JPH06291581A - Surface acoustic wave device and manufacture of the same - Google Patents

Abstract

PURPOSE:To provide the manufacturing method of a surface acoustic wave device in which the vapor-deposited film of an aluminium or aluminium alloy with satisfactory adherence with a piezoelectric substrate can be formed in a state that the surface of the vapor-deposited film is smooth. CONSTITUTION:At the time of vapor-depositing the aluminium or the aluminium alloy on a piezoelectric substrate 1 by a vacuum vapor-depositing method, for example, by the film thickness 6000Angstrom , the substrate temperature is set as 20 deg.C and the film thickness 1000-2000Angstrom is vapor-deposited. Next, in a high vacuum state, the substrate temperature is decreased, for example, to 50 deg.C, the vapor-depositing speed is fastened, and the residual film thickness (4000-5000Angstrom ) is vapor-deposited. Thus, the adherence of the vapor-deposited film with the substrate 1 can be satisfactory by increasing the substrate temperature, and vapor-depositing the film at first, and the projecting and recessing parts of the surface of the vapor-deposited film can be buried with fine crystal particles and smoothed, and the resistivity of the vapor-deposited film can be reduced by decreasing the substrate temperature, fastening the vapor- depositing speed, and vapor-depositing the film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device used for a high frequency filter or the like and a method for forming a vapor deposition film for forming a sonoelectric conversion electrode thereof.

[0002]

2. Description of the Related Art The main part of a surface acoustic wave device is a piezoelectric substrate and a sound-electric conversion electrode on the surface thereof. In the production of a surface acoustic wave device, it is necessary to form the sonoelectric conversion electrode as designed in order to produce an element having good characteristics. Therefore, a sound-electric conversion electrode, for example, a vapor-deposited film mainly composed of aluminum, has good adhesion to the substrate, the specific resistance of the electrode material is as close as possible to the bulk (substrate) resistance, and the vapor-deposited film surface is smooth and uniform. Is required. However, for example, in the case of vacuum-depositing aluminum, in order to improve the adhesion with the substrate, the substrate temperature should be at least 2
It is necessary to set it to 00 ° C. When the substrate temperature is raised to 200 ° C., the vapor deposition rate becomes slow, the crystal grains become large, the vapor deposition surface becomes rough, and the specific resistance becomes large. On the other hand, in order to smooth the vapor deposition surface and reduce the specific resistance, it is preferable to increase the vapor deposition rate without increasing the substrate temperature to make the crystal grains finer. In this way, the vapor deposition film forming one element is required to have contradictory conditions.

A surface acoustic wave device using a piezoelectric material is composed of a piezoelectric substrate and a sound-electric conversion electrode formed on the surface thereof. The piezoelectric substrate is made of, for example, crystal, lithium niobate, lithium tantalate, α-aluminum phosphate, piezoelectric ceramic, or the like. The sound-electricity conversion electrode is formed by forming a piezoelectric film, for example, a vapor-deposited film or sputtered film of cadmium sulfide, zinc oxide, aluminum nitride or the like on a predetermined substrate. These surface acoustic wave devices are used in various applications by combining the above-mentioned piezoelectric material with various shapes of acoustic-electric conversion electrodes.
A surface acoustic wave device, for example, a high frequency bandpass filter composed of a lithium niobate substrate can be formed through the manufacturing process shown in FIG. 2 (cross-sectional views of each manufacturing process).

First, as shown in FIG. 2A, a sound-electricity conversion electrode layer 2 is formed on the surface of a lithium niobate substrate 1 having a predetermined plate thickness whose surface is mirror-polished. The sound-electricity conversion electrode layer 2 is formed by, for example, a vacuum vapor deposition method at a substrate temperature of 20.
An aluminum film formed under the vapor deposition conditions of 0 ° C. and a vapor deposition rate of 50 Å / sec is used. Next, the lithium niobate substrate 1 on which the sound-electric conversion electrode layer 2 is formed is washed with pure water, baked at 200 ° C., and a positive photoresist film 4 as shown in FIG. 2B is applied. . This photoresist film 4 is exposed by a 5: 1 reduction type exposure machine (step and repeater) using, for example, a 5 times reticle (photomask), and then developed, and then developed (FIG. 2C). As shown in FIG. 4, an etching mask 4 having a predetermined shape for forming a sound-electric conversion electrode is formed.
Form A. Then, the acoustic-electric conversion electrode layer 2 is etched with a phosphoric acid-based aluminum etching solution using the mask 4A to form the acoustic-electric conversion electrode 2B as shown in FIG. After that, as shown in FIG. 2E, the etching mask 4A is removed. Then, although not shown, the piezoelectric substrate 1 on which the sound-electric conversion electrodes 2B are formed is cut into a predetermined size, fixed in a predetermined package, and the input / output terminal and the ground terminal are wired by wire bonding, and a sealing member is used. A high frequency band pass filter is completed by sealing.

[0005]

According to the above-mentioned prior art, when aluminum or aluminum alloy is vapor-deposited on a piezoelectric substrate by a vacuum vapor deposition method, for example, at a substrate temperature of 200.degree. When 6000Å is deposited,
The crystal grains of the vapor deposition film of aluminum or aluminum alloy are large, the irregularities on the surface of the vapor deposition film are large, and light is diffusely reflected. When a photoresist is applied to this vapor-deposited surface and the acoustic-electric conversion electrode pattern of the surface acoustic wave device is exposed by, for example, a 5: 1 reduction type exposure machine (step and repeater), the vapor-deposited film surface has irregularities. Due to the irregular reflection of the exposure light, the acoustic-electric conversion electrode pattern is deformed, and the acoustic-electric conversion electrode as designed cannot be formed.
The present invention eliminates these drawbacks, a vapor deposition film of aluminum or aluminum alloy with good adhesion to the piezoelectric substrate,
The purpose is to form a vapor-deposited film with a smooth surface.

[0006]

In order to achieve the above object, the present invention provides a piezoelectric substrate on which a sonoelectric conversion electrode made of, for example, aluminum or an aluminum alloy is formed by a vacuum deposition method.
When vapor deposition with a film thickness of 00Å, first, the substrate temperature is 200
A film having a thickness of 1000 to 2000Å is vapor-deposited at a temperature of ℃, and then the substrate temperature is lowered to 50 ° C. in a high vacuum state, and the remaining film thickness (4000 to 5000Å) is vapor-deposited.

[0007]

As a result, when aluminum or aluminum alloy is vapor-deposited on the piezoelectric substrate by the vacuum vapor deposition method, the temperature of the substrate is first increased to improve the adhesion of the vapor-deposited film to the substrate. By lowering the substrate temperature and increasing the vapor deposition rate, the irregularities on the surface of the deposited film that were generated when the initial substrate temperature was high were filled with fine crystal grains to smooth the surface and the specific resistance of the deposited film. Can be reduced.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention applied to a high frequency bandpass filter will be described below with respect to the configuration of the present invention. 1 (a) to 1 (a) to 1 (c) showing the manufacturing method of the high-frequency bandpass filter according to one embodiment of the present invention for each manufacturing step.
This will be described with reference to the sectional view of (e). First, as shown in FIG. 1A, the sound-electric conversion electrode layers 2 and 3 are sequentially formed on the surface of a lithium niobate substrate 1 having a predetermined plate thickness whose surface is mirror-polished. Sonic conversion electrode layers 2 and 3
In order to improve the sound-electricity conversion function, a material having a small electric resistance and a light weight, for example, an aluminum or aluminum alloy film formed by a vacuum evaporation method is used. The sound-electricity conversion electrode layers 2 and 3 made of aluminum or an aluminum alloy are first deposited under a deposition temperature of 200 ° C. and a deposition rate of 50 Å / sec to a film thickness of 1000 to 2000 Å.
And

Next, the substrate temperature is kept at 50 ° C. in the high vacuum state.
To 400-500 at a deposition rate of 100Å / sec.
A film thickness of 0Å is vapor-deposited to form the acoustic-electric conversion electrode layer 3. Here, since the sound-electricity conversion electrode layer 2 is vapor-deposited at a substrate temperature of 200 ° C., the adhesion with the substrate 1 is sufficiently good. Next, this substrate 1 is washed with pure water and then baked at 200 ° C.
As shown in FIG. 1B, a positive type photoresist film 4 is applied. This photoresist film 4 is exposed by a 5: 1 reduction type exposure machine (step-and-repeater) using, for example, a reticle (photomask) of 5 times. Here, since the acoustic-electric conversion electrode layer 3 is vapor-deposited at a substrate temperature of 50 ° C. and an evaporation rate of 100 Å / sec, the surface is smooth, and the acoustic-electric conversion electrode pattern is not deformed or disturbed due to irregular reflection of exposure light. Absent. Then, the photoresist film 4 is developed, and as shown in FIG. 1C, an etching mask 4A having a predetermined shape for forming a sound-electric conversion electrode is formed.

Next, using the etching mask 4A, the acoustic-electric conversion electrode layers 2 and 3 of aluminum or aluminum alloy are etched with a phosphoric acid-based etching solution, and as shown in FIG. The electrodes 2A and 3A are formed. Here, since the sound-electricity conversion electrode layers 2 and 3 of aluminum or aluminum alloy are continuously vacuum-deposited in a high vacuum, they are continuous films, and a gap is not caused by etching. Thereafter, as shown in FIG. 1E, the photoresist etching mask 4A is removed with a photoresist removing solution. Then, although not shown, the piezoelectric substrate 1 on which the sound-electric conversion electrodes 2A and 3A are formed is cut into a predetermined size, fixed in a predetermined package, and the input / output terminal and the ground terminal are wired by wire bonding and sealed. A high frequency band pass filter is completed by sealing with a member.

Although the present invention has been specifically described based on the above embodiment, it is obvious that the present invention is not limited to the above embodiment and can be variously modified without departing from the scope of the invention. For example, in the present invention, the substrate may be made of a piezoelectric material such as quartz, lithium tantalate, or zinc oxide. Further, the sound-electricity conversion electrode may be formed of a vapor-deposited film or a sputtered film of cadmium sulfide, zinc oxide, aluminum nitride, etc. other than aluminum or an aluminum alloy.

[0012]

According to the present invention, in the formation of an aluminum or aluminum alloy vapor deposition film in the production of a surface acoustic wave device in which a sound-electric conversion electrode is formed on a piezoelectric substrate,
By performing vapor deposition under a plurality of different vapor deposition conditions in a single vapor deposition, a vapor deposition film having good adhesion to the piezoelectric substrate can be obtained, and a vapor deposition film having a smooth surface and a low specific resistance. As a result, the acoustic-electric conversion electrode as designed can be formed in a state where the end linearity is enhanced, and the high frequency characteristics of the surface acoustic wave device can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a manufacturing process of a high-frequency bandpass filter according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a manufacturing process of a conventional high frequency bandpass filter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric substrate 2,3 Acoustic-electric conversion electrode layer 2A, 3A Acoustic-electric conversion electrode 4 Photoresist film 4A Etching mask.

Claims (3)

[Claims] 1. A method of manufacturing a surface acoustic wave device, characterized in that a vapor deposition film formed on a piezoelectric substrate is vapor-deposited under at least two or more different vapor deposition conditions in a film thickness direction. Device manufacturing method. 2. In a method of manufacturing a surface acoustic wave device, a vapor deposition film formed on a piezoelectric substrate is first exposed to the piezoelectric substrate temperature in a high vacuum atmosphere at a predetermined level of good adhesion to the piezoelectric substrate. A method for manufacturing a surface acoustic wave device, comprising: depositing a predetermined film thickness at a high temperature, then setting a substrate temperature to a predetermined low temperature, and depositing a predetermined film thickness. 3. A surface acoustic wave device having a piezoelectric substrate, a sound-electric conversion electrode and an input / output terminal formed on the substrate, wherein the sound-electric conversion electrode is formed at a high temperature in a portion in contact with the substrate. A surface acoustic wave device comprising a vapor-deposited film and a vapor-deposited film formed on the vapor-deposited film at a temperature lower than the above temperature.