JP2014040339A - Method for manufacturing piezoelectric oxide single crystal wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide means capable of reducing the warp of a piezoelectric oxide single crystal wafer after slicing, preventing the wafer from cracking in a double-sided lapping process and improving the yield of the piezoelectric oxide wafer.SOLUTION: A method for manufacturing a piezoelectric oxide single crystal wafer comprises the steps of: slicing a piezoelectric oxide single crystal by a wire saw to form a single crystal wafer; etching the single crystal wafer using a mixed acid made of a hydrofluoric acid and a nitric acid; and at least performing double-sided lapping and single-sided mirror polishing. An LT single crystal wafer is etched for 4 hours or more at room temperature, and a LN single crystal wafer is etched for 25 minutes or more at room temperature. Thereby, a warp amount of the single crystal wafer after etching can be reduced to approximately 25-45% of a warp amount after slicing.

Description

  The present invention relates to a method for manufacturing a piezoelectric oxide single crystal wafer, and more particularly to a method for manufacturing a lithium tantalate single crystal wafer and a lithium niobate single crystal wafer.

  The lithium tantalate (LT) single crystal and the lithium niobate (LN) single crystal are ferroelectric materials having melting points of about 1650 ° C. and about 1255 ° C., and Curie points of about 600 ° C. and about 1200 ° C., respectively. It has piezoelectricity. LT wafers and LN wafers manufactured using this LT single crystal or LN single crystal are mainly used as surface acoustic wave (SAW) filters for removing signal noise from mobile phones, filters for televisions, optical elements, and other device materials. It is used. Either single crystal wafer is selected depending on the properties required by the device.

  Next, the manufacturing process of the LT single crystal wafer and the LN single crystal wafer will be described. Since these are handled similarly 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 into a disk-shaped wafer having a predetermined thickness along a desired crystal orientation by a cutting device such as a wire saw.

  The obtained LT single crystal wafer is further processed as follows. First, by chamfering the outer periphery of the wafer by beveling using a diamond grindstone of about # 600 to # 1000, cracks in the subsequent processes are prevented and the diameter of the wafer is formed to a predetermined size. .

  Next, double-sided lapping is performed on both sides of the LT single crystal wafer by lapping using # 800 to # 2000 slurry abrasive grains. This removes damage on both sides of the wafer due to slicing, and the wafer is aligned to a predetermined thickness while obtaining flatness and parallelism.

  In the case of surface acoustic wave filter applications, a single-sided lapping or blasting process using # 240 to # 2500 slurry abrasive grains is used to create a difference in spurious characteristics depending on the purpose. The surface is roughened to reduce bulk spurious as necessary. Then, as a finish, the surface corresponding to the opposite side 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 unnecessary, and both surfaces are mirror-polished by mechanochemical polishing using a slurry such as colloidal silica after double-sided lapping of an LT single crystal wafer. .

  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. For example, when obtaining a surface acoustic wave filter, the LT single crystal wafer is separated into a large number of LT single crystal pieces by dicing, and excitation electrodes composed of a pair of comb-shaped electrodes intersecting each other are provided on the mirror-polished side. It is done.

  In the manufacture of such LT single crystal wafers and LN single crystal wafers, cracking is the most problematic in terms of yield. Glassy LT single crystal wafers and LN single crystal wafers are very fragile. For example, if the finished thickness of these single crystal wafers is 0.2 mm to 0.3 mm, the thickness of the single crystal wafer immediately after slicing the single crystal is taken into account even if the allowance for the process such as double-sided lapping and single-side polishing is taken into account. Is only about 0.3 mm to 0.4 mm. Therefore, in the process after slicing, it is necessary to pay attention to the cracking of the wafer as a whole.

  In particular, cracks in the LT single crystal wafer and the LN single crystal wafer may be caused by warpage of the single crystal wafer. Conventionally, since the single crystal wafer is warped after the single-sided lapping or single-sided mirror polishing process, measures against such warp have been taken. For example, in Patent Document 1, after a single-sided lapping for roughening the back surface, a wafer having a diameter of 60 mm with a warpage of about 80 μm to 120 μm produced by this process is mixed with hydrofluoric acid and nitric acid in a volume ratio of 1: 2. It is described that it is put into the mixed acid, heated to about 60 ° C. to 120 ° C. and held for 1 hour, and this single crystal wafer is etched to make its warpage about 15 μm.

  Such warping due to single-sided lapping or single-sided mirror polishing is generally known as the Twiman effect. The Twiman effect is a phenomenon in which, after a wafer is processed, if the residual stress on both sides is different, the wafer is warped to compensate for the difference. That is, when a difference in surface roughness or processing strain occurs in the LT single crystal wafer or LN single crystal wafer due to the processing as described above, the surface area is large and the surface is high in roughness or has a large processing strain. In addition, the entire wafer is deformed to form a convex shape.

  For warping caused by the difference in surface roughness or processing distortion that occurs in the single-sided lapping process or single-side polishing process, the necessary amount from the surface of the wafer using means that does not give distortion such as etching. It is possible to cope with the problem by removing the processing strain only and reducing the internal stress remaining inside the wafer.

  Further, hydrofluoric acid, nitric acid, and a mixed acid thereof are used for etching for removing processing strain in the LT single crystal wafer and the LN single crystal wafer. For example, Patent Document 2 discloses that, for an LT single crystal wafer that has been single-sided mirror-finished after lapping, the etching time and the temperature of the acid that is the etchant are controlled to regulate the amount of warpage. First, the wafer is immersed in a mixed acid in which nitric acid and hydrofluoric acid are mixed at a volume ratio of 1: 3 at 40 ° C. for 10 to 30 minutes. Also in Patent Document 3, etching is performed for 1 hour at room temperature using a mixed acid in which hydrofluoric acid and nitric acid are mixed at a volume ratio of 1: 2, and the processing strain on the surface of the LT single crystal wafer after double-sided lapping is reduced. It is disclosed to remove some. Further, although not related to warpage, Patent Document 4 discloses that the wafer is made of hydrofluoric acid, nitric acid, or a mixed acid thereof for the purpose of reducing micro-waviness on the surface of the LT single crystal wafer or the LN single crystal wafer. It is disclosed to immerse for about 20 minutes.

  These etching processes effectively prevent the cracking of wafers in the manufacturing process of LT single crystal wafers and LN single crystal wafers, particularly in the element processing process for obtaining surface acoustic wave filters and television filters from these wafers. , Which contributes to improving the yield in the process. However, when these wafers are cut out from the manufacture of LT single crystals and LN single crystals, and the overall wafer processing steps for obtaining LT single crystal wafers and LN single crystal wafers are further improved, the yield can be further improved. is necessary.

Japanese Patent Publication No. 56-36808 JP 2003-17983 A JP 2000-82931 A JP 2003-165595 A

  The present invention has reviewed a process for processing an LT single crystal wafer and an LN single crystal wafer into a wafer for obtaining an element for use in a surface acoustic wave filter or a television filter, and has not taken measures until now, immediately after slicing. It is an object of the present invention to provide means for improving the yield in the initial process by paying attention to the cracking of these wafers in the initial process until the double-sided lapping.

  The method for producing a piezoelectric oxide single crystal wafer according to the present invention includes a single crystal wafer obtained by slicing a grown piezoelectric oxide single crystal with a wire saw by a single crystal growth method such as a Czochralski method (CZ method). And a manufacturing method for obtaining a piezoelectric oxide single crystal wafer by performing at least double-sided lapping and single-side mirror polishing on the single crystal wafer.

  In particular, in the present invention, after the slicing, before the double-sided lapping, the single crystal wafer is etched using a mixed acid composed of hydrofluoric acid and nitric acid, thereby warping the single crystal wafer after etching. The amount can be reduced to 25% to 45% of the warping amount after slicing.

  In the case where the piezoelectric oxide single crystal wafer is a lithium tantalate single crystal wafer, the etching is preferably performed by immersing the single crystal wafer in the mixed acid for 4 hours or more while keeping the mixed acid at room temperature. .

  On the other hand, when the piezoelectric oxide single crystal wafer is a lithium niobate single crystal wafer, the etching is performed by immersing the single crystal wafer in the mixed acid for 25 minutes or more while keeping the mixed acid at room temperature. Is preferred.

  By using the method for manufacturing a piezoelectric oxide wafer of the present invention, the warpage of the piezoelectric oxide single crystal wafer after slicing is reduced, and cracking of the wafer is prevented in the double-sided lapping process, thereby preventing the piezoelectric oxidation. The yield of the physical wafer can be further improved.

FIG. 1 is a diagram showing a warped state of an LT single crystal wafer after etching. FIG. 2 shows a warped state of the LT single crystal wafer after slicing. FIG. 3 is a schematic cross-sectional view of a commonly used double-sided lapping apparatus.

  The present inventor has conducted extensive research on wafer warpage in the manufacturing process of a piezoelectric oxide wafer, reexamined the warpage property of the wafer immediately after slicing, and performed predetermined etching on the single crystal wafer after slicing. As a result, the inventors have obtained knowledge that the warpage can be reduced, and have completed the present invention.

  The present invention provides a single crystal wafer obtained by subjecting a piezoelectric oxide single crystal grown by a single crystal growth method such as the Czochralski method (CZ method) to poling, end cutting, and cylindrical grinding, and then slicing the single crystal wafer. The single crystal wafer is subjected to various processes such as beveling, double-sided lapping, edge polishing, and main surface polishing (single-side mirror polishing), and further separated into a large number by dicing to produce a piezoelectric oxide single crystal wafer. About.

  Here, the target piezoelectric oxide single crystal mainly corresponds to a lithium tantalate (LT) single crystal and a lithium niobate (LN) single crystal having a piezoelectric effect, but the present invention is not limited to these, Also included is a method for manufacturing a piezoelectric oxide single crystal in which an additive element is further added to these piezoelectric oxides, and a wafer of piezoelectric oxide single crystals that require poling treatment such as langasite and lithium tetraborate. Is done.

  As described above, in the manufacturing process of piezoelectric oxide single crystal wafers such as LT single crystal wafers and LN single crystal wafers, the most serious problem in terms of yield is wafer cracking. A glass-like oxide single crystal wafer is a very fragile substance. Therefore, in the wafer processing process, consideration is given to the cracking of the wafer as a whole. Of typical processing processes such as beveling, double-sided lapping and single-sided polishing, double-sided lapping is a process that requires special attention. Yes. In other words, in beveling, the wafer is sucked and fixed to a rotary stage and the end surface thereof is ground.In single-side polishing, the back surface of the wafer is adhered or adsorbed to a polish block, and its main surface is mirror-polished. On the other hand, in double-sided wrapping, the wafer is basically processed while being pressed in a free state with no support, so that the wafer is easily cracked.

  More specifically, the double-sided wrapping is performed by the double-sided wrapping apparatus 1 shown in FIG. This double-sided lapping apparatus 1 is usually provided with upper and lower polishing surface plates 2 and 3 each having a polishing cloth or the like mounted on opposite surfaces, and a carrier plate 4 disposed therebetween. In double-sided lapping, the wafer 5 is supported and fixed on the carrier plate 4, and then the carrier plate 4 is set between the polishing surface plates 2 and 3. Then, a polishing platen 2, 3, and a wafer 5 are made from abrasive grains 6 mainly composed of fine particles such as aluminum oxide and silicon carbide, and a slurry of about # 800 to # 2000 in which water, rust preventive material, dispersing agent and the like are turbid. And both sides of the wafer 5 are polished by sliding while applying pressure to both.

  Thus, in the double-sided wrapping, a load is applied to the wafer to force the wafer warped by the press of the surface plate to be flat. At the same time, the position of the wafer 5 is held by the carrier plate 4. Since the wafer 5 is processed while being pressed in a free state, if the wafer is warped, a large force is applied locally, causing the wafer to crack.

  However, until now, sufficient measures have not been taken for warping of the single crystal wafer in the process from slicing the single crystal wafer to double-sided lapping. The reason is that a piezoelectric oxide single crystal such as an LT single crystal wafer or an LN single crystal wafer is sliced into a single crystal wafer by a wire saw using a thin wire having a small rigidity as a blade, and thus warping of the wafer after slicing is performed. This is because it was considered that the slice shape of the wafer itself was warped due to wire blurring during slicing. That is, due to the mechanism, it is unlikely that there will be a difference in surface roughness or processing strain between the front and back of the wafer. Therefore, the etching is effective in eliminating the warpage based on the difference in surface roughness and processing strain. It is because it was thought that it was not possible to obtain.

  The cause of wafer cracking at the time of double-sided lapping is due to the accuracy of the wire saw in addition to this warping, and the wafer before slicing and before double-sided wrapping has a thickness variation of about 10 μm to 20 μm. In the initial stage, the press pressure is not uniformly applied to the wafer, or a wire saw cut mark called a saw mark is the starting point, so that the wafer is easily cracked in double-sided lapping.

  For these problems, if the wire saw processing speed is significantly reduced, the warpage will approach a minimum, but in view of production efficiency and cost, a certain level of warpage is permitted at a realistic processing speed. It is reality. Therefore, these warpages have been solved by double-sided lapping itself, but the wafer cracking in double-sided lapping is a factor that hinders the improvement of the yield of LT single crystal wafers and LN single crystal wafers. .

  On the other hand, the present inventors reviewed the properties of warping after slicing of the piezoelectric oxide single crystal, and these are the shapes in which the wafer is simply warped due to the wire blur of the wire saw at the time of slicing. It was not only that, but at the same time, the knowledge that it was also warped by the Twiman effect due to the difference in surface condition was obtained.

  When the warp of the single crystal wafer is caused by processing strain, as described above, the deformation is canceled by removing the required amount of processing strain on the front and back surfaces by means such as etching that does not give strain. Will be able to. In this sense, it can be said that the warp caused by the processing strain is merely an apparent warp. As long as the wire saw mechanism is taken into account, it can be said that there is no difference in surface roughness and processing strain on the front and back of the wafer. Therefore, warping due to the LT single crystal wafer and LN single crystal wafer after slicing is the difference in processing strain. However, when the inventors actually performed a predetermined etching on the single crystal wafer after slicing, it was confirmed that the warpage was reduced. It was. Because this etching does not cause the warp to become zero, the warpage is a combination of the warpage of the shape itself caused by blurring when slicing with a wire saw and the warpage due to the Twiman effect due to the difference in processing distortion between the front and back surfaces. It can be said that.

  Such a difference in processing distortion cannot be considered to be mainly caused by the slice itself as described above. Although it has not been clarified in detail about this point, the LT single crystal and the LN single crystal are subjected to a single polarization process called poling after growth. I think this is because anisotropy appears in a superimposed manner.

  Therefore, in the present invention, by performing predetermined etching on the LT single crystal wafer and LN single crystal wafer after slicing in advance, it becomes possible to provide a wafer with reduced warpage to the double-sided lapping process, and at the time of double-sided lapping. It is possible to reduce the load on the wafer and improve the yield.

  As described above, the present invention is characterized in that the piezoelectric oxide single crystal wafer is etched after slicing and before double-sided lapping from the viewpoint of removing processing distortion caused by poling. For this reason, the processes from the growth of the piezoelectric oxide single crystal to the slicing to the wafer, and the processes such as edge polishing and main surface polishing by single-sided mirror polishing after double-sided lapping are the same as the conventional processes. Therefore, only the etching which is a feature of the present invention will be described below, and the other description will be omitted or simplified.

  As an etchant in the etching step after slicing a piezoelectric oxide such as lithium tantalate or lithium niobate, hydrofluoric acid can be suitably used as in the etching after single-sided lapping or single-sided mirror polishing. Fluorine nitric acid is a mixed acid of an aqueous hydrogen fluoride solution and an aqueous nitric acid solution. Both hydrogen fluoride aqueous solution and nitric acid aqueous solution are commercially available as aqueous solutions having a concentration of about 50% to 60%, and these aqueous solutions are 1.5: 1 to 1 by volume ratio of hydrofluoric acid aqueous solution and nitric acid aqueous solution. It can be mixed to be 1: 1.5, usually 1: 1, to obtain an etching solution.

  Etching is performed by immersing the single crystal wafer in this etching solution. The etching time can be shortened as the temperature of the etching solution increases. However, if the residual thermal stress increases, the wafer may be cracked or warped. Therefore, etching is performed at room temperature (15 ° C. to 35 ° C.). It is preferable to carry out. However, the etching temperature can be set to 60 ° C. to 110 ° C. as long as the problem of residual thermal stress can be cleared by providing steps of heating and cooling stepwise before and after. When the etching temperature is normal temperature, the etching time is preferably 4 hours or more for the LT single crystal wafer, and 25 minutes or more for the LN single crystal wafer. In particular, when the etching temperature is about room temperature (25 ° C.), in the case of an LT single crystal wafer, the etching time is more preferably 5 hours or more, and in the case of an LN single crystal wafer, the etching time is 30 hours. More preferably, it is more than minutes. The upper limit of the etching time is not particularly defined and is appropriately selected depending on the etching conditions, etc. From the viewpoint of production efficiency, when the etching temperature is room temperature, the LT single crystal wafer It is preferably about 8 hours or about 60 minutes for an LN single crystal wafer.

  Note that the etching time of the LN single crystal wafer is shorter than that of the LT single crystal wafer because the LN single crystal is relatively easily dissolved in the etching solution. If the etching time is too short, it is considered possible to remove damage on the wafer surface due to processing stress during slicing, but it is difficult to eliminate the warpage.

  In the present invention, the amount of warpage of the etched single crystal wafer is reduced to about 25% to 45%, preferably about 25% to 30% of the warped amount after slicing by etching under such conditions. can do. For example, in the case of an LT single crystal wafer having a diameter of 6 inches and a thickness of 0.35 mm, the warpage amount after slicing is about 70 μm, but by applying the present invention, the warpage amount is reduced to about 20 μm. Can do. In addition, in the case of an LN single crystal wafer having a diameter of 4 inches and a thickness of 0.35 mm, the warping amount after slicing is about 35 μm, but by applying the present invention, the warping amount can be reduced to about 9 μm. Can do. Therefore, according to the present invention, it becomes possible to effectively prevent the cracking of the wafer in the lapping process described later, and the yield rate in this lapping process can be 99% or more.

  After the etching is completed, the wafer is taken out from the etching solution, washed with water, and dried. As a drying method, known means such as vacuum drying, spin drying, and hot air drying can be used, but spin drying is preferable from the viewpoint of cost and ease of operation.

  In the present invention, “warping” literally means cutting into a curved shape so that the wafer is warped. The amount of warpage is measured, for example, according to the definition of Sori defined in the technical standard QIAJ-B-007 “Single crystal wafer for surface acoustic wave device” established by the Japan Quartz Device Industry Association. That is, the plane that is in contact with the back surface of the wafer is taken as a reference plane, and the maximum deviation from the plane is expressed.

  In the present invention, by reexamining the warpage of the wafer due to the slicing, conventionally, the wafer damage due to the processing stress on the wafer surface due to the slicing has only been removed by etching. In the meantime, the wafer is prevented from being warped by a predetermined etching, thereby preventing the wafer from cracking in the double-sided lapping process and improving the yield in the manufacturing process of the piezoelectric oxide single crystal wafer, particularly in the wafer processing process. There is a feature in that. The present invention is not limited by other manufacturing processes.

  Also, in other processes, various processes are added according to the characteristics required for the wafer. For example, after double-sided lapping or double-sided polishing, the wafer surface is damaged due to processing stress of lapping or polishing. Etching or after single-sided mirror polishing, before the single-sided mirror polishing in order to reduce the processing distortion in advance, separately etching for warping due to the Twiman effect due to the difference in surface roughness between the front and back surfaces In addition, the case where the ingot is preliminarily annealed in order to remove the residual thermal stress generated in the growth stage is also included in the scope of the present invention.

  The predetermined etching process of the present invention may be performed in a process from slicing a single crystal wafer to a double-sided lapping process, and there is no problem before and after other processing processes such as a beveling process normally performed during the process. .

Example 1
After growing the LT single crystal by the Czochralski method, the obtained bulk is heated to 650 ° C., a voltage of 300 V is applied, and poling is performed for 1 hour, and the LT single crystal is subjected to a single polarization treatment. did. Then, after end cutting and cylindrical grinding, an ingot was sliced into a thin plate wafer at a processing speed of 0.1 mm / min using a wire saw (manufactured by Yasunaga Co., Ltd., F-600S), and the diameter was 6 inches. 200 LT single crystal wafers having a thickness of (152 mm) and a thickness of 0.35 mm were obtained. At this time, the average value of the warpage of the wafer was 70 μm.

From these LT single crystal wafers, mixed acid in which 55% hydrofluoric acid aqueous solution (Morita Chemical Co., Ltd.) and 60% nitric acid aqueous solution (Kanto Chemical Co., Ltd.) were mixed at a volume ratio of 1: 1. The etching according to the present invention was performed for 5 hours in a state where the resulting etching solution was kept at room temperature (25 ° C.). The average value of the warpage amount of the wafer after etching was 20 μm, and it could be reduced to 28.6% based on the average value of the warpage amount after slicing.

  Thereafter, the single crystal wafer was put into a double-sided lapping apparatus (DSM16B, manufactured by Speed Fam Co., Ltd.), and double-sided lapping was applied to the single crystal wafer at a pressure of 80 N and a polishing rate of 4 μm / min. In double-sided lapping, a slurry in which # 1000 GC abrasive grains (manufactured by Fujimi Incorporated) was turbid in water was used as abrasive grains. By this step, the wafer was polished until the wafer thickness became 0.25 mm. There was no cracking due to this step, and the yield was 100%.

(Example 2)
Etching and double-sided lapping were performed on an LT single crystal wafer having a diameter of 6 inches and a thickness of 0.35 mm in the same manner as in Example 1 except that the etching time was 7 hours. The average value of the warpage amount of the wafer after etching was 20 μm, and it could be reduced to 28.6% based on the average value of the warpage amount after slicing. Moreover, there was no crack by double-sided lapping, and the yield was 100%.

(Example 3)
Etching and double-sided lapping were performed on an LT single crystal wafer having a diameter of 6 inches and a thickness of 0.35 mm in the same manner as in Example 1 except that the temperature of the etching solution was 15 ° C. The average value of the amount of warpage of the wafer after etching was 30 μm, and could be reduced to 42.9% based on the average value of the amount of warpage after slicing. Moreover, in double-sided lapping, two cracks occurred and the yield was 99.0%.

Example 4
Etching and double-sided lapping were performed on an LT single crystal wafer having a diameter of 6 inches and a thickness of 0.35 mm in the same manner as in Example 1 except that the temperature of the etching solution was 15 ° C. and etching was performed for 7 hours. did. The average value of the amount of warpage of the wafer after etching was 25 μm, and could be reduced to 35.7% based on the average value of the amount of warpage after slicing. Moreover, there was no crack by double-sided lapping, and the yield was 100%.

(Comparative Example 1)
Etching according to the present invention was not performed on the LT single crystal wafer, and double-sided lapping similar to that in Example 1 was performed while maintaining the warping amount after slicing (average 70 μm). The thickness of the wafer after double-sided lapping was 0.25 mm, 19 double-sided lapping caused 19 cracks, and the yield was 90.5%.

(Comparative Example 2)
Etching and double-sided lapping were performed on an LT single crystal wafer having a diameter of 6 inches and a thickness of 0.35 mm in the same manner as in Example 1 except that the etching time was 3 hours. The average value of the warpage amount of the wafer after etching was 45 μm, and it could be reduced to 64.3% based on the average value of the warpage amount after slicing. Further, 15 sheets were cracked by double-sided lapping, and the yield was 92.5%.

(Example 5)
After growing the LN single crystal by the Czochralski method, the obtained bulk is heated to 1200 ° C., a voltage of 300 V is applied, and poling is performed for 1 hour, and the LN single crystal is subjected to a single polarization treatment. did. Then, after end cutting and cylindrical grinding, using a wire saw, slicing was performed at a processing speed of 0.3 mm / min, and an LN single crystal wafer having a diameter of 4 inches (102 mm) and a thickness of 0.35 mm was obtained. I got a sheet. The average value of the warpage of the wafer at this time was 35 μm.

  With respect to these LN single crystal wafers, an etching solution composed of a mixed acid obtained by mixing a 50% hydrofluoric acid aqueous solution and a 60% nitric acid aqueous solution at a volume ratio of 1: 1 is maintained at room temperature (25 ° C.). The etching of the present invention was performed for 30 minutes. The average value of the amount of warpage of the wafer after etching was 9 μm, and could be reduced to 25.7% based on the average value of the amount of warpage after slicing.

  Thereafter, the single crystal wafer was put into a double-sided lapping apparatus, and double-sided lapping was performed on the single crystal wafer at a pressure of 40 N and a polishing rate of 10 μm / min. In double-sided lapping, a slurry in which # 1000 GC abrasive grains were turbid in water was used as abrasive grains. By this step, the wafer was polished until the wafer thickness became 0.25 mm. There was no cracking due to this step, and the yield was 100%.

(Example 6)
Etching and double-sided lapping were performed on an LN single crystal wafer having a diameter of 4 inches and a thickness of 0.35 mm in the same manner as in Example 5 except that the etching time was 50 minutes. The average value of the amount of warpage of the wafer after etching was 9 μm, and could be reduced to 25.7% based on the average value of the amount of warpage after slicing. Moreover, there was no crack by double-sided lapping, and the yield was 100%.

(Example 7)
Etching and double-sided lapping were performed on an LN single crystal wafer having a diameter of 4 inches and a thickness of 0.35 mm in the same manner as in Example 5 except that the temperature of the etching solution was 15 ° C. and etching was performed for 30 minutes. did. The average value of the amount of warpage of the wafer after etching was 15 μm, and could be reduced to 42.9% based on the average value of the amount of warpage after slicing. Moreover, in double-sided lapping, three cracks occurred and the yield was 99.4%.

(Example 8)
Etching and double-sided lapping were performed on an LN single crystal wafer having a diameter of 4 inches and a thickness of 0.35 mm in the same manner as in Example 5 except that the temperature of the etching solution was 15 ° C. and etching was performed for 50 minutes. did. The average value of the amount of warpage of the wafer after etching was 11 μm, and could be reduced to 31.4% based on the average value of the amount of warpage after slicing. Moreover, there was no crack by double-sided lapping, and the yield was 100%.

(Comparative Example 3)
Etching according to the present invention was not performed on the LN single crystal wafer, and the same double-sided lapping as in Example 5 was performed while maintaining the warping amount after slicing (average value: 35 μm). The thickness of the wafer after double-sided lapping was 0.25 mm, 22 double-sided cracks were generated, and the yield was 95.6%.

(Comparative Example 4)
Etching and double-sided lapping were performed on a LT single crystal wafer having a diameter of 4 inches and a thickness of 0.35 mm in the same manner as in Example 5 except that the etching time was 20 minutes. The average value of the warpage amount of the wafer after etching was 24 μm, and it could be reduced to 68.6% based on the average value of the warpage amount after slicing. Moreover, 19 sheets were cracked by double-sided lapping, and the yield was 96.2%.

DESCRIPTION OF SYMBOLS 1 Double-sided lapping apparatus 2 Upper polishing surface plate 3 Lower polishing surface plate 4 Carrier plate 5 Wafer 6 Abrasive grain

Claims (3)

  In the method of manufacturing a piezoelectric oxide single crystal wafer, the piezoelectric oxide single crystal is sliced with a wire saw to form a single crystal wafer, and at least double-sided lapping and single-sided mirror polishing are performed on the single crystal wafer. Before performing double-sided lapping, the single crystal wafer is etched using a mixed acid composed of hydrofluoric acid and nitric acid, so that the warp amount of the single crystal wafer after etching is 25% of the warp amount after slicing. A method for producing a piezoelectric oxide single crystal wafer, which can be reduced to -45%.   The piezoelectric oxide single crystal wafer is a lithium tantalate single crystal wafer, and the etching is performed by immersing the single crystal wafer in the mixed acid for 4 hours or more while keeping the mixed acid at room temperature. The method for producing a piezoelectric oxide single crystal wafer according to claim 1. The piezoelectric oxide single crystal wafer is a lithium niobate single crystal wafer, and the etching is performed by immersing the single crystal wafer in the mixed acid for 25 minutes or more while keeping the mixed acid at room temperature. The method for producing an oxide single crystal wafer according to claim 1.