JPH08162880A - Surface acoustic wave element - Google Patents

Abstract

PURPOSE: To obtain a high yield through the reduction in number of processes and to minimize the cost increase by making a protection film of the surface acoustic wave element with a photosensing high polymer resin. CONSTITUTION: The surface acoustic wave element is made up of a comb-line metallic electrode section 12 formed on a piezoelectric substrate 11, a bonding pad section 13 connecting electrically to the metallic electrode section 12, and a protection means 14 made of a photosensing high polymer resin coating the metallic electrode 12. Since the metallic electrode 12 formed on the piezoelectric substrate 11 is coated on the protection means 14 made of the photosensing high polymer resin, defect of the metallic electrode 12 resulting in causing a defect is avoided when the surface acoustic wave element is mounted to a package due to high frequency processing of the frequency utilizing band and the miniaturization in the device. Furthermore, the yield is improved for the mount process and then the cost is reduced.

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, and more particularly to improvement of a protective film therefor.

[0002]

2. Description of the Related Art In a surface acoustic wave device using a surface acoustic wave element having a comb-shaped metal electrode formed on a piezoelectric substrate and used as a filter or a resonator, when the surface acoustic wave element is mounted on a package. In addition, when a manufacturing defect occurs, such as a pattern defect on the metal electrode due to contact with the mounting jig, or a metal splash is caused by a metal splash generated by welding during sealing of the package, causing a defect. was there.

Moreover, in recent years, the electrode line width of the metal electrode and the space between the electrode lines have become finer as the frequency band of the surface acoustic wave device has become higher, and the chip size has become smaller as the surface acoustic wave device has become smaller. In particular, the occurrence of defects in the mounting process has increased.

Therefore, conventionally, the metal electrode provided on the piezoelectric substrate is covered with a protective film made of silicon oxide (SiO ₂ ) to prevent the occurrence of defects in the metal electrode.

[0005]

However, conventionally,
Since the protective film is formed of silicon oxide, in the protective film forming process, the number of steps of the forming process when performing the patterning operation for removing the silicon oxide film in the bonding pad portion for wire bonding increases. However, there are various problems that a film forming apparatus and an etching apparatus are required to form the protective film, and that the frequency adjusting process after forming the protective film becomes complicated.

That is, at the time of forming the protective film of silicon oxide, as shown in the flow chart of FIG. 5, at least (1) the sputtering method or the CVD (Chemical) is used.
Depositing a silicon oxide film by the Vapor Deposition method, etc., (2) resist coating on the entire surface of the piezoelectric substrate, (3) prebaking, (4) exposing a desired pattern using a photomask, and (5) bonding by development Remove the resist on the pad, (6) Post bake,
(7) RIE (Reactive Ion Etchi)
ng) and other dry etching methods to remove the silicon oxide film from the bonding pad portion, and (8) O ₂ asher etc. were used to remove the photoresist.

Moreover, during such a process, a film forming apparatus requiring a vacuum container and a dry etching apparatus are indispensable. In the etching process, hydrogen oxide (HF) or ammonium fluoride (NH ₄ F) that is generally used as an etchant for wet etching silicon oxide is generally used for the metal electrode of the surface acoustic wave element. Since the selectivity of aluminum (Al) or aluminum alloy used is low, dry etching is performed instead of wet etching.

Further, in the surface acoustic wave element, the frequency increases as the electrode film thickness decreases due to the mass loading effect.
On the contrary, it has a characteristic that the frequency decreases as the film thickness of the electrode increases. Therefore, if silicon oxide is laminated on the metal electrode portion as a protective film, a frequency shift of the surface acoustic wave element occurs. This frequency shift can be controlled to some extent by controlling the film thickness of silicon oxide to a predetermined thickness during film formation, but when the frequency standard is strict, yields are generated due to frequency variations, and The sex has been reduced.

For this reason, ECR (Electron Cy
The frequency adjustment process is performed by changing the film thickness of silicon oxide using an ion beam etching device, but this ECR ion beam etching device is very expensive and the control of process conditions is complicated. Therefore, the cost required for the frequency adjustment process has been significantly increased.

The present invention solves the above problems by reducing the number of steps when forming a protective film for a metal electrode of a surface acoustic wave element, and forming a protective film by a relatively simple and inexpensive device. It is also an object of the present invention to provide a surface acoustic wave device that can adjust the frequency and can obtain a high yield and can suppress the increase in cost to a minimum.

[0011]

In order to solve the above-mentioned problems, the first aspect of the present invention is to provide a comb-shaped metal electrode portion formed on a piezoelectric substrate and electrically connected to the metal electrode portion. A bonding pad portion and a protection means made of a photosensitive polymer resin that covers the metal electrode portion.

In order to solve the above problems, the second aspect of the present invention uses a photosensitive polyimide as the photosensitive polymer resin.

[0013]

The present invention is configured as described above, and by forming the protective film of the metal electrode of the surface acoustic wave element with a photosensitive polymer resin, as compared with a conventional device using a protective film made of silicon oxide, It is possible to obtain a surface acoustic wave element that is relatively low in price and easy to manufacture, because the number of manufacturing steps can be significantly reduced, an expensive manufacturing device and a frequency adjusting device are not required, and the manufacturing cost is not significantly increased. Can be done.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to an embodiment shown in FIGS. FIG. 1 is a plan view of a surface acoustic wave element 10 that constitutes a surface acoustic wave device 17, and FIG. 2 is a sectional view taken along the line AA ′ of FIG. Piezoelectric substrate 11
A comb-shaped metal electrode 12 containing aluminum as a main component and a bonding pad portion 13 electrically connected to the metal electrode 12 are provided on the top. Furthermore, the surface of the metal electrode 12 is a photosensitive polyimide (PI) which is a photosensitive polymer resin.
MEL G-5035: manufactured by Asahi Kasei Kogyo Co., Ltd.). 16 is a package.

Next, the process of forming the protective film 14 will be described with reference to the flow chart shown in FIG. In step 20, first, a photosensitive polyimide (PIMEL) is formed on the piezoelectric substrate 11 having the metal electrode 12 and the bonding pad portion 13.
G-5035) is dropped, the whole piezoelectric substrate 11 is coated with a photosensitive polyimide by a spin coater, and the process proceeds to Step 21. In step 21, the piezoelectric substrate 11 is dried and baked in a clean oven at about 80 ° C. for about 10 minutes, and the process proceeds to step 22.

In step 22, in order to remove the photosensitive polyimide coated on the bonding pad portion 13 of the piezoelectric substrate 11, the piezoelectric substrate 11 is exposed using a photomask that covers the bonding pad portion 13. Go to step 23. In step 23, NM
By developing the unexposed portion with a developer such as D.3 (manufactured by Tokyo Ohka Kogyo Co., Ltd.), the photosensitive polyimide of the bonding pad portion 13 is removed and only the metal electrode 12 is coated on the piezoelectric substrate 11. Pattern the photosensitive polyimide, and proceed to step 24. In step 24, the piezoelectric substrate 11 is placed in a clean oven at about 140 ° C. for about 30 minutes,
It is heated and cured at about 400 ° C. for about 1 to 2 hours, and the formation process of the protective film 14 having a pattern formed is completed.

However, in the surface acoustic wave element 10 thus formed, the frequency of excitation has been shifted, so it is necessary to perform a frequency adjusting step for controlling the film thickness of the protective film 14. Next, the frequency adjusting process using an O ₂ (oxygen) ashing device for removing the protective film 14 by ashing using oxygen (O ₂ ) plasma will be described with reference to the flowchart shown in FIG.

First, after putting the piezoelectric substrate 11 in the ashing container, in step 30, the ashing container is set to 10 ⁻⁶ ton.
The vacuum degree is set to about rr, and oxygen is introduced into the container at 1 torr in step 31. Next, in step 32, the probe pin is brought into contact with the bonding pad portion 13 to monitor the frequency, and the process proceeds to step 33. In step 33, while monitoring the frequency with the probe pin, RF (Ra
The power is turned on to generate oxygen plasma, and the protective film 14 is peeled off.

Next, at step 34, when the frequency reaches a predetermined standard range, the RF power source is turned off, the piezoelectric substrate 11 is taken out from the container, and the frequency adjusting step is completed.

Thereafter, the piezoelectric substrate 11 formed as described above is diced into chips, and the chipped surface acoustic wave device 10 is mounted on the base 16a of the package 16.
Then, the bonding pad portion 13 and the base 16a are connected by wire bonding, and then the base 16a and the cap 16b of the package 16 are sealed to complete the surface acoustic wave device 17.

When the surface acoustic wave element 11 is mounted on the package 16, since the metal electrode 12 is covered with the protective film 14, even if the jig used for mounting is slightly contacted with the metal, The electrode 12 is not damaged, and
The fine metal electrodes 12 are not short-circuited by the metal splash generated during the sealing welding of the package 16.

According to this structure, the metal electrode 12 is covered with the protective film 14 made of photosensitive polyimide instead of the conventional protective film made of silicon oxide. Despite the miniaturization of the wave element 11, the metal electrode 12 is not damaged even by the handling error at the time of mounting on the package 16 or the small splash at the time of sealing as in the case of the conventional protective film, and the failure at the mounting process is caused. As a result, the yield is improved and the manufacturing cost is reduced.

Moreover, the number of steps of the film forming process can be reduced as compared with the conventional protective film made of silicon oxide, and the film formation of the protective film is facilitated, so that the cost can be reduced. or,
Since the patterning of the protective film 14 is performed by a photolithography process, existing equipment can be used, and a new film deposition apparatus or dry etching apparatus that requires a vacuum container can be newly used for forming the protective film. The cost can be reduced because there is no need to introduce it.

Further, even in the frequency adjusting process after the protective film 14 is formed, the EC which is conventionally required and complicated in control is complicated.
The cost can also be reduced because the thickness of the protective film 14 can be easily controlled by an O ₂ ashing device or the like, which is relatively inexpensive and easy to replace, instead of the R ion beam etching device.

The present invention is not limited to the above-mentioned embodiments, and modifications can be made without departing from the spirit thereof.
For example, the protective film is not limited to the photosensitive polyimide as long as it is a photosensitive polymer resin, and may be a photoresist or the like, and the formation conditions for forming the protective film are arbitrary.

[0026]

As described above, according to the present invention, since the metal electrode formed on the piezoelectric substrate is covered with the protective means made of the photosensitive polymer resin, the frequency band can be increased. Alternatively, even when the device is miniaturized, when the surface acoustic wave element is mounted on the package, the metal electrode is not damaged and a defect does not occur, the yield in the mounting process can be improved, and the cost can be reduced.

Further, as compared with the conventional method, the number of steps for forming the protective film can be reduced, and the film forming and frequency adjusting steps can be performed by the existing equipment or low-priced equipment, so that the manufacturing cost can be greatly reduced. Becomes

[Brief description of drawings]

FIG. 1 is a schematic plan view showing a surface acoustic wave element according to an embodiment of the present invention.

FIG. 2 shows a surface acoustic wave device according to an embodiment of the present invention as shown in FIG.
It is a schematic sectional drawing seen from the -A 'line.

FIG. 3 is a flowchart showing a process of forming a protective film according to an embodiment of the present invention.

FIG. 4 is a flowchart showing a frequency adjusting process according to an embodiment of the present invention.

FIG. 5 is a flowchart showing a conventional process for forming a protective film made of silicon oxide.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Surface acoustic wave element 11 ... Piezoelectric substrate 12 ... Metal electrode 13 ... Bonding pad part 14 ... Protective film 16 ... Package

Claims (2)

[Claims] 1. A comb-shaped metal electrode portion formed on a piezoelectric substrate, a bonding pad portion electrically connected to the metal electrode portion, and a photosensitive polymer resin covering the metal electrode portion. A surface acoustic wave device comprising: a protection means. 2. The surface acoustic wave device according to claim 1, wherein the photosensitive polymer resin is photosensitive polyimide.