JP2017226026A - Manufacturing method of piezoelectric monocrystal wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method capable of reducing a crack of a wafer in a double-side wrapping process, in manufacture of an LT monocrystal wafer and an LN monocrystal wafer, in the present invention.SOLUTION: A manufacturing method comprises a slice process of forming a monocrystal wafer 50 by slicing a piezoelectric monocrystal by a wire saw, a wrapping process of roughly polishing both surfaces of the monocrystal wafer and a polishing process of mirror-polishing at least one surface of the roughly polished monocrystal wafer, and in the wrapping process, rough polishing is executed by maintaining the temperature of slurry of dispersing an abrasive grain 60 in water at 21°C-24°C.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for manufacturing a piezoelectric single crystal wafer.

  The lithium tantalate single crystal (hereinafter abbreviated as LT) and the lithium niobate (hereinafter abbreviated as LN) single crystal have melting points of about 1650 ° C. and about 1250 ° C., respectively, and Curie points of about 600 ° C., respectively. It is a ferroelectric substance of about 1200 ° C. and has piezoelectricity. The LT single crystal wafer or the LN single crystal wafer manufactured from this LT single crystal or LN single crystal is mainly a surface acoustic wave (hereinafter abbreviated as SAW) filter for removing signal noise of a mobile phone, an optical element, or the like. It is used as a device material. Either single crystal wafer is selected depending on the properties required by the device.

  Next, the manufacturing process of the LT crystal wafer and the LN single crystal wafer will be described. Since these are handled in the same manner in terms of crystallography and manufacturing process, the description will focus on the LT single crystal wafer.

  The LT single crystal is grown by a single crystal growing method such as the Czochralski method (CZ method). First, in the ingot state, after the end of a crystal having a short diameter is cut, the LT single crystal is subjected to a single polarization process (polling). This poling treatment polarizes the crystal by applying a voltage at a temperature equal to or higher than the Curie point in the <001> axis direction of the LT single crystal.

  Next, circumferential grinding is performed to process an orientation flat (OF) that serves as a reference plane for producing a surface acoustic wave element, that is, a plane indicating the crystal orientation and the propagation direction of the surface acoustic wave, and to adjust the outer diameter. , Applied to the LT single crystal. After performing these processes, the LT single crystal is sliced along a desired crystal orientation by a cutting device such as a wire saw and formed as a disk-shaped wafer having a predetermined thickness.

  The obtained LT single crystal wafer is subjected to the following processing. First, by chamfering the outer periphery of the wafer by beveling using a diamond grindstone with a count of about # 400 to # 1000, cracks in the subsequent processes are prevented and the wafer diameter is set to a predetermined size. To form.

  Next, lapping is performed on both sides of the LT single crystal wafer by lapping using a slurry composed of # 240 to # 2500 abrasive grains and water. As a result, damage to both surfaces of the wafer due to slicing is removed, and the wafer is aligned to a predetermined thickness while obtaining flatness and parallelism, and the back surface of the LT single crystal wafer is roughened.

  Then, as a finish, in the case of SAW filter application, one surface of the roughened surface is mirror-polished by mechanochemical polishing using a slurry such as colloidal silica.

  On the other hand, in the case of optical element use, roughening is not required, and after both surfaces of an LT single crystal wafer are both surfaces are mirror-polished by mechanochemical polishing using a slurry such as colloidal silica.

  Thus, the obtained LT single crystal wafer is usually a disk shape having a diameter of 3 to 6 inches (76 mm to 152 mm) and a thickness of about 0.1 mm to 0.5 mm.

  Patent Document 1 describes a wafer substrate polishing method as described above and a wafer made of a piezoelectric single crystal.

JP 2007-260793 A

  Incidentally, in the manufacture of the LT single crystal wafer and the LN single crystal wafer as described above, the most serious problem is the occurrence of cracks in the wafer during the manufacture. As a result of the cracking of the wafer, the yield decreases and the manufacturing cost also increases. In particular, cracks in the double-sided lapping process, which is a process after slicing, occupy most of the manufacturing process, and a manufacturing method with less generation of cracks is required.

  An object of the present invention is to provide a manufacturing method capable of reducing wafer cracking in a double-sided lapping process in the manufacture of LT single crystal wafers and LN single crystal wafers.

In order to achieve the above object, a method for manufacturing a piezoelectric single crystal wafer according to one aspect of the present invention includes a slicing step of slicing a piezoelectric single crystal with a wire saw to form a single crystal wafer;
A lapping step of rough polishing both surfaces of the single crystal wafer;
A polishing step of mirror polishing at least one surface of the coarsely polished single crystal wafer,
In the lapping step, rough polishing is performed while maintaining the temperature of the slurry in which the abrasive grains are dispersed in water at 21 ° C. or higher and 24 ° C. or lower.

  According to the present invention, it is possible to remarkably reduce the rate of occurrence of wafer cracking in the double-sided lapping process, and to improve the yield of piezoelectric oxide wafers.

It is the figure which showed an example of the double-sided lapping apparatus used for the manufacturing method of the piezoelectric single crystal wafer which concerns on embodiment of this invention. It is the figure which showed an example of the state under grinding | polishing of the double-sided lapping process of the manufacturing method of the piezoelectric single crystal wafer which concerns on this embodiment. It is an enlarged view for showing the state of slurry 60 during polishing in the double-sided lapping step. It is the figure which showed the crack generation rate of the wafer of Examples 1-4 and Comparative Examples 1-6.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a view showing an example of a double-sided lapping apparatus 10 used in a method for manufacturing a piezoelectric single crystal wafer according to an embodiment of the present invention.

  The double-sided lapping apparatus 10 used in the method for manufacturing a piezoelectric single crystal wafer according to this embodiment includes an upper surface plate 20, a lower surface plate 30, a carrier plate 40, an upper rotating shaft 70, and an upper surface. A rotating disk 71, a lower rotating shaft 80, and a lower rotating disk 81 are provided.

  The upper surface plate 20 and the lower surface plate 30 face each other in the vertical direction to constitute a pair of polishing surface plates. A carrier plate 40 is installed on the surface of the lower surface plate 30, and a wafer 50 is held in the carrier plate 40.

  The upper surface plate 20 is supported on the surface of the lower surface of the upper rotating plate 71. A rotating shaft 70 is provided at the center of the upper surface of the upper rotating disk 71, and the upper rotating disk 71 is configured to be rotatable by the rotating shaft 70. Similarly, the lower surface plate 30 is supported on the surface of the lower rotating plate 81, and a rotation shaft 80 is provided at the center of the lower surface of the lower rotating plate 81. Then, the rotation of the rotary shaft 80 is configured such that the lower rotating plate 81 and the lower surface plate 30 supported by the lower rotating plate 81 rotate. The surface plates 20 and 30 may be made of cast iron, for example.

  FIG. 2 is a view showing an example of a state during polishing in the double-sided lapping process of the method for manufacturing a piezoelectric single crystal wafer according to the present embodiment. FIG. 3 is an enlarged view for showing the state of the slurry 60 during polishing in the double-sided lapping process.

  As shown in FIG. 3, when lapping polishing is performed, slurry 60 is supplied between the upper surface plate 20 and the wafer 50 and between the lower surface plate 30 and the wafer 50, and the surface plate 20, A rotational motion is performed while applying a load to 30.

  As shown in FIG. 1, first, the carrier plate 40 is set on the lower surface plate 30, and the wafer 50 is also supported and fixed to the carrier plate 40. 2 and 3, the upper surface plate 20 is lowered, and the wafer 50 is supported and fixed by the carrier plate 4 set between the upper and lower surface plates 20 and 30. Then, a slurry that is a mixture of abrasive grains 60 and water consisting of # 240 to # 2500 of silicon carbide is supplied between the upper and lower surface plates 20 and 30 and the wafer 50, and the upper and lower surface plates 20 and 30 are supplied. The both sides of the wafer 50 are polished by rotating while sliding while applying a load.

  Note that a commercially available double-sided lapping apparatus can be used as the double-sided lapping apparatus for carrying out the method for manufacturing a piezoelectric single crystal wafer according to the present embodiment, for example, 16B-5L-V manufactured by Speed Fem Co., Ltd. May be used. The slurry is supplied from, for example, a slurry supply tank (not shown) provided in the double-side wrapping apparatus 10. A stirring motor is attached to the slurry supply tank, and the slurry is stirred by a stirring blade. The slurry used for processing returns to the tank from the discharge port of the double-sided lapping apparatus 10, is supplied to the wafer 50 again, and is circulated for use.

  A cooling device (not shown) such as a chiller device may be attached to the slurry supply tank in order to keep the temperature constant. A cooling device such as an accompanying chiller device may have a cooling capacity capable of maintaining the slurry temperature at 21 ° C. or higher and 24 ° C. or lower. When a chiller device is used as the cooling device, a commercially available chiller device can be used as the chiller device. For example, a handy cooler with a titanium cooling coil (manufactured by ASONE, Pasolina Compact Handy Cooler 202TN) may be used. . When using a chiller device, the slurry is cooled by immersing a titanium cooling coil in the slurry supply tank.

  In addition, by using a controller (control device) for the cooling device, the slurry temperature can be detected and the slurry temperature can be controlled to be a predetermined set temperature. As the controller for the cooling device, a commercially available product can be used. For example, a controller for a Pasolina compact handy cooler 202TN with a thermocouple at the tip can be used to check the slurry temperature, and the set temperature. It is controlled to become.

  Next, a method for manufacturing a piezoelectric single crystal wafer according to an embodiment of the present invention performed using the double-sided lapping apparatus 10 having such a configuration will be described.

  The type of the piezoelectric single crystal wafer is not particularly limited. For example, it may be a lithium tantalate single crystal wafer or a lithium niobate single crystal wafer.

  First, the whole process is as follows. First, for example, the outer periphery of an ingot grown by the Czochralski method is formed into a cylindrical shape by cylindrical grinding or the like, and this is sliced to a predetermined thickness to obtain a circular plate-shaped wafer substrate. This process is a slicing process.

  Next, in order to reduce the thickness variation in the wafer surface and between the wafers generated in the slicing process, and to obtain a rough surface roughness required for device fabrication, double-sided rough surface polishing is performed to a predetermined thickness. This is a lapping process, and the method for manufacturing a piezoelectric single crystal wafer according to this embodiment is characterized by a lapping process.

  Thereafter, single-sided mirror polishing is performed on the wafer whose both surfaces are roughened, thereby obtaining a single-sided mirror wafer in which one surface is a mirror surface and the other surface is a rough surface. This process is a polishing process. Except for the subsequent cleaning or the like, the manufacturing of the piezoelectric single crystal wafer is completed by the completion of the polishing process.

  In the method for manufacturing a piezoelectric single crystal wafer according to the embodiment of the present invention, the above-described slicing step, lapping step, and polishing step are sequentially performed. In the lapping step, the temperature of the slurry is maintained at 21 ° C. or higher and 24 ° C. or lower. Lapping processing, that is, rough polishing on both sides of the wafer 50 is performed. As described above, the temperature of the slurry may be adjusted by using a cooling device such as a chiller device, and other temperature adjusting means may be used as long as the temperature of the slurry can be maintained at 21 ° C. or higher and 24 ° C. or lower. There is no limitation on the means. By maintaining the temperature of the slurry at 21 ° C. or more and 24 ° C. or less, the occurrence of cracks in the wafer 50 in the lapping process can be significantly reduced. For example, compared with the case where the temperature of the slurry is 25 ° C. or more, The inventor has confirmed through experiments that the crack generation ratio can be reduced to 1.0% or less. Hereinafter, this point will be described in more detail with reference to examples.

  Examples of the present invention and comparative examples are shown in Table 1.

（実施例１）
チョクラルスキー法によりＬＴ単結晶を育成した後、得られたＬＴ単結晶の円柱状のバルクを６５０℃に加熱し、３００Ｖの電圧を印加して１時間のポーリングを行い、ＬＴ単結晶に単一分極処理を施した。その後、端部カットおよび円筒研削をした後、ワイヤーソー（株式会社タカトリ製、ＭＷＳ−６１２ＳＤ）を用いて、直径４インチ、厚さ０．４２ｍｍのＬＴ単結晶ウエハにスライスした（スライス工程）。

Example 1
After growing the LT single crystal by the Czochralski method, the cylindrical bulk of the obtained LT single crystal is heated to 650 ° C., and a voltage of 300 V is applied to perform poling for 1 hour. Unipolarization treatment was performed. Then, after performing end cutting and cylindrical grinding, it was sliced into a LT single crystal wafer having a diameter of 4 inches and a thickness of 0.42 mm using a wire saw (manufactured by Takatori Co., Ltd., MWS-612SD) (slicing step).

  Then, the lapping process was implemented using the double-sided lapping apparatus provided with the slurry supply tank accompanying a chiller apparatus. Specifically, double-sided lapping was performed on 300 LT single crystal wafers obtained in the above-described slicing process using a slurry of GC # 1000 abrasive grains made of silicon carbide and water. The slurry temperature was maintained at 21-23 ° C. Polishing was performed until the wafer thickness became 0.38 mm. As shown in the second column from the right in Table 1, no cracking occurred due to double-sided lapping.

(Example 2)
In the same manner as in Example 1, a LT single crystal wafer having a diameter of 6 inches and a thickness of 0.42 mm was produced, and the slurry temperature was maintained at 21 to 23 ° C., and double-sided lapping was performed on 300 wafers. As shown in the second column from the right in Table 1 and the rightmost column, the occurrence of cracks due to double-sided lapping was one sheet, and the crack generation ratio was 0.7%. In the second embodiment, the diameter of the wafer is larger than that in the first embodiment.

(Example 3)
After growing the LN single crystal by the Czochralski method, the cylindrical bulk of the obtained LT single crystal is heated to 1200 ° C., and a voltage of 300 V is applied to perform poling for 1 hour. Unipolarization treatment was performed. Then, after end cutting and cylindrical grinding, it was sliced into an LN single crystal wafer having a diameter of 4 inches and a thickness of 0.42 mm using a wire saw (manufactured by Takatori Co., Ltd., MWS-612SD). In Example 3, the bulk heating temperature is higher than that in Example 1. Other conditions are the same as in the first embodiment.

  Then, using a double-sided lapping machine equipped with a slurry tank attached to the chiller device, these LN single crystal wafers were made from a slurry of GC # 2500 abrasive grains made of silicon carbide and water, and 300 wafers. And double-sided lapping. The slurry temperature was maintained at 22-24 ° C. Polishing was performed until the wafer thickness became 0.38 mm. As shown in Table 1, the occurrence of cracks due to double-sided lapping was 1 and the crack generation rate was 0.3%.

Example 4
In the same manner as in Example 3, an LN single crystal wafer having a diameter of 6 inches and a thickness of 0.42 mm was manufactured, and the slurry temperature was maintained at 22 to 24 ° C., and double-sided lapping was performed on 300 wafers. As shown in Table 1, the occurrence of cracks due to double-sided lapping was 1 and the crack generation rate was 0.3%.

(Comparative Example 1)
In the same manner as in Example 1, a LT single crystal wafer having a diameter of 4 inches and a thickness of 0.42 mm was produced, and the slurry temperature was maintained at 25 to 27 ° C., and double-sided lapping was performed on 300 wafers. As shown in Table 1, the number of cracks generated by double-sided lapping was 13 and the crack generation rate was 4.3%.

(Comparative Example 2)
In the same manner as in Example 1, a LT single crystal wafer having a diameter of 6 inches and a thickness of 0.42 mm was produced, and the slurry temperature was maintained at 26 to 28 ° C., and double-sided lapping was performed on 300 wafers. As shown in Table 1, the number of cracks generated by double-sided lapping was 22 and the crack generation rate was 7.3%.

(Comparative Example 3)
In the same manner as in Example 1, a LT single crystal wafer having a diameter of 6 inches and a thickness of 0.42 mm was produced, and the slurry temperature was maintained at 26 to 28 ° C., and double-sided lapping was performed on 300 wafers. As shown in Table 1, the number of cracks generated by double-sided lapping was 47, and the crack generation ratio was 15.6%.

(Comparative Example 4)
In the same manner as in Example 3, an LN single crystal wafer having a diameter of 4 inches and a thickness of 0.42 mm was produced, and the slurry temperature was maintained at 25 to 27 ° C., and double-sided lapping was performed on 300 wafers. As shown in Table 1, the number of cracks generated by double-sided lapping was 20, and the crack generation rate was 6.0%.

(Comparative Example 5)
In the same manner as in Example 3, an LN single crystal wafer having a diameter of 6 inches and a thickness of 0.42 mm was produced, and the slurry temperature was maintained at 25 to 27 ° C., and double-sided lapping was performed on 300 wafers. As shown in Table 1, the number of cracks generated by double-sided lapping was 25, and the crack generation rate was 8.3%.

(Comparative Example 6)
In the same manner as in Example 1, an LT single crystal wafer having a diameter of 6 inches and a thickness of 0.42 mm was produced, and double-sided lapping was performed on 100 wafers without a chiller device. Since the inside of the slurry supply tank is constantly stirred, the slurry temperature rises from normal temperature (25 ° C.) to nearly 27 ° C. Since the slurry is supplied and the slurry whose temperature has been increased by processing returns to the tank, the slurry temperature in the slurry supply tank becomes 27 ° C. or higher. Since there is no chiller device, the temperature cannot be kept constant. As shown in Table 1, the number of cracks generated by double-sided lapping was 30 and the crack generation rate was 30.0%. Since the generation rate was 30.0%, up to 100 sheets were used.

  FIG. 4 is a diagram showing the crack generation rates of the wafers of Examples 1 to 4 and Comparative Examples 1 to 6. As shown in FIG. 4, in Examples 1 to 4, the crack generation rate is an extremely low value of less than 1%, and the wafer crack generation rate can be significantly reduced as compared with Comparative Examples 1 to 6. It has been shown. In FIG. 4, the data without the horizontal axis number without slurry temperature restriction is a comparative example that was not included in the above description, but the crack occurrence rate is still high when there is no slurry temperature restriction. , Nearly 30%.

  As described above, according to the method for manufacturing a piezoelectric single crystal wafer according to the embodiments and examples of the present invention, by performing the lapping process while maintaining the slurry temperature at 21 to 24 ° C., the crack generation rate of the wafer is reduced. It can be significantly reduced and the productivity can be greatly improved.

  The preferred embodiments and examples of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments and examples, and the above-described actual embodiments and examples can be made without departing from the scope of the present invention. Various modifications and substitutions can be made to the embodiments.

DESCRIPTION OF SYMBOLS 10 Double-sided lapping apparatus 20 Upper surface plate 30 Lower surface plate 40 Carrier plate 50 Wafer 60 Abrasive grain 70, 80 Rotating shaft 71, 81 Rotating plate

Claims (4)

Slicing the piezoelectric single crystal with a wire saw to form a single crystal wafer;
A lapping step of rough polishing both surfaces of the single crystal wafer;
A polishing step of mirror polishing at least one surface of the coarsely polished single crystal wafer,
A method for producing a piezoelectric single crystal wafer, wherein in the lapping step, rough polishing is performed while maintaining the temperature of a slurry in which abrasive grains are dispersed in water at 21 ° C. or higher and 24 ° C. or lower.   2. The method for producing a piezoelectric single crystal wafer according to claim 1, wherein the temperature of the slurry is maintained at 21 ° C. or more and 24 ° C. or less by being cooled by a cooling unit.   3. The method for manufacturing a piezoelectric single crystal wafer according to claim 2, wherein the temperature of the slurry is maintained at 21 ° C. or more and 24 ° C. or less by the control device for the cooling means.   The method for manufacturing a piezoelectric single crystal wafer according to any one of claims 1 to 3, wherein the single crystal wafer is a lithium tantalate single crystal wafer or a lithium niobate single crystal wafer.

Images