JPS6141445B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a manufacturing method for forming a strong wire bonding portion of an elastic surface filter.

Surface acoustic wave filter
Naturally, when used in the high-frequency band (band, GHz band, etc.), it is necessary to make the interdigital electrode width finer due to its high frequency properties, and to reduce the film thickness due to the dispersion of sound velocity. In the manufacturing process of surface acoustic wave filters, reducing the thickness of the metal layer that serves as the electrode greatly affects the wire bonding strength and the reliability of the device. For example, when a 25〓〓 gold wire is ultrasonically bonded to an aluminum film with a thickness of about 2000Å, the yield is about 20-30%.
At a film thickness of 1000 Å, bonding is almost impossible. For this reason, conventionally, when forming interdigital electrodes with a film thickness of 2000 Å or less, after forming a predetermined electrode pattern, only the bonding pad portions were masked and deposited again using a mask to ensure a film thickness that would allow bonding. This method involves covering the surface of the electrode pattern with a special mask and redepositing it on the bonding pad area, or using a lift-off method in which the photoresist process is performed again on the electrode pattern, the area excluding the bonding pad area is covered with resist, and then vapor deposition is performed. etc., which had the drawbacks of complicated processes and lack of mass production.

The present invention eliminates the above-described drawbacks of the prior art and provides a method for manufacturing a surface acoustic wave filter having a bonding pad portion that is strong and easy to manufacture.

The key point of the present invention is to form a multilayer metal film of different types on a piezoelectric substrate, first remove by etching the parts of the multilayer metal film other than the areas that will become the interdigital electrodes and wiring electrodes, and then remove the resist. A surface acoustic wave filter in which the second metal layer on the substrate is removed by chemical etching with the film remaining, leaving only the wiring electrode portion 5, thereby forming an interdigital electrode of the first metal layer. This is the manufacturing method.

Hereinafter, the present invention will be explained based on examples and drawings.

FIGS. 1, 2, and 3 are cross-sectional views of the device structure at the main steps of the manufacturing process according to the present invention. As shown in FIG. 1, a first metal film, an aluminum film 2 with a thickness of 2000 Å, is formed on a piezoelectric substrate 1, a chromium film 3 with a thickness of about 500 Å is formed as a second layer, and a third layer is formed. A metal film 4 having a thickness of 2000 Å is formed in the second layer. A predetermined resist pattern consisting of wiring electrode portions 5 and interdigital electrode portions 6 is formed at one mask level on the metal surface of such a multilayer structure film by a well-known photoresist process. Then, as shown in FIG. 2, using the resist pattern as a mask, unnecessary portions are removed by etching using a drive dry process and ion etching. In this case, plasma etching or reactive sputtering techniques may be used. The wiring electrode portion 5 of the pattern from which the unnecessary portions have been removed is formed to have a cross-sectional area more than twice that of the interdigital electrode portion. Next, chemical etching is performed for a predetermined time using a well-known chromium etchant until the interdigital electrode portion of the chromium film 3 formed in the second layer counting from the piezoelectric substrate 1 side is completely removed. In the above process, since the wiring electrode portion 5 has a more flexible area than the interdigital electrode portion 6, there is almost no damage due to etching.

After the above process and resist removal process, the third
As shown in the figure, a wiring electrode portion 6 having a sufficient film thickness consists of a first layer of an interdigital electrode made of an aluminum metal film 2 and a second layer of a chromium metal film and a gold film 3.
form.

As explained above, the method for manufacturing a surface acoustic wave filter according to the present invention eliminates the drawbacks of the conventional technology, and can obtain a high film thickness of the wiring electrode part that is easy to manufacture and suitable for mass production, so strong wire bonding can be freely performed. This allows connection with highly reliable external circuits.

[Brief explanation of the drawing]

FIGS. 1, 2, and 3 are explanatory views of the cross-sectional structure of the surface acoustic wave filter at each step in the manufacturing process according to the present invention. 1: piezoelectric substrate, 2: aluminum metal film,
3: Chromium metal film, 4: Gold metal film, 5: Resist film for forming wiring electrode portion, 6: Resist film for forming interdigital electrode portion.

Claims (1)

[Claims] 1. A method for manufacturing a surface acoustic wave filter in which an interdigital electrode and a wire wiring portion for electrically connecting the electrode and an external circuit are formed on a piezoelectric substrate, in which two layers of different types of metal films are formed on the substrate. After forming the above, using the resist pattern as a mask, unnecessary parts of the multilayer metal film other than the interdigital electrodes and wire wiring portions are removed by etching, and then the interdigital film formed in the second layer from the substrate side is removed. A method of manufacturing a surface acoustic wave filter in which only the wiring electrode part is made thicker by etching the entire shaped electrode part.