JP2010251978A - Method of manufacturing composite piezoelectric substrate and composite piezoelectric substrate - Google Patents

Abstract

In a method of manufacturing a composite piezoelectric substrate in which a piezoelectric substrate and an insulating substrate are bonded together with an adhesive, the amount of warping after heat treatment is small even if an inexpensive insulating substrate is used, and Provided is a method for manufacturing a composite piezoelectric substrate in which variation in warp size is small and stable.
A first step of applying an adhesive to at least one of the main surfaces of the piezoelectric substrate and the insulator substrate; and bonding the piezoelectric substrate and the insulator substrate to each other via the adhesive. A second step of combining, a third step of controlling the temperature of the bonded substrates to be 25 ± 5 ° C., and irradiating the adhesive with ultraviolet light to cure the adhesive; A fourth step of grinding the bonded substrates to a desired thickness, and a fifth step of heating the bonded substrates after the grinding to completely cure the adhesive. A method for manufacturing a composite piezoelectric substrate.
[Selection] Figure 1

Description

  The present invention relates to a method of manufacturing a composite piezoelectric substrate (hereinafter also referred to as a composite piezoelectric substrate), and more particularly to a method of manufacturing a composite piezoelectric substrate used for a surface acoustic wave device or the like.

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

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-shaped electrodes and the acoustic 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 warp after being held at 150 ° C. for 1 hour is approximately 200 μm or less.

Japanese Patent Publication No. 3929983

Here, as an important characteristic required for the composite piezoelectric substrate, there is a small increase in warpage after heat treatment.
This is because heat treatment may be required in the SAW device manufacturing process, and if the substrate warps after such heat treatment, it is difficult to adsorb the composite piezoelectric substrate to the stage in a subsequent dicing process or the like. This is because productivity is greatly reduced.

However, in the invention described in Patent Document 1, a sapphire substrate is used as the support substrate. Since the sapphire substrate has a small coefficient of linear thermal expansion, the warp during heat treatment is small. However, since it is expensive, it is not an inexpensive composite piezoelectric substrate, which has a problem.
In recent years, there has been a demand for an inexpensive composite piezoelectric substrate that further reduces warpage.

  The present invention has been made in view of the above problems, and an inexpensive insulator substrate is used in a method of manufacturing a composite piezoelectric substrate in which a piezoelectric substrate and an insulator substrate are bonded together with an adhesive. A method for manufacturing a composite piezoelectric substrate having a small amount of warp after heat treatment and a small variation in warp size and being stable, and a composite piezoelectric substrate manufactured by the manufacturing method are provided. For the purpose.

  In order to solve the above-described problems, in the present invention, at least a first step of applying an adhesive to the main surface of one of the piezoelectric substrate and the insulator substrate, and the piezoelectric substrate and the insulation through the adhesive A second step of bonding the body substrates to each other, and controlling the temperature of the bonded substrates to be 25 ± 5 ° C., and irradiating the adhesive with ultraviolet light to cure the adhesive A third step, a fourth step of grinding the bonded substrates to a desired thickness, and a fifth step of completely curing the adhesive by heating the bonded substrates after the grinding, A method of manufacturing a composite piezoelectric substrate characterized by comprising:

  In this way, when the adhesive is cured by irradiating with ultraviolet light, the substrate temperature of the bonded substrates is controlled to 25 ± 5 ° C., so that the composite is produced regardless of the material of the substrate used. The amount of warping of the piezoelectric substrate can be made smaller than before.

Here, in the third step, it is preferable to control the temperature change of the bonded substrates when irradiated with ultraviolet light to be within ± 1 ° C.
In this way, by controlling the temperature change of the bonded substrates when irradiated with ultraviolet light to be within ± 1 ° C., the amount of warpage of the composite piezoelectric substrate to be manufactured can be made more than before. It can be surely small.

In the fifth step, it is preferable to remove a grinding strain layer generated by grinding before the heating.
In this way, by removing the grinding strain layer containing many defects generated by grinding before the heat treatment for completely curing the adhesive, it has a desired thickness and a small amount of warpage. A high quality composite piezoelectric substrate can be manufactured.

The piezoelectric substrate is preferably made of LiTaO ₃ or LiNbO ₃ .
As described above, the piezoelectric substrate made of either LiTaO ₃ or LiNbO ₃ has a large electromechanical coupling coefficient, and the temperature fluctuation of the operating frequency is suppressed by the effect of the combined piezoelectric substrate. An inexpensive composite piezoelectric substrate can be provided.

Further, in the fifth step, the bonded substrate is introduced into a heating chamber, the temperature in the chamber when the adhesive is completely cured is 80 ° C. or more, and the substrate of the bonded substrate is It is preferable to control the temperature unevenness to be ± 1 ° C.
Thus, the adhesive can be reliably cured completely by setting the temperature of the heating chamber for curing the adhesive to 80 ° C. or higher. In addition, by controlling the temperature unevenness of the bonded substrates to ± 1 ° C. and heating and curing, the adhesive can be cured more reliably, and a stable composite piezoelectric substrate Can be manufactured.

  According to the present invention, there is provided a composite piezoelectric substrate manufactured by the composite piezoelectric substrate manufacturing method according to the present invention, wherein the warp value when the substrate temperature is 25 ± 5 ° C. is 100 μm. Provided is a composite piezoelectric substrate characterized by the following.

  As described above, according to the composite piezoelectric substrate manufacturing method of the present invention, a composite piezoelectric substrate having a smaller warp than the conventional one can be obtained. The combined piezoelectric substrate manufactured by the piezoelectric substrate can have a very small warp value of 100 μm or less when the substrate temperature is 25 ± 5 ° C.

  As described above, according to the composite piezoelectric substrate manufacturing method of the present invention, a composite piezoelectric substrate with a small amount of warpage can be manufactured stably and with high yield. In addition, an inexpensive composite piezoelectric substrate with a small amount of warp can be obtained.

It is the figure which showed an example of the outline of the composite piezoelectric substrate of this invention. It is the figure which showed the relationship between the board | substrate temperature of the bonded board | substrate at the time of ultraviolet light irradiation for adhesive agent hardening | curing, and the amount of warping of the composite piezoelectric substrate. This shows the relationship between the amount of change in the temperature of the bonded substrate and the amount of warping in the composite piezoelectric substrate when the substrate temperature of the bonded substrate is fixed at the time of ultraviolet light irradiation for curing the adhesive. It is a figure.

Hereinafter, the present invention will be described more specifically.
As described above, in the method of manufacturing a composite piezoelectric substrate in which a piezoelectric substrate and an insulating substrate are bonded together with an adhesive, even if an inexpensive insulating substrate is used, the amount of warpage after heat treatment is small. In addition, there has been a demand for the development of a composite piezoelectric substrate having a small and stable variation in warp size and a composite piezoelectric substrate manufactured by the manufacturing method.

  Therefore, the present inventor has intensively studied the cause of the warp becoming large after heat treatment.

As a result, it has been found that the size of the warpage of the composite piezoelectric substrate produced by bonding the piezoelectric substrate and the insulating substrate through an adhesive greatly varies depending on the curing conditions of the adhesive.
Therefore, if the curing conditions of the adhesive are not stabilized, the warpage of the composite piezoelectric substrate that has been completed will not only have large variations, but it will also not be possible to have a good warp. .

In view of this, the inventors have intensively studied adhesive curing conditions for producing a composite piezoelectric substrate that can reduce the size of the warp and have a small variation between lots with a high yield.
And this inventor paid attention to the substrate temperature and temperature variation of the board | substrate bonded together when irradiating an ultraviolet light and hardening an adhesive agent, and examined variously.

  As a result, as shown in FIG. 2, it was discovered that it is important to set the substrate temperature of the substrate on which the piezoelectric substrate and the insulator substrate are bonded to each other at 25 ± 5 ° C. during the ultraviolet light irradiation for curing the adhesive. The present invention has been completed.

Hereinafter, the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto. FIG. 1 is a view showing an example of a composite piezoelectric substrate of the present invention.
The composite piezoelectric substrate 10 of the present invention is obtained by bonding at least the piezoelectric substrate 11 and the insulator substrate 12 via the adhesive 13, and the composite piezoelectric substrate 10 has a substrate temperature. Is a warp value of 100 μm or less at 25 ± 5 ° C.

  In this way, if the piezoelectric substrate is a composite piezoelectric substrate having a warp value of 100 μm or less when the substrate temperature is 25 ± 5 ° C., for example, in the SAW device manufacturing process, handling becomes difficult due to the warpage of the substrate. Can be prevented, and the problem of a significant reduction in productivity can be avoided.

  The composite piezoelectric substrate of the present invention as described above can be manufactured by the following manufacturing method. However, of course, it is not limited to this.

First, at least a piezoelectric substrate and an insulator substrate are prepared.
As the prepared piezoelectric substrate and insulator substrate, those having desired physical properties can be prepared. However, the piezoelectric substrate can be made of either LiTaO ₃ or LiNbO ₃ . Further, in the present invention, the warp can be reduced without necessarily using an expensive substrate such as a sapphire substrate as the insulator substrate to be prepared.
If the piezoelectric substrate is made of LiTaO ₃ or LiNbO ₃ , these are crystalline materials having a large electromechanical coupling coefficient, so that the bandwidth as a frequency selection filter is wide, the insertion loss is small, and the operating frequency A composite piezoelectric substrate capable of manufacturing a SAW device in which the temperature fluctuation is suppressed can be manufactured.
In addition, a piezoelectric substrate made of these piezoelectric crystal materials can be obtained with a high quality by growing these single crystal rods by, for example, the Czochralski method and slicing them to a desired thickness. Also, the substrate orientation can be appropriately selected according to the type of piezoelectric crystal material, the use of the SAW device, desired characteristics, such as 36 ° rotation Y-cut, 42 ° rotation Y-cut, 48 ° rotation Y-cut, etc. .

As a first step, an ultraviolet curable adhesive is applied to at least one main surface of the prepared piezoelectric substrate and insulator substrate.
The ultraviolet curable adhesive is not particularly limited as long as it is cured by being irradiated with ultraviolet rays. For example, an adhesive mainly composed of epoxy methacrylate or an epoxy resin having a dioxy structure can be used.
Moreover, although the general application | coating method can be used for the coating method, there exist spin coating etc., for example.

  Thereafter, as a second step, the piezoelectric substrate and the insulator substrate are bonded to each other via the previously applied adhesive to obtain a bonded substrate.

And as a 3rd process, the substrate temperature of the board | substrate bonded together is controlled so that it may become 25 +/- 5 degreeC, and an ultraviolet light is irradiated and hardened | cured to an adhesive agent.
In this way, by controlling the substrate temperature of the bonded substrates at the time of ultraviolet light irradiation to be 25 ± 5 ° C., the adhesive can be cured at room temperature, and a composite piezoelectric substrate with a small warp Can be manufactured with good yield.

  Here, when the bonded substrate is irradiated with ultraviolet light to cure the adhesive, the substrate temperature is 50 ° C. or more from room temperature (100 ° C. when the illuminance is strong) unless the bonded substrate and its surroundings are cooled. To the extent). Therefore, in order to set the substrate temperature to 25 ± 5 ° C. as in the present invention, the periphery of the bonded substrates is cooled so that the substrate temperature becomes 25 ± 5 ° C. when irradiated with ultraviolet light. Control is required. Thus, it has been found that when the adhesive is cured at a high temperature such as 80 ° C. or higher, warping occurs when the temperature returns to room temperature.

As shown in FIG. 2, when the temperature of the substrate at the time of curing is outside the range of 25 ± 5 ° C., the warpage of the combined piezoelectric substrate becomes large when the temperature returns to room temperature at the end of manufacture. For this reason, at the time of ultraviolet light irradiation, it is necessary to control the temperature of the bonded substrates so as to fall within 25 ± 5 ° C.
Here, FIG. 2 is a diagram showing the relationship between the substrate temperature of the bonded substrates during ultraviolet light irradiation and the amount of warping of the composite piezoelectric substrate. In FIG. 2, the temperature change of the substrate during ultraviolet light irradiation was controlled to be within 0.5 ° C. In FIG. 2, the warping direction of the composite piezoelectric substrate is such that the + direction is concave on the piezoelectric substrate side (convex on the insulator substrate side), and the-(minus) direction is on the insulator substrate side. This is the case when it becomes concave (convex on the piezoelectric substrate side).

Further, in this third step, the temperature change of the bonded substrates when irradiated with ultraviolet light can be controlled to be within ± 1 ° C.
As shown in FIG. 3, it has been found that the amount of warpage of the substrate can be further reduced by suppressing the temperature change of the substrate during irradiation with ultraviolet light to 1 ° C. or less. Here, FIG. 3 shows the relationship between the amount of change in the substrate temperature of the bonded substrates during ultraviolet light irradiation and the amount of warping of the composite piezoelectric substrate (the substrate temperature at the start of irradiation is constant at 25 ° C.). FIG.
In this way, by suppressing the temperature change of the bonded substrates during ultraviolet light irradiation to 1 ° C. or less, a composite piezoelectric substrate having a smaller warp value can be stably manufactured.

  Thereafter, as a fourth step, the bonded substrate is mainly ground on the piezoelectric substrate side to a desired thickness. This step can be performed as usual.

  Then, as the fifth step, the bonded substrates after grinding are heated to completely cure the adhesive. Thereby, a composite piezoelectric substrate can be manufactured.

Here, before the heating for complete curing, the grinding strain layer generated by grinding can be removed.
The grinding strain layer can be removed by polishing, for example.
Thus, by removing the grinding strain layer having many defects before heating, a composite piezoelectric substrate composed of a piezoelectric substrate having good crystallinity can be obtained. Further, by removing the grinding strain layer by polishing or the like, the bonded piezoelectric substrate can be processed to a desired thickness with high accuracy, and a high flatness and a desired thickness are combined. A piezoelectric substrate can be manufactured efficiently.

Further, in the fifth step, the bonded substrate is introduced into the heating chamber, the temperature in the chamber when the adhesive is completely cured is set to 80 ° C. or more, and the temperature unevenness of the bonded substrate is reduced. It can be controlled to be ± 1 ° C.
As a result, the adhesive can be stably and surely completely cured. Then, by setting the temperature unevenness of the bonded substrates at the time of heating to ± 1 ° C., the adhesive can be more completely cured without unevenness, and a composite piezoelectric substrate with a smaller amount of warpage can be obtained. Can be manufactured.

  According to the method for manufacturing a composite piezoelectric substrate of the present invention as described above, a composite piezoelectric substrate having a smaller amount of warp and a stable amount of warp can be manufactured with high yield. At this time, warping can be suppressed without necessarily using an expensive insulator substrate.

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these.
Example 1
An alumina substrate having a diameter of 4 inches (100 mm), a thickness of 215 μm, a surface roughness Ra of each of the bonded surface and the opposite surface is 0.3 μm, Young's modulus is 340 GPa, and resistivity is 10 ¹⁵ Ωcm. Prepared as an insulator substrate.
In addition, as a piezoelectric substrate, a 36-degree rotated Y-cut lithium tantalate (LiTaO ₃ ) substrate having a diameter of 4 inches (100 mm) is prepared, and rough roughening of the front and back surfaces is performed by double-sided rough polishing so that the thickness of the piezoelectric substrate becomes 160 μm. Was finished to be 0.13 μm.

And the ultraviolet curing adhesive which has an epoxy methacrylate as a main component on this alumina substrate was apply | coated uniformly on the bonding surface by spin coating.
Further, the bonding surface of the LiTaO ₃ substrate was washed, and the above-described adhesive was applied in the same manner, and the adhesive application surface of the alumina substrate and the adhesive application surface of the LiTaO ₃ substrate were bonded together.

Next, the bonded substrate was irradiated with ultraviolet rays having an illuminance of 50 mW / cm ² for 5 minutes to cure the adhesive. At this time, the substrate temperature was controlled so that the substrate temperature of the bonded substrates was 25 ° C. and the temperature change was ± 0.5 ° C., and ultraviolet light was irradiated.
At this time, the thickness of the adhesive layer was uniformly 5 μm within the bonded substrate surface.

Then, after the bonded substrates were chamfered, the surface side of the LiTaO ₃ substrate, which is a piezoelectric substrate, was scraped off by 120 μm, and the thickness of the LiTaO ₃ substrate was adjusted to 30 μm by polishing.
The bonded substrate thus produced is introduced into a chamber heated to 150 ° C., and the adhesive is completely removed by controlling and heating so that the temperature unevenness in the substrate surface becomes ± 0.5 ° C. Cured to produce a composite piezoelectric substrate.

  As a result of evaluating the amount of warpage of the composite piezoelectric substrate produced at 24.5 ° C., the amount of warpage was −30 μm.

(Examples 2, 3, 4, 5 and Comparative Examples 1 and 2)
In Example 1, the substrate temperature at the time of ultraviolet light irradiation was 18 ° C. (Comparative Example 1), 20 ° C. (Example 2), 22 ° C. (Example 3), 28 ° C. (Example 4), 30 ° C. (Example) 5) A composite piezoelectric substrate was manufactured in the same manner as in Example 1 except that the temperature was 32 ° C. (Comparative Example 2), and the amount of warpage was similarly evaluated.

As a result, the amount of warpage of the composite piezoelectric substrate of Example 2 was 165 μm, Example 3 was 85 μm, Example 4 was −140 μm, Example 5 was −210 μm, Comparative Example 1 was 270 μm, and Comparative Example 2 was It was −300 μm.
That is, by keeping the substrate temperature at the time of ultraviolet light irradiation within a range of 20 to 30 ° C. (25 ± 5 ° C.), a combined piezoelectric with a warping amount of 175 to -225 μm which is a range in which handling is not difficult. It has been found that a substrate can be manufactured, and in particular, can be made to ± 100 μm or less.
Conventionally, when ultraviolet light irradiation was performed at about 80 ° C. using an alumina substrate, the amount of warpage was −400 μm or more, which was a significant improvement compared to this.

  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 exhibits the same function and effect. It is included in the technical scope.

  DESCRIPTION OF SYMBOLS 10 ... Composite piezoelectric substrate, 11 ... Piezoelectric substrate, 12 ... Insulator substrate, 13 ... Adhesive.

Claims (6)

At least a first step of applying an adhesive to the main surface of one of the piezoelectric substrate and the insulator substrate;
A second step of bonding the piezoelectric substrate and the insulator substrate to each other via the adhesive;
A third step of controlling the temperature of the bonded substrates to be 25 ± 5 ° C. and irradiating the adhesive with ultraviolet light to cure the adhesive;
A fourth step of grinding the bonded substrates to a desired thickness;
And a fifth step of completely curing the adhesive by heating the bonded substrates after the grinding, and a method for producing a composite piezoelectric substrate.   2. The composite piezoelectric substrate according to claim 1, wherein in the third step, the temperature change of the bonded substrates when irradiated with ultraviolet light is controlled to be within ± 1 ° C. 3. Manufacturing method.   3. The method of manufacturing a composite piezoelectric substrate according to claim 1, wherein, in the fifth step, the grinding strain layer generated by grinding is removed before the heating. 4. The method for manufacturing a composite piezoelectric substrate according to any one of claims 1 to 3, wherein the piezoelectric substrate is made of LiTaO ₃ or LiNbO ₃ .   In the fifth step, the bonded substrate is introduced into a heating chamber, the temperature in the chamber when the adhesive is completely cured is set to 80 ° C. or more, and the substrate temperature unevenness of the bonded substrate 5. The method of manufacturing a composite piezoelectric substrate according to claim 1, wherein the temperature is controlled to be ± 1 ° C. 5.   6. A composite piezoelectric substrate manufactured by the method for manufacturing a composite piezoelectric substrate according to claim 1, wherein the substrate temperature is 25 ± 5 ° C. A composite piezoelectric substrate having a value of 100 μm or less.

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