JP2009021701A - Method of manufacturing piezoelectric substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a piezoelectric substrate to obtain a piezoelectric substrate, while suppressing expansion and contraction due to a temperature change sufficiently with high yield. <P>SOLUTION: A protective base material 12 is provided on one main surface 11a of the piezoelectric substrate 11 made of lithium tantalate, lithium niobate, quartz, lithium tetraborate, zinc oxide, or the like. The other main surface 11b of the substrate 11 is grooved to form a rib 11c at the periphery. A material 16 having a coefficient of linear expansion smaller than that of the substrate 11 is buried to a groove section 15 formed by the grooving by spraying, to remove the protective base material 12. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a piezoelectric substrate, and more particularly to a method for manufacturing a piezoelectric substrate used for a surface acoustic wave device or the like.

A surface acoustic wave (SAW) device is formed by forming a comb-type electrode on a piezoelectric substrate such as a lithium tantalate (LiTaO ₃ ) (LT) substrate or a lithium niobate (LiNbO ₃ ) (LN) substrate. It is a device. This device has the function of an ultra-small bandpass filter that utilizes the electromechanical properties of a piezoelectric body. In the SAW device, the pitch of the comb-shaped electrode on the micron order is sensitively reflected in the filter characteristics. Thermal expansion coefficient of the LT or LN is 6 times that of silicon and (LT approximately 16 × 10 ^-6 / K for silicon of about 2.6 × 10 ^-6 / K, LN about 15 × 10 ^-6 / K) Therefore, when an LT substrate or an LN substrate is used for a SAW device, a change in filter characteristics due to a temperature change becomes a big problem. For this reason, such thermal compensation of the piezoelectric substrate is suppressed or temperature compensation is performed by other methods.

For example, when manufacturing a SAW device, a substrate having a small thermal expansion coefficient is bonded to a piezoelectric substrate to suppress expansion and contraction due to a temperature change of the piezoelectric substrate. Patent Document 1 discloses that an LT substrate and a sapphire substrate are bonded using a direct bonding method. Patent Document 2 discloses that a piezoelectric substrate and a single crystal substrate are bonded using bonding by a solid-layer reaction. Patent Document 3 discloses that an LT (LN) substrate and a silicon substrate are bonded using bonding by hydrophilization treatment and heat treatment.
JP 2004-343359 A JP-A-9-208399 Japanese Patent No. 2607199

  2. Description of the Related Art In recent years, in a mobile phone or the like on which a SAW device is mounted, many systems are coexisting, and it is assumed that frequency bands used in these systems are adjacent to each other. In such a case, it is required to make the frequency shift as small as possible (on the order of several MHz). Therefore, it is required for the piezoelectric substrate that the filter characteristics due to temperature change do not change as much as possible. However, the piezoelectric substrate obtained by bonding the substrates having a small thermal expansion coefficient as in the prior art cannot meet the demand for further reducing the frequency shift as described above. Therefore, the present situation is that there is no piezoelectric substrate that can meet the demand for a smaller frequency shift.

  The present invention has been made in view of this point, and an object of the present invention is to provide a method for manufacturing a piezoelectric substrate that can sufficiently suppress expansion and contraction due to a temperature change and obtain a piezoelectric substrate with a high yield.

  The method for manufacturing a piezoelectric substrate of the present invention includes a step of forming a groove on one main surface of a substrate to form a rib on a peripheral portion, and a groove formed by the groove processing, with a linear expansion coefficient of the substrate. And embedding a small first material by thermal spraying.

  According to this method, since the rib is provided at the weakest peripheral portion in the processing when the substrate is thinned, it is possible to prevent damage such as cracking of the substrate when the substrate is thinned. Thereby, expansion and contraction due to temperature change can be sufficiently suppressed, and a piezoelectric substrate can be obtained with high yield.

  In the method for manufacturing a piezoelectric substrate of the present invention, the groove processing includes a step of forming a mask on a peripheral portion of the other main surface of the substrate, and a blasting process on the other main surface of the substrate provided with the mask. And a step of performing a grinding process.

  In the method for manufacturing a piezoelectric substrate of the present invention, it is preferable that the groove processing is performed so as to form a stepped portion having a deeper depth toward the center at the peripheral portion.

  In the method for manufacturing a piezoelectric substrate of the present invention, the material constituting the substrate is preferably selected from the group consisting of lithium tantalate, lithium niobate, crystal, lithium tetraborate, and zinc oxide. .

In the production method of the piezoelectric substrate of the present invention, the substrate is formed of a second material having a linear expansion coefficient of ^{10 × 10 -6 / K~20 × 10} -6 / K, the first material, - It is preferable to have a linear expansion coefficient of 1 × 10 ⁻⁶ / K to 10 × 10 ⁻⁶ / K.

  According to the present invention, a groove is formed on one main surface of a substrate to form a rib on a peripheral portion, and a material smaller than the linear expansion coefficient of the substrate is embedded in the groove formed by the groove processing by thermal spraying. Therefore, expansion and contraction due to temperature change can be sufficiently suppressed, and a piezoelectric substrate can be obtained with high yield.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
In the method for manufacturing a piezoelectric substrate according to the present invention, a groove is formed on one main surface of the substrate to form a rib on a peripheral portion, and the groove formed by the groove processing has a smaller coefficient of linear expansion than the substrate. The material is embedded by thermal spraying.

As the substrate, it is preferable that the linear expansion coefficient to select a material that is ^{10 × 10 -6 / K~20 × 10} -6 / K. Examples of the material constituting the substrate include lithium tantalate, lithium niobate, crystal, lithium tetraborate, and zinc oxide. In addition, when using a board | substrate for a SAW device, in order to exhibit the characteristic as a SAW device, it is necessary to make a board | substrate thin.

  Examples of the electronic device mounted on the piezoelectric substrate include a SAW device. Further, on the other main surface of the substrate, electronic elements and circuit patterns usually used for devices can be listed. In addition, there is no restriction | limiting in particular about the shape and formation method of an electronic element or a circuit pattern.

  When an electronic element or the like is provided on the substrate, it is desirable to use a protective base material. As the protective base material, a material having rigidity capable of supporting and holding the substrate during the thinning process of the substrate can be used. Examples of such a protective substrate include a glass substrate, a metal substrate, a silicon substrate, and a plastic substrate. In addition, the protective base material can be disposed on the electronic element side of the substrate using an adhesive such as hot wax or an adhesive.

  When a groove is formed on one main surface of the substrate to form a rib on the peripheral edge, the groove is formed so that the thickness of the substrate is 50 μm or less. Therefore, the height of the ribs at the peripheral edge is a thickness obtained by subtracting the depth of the groove from the thickness of the substrate. Examples of the grooving include blasting and grinding. The blasting process is performed on the substrate along the adhesive profile between the substrate and the protective substrate in a state where the substrate is supported by the protective substrate. For this reason, even if an adhesive is interposed between the substrate and the protective base material, the substrate can be thinned with high in-plane uniformity. In this case, a mask is formed on the peripheral edge of the other main surface of the substrate, and blasting is performed on the other main surface of the substrate provided with this mask. As this mask, a blast tape or a metal mask can be used. The conditions for blasting and grinding are appropriately set according to the substrate material.

A material smaller than the linear expansion coefficient of the substrate is embedded in the groove formed by the groove processing by thermal spraying. This material is preferably a material having a linear expansion coefficient of −1 × 10 ⁻⁶ / K to 10 × 10 ⁻⁶ / K. Such materials include metals such as Ti, W, Mo, Ta, Si, and alloys thereof; aluminum oxide, silicon oxide, magnesium oxide, zirconium oxide, titanium oxide, silicon carbide, boron carbide, aluminum nitride, aluminum nitride And ceramics such as silicon nitride and a solid solution of these compounds, and a mixture of these metals and compounds may be used. Further, considering that there is no change over time due to oxidation, good electrical insulation, and a small linear expansion coefficient, alumina-based materials (for example, alumina and alumina-silica-based materials) are preferable.

  In a structure in which a sprayed film is formed in a groove provided in a substrate, the thickness of the substrate is very thin, so that the sprayed film functions to maintain the rigidity of the substrate. Therefore, the thickness of the sprayed film is relatively increased in consideration of the rigidity with respect to the substrate, for example, the total thickness of the substrate and the sprayed film is 0.05 mm to 2 mm, particularly 0.2 mm to 0.5 mm. It is preferable to make it. Therefore, the sprayed film suppresses the thermal expansion of the substrate and plays a role as a base of the substrate, that is, a support member for the substrate.

  In the substrate, the sprayed film must be formed in a thick film without cracking or warping while exhibiting a temperature compensation effect for suppressing thermal expansion of the substrate. For example, a film formed by a CVD method or a PVD method exhibits a temperature compensation effect, but since the film formation temperature is relatively high, warping and cracking occur and the defect rate increases. In addition, a film formed by these methods cannot be formed thick enough to serve as a base of a substrate because of a large stress during film formation. Thus, there is a trade-off relationship between the temperature compensation effect and the film stress, and this relationship is influenced by the thickness of the substrate.

  The sprayed film may be composed of one layer or a plurality of layers. By forming the sprayed film with a plurality of layers in this manner, various materials can be combined, so that the linear expansion coefficient of the sprayed film can be easily adjusted. Further, an undercoat (intermediate film) may be provided between the substrate and the sprayed film to improve the adhesion of the sprayed film. Further, the adhesion of the sprayed film may be improved by adjusting the roughness of the sprayed film deposition surface of the groove portion of the substrate. In this case, the material constituting the undercoat is not particularly limited as long as it exhibits the effect of improving the adhesion of the sprayed film.

  After the sprayed film is formed in the groove formed by the groove processing, the sprayed film is ground to smooth the sprayed film surface. The mask is also removed during the grinding process.

  1A to 1F are cross-sectional views for explaining a method of manufacturing a piezoelectric substrate according to an embodiment of the present invention. First, as shown to Fig.1 (a), the board | substrate 11 is prepared and the protective base material 12 is provided on one main surface 11a of the board | substrate. That is, the protective base material 12 is attached on one main surface 11 a of the substrate 11 via the adhesive layer 13.

  Next, as shown in FIG. 1B, a blast tape 14 as a mask is provided on the peripheral edge of the other main surface 11 b of the substrate 11. Next, as shown in FIG. 1 (c), with the blast tape 14 as a mask, the other main surface 11b of the substrate 11 is blasted to form a groove to form ribs 11c at the peripheral edge (mask region). . A region defined by the ribs 11 c becomes the groove 15.

  Here, when grooving is performed on the substrate 11, it is preferable to form a step portion 11d having a deeper depth toward the center at the peripheral portion as shown in FIG. In film formation by thermal spraying, which will be described later, the stress is concentrated on the corners of the groove 15 and the edge of the thermal spray film formed tends to be rolled up. In addition, voids due to overhang are easily formed at the corners of the groove 15. By providing the step portion 11d as described above, it is possible to sufficiently prevent the sprayed film from rolling up and generating voids. Such a stepped portion 11d is formed, for example, by performing a blasting process using a mask having a relatively large width from the periphery and then performing a blasting process again using a mask having a relatively small width from the periphery. Can do. Although FIG. 2 shows a case where the stepped portion has two steps, in the present invention, the number of steps of the stepped portion is not particularly limited.

  Next, as shown in FIG. 1D, a material having a coefficient of linear expansion smaller than that of the substrate 11 is embedded in the grooves 15 formed by the groove processing by thermal spraying. Thereby, the sprayed film 16 is formed in the groove 15. Here, the thermal spraying method uses electric energy (arc, plasma) or combustion energy as a heat source, puts powder or rod-shaped material of the deposit material into this, and sprays it on the surface of the substrate as molten or semi-molten particles. This is a method for forming a film. By adopting the thermal spraying method, it is possible to suppress the thermal influence on the substrate 11 during film formation as much as possible.

  In film formation by the thermal spraying method, when fine particles in a molten or semi-molten state reach the base material, they are rapidly solidified on the substrate 11 and fine cracks are generated in the fine particles. The fine particles having such fine cracks are laminated to form a film. Therefore, the film formed by the thermal spraying method is in a relatively porous state, and therefore the stress after film formation is small. For this reason, it is possible to form a thick film (about several hundred μm) without peeling from the substrate 11. As a result, a thick film without warping can be formed on the substrate 11.

  Next, as shown in FIG. 1E, the sprayed film 16 formed in the groove 15 of the substrate 11 is ground to smooth the surface of the sprayed film 16. By this grinding process, the blast tape 14 as a mask is also removed. Next, as shown in FIG. 1 (f), the protective base material 12 is peeled and removed from the main surface 11 a side of the substrate 11, and the adhesive layer 13 is removed by washing the peeled surface.

  In the method according to the present invention, the rib 11c is provided at the weakest peripheral portion in the processing when the substrate 11 is thinned, so that it is possible to prevent damage such as cracking of the substrate 11 when the substrate 11 is thinned. It becomes. Further, unlike the grinding process, the blasting process used for thinning the substrate 11 follows the profile of the adhesive layer 13 between the substrate 11 and the protective base material 12 in a state where the substrate 11 is supported by the protective base material 12. Is applied to the substrate 11. For this reason, even if the adhesive layer 14 is interposed between the substrate 11 and the protective base material 13, the substrate 11 can be thinned with high in-plane uniformity.

Next, examples performed for clarifying the effects of the present invention will be described.
Example 1
A lithium tantalate substrate (LT substrate) having a linear expansion coefficient of 16 × 10 ⁻⁶ / K, a diameter of 4 inches, and a thickness of 0.25 mm was prepared. In addition, the linear expansion coefficient was measured in the differential expansion mode of the thermomechanical analyzer (TMA-8310) of the system of Thermo Plus 2 (manufactured by Rigaku Corporation) (Industrial Technology Center).

  Next, a glass substrate having a thickness of 5 mm was bonded to the pattern forming side of the LT substrate using hot wax. Next, masking was performed by attaching a blast tape to a peripheral portion 5 mm on one main surface of the LT substrate. Next, the other main surface of the LT substrate was blasted to form a groove portion having a depth of 0.22 mm. As a result, ribs having a height of 0.22 mm were formed on the peripheral edge of the LT substrate, and the thickness of the LT substrate was 30 μm.

Next, mullite (alumina-silica) powder was sprayed onto the groove portion of the LT substrate by a thermal spraying method to form a sprayed film having a thickness of 0.5 mm on the groove portion of the LT substrate. The thermal spraying process was performed using a direct current plasma spraying apparatus with Ar and H ₂ plasma gas at a power output of 40 kW.

  Next, the thermal spray film formed on the LT substrate was ground to adjust the thickness of the LT substrate to 350 μm. Next, the glass substrate attached to the LT substrate was peeled, and the peeled surface was washed to remove hot wax.

  When the defect rate of the LT substrate was examined, it was about 30%, and it was found that the yield was improved. The result is shown in FIG. Note that the defect rate was determined by the ratio of how many defective wafers were present in 50 wafers, where wafer cracks, cracks, or voids during sprayed film formation were considered defective products. Wafer cracks, cracks, and the occurrence of voids during sprayed film formation were visually determined with a microscope.

(Example 2)
A thermal sprayed film of the LT substrate was formed in the same manner as in Example 1 except that a stepped portion as shown in FIG. 2 was provided in the groove portion of the LT substrate. In this case, when the defect rate of the LT substrate was examined, it was about 10%, and it was found that the yield was improved. The results are also shown in FIG.

(Comparative example)
A thermal sprayed film of the LT substrate was formed in the same manner as in Example 1 except that the peripheral portion of the LT substrate was subjected to blasting without masking. In this case, when the defect rate of the LT substrate was examined, it was about 100%, and it was found that defects occurred in all the wafers. The results are also shown in FIG.

  The present invention is not limited to the above embodiment, and can be implemented with various modifications. For example, the dimensions, number, material, and the like in the above embodiment are not limited to this. Moreover, although the case where the blasting process is adopted for thinning is described in the above embodiment, the present invention is not limited to this, and the same applies to the case where the grinding process is adopted for thinning. In addition, the present invention can be implemented with various modifications without departing from the scope of the present invention.

(A)-(f) is sectional drawing for demonstrating the manufacturing method of the piezoelectric substrate which concerns on embodiment of this invention. It is sectional drawing for demonstrating the other example of the groove process in the manufacturing method of the piezoelectric substrate which concerns on embodiment of this invention. It is a figure for demonstrating the effect of the manufacturing method of the piezoelectric substrate which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Board | substrate 11a, 11b Main surface 11c Rib 11d Step part 12 Protection base material 13 Adhesive layer 14 Blasting tape 15 Groove part 16 Thermal spray film

Claims (5)

  Forming a rib on one main surface of the substrate to form a rib on a peripheral edge; and embedding a first material smaller than the linear expansion coefficient of the substrate by thermal spraying in the groove formed by the groove processing; A method for manufacturing a piezoelectric substrate comprising the steps of:   The grooving includes a step of forming a mask on a peripheral portion of the other main surface of the substrate, and a step of performing a blasting process or a grinding process on the other main surface of the substrate provided with the mask. 2. The method of manufacturing a piezoelectric substrate according to claim 1, wherein   3. The method for manufacturing a piezoelectric substrate according to claim 1, wherein the groove processing is performed so as to form a stepped portion having a deeper depth toward a center at a peripheral edge portion. 4.   The material constituting the substrate is selected from the group consisting of lithium tantalate, lithium niobate, crystal, lithium tetraborate, and zinc oxide. A method for manufacturing a piezoelectric substrate according to claim 1. The substrate is composed of a second material having a linear expansion coefficient of ^{10 × 10 -6 / K~20 × 10} -6 / K, the first ^{material, -1 × 10 -6 / K~10 ×} 10 ^{5. The} method for manufacturing a piezoelectric substrate according to claim 1, wherein the method has a linear expansion coefficient of ⁻⁶ / K.

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