JPH0685592A - Manufacture of saw element - Google Patents

Abstract

PURPOSE:To manufacture a surface acoustic wave (SAW) element, which reduces the loss of insertion, decreases the number of gratings in a reflector and can be miniaturized, with high accuracy by applying the plating of metal, which specific gravity is larger than that of Al or alloy, after simultaneously forming an interdigital transducer (IDT) and the reflector composed of Al or the alloy with one time of photo-lithography on the surface of a substrate. CONSTITUTION:An Al thin film is filmed on the surface of a piezoelectric substrate 1, and photoresist is applied onto the surface. Next, the photoresist is exposed and developed later by using a mask drawing the patterns of the IDT and the reflector and with this photoresist as the mask, the Al thin film is etched so as to provide an IDT pattern 4 made of Al and resonator patterns 5 and 6 on both sides. Afterwards, it is masked by the organic resist of the IDT pattern 4, and non-field plating 5a and 6a of Au, for example, is performed in the state of activating the surfaces of the reflector patterns 5 and 6 with any suitable surface processing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a surface acoustic wave device used in, for example, a resonator or a filter.

[0002]

2. Description of the Related Art Generally, a surface acoustic wave device has an interdigital transducer (hereinafter referred to as "interdigital transducer") on a surface of a piezoelectric substrate.
And a reflector for reflecting the surface acoustic wave excited by this IDT.

IDTs and reflectors are usually obtained by patterning the same metal on a substrate using photolithographic techniques. As a metal used for each of these electrodes, in order to improve the conversion efficiency of the electric signal into the surface acoustic wave by the IDT and reduce the insertion loss, Al or Al which is a metal having a small specific gravity is the main component. Alloys are used.

By the way, it is convenient for the material of the IDT to be light as described above, but the reflection efficiency of the reflector depends on the specific gravity of the material used, and when a light metal such as Al is used, the reflection efficiency is low. There is a problem that desired reflection cannot be obtained unless the number of gratings is increased.

In order to solve such a problem, conventionally,
By repeating the electrode forming process using photolithography twice, the materials of the IDT and the reflector are made different, for example, the IDT is made of Al and the reflector is made of Au or a two-layer structure of Al and Au, so that the insertion loss can be improved. There is proposed a surface acoustic wave device which has a small number of reflectors and which can be miniaturized by reducing the number of gratings of reflectors (Japanese Patent Laid-Open No. 2-2999312).
issue).

[0006]

However, in the above proposals, regardless of whether the structure of the reflector is a one-layer structure or a two-layer structure, the steps of film formation-resist coating-exposure-etching resist removal are performed in two steps. It has to be done over time, which not only complicates the process and raises the cost,
Due to the limitation of the positioning accuracy in each photolithography process, there is a drawback in that the patterning result of each material may deviate on the order of submicrons. Each of the IDT and the reflector has a structure having a large number of gratings at a pitch of about several microns which is determined according to the wavelength, and if such a deviation occurs, the element characteristics will deteriorate.

The present invention has been made in order to eliminate such drawbacks, and provides a surface acoustic wave device which has a small insertion loss and a small number of reflector gratings and which can be miniaturized by a simple process. It is intended to provide a method that can be manufactured with high accuracy.

[0008]

In order to achieve the above object, a method of manufacturing a surface acoustic wave device according to the present invention is an IDT made of Al or an alloy thereof on a surface of a piezoelectric substrate by a single photolithography process. And the reflector is formed at the same time, and then the surface of the reflector is characterized by plating a metal having a specific gravity larger than that of Al or its alloy.

[0009]

The function is such that the IDT is formed of Al or its alloy, and the reflector is also based on Al or its alloy, and a plating layer made of a metal such as Au having a larger specific gravity is formed above the reflector. .

Formed by photolithography process
When the electric field or electroless plating is selectively applied to the reflector made of Al or its alloy, the plating layer is surely formed without being displaced with respect to the surface of the base Al or its alloy, The desired purpose can be achieved.

[0011]

1 to 2 are schematic explanatory views of the procedure of an embodiment of the present invention. First, the Al thin film 2 is formed on the surface of the piezoelectric substrate 1.
Is formed into a film having a thickness of 3000 Å, and the photoresist 3 is applied to the surface thereof. This state is shown in a sectional view in FIG.

Next, the photoresist 3 is exposed using a mask on which both the IDT and reflector patterns are drawn, and then developed, and the Al thin film 2 is etched by using this as a mask, and as shown in FIG. As shown in a cross-sectional end view and a plan view in (B), an IDT pattern 4 made of Al and resonator patterns 5 and 6 on both sides thereof are obtained. Note that FIG. (A) is a sectional end view taken along the line AA in FIG.

After that, while masking the IDT pattern 4 with an organic resist or the like, the surfaces of the reflector patterns 5 and 6 are activated by appropriate surface treatment, and electroless plating of Au, for example, with a thickness of 1000 Å is performed. .
As a result, Au plating layers 5a and 6a are formed only on the surfaces of the reflector patterns 5 and 6, as shown in FIG. 3 which is a sectional end view of the same portion as FIG.

In the above-described embodiments of the present invention, it was confirmed that the widthwise displacement between the reflector patterns 5 and 6 and the Au plating layers 5a and 6a is within several hundred Å. Also, the grating width of each reflector pattern 5 and 6 is 3 μm, and the pitch is 6 μm.
As a result, when the number of grids of 200 was manufactured and the characteristics were investigated, it was confirmed that
It was confirmed that the same reflection as that of the comparative example in which the number of grids of each was 300 was performed without the Au plating layers 5a and 6a, and other element characteristics such as insertion loss were also compared. There was nothing inferior to. As a result, while keeping the insertion loss small, the total number of elements in this example is 1.2 because the number of gratings in each reflector is reduced.
It could be shortened by about mm.

The Au plating layers 5a and 6a can be formed by electroless plating as well as electroless plating as in the above example. in this case,
By using each reflector pattern as a cathode,
It is not necessary to mask the T pattern. here,
When electroplating is used, when forming multiple elements on the surface of the piezoelectric substrate before dicing, the reflectors of each element must be connected to each other by using the electrode pads connected to each reflector. By setting it as a pattern connected to
It becomes possible to perform plating efficiently.

The material of the IDT and the reflector pattern formed by photolithography may be Al or an alloy containing Al as a main component, and may be the material of the plating layer applied to the surface of the reflector pattern. , Au, Cu,
Ag, Pt, etc. can be adopted.

[0017]

As described above, according to the present invention,
By one photolithography process and plating process,
A small surface acoustic wave element with a small insertion loss and a small number of reflector gratings can be obtained, which simplifies the process and reduces the manufacturing cost compared with the case where two photolithography processes are performed. Not only can the reduction be achieved, but the positional accuracy of the reflector on the plane between the layers is improved as compared with the case where two photolithography processes are performed, and there is no fear of degrading other device characteristics.

[Brief description of drawings]

FIG. 1 is a schematic sectional view for explaining a procedure of an embodiment of the present invention.

FIG. 2 is a schematic sectional end view (A) and a plan view thereof (B) for explaining the procedure of the embodiment of the present invention.

FIG. 3 is a schematic sectional end view for explaining the procedure of the embodiment of the present invention.

[Explanation of symbols]

 1 Piezoelectric Substrate 2 Al Thin Film 3 Photoresist 4 Al IDT Pattern 5, 6 Al Reflector Pattern 5a, 6a Au Plating Layer

Claims (1)

[Claims] 1. An interdigital transducer and a reflector made of aluminum or an alloy thereof are simultaneously formed on the surface of a piezoelectric substrate by a single photolithography process, and then aluminum or an alloy thereof is formed on the surface of the reflector. A method of manufacturing a surface acoustic wave device, which comprises plating a metal having a larger specific gravity than that of the surface acoustic wave device.