ion beam sputtering,
There is a method such as ion-assisted vapor deposition, and a rare gas such as Ar or He can be used as an inert gas introduced at an early stage of film formation.

The film formation while introducing the inert gas and the subsequent film formation may be performed in the same film forming apparatus or in different film forming apparatuses.

In addition, the initial film formation while introducing an inert gas is preferably performed only to obtain a film thickness of 500 ° or less.

[0011]

In general, the specific resistance of a metal film depends on the film quality (crystal state,
Crystal grain size, etc.). This film quality is greatly affected not only by the film forming conditions such as the temperature and the film forming speed of the substrate on which the metal film is formed, but also by the surface condition of the substrate. In the present invention, by irradiating the substrate with an inert gas in the initial stage of film formation, the nuclear density in the initial stage of film formation can be increased and the specific resistance of the metal film can be reduced.

[0012]

Therefore, according to the present invention, an electrode having a low specific resistance can be formed on a piezoelectric substrate . Therefore, according to the present invention, a reduction in loss of the surface acoustic wave device can be expected.

[0013]

EXAMPLES Examples of the present invention will be described below.

Example 36 Aluminum was formed on a Y-cut LiTaO ₃ substrate rotated by 36 ° by ion-assisted vapor deposition using Ar gas. When the aluminum film thickness monitor showed 100 °, the supply of Ar gas was stopped. The deposition is continued as it is, and the desired film thickness (300, 700, 1000, 200
0, 5000 °), the vapor deposition was terminated.

The conditions for vapor deposition are as follows. Degree of vacuum when supplying Ar: 10 Pa Degree of vacuum when stopping Ar supply: 10 ⁻³ Pa Deposition rate: 5 ° / sec Ar flow rate: 100 SCCM Ar ⁺ Acceleration voltage: 100 V Comparative Example 1 Using the same apparatus as in the example, Ar ⁺ The aluminum film was formed under the same conditions as in the example except that the assist was not performed, and the desired film thickness (300, 700, 1) was obtained.
000, 2000, 5000 °), the vapor deposition was terminated.

COMPARATIVE EXAMPLE 2 Using the same apparatus as in the example, assisting with Ar ⁺ was performed to a desired film thickness (300, 700, 1000, 2000, 50
A film of aluminum was formed under the same conditions as in the example, except that the process was continued until 00 °).

As described above, the resistance value of the aluminum film was measured by the four-probe method using the aluminum film-formed substrates produced in the Examples and Comparative Examples 1 and 2, and converted into the specific resistance. The result is shown in FIG.

FIG. 1 shows that according to the embodiment, it is possible to produce a metal film having a lower specific resistance as compared with Comparative Examples 1 and 2.

In each of Example and Comparative Example 1, a surface acoustic wave device was manufactured using a substrate having a metal film having a thickness of 1000 °, and the frequency characteristics were measured. The result is shown in FIG. 2A shows an example, and FIG. 2B shows a comparative example 1. From FIG.
There is a peak-cross difference of about 1 dB between the two, and it can be seen that according to the example, a reduction in loss of the surface acoustic wave device can be expected.

[Brief description of the drawings]

FIG. 1 is a diagram showing specific resistances obtained in Examples according to the present invention and Comparative Examples 1 and 2.

FIG. 2 shows a frequency characteristic of a surface acoustic wave device manufactured based on the example according to the present invention and Comparative Example 1,
(A) shows an example and (b) shows a comparative example 1.

────────────────────────────────────────────────── (5) References JP-A-2-302385 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03H 3/08 H01L 21/28 H01L 21 / 285 301

Claims (1)

(57) [Claims] 1. A method of forming an electrode on a piezoelectric substrate by a vapor phase film forming method, wherein the inert gas is irradiated to the piezoelectric substrate only at an initial stage of film formation. Method of forming electrodes of wave element.