JP2010273127A - Method of manufacturing composite piezoelectric substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a composite piezoelectric substrate which is reduced in warpage after heat treatment and is less susceptible to cracking. <P>SOLUTION: In the method of manufacturing a composite piezoelectric substrate where at least a piezoelectric substrate and an insulator substrate are stuck with adhesive and then the adhesive is cured by heat treating the substrates thus stuck, a substrate having a conductivity of 1×10<SP>-14</SP>[Ω<SP>-1</SP>cm<SP>-1</SP>] or less is used as the insulator substrate, and the adhesive is cured by heat treatment while performing neutralization. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a composite piezoelectric substrate (hereinafter also referred to as a composite piezoelectric substrate).

  A surface acoustic wave (SAW) device in which a comb electrode for exciting a surface acoustic wave is formed on a piezoelectric substrate is used as a component for frequency adjustment / selection in high-frequency communication such as a cellular phone.

  The piezoelectric substrate material used for this has a very high conversion efficiency (hereinafter referred to as an electromechanical coupling coefficient) from an electric signal to mechanical vibration, and a filter determined by the electrode interval of the comb electrodes and the sound velocity of the elastic wave. It is required that the center frequency does not vary with temperature (hereinafter referred to as frequency-temperature characteristics).

  In other words, it is preferable to have a piezoelectric substrate having both a large electromechanical coupling coefficient and a small frequency temperature coefficient. An example of a piezoelectric substrate that realizes such characteristics is a composite piezoelectric substrate in which a piezoelectric substrate and another substrate are bonded.

As an example of such a composite piezoelectric substrate, Patent Document 1 includes an amorphous junction region having a thickness of 0.3 nm to 2.5 nm at a junction interface between a lithium tantalate substrate and a sapphire substrate. A bonded substrate is disclosed.
Specifically, in the bonded substrate described in Patent Document 1, the thickness of the bonded region is 1.5 nm or more, and the amount of warpage after being held at 150 ° C. for 1 hour is approximately 200 μm or less.

  Here, as an important characteristic required for the bonded substrate, there is a small increase in warpage after the heat treatment. This is because it may be necessary to perform a heat treatment in the SAW device manufacturing process, and if the substrate warps after the heat treatment, a crack occurs or the substrate is adsorbed to the stage in a subsequent dicing process or the like. This is because it becomes difficult and productivity is greatly reduced.

However, in the invention described in Patent Document 1, a sapphire substrate is used as a support substrate. However, since the sapphire substrate is expensive, there is a problem that an inexpensive composite piezoelectric substrate cannot be obtained.
In recent years, there has been a demand for a composite piezoelectric substrate in which the amount of increase in warpage is further reduced.

Japanese Patent Publication No. 3929983

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an inexpensive composite piezoelectric substrate manufacturing method capable of reducing the increase in warpage after heat treatment and preventing the occurrence of cracks.

In order to solve the above-described problem, according to the present invention, at least a piezoelectric substrate and an insulator substrate are bonded together with an adhesive, and the bonded substrate is cured by performing a heat treatment on the bonded substrate. A method of manufacturing a piezoelectric substrate having a conductivity of 1 × 10 ⁻¹⁴ [Ω ⁻¹ · cm ⁻¹ ] or less is used as the insulator substrate, and the curing of the adhesive by the heat treatment is performed by a charge removal process. The present invention provides a method for manufacturing a composite piezoelectric substrate, which is performed while applying the method.
According to such a method for manufacturing a composite piezoelectric substrate, the conductivity is 1 × 10 ⁻¹⁴ [Ω ⁻¹ · cm ⁻ , which is inexpensive but generally tends to increase the warpage of the composite piezoelectric substrate. ¹ ] Even when the following insulator substrate is used, it is possible to provide a composite piezoelectric substrate in which the increase in warpage after heat treatment is small and the generation of cracks is suppressed.

Further, it is preferable to use a substrate whose main component is alumina as the insulator substrate.
As described above, when an insulating substrate containing alumina as a main component is used, the amount of warpage after heat treatment can be further reduced, and an inexpensive composite piezoelectric substrate can be obtained.

Moreover, as the piezoelectric _substrate, LiTaO _3, LiNbO _3, it is preferable to use those made of Li ₂ B 4 either _{O 7.}
Thus, if the piezoelectric substrate is LiTaO ₃ , LiNbO ₃ , or Li ₂ B ₄ O ₇ , the electromechanical coupling coefficient is large, and the temperature fluctuation of the operating frequency is suppressed by the effect of the combined piezoelectric substrate. It is possible to provide a low-cost compounded piezoelectric substrate.

  According to the present invention, it is possible to obtain a composite piezoelectric substrate that is small in warpage increase after heat treatment, suppresses the generation of cracks, and is inexpensive.

It is explanatory drawing of the manufacturing method of the composite piezoelectric substrate which concerns on this invention.

Hereinafter, the present invention will be described more specifically.
As described above, a method for manufacturing a composite piezoelectric substrate that can suppress the occurrence of cracks with a small increase in warpage after heat treatment has been awaited.

Here, the principle that a general composite piezoelectric substrate warps after heat treatment will be described.
Piezoelectric substrates such as LiTaO ₃ and LiNbO ₃ have pyroelectricity as is well known. In the SAW device manufacturing process, the piezoelectric substrate is repeatedly heated and cooled. However, if a temperature difference is applied to the piezoelectric substrate, a surface potential of several kilovolts is generated due to pyroelectricity. The potential is maintained and the piezoelectric substrate is warped.

On the other hand, the composite piezoelectric substrate deforms like a bimetal when the temperature changes due to the difference in expansion coefficient between the piezoelectric substrate and the support substrate.
At this time, stress due to bimetal deformation is applied to the piezoelectric substrate, and this stress generates surface charges on the piezoelectric substrate.

  That is, in a state where temperature is applied to the composite piezoelectric substrate, both stress due to the bimetal effect and charging (surface charge) due to the pyroelectric effect are generated in the piezoelectric substrate, and the warpage is further increased.

Next, when the temperature returns to the initial temperature, the deformation due to the bimetal effect is eliminated, but the deformation of the composite piezoelectric substrate remains due to the surface potential generated by the pyroelectric property of the piezoelectric substrate. Therefore, the composite piezoelectric substrate is warped after heat treatment.
In particular, when an insulator substrate having a conductivity of 1 × 10 ⁻¹⁴ [Ω ⁻¹ · cm ⁻¹ ] or less is used as a support substrate of the composite piezoelectric substrate, the piezoelectric substrate to be bonded to the high resistance insulator substrate is Since the surface charge tends to accumulate, the amount of warping tends to increase.

However, the inventors have at least a method of manufacturing a composite piezoelectric substrate in which the adhesive is cured by bonding the piezoelectric substrate and the insulator substrate with an adhesive and performing heat treatment on the bonded substrate. Even when an insulator substrate having a conductivity of 1 × 10 ⁻¹⁴ [Ω ⁻¹ · cm ⁻¹ ] or less is used, by performing curing of the adhesive by heat treatment while performing a charge removal treatment, It has been found that charging due to the pyroelectric effect of the piezoelectric substrate can be suppressed.
In such a composite piezoelectric substrate manufacturing method, if the ambient temperature of the substrate on which the piezoelectric substrate and the insulator substrate are bonded is changed during the heat treatment, deformation due to the bimetal effect occurs, but the pyroelectricity of the piezoelectric substrate is increased. Charge due to the effect is suppressed. Therefore, when the temperature returns to the initial temperature after the heat treatment, the deformation due to the bimetal effect is eliminated, the composite piezoelectric substrate returns to its original shape, almost no warpage occurs, and the occurrence of cracks can also be prevented. Completed.

  Hereinafter, the present invention will be described in detail with reference to FIG. 1, but the present invention is not limited thereto. FIG. 1 is an explanatory view of a method of manufacturing a composite piezoelectric substrate according to the present invention.

According to the method for manufacturing a composite piezoelectric substrate of the present invention, first, an insulator substrate 2 having a conductivity of 1 × 10 ⁻¹⁴ [Ω ⁻¹ · cm ⁻¹ ] or less and a piezoelectric substrate 1 are prepared.
According to the method for manufacturing a composite piezoelectric substrate of the present invention, even when using the insulator substrate 2 that tends to increase the amount of warpage of such a composite piezoelectric substrate, the amount of increase in warpage can be reduced and cracks can be reduced. Can be prevented. Therefore, it is not always necessary to use an expensive material such as a sapphire substrate.

In addition, as the piezoelectric substrate 1 used in the present invention, a substrate made of any one of LiTaO ₃ , LiNbO ₃ , and Li ₂ B ₄ O ₇ can be used. If the piezoelectric substrate 1 is LiTaO ₃ , LiNbO ₃ , or Li ₂ B ₄ O ₇ , the electromechanical coupling coefficient is large, and the operating frequency temperature fluctuation is suppressed by the effect of the combined piezoelectric substrate. A composite piezoelectric substrate can be provided.

  Further, as the insulator substrate 2, a substrate whose main component is alumina can be used. Since the insulator substrate 2 containing alumina as a main component has a large Young's modulus of about 300 to 400 GPa and is hard, an increase in warpage after heat treatment is small, and an inexpensive composite piezoelectric substrate can be obtained.

Thereafter, the adhesive 3 is applied to one or both of the piezoelectric substrate 1 and the insulator substrate 2, and the substrate 4 is bonded to the piezoelectric substrate 1 and the insulator substrate 2 by bonding them together under vacuum, for example. It can be.
In addition, it is preferable to clean the surface of each substrate before bonding so that no foreign matter enters the bonding surface. Moreover, when using an ultraviolet curing adhesive as the adhesive agent 3, an adhesive agent can be temporarily hardened by irradiating an ultraviolet-ray after bonding. And after hardening an adhesive agent in this way, an adhesive agent can be hardened completely by performing the heat processing for hardening the adhesive agent mentioned later.

In the method for manufacturing a composite piezoelectric substrate of the present invention, the substrate 4 bonded as described above is subjected to a heat treatment to cure the adhesive 3 (cured adhesive: 3 ′), thereby being combined. The piezoelectric substrate 5 is obtained, and the adhesive 3 is cured by this heat treatment while performing a charge removal process.
As the charge removal treatment, for example, an ionizer can be used to remove the charge by neutralizing the bonded substrate 4 with ions of opposite polarity.

  In the present invention, the “heat treatment” refers to a process of heating the substrate 4 in which the piezoelectric substrate 1 and the insulator substrate 2 are bonded together with the adhesive 3 or cooling after heating, and the combined piezoelectric of the present invention. In the method for manufacturing a substrate, this heat treatment step is performed while performing a charge removal process.

As described above, in the method for manufacturing a composite piezoelectric substrate of the present invention, the bonded substrate 4 is heated and cooled while being subjected to a charge removal process using an ionizer or the like. The surface potential due to the nature does not occur.
Therefore, if the composite piezoelectric substrate manufacturing method of the present invention is used, the bonded substrate 4 is heated and cooled to cause deformation due to the bimetal effect, but the piezoelectric substrate 1 is not charged due to the pyroelectric effect. When the temperature returns to the initial temperature later (after heating / cooling), the deformation due to the bimetal effect is eliminated, the shape returns to the original shape, and the amount of increase in warpage can be reduced. Moreover, since deformation due to charging of the piezoelectric substrate 1 can be suppressed, generation of cracks after heat treatment can be prevented.

Thereafter, the processing can be performed according to a regular method. For example, after the composite piezoelectric substrate 5 manufactured as described above is chamfered, the surface side of the piezoelectric substrate 1 is scraped off by grinding and lapping, and further polished. By applying the processing, the piezoelectric substrate 1 can be processed to have a predetermined thickness.
At this time, it is better to remove the outer periphery of the piezoelectric substrate 1 of the composite piezoelectric substrate 5 by a width of, for example, 0.1 mm or more and 3 mm or less after performing the chamfering process by bonding as described above. This removal step can be performed using, for example, a special chamfering wheel. If such a composite piezoelectric substrate 5 is removed from the outer periphery of the piezoelectric substrate 1 by 0.1 mm or more and 3 mm or less, processing distortion, cracks, etc. are generated in the piezoelectric substrate 1 in the subsequent grinding process of the piezoelectric substrate 1 or the like. Can be further suppressed.

  Further, in the present invention, the adhesive 3 can be further cured by performing a heat treatment after the grinding step or the like of the piezoelectric substrate 1 described above. The increase in the amount of warpage can be suppressed, and the occurrence of cracks can be prevented.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not limited by these description.

(Example)
It has a diameter of 4 inches (100 mm) and a thickness of 215 μm. The surface roughness Ra of the bonded surface and the opposite surface is both 0.3 μm, the Young's modulus is 340 GPa, and the conductivity is 1 × 10. ^An alumina substrate having ⁻¹⁵ [Ω ⁻¹ · cm ⁻¹ ] was prepared.
Moreover, the electrical conductivity is 1 × 10 ⁻¹⁴ [Ω ⁻¹ · cm ⁻¹ ] as a piezoelectric substrate, and a 36 ° rotated Y-cut lithium tantalate (LiTaO ₃ ) substrate having a diameter of 4 inches (100 mm) is prepared. The piezoelectric substrate was finished to have a surface roughness of 0.13 μm by double-sided rough polishing so that the thickness of the piezoelectric substrate was 160 μm.

Then, a conductive ultraviolet curable adhesive mainly composed of epoxy was spin-coated on the alumina substrate and uniformly applied onto the bonded surface.
Further, the bonding surface of the LiTaO ₃ substrate is washed and the adhesive is applied in the same manner, and the adhesive application surface of the alumina substrate and the adhesive application surface of the LiTaO ₃ substrate are set at a pressure of 1 × 10 ⁻³ mbar. Bonded together under vacuum.

Next, the bonded substrate was irradiated with ultraviolet rays having an illuminance of 50 mW / cm ² for 5 minutes to temporarily cure the adhesive. At this time, the adhesive layer was uniformly 5 μm in thickness within the bonded substrate surfaces.

Next, curing was performed at a temperature of 65 ° C. for 2 hours while cooling the substrate to a room temperature while irradiating an ionizer on the substrate on which the alumina substrate and the LiTaO ₃ substrate were bonded.
When the warpage of the composite piezoelectric substrate was measured at an ambient temperature of 23 ° C., it was 30 μm.
Further, when the surface potential of the LiTaO ₃ substrate portion of the composite piezoelectric substrate composed of the alumina substrate and the LiTaO ₃ substrate was measured with a surface potentiometer, the surface potential was 0 (V).

Then, after chamfering the composite piezoelectric substrate, about 0.5 mm of the outer periphery of the LiTaO ₃ substrate which is a piezoelectric substrate was scraped off with a special chamfering wheel. Next, the surface side (the side opposite to the bonding surface) of the LiTaO ₃ substrate is scraped off by 110 μm by lapping and grinding, and then the composite piezoelectric substrate is cured at 120 ° C. for 2 hours while being irradiated with an ionizer from the beginning. And cooled to room temperature.

Further, the thickness of the LiTaO ₃ substrate was set to 30 μm by polishing.
When the warpage of the composite piezoelectric substrate was measured at an ambient temperature of 23 ° C., it was 40 μm. Further, when the surface potential of the LiTaO ₃ substrate portion of the composite piezoelectric substrate of the alumina substrate and the LiTaO ₃ substrate was measured with a surface potentiometer, the surface potential was 0 (V).
Further, when the inside of the wafer surface was observed with a microscope, no cracks occurred in the LiTaO ₃ substrate portion.

Further, while irradiating the composite piezoelectric substrate with an ionizer, the composite piezoelectric substrate was heated at a temperature of 180 ° C. for 2 hours and cooled to room temperature.
The warpage of this composite piezoelectric substrate was measured at an ambient temperature of 23 ° C. and found to be 45 μm.
Further, when the surface potential of the LiTaO ₃ substrate portion of the composite piezoelectric substrate of the alumina substrate and the LiTaO ₃ substrate was measured with a surface potentiometer, the surface potential was 0 (V).
Further, when the inside of the wafer surface was observed with a microscope, no cracks occurred in the LiTaO ₃ substrate portion.

(Comparative example)
It has a diameter of 4 inches (100 mm) and a thickness of 215 μm. The surface roughness Ra of the bonded surface and the opposite surface is 0.3 μm, the Young's modulus is 340 GPa, and the conductivity is 1 × 10. ^An alumina substrate having ⁻¹⁵ [Ω ⁻¹ · cm ⁻¹ ] was prepared.
Moreover, the electrical conductivity is 1 × 10 ⁻¹⁴ [Ω ⁻¹ · cm ⁻¹ ] as a piezoelectric substrate, and a 36 ° rotated Y-cut lithium tantalate (LiTaO ₃ ) substrate having a diameter of 4 inches (100 mm) is prepared. The piezoelectric substrate was finished to have a surface roughness of 0.13 μm by double-sided rough polishing so that the thickness of the piezoelectric substrate was 160 μm.

Then, a conductive ultraviolet curable adhesive mainly composed of epoxy was spin-coated on the alumina substrate and uniformly applied onto the bonded surface.
Further, the bonding surface of the LiTaO ₃ substrate is washed and the adhesive is applied in the same manner, and the adhesive application surface of the alumina substrate and the adhesive application surface of the LiTaO ₃ substrate are set at a pressure of 1 × 10 ⁻³ mbar. Bonded together under vacuum.

Next, the bonded substrate was irradiated with ultraviolet rays having an illuminance of 50 mW / cm ² for 5 minutes to temporarily cure the adhesive. At this time, the adhesive layer was uniformly 5 μm in thickness within the bonded substrate surfaces.

Next, the substrate on which the alumina substrate and the LiTaO ₃ substrate were bonded together was cured at a temperature of 65 ° C. for 2 hours, and then cooled to room temperature.
When the warpage of the composite piezoelectric substrate was measured at an ambient temperature of 23 ° C., it was 40 μm.
Further, when the surface potential of the LiTaO ₃ portion of the composite piezoelectric substrate composed of the alumina substrate and the LiTaO ₃ substrate was measured with a surface potentiometer, the surface potential was 0.8 (kV).

Then, after chamfering the composite piezoelectric substrate, about 0.5 mm of the outer periphery of the LiTaO ₃ substrate which is a piezoelectric substrate was scraped off with a special chamfering wheel. Next, the surface side (the side opposite to the bonding surface) of the LiTaO ₃ substrate was scraped off by 110 μm by lapping and grinding, and then this composite piezoelectric substrate was cured at a temperature of 120 ° C. for 2 hours and then cooled to room temperature.

Further, the thickness of the LiTaO ₃ substrate was set to 30 μm by polishing.
When the warpage of the composite piezoelectric substrate was measured at an ambient temperature of 23 ° C., it was 400 μm. Further, when the surface potential of the LiTaO ₃ substrate portion of the composite piezoelectric substrate of the alumina substrate and the LiTaO ₃ substrate was measured with a surface potentiometer, the surface potential was 3 (kV).
Further, when the inside of the wafer surface was observed with a microscope, a crack having a total length of 50 mm occurred in the outer peripheral portion of the LiTaO ₃ substrate.

Further, the composite piezoelectric substrate was heated at a temperature of 180 ° C. for 2 hours and then cooled to room temperature.
When the warpage of the composite piezoelectric substrate was measured at an ambient temperature of 23 ° C., it was 800 μm. Further, when the surface potential of the LiTaO ₃ substrate portion of the composite piezoelectric substrate of the alumina substrate and the LiTaO ₃ substrate was measured with a surface potentiometer, the surface potential was 6 (kV).
Further, when the inside of the wafer surface was observed with a microscope, cracks in the outer peripheral portion of the LiTaO ₃ substrate were 120 mm in total length.

  As described above, according to the composite piezoelectric substrate manufacturing method of the present invention, it is possible to provide an inexpensive composite piezoelectric substrate in which the amount of increase in warping after heat treatment is small and the generation of cracks is suppressed.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. It is contained in the technical range.

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric substrate, 2 ... Insulator board | substrate, 3 ... Adhesive agent, 3 '... Hardened adhesive agent, 4 ... Bonded board | substrate, 5 ... Composite piezoelectric substrate.

Claims (3)

At least a method for manufacturing a composite piezoelectric substrate in which a piezoelectric substrate and an insulator substrate are bonded together with an adhesive, and the adhesive is cured by performing a heat treatment on the bonded substrate, the insulator A composite piezoelectric material characterized in that a substrate having a conductivity of 1 × 10 ⁻¹⁴ [Ω ⁻¹ · cm ⁻¹ ] or less is used as a substrate, and the curing of the adhesive by the heat treatment is performed while performing a charge removal treatment. A method for manufacturing a substrate.   2. The method of manufacturing a composite piezoelectric substrate according to claim 1, wherein the insulator substrate is composed mainly of alumina. _{3. The} method for manufacturing a composite piezoelectric substrate according to claim 1, wherein the piezoelectric substrate is made of any one of LiTaO ₃ , LiNbO ₃ , and Li ₂ B ₄ O ₇ .

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