JPH08298429A - Single crystal substrate for surface acoustic wave device and its manufacture and surface acoustic wave device - Google Patents

Abstract

PURPOSE: To eliminate a fault due to a bulk wave by providing plural holes or grooves or projections having a depth of a specific percentage of the thickness of a piezoelectric single crystal substrate at a position of a side opposite to an electrode forming side in crossing a propagation direction of the surface acoustic wave. CONSTITUTION: A photo resist film is formed on the side of a piezoelectric single crystal substrate made of a lithium tantalate or a lithium niobate and opposite to its electrode forming side. Then exposure and development processing by an ultraviolet ray, for example, is applied to the photo resist film to form a resist pattern having holes, grooves or projections matching a hole, groove, projection forming pattern. Then horning processing is applied via the resist pattern to form plural holes and/or grooves or projections having a depth or a height of 5 to 70% of the thickness of the substrate. Thus, noise due to a bulk wave is sufficiently reduced and the processing yield and manufacture yield are remarkably improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single crystal piezoelectric substrate for a surface acoustic wave device, a method for manufacturing the same and a surface acoustic wave device.

[0002]

2. Description of the Related Art In recent years, many surface acoustic wave devices have been used as elements such as filters, delay lines, and oscillators of electronic equipment that uses radio waves. In particular, surface acoustic wave filter devices that are small and lightweight and have high sharp cutoff performance as filters have become widely used as filters for RF and IF stages of mobile terminal devices in the field of television receivers and mobile communications. Therefore, it is required to improve productivity as well as characteristics.

In a conventional surface acoustic wave device, a lithium tantalate (LiTaO ₃ ) single crystal wafer or a lithium niobate (LiNbO ₃ ) single crystal wafer exhibiting piezoelectricity is used as a substrate, and a main surface of such a substrate is formed. It is configured by providing an interdigital transducer (comb-shaped transducer). In such a configuration, the surface acoustic wave is excited and received by the transducer, but at the same time, an unnecessary wave (obstacle wave) such as a bulk wave is also excited and received.

Such bulk waves cause spurious interference in frequency characteristics. Therefore, in order to remove spurious interference, the entire back surface of the piezoelectric single crystal substrate used in the surface acoustic wave device is roughened by polishing with a rough abrasive or by honing, or by dicer cutting or mask honing. Bulk wave countermeasures such as forming a groove on the back surface of the substrate have been implemented.

[0005]

However, the above-described bulk wave countermeasure has some effects when downsizing the surface acoustic wave device, but when strict characteristics are required, There is a problem that the obstacle due to the bulk wave cannot be sufficiently eliminated.

Further, there has recently been a demand for automation accompanying the stepperization of the manufacturing process, and high precision and miniaturization, but there has been a problem that the processing yield and the manufacturing yield are reduced together with them.

The present invention has been made in order to solve such a problem, and is a single crystal substrate for a surface acoustic wave device having a good manufacturing yield after sufficiently eliminating the obstacles caused by bulk waves, and the manufacturing thereof. It is an object to provide a method and a surface acoustic wave device.

[0008]

A single crystal substrate for a surface acoustic wave device according to claim 1 is a surface opposite to an electrode formation surface of a piezoelectric single crystal substrate, and a position crossing a surface wave propagation direction. Is formed with a plurality of holes and / or grooves having a depth of 5% to 70% of the thickness of the piezoelectric single crystal substrate.

A single crystal substrate for a surface acoustic wave device according to a second aspect of the present invention is a piezoelectric single crystal substrate having a piezoelectric single crystal substrate thickness which is a surface opposite to an electrode formation surface of the piezoelectric single crystal substrate and which crosses a surface wave propagation direction. A plurality of protrusions having a height of 5% to 70% of the height is formed.

A single crystal substrate for a surface acoustic wave device according to claim 3 is the single crystal substrate for a surface acoustic wave device according to claim 1 or 2, wherein the piezoelectric single crystal substrate is made of lithium tantalate or lithium niobate. It is characterized by

According to a fourth aspect of the present invention, there is provided a method of manufacturing a single crystal substrate for a surface acoustic wave device, wherein a step of forming a photoresist film on a surface of the piezoelectric single crystal substrate opposite to an electrode forming surface and a step of forming the photoresist film on the photoresist film. Exposing and developing to form a resist pattern having a plurality of holes and / or grooves, or a plurality of protrusions at positions crossing the propagation direction of surface waves;
Honing treatment is applied to the piezoelectric single crystal substrate through a resist pattern to form multiple holes and / or grooves or multiple protrusions at a depth or height of 5% to 70% of the thickness of the piezoelectric single crystal substrate. And a step of performing.

A surface acoustic wave device according to a fourth aspect of the present invention is a surface acoustic wave device comprising a piezoelectric single crystal substrate and a comb-shaped electrode formed on one main surface of the piezoelectric single crystal substrate. The single crystal substrate for a surface acoustic wave device according to any one of claims 1 to 3.

In the single crystal substrate for a surface acoustic wave device according to claim 1, the plurality of holes and / or grooves formed on the surface of the piezoelectric single crystal substrate opposite to the surface on which the electrodes are formed are in the propagation direction of the surface wave. Any shape can be used as long as it can effectively prevent the propagation of unwanted waves (disturbance waves) such as bulk waves in the same direction as the circular shape or polygonal shape of the hole. Examples thereof include a square shape, a U-shape, and a V-shape.
Alternatively, the holes and the grooves can be formed together.

The depth of the plurality of holes and / or grooves is preferably 5% to 70% of the thickness of the piezoelectric single crystal substrate. By setting it in this range, it is possible to efficiently prevent the propagation of unnecessary waves (obstacle waves) such as bulk waves and to maintain the mechanical strength of the substrate.

In the single crystal substrate for a surface acoustic wave device according to a second aspect of the invention, the portions corresponding to the above-mentioned plurality of holes and / or grooves are changed into protrusions. In the present invention, it is preferable to use lithium tantalate or lithium niobate as the piezoelectric single crystal substrate.

The holes, grooves and protrusions as described above are formed, for example, as follows. That is, first, a photoresist film is formed on the surface of the piezoelectric single crystal substrate opposite to the surface on which the electrodes are formed. It is preferable to use an ultraviolet curable resist film as the photoresist film. Next, this photoresist film is exposed to, for example, ultraviolet rays and developed to form a resist pattern having holes, grooves, and protrusions corresponding to the above-described formation pattern of holes, grooves, and protrusions. Then, the piezoelectric single crystal substrate is subjected to a honing process through a resist pattern having holes, grooves and protrusions to form fine holes, grooves or protrusions with a predetermined depth.

[0017]

[Operation] On the surface of the piezoelectric single crystal substrate opposite to the electrode formation surface,
A plurality of holes with a depth of 5% to 70% of the substrate thickness and /
Alternatively, by forming the groove, the processing yield and the manufacturing yield can be improved, and the obstacle due to the bulk wave can be sufficiently eliminated.

[0018]

Embodiments of the present invention will be described below. Example 1 First, double-sided lapping, outer diameter 76 mm, thickness 0.52 mm
A 126 ° Y LiNbO ₃ single crystal wafer was prepared. Then L
Back surface of iNbO ₃ single crystal wafer (surface opposite to electrode formation surface)
Then, a UV-curable urethane resin film (photoresist film) is adhered by thermocompression bonding, and 35 mj of energy of ultraviolet light is applied to this photoresist film for several seconds through a photomask having a predetermined light-shielding pattern. It was irradiated and exposed. After that, the photoresist film was developed with a weak alkaline solution such as sodium carbonate to form a desired hole pattern at a position crossing the propagation direction of the surface wave. Next, an electrostatic removal brush whose one end side was grounded in advance was attached to the mask surface, and alundum (No. 240) was sprayed from the honing nozzle to perform honing processing.

After the honing process, the photoresist film was dissolved and removed, and the honing surface was observed.
The hole pattern was 70 μm and the depth was about 5% of the wafer thickness. This pattern had neither pattern collapse nor unevenness.

When the above 100 wafers were examined, the hole diameter was within the range of 270 μm ± 5 μm, and the hole depth was 25.
Within the range of μm ± 3 μm, there was little variation. In addition, we fabricated an IF filter for TV (shape: 1.8 mm × 1.8 mm) using these wafers and evaluated the characteristics. The bulk wave noise was reduced to -50 dB, and the filter manufacturing yield was 97%. It was good.

Example 2 Using the same LiNbO ₃ single crystal wafer and photoresist film as in Example 1, development and exposure were performed under the same conditions as in Example 1. The exposure time of ultraviolet rays was longer than that in Example 1. After performing the same honing processing as in Example 1, the photoresist film was dissolved and removed, and the honing surface was observed. As a result, a hole pattern with an outer diameter of 270 μm and a depth of about 30% of the wafer thickness was formed. Was there. This pattern had neither pattern collapse nor unevenness.

When 100 wafers were examined, the hole diameter was 270 μm ± 6 μm and the hole depth was 150.
Within the range of μm ± 6 μm, there was little variation. In addition, we fabricated an IF filter for TV (shape: 1.8 mm × 1.8 mm) using these wafers and evaluated the characteristics. As a result, the bulk wave noise was reduced to -50 dB, and the filter manufacturing yield was 98%. It was good.

Example 3 Using the same LiNbO ₃ single crystal wafer and photoresist film as in Example 1, development and exposure were performed under the same conditions as in Example 1. The exposure time of ultraviolet rays was longer than that in Example 1. After performing the same honing processing as in Example 1, the photoresist film was dissolved and removed, and the honing surface was observed. As a result, a hole pattern with an outer diameter of 270 μm and a depth of about 50% of the wafer thickness was formed. Was there. This pattern had neither pattern collapse nor unevenness.

When 100 wafers described above were investigated, the hole diameter was within the range of 270 μm ± 10 μm and the hole depth was 260.
Within the range of μm ± 7 μm, there was little variation. In addition, we fabricated an IF filter for TV (shape: 1.8 mm × 1.8 mm) using these wafers and evaluated the characteristics. The bulk wave noise was reduced to -50 dB, and the filter manufacturing yield was 97%. It was good.

Example 4 Using the same LiNbO ₃ single crystal wafer and photoresist film as in Example 1, development and exposure were performed under the same conditions as in Example 1. The exposure time of ultraviolet rays was longer than that in Example 1. After performing the same honing processing as in Example 1, the photoresist film was dissolved and removed, and the honing surface was observed. As a result, a hole pattern having an outer diameter of 270 μm and a depth of about 70% of the wafer thickness was formed. Was there. This pattern had neither pattern collapse nor unevenness.

When the above 100 wafers were investigated, the hole diameter was within the range of 270 μm ± 12 μm, and the hole depth was 364.
Within the range of μm ± 8 μm, there was little variation. Also, using these wafers, an IF filter for TV (shape: 1.8 mm × 1.8 mm) was manufactured and the characteristics were evaluated. The noise of the bulk wave was reduced to -50 dB, and the manufacturing yield of the filter was 96%. It was good.

Example 5 126 having an outer diameter of 76 mm and a thickness of 0.52 mm, which was subjected to double-sided lapping.
A Y LiNbO ₃ single crystal wafer was prepared. Next, LiNbO ₃
UV-curable urethane resin film (photoresist film) on the back surface of the single crystal wafer (the surface opposite to the electrode formation surface)
Are adhered to each other by thermocompression bonding, and the photoresist film is covered with a photomask having a predetermined light-shielding pattern.
Exposure was performed by irradiating ultraviolet rays with an energy amount of 5 mj for several seconds. After that, the photoresist film was developed with a weak alkaline solution such as sodium carbonate to form a desired groove pattern at a position crossing the propagation direction of the surface wave. Next, an electrostatic removal brush whose one end side was grounded in advance was attached to the mask surface, and alundum (No. 240) was sprayed from the honing nozzle to perform honing processing. After the honing process, the photoresist film was dissolved and removed, and the honing process surface was observed. As a result, it was found that the groove pattern had a depth of about 30% of the wafer thickness. This pattern had neither pattern collapse nor unevenness.

When the above 100 wafers were examined, the variation in the groove depth was small. In addition, using these wafers, an IF filter for TV (shape: 1.8 mm ×
When 1.8 mm) was produced and the characteristics were evaluated, the noise of the bulk wave and the manufacturing yield of the filter were as good as in Example 1.

Example 6 126 having an outer diameter of 76 mm and a thickness of 0.52 mm, which was subjected to double-sided lapping.
A Y LiNbO ₃ single crystal wafer was prepared. Next, LiNbO ₃
UV-curable urethane resin film (photoresist film) on the back surface of the single crystal wafer (the surface opposite to the electrode formation surface)
Are adhered to each other by thermocompression bonding, and the photoresist film is covered with a photomask having a predetermined light-shielding pattern.
Exposure was performed by irradiating ultraviolet rays with an energy amount of 5 mj for several seconds. Then, the photoresist film was developed with a weak alkaline solution such as sodium carbonate to form a desired protruding pattern at a position crossing the propagation direction of the surface wave. Next, an electrostatic removal brush whose one end side was grounded in advance was attached to the mask surface, and alundum (No. 240) was sprayed from the honing nozzle to perform honing processing.

After the honing process, the photoresist film was dissolved and removed, and the honing surface was observed.
The protrusion pattern was 70 μm and the height was about 30% of the wafer thickness. This pattern had neither pattern collapse nor unevenness.

When the above 100 wafers were investigated, the variation in groove depth was small. In addition, using these wafers, an IF filter for TV (shape: 1.8 mm ×
When 1.8 mm) was produced and the characteristics were evaluated, the noise of the bulk wave and the manufacturing yield of the filter were as good as in Example 1. In addition, instead of the LiNbO ₃ single crystal wafer
When an IF filter for television was produced in the same manner as in Example 6 using a LiTaO ₃ single crystal wafer, it was as good as in Example 1.

Comparative Example 1 Using the same LiNbO ₃ single crystal wafer and photoresist film as in Example 1, development and exposure were performed under the same conditions as in Example 1. The exposure time of ultraviolet rays was shorter than that in Example 1. After performing the same honing as in Example 1, the photoresist film was dissolved and removed, and the honing surface was observed. As a result, a hole pattern with an outer diameter of 270 μm and a depth of about 2% of the wafer thickness was formed. Was there. This pattern had neither pattern collapse nor unevenness.

When the above 100 wafers were investigated, the hole diameter was within the range of 270 μm ± 3 μm and the hole depth was 10 mm.
Within the range of μm ± 2 μm, there was little variation. Moreover, when an IF filter for TV (shape: 1.8 mm × 1.8 mm) was manufactured using these wafers, the manufacturing yield of the filter was 68%.

Comparative Example 2 Using the same LiNbO ₃ single crystal wafer and photoresist film as in Example 1, development and exposure were performed under the same conditions as in Example 1. The exposure time of ultraviolet rays was longer than that in Example 1. After performing the same honing processing as in Example 1, the photoresist film was dissolved and removed, and the honing surface was observed. As a result, a hole pattern with an outer diameter of 270 μm and a depth of about 80% of the wafer thickness was formed. Was there. This pattern had neither pattern collapse nor unevenness.

When the above 100 wafers were investigated, the hole diameter was within the range of 270 μm ± 15 μm and the hole depth was 416.
Within the range of μm ± 10 μm, there was little variation. Moreover, when an IF filter for TV (shape: 1.8 mm × 1.8 mm) was produced using these wafers, the production yield of the filter was 42%. FIG. 1 shows the relationship between the manufacturing yield of the surface acoustic wave devices and the ratio of the hole depth in Examples 1 to 4 and Comparative Examples 1 and 2.

[0036]

The single crystal substrate for a surface acoustic wave device according to any one of claims 1 to 3 has a plurality of holes and / or grooves having a depth of 5% to 70% of the thickness of the piezoelectric single crystal substrate. Therefore, the surface acoustic wave device using this substrate can significantly reduce the bulk wave noise.

In the method for manufacturing a single crystal substrate for a surface acoustic wave device according to a fourth aspect of the present invention, a desired hole depth can be improved with good yield by performing honing using an ultraviolet exposure film.
The manufacturing yield and characteristics of the surface acoustic wave device can be significantly improved.

Since the surface acoustic wave device according to the fifth aspect uses the single crystal substrate according to the first to third aspects, it is possible to improve the characteristics by lowering the bulk wave noise and increase the manufacturing yield.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the manufacturing yield of surface acoustic wave devices and the ratio of hole depth.

Claims (5)

[Claims] 1. A piezoelectric single crystal substrate for a surface acoustic wave device, wherein the piezoelectric single crystal substrate has a thickness on the surface opposite to the electrode formation surface of the piezoelectric single crystal substrate at a position crossing the propagation direction of surface waves. A single crystal substrate for a surface acoustic wave device, comprising a plurality of holes and / or grooves having a depth of 5% to 70%. 2. A piezoelectric single crystal substrate for a surface acoustic wave device, wherein the piezoelectric single crystal substrate has a thickness on the surface opposite to the electrode formation surface of the piezoelectric single crystal substrate at a position crossing the propagation direction of surface waves. A single crystal substrate for a surface acoustic wave device, comprising a plurality of protrusions having a height of 5% to 70%. 3. The single crystal substrate for a surface acoustic wave device according to claim 1 or 2, wherein the piezoelectric single crystal substrate is made of lithium tantalate or lithium niobate. Crystal substrate. 4. A step of forming a photoresist film on the surface of the piezoelectric single crystal substrate opposite to the surface on which the electrode is formed, and a position where the photoresist film is exposed and developed to cross the surface wave propagation direction. Multiple holes and / or grooves,
Or a step of forming a resist pattern having a plurality of protrusions, and a honing process is performed on the piezoelectric single crystal substrate through the resist pattern to form the plurality of holes and / or grooves, or a plurality of protrusions in the piezoelectric single crystal. 5% of board thickness
And a step of forming the single crystal substrate for a surface acoustic wave device at a depth of 70% or a height of 70%. 5. A surface acoustic wave device comprising a piezoelectric single crystal substrate and a comb-shaped electrode formed on one main surface of the piezoelectric single crystal substrate, wherein the piezoelectric single crystal substrate is any one of claims 1 to 3. A surface acoustic wave device, which is the single crystal substrate for a surface acoustic wave device according to item 1.