JP2002217665A - Manufacturing method of surface acoustic wave element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for enlarging a range of film thickness specifications when an electrode metallic film is formed on a piezoelectric substrate and reducing the cost of a surface acoustic wave element and decreasing the batch amount of defective elements to be discarded. SOLUTION: In the manufacturing method for the surface acoustic wave element, an electrode metallic film is formed on a piezoelectric substrate. After the film thickness of the metallic film is measured, the metallic film is patterned under prescribed conditions based on the measured thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a surface acoustic wave device such as a surface acoustic wave filter and a surface acoustic wave resonator, and more particularly, to a method for manufacturing a surface acoustic wave device having an improved electrode forming process. It relates to a manufacturing method.

[0002]

2. Description of the Related Art In manufacturing a surface acoustic wave device,
A metal film for an electrode is formed on the entire surface of the piezoelectric substrate, and then patterned to form an electrode such as an interdigital transducer (IDT). In the surface acoustic wave element, the film thickness and line width of the electrode, the influence on the substrate at the time of over-etching when patterning is performed by etching, and the like greatly affect the basic characteristics of the surface acoustic wave element. In the method of manufacturing the surface acoustic wave device, variations in the film thickness and line width of the electrode had to be made.

Therefore, conventionally, conditions for forming a metal film for an electrode and conditions for patterning such as photolithography and etching are determined so that the characteristics of the surface acoustic wave element fall within the allowable frequency range of the surface acoustic wave element. Have been.

For example, it is assumed that the relationship shown in FIG. 5 exists between the center frequency of the finally obtained surface acoustic wave device, the film thickness of the electrode, and the line width of the electrode. In this case, assuming that the desired frequency is in a range between f1 and f2, a line width and a film thickness range for obtaining such frequency characteristics are set. That is, when the film thickness is in the range of t11 to t12, the line width x11 to x1
2 so that f1 to f
2 frequency characteristics can be obtained. Further, when patterning is performed by etching, the etching conditions are determined so that the influence on the substrate during over-etching is reduced as much as possible. On the other hand, the ratio of the film thickness / line width of the electrode may have a great influence on the frequency characteristics of the surface acoustic wave element. Accordingly, as shown in FIG. 6, when the thickness / line width ratio needs to be in the range of y1 to y2, the thickness of the electrode is changed from t13 to t1 accordingly.
4, and the line width were set in the range of x13 to x14.
In this case, by setting the film thickness and the line width in the specific ranges described above, the film thickness / line width ratio can be reliably set in the range of y1 to y2.

[0005]

However, in the manufacturing method of the surface acoustic wave device, the standard range of the electrode film thickness, for example, the range of t11 to t12 in FIG. 5 and the range of t13 to t14 in FIG. 6 are very narrow. . Therefore, when a metal film for an electrode is formed on a piezoelectric substrate, it is very difficult to control the film thickness within these ranges. Therefore, a batch in which a metal film having a film thickness not satisfying the standard value is formed frequently occurs. In this case, the batch is treated as a defective product, thus causing a large increase in the cost of the surface acoustic wave device.

The present invention solves the above-mentioned drawbacks of the prior art, and does not extend the standard range of the film thickness when a metal film for an electrode is formed on a piezoelectric substrate. An object of the present invention is to provide a manufacturing method capable of reducing the cost of the surface acoustic wave device.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a method of manufacturing a surface acoustic wave device including a piezoelectric substrate and an electrode formed on the piezoelectric substrate, wherein a metal for an electrode is provided on the piezoelectric substrate. Forming a film, measuring the film thickness of the metal film, and patterning the metal film under conditions determined based on the measured film thickness.

That is, in the manufacturing method according to the present invention, before the patterning, the thickness of the metal film is measured, and then the conditions after the film formation, particularly the patterning process, are determined based on the value of the film thickness. , Patterning is performed.

The method of patterning the metal film is not particularly limited, but in a specific aspect of the present invention, the patterning is performed by photolithography, and in another specific aspect, etching is performed by etching.

When patterning is performed by photolithography, conditions for photolithography are determined according to the film thickness, and photolithography is performed. Such conditions include exposure conditions for photolithography. it can.

In the case where patterning is performed by etching, etching conditions are determined according to the above film thickness value. Further, when over-etching is performed at the time of etching, the conditions for over-etching may be determined based on the above film thickness.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention. FIG. 3 (a)
3A and 3B are a plan view and a front sectional view of a surface acoustic wave device obtained according to one embodiment of the present invention.

The surface acoustic wave device 1 has a piezoelectric substrate 2 and an electrode 3 formed on the piezoelectric substrate 2. In this embodiment, a quartz substrate is used as the piezoelectric substrate 2. However, another piezoelectric single crystal such as lithium tantalate or niobium tantalate, or a piezoelectric ceramic such as a lead zirconate titanate-based ceramic is used. A flexible substrate can be used. Further, a substrate formed by forming a piezoelectric thin film such as a ZnO thin film on an insulating substrate may be used as the piezoelectric substrate 2.

The electrode 3 is a comb-shaped electrode having a plurality of electrode fingers 3a. Although not particularly shown in FIG. 3, other comb-shaped electrodes may be formed as necessary, and reflectors are provided on both sides of the region where the comb-shaped electrodes are formed in the surface wave propagation direction. It may be formed.

With reference to FIG. 4, a method of manufacturing the surface acoustic wave device 1 according to the present embodiment will be described. First, the piezoelectric substrate 2 is prepared, and an electrode metal film is formed on the entire surface of the piezoelectric substrate 2. In this embodiment, a thin film made of an aluminum alloy is formed as a metal film for an electrode. However, a metal film other than an aluminum alloy may be used to form a metal film.

The method of forming the metal film for an electrode is not particularly limited, and can be performed by various methods such as vapor deposition, plating, sputtering, or curing by applying a conductive paste.

In this embodiment, after forming the metal film, the thickness of the metal film is measured. Then, based on the obtained film thickness, exposure conditions and etching conditions for photolithography performed in a later step are set.

That is, after measuring the film thickness of the metal film, a photoresist layer is formed on the metal film, a mask is placed, and exposure is performed. The conditions for this exposure are determined based on the film thickness.

After the exposure, the photoresist layer is developed, and then the electrode is etched. At the time of etching, etching is performed under conditions determined according to the thickness of the metal film described above.

The electrode 3 is formed by patterning the metal film in this manner. Thereafter, the resist on the electrode 3 is removed using a solvent, so that the surface acoustic wave element 1 is removed.
Is obtained.

The feature of this embodiment is that, after measuring the thickness of the metal film, the exposure condition and the etching condition by photolithography are determined based on the obtained film thickness as described above. This will be described more specifically with reference to FIGS.

The relationship shown in FIG. 1 exists between the film thickness of the electrode 3 in the surface acoustic wave device 1 and the center frequency. In FIG. 1, x1 to x4 indicate the line width of the electrode finger 3a, and satisfy x1 <x2 <x3 <x4. Generally, electrode 3
The center frequency of the surface acoustic wave element 1 decreases as the film thickness of the surface acoustic wave element 1 increases and as the line width of the electrode finger 3a increases.

Therefore, when the film thickness is large as shown in FIG. 1 by a thickness t1, if the line width of the electrode finger 3a is reduced as shown by x1, a desired frequency characteristic is realized. be able to. Conversely, when the thickness of the electrode is as thin as t4, the line width of the electrode finger 3a is represented by x4,
Desired frequency characteristics can be obtained.

Therefore, in this embodiment, after a metal film is first formed on the entire surface and its thickness is measured,
Conditions for photolithography and etching are set so that the line width of the electrode finger 3a becomes thinner or thicker. In other words, the electrode finger 3a is formed in accordance with the thickness of the metal film formed on the entire surface. Photolithography conditions and etching conditions are determined so that the line width becomes thicker or thinner. Therefore, conventionally, the film thickness t1 which was inappropriate because the film thickness was too large, or the film thickness t1 where the desired frequency characteristic was not obtained because the film thickness was too small.
In the case of No. 4, the photolithography condition and the etching condition are selected as described above, and the line width of the electrode finger is adjusted, so that the surface acoustic wave device 1 having a desired frequency characteristic can be obtained.
Can be obtained.

Further, even when the frequency shifts due to the influence on the piezoelectric substrate 2 during the over-etching, the over-etching condition may be determined according to the measured film thickness of the metal film. Thereby, the shift of the frequency can be suppressed.

Therefore, according to the manufacturing method of this embodiment, when a metal film is formed on a conventional wafer, the film thickness is too thin or too thick. The surface acoustic wave element having the frequency characteristics described above can be provided, and the productivity of the surface acoustic wave element can be increased.

As described above, in the frequency characteristics of the surface acoustic wave device, the ratio of the film thickness of the electrode 3 to the line width of the electrode finger 3a affects the characteristics of the surface acoustic wave device. If the ratio of film thickness / line width of the electrode finger has to be determined with higher accuracy, depending on the measured value of the metal film,
What is necessary is just to control the line width of the electrode finger. That is, as shown in FIG. 2, a metal film is formed on a piezoelectric substrate, and when the film thickness obtained by measuring the thickness of the metal film is as thick as t5, the line width of the electrode finger is obtained. , For example, x5 in FIG.
On the contrary, if the film thickness is too thin as shown by t8, if the line width of the electrode finger is increased as x8, the desired film thickness / line width is obtained. Ratio can be realized. Therefore, when it is necessary to control the ratio of the film thickness to the electrode finger line width, the photolithography condition and the etching condition may be set in the same manner based on the measured value of the metal film.

Also in this case, when the frequency shifts due to the influence on the piezoelectric substrate 2 during overetching, the overetching condition may be adjusted based on the measured value of the thickness of the metal film. Alternatively, without adjusting the over-etching condition, it is also possible to suppress the fluctuation of the frequency characteristic by performing the frequency adjustment step according to a conventionally known method.

As described above, the present invention is characterized by the patterning of the metal film when forming the electrodes of the surface acoustic wave device. Therefore, the surface acoustic wave device to which the present invention is applied is not particularly limited. Instead, the present invention can be applied to the manufacture of various surface acoustic wave resonators and surface acoustic wave filters.

[0030]

In the method of manufacturing a surface acoustic wave device according to the present invention, after a metal film for an electrode is formed on a piezoelectric substrate, the metal film is patterned under conditions determined based on the thickness of the metal film. Is performed to form an electrode. In the conventional manufacturing method, based on the relationship between the previously determined characteristics and the film thickness,
When the thickness of the metal film was out of the standard range, the piezoelectric substrate on which the metal film was formed was selected as a defective product.

On the other hand, according to the present invention, the electrodes are formed by patterning under the conditions determined based on the measured film thickness of the metal film. Even when a thick metal film or a thin metal film is formed, a surface acoustic wave element having desired characteristics can be manufactured by patterning under conditions determined based on the measured film thickness. can do.

Therefore, the productivity of the surface acoustic wave device can be increased, and the conditions for forming the metal film on the piezoelectric substrate can be expanded. The patterning is performed by various methods. In a specific aspect of the present invention, the patterning is performed by photolithography. In this case, exposure conditions for photolithography may be set according to the thickness of the metal film.

In the case where the patterning includes an etching step, a surface acoustic wave device having desired characteristics can be obtained by setting the concentration of an etchant used for the etching, the etching time, and the like.

Further, when the over-etching step is performed, the condition of the over-etching step may be performed based on the measured value of the thickness of the metal film, thereby suppressing the variation of the frequency characteristic at the time of the over-etching. can do.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship among a film thickness of a metal film formed on a piezoelectric substrate, a center frequency of a surface acoustic wave element, and a line width of an electrode finger in one embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a film thickness of a metal film formed on a piezoelectric substrate, a ratio of an electrode film thickness to a line width of an electrode finger, and a line width of an electrode finger in one embodiment of the present invention. FIG.

FIGS. 3A and 3B are a schematic plan view and a front sectional view of a surface acoustic wave device obtained according to one embodiment of the present invention.

FIG. 4 is a flowchart for explaining a method of manufacturing a surface acoustic wave device according to one embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between an electrode film thickness for selecting defective products and a center frequency of a surface acoustic wave element in a conventional method for manufacturing a surface acoustic wave element.

FIG. 6 is a view showing a relationship among an electrode film thickness, a film thickness / line width ratio of an electrode finger, and a line width of an electrode finger for selecting defective products in a conventional method of manufacturing a surface acoustic wave element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Surface acoustic wave element 2 ... Piezoelectric substrate 3 ... Electrode 3a ... Electrode finger

Claims (5)

[Claims] 1. A method for manufacturing a surface acoustic wave device comprising a piezoelectric substrate and an electrode formed on the piezoelectric substrate, comprising: forming a metal film for an electrode on the piezoelectric substrate; A method for manufacturing a surface acoustic wave device, comprising: a step of measuring a film thickness of a metal film; and a step of patterning the metal film under conditions determined based on the measured film thickness. 2. The method according to claim 1, wherein said patterning is performed by photolithography. 3. The method for manufacturing a surface acoustic wave device according to claim 2, wherein the condition determined according to the film thickness is an exposure condition for photolithography. 4. The method according to claim 1, wherein said patterning is performed by etching. 5. The method for manufacturing a surface acoustic wave device according to claim 4, wherein an over-etching step is further performed during the etching, and conditions of the over-etching step are determined based on the film thickness.