Method for manufacturing oxide single crystal substrate

Abstract

To provide a method for manufacturing an oxide single crystal substrate, capable of cutting the straight body part of an oxide single crystal, such as lithium tantalate into a predetermined diameter while preventing cracks from occurring.SOLUTION: A method for manufacturing an oxide single crystal substrate comprises: a mounted surface formation step of cutting the shoulder part or the tail part of an oxide single crystal including a straight body part having an approximately cylindrical shape, the shoulder part having inclined surfaces on the top and bottom of the straight body part and projecting in a mountain shape and the tail part so as to leave the inclined surface to form a mounted surface mounted on a predetermined crystal mounting reference plane; the crystal fixing step of fixing the oxide single crystal in the state of mounting the mounted surface to the crystal mounting reference surface; and the water jet cutting step of ejecting high pressure water including an abrasive along the axis direction of the straight body part toward any inclined surface of the shoulder part and tail part of the fixed oxide single crystal to cut the straight body part of the oxide single crystal into a predetermined diameter.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for producing an oxide single crystal substrate. [Background technology]

[0002] Oxide single crystals such as lithium tantalate (hereinafter sometimes abbreviated as LT) single crystals and lithium niobate (hereinafter sometimes abbreviated as LN) single crystals have piezoelectric properties, and there is a great demand for SAW (surface acoustic wave) devices that utilize this piezoelectricity, and the market is showing explosive growth, especially in mobile communications applications such as mobile phones.

[0003] The LT and LN single crystals that form the basis of SAW devices are often grown by a pulling method known as the Czochralski method (CZ method). A disk-shaped substrate is cut from the grown LT or LN single crystal, polished, electrodes are formed, cut into chips, and packaged to complete the SAW device. Unless otherwise specified, the term "crystal" used in this specification refers to a single crystal. The following explanation will use an LT single crystal as an example.

[0004] In the CZ method, a single crystal is typically grown in an electric furnace using a high-melting-point noble metal crucible, and after growth, the single crystal is cooled at a predetermined cooling rate and then removed from the electric furnace.

[0005] The grown single crystal undergoes annealing to remove distortion and single polarization before being delivered to the processing stage. In this stage, the shoulders and tails of the grown single crystal are cut off (so-called faceting), and then cylindrical grinding is performed to create a cylindrical shape slightly thicker than the final product. The resulting substrates are then cut into substrates using a multi-wire saw. The outer periphery of the cut substrate is finally beveled to the desired diameter, and the edges are chamfered. The substrate surface is then lapped and polished to a mirror finish, resulting in the finished single crystal substrate. LT substrates are available in sizes ranging from 4 to 6 inches in diameter.

[0006] In the cylindrical grinding process, the grown crystal is processed into a cylindrical ingot with flat top and bottom surfaces. Generally, crystals grown by the CZ method have a conical shoulder at the start of growth (the upper part of the crystal), a body with a nearly uniform diameter, and a conical tail at the bottom where the crystal is separated from the melt.

[0007] For this reason, in the cylindrical grinding process, a surface finishing process is performed as a pre-processing step in which the shoulder and tail of the mountain-shaped (conical) ingot are cut off with a single wire saw, and then the side of the body is ground using a processing machine (grinding wheel) such as a cylindrical grinder to make it slightly larger than the final product. Finally, an end face grinding process is performed in which the top and bottom surfaces of the body are finished using a surface grinder to produce a cylindrical ingot. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-82007 Summary of the Invention [Problem to be solved by the invention]

[0009] Although the straight body portion is grown under controlled conditions to have a predetermined diameter, variations occur. For this reason, the diameter is set to be approximately 10 mm to 30 mm larger than the required diameter to ensure the final substrate diameter.

[0010] In the cylindrical grinding process, as described above, the straight body portion is ground using a processing machine (grinding wheel) such as a cylindrical grinder to process it into a single crystal ingot of a specified diameter, but the crystal powder (so-called crystal scrap) of the straight body portion cut out by cylindrical grinding contains abrasive grains that have fallen off the grinding wheel, so it is ultimately disposed of as waste. However, LT and LN raw materials are expensive, and the crystal scrap generated during processing can be reused as recycled raw material if it maintains its crystalline shape.

[0011] For this reason, a processing method that allows the crystal scraps to maintain their crystalline shape is desired, and for example, the processing method described in Patent Document 1 is being considered. Specifically, Patent Document 1 discloses a laser processing method, a water jet processing method, and the like, for cutting an ingot made of an iridium-based alloy into a predetermined size.

[0012] However, unlike iridium-based alloys, piezoelectric oxide single crystals such as LT and LN are prone to cracking even with a slight impact, making it difficult to adopt the method disclosed in Patent Document 1. Therefore, grinding processing using a processing machine (grinding wheel) such as the cylindrical grinder described above has traditionally been used.

[0013] The present invention has been made in light of these problems, and an object of the present invention is to provide a method for manufacturing an oxide single crystal substrate that can cut out the straight body portion of an oxide single crystal such as LT or LN to a predetermined diameter while suppressing the occurrence of cracks. [Means for solving the problem]

[0014] That is, the method for producing an oxide single crystal substrate according to the present invention comprises the steps of: an installation surface forming step of cutting the shoulder or tail of an oxide single crystal having a substantially cylindrical body portion and a mountain-shaped protruding shoulder or tail portion with inclined surfaces above and below the body portion, leaving the inclined surfaces, to form an installation surface that can be installed on a predetermined crystal installation reference surface; a crystal fixing step of fixing the oxide single crystal that has been subjected to the mounting surface surface exposure step in a state in which the mounting surface is placed relative to the crystal mounting reference surface; a water jet cutting process in which high-pressure water containing an abrasive is sprayed along the axial direction of the straight body portion toward the inclined surface of either the shoulder portion or the tail portion of the fixed oxide single crystal, thereby cutting out the straight body portion of the oxide single crystal to a predetermined diameter; The present invention is characterized by the following features. [Effects of the Invention]

[0015] According to the method for producing an oxide single crystal substrate of the present invention, it is possible to cut out the straight body portion of an oxide single crystal such as LT or LN to a predetermined diameter while suppressing the occurrence of cracks. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram showing a manufacturing process for an oxide single crystal substrate according to a conventional example. [Figure 2] 1A to 1C are diagrams showing the steps for producing an oxide single crystal substrate according to the present invention. [Figure 3] 1 is an explanatory diagram of an oxide single crystal having a shoulder, a body, and a tail, grown by a pulling method. [Figure 4] FIG. 10 is an explanatory diagram of an oxide single crystal in which a part of the tail portion is polished to serve as a surface to be placed in the step of polishing the surface to be placed. [Figure 5] FIG. 1 is an explanatory diagram of an oxide single crystal in which the water jet cut portions of the mountain-shaped slopes in the shoulder and tail portions and the adjacent portions, as well as the adjacent portions of the shoulder and tail portions in the body portion, are coated with resin. [Figure 6] FIG. 2 is an explanatory diagram of a water jet cutting process according to the present invention for cutting out a straight body portion of an oxide single crystal to a predetermined diameter. [Figure 7] FIG. 10 is an explanatory diagram of a water jet cutting process according to a modified example of the present invention, in which a straight body portion of an oxide single crystal is cut to a predetermined diameter. DETAILED DESCRIPTION OF THE INVENTION

[0017] The method for manufacturing an oxide single crystal substrate according to an embodiment of the present invention will be described in detail below, taking as an example a conventional method for manufacturing an oxide single crystal substrate.

[0018] The oxide single crystal substrate is fabricated from a piezoelectric oxide single crystal such as lithium niobate (LiNbO3:LN) single crystal or lithium tantalate (LiTaO3:LT) single crystal.

[0019] Hereinafter, the LT single crystal will be described as a representative example of an oxide single crystal.

[0020] [1] Conventional method for manufacturing an oxide single crystal substrate (I) Method for manufacturing oxide single crystal substrate LT single crystals are grown by single crystal growth methods such as the Czochralski method (CZ method), in which a seed crystal is immersed in a melt obtained by melting raw material powder and then pulled up to grow a single crystal. For example, by using a high-frequency induction heating device, large single crystals can be stably produced.

[0021] The grown LT single crystal is subjected to an annealing treatment to remove distortion and a single polarization treatment (poling) as shown in the manufacturing process diagram in Figure 1. This poling treatment involves heating the grown LT single crystal to a temperature above the Curie point, for example, 600 to 700°C, and applying a voltage of, for example, 200 to 500 V in the Z-axis direction, thereby polarizing the single crystal for approximately 0.5 to 2 hours.

[0022] After the poling process, the LT single crystal is delivered to the substrate processing process.

[0023] As shown in the manufacturing process diagram of Figure 1, the substrate processing process involves a shoulder and tail surface finishing process, a cylindrical processing process (cylindrical grinding), and an end face grinding process to obtain a cylindrical ingot, which is then subjected to a slicing process, a beveling process, a lapping process, and a polishing process to obtain a single crystal substrate. Each process will be described in detail below.

[0024] [Shoulder and tail surface finishing process] 3, an LT single crystal 10 grown by the pulling method has a conical shoulder 11 at the growth start point (upper part of the crystal), a body 12 with approximately the same diameter, and a conical tail 13 at the bottom of the crystal where the crystal is separated from the melt. That is, the shoulder 11 and the tail 13 each have an inclined surface (conical inclined surface) that is inclined with respect to the axial direction of the body 12.

[0025] The shoulder and tail surface finishing step is a step in which the shoulder 11 at the top of the crystal and the tail 13 at the bottom of the crystal are cut off using a single wire saw or the like.

[0026] [Cylindrical machining process (cylindrical grinding)] The cylindrical processing process is a process in which the side of the straight body portion 12, from which the shoulder portion 11 and tail portion 13 have been cut in the facing process, is ground using a processing machine (grinding wheel) such as a cylindrical grinder to finish it slightly larger than the final product.

[0027] [End face grinding process] The end face grinding process is a process in which the top and bottom surfaces of the straight body portion 12, which has been finished in the cylindrical processing process to be slightly larger than the final product, are finished using a surface grinder.Through these processes, a cylindrical ingot is obtained from the LT single crystal 10.

[0028] [Slicing process] The slicing step is a step of slicing a cylindrical single crystal ingot into a disk-shaped substrate using a multi-wire saw or the like with free abrasive grains.

[0029] [Bevel process] The beveling process is a process in which the disk-shaped substrate obtained in the slicing process is held on a rotatable substrate grinding stage, and while the substrate is rotating, the stage is brought close to a rotating grinding wheel to chamfer the edge surface of the outer periphery of the substrate.

[0030] [Wrapping process] The lapping step is a step in which both the front and back surfaces of the substrate are lapped using free abrasive grains to make them smooth.

[0031] [Polishing process] The polishing step involves mirror-polishing one or both sides of the lapped substrate to obtain a single crystal substrate.

[0032] (II) Problems with the conventional method for manufacturing an oxide single crystal substrate In the cylindrical processing step (cylindrical grinding) in the conventional method for manufacturing an oxide single crystal substrate, as described above, the straight body portion is ground using a processing machine (grinding stone) such as a cylindrical grinder. However, since the crystal powder (so-called crystal chips) of the straight body portion ground out by cylindrical grinding contains abrasive grains that have fallen off the grinding stone, there has been a problem in that the ground out crystal powder such as LT or LN cannot be reused as a recycled raw material.

[0033] [2] The method for manufacturing an oxide single crystal substrate according to the present invention (I) Method for manufacturing oxide single crystal substrate The method for producing an oxide single crystal substrate according to the present invention differs from conventional methods in which the straight body portion is ground using a processing machine (grinding wheel) such as a cylindrical grinder, in that it employs a water jet cutting method in which high-pressure water containing an abrasive is sprayed to cut out the straight body portion to a predetermined diameter. As shown in the manufacturing process diagram of FIG. 2, the method comprises an annealing step, a mounting surface surface preparation step, a poling step, a crystal fixing step, a water jet cutting step, a substrate processing surface surface preparation step, and optionally a cylindrical grinding step, an end face grinding step, a slicing step, a beveling step, a lapping step, and a polishing step.

[0034] The method for producing an oxide single crystal substrate according to the present invention will be described below, but explanations of steps with the same names as those shown in FIG. 1 will be omitted.

[0035] [Installation surface leveling process] The process of surface alignment is a process of cutting the shoulder or tail of the grown LT single crystal using a single wire saw or the like, leaving only a mountain-shaped inclined surface (the inclined surface of the shoulder or tail, i.e., the surface inclined relative to the axial direction of the straight body) located on the base end side (straight body side) of the shoulder or tail of the grown LT single crystal, and then aligning it into a surface that can be placed on a predetermined crystal placement reference surface A (see Figures 4, 6, and 7).

[0036] When cutting the straight body portion to a specified diameter in the water jet cutting process, the area of ​​the LT single crystal where the high-pressure water containing abrasive is injected and the area around where the high-pressure water exits the LT single crystal after cutting are subject to a strong impact from the high-pressure water, which can easily cause cracks.

[0037] Therefore, when the LT single crystal is fixed in the water jet cutting device, the above-mentioned surface preparation is performed so that the position of the LT single crystal where high-pressure water is injected and cut is adjusted to the mountain-shaped slope of the shoulder and tail portions, thereby avoiding the occurrence of cracks in the LT single crystal.

[0038] The crystal installation reference plane is determined in advance in consideration of the desired plane orientation of the LT single crystal substrate (the direction of the perpendicular line from the main surface of the substrate), etc.

[0039] The step of polishing the mounting surface may be performed on either the shoulder or the tail, but is preferably performed on the tail portion 13, as shown in Figure 4. During crystal growth, after the body portion 12 with a predetermined diameter is grown, the tail portion 13 is suddenly separated from the melt under high-speed conditions, which causes large internal stresses and makes it susceptible to cracking even with a small impact. Therefore, by performing the step of polishing the mounting surface on the tail portion 13 and cutting it while leaving the mountain-shaped slope of the tail portion 13, it is possible to alleviate the internal stress in the tail portion 13.

[0040] [Crystal fixation process] The crystal fixing step is a step of fixing the LT single crystal that has undergone the step of aligning the mounting surface in a state where the mounting surface is placed relative to the crystal mounting reference surface.

[0041] When cutting out a straight body portion to a specified diameter in the water jet cutting process, the area of ​​the LT single crystal where the high-pressure water is injected and the area around where the high-pressure water exits the LT single crystal after cutting are subject to a strong impact from the high-pressure water, as described above, and are therefore prone to cracking.

[0042] For this reason, the shoulder or tail portion is faceted in the mounting surface faceting process so that the position of the LT single crystal to be cut by injecting high-pressure water is adjusted to the mountain-shaped inclined surface of the shoulder or tail portion. For example, the mounting surface of the faceted tail portion 13 shown in FIG. 4 can be placed on the mounting surface of a pedestal 22 (see FIG. 6) that is placed on the table surface of the water jet cutting device, thereby fixing the LT single crystal.

[0043] The method for fixing the LT single crystal to the pedestal 22 (see FIG. 6) is not particularly limited, and examples include methods using an adhesive or the like. The mounting surface of the faceted tail portion 13 may be bonded and fixed to the mounting surface of the SUS pedestal 22, for example, using an epoxy adhesive. In order to reliably fix the LT single crystal to the mounting surface of the pedestal 22, the faceted area of ​​the shoulder or tail portion in the mounting surface faceting step is 50% to 80%, preferably 60% to 80%, of the diameter of the LT single crystal to be fixed. In addition, to prevent the pedestal 22 from being cut by high-pressure water, the size of the pedestal 22 should be about 50% of the diameter of the straight body portion 12.

[0044] In FIG. 6, the method of fixing the LT single crystal 10 is employed in which the installation surface of the faceted tail portion 13 is placed on the installation surface of a pedestal 22 that is placed on the surface of the table 21 of the water jet cutting device 20. However, instead of the method of placing the installation surface of the faceted tail portion 13 on the pedestal 22, a method may be employed in which the straight body portion 12 of the LT single crystal 20 is held by a holding member 30 shown in FIG. 7 to fix the LT single crystal 10.

[0045] However, when the method of fixing the LT single crystal 10 using the holding member 30 is adopted, the periphery of the straight body portion 12 of the LT single crystal 10 is water jet cut and the center of the straight body portion 12 is hollowed out, which may make it difficult to stably fix the main body of the LT single crystal 10.

[0046] Therefore, as a method for fixing the LT single crystal that has undergone the step of polishing the mounting surface, a method in which the polished mounting surface of the tail portion 13 is mounted on the pedestal 22 is preferred.

[0047] [Water jet cutting process] The water jet cutting process involves spraying high-pressure water containing an abrasive toward the inclined surface of either the shoulder or tail of a fixed LT single crystal along the axial direction of the straight body (vertically from above in this embodiment shown in Figure 6 ), thereby cutting out the straight body of the LT single crystal to a predetermined diameter. In this embodiment, the sprayed high-pressure water containing an abrasive is sprayed toward the inclined surface of one of the shoulder or tail, penetrates the straight body of the LT single crystal along the axial direction, and ejects from the inclined surface of the other of the shoulder or tail. In the example shown in Figure 6 , the high-pressure water is sprayed toward the inclined surface of the shoulder where the mounting surface is not faceted, and then penetrates the straight body and ejects from the inclined surface of the tail where the mounting surface is faceted. However, the spraying direction of the high-pressure water may be reversed. That is, a configuration may be adopted in which the high-pressure water is sprayed toward the inclined surface of the tail where the mounting surface is not faceted, and then penetrates the straight body and ejects from the inclined surface of the shoulder where the mounting surface is faceted.

[0048] The water jet cutting method, its processing conditions, and the water jet cutting device will be specifically described below.

[0049] (1) Water jet cutting method The water jet cutting method involves cutting by drawing an abrasive material (garnet, etc.) into high-pressure water. The position of the nozzle from which the high-pressure water is sprayed can be freely adjusted, making it easy to change the crystal diameter and set the orientation flat, resulting in excellent productivity.

[0050] However, while the water jet cutting method is sometimes applied to cutting out metal crystals such as the iridium-based alloys mentioned above, it has been considered difficult to use with piezoelectric oxide single crystals such as LT and LN because they are prone to cracking even with a slight impact.

[0051] For example, when attempting to cut the straight body portion of an LT single crystal to a specified diameter using the water jet cutting method, as described above, the part of the LT single crystal where the high-pressure water containing abrasive is injected and the area around where the high-pressure water exits the LT single crystal after cutting is complete are subject to strong impact from the high-pressure water, making them prone to cracking, and it has been considered difficult to apply the water jet cutting method.

[0052] (1-1) Mountain-shaped slope Therefore, in the present invention, a "water jet cutting process" is carried out before the "shoulder and tail surface finishing process" of the conventional method (in the present invention, the substrate processing surface finishing process).

[0053] Specifically, when the LT single crystal is fixed to the water jet cutting device, the above-mentioned "mounting surface surface alignment process" is performed so that the position of the LT single crystal to be cut by injecting high-pressure water (the position to be cut by high-pressure water) is adjusted to the mountain-shaped inclined surface of the shoulder and tail parts, and then the "substrate processing surface surface alignment process" is performed after the "water jet cutting process".

[0054] Furthermore, because the cutting positions in the "water jet cutting process" are the mountain-shaped slopes of the shoulder and tail portions, the impact of the high-pressure water on the LT single crystal is mitigated, making it possible to prevent cracks from occurring in the LT single crystal.Furthermore, the crystal scraps produced in the "water jet cutting process" maintain their crystalline shape as crystal scraps, making it possible to reuse them as recycled raw material.

[0055] (1-2) Coating resin 6, at least a portion of the inclined mountain-shaped surfaces in the shoulder 11 and tail 13 of the LT single crystal 10 may be coated with resin 29, and it is preferable to coat the portion to be water-jet cut with resin 29, and it is even more preferable to coat the portion adjacent to the portion to be water-jet cut with resin 29. Even more preferably, in addition to the portion to be water-jet cut and the portion adjacent to the shoulder 11 and tail 13 on the inclined mountain-shaped surfaces in the shoulder 11 and tail 13, the portion adjacent to the shoulder 11 and tail 13 on the body 12 may also be coated with resin 29.

[0056] By covering the above-mentioned portion of the mountain-shaped inclined surface onto which the high-pressure water containing abrasive is injected with resin 29, the impact of the water jet is alleviated and the occurrence of cracks can be prevented.

[0057] The coating resin is not particularly limited, but it is preferable that it has adhesive properties to prevent peeling during water jet cutting, and for example, a two-component epoxy adhesive is preferable. The thickness of the coating resin is at least 1.0 mm, preferably 2 mm to 3 mm. If the thickness of the coating resin is too thin, the impact mitigation effect is reduced. The width of the resin covering is preferably 5 mm or more on at least one side of the processing position, preferably 10 mm to 15 mm.

[0058] After the water jet cutting process is completed, the epoxy adhesive can be washed away with hot water (about 60°C).

[0059] (1-3) Processing conditions The processing conditions for water jet cutting are not particularly limited as long as they allow cutting out of LT single crystal (piezoelectric oxide single crystal) and can prevent cracks from occurring during the water jet cutting process.

[0060] Garnet-based abrasives are common, and can also be used with LT single crystals (piezoelectric oxide single crystals). The particle size of the abrasive is #30 to #1000. It is also possible to use recycled abrasives obtained by drying and sieving the abrasives used in water jet cutting. Mixing recycled abrasives with unused abrasives can reduce processing costs.

[0061] The pressure, flow rate, and processing speed of the high-pressure water can be set appropriately according to the capabilities of the water jet cutting device. For example, the pressure of the high-pressure water is 300 to 600 MPa, the flow rate of the high-pressure water is 3 to 4 L / min, the processing speed is 5 to 30 mm / min, and the nozzle diameter from which the high-pressure water is sprayed is φ0.1 mm to φ0.4 mm.

[0062] (2) Water jet cutting device As shown in Fig. 6, the water jet cutting device 20 includes a table 21 on which a pedestal 22 and other components are placed below the device body 23, and an abrasive head 25, which is supplied with abrasive material 26 and high-pressure water 27 and can be controlled to move horizontally and vertically, is located above the device body 23. The abrasive head 25 is configured to spray the high-pressure water 27 containing the abrasive material 26 from the nozzle tip toward, for example, the mountain-shaped slope of the crystal shoulder 11. The device body 23 is filled with water, and the LT single crystal 10 fixed to the installation surface of the pedestal 22 can be immersed in water for processing. The reference numeral 28 in Fig. 6 denotes a shielding plate for blocking droplets of the high-pressure water 27 from splashing off the mountain-shaped slope.

[0063] [Substrate processing surface leveling process] The substrate processing surface finishing process is a process in which the shoulder 11 and tail 13 of the LT single crystal 10 that has undergone the water jet cutting process are cut parallel to the mounting surface (see mounting surface finishing process) using a single wire saw or the like to finish the surface as the substrate processing surface, and is a process equivalent to the ``shoulder and tail surface finishing process'' in the conventional method.

[0064] [Cylindrical grinding process] This is a process in which the straight body portion 12 of the LT single crystal 10 cut to a predetermined diameter in the water jet cutting process is ground by a processing machine such as a cylindrical grinder.

[0065] Since the straight body portion 12 is cut out to a predetermined diameter in the water jet cutting process, the cylindrical grinding process is a process that is performed as needed to adjust the surface of the straight body portion 12 to a desired diameter.

[0066] [End face grinding process] The end face grinding process is a process in which the top and bottom surfaces of the straight body portion 12, which has been finished in the cylindrical processing process to be slightly larger than the final product, are finished using a surface grinder, as in the conventional process.Through these processes, a cylindrical ingot is obtained from the LT single crystal 10.

[0067] (II) Effects of the manufacturing method according to the present invention As described above, the position of the LT single crystal 10 cut by the water jet cutting process is the mountain-shaped slope of the shoulder portion 11 and the tail portion 13, so the impact of the high-pressure water on the LT single crystal 10 is mitigated, making it possible to prevent cracks from occurring in the LT single crystal 10.Furthermore, the crystal scraps produced by the water jet cutting process maintain their crystalline shape as crystal scraps, which has the effect of allowing them to be reused as recycled raw material. [Example]

[0068] Examples of the present invention will be specifically described below with reference to comparative examples.

[0069] [Example 1] An LT single crystal 10 shown in Figure 3 was prepared by the Czochralski method, with a diameter of 6 inches and a RY of 38°. The length of the straight body was 75 mm.

[0070] Next, an LT single crystal substrate was fabricated from the LT single crystal 10.

[0071] First, the tip side of the tail portion 13 of the LT single crystal 10 was cut with a single wire saw, leaving a mountain-shaped inclined surface located on the base end side (straight body side) of the tail portion 13, and then a surface finishing process (surface finishing process for the surface to be placed) was performed to prepare a surface to be placed that could be placed on a predetermined crystal placement reference surface A shown in Figure 4.

[0072] Next, the cutting was performed by water jet cutting, with the diameter set to 10 mm smaller than the diameter of the LT single crystal.

[0073] First, as shown in Fig. 5, an adhesive made of an epoxy resin was applied to the portions of the mountain-shaped slopes of the shoulder 11 and tail 13 of the LT single crystal 10 to be water jet cut and their neighboring portions, as well as the adjacent portions of the shoulder 11 and tail 13 in the body portion 12, to cover these portions with resin 29. The adhesive was applied to the above-mentioned portions in a range of 1 cm to 2 cm wide and 1 mm to 2 mm thick, centered on the portion to be water jet cut.

[0074] Next, the mounting surface of the tail portion 13, which has been surface-ground by the above-mentioned mounting surface surface-grounding process, is fixed to the mounting surface of the pedestal 22 shown in Figure 6 using an epoxy adhesive, and thereafter, the pedestal 22 to which the LT single crystal 10 is fixed is placed on the surface of the table 21 of the water jet cutting device 20 shown in Figure 6, and cutting processing is performed by the water jet cutting method.

[0075] The abrasive used was garnet type #80, and the cutting process was performed with high-pressure water at a pressure of 350 MPa, a flow rate of 4 L / min, and a processing speed of 5 mm / min. The LT single crystal 10 was immersed in water during the processing.

[0076] This cutting process resulted in an end piece of material approximately 5 mm thick and approximately 75 mm long. Furthermore, this process did not cause any cracks in the LT single crystal 10.

[0077] Thereafter, the shoulder 11 and tail 13 of the LT single crystal 10 were cut parallel to the mounting surface of the tail 13 using a single wire saw to prepare a substrate processing surface, and then cylindrical grinding was performed using a cylindrical grinder. Since the straight body 12 of the LT single crystal 10 had been machined to a predetermined diameter by water jet cutting, the cylindrical grinding process using the cylindrical grinder was a process for smoothing the surface of the straight body 12, and 0.5 mm was ground on each side. Finally, the top and bottom surfaces of the straight body 12 were end-ground using a surface grinder.

[0078] This produced a cylindrical ingot.

[0079] Next, the produced cylindrical ingot was sliced ​​into disk-shaped substrates using a multi-wire saw with free abrasive grains, and the sliced ​​disk-shaped substrates were held on a rotatable substrate grinding stage. While the substrate was rotating, the stage was brought close to a rotating grindstone to chamfer the edge surfaces of the outer periphery of the substrate. Furthermore, both the front and back surfaces of the chamfered substrate were lapped with free abrasive grains, and then one side of the substrate was mirror-polished to obtain a single crystal substrate.

[0080] The scrap material obtained by the water jet cutting process, approximately 5 mm thick and 75 mm long, was reused as recycled raw material.

[0081] [Comparative Example 1] As in Example 1, an LT single crystal 10 shown in Fig. 3 having a diameter of 6 inches and a RY of 38° was prepared by the Czochralski method. The length of the straight body was 75 mm.

[0082] Then, an LT single crystal substrate was produced from the LT single crystal 10.

[0083] First, the shoulder 11 and tail 13 of the LT single crystal 10 shown in Figure 3 were cut using a single wire saw. Next, the side of the straight body 12 of the LT single crystal 10 from which the shoulder 11 and tail 13 had been cut was cylindrically ground by about 10 mm using a cylindrical grinding machine (grinding wheel) to a predetermined diameter, and then the top and bottom surfaces of the straight body 12 were end-ground using a surface grinding machine to produce a cylindrical ingot.

[0084] Then, as in Example 1, the produced cylindrical ingot was sliced ​​into disk-shaped substrates using a multi-wire saw with free abrasive grains, and the sliced ​​disk-shaped substrates were held on a rotatable substrate grinding stage. While the substrates were rotating, the stage was brought close to a rotating grindstone to chamfer the edge surfaces of the outer periphery of the substrates. Furthermore, both the front and back surfaces of the chamfered substrates were lapped with free abrasive grains, and one side of the substrate was mirror-polished to obtain a single crystal substrate.

[0085] The crystal powder of the straight body portion 12 cut out by cylindrical grinding using the cylindrical grinding machine contained abrasive grains that had fallen off the grindstone, and was ultimately disposed of as waste.

[0086] According to each of the embodiments described above, high-pressure water containing an abrasive is sprayed along the axial direction of the straight body portion toward the mountain-shaped inclined surfaces of the shoulder and tail portions of the oxide single crystal fixed to the water jet cutting device.Therefore, the positions cut by the water jet cutting process are the mountain-shaped inclined surfaces of the shoulder and tail portions, and therefore the impact of the high-pressure water on the oxide single crystal is mitigated, making it possible to prevent cracks from occurring in the oxide single crystal.Furthermore, the crystal scraps from the water jet cutting process maintain their crystalline shape as crystal scraps, and can be reused as recycled raw material. [Explanation of symbols]

[0087] A Crystal installation reference plane 10LT single crystal 11 Shoulder 12 Straight body part 13 Tail section 20 Water jet cutting device 21 tables 22 Pedestal 23 Device body 25 Abrasive Head 26 Abrasives 27 High-pressure water 28 Shielding plate 29 Resin 30 Retaining member

Claims

1. an installation surface forming step of cutting the shoulder or tail of an oxide single crystal having a substantially cylindrical body portion and a mountain-shaped protruding shoulder or tail portion with inclined surfaces above and below the body portion, leaving the inclined surfaces, to form an installation surface that can be installed on a predetermined crystal installation reference surface; a crystal fixing step of fixing the oxide single crystal that has been subjected to the mounting surface surface exposure step in a state in which the mounting surface is placed relative to the crystal mounting reference surface; a water jet cutting process in which high-pressure water containing an abrasive is sprayed along the axial direction of the straight body portion toward the inclined surface of either the shoulder portion or the tail portion of the fixed oxide single crystal, thereby cutting out the straight body portion of the oxide single crystal to a predetermined diameter; 1. A method for producing an oxide single crystal substrate, comprising:

2. 2. The method for producing an oxide single crystal substrate according to claim 1, wherein the tail portion is cut off leaving the inclined surface as the mounting surface.

3. 3. The method for producing an oxide single crystal substrate according to claim 1, wherein the crystal mounting reference plane is a mounting surface of a pedestal placed on a table surface of a water jet cutting device.

4. 2. The method for producing an oxide single crystal substrate according to claim 1, wherein at least a part of the inclined surfaces at the shoulder and tail of the oxide single crystal is covered with a resin.

5. a substrate processing surface forming step of cutting the shoulder portion and the tail portion of the oxide single crystal that has been subjected to the water jet cutting step parallel to the installation surface to form a substrate processing surface; 2. The method for producing an oxide single crystal substrate according to claim 1, further comprising a step of grinding the straight body portion of the oxide single crystal that has been subjected to the substrate processing surface shaping step by a cylindrical grinding process.

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