Manufacturing method of piezoelectric single crystal substrate

Abstract

To provide a method capable of surely discriminating the front and back of a substrate during a manufacturing process.SOLUTION: A method for manufacturing a piezoelectric monocrystal substrate comprises a groove forming step, a first marking step, a slicing step, a second marking step, a beveling step, an edge polishing step, a wrapping step, and a polishing step. The groove forming step forms a groove extending in an axis direction of a piezoelectric monocrystal ingot and serving as a notch on a side surface of the ingot. The first marking step forms a first mark on the side surface of the ingot. The slicing step slices the ingot in which the groove and the first mark are formed. The second marking step forms a second mark on at least one surface of a thin plate. The beveling step bevels an outer peripheral end part of the thin plate to remove the first mark. The edge polishing step forms a third mark by subjecting the side surface of the thin plate to edge polishing. The wrapping step adjusts a shape and thickness of a surface by polishing the thin plate having been subjected to edge polishing. The polishing step obtains the piezoelectric monocrystal substrate by subjecting the principal surface side of the thin plate to mirror polishing.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Substrates obtained from single crystals are used as various materials. For example, piezoelectric single crystal substrates (hereinafter sometimes abbreviated as "single crystal substrates") such as lithium tantalate single crystal substrates (LT single crystal substrates) obtained from lithium tantalate (LT) single crystals and lithium niobate single crystal substrates (LN single crystal substrates) obtained from lithium niobate (LN) single crystals are used as materials for surface acoustic wave elements (SAW filters) for removing noise in electrical signals used in mobile communication devices.

[0003] LT single crystals and LN single crystals are mainly manufactured by the Czochralski method, and are usually grown in an electric furnace using a high-melting-point precious metal crucible, cooled at a specified cooling rate, and then removed from the electric furnace. The grown single crystal is subjected to a heat treatment under soaking at a temperature close to the melting point to remove residual strain caused by thermal stress, and then a poling treatment to make it a single polarization, that is, a series of treatments are performed in which the single crystal is heated from room temperature to a specified temperature above the Curie temperature, a voltage is applied to the single crystal, and the temperature is lowered to a specified temperature below the Curie temperature while the voltage is applied, and then the voltage application is stopped and the crystal is cooled to room temperature. After the poling treatment, the outer surface of the grown single crystal is ground to adjust the outer shape, and the cylindrically processed single crystal ingot is processed into a wafer-shaped single crystal substrate.

[0004] The procedure for processing a cylindrical single crystal ingot usually involves machining steps such as a cylindrical grinding step, a slicing step, a beveling step, a lapping step, and a polishing step, in that order. In some cases, an etching step is performed between the lapping step and the polishing step. Through the above-mentioned machining steps, a wafer-shaped single crystal substrate is manufactured from the single crystal ingot.

[0005] Conventionally, LT and LN single crystal substrates with a diameter of 150 mmφ or less have had a straight line portion called an orientation flat (OF) at a specified position on the outer circumference to identify the crystal orientation, as shown in Figure 10. In addition, a straight line portion called an index flat (IF), which is shorter than the OF, has been provided to determine the front and back sides during the processing process and to determine the front and back sides of double-sided mirror-finished substrates.

[0006] However, when an OF or IF is provided on a LT or LN single crystal substrate with a diameter of more than 150 mmφ, the effective area for cutting out a device from the substrate is reduced, and the weight of a large-diameter LT or LN single crystal substrate is inevitably increased. Moreover, when an LT or LN single crystal substrate provided with an OF or IF is processed by rotating it at high speed using a spin coater or the like in the device fabrication process, it has been found that problems occur due to the OF or IF being chipped. That is, the LT or LN single crystal substrate provided with an OF or IF is naturally not a perfect circle on its periphery, and the OF or IF is chipped. When such a LT or LN single crystal substrate with a chipped periphery is rotated at high speed using a spin coater or the like, an unbalanced load is generated, and as a result, the LT or LN single crystal substrate vacuum-adsorbed on the rotor of the spin coater is detached or scattered at high speed, causing problems.

[0007] Therefore, instead of the single crystal substrate with OF or IF as shown in Fig. 10, LT or LN single crystal substrate with V-shaped notch as shown in Fig. 11 was developed. This single crystal substrate has a notch cut into one edge of the outer circumference as a method of identifying crystal orientation in place of OF.

[0008] A LT or LN single crystal substrate having a notch is processed by the following procedure, for example, as described in Patent Document 1 below. In the cylindrical grinding process, the surface of the LT or LN single crystal is cylindrically ground to process it into a cylindrical single crystal ingot (ingot), and a V-shaped groove is formed in a specific direction on the side of the ingot (this groove becomes a provisional notch when the ingot is sliced). In the slicing process, the ingot is sliced ​​into a disk-shaped substrate using free abrasive grains with a wire saw. In the beveling process, the substrate with the provisional notch formed in the slicing process is held on a rotatable substrate grinding stage, and the stage is brought close to a rotating grindstone while rotating the substrate to chamfer the edge surface of the outer periphery of the substrate. After the chamfering operation is completed, the rotation of the stage is stopped and the stage is moved away from the rotating grindstone, and a notch grinding grindstone is rotated instead of the rotating grindstone, and the stage is brought close to a notch formation position to form a notch. After the formation of the notch is completed, both the front and back surfaces are lapped using free abrasive grains in a lapping process, processing distortion is removed in an etching process, and then one side of the surface is mirror-polished in a polishing process. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 4151155 Summary of the Invention [Problem to be solved by the invention]

[0010] Incidentally, SAW filters use LT single crystal substrates processed with a substrate principal surface orientation of about 42°RY and LN single crystal substrates processed with a principal surface orientation of about 128°RY. Here, for example, 42°RY is a direction rotated 42° from the Y axis to the Z axis direction in the YZ plane with the X axis as the rotation axis. As shown in FIG. 11, a substrate processed perpendicular to such an orientation is called a substrate with a principal surface orientation of 42°RY. Such LT and LN single crystal substrates have an inclination of the crystal axis, and only the surface with a specified crystal orientation is used, so it is necessary to distinguish the front and back of the substrate. For a single crystal substrate provided with OF or IF, the front and back can be distinguished by the position of the IF with the OF as the reference. For example, single crystal substrates with OFs and IFs are manufactured by attaching a temporary OF of approximately the same length as the OF to be provided in the beveling process in the desired crystal orientation in the cylindrical grinding process, attaching a temporary IF of approximately the same length as the IF to be provided in the beveling process, forming a wafer-shaped single crystal substrate in the slicing process, and then chamfering the edge in the beveling process to obtain the desired edge shape, while forming the OF and IF based on the temporary OF and temporary IF. Therefore, since the OF and IF are always present in the single crystal substrate in the wafer form after the slicing process, it is easy to distinguish the front and back of the substrate (front and back surfaces).

[0011] On the other hand, after a notched single crystal substrate is made into a wafer-shaped single crystal substrate in the slicing process, it has only a temporary notch or a notch formed in the beveling process on the outer periphery, so it is difficult to distinguish between the front and back sides until the front side is mirror-polished on one side in the polishing process. For this reason, there are cases where the front and back sides are mistaken in the slicing process, beveling process, lapping process, etching process, and polishing process. If the front and back sides are mistaken in the slicing process, beveling process, lapping process, etching process, polishing process, etc., the back side is mirror-polished in the polishing process, so there is a problem that the substrate with the wrong front and back sides cannot be used as a surface acoustic wave element.

[0012] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide a method for reliably determining the front and back sides of a notched piezoelectric single crystal substrate during the manufacturing process up to the polishing step. [Means for solving the problem]

[0013] According to an aspect of the present invention, there is provided a method for manufacturing a piezoelectric single crystal substrate having a notch used for identifying a predetermined crystal orientation, the method comprising: a groove forming step of forming a groove that extends in the axial direction of the ingot and serves as a notch on a side surface of a piezoelectric single crystal ingot that has been subjected to cylindrical grinding; a first marking step of forming a first mark on a portion of the side surface of the ingot that is asymmetric with respect to the axis of the ingot from the groove; a slicing step of slicing the ingot with the groove and first mark formed therein into a thin plate; and a second marking step of forming a second mark on at least one side of the thin plate sliced ​​from the ingot. a beveling step of chamfering the outer peripheral edge of the thin plate on which the second mark has been formed and removing the first mark; an etch-polishing step of partially edge-polishing a portion of the side surface of the thin plate from which the first mark has been removed that is asymmetric with the groove with respect to the axis of the ingot to form a third mark; a lapping step of polishing the edge-polished thin plate to adjust the surface shape and thickness; and a polishing step of mirror-polishing the main surface side of the thin plate whose surface shape and thickness have been adjusted to obtain a piezoelectric single crystal substrate having a notch and a third mark.

[0014] The first mark and the second mark may be formed with paint. The first marking step and the second marking step may each include forming the first mark and the second mark using a pen. The edge polishing may include using abrasive grains of #1500 to #3000. The third mark may be more transparent on the side surface than a portion other than the third mark. Effect of the Invention

[0015] According to the method for manufacturing a piezoelectric single crystal substrate of the present invention, the front and back sides can be distinguished from each other by the positional relationship between the groove (notch) on the outer periphery of the substrate and the first mark before the beveling in the slicing process and the beveling process, the front and back sides can be distinguished from each other by the second mark on the front or back side made in the slicing process after the beveling in the beveling process, and the front and back sides can be distinguished from each other by the positional relationship between the groove (notch) on the outer periphery of the substrate and the third mark (the part where the edge polishing was applied) from the lapping process to before the polishing in the polishing process. In addition, the front and back sides can be distinguished from each other after the polishing in the polishing process because the main surface (front side) is a mirror surface. As described above, according to the present invention, the front and back sides can be distinguished in all processes, and there is no risk of the front and back sides being mistaken for mirror polished in the polishing process, and there is no problem that the front and back sides cannot be used as a surface acoustic wave element due to the mistaken front and back sides. [Brief description of the drawings]

[0016] [Figure 1] 2 is a flowchart showing an example of a method for manufacturing a piezoelectric single crystal substrate according to an embodiment. [Diagram 2] FIG. 1 is a diagram showing an example of a cylindrical grinding process. [Diagram 3] 11A to 11C are diagrams illustrating an example of a groove forming step. [Figure 4] FIG. 2 is a diagram showing an example of a first marking step, where (A) is a perspective view and (B) is a cross-sectional view. [Diagram 5] FIG. 13 is a diagram illustrating an example of a slicing process. [Figure 6] FIG. 11 is a cross-sectional view showing an example of a second marking step. [Figure 7] FIG. 1 shows an example of a bevel process, where (A) shows the state in which the upper end of the outer peripheral end of a thin plate is beveled, and (B) and (C) show examples of the outer peripheral end of a thin plate after beveling, where (B) is a side view and (C) is a plan view. [Figure 8] FIG. 13 is a diagram illustrating an example of an edge polishing process. [Figure 9] 1A to 1C are diagrams illustrating an example of a lapping process and a polishing process. [Figure 10]FIG. 1 is a diagram showing an example of a conventional single crystal substrate with OF. [Figure 11] FIG. 1 is a diagram showing an example of a conventional notched single crystal substrate. [Figure 12] FIG. 1 is a diagram showing an example of an LT single crystal substrate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Specific embodiments of the present invention will be described in detail below. The present invention is not limited to the following embodiments, and can be modified as appropriate without departing from the gist of the present invention. In each drawing, a part or whole is depicted diagrammatically as appropriate, and the scale is changed. In the following description, the expression "A to B" means "A or more and B or less."

[0018] First, a conventional method for manufacturing a piezoelectric oxide single crystal substrate having a notch will be briefly described. The conventional manufacturing method was performed, for example, in the following manner as described above. First, in a cylindrical grinding process, the surface of a piezoelectric single crystal such as an LT single crystal or an LN single crystal is cylindrically ground to process it into a cylindrical single crystal ingot (ingot), and a V-shaped groove is formed in a specific direction on the side of the ingot (this groove becomes a provisional notch when the ingot is sliced). In a slicing process, the ingot is sliced ​​into a disk-shaped substrate using free abrasive grains with a wire saw. In a beveling process, the substrate on which the provisional notch obtained in the slicing process is formed is held on a rotatable substrate grinding stage, and the stage is brought close to a rotating grindstone while rotating the substrate to chamfer the edge surface of the outer periphery of the substrate. After the chamfering operation is completed, the rotation of the stage is stopped and the stage is moved away from the rotating grindstone, and a notch grinding grindstone is rotated instead of the rotating grindstone, and the stage is brought close to a notch formation position to form a notch. After the formation of the notch is completed, both the front and back surfaces are lapped using free abrasive grains in a lapping process, processing distortion is removed in an optional etching process, and then the main surface (front surface) is mirror-polished on one side in a polishing process. Piezoelectric single crystal substrates such as LT single crystal substrates and LN single crystal substrates have an inclination in the crystal axis as shown in Figure 12, and only surfaces with a specified crystal orientation are used, so it is necessary to distinguish between the front and back of the substrate. In the manufacturing process of a piezoelectric single crystal substrate with only one notch, as in such a conventional manufacturing method, as described above, it is difficult to distinguish between the front and back of the substrate during the manufacturing process, and the front and back of the substrate may be used incorrectly.

[0019] Therefore, in the manufacturing method of the single crystal substrate of this embodiment, a second mark is formed on at least one of the front or back surfaces of a thin plate sliced ​​from an ingot of a piezoelectric single crystal having a groove that becomes a notch and a first mark that is removed in the beveling process formed on the side surface, and a third mark is formed on the outer periphery of the substrate after the beveling process. According to this manufacturing method, the front and back can be determined based on the positional relationship between the groove (notch) and the first mark on the outer periphery of the substrate before the beveling process in the slicing process and the beveling process, and the front and back can be determined based on the second mark on the front or back surface made in the slicing process after the beveling process, and the front and back of the substrate can be determined based on the positional relationship between the groove (notch) and the third mark (the part where the edge polishing is applied) on the outer periphery of the substrate from the lapping process to before the polishing process in the polishing process. In addition, the main surface (front surface) is a mirror surface after the polishing process, so the front and back can be determined. As described above, according to the present invention, it is possible to distinguish between the front and back sides in all processes, and there is no risk of mistaking the front and back sides for mirror polishing in the polishing process, thereby eliminating the problem of being unable to use the device as a surface acoustic wave element due to mistaking the front and back sides.

[0020] An example of a method for manufacturing a piezoelectric single crystal substrate according to this embodiment (hereinafter, abbreviated as a method for manufacturing a single crystal substrate) will be described in detail below. Fig. 1 is a flow chart showing an example of a method for manufacturing a single crystal substrate. The method for manufacturing a single crystal substrate according to this embodiment is a method for manufacturing a piezoelectric single crystal substrate having a notch used for identifying a predetermined crystal orientation, and includes a cylindrical grinding step S1, a groove forming step S2, a first marking step S3, a slicing step S4, a second marking step S5, a beveling step S6, an edge polishing step S7, a lapping step S8, and a polishing step S9, as shown in Fig. 1.

[0021] The piezoelectric single crystal used in this embodiment is a lithium tantalate (LT) single crystal (LT single crystal), a lithium niobate (LN) single crystal (LN single crystal), or the like, and has piezoelectricity. The piezoelectric single crystal substrate CPX is used as a device material such as a surface acoustic wave (hereinafter abbreviated as SAW) filter for removing signal noise in a mobile phone, or an optical element. The method for growing the piezoelectric single crystal is not particularly limited, and may be a single crystal growth method such as the Czochralski method (CZ method).

[0022] (Cylindrical grinding process S1) 2 is a diagram showing an example of the cylindrical grinding step S1. The cylindrical grinding step S1 is a step of performing cylindrical grinding on the side (cylindrical side surface, outer peripheral surface) of a grown piezoelectric single crystal ingot (hereinafter, abbreviated as ingot) to obtain a single crystal ingot C1 with a uniform outer diameter. The cylindrical grinding can be performed by a known method. Note that the manufacturing method of the single crystal substrate of this embodiment does not need to include the cylindrical grinding step S1. For example, the manufacturing method of the single crystal substrate of this embodiment can be performed using a piezoelectric single crystal ingot that has been previously manufactured and has been subjected to cylindrical grinding.

[0023] (Groove formation process S2) 3 is a perspective view showing an example of the groove forming step S2. The groove forming step S2 is a step of forming a predetermined groove 10 in the side surface of the ingot C1 that has been subjected to cylindrical grinding. The groove 10 can be formed by a known method such as by polishing the side surface of the ingot C1 to form a groove.

[0024] The groove 10 is formed to extend in the direction of the central axis AX1 of the ingot C1. The groove 10 is formed at a position that indicates a predetermined crystal orientation and is used to identify the predetermined crystal orientation. The groove 10 is a portion that is not removed by the beveling process S6 but remains, and ultimately becomes a notch 13 (see FIG. 8) that is used to identify the predetermined crystal orientation. The notch 13 is machined into its final shape by the beveling process S6 based on the shape of the groove 10. The depth of the groove 10 and the machining allowance in the beveling process S6 are adjusted so that the groove 10 is not removed by the beveling process S6 and becomes the notch 13 after the beveling process S6. In the case of a LT single crystal, the groove 10 is formed to indicate a crystal orientation in the +X direction shown in FIG. 12.

[0025] The cross-sectional shape of the groove 10 is preferably V-shaped as shown in Fig. 3. However, the cross-sectional shape of the groove 10 is not limited to V-shape, and may be, for example, U-shape.

[0026] The depth of the groove 10 is not particularly limited, but is preferably, for example, 0.7 mm to 1.5 mm from the viewpoints of ease of recognition, processing loss, and the like.

[0027] (First marking process S3) 4(A) and (B) are diagrams showing an example of the first marking step, where (A) is a perspective view and (B) is a cross-sectional view. The first marking step S3 is a step of forming a first mark M1 on the side (outer peripheral surface) of the ingot C1 in a portion that is asymmetric with the groove 10 with respect to the axis AX1 of the ingot C1.

[0028] The first mark M1 is formed on the outer periphery side of the bottom of the groove 10. The first mark M1 is formed at a position where the front and back of the substrate can be determined. For example, the first mark M1 is disposed at a position where θ is not 180° when the angle rotated around the central axis AX1 from the position of the groove 10 shown in FIG. 4(B) is θ. That is, the first mark M1 is disposed at a position asymmetrical with the groove 10 with respect to the central axis AX1 of the ingot C1. This makes it possible to determine the front and back of the substrate from the positional relationship (relative position) between the groove 10 and the first mark M1. When the above θ is 180°, it becomes difficult to determine the front and back of the substrate from the slicing step S4 to the second marking step S5 described later. The position of the first mark M1 is not particularly limited, but it is preferable that the distance L1 (see FIG. 4(B)) from the groove 10 to the first mark M1 is 1 to 5 cm because it is easy to determine the front and back. 4(B), the position of the first mark M1 relative to the groove 10 in the thin plate CP1 after the slicing process S4 described later is the front side when the mark is rotated clockwise, and the back side when the mark is rotated counterclockwise, making it easy to distinguish the front and back sides of the substrate. Note that the position of the first mark M1 is not limited as long as it is a position that allows the front and back sides of the substrate to be distinguished.

[0029] The method of forming (marking) the first mark M1 is not particularly limited. For example, the first mark M1 can be formed by laser marker processing, blast processing, coating of paint with a pen, or other methods. For example, in the case of laser marker processing, CO2 laser (λ=10.6 μm), YAG laser (λ=1.06 μm), YVO4 SHG laser (λ=532 nm), or YAG fourth harmonic laser (λ=265 nm) can be used. In addition, in the case of blast processing, sandblast processing using FO abrasive grains of about #4000 can be used. In this embodiment, the above marking can be distinguished between the front and back after the subsequent slicing process S4, and can be removed in the subsequent bevel process S6. Therefore, it is preferable to perform the marking by coating of paint (ink) with a pen, which reduces the number of processing steps. In the above marking, the type of pen and paint (ink) is not particularly limited, but a pen such as a marker pen can be used, for example. In the case of marking with a pen, there are no limitations on the position and size of the first mark M1. For example, the first mark M1 may be formed by marking the side of the ingot C1 with a pen such as a marker to a thickness of 5 mm at a position 2 cm clockwise from the groove 10.

[0030] (Slicing process S4) FIG. 5 is a diagram showing an example of the slicing step S4. The slicing step S4 is a step of slicing the ingot C2 in which the groove 10 and the first mark M1 are formed, and processing it into a thin plate CP1. The slicing step S4 can be performed by a known method. The slicing step S4 can be performed, for example, by a known wire saw device such as a multi-wire saw device. The groove 10 and the first mark M1 are formed in the thin plate CP1 formed by the slicing step S4. This makes it possible to identify the front and back of the substrate in the thin plate CP1 formed by the slicing step S4. For example, when marking is performed using a pen (paint, ink) at a position 2 cm away from the groove 10 in a clockwise direction, if the position of the first mark M1 is in the clockwise direction with respect to the groove 10, it is the front side, and if it is in the counterclockwise direction, it is the back side, and it is easy to identify the front and back of the substrate.

[0031] (Second marking process S5) FIG. 6 is a diagram showing an example of the second marking step S5. The second marking step S5 is a step of forming a second mark M2 on at least one of the front surface (main surface) and the back surface of the thin plate CP1 sliced ​​from the ingot C2. The second marking step S5 forms a thin plate CP2 having the second mark M2 formed on one surface of the thin plate CP1. In the second marking step S5, after the slicing step S4, the main surface F side of the thin plate CP1 can be identified by the groove 10 formed in the thin plate CP1 and the first mark M1. The position, size, and shape of the second mark M2 are not particularly limited as long as they can be recognized visually. For example, letters or symbols of about 5 mm square can be used.

[0032] The method of marking in the second marking step S5 is not particularly limited, and for example, as in the first marking step described above, methods such as laser marker processing, blast processing, and coating of paint with a pen can be used. Examples of the methods of laser marker processing, blast processing, and coating of paint with a pen are similar to those in the first marking step, so their explanations are omitted. It is preferable that the marking in the second marking step S5 is performed so that the second mark M2 can be removed by surface polishing or the like in the subsequent lapping step S8. When marking is performed by laser marker processing or blast processing, the surface of the substrate is scraped for marking, so it is preferable to set and manage the depth of the marking (second mark) to be equal to or less than the machining allowance in the lapping step S8. For this reason, it is preferable that the marking in the second marking step S5 is performed by coating of paint (ink) with a pen, because the paint is applied on the substrate, so there is no need to manage the depth, and the number of processing steps is small.

[0033] (Bevel process S6) 7(A) to (C) are diagrams showing an example of the beveling process S6, where (A) is a diagram showing a state in which the upper end of the outer peripheral end of the thin plate is beveled (beveling process), and (B) and (C) are diagrams showing examples of the outer peripheral end of the thin plate after beveling, where (B) is a cross-sectional view and (C) is a plan view. The beveling process S6 is a process in which the outer peripheral end E of the thin plate CP2 on which the second mark M2 is formed is chamfered and the first mark M1 is removed. In the beveling process S6, the outer peripheral portion of the thin plate CP2 is ground and a notch 13 is machined at the position of the groove 10, and the beveling process S6 can obtain the thin plate CP3 in which the notch 13 shown in FIG. 7(C) is formed and the first mark M1 is removed.

[0034] The bevel step S6 can be performed using an apparatus similar to that used in conventional beveling. For example, as shown in Fig. 7(A), the bevel step S6 uses an apparatus in which a ring-shaped chamfering grindstone 32 is fixed to a groove on the circumferential surface of a core disk. In the bevel step S6, as shown in Fig. 7(A), the outer peripheral end E of the thin plate CP2 held on the substrate holder 31 is pressed against the upper inclined surface of the rotating chamfering grindstone 32 to polish the corners of the upper edge of the thin plate CP2, and then the substrate holder 31 is lowered by a predetermined amount to press the corners of the lower edge of the thin plate CP2 against the lower inclined surface of the chamfering grindstone 32 to polish it.

[0035] As described above, in the beveling process S6, the removal amount is adjusted so as to remove the first mark M1. The removal amount in the beveling process S6 is not particularly limited, but from the viewpoint of reducing loss due to processing, the smaller the removal amount, the more preferable. When the first mark M1 is formed by the above-mentioned pen (paint, ink), the removal amount due to the beveling can be reduced, which is easy, and is therefore preferable.

[0036] After the bevel process S6, the first mark M1 disappears, but the second mark M2 remains. Therefore, in the processes after the bevel process S6, the front and back of the substrate can be distinguished by the second mark M2 formed in the second marking process S5.

[0037] (Edge polishing process S7) 8 is a plan view showing an example of the edge polishing step S7. The edge polishing step S7 is a step of forming a third mark M3 by partially performing edge polishing (edge ​​polishing processing) on ​​a portion of the side surface of the thin plate CP3 from which the first mark M1 has been removed in the beveling step S6 that is asymmetric with the groove 10 with respect to the axis AX1 (center of the substrate) of the ingot C1. The edge polishing step S7 obtains a thin plate CP4 in which the third mark M3 has been formed on the thin plate CP3. The thin plate CP4 has a notch 13, a second mark M2, and a third mark M3.

[0038] The third mark M3 is formed at a position where the front and back of the substrate can be determined. For example, the third mark M3 is disposed at a position where θ is not 180° when the angle rotated around the central axis AX1 from the position of the groove 10. In other words, the third mark M3 is disposed at a position asymmetrical to the groove 10 with respect to the central axis AX1 (center of the substrate) of the ingot C1. This makes it possible to determine the front and back of the substrate from the positional relationship (relative position) between the groove 10 and the third mark M3.

[0039] In the bevel process S6, the thin plate CP3 is tapered or rounded. In the edge polishing process S7, a part of the circumference of the outer periphery of the thin plate CP3 is edge polished to form a third mark M3. There is no particular limitation on the method of edge polishing. For example, the edge polishing may be performed using a sheet-feed edge polishing machine. The edge polishing is performed, for example, by bringing a rotating abrasive 40 such as an abrasive cloth into contact with a part of the outer periphery of the fixed thin plate CP3, as shown in FIG. 8(A).

[0040] The position where the edge polishing is performed is not particularly limited as long as it is a position asymmetric with respect to the central axis AX1 (center of the substrate) of the ingot C1 with respect to the groove 10 (a position where θ is not 180° when the angle rotated around the central axis AX1 from the position of the groove 10 is θ), but since the front and back are determined based on the position of the third mark M3 (the position where the edge polishing is performed) with the groove 10 as a reference, it is preferable that the position is close to the groove 10. For example, a position 1 cm to 3 cm away from the groove 10 (notch 13) is preferable from the viewpoint of ease of processing and good visibility of the third mark M3. The surface (end surface) of the outer periphery of the thin plate CP3 is a surface that has been beveled, and is generally a cloudy surface and not transparent. In this edge polishing step S7, by performing edge polishing on a part of the circumference (outer periphery) of the thin plate CP3, the surface (part, area) where the edge polishing is performed becomes transparent, and the third mark M3 is formed. The third mark M3 does not have to be (completely) transparent as long as it can be identified on the outer periphery, but it is preferable that the third mark M3 is more transparent (higher transparency) than the other parts of the side (peripheral surface) of the thin plate CP4. Among them, when the third mark M3 is transparent, it is more preferable that the third mark M3 is transparent, since it is possible to easily identify the third mark M3. For this reason, when edge polishing is performed on a part on the circumference of the thin plate CP3, it is preferable to perform the polishing to the extent that the processed part becomes transparent. That is, it is preferable that the third mark M3 is transparent. When the processed part is made transparent as described above, the edge polishing can be performed with an abrasive cloth using, for example, abrasive grains of #1500 to #3000. The size (length) of the third mark M3 is not particularly limited, and may be visually visible, for example, about 5 mm.

[0041] (Wrapping process S8) FIG. 9 is a plan view showing an example of the lapping step S8 and the polishing step S9. The lapping step S8 is a step of polishing the thin plate CP4 having the third mark M3 and edge polished to adjust the surface shape and thickness. As described above, from the beveling step S6 to before the lapping step S8, the front and back sides of the substrate can be determined by the notch 13, the second mark M2 formed in the second marking step S5, and the third mark M3 formed in the edge polishing step S7. As a result, the lapping step S8 can be performed after determining the front and back sides of the substrate. The lapping step S8 can be performed by a known method. For example, the lapping step S8 can use a double-sided lapping device. The conditions of the lapping step S8 are not particularly limited, but as described above, it is preferable to adjust the machining allowance so that the second mark M2 is removed. When the second mark M2 is formed by the above-mentioned pen (paint, ink), it is preferable because the machining allowance by the lapping process can be reduced and it is easy.

[0042] After the lapping step S8, the surface shape and thickness of the substrate are adjusted, and the second mark M2 is removed to obtain a thin plate CP5. The thin plate CP5 includes a notch 13 and a third mark M3. After the lapping step S8, the second mark M2 is removed, but the front and back of the substrate can be determined based on the positional relationship (relative position) between the notch 13 and the third mark M3 formed in the edge polishing step S7.

[0043] After the lapping step S8, an etching step (etching process) may be performed as necessary. The etching step is a step for removing processing distortion. The etching step is, for example, chemical etching using acid. There is no particular limit to the amount of etching in the etching step, but, for example, the amount of etching is about 0.5 μm. Normally, even after the above-mentioned etching process is performed, there is no change in the third mark M3 (the portion where the edge polishing is performed), so even after the etching step is performed, it is easy to determine the front and back of the substrate (thin plate).

[0044] (Polishing process S9) The polishing step S9 is a step of mirror-polishing the main surface F side of the thin plate CP5, the surface shape and thickness of which have been adjusted in the lapping step S8, to obtain a piezoelectric single crystal substrate CPX having a notch 13 and a third mark M3. As described above, in the steps following the edge polishing step S7, the front and back sides of the substrate can be determined from the positional relationship (relative position) between the notch 13 and the third mark M3 formed in the edge polishing step S7. In the polishing step S9, after determining the front and back sides of the substrate, the main surface F side is mirror-polished.

[0045] The polishing step S9 is a single-sided polishing step for mirror-polishing (polishing) the surface on the main surface F side of the thin plate CP5 after the lapping step S8. The polishing step S9 can be performed using a known single-sided polishing device. The single-sided polishing device is, for example, a device that fixes the back surface of the thin plate to an upper platen, presses it against a lower platen to which an abrasive cloth is attached, supplies an abrasive liquid between the front surface of the thin plate and the abrasive cloth, and rotates the thin plate and the abrasive cloth to mirror-polish the thin plate.

[0046] By the above-mentioned polishing step S9, the surface on the main surface F side is mirror-polished to obtain a piezoelectric single crystal substrate CPX having a notch 13 and a third mark M3 as shown in FIG.

[0047] As described above, in the manufacturing method of the piezoelectric single crystal substrate of this embodiment, it is possible to distinguish between the front and back sides in all steps, preventing errors in distinguishing between the front and back sides in each step and preventing the back side from being mistakenly mirror-polished in the polishing step.

[0048] As described above, the method for manufacturing a piezoelectric single crystal substrate according to this embodiment is a method for manufacturing a piezoelectric single crystal substrate having a notch 13 used to identify a predetermined crystal orientation, and includes a groove forming step S2 for forming a groove 10 that extends in the axial direction of the ingot C1 and becomes the notch 13 on a side surface of a cylindrically ground piezoelectric single crystal ingot C1, a first marking step S3 for forming a first mark M1 on a portion of the side surface of the ingot C1 that is asymmetric to the groove 10 with respect to the axis AX1 of the ingot C1, a slicing step S4 for slicing the ingot C2 in which the groove 10 and the first mark M1 are formed into a thin plate CP1, and a slicing step S5 for marking a second mark M on at least one side of the thin plate CP1 sliced ​​from the ingot C2. The method includes a second marking step S5 for forming a notch 13 and a third mark M3 on the thin plate CP5, a beveling step S6 for chamfering the outer peripheral end of the thin plate CP2 on which the second mark M2 is formed and removing the first mark M1, an edge polishing step S7 for partially polishing the edge of the thin plate CP3 from which the first mark M1 is removed, at a portion asymmetric with the groove 10 with respect to the axis AX1 of the ingots C1 and C2, and a lapping step S8 for polishing the thin plate CP4 on which the edge polishing has been performed and adjusting the surface shape and thickness, and a polishing step S9 for mirror-polishing the main surface F side of the thin plate CP5 whose surface shape and thickness have been adjusted, to obtain a piezoelectric single crystal substrate CPX having a notch 13 and a third mark M3. Note that in the method for producing a piezoelectric single crystal substrate of this embodiment, the configurations other than those described above are optional.

[0049] According to the manufacturing method of the piezoelectric single crystal substrate of this embodiment, the front and back sides can be distinguished from each other by the positional relationship between the groove (notch) on the outer periphery of the substrate and the first mark before the beveling in the slicing process and the beveling process, the front and back sides can be distinguished from each other by the second mark on the front or back side made in the slicing process after the beveling in the beveling process, and the front and back sides can be distinguished from each other by the positional relationship between the groove (notch) on the outer periphery of the substrate and the third mark (the part where the edge polishing was applied) from the lapping process to before the polishing in the polishing process. In addition, the front and back sides can be distinguished from each other after the polishing in the polishing process because the main surface (front side) is a mirror surface. As described above, according to the present invention, the front and back sides can be distinguished in all processes, and the front and back sides are not mistaken for the front and back sides and the back side is polished to a mirror finish in the polishing process, and the problem of not being able to use the surface acoustic wave element due to the front and back sides being mistaken for each other is eliminated. EXAMPLES

[0050] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0051] [Example 1] A lithium tantalate single crystal 36°RY grown ingot with a diameter of 210 mm was prepared as a piezoelectric single crystal. This ingot was surfaced at the 42°RY plane and cylindrically ground to a diameter of 201 mmφ. A V-shaped groove (V groove) with a depth of 1 mm was provided in the +X direction of the cylindrically ground ingot at a position corresponding to the +X direction in Figure 12 as shown in Figure 3, and a mark with a thickness of 5 mm was made at a position 2 cm away from the V groove in the clockwise direction as viewed from the surface (main surface) with a marker. In the slicing process, the ingot was sliced ​​using a wire saw cutting device to obtain 80 substrates with a thickness of 580 μm. Marking was made with a marker near the V groove on the surface after slicing. In the beveling process, the ingot was ground to a diameter of 200.05 mmφ, and a notch was made at the position of the V groove. After the bevel process, a sheet-fed edge polishing machine was used to press a 38mm diameter #3000 diamond polishing cloth, 25mm long and rotating at 2500rpm, against the V-groove at a position 2cm clockwise from the V-groove with a pressure of 100g for 20 seconds to perform edge polishing to a width of 5mm. The edge-polished portion was transparent. In the lapping process, the front and back surfaces were polished by 25μm each using GC#1000. In the etching process, etching was performed by 0.5μm, and in the polishing process, the front surface was mirror-polished to 30μm.

[0052] Using an oscilloscope to determine the front and back of the wafers based on the waveform pattern when the sides were touched, it was confirmed that the front (main) surface of all 80 wafers was mirror-polished.

[0053] [Comparative Example 1] A lithium tantalate single crystal 36°RY grown ingot with a diameter of 210 mm was prepared as a piezoelectric single crystal. This ingot was surfaced at a 42°RY plane and cylindrically ground to a diameter of 201 mmφ. A V groove with a depth of 1 mm was provided in the +X direction of the cylindrically ground ingot at a position corresponding to the +X direction of FIG. 12 as shown in FIG. 3, and a mark with a thickness of 5 mm was made at a position 2 cm away from the V groove in the clockwise direction as viewed from the front surface (main surface) with a marker. In the slicing process, the ingot was sliced ​​using a wire saw cutting device to obtain 80 substrates with a thickness of 580 μm. In the beveling process, the ingot was ground to a diameter of 200.05 mmφ, and notches were made at the positions of the V grooves. In the lapping process, the front and back surfaces were polished by 25 μm each using GC#1000. In the etching process, etching was performed by 0.5 μm, and in the polishing process, the front surface was mirror-polished by 30 μm.

[0054] Using an oscilloscope to determine the front and back of the wafers based on the waveform pattern when the sides were touched, it was confirmed that the backs of 5 out of 80 wafers were mirror-polished.

[0055] [Comparative Example 2] A lithium tantalate single crystal 36°RY grown ingot with a diameter of 210 mm was prepared as a piezoelectric single crystal. This ingot was surfaced at the 42°RY plane and cylindrically ground to a diameter of 201 mmφ. A V-shaped groove with a depth of 1 mm was provided in the +X direction of the cylindrically ground ingot at a position corresponding to the +X direction in Figure 12, as shown in Figure 3. In the slicing process, it was sliced ​​using a wire saw cutting device to obtain 80 substrates with a thickness of 580 μm. In the beveling process, it was ground to a diameter of 200.05 mmφ, and notches were processed at the positions of the V grooves. In the lapping process, the front and back surfaces were polished by 25 μm each using GC#1000. In the etching process, it was etched by 0.5 μm, and in the polishing process, the front surface was mirror-polished to 30 μm.

[0056] Using an oscilloscope to determine the front and back of the wafers based on the waveform pattern when the sides were touched, it was confirmed that 10 out of 80 wafers had mirror-polished backs.

[0057] From the results of the above examples and comparative examples, it is confirmed that the method for manufacturing a piezoelectric single crystal substrate according to this embodiment can reliably distinguish between the front and back of the substrate during all manufacturing steps in the process for manufacturing a piezoelectric single crystal substrate having a notch.

[0058] The technical scope of the present invention is not limited to the aspects described in the above-mentioned embodiments. One or more of the requirements described in the above-mentioned embodiments may be omitted. The requirements described in the above-mentioned embodiments may be combined as appropriate. In addition, to the extent permitted by law, the disclosures of all documents cited in the above-mentioned embodiments are incorporated by reference and made part of the description in this text. [Industrial Applicability]

[0059] According to the method for manufacturing a piezoelectric single crystal substrate of this embodiment, it is possible to reliably determine the front and back sides of the substrate in all manufacturing processes, and there is no risk of mistaking the front side (main surface) for the back side and mirror-polishing the back side in the polishing process. This eliminates the problem of being unable to use the substrate as a surface acoustic wave element due to mistaking the front side (main surface) for the back side. [Explanation of symbols]

[0060] C1, C2: Piezoelectric single crystal ingot CP1 to CP5: Thin plates (piezoelectric single crystal thin plates) CPX: Piezoelectric single crystal substrate 10: Groove 13:Notch M1: First Mark M2: Second Mark M3: The third mark AX1: Central axis

Claims

1. A method for manufacturing a piezoelectric single crystal substrate having a notch used for identifying a predetermined crystal orientation, comprising the steps of: a groove forming step of forming a groove that extends in the axial direction of the ingot and becomes the notch on a side surface of the cylindrically ground piezoelectric single crystal ingot; a first marking step of forming a first mark on a side surface of the ingot in a portion asymmetric with respect to an axis of the ingot relative to the groove; a slicing step of slicing the ingot in which the groove and the first mark are formed into a thin plate; a second marking step of forming a second mark on at least one surface of the thin plate sliced ​​from the ingot; a beveling process for beveling an outer peripheral edge of the thin plate on which the second mark is formed, thereby removing the first mark; an etch-polishing step of partially performing edge polishing on a portion of the side surface of the thin plate from which the first mark has been removed that is asymmetric with the groove with respect to the axis of the ingot to form a third mark; a lapping process for polishing the thin plate to which the edge polishing has been applied, and adjusting the surface shape and thickness; a polishing step of mirror-polishing a main surface side of the thin plate whose surface shape and thickness have been adjusted to obtain a piezoelectric single crystal substrate having the notch and the third mark.

2. The method for manufacturing a piezoelectric single crystal substrate according to claim 1 , wherein the first mark and the second mark are formed with paint.

3. 3. The method for producing a piezoelectric single crystal substrate according to claim 1, wherein the first marking step and the second marking step each include forming the first mark and the second mark using a pen.

4. 4. The method for producing a piezoelectric single crystal substrate according to claim 1, wherein the edge polishing is performed using abrasive grains of #1500 to #3000.

5. 5. The method for producing a piezoelectric single crystal substrate according to claim 1, wherein the third mark is more transparent on the side surface of the thin plate than a portion other than the third mark.

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