JP2017135551A - Method for manufacturing piezoelectric composite substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a piezoelectric composite substrate for a simple and efficient surface acoustic wave device with high characteristics, without the necessity of a high facility investment.SOLUTION: When manufacturing a composite substrate by bonding a monocrystalline substrate of lithium tantalate monocrystalline or lithium niobate monocrystalline with a silicon substrate lower than the substrate in thermal expansion coefficient through an adhesive layer together at a room temperature, the substrates are bonded together with an organic adhesive layer with a thickness of 10-40 μm by an epoxy resin adhesive including ceramic particles. After that, the monocrystalline substrate of lithium tantalate monocrystalline or lithium niobate monocrystalline is ground to a thickness of no larger than 1/5 of the support substrate, whereby the warp of the lithium tantalate monocrystalline or lithium niobate monocrystalline larger than the support substrate in thermal expansion can be suppressed, and the delamination or cracking thereof can be prevented.SELECTED DRAWING: None

Description

The present invention relates to a method for manufacturing a piezoelectric composite substrate, and more specifically, manufacture of a piezoelectric composite substrate obtained by bonding a piezoelectric substrate used for a surface acoustic wave device and a support substrate via an organic adhesive layer. Regarding the method.

A SAW (Surface Acoustic Wave) filter is known as a device using a surface acoustic wave. This SAW filter is used for mobile phones and smartphones, is used to select an arbitrary frequency, and is an important component for communication. A substrate used when manufacturing the SAW filter is a piezoelectric material such as lithium tantalate (LiTaO ₃ , hereinafter referred to as LT) or lithium niobate (LiNbO ₃ , hereinafter referred to as LN). The body is used.

Comb electrodes made of Al or Al alloy are formed on these substrates, and the frequency to be selected is determined by the distance between the electrodes. The interval between the comb-shaped electrodes is on the order of several microns, and LT having a good temperature characteristic is generally used. However, the coefficient of linear expansion of LT is as large as 16 × 10 ⁻⁶ / K in the X-axis direction and 4.1 × 10 ⁻⁶ K in the Y-axis direction. As a result, there is a possibility that the frequency passing region will move, resulting in a problem that crosstalk and communication cannot be performed. In addition, exposure to heat changes may cause internal stress and cause cracks or defects.

  On the other hand, smart phones and mobile phones have been highly integrated, and the above SAW filters have been modularized together with amplifiers and have been exposed to high temperatures. As described above, a problem due to temperature rise has become apparent, and even when exposed to high temperatures, the frequency pass region of the SAW filter does not change, and the temperature characteristics are required to be stable.

  Therefore, various studies have been made to solve these problems. For example, Patent Document 1 proposes a composite substrate in which a relatively inexpensive silicon having a thermal expansion coefficient smaller than that of LN or LT is bonded and bonded to an LN or LT substrate as a support substrate. Patent Document 2 proposes a substrate in which sapphire is bonded to an LN or LT substrate as a support substrate. Further, Patent Document 3 proposes a substrate in which a substrate having a small linear expansion coefficient is attached to an LN or LT substrate with an organic adhesive. Patent Document 4 proposes a composite substrate in which a piezoelectric element is bonded to a substrate having a linear expansion coefficient smaller than that of the piezoelectric element by heat treatment. Furthermore, Patent Document 5 proposes bonding of a substrate and LT and LN by room temperature bonding.

JP 2004-096677 A JP 2004-186868 A JP 2001-053579 A Japanese Patent No. 3435789 Japanese Patent No. 3777482

  However, silicon is inexpensive and has a linear expansion coefficient lower than that of LT, but has conductivity, and stray capacitance is generated, which causes a problem in stability as a device. For this reason, as described in Patent Document 1, simply bonding a silicon substrate does not result in a composite substrate with little fluctuation due to temperature. Moreover, since sapphire is an expensive substrate, as described in Patent Document 2, if sapphire is used as a support substrate, excessive costs are incurred, which is not preferable.

  On the other hand, the organic adhesive used in Patent Document 3 has a glass transition temperature of 100 ° C. or lower, and is softened at a temperature of 200 ° C. or higher applied during the manufacture of the SAW filter. There is a concern that this is insufficient. In addition, since wettability, elongation, and the like of the organic adhesive are not taken into consideration, if the crystal to be polished is polished to 35 μm or less, there is a possibility that the unevenness of the adhesive will start and cracks and cracks may occur.

  Further, as described in Patent Document 4, when manufacturing a composite substrate in which a piezoelectric element is bonded to a substrate having a coefficient of linear expansion smaller than that of the piezoelectric element by heating, bonding to the substrate returns to room temperature. However, there is a problem that the substrate warps due to the difference in linear expansion coefficient between the piezoelectric element and the substrate. Furthermore, as described in Patent Document 5, in the case of using a high vacuum apparatus, in addition to a long tact time and low productivity, the apparatus is expensive, so there is a problem in terms of cost.

  The present invention has been made in view of the above problems, and is capable of manufacturing a piezoelectric composite substrate capable of manufacturing a piezoelectric composite substrate suitable for a surface acoustic wave device having excellent frequency temperature characteristics at a lower cost. It aims to provide a method.

  As a result of diligent studies to achieve the above-mentioned object, the present inventor has formed an organic adhesive layer between a lithium tantalate single crystal or a single crystal substrate of lithium niobate single crystal and a silicon substrate having a lower thermal expansion coefficient than the substrate. Then, when producing a composite substrate by bonding at room temperature, an adhesive layer is applied with a thickness of 10 μm or more and 40 μm or less with an epoxy resin adhesive containing ceramic particles, bonded, and then the lithium tantalate single crystal Alternatively, a warp of a lithium tantalate single crystal or a lithium niobate single crystal having a thermal expansion larger than that of the support substrate can be suppressed by polishing a single crystal substrate of lithium niobate single crystal to a thickness of 1/5 or less of the support substrate. The present invention was completed by finding that peeling and cracking can be prevented.

That is, the first invention of the present invention is
A method for producing a piezoelectric composite substrate obtained by bonding a lithium tantalate single crystal or lithium niobate single crystal piezoelectric substrate and a support substrate made of silicon via an organic adhesive layer,
Process A: An organic adhesive layer is applied to a thickness of 10 μm or more and 40 μm or less with a single crystal substrate of lithium tantalate single crystal or lithium niobate single crystal and a support substrate made of silicon with an epoxy resin adhesive containing ceramic particles. And then bonding step B: a step of polishing the lithium tantalate single crystal or lithium niobate single crystal single crystal substrate of the bonded substrate obtained in step A to a thickness of 1/5 or less of the supporting substrate. A method of manufacturing a piezoelectric composite substrate, comprising:

  In the first invention of the present invention, the ceramic is preferably at least one selected from the group consisting of alumina, aluminum nitride, zirconia, and magnesium oxide.

Hereinafter, specific embodiments of the present invention will be described in detail. In addition, this invention is not limited to the following embodiment, In the range which does not change the summary of this invention, it can change suitably.

[1. Composite board]
The composite substrate according to the present embodiment is a composite substrate having a configuration including a piezoelectric substrate, a support substrate, and an organic adhesive layer for bonding them together.

Here, examples of the piezoelectric substrate include a substrate capable of propagating an elastic wave (particularly, a surface acoustic wave). The material of the piezoelectric substrate is lithium tantalate, lithium niobate, lithium niobate-lithium tantalate solid solution. Single crystal, lithium borate, langasite, quartz, etc. are mentioned. In particular, in surface acoustic wave device applications used for SAW filters, lithium tantalate single crystals or lithium niobate single crystals can be suitably used.

In addition, examples of the material of the support substrate include materials having a smaller thermal expansion coefficient than that of the piezoelectric substrate, such as silicon, sapphire, aluminum nitride, alumina, borosilicate glass, quartz glass, and quartz. However, in terms of cost and quality stability. The silicon substrate can be most preferably used.

The piezoelectric substrate is not particularly limited as long as it is a substrate of the above-mentioned material. For example, the size of the piezoelectric substrate is preferably a substrate having a diameter of 50 μm to 150 mm and a thickness of 150 μm to 500 μm. Can be used.

The support substrate is not particularly limited as long as it is a substrate of the above-mentioned material. For example, the size of the support substrate is preferably a substrate having a diameter of 50 μm to 150 mm and a thickness of 150 μm to 500 μm. Can be used for

The piezoelectric substrate is further polished after the first prepared substrate is bonded to the support substrate via an adhesive layer, and the thickness of the piezoelectric substrate as the final composite substrate is equal to 1 of the thickness of the support substrate. The thickness is preferably / 5 or less, and more preferably 1/10 or less.

Specifically, the thickness of the piezoelectric substrate is preferably 5 μm or more and 100 μm. Moreover, it is more preferable to set it as 5 micrometers or more and 30 micrometers or less. If it is thinner than 5 μm, cracks may occur when polishing, and if it is thicker than 100 μm, the composite substrate may crack when heated, such being undesirable.

  As an adhesive for forming the organic adhesive layer, an epoxy resin adhesive containing ceramic particles is used. The adhesive used in the present invention is preferably an epoxy resin adhesive containing ceramic particles in order to have excellent heat resistance and at the same time maintain flexibility, and the ceramic particles further include alumina, aluminum nitride, zirconia, It is preferably at least one selected from the group of magnesium oxide.

In the surface acoustic wave device application used for the SAW filter, which is an application of the piezoelectric composite substrate of the present invention, the temperature of the SAW device may exceed 100 ° C. due to modularization, and measures to prevent frequency change are required. Therefore, it has been investigated to attach a piezoelectric substrate to a support substrate made of silicon having a low thermal expansion coefficient to suppress the elongation of the piezoelectric substrate, but usually, an adhesive is applied as a means to easily suppress the elongation of the substrate. A method of curing at room temperature or by heating and pasting to the back surface of the piezoelectric substrate is performed.

Commonly used adhesives are UV paints with excellent mass productivity, or organic epoxy adhesives with strong adhesive strength, but these resins have a glass transition temperature of around 100 ° C and are also heat resistant. It is a 150 degreeC level. It is said that heat of 200 to 300 ° C. is applied when an Al electrode is formed during the manufacture of a SAW filter, and the adhesive causes discoloration, volume change, decrease in adhesion, etc. due to thermal deterioration, and is used for a SAW filter. Not suitable for bonded substrates.

Therefore, we examined the use of epoxy resin adhesives containing ceramic particles that are resistant to heat and have excellent adhesion to glass, and obtained knowledge that alumina, aluminum nitride, zirconia, magnesium oxide, etc. are suitable as the ceramics to be included. It was. It is important to dry and cure at room temperature in order to attach crystals with different linear expansion coefficients. If the temperature exceeds 100 ° C. in the drying step during the production of the piezoelectric substrate, the bonded substrate may be warped with a substrate having a low linear expansion coefficient as a convex surface. Therefore, in the present invention, in order to dry at room temperature, an adhesive that causes a dehydration reaction in which a reaction proceeds by desorption of water molecules between ceramic molecules is desirable, and an epoxy resin containing ceramics such as alumina particles. The result that an adhesive was preferable was obtained.

[2. Manufacturing method of composite substrate]
Next, a method for manufacturing the piezoelectric composite substrate according to the present embodiment will be described. The method for manufacturing the piezoelectric composite substrate according to the present embodiment is as follows.
A method for producing a piezoelectric composite substrate obtained by bonding a lithium tantalate single crystal or lithium niobate single crystal piezoelectric substrate and a support substrate made of silicon via an organic adhesive layer,
Process A: An organic adhesive layer is applied to a thickness of 10 μm or more and 40 μm or less with a single crystal substrate of lithium tantalate single crystal or lithium niobate single crystal and a support substrate made of silicon with an epoxy resin adhesive containing ceramic particles. And then bonding step B: a step of polishing the lithium tantalate single crystal or lithium niobate single crystal single crystal substrate of the bonded substrate obtained in step A to a thickness of 1/5 or less of the supporting substrate. A method of manufacturing a piezoelectric composite substrate, comprising:

Below, each process is demonstrated in detail.
(Process A)
In step A, the piezoelectric substrate and the support substrate are bonded together with an inorganic adhesive.
The piezoelectric substrate and the supporting substrate described above are prepared. When a substrate that is usually marketed is mirror-polished, the average surface roughness (Ra) of the substrate surface is on the order of several nm. In order to increase the bonding strength, a roughening treatment can be performed by a known method such as machining or blasting.

Next, an epoxy resin adhesive containing ceramic particles is applied to either the prepared piezoelectric substrate or support substrate. As described above, the epoxy resin adhesive containing ceramic particles is an epoxy resin adhesive containing at least one kind of ceramic particles selected from the group of alumina, aluminum nitride, zirconia, and magnesium oxide. The thickness of the organic adhesive layer is in the range of 10 μm to 40 μm. The method for applying the organic adhesive is not particularly limited, and can be uniformly applied to a predetermined film thickness using, for example, an applicator. The method for bonding the piezoelectric substrate and the support substrate is, for example, by pressing at a pressure of about 1.25 MPa in the center of the piezoelectric substrate or the support substrate and then curing the epoxy resin adhesive at room temperature. A laminated substrate can be manufactured.

(Process B)
Step B is a step of polishing the piezoelectric substrate of the bonded substrate obtained in Step A to a thickness of 1/5 or less of the support substrate.

Since it is used as a substrate suitable for surface acoustic wave devices with excellent temperature characteristics, the thickness of the piezoelectric substrate is less than the thickness of the support substrate in order to suppress expansion of the piezoelectric substrate by strong adhesion to the support substrate. It is necessary to make it thinner. The thickness of the piezoelectric substrate as the final composite substrate is preferably 1/5 or less of the thickness of the support substrate, and more preferably 1/10 or less. Specifically, the thickness of the piezoelectric substrate is preferably 5 to 100 μm, and more preferably 5 to 30 μm. If the thickness of the piezoelectric substrate is less than 5 μm, cracks may occur when polishing, and if it is more than 100 μm, the composite substrate may crack when heated, such being undesirable.

The piezoelectric composite substrate thus obtained has a piezoelectric substrate firmly bonded to a support substrate, suppresses fluctuations in the frequency characteristics of the piezoelectric substrate due to temperature changes, and is used for surface acoustic wave devices having excellent temperature characteristics. It can be used as a suitable substrate.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

[Example 1]
First, a silicon substrate having an orientation flat portion (OF portion), a diameter of 100 mm (4 inches), and a thickness of 350 μm was prepared as a support substrate. In addition, a lithium tantalate substrate having an OF portion, a diameter of 100 mm, and a thickness of 350 μm was prepared as a piezoelectric substrate. To the prepared silicon substrate, 3 g of “Duralco 4700” manufactured by Duralco was dropped as an epoxy resin adhesive containing alumina particles. Next, a lithium tantalate substrate is placed from directly above, a 1 kg load is applied, an adhesive is spread over the entire surface of the substrate to a thickness of 25 μm, and then dried in the atmosphere at a temperature of 90 ° C. for 1 hour. And cured.

Then, only the lithium tantalate substrate among the produced bonded substrates was mirror-polished to 40 μm by polishing to obtain a piezoelectric composite substrate. Thereafter, the obtained substrate was heated and dried at a temperature of 175 ° C. for 1 hour to completely cure the adhesive.

The piezoelectric composite substrate obtained as described above was evaluated as follows.
The piezoelectric composite substrate was placed in an electric furnace, heated to 280 ° C. at a rate of 5 ° C./min, and kept at 280 ° C. for 2 hours. Thereafter, the temperature was returned to room temperature, and the appearance was observed. As a result, the adhesive layer was not changed.

A compressive stress of 500 kg was applied using a sample having the same thermal history, but the piezoelectric composite substrate did not peel off. Moreover, although the same sample was heated to 200 degreeC and the curvature was measured, curvature was not observable.

[Comparative Example 1]
The same piezoelectric substrate and supporting substrate as in Example 1 were prepared, and an epoxy resin organic adhesive (made by Taiyo Wire Mesh Co., Ltd.) “DURALCO 4461P” containing no ceramic particles as an adhesive was applied to a silicon substrate with a thickness of 25 μm. Otherwise, a piezoelectric composite substrate was obtained in the same manner as in Example 1. As a result of evaluation in the same manner as in Example 1, the adhesive layer turned dark brown, and the piezoelectric composite substrate peeled off when compressive stress was applied.

[Comparative Example 2]
A UV adhesive was applied to a silicon substrate with a thickness of 2 μm and bonded to the LT substrate. It was subjected to a heat resistance test at 280 ° C. for 2 hours in the atmosphere. When the appearance was taken out and the appearance was observed, the UV adhesive turned dark brown, and the adhesive was unevenly distributed by heat and peeled off when the substrates were pulled together.

Claims (2)

A method for producing a piezoelectric composite substrate obtained by bonding a lithium tantalate single crystal or lithium niobate single crystal piezoelectric substrate and a support substrate made of silicon via an organic adhesive layer,
Process A: An organic adhesive layer is applied to a thickness of 10 μm or more and 40 μm or less with a single crystal substrate of lithium tantalate single crystal or lithium niobate single crystal and a support substrate made of silicon with an epoxy resin adhesive containing ceramic particles. And then bonding step B: a step of polishing the lithium tantalate single crystal or lithium niobate single crystal single crystal substrate of the bonded substrate obtained in step A to a thickness of 1/5 or less of the supporting substrate. Manufacturing method of piezoelectric composite substrate characterized by having 2. The method of manufacturing a piezoelectric composite substrate according to claim 1, wherein the ceramic is at least one selected from the group consisting of alumina, aluminum nitride, zirconia, and magnesium oxide.