JP2003124767A - Surface acoustic wave element and production method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a surface acoustic wave (SAW) element which has an improved linear thermal expansion coefficient and a reduced delay time temperature coefficient. SOLUTION: Two substrates of different linear thermal expansion coefficients are used for first and second substrates, the difference of the linear thermal expansion coefficients in the direction of the smallest thermal expansion coefficient on the first substrate and a direction to be matched with the direction of the smallest thermal expansion coefficient on the first substrate when bonding the second substrate is settled within 4 ppm/ deg.C and further in a direction perpendicular to the exciting direction of SAW on the first substrate, a slit pattern is formed for relaxing stress caused by the first substrate, the second substrate or on both the substrates due to difference of linear thermal expansion coefficients.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an element using surface acoustic waves used in mobile phones and the like, and a method for manufacturing a substrate thereof.

[0002]

2. Description of the Related Art Conventionally, a surface acoustic wave element used in a mobile phone or the like is disclosed in, for example, the Institute of Electronics, Information and Communication Engineers, Journal of the Institute of Electronics, Information and Communication A 76-A Vol. J76-A No.
2 pp185-192 1993/2), a comb-shaped interdigitated electrode of a metal thin film is formed on a single crystal piezoelectric substrate such as a lithium tantalate substrate, a lithium niobate substrate and a lithium tetraborate substrate. It is configured.

In recent years, as the performance of mobile phones and the like has improved, it has been reported that the temperature coefficient of delay time of the surface acoustic wave element substrate used therefor has been improved. For example, Japanese Patent Laid-Open No. 11-5
There is a case where a single crystal piezoelectric substrate and a glass substrate are directly bonded as shown in No. 5070. Furthermore, there is a case in which a single crystal piezoelectric substrate and a minus expansion glass are bonded with an ultraviolet curable resin as shown in Nov. 1999, page 51 of the 20th ultrasonic symposium proceedings.

[0004]

Due to the rapid expansion of the market for mobile phones and the like, in recent years, there has been a tendency for the frequency bands for transmission and reception to become wider, and even for systems in which the frequency interval between the transmission band and the reception band is very narrow. Existing. For this reason, even higher performance is required for various devices built into mobile phones and the like. In particular, in a conventional surface acoustic wave element in which a comb-shaped interdigital electrode of a metal thin film is formed on a single crystal piezoelectric substrate such as a lithium tantalate substrate or a lithium niobate substrate, the delay time temperature coefficient Reduction is a major issue.

The temperature coefficient of delay time of the surface acoustic wave element is determined by the difference between the linear thermal expansion coefficient of the single crystal piezoelectric substrate and the temperature coefficient of the surface acoustic wave propagation velocity. These values are unique to the single crystal piezoelectric substrate, and in terms of linear thermal expansion coefficient,
For example, 36 degrees to 46 degrees from the Y axis in the Z axis direction around the X axis
In the X-axis of the lithium tantalate substrate having the plane orientation rotated by the angle of, that is, in the surface acoustic wave propagation direction, about 16.
It is a large value of 1 ppm / ° C.

Recently, as a method of reducing the linear thermal expansion coefficient of a single crystal piezoelectric substrate, a bonded substrate in which a base substrate having a small linear thermal expansion coefficient and a single crystal piezoelectric substrate are bonded has been proposed. This is intended to improve the linear thermal expansion coefficient by suppressing the linear thermal expansion coefficient of the single crystal piezoelectric substrate by the linear thermal expansion coefficient of the base substrate. However, this method means that the expansion and contraction of the single crystal piezoelectric substrate is suppressed by the base substrate with a force, and a stress corresponding to the difference in the coefficient of linear thermal expansion occurs at the substrate bonding interface, which causes the problem that the substrate is damaged. Occurs.

As a solution to the substrate damage, a method of reducing the thickness of the single crystal piezoelectric substrate has been proposed. However, the effect is not sufficient, and if the substrate size becomes large, the substrate damage also becomes a problem. Become.

Further, in Japanese Unexamined Patent Publication No. 9-27645, the heat treatment process is divided into two steps, and after the first heat treatment performed at low temperature, the bonded substrate is divided into small pieces, and then the second heat treatment is performed at high temperature. Although the method is described, in this method, the bonded substrate is not in the shape of a wafer, so that a problem occurs during the manufacturing process of the comb-shaped interdigital finger electrodes. The present invention solves the above problems and realizes a surface acoustic wave device-bonded substrate having an improved delay time temperature coefficient and a surface acoustic wave device by improving the linear thermal expansion coefficient of a single crystal piezoelectric substrate. The purpose is to do.

[0009]

In order to achieve the above object, a surface acoustic wave device according to the present invention comprises a first substrate which is a single crystal piezoelectric substrate and a second substrate which is bonded to the first substrate. A method for manufacturing a surface acoustic wave device, comprising: a comb-shaped interdigital finger electrode that is formed on a surface of the first substrate opposite to a surface where the first substrate and the second substrate are joined and excites and propagates a surface acoustic wave. Substrates with different linear thermal expansion coefficients are used for the second substrate and
The difference in linear thermal expansion coefficient between the direction in which the linear thermal expansion coefficient of the first substrate is the smallest and the direction in which the linear thermal expansion coefficient of the second substrate is the smallest is 4 ppm / ° C or less. In addition, the notch pattern is formed on the first substrate, the second substrate, or both of them along the direction orthogonal to the direction in which the linear thermal expansion coefficient of the first substrate is the largest. When two substrates having different linear thermal expansion coefficients are joined and subjected to heat treatment, stress corresponding to the difference in linear thermal expansion coefficient is generated at the substrate bonding interface. Here, by making the linear thermal expansion coefficient of the second substrate substantially match the linear thermal expansion coefficient of the first substrate in the direction of the smallest thermal expansion coefficient, the stress generated at the substrate bonding interface is made unidirectional. Can be limited. For this reason, the shape of the notch pattern that relieves stress is a simple linear shape, the stress is relieved by the linear notches formed at arbitrary intervals, and substrate bonding that does not cause substrate damage or substrate warpage is possible Becomes

By the above means, a high-temperature heat treatment is possible even when the substrate is heated during the manufacturing process of the comb-shaped interdigital finger electrode, which is a very effective manufacturing method for bonding the surface acoustic wave element substrate.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Specific examples of the present invention will be described.

FIG. 1 is a perspective view showing an example of a surface acoustic wave device manufactured according to the present invention.

Here, for example, as the first substrate 1, a lithium tantalate substrate having a plane orientation rotated about the X axis in the Z axis direction from the Y axis at an angle of 36 ° to 46 ° is used. As the substrate 2, a glass substrate having a linear thermal expansion coefficient of 4 ppm / ° C. was used. Regarding the size of the substrate, both the first substrate 1 and the second substrate 2 were circular substrates having a thickness of 360 μm and a diameter of 3 inches. Further, the adhesive layer 10 has a glass transition temperature of 20.
An ultraviolet curable resin having a temperature of 0 ° C. or higher was used.

The surface acoustic wave device manufactured according to the present invention is a first substrate 1 which is a single crystal piezoelectric substrate, a second substrate 2 bonded to the first substrate 1, and a second substrate of the first substrate 1. Board 2
A surface acoustic wave device having a comb-shaped interdigital finger electrode 3 formed on a surface opposite to a surface to be joined with and interposing a comb-shaped interdigital finger electrode 3 between the first substrate 1 and the second substrate 2. The bonded substrate 6 bonded by the layer 10 is used as a surface acoustic wave element substrate. Comb type interdigital electrode 3 formed on the first substrate 1
The surface acoustic wave excited by is propagated on the first substrate 1 and functions as a surface acoustic wave element.

The temperature coefficient of delay time in the surface acoustic wave device in which the comb-shaped cross electrodes 3 are formed on the first substrate 1 is the coefficient of linear thermal expansion in the surface acoustic wave propagation direction 4 of the first substrate 1 and the surface acoustic wave propagation. It is determined by the difference between the velocity and the temperature coefficient. These values are values unique to the single crystal piezoelectric substrate, and are, for example, elastic surfaces of a lithium tantalate substrate having a plane orientation rotated about the X axis from the Y axis in the Z axis direction at an angle of 36 ° to 46 °. The linear thermal expansion coefficient in the wave propagation direction 4 (X-axis direction) is about 16.
It is not a good value of 1 ppm / ° C.

In order to realize a surface acoustic wave device having a small delay time temperature coefficient by using a single crystal piezoelectric substrate having a large electromechanical coupling coefficient, in the present invention, the first substrate 1 which is a single crystal piezoelectric substrate is treated with a linear heat treatment. A bonded substrate bonded to the second substrate 2 having a small expansion coefficient is used. This is because the coefficient of linear thermal expansion of the first substrate 1 is suppressed by the coefficient of linear thermal expansion of the second substrate 2, so that the temperature coefficient of delay time is improved. However, the coefficient of linear thermal expansion of the first substrate 1 does not directly become the coefficient of linear thermal expansion of the second substrate 2, but the difference in linear thermal expansion coefficient between the first substrate 1 and the second substrate 2 causes Since the numerical value is based on the thermal stress generated in the above, the substrate thickness of the first substrate 1 and the second substrate 2 is important. As a result of the study, by reducing the thickness of the first substrate 1 so that the thickness of the second substrate 2 is three times or more the thickness of the first substrate 1, the elastic surface of the bonding substrate 6 is reduced. It has been found that the linear thermal expansion coefficient in the wave propagation direction 4 can be improved significantly. In addition, by applying the adhesive layer 10 to the substrate bonding, the first substrate 1 and the second substrate 1
It is not necessary to perform mirror-finishing on the bonding surface of the substrate 2 and the unevenness having the center line average roughness of 0.15 μm or more is provided on the bonding surface of the first substrate 1 to prevent the influence of the reflected wave of the surface acoustic wave from the bonding interface. It is possible to suppress.

Here, the plate thickness of the lithium tantalate substrate having a plane orientation rotated from the Y axis in the Z axis direction by 36 ° to 46 ° about the X axis, which is the first substrate 1, is 50 μm.
m, the thickness of the glass substrate, which is the second substrate 2, is 360μ.
m, the thickness of the ultraviolet curable resin that is the adhesive layer 10 is 6 μm
The surface acoustic wave device was manufactured and the temperature coefficient of delay time was measured, and the result was 18 ppm / ° C. The temperature coefficient of delay time of the conventional surface acoustic wave device without substrate bonding is 31p.
Since it was pm / ° C, the present invention had an improvement effect of 13 ppm / ° C. Moreover, it is clear that a greater effect will be exhibited by making the plate thickness of the first substrate 1 thinner.

FIG. 2 is a view showing a bonding direction when the first substrate 1 and the second substrate 2 are bonded. Here, the linear thermal expansion coefficients of the first substrate 1 and the second substrate 2 will be considered. The direction in which the linear thermal expansion coefficient of the lithium tantalate substrate having the plane orientation rotated about the X axis, which is the first substrate 1 from the Y axis in the Z axis direction at an angle of 36 ° to 46 °, is 1
1 is about 1 in the X-axis direction, which is the surface acoustic wave propagation direction 4.
The direction 13 having the smallest linear thermal expansion coefficient is 6.1 ppm / ° C., and the direction 13 is orthogonal to the propagation direction 4 of the surface acoustic wave.
It is ppm /. On the other hand, the glass substrate used as the second substrate 2 has a direction 12 that coincides with the direction 11 having the largest linear thermal expansion coefficient of the first substrate 1 at the time of bonding, and the first substrate 1.
The linear thermal expansion coefficient is 4 ppm / ° C. in both the direction 14 and the direction 13 in which the substrate 1 has the smallest linear thermal expansion coefficient. In the present invention, the linear thermal expansion in the direction 13 in which the linear thermal expansion coefficient of the first substrate 1 is the smallest and the linear thermal expansion 14 in the direction 14 in which the linear thermal expansion coefficient of the first substrate 1 in the second substrate 2 is the minimum It is a feature that the stress due to the difference in linear thermal expansion coefficient is limited to only one direction 11 having the largest linear thermal expansion coefficient by making the expansion coefficients substantially equal.

FIG. 3 shows a first embodiment of the surface acoustic wave device substrate according to the present invention. The first substrate 1 is a lithium tantalate substrate having a plane orientation rotated about the X axis from the Y axis in the Z axis direction at an angle of 36 ° to 46 °, and the second substrate 2
When the glass substrates are bonded together, the linear thermal expansion coefficients of the substrates are different, so stress is generated at the bonding interface due to the difference in the linear thermal expansion coefficients, and there is a possibility that substrate damage, substrate warpage, or the like will occur. The direction 11 having the largest linear thermal expansion coefficient of the first substrate 1 (the same direction as the surface acoustic wave propagation direction 4) has a linear thermal expansion coefficient of 16.1 ppm / ° C., and the linear thermal expansion of the second substrate 2 is There is a difference of about 4 times from the coefficient of 4 ppm / ° C., and it is necessary to relieve stress when joining in this direction. On the other hand, the direction 13 in which the linear thermal expansion coefficient of the first substrate 1 is the smallest 13
Since the coefficient of linear thermal expansion of the second substrate 2 is equal to 4 ppm / ° C., the stress caused by the difference in coefficient of linear thermal expansion can be ignored,
No need for stress relaxation. Therefore, the notch pattern 9 for stress relaxation is formed by making a notch with a dicing saw or the like along a direction orthogonal to the direction 11 in which the first substrate 1 has the largest linear thermal expansion coefficient.
The first embodiment shown in FIG. 3 is characterized in that a notch pattern 9 for stress relaxation is formed on the first substrate 1.

FIG. 4 shows a second embodiment of the surface acoustic wave device substrate according to the present invention. As shown in the figure, the present embodiment is characterized in that the notch pattern 9 for stress relaxation is formed on the second substrate 2.

FIG. 5 shows a third embodiment of the surface acoustic wave element substrate according to the present invention. As shown in the figure, the present embodiment is characterized in that the notch pattern 9 for stress relaxation is formed on both the first substrate 1 and the second substrate 2.

As shown in FIGS. 3 to 5, the cut pattern 9 is formed along the direction orthogonal to the direction 11 in which the first substrate 1 has the largest linear thermal expansion coefficient. Since the stress generated at the bonding interface due to the dispersion is dispersed, it is possible to realize substrate bonding without substrate damage and substrate warpage. Furthermore, high-temperature heat treatment can be performed even when the substrate is heated during the manufacturing process of the comb-shaped interdigital finger electrode 3. The first to third embodiments have the same stress relaxation effect.

FIG. 6 shows a method for manufacturing a surface acoustic wave device substrate according to the first embodiment of the present invention.

First, the first substrate 1 and the second substrate 2 are cleaned.

Next, the two substrates to be joined are joined by sandwiching the adhesive layer 10 made of an ultraviolet effect resin. Then, by irradiating the bonding substrate 6 with ultraviolet rays, the adhesive layer 1
Cure 0 to complete the bond. Then, the first substrate 1
The cut pattern 9 is formed from the surface on the opposite side of the bonding interface of (1) using a dicing saw. In this manufacturing method, the plate thickness of 360 μm of the first substrate 1 is completely cut by a dicing saw.

Next, the first substrate 1 is thinned so that the bonding substrate 6 has the linear thermal expansion coefficient of the second substrate 2 dominant. Using the substrate polishing apparatus, the substrate polishing is performed so that the plate thickness of the first substrate 1 becomes one third or less of the plate thickness of the second substrate 2. In the polishing process, rough polishing to finish polishing are performed in stages to achieve mirror polishing.

Further, the comb-shaped interdigital finger electrode 3 made of a metal thin film is manufactured on the first substrate 1 bonded to the second substrate 2 by a usual electrode manufacturing process.

FIG. 7 shows another method of manufacturing the surface acoustic wave device substrate according to the first embodiment of the present invention.

First, the cut pattern 9 is formed on the bonding surface side of the first substrate 1 by using a dicing saw. Here, a notch having a depth of 20 μm is formed on the bonding surface side of the first substrate 1 with a dicing saw.

Then, the first substrate 1 and the second substrate 2 are cleaned.

Next, the two substrates to be joined are joined by sandwiching the adhesive layer 10 made of an ultraviolet curable resin therebetween. Then, by irradiating the bonding substrate 6 with ultraviolet rays, the adhesive layer 1
0 is hardened and complete substrate bonding is performed.

Next, the first substrate 1 is thinned so that the bonding substrate 6 has the linear thermal expansion coefficient of the second substrate 2 dominant. Using the substrate polishing apparatus, the substrate polishing is performed so that the plate thickness of the first substrate 1 becomes one third or less of the plate thickness of the second substrate 2. In the polishing process, rough polishing to finish polishing are performed in stages to achieve mirror polishing.

Further, a comb-shaped interdigital finger electrode 3 as shown in FIG. 1 is produced on the first substrate 1 joined to the second substrate 2 by a usual electrode producing process.

FIG. 8 shows a method of manufacturing a surface acoustic wave device substrate according to a second embodiment of the present invention.

The difference from the first embodiment is that a notch pattern 9 is formed on the second substrate 2 to reduce the stress generated at the substrate bonding interface due to the difference in linear thermal expansion coefficient.

FIG. 9 shows a method of manufacturing a surface acoustic wave device substrate according to a third embodiment of the present invention.

The difference from the first embodiment is that a notch pattern 9 is formed on both the first substrate 1 and the second substrate 2 to reduce the stress generated at the substrate bonding interface due to the difference in linear thermal expansion coefficient. It is a point.

FIG. 10 is a perspective view showing an example of a surface acoustic wave element of another embodiment produced according to the present invention. The surface acoustic wave element shown in the figure is a first substrate 1 which is a single crystal piezoelectric substrate.
And a comb shape for exciting a surface acoustic wave formed on the surface of the first substrate 1 opposite to the bonding surface between the second substrate 2 bonded to the first substrate 1 and the second substrate 2. A surface acoustic wave element including a crossing electrode 3 and a linear thermal expansion coefficient of the second substrate 2 in a surface acoustic wave propagation direction 4 of the first substrate 1 is a line of the first substrate 1 in the same direction. Bonded so as to be smaller than the coefficient of thermal expansion. In the surface acoustic wave device according to the first embodiment, the first substrate 1 and the second substrate 2 are bonded by direct bonding, and the direct bonding substrate 7 is used as a surface acoustic wave device substrate.

FIG. 11 shows a fourth embodiment of the surface acoustic wave element substrate according to the present invention. The difference from the first embodiment is that the first substrate 1 and the second substrate 2 are directly joined to each other.

FIG. 12 shows a method for manufacturing a surface acoustic wave device substrate according to a fourth embodiment of the present invention.

First, the cut pattern 9 is formed on the bonding surface side of the first substrate 1 by using a dicing saw. Here, the cut pattern 9 having a depth of 20 μm is formed on the bonding interface side of the first substrate 1 with a dicing saw.

Next, after the bonded surfaces of the first substrate 1 and the second substrate 2 are mirror-polished and washed, the two substrates to be bonded are treated with hydrogen peroxide (H ₂ O ₂ ) and an aqueous ammonia solution ( NH
₃ ) It is immersed in a mixed solution of pure water (H ₂ O) for about 10 minutes, and then rinsed with pure water. This has the effect of imparting hydrophilicity to the surfaces of the first substrate 1 and the second substrate 2 and binding the substrates by Van der Waals force acting between water molecules adsorbed on the substrate surfaces when the substrates are joined.

Next, after the two substrates are dried, the mirror-polished surfaces of the two substrates are made to face each other in an air atmosphere at room temperature to bond the substrates. Here, it is particularly important to obtain a particle-free bonding interface, and it is desirable to bond the substrates in a clean room having a cleanness of class 10 or higher after the cleaning. In addition, by performing cleaning just before bonding the substrates, it is possible to achieve both a particle-free interface and a hydrophilic interface.

Next, the direct bonding substrate 7 is heat-treated at a temperature of 300 ° C. for about 2 hours to change from hydrogen bonding to covalent bonding to complete bonding.

Next, the first bonded substrate 7 is thinned so that the linear thermal expansion coefficient of the second bonded substrate 2 becomes dominant. Using the substrate polishing apparatus, the substrate polishing is performed so that the plate thickness of the first substrate 1 becomes one third or less of the plate thickness of the second substrate 2. In the polishing process, rough polishing to finish polishing are performed in stages to achieve mirror polishing.

Further, a comb-shaped interdigital finger electrode 3 as shown in FIG. 1 is produced on the first substrate 1 joined to the second substrate 2 by a usual electrode producing process.

Although only the method for manufacturing the surface acoustic wave element substrate of the first embodiment has been described here for simplification of the description, each embodiment can be carried out if the embodiments of the second to third embodiments are carried out. The effect shown in is obtained in the same manner.

Although the dicing saw is used for processing the cut pattern 9 in the above-described embodiment, after patterning an arbitrary shape using a resist or the like as a mask material, processing by dry etching or hydrofluoric acid ( HF)
The cutting process may be performed by wet etching with a system-based etching solution, and the manufacturing method is not particularly limited as long as the cutting pattern 9 is formed.

In the above-described embodiment, the thinning of the first substrate 1 is realized by the polishing process. However, the thickness of the second substrate 2 is not more than one third of the thickness of the second substrate 2 in advance. The first substrate 1 may be prepared and joined, and if the plate thickness of the first substrate 1 is one third or less of the plate thickness of the second substrate 2, The manufacturing method is not particularly limited.

In the embodiment shown above, a lithium tantalate substrate having a plane orientation rotated about the X axis in the Z axis direction from the Y axis at an angle of 36 ° to 46 ° will be described as the first substrate 1. However, as the first substrate 1, lithium tantalate having the X-axis as the plane orientation was rotated about the X-axis in the Z-axis direction from the Y-axis at angles of 0 ° to 15 ° and 41 to 64 °. The same effect is obtained when a lithium niobate substrate having a plane orientation is used.

Although a glass substrate is used as the second substrate 2, silicon oxide, diamond, lithium tetraborate, aluminum nitride, silicon nitride, boron, boron oxide, boron nitride, lithium tantalate, The same effect can be obtained with a substrate made of lithium niobate or a composite material thereof.

[0052]

As described above, the present invention proposes a method for manufacturing a bonded substrate for a surface acoustic wave device, which enables bonding without damage to the substrate or warpage of the substrate. is there.

According to the manufacturing method of the present invention, a high-temperature heat treatment can be performed even when the substrate is heated when the comb-shaped interdigital electrode is manufactured, and therefore, it is a very effective method for bonding the surface acoustic wave element substrate. is there. The fabricated surface acoustic wave device has an improved linear thermal expansion coefficient, a small delay time temperature coefficient, and a large electromechanical coupling coefficient, which makes it suitable for systems with extremely narrow frequency intervals between the transmission band and the reception band in recent years. However, it can sufficiently deal with it, and it increases the possibility of the surface acoustic wave element.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of a surface acoustic wave device manufactured according to the present invention.

FIG. 2 is a schematic diagram showing a bonding direction when bonding a substrate for a surface acoustic wave device according to the present invention.

FIG. 3 is a perspective view showing a first embodiment of the surface acoustic wave element substrate according to the present invention.

FIG. 4 is a perspective view showing a second embodiment of the surface acoustic wave element substrate according to the present invention.

FIG. 5 is a perspective view showing a third embodiment of the surface acoustic wave element substrate according to the present invention.

FIG. 6 is a perspective view showing a method of manufacturing a surface acoustic wave device substrate according to a first embodiment of the present invention.

FIG. 7 is a perspective view showing another manufacturing method of the first embodiment of the surface acoustic wave element substrate according to the present invention.

FIG. 8 is a perspective view showing a manufacturing method of a second embodiment of the surface acoustic wave element substrate according to the present invention.

FIG. 9 is a perspective view showing a method of manufacturing a surface acoustic wave device substrate according to a third embodiment of the present invention.

FIG. 10 is a perspective view showing an example of a surface acoustic wave element of another form produced according to the present invention.

FIG. 11 is a perspective view showing a fourth embodiment of the surface acoustic wave element substrate according to the present invention.

FIG. 12 is a perspective view showing a method of manufacturing a surface acoustic wave substrate according to a fourth embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... 1st board | substrate, 2 ... 2nd board, 3 ... comb-shaped interdigital electrode, 4 ... 1st board | substrate surface acoustic wave propagation direction, 5 ... 1st board | substrate surface acoustic wave propagation direction, and after board | substrate joining Second matching
Direction of substrate, 6 ... Bonding substrate 7 ... Direct bonding substrate, 9 ... Cut pattern, 10 ... Adhesive layer, 11 ... Direction in which linear thermal expansion coefficient of first substrate is largest, 12 ... Linear heat of first substrate The direction of the second substrate, which coincides with the direction having the largest expansion coefficient after substrate bonding, 13 ...
Direction of the substrate having the smallest linear thermal expansion coefficient, 14 ... the direction of the second substrate which is the same as the direction having the smallest linear thermal expansion coefficient of the first substrate after the substrate bonding.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Atsushi Isobe             1-280, Higashi Koikekubo, Kokubunji, Tokyo             Central Research Laboratory, Hitachi, Ltd. F term (reference) 5J097 AA09 AA28 AA31 EE03 EE08                       GG03 GG04 HA03

Claims (17)

[Claims] 1. A first substrate which is a single crystal piezoelectric substrate, a second substrate bonded to the first substrate, and a side opposite to a bonding surface of the first substrate and the second substrate. In a method of manufacturing a surface acoustic wave device, comprising: a comb-shaped interdigital electrode for exciting an acoustic wave formed on the surface of the first substrate, the first substrate is bonded when the first substrate and the second substrate are bonded together. The linear thermal expansion coefficient of the second substrate in the propagation direction of the surface acoustic wave of
Is smaller than the linear thermal expansion coefficient of the substrate in the same direction, and the linear thermal expansion coefficient of the direction in which the linear thermal expansion coefficient of the first substrate is the smallest and the linear thermal expansion coefficient of the first substrate are the smallest. A method for manufacturing a surface acoustic wave element, characterized in that the bonding is performed so that the difference between the direction and the linear thermal expansion coefficient of the second substrate in the direction that coincides with the bonding after substrate bonding is within 4 ppm / ° C. 2. The method of manufacturing a surface acoustic wave device according to claim 1, wherein notches are formed at arbitrary intervals in a direction orthogonal to a direction having the largest linear thermal expansion coefficient of the first substrate. 3. A notch having an arbitrary interval is formed in the second substrate in a direction orthogonal to a direction in which the linear thermal expansion coefficient of the first substrate is the largest, and a direction that coincides after the substrates are joined. The method for manufacturing a surface acoustic wave device according to claim 1 or 2. 4. The method of manufacturing a surface acoustic wave device according to claim 2, wherein the notch does not completely cut the substrate. 5. The method of manufacturing a surface acoustic wave device according to claim 2, wherein the notch completely cuts the substrate. 6. The surface acoustic wave device according to claim 2, wherein the notch is formed on a joint interface side between the first substrate and the second substrate. Production method. 7. The method of manufacturing a surface acoustic wave device according to claim 2, wherein the first cut is formed on a surface forming a comb-shaped interdigital finger electrode for exciting an acoustic wave. . 8. The surface acoustic wave according to claim 1, wherein the first substrate and the second substrate are bonded with an ultraviolet curable resin. Device manufacturing method. 9. The production of a surface acoustic wave device according to claim 8, wherein the ultraviolet curable resin used for joining the first substrate and the second substrate has a glass transition temperature of 200 ° C. or higher. Method. 10. The joint surface of the first substrate, the joint surface of the second substrate, or the joint surface of both of the substrates has a surface roughness of 0.15 μm or more in terms of center line average roughness. The method for manufacturing a surface acoustic wave device according to claim 8 or 9, 11. The bonding surface of the first substrate and the second substrate is mirror-polished.
A method for manufacturing the surface acoustic wave element according to claim 1. 12. The method of manufacturing a surface acoustic wave device according to claim 1, wherein the first substrate and the second substrate are directly bonded to each other. 13. The method of manufacturing a surface acoustic wave device according to claim 1, wherein the thickness of the first substrate is 50 μm or less. 14. The notch of the arbitrary shape formed on the first substrate and the second substrate is formed by a dicing saw, or by wet etching or dry etching using a photoresist as a mask material. The method for manufacturing a surface acoustic wave device according to any one of claims 2 to 7, which is characterized in that. 15. The first substrate is lithium tantalate having a plane orientation rotated about the X axis in the Z axis direction from the Y axis by an angle in the range of 36 to 46 °, and the X axis is the plane orientation. Lithium tantalate, or lithium niobate having a plane orientation rotated about the X axis from the Y axis in the Z axis direction at angles of 0 to 15 ° and 41 to 64 °. Item 15. A method for manufacturing a surface acoustic wave device according to any one of items 1 to 14. 16. The second substrate is diamond, aluminum nitride, silicon, silicon oxide, silicon nitride, boron, boron oxide, boron nitride, lithium tantalate, lithium niobate, lithium tetraborate, or a combination thereof. It is a material, The manufacturing method of the surface acoustic wave element in any one of Claims 1-15. 17. A bonding surface of a first substrate, a second substrate bonded to the first substrate directly or through an intermediate material, and a bonding surface of the first substrate opposite to the second substrate. In a surface acoustic wave element having an electrode for exciting an elastic wave formed on the side surface thereof, the coefficient of linear thermal expansion of the second substrate in the propagation direction of the surface acoustic wave of the first substrate is Smaller than the linear thermal expansion coefficient in the propagation direction of the surface acoustic wave of the first substrate,
Further, the linear thermal expansion coefficient of the second substrate in the direction in which the linear thermal expansion coefficient of the first substrate is the smallest and the linear thermal expansion coefficient of the second substrate in the direction in which the linear thermal expansion coefficient of the first substrate is the smallest. A surface acoustic wave element, wherein the first and second substrates are joined so that the difference from the expansion coefficient is within 4 ppm / ° C.