Piezoelectric single crystal substrate and manufacturing method thereof

Abstract

To provide a piezoelectric single crystal substrate capable of surely determining the front and rear of the piezoelectric single crystal substrate having a notch and both mirror-polished surfaces, and a method for manufacturing the same.SOLUTION: A piezoelectric single crystal substrate has a notch in a chamfered periphery. The periphery has a first notch formed in a crystal orientation direction using the center of the piezoelectric single crystal substrate as a reference and a second notch located at a position asymmetrical to the first notch, and the second notch has a surface roughness different from that of the first notch and allows visual determination.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Substrates obtained from single crystals are used as various materials. For example, piezoelectric single crystal substrates (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 cylindrical grinding, slicing, beveling, lapping, and polishing, in that order. Etching may also be performed between the lapping and polishing steps. Through the above-mentioned machining steps, a wafer-shaped single crystal substrate is manufactured from the single crystal ingot.

[0005] Conventionally, single crystal substrates with a diameter of 150 mm 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 9. 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 a single crystal substrate with a diameter of more than 150 mmφ is provided with OFs and IFs, the effective area for cutting out a device from the substrate is reduced, and the weight of a large-diameter single crystal substrate is inevitably increased. Moreover, when a single crystal substrate provided with OFs and IFs 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 chipping of the OFs and IFs. In other words, a single crystal substrate provided with OFs and IFs naturally does not have a perfect circular periphery, and the OFs and IFs are chipped. When such a 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 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. 9, the single crystal substrate with a V-shaped notch as shown in Fig. 10 was developed. This single crystal substrate has a notch cut into one edge of the outer periphery as a method of identifying crystal orientation in place of OF.

[0008] A single crystal substrate having a notch is processed by the following procedure as described in Patent Document 1, for example. In the cylindrical grinding process, the surface of the 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 rotary grindstone while the substrate is rotating 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 rotary grindstone, and a notch grinding grindstone is rotated instead of the rotary 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.

[0009] In the case of the piezoelectric single crystal substrate having a mirror-polished front surface and a non-mirror-polished back surface as described above, the front and back surfaces can be distinguished by visually checking the degree of polishing. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent No. 4151155 Summary of the Invention [Problem to be solved by the invention]

[0011] Meanwhile, in recent years, SAW filters have become increasingly sophisticated. In such sophisticated SAW filters, the line width of the circuit drawn on the piezoelectric single crystal substrate has become more precise, and therefore, in order to improve the accuracy of the line width during exposure of the circuit pattern, there is a demand for the flatness of the piezoelectric single crystal substrate to be further improved. In order to further improve the flatness of the piezoelectric single crystal substrate, in recent years, both sides of the piezoelectric single crystal substrate have often been simultaneously mirror-polished. However, a problem has arisen in that it is not possible to distinguish between the front and back of a piezoelectric single crystal substrate having both sides mirror-polished in this way by the degree of grinding of the surfaces.

[0012] Conventionally, in single crystal substrates with OFs and IFs, the front and back can be distinguished by the position of the IFs based on the OFs. Therefore, even in piezoelectric single crystal substrates with mirror polished surfaces, the presence of OFs and IFs always makes it easy to distinguish the front and back (front and back) of the substrate.

[0013] On the other hand, when a notched single crystal substrate is mirror-polished on both sides, the appearances of the front and back sides are identical, which creates the problem of being unable to distinguish between the front and back sides.

[0014] Therefore, an object of the present invention is to provide a piezoelectric single crystal substrate and a manufacturing method thereof that can easily and reliably distinguish between the front and back sides of a piezoelectric single crystal substrate having a notch, and in particular, that can reliably distinguish between the front and back sides of a piezoelectric single crystal substrate having a notch and both sides of which are mirror-polished. [Means for solving the problem]

[0015] According to an aspect of the present invention, there is provided a piezoelectric single crystal substrate having a chamfered outer periphery and a notch on the outer periphery, the piezoelectric single crystal substrate having a first notch formed in the outer periphery in a crystal orientation direction based on the center of the piezoelectric single crystal substrate and a second notch at a position asymmetrical to the first notch, the second notch having a different surface roughness than the first notch and being visually distinguishable.

[0016] In the piezoelectric single crystal substrate according to the embodiment of the present invention, the second notch may be configured to form an angle of 45° or less with the first notch with respect to the center of the piezoelectric single crystal substrate. The second notch may be configured to be semi-transparent. The piezoelectric single crystal substrate may have mirror surfaces on both sides.

[0017] According to another aspect of the present invention, there is provided a method for manufacturing a piezoelectric single crystal substrate, comprising: forming a first notch in the crystal orientation direction of a piezoelectric single crystal thin plate having a beveled outer periphery, based on the center of the thin plate, at the outer periphery, and forming a second notch, which has a different surface roughness from the first notch and is visually distinguishable, at a position asymmetrical to the first notch. Effect of the Invention

[0018] According to the present invention, it is possible to provide a piezoelectric single crystal substrate and a manufacturing method thereof, which can easily and reliably distinguish between the front and back sides of a piezoelectric single crystal substrate having a notch, and in particular, which can reliably distinguish between the front and back sides of a piezoelectric single crystal substrate having a notch and both sides of which are mirror-polished. [Brief description of the drawings]

[0019] [Figure 1] 1A and 1B are diagrams illustrating an example of a piezoelectric single crystal substrate according to an embodiment of the present invention, where 1A is a plan view and 1B is a side view seen in the direction A shown in 1A. [Diagram 2] 2 is a flowchart showing an example of a method for manufacturing a piezoelectric single crystal substrate according to an embodiment. [Diagram 3] FIG. 1 is a diagram showing an example of a cylindrical grinding process. [Figure 4] 11A to 11C are diagrams illustrating an example of a groove forming step. [Diagram 5] FIG. 1 shows an example of a marking process, where (A) is a perspective view and (B) is a cross-sectional view. [Figure 6] FIG. 13 is a diagram illustrating an example of a slicing process. [Figure 7]FIG. 1 shows an example of a bevel process, where (A) shows the state in which the upper end of the outer periphery of a thin plate is beveled, and (B) and (C) show examples of the outer periphery of a thin plate after beveling, where (B) is a side view and (C) is a plan view. [Figure 8] 1A to 1C are diagrams illustrating an example of a lapping process and a polishing process. [Figure 9] FIG. 1 is a diagram showing an example of a conventional single crystal substrate with OF. [Figure 10] FIG. 1 is a diagram showing an example of a conventional notched single crystal substrate. [Figure 11] FIG. 1 is a diagram showing an example of an LT single crystal substrate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] 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."

[0021] As described above, the piezoelectric single crystal substrate is used as a material for surface acoustic wave elements (SAW filters). For example, 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 are used for SAW filters. 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 a single crystal substrate has an inclination of the crystal axis and only a 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 and IF, the front and back can be distinguished by the position of the IF based on the OF. Therefore, even if a piezoelectric single crystal substrate has both sides mirror-polished, the OF and IF always exist, so that it is easy to distinguish the front and back (front and back) of the single crystal substrate.

[0022] However, as mentioned above, as the diameter of substrates increases, the number of substrates with notches instead of OF or IF is increasing, but it can be difficult to distinguish between the front and back of a substrate with a notch. In particular, it is impossible to determine the front and back of a substrate with a notch that has been mirror-polished on both sides.

[0023] The piezoelectric single crystal substrate according to this embodiment allows easy determination of the front and back sides even in a notched substrate with mirror polished surfaces, which previously had the problem of making it impossible to determine the front and back sides as described above. The piezoelectric single crystal substrate according to this embodiment will be described below. Figures 1(A) and (B) are diagrams showing an example of a piezoelectric single crystal substrate according to an embodiment. (A) is a plan view. (B) is a side view seen in the direction A shown in (A).

[0024] The piezoelectric single crystal substrate CPX (hereinafter sometimes abbreviated as "single crystal substrate") of this embodiment is a piezoelectric single crystal substrate having a chamfered outer periphery 10 and a notch 11 on the outer periphery 10, and is characterized in that the outer periphery 10 has a first notch 11 formed in the crystal orientation direction with the center of the piezoelectric single crystal substrate CPX as the reference, and a second notch 12 at a position asymmetrical to the first notch 11, and the second notch 12 has a different surface roughness than the first notch 11 and is visually distinguishable.

[0025] The piezoelectric single crystal used for the single crystal substrate CPX of this embodiment is a single crystal having piezoelectricity, such as lithium tantalate (LT) single crystal (LT single crystal) or lithium niobate (LN) single crystal (LN single crystal).

[0026] The outer peripheral portion 10 of the single crystal substrate CPX of this embodiment is a beveled surface that has been beveled to prevent cracking or chipping of the substrate. The outer peripheral portion 10 has a chamfered shape due to the beveling. The chamfered shape is not particularly limited as long as the corners are chamfered, and may be, for example, a bevel shape, an R shape, a curved surface shape, a tapered shape, or the like. The beveling is a process for forming the above chamfered shape. The beveling is performed by grinding with a grindstone or the like.

[0027] In the single crystal substrate CPX of this embodiment, two notches are provided in a part of the outer periphery 10 of the single crystal substrate CPX. The single crystal substrate CPX of this embodiment has a first notch 11 and a second notch. The first notch 11 is formed in the outer periphery 10 of the substrate in a predetermined crystal orientation direction. The shape of the first notch 11 is not particularly limited, and may be any shape that can be recognized visually. The shape of the first notch 11 may be, for example, a V-shaped or U-shaped cross-sectional shape. The depth of the first notch 11 is not particularly limited, but is preferably 0.7 mm to 1.5 mm.

[0028] The second notch 12 is formed in the outer periphery 10 of the substrate in a position asymmetric with the first notch 11, similar to the first notch 11. It may be formed in a position other than direction P1 (see FIG. 1(A)) that is 180° from the position of the first notch 11 with the center C of the substrate as the reference. In other words, the position of the second notch 12 is not particularly limited as long as it is a position asymmetric with the first notch 11 with the center C of the single crystal substrate CPX as the reference.

[0029] The position of the second notch 12 is preferably formed at a position where the angle θ1 between the first notch 11 and the center C of the single crystal substrate CPX is 45° or less. Furthermore, the position of the second notch 12 is more preferably on the circumference (on the outer periphery 10) at a distance L1 from the first notch 11 by 1 cm to 3 cm. By forming the first notch 11 and the second notch 12 close to each other, they are within the same field of view, making it easy to distinguish between the front and back of the single crystal substrate.

[0030] The shape of second notch 12 is not particularly limited. Like first notch 11, second notch 12 may have a V-shaped or U-shaped cross section. The depth of second notch 12 is not particularly limited, but is preferably 0.7 mm to 1.5 mm. The shapes of first notch 11 and second notch 12 may be different or the same. Note that it is more preferable to have different shapes between first notch 11 and second notch 12, since this makes it easier to distinguish the front and back of the single crystal substrate.

[0031] The first notch 11 and the second notch 12 have different surface roughness and are visually distinguishable from each other. The outer periphery 10 of the single crystal substrate CPX has a chamfered shape by bevel processing (see FIG. 1(B)).

[0032] Bevel processing is performed by grinding with a grindstone or the like. The ground surface is generally a dull, opaque surface. The processed surface that forms the notch is processed with the grindstone used for bevel processing, so it is the same surface as the beveled ground surface.

[0033] Therefore, this embodiment is characterized in that the grit size of the grindstone used when machining either the first notch 11 or the second notch 12 is changed, thereby changing the surface condition of the machined surfaces of the first notch 11 and the second notch 12.

[0034] The outer peripheral portion 10 of the single crystal substrate CPX is beveled using a grindstone with a grit size of about #800, and the surface state is a dull, opaque surface including the notch portion. For this reason, in order to facilitate visual discrimination, it is preferable to make the surface state of one of the processed surfaces of the first notch 11 and the second notch 12 semi-transparent by using a grindstone with a high grit size. In other words, it is preferable that the surface roughness of the first notch 11 and the surface roughness of the second notch 12 are such that one is opaque and the other is semi-transparent. The surface state (surface roughness) of the notch is not particularly limited as long as there is a difference that can be visually discriminated. For example, when one grindstone used to machine the first notch 11 and the second notch 12 has a grit size of #800 and the other grindstone has a higher grit size, the grit size is preferably #1200 or more, and more preferably #1500 or more and #2000 or less, and the surface roughness in this case will be 0.05 μm to 0.1 μm in terms of Ra.

[0035] As described above, the front and back of the single crystal substrate CPX can be distinguished by changing the size of the notch, but the notch size is 0.7 mm to 1.5 mm, and a change (difference) in size within this range makes it difficult to distinguish visually at a glance. However, as in this embodiment, it is easier to distinguish by the surface condition of the notch portion (the first notch 11 and the second notch 12 are collectively referred to as the "notch portion"), particularly in the case of opaque and semi-transparent. Furthermore, in the single crystal substrate CPX, it is more preferable to combine a change (difference) in the size of the notch with the change (difference) in the surface condition as described above, since this makes it even easier to distinguish (identify) the notches.

[0036] As described above, the single crystal substrate CPX according to this embodiment has, in the outer circumferential portion 10, a first notch 11 formed in the crystal orientation direction with respect to the center C of the piezoelectric single crystal substrate CPX as a reference, and a second notch 12 at a position asymmetrical to the first notch 11, and the second notch 12 has a different surface roughness from the first notch 11 and is visually distinguishable. Note that in the single crystal substrate CPX of this embodiment, the configuration other than the above is optional. The single crystal substrate CPX according to this embodiment can reliably distinguish the front and back of the single crystal substrate CPX based on the relative positions and surface condition of the first notch 11 and the second notch 12. In particular, the single crystal substrate CPX according to this embodiment can reliably distinguish the front and back of the substrate even in a substrate having both sides mirror-polished, which was conventionally impossible to distinguish the front and back by visual inspection. The single crystal substrate according to this embodiment can reliably distinguish the front and back of the substrate, thereby preventing the problem of being unable to use the substrate as a material for a surface acoustic wave element or the like due to mistaking the front and back.

[0037] The state of the front or back surface of the single crystal substrate CPX is not particularly limited. For example, in the single crystal substrate CPX, the front or back surface may be a mirror surface or may not be a mirror surface. When the front and back surfaces of the single crystal substrate CPX are mirror surfaces, the front and back surfaces of the substrate, which were conventionally impossible to determine visually as described above, can be reliably determined, so that the effect of the single crystal substrate CPX according to this embodiment becomes more prominent. Furthermore, even if the front or back surface of the single crystal substrate CPX is not a mirror surface, the front and back surfaces of the substrate can be reliably determined, so that, for example, mistakes between the front and back surfaces during the manufacturing process can be prevented.

[0038] An example of the method for manufacturing a single crystal substrate of this embodiment will be described below. FIG. 2 is a flow chart showing an example of the method for manufacturing a single crystal substrate. Note that the method for manufacturing a single crystal substrate described below is only an example, and does not limit the method for manufacturing a single crystal substrate of this embodiment. Furthermore, the matters described in the above-mentioned single crystal substrate of this embodiment are applicable to the method for manufacturing a single crystal substrate of this embodiment, and the description will be omitted or simplified as appropriate. Furthermore, it is assumed that the matters described in the above-mentioned method for manufacturing a single crystal substrate of this embodiment are also applicable to the above-mentioned single crystal substrate of this embodiment.

[0039] As shown in FIG. 2, the method for manufacturing a single crystal substrate in this embodiment includes a cylindrical grinding step S1, a groove forming step S2, a marking step S3, a slicing step S4, a beveling step S5, a lapping step S6, and a polishing step S7.

[0040] (Cylindrical grinding process S1) 3 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.

[0041] (Groove formation process S2) 4 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 14 in the side surface of the ingot C1 that has been subjected to cylindrical grinding. The groove 14 can be formed by a known method such as forming a groove by grinding the side surface of the ingot C1.

[0042] The groove 14 is formed so as to extend in the direction of the central axis AX1 of the ingot C1. The groove 14 is formed in two places, a first groove 14a which becomes the first notch 11, and a second groove 14b which becomes the second notch 12. The first groove 14a is formed at a position which indicates a predetermined crystal orientation and is used to identify the predetermined crystal orientation. The second groove 14b is formed at a position which is asymmetric with the first groove 14a. The second groove 14b is not particularly limited as long as it is at a position other than 180° from the position of the first groove 14a, in other words, the position of the second groove 14b is asymmetric with the first groove 14a with respect to the center AX1 of the single crystal C2. It is preferable that the position of the second groove 14b is formed so that the angle θ1 between the first groove 14a and the center AX1 of the single crystal is 45° or less. Furthermore, the position of the second groove 14b is more preferably on the circumference (on the outer periphery 10) 1 cm to 3 cm away from the first groove 14a.

[0043] The first groove 14a and the second groove 14b are the portions that remain without being removed by the beveling process S5 and ultimately become the first notch 11 and the second notch 12 (see FIG. 1(A)) that are used for identifying a predetermined crystal orientation, etc. The first notch 11 and the second notch 12 are machined into their final shapes by the beveling process S5 based on the shapes of the first groove 14a and the second groove 14b, respectively. The depths of the first groove 14a and the second groove 14b and the machining allowance in the beveling process S5 are adjusted so that the first groove 14a and the second groove 14b are not removed by the beveling process S5 and become the first notch 11 and the second notch 12 after the beveling process S5. In the case of a LT single crystal, the first groove 14a is formed so as to indicate a crystal orientation in the +X direction shown in FIG.

[0044] The cross-sectional shape of the first groove 14a and the second groove 14b is preferably V-shaped as shown in Fig. 4. The cross-sectional shape of the first groove 14a and the second groove 14b is not limited to V-shaped, and may be U-shaped, for example. The depth of the first groove 14a and the second groove 14b is not particularly limited, but is preferably 0.7 mm to 1.5 mm, for example, from the viewpoints of easy recognition and processing loss. The shape of the first groove 14a and the second groove 14b may be changed.

[0045] (Marking process S3) 5(A) and (B) are diagrams showing an example of the marking step, where (A) is a perspective view and (B) is a cross-sectional view. The marking step S3 is a step of forming a mark M1 on the side surface (outer peripheral surface) of the ingot C1 in a portion that is asymmetric with the grooves 14 (the first groove 14a and the second groove 14b) with respect to the axis AX1 of the ingot C1.

[0046] The mark M1 is formed on the outer periphery side of the bottom of the first groove 14a and the second groove 14b. The mark M1 is formed at a position where the front and back of the substrate can be determined. For example, the mark M1 is disposed at a position where, when the angle rotated around the central axis AX1 from the position of the first groove 14a shown in FIG. 5B is θ2, the mark M1 is not disposed at a position where θ2 is 180° and where the mark M1 does not interfere with the second groove 14b. This makes it possible to determine the front and back of the substrate from the positional relationship (relative position) between the first groove 14a, the second groove 14b, and the mark M1. If the first groove 14a, the second groove 14b, and the mark M1 are disposed symmetrically with respect to the central axis AX1, it becomes difficult to determine the front and back of the substrate after the slicing step S4 described later. The position of the mark M1 is not particularly limited, but it is preferable that the distance L2 (see FIG. 5(B)) from the first groove 14a or the second groove 14b to the mark M1 is 1 to 5 cm, since this makes it easier to distinguish between the front and back sides. For example, in the example shown in FIG. 5(B), the position of the mark M1 relative to the first groove 14a and the second groove 14b in the thin plate CP1 after the slicing step S4 described below is the front side when the mark M1 is rotated clockwise and the back side when the mark M1 is rotated counterclockwise, making it easier to distinguish between the front and back sides of the substrate. The position of the mark M1 is not particularly limited, so long as it is a position that makes it easier to distinguish between the front and back sides of the substrate.

[0047] The method of forming (marking) the mark M1 is not particularly limited. For example, the 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-mentioned marking can be distinguished between the front and back after the subsequent slicing process S4, and can be removed in the subsequent bevel process S5. 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-mentioned 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 mark M1. For example, the 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 away from the second groove 14b.

[0048] (Slicing process S4) FIG. 6 is a diagram showing an example of the slicing step S4. In the slicing step S4, the ingot C2 in which the first groove 14a, the second groove 14b and the mark M1 are formed is sliced ​​and processed into a thin plate CP1. The slicing step S4 can be performed by a known method. The slicing step S4 can be performed by a known wire saw device such as a multi-wire saw device. The thin plate CP1 formed in the slicing step S4 has the first groove 14a, the second groove 14b and the mark M1 formed therein. This allows the thin plate CP1 formed in the slicing step S4 to distinguish between the front and back of the substrate. For example, when marking is performed using a pen (paint, ink) or the like at a position 2 cm away from the second groove 14b in the clockwise direction, the mark M1 is the front side when the mark M1 is in the clockwise direction relative to the second groove 14b, and the mark M1 is the back side when the mark M1 is in the counterclockwise direction, and therefore it is easy to distinguish between the front and back of the substrate.

[0049] (Bevel process S5) 7(A) to (C) are diagrams showing an example of the beveling process S5, where (A) is a diagram showing a state in which the upper end of the outer periphery of the thin plate is beveled, (B) and (C) are diagrams showing an example of the outer periphery of the thin plate after beveling, (B) is a cross-sectional view, and (C) is a plan view. The beveling process S5 is a process in which the outer periphery 10 of the thin plate CP1 is chamfered to form the first notch 11 and the second notch 12, and the mark M1 is removed. In the beveling process S5, the outer periphery 10 of the thin plate CP1 is ground, and the first notch 11 and the second notch 12 are formed at the positions of the first groove 14a and the second groove 14b. By the beveling process S5, the thin plate CP3 shown in FIG. 7(C) in which the first notch 11 and the second notch 12 are formed and the mark M1 is removed can be obtained. The thin plate CP3 is included in the single crystal substrate CPX of this embodiment described above.

[0050] The beveling process S5 can be performed using an apparatus similar to that used for conventional beveling. For example, as shown in FIG. 7(A), the beveling process S5 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 beveling process S5, as shown in FIG. 7(A), the outer periphery 10 of the thin plate CP1 held on the substrate holder 31 is pressed against the upper inclined surface of the rotating chamfering grindstone 32 to grind the corners of the upper edge of the thin plate CP1, and then the substrate holder 31 is lowered by a predetermined amount to press the corners of the lower edge of the thin plate CP1 against the lower inclined surface of the chamfering grindstone 32 to grind them. As a result, the outer periphery of the thin plate CP1 is chamfered, and a thin plate CP2 from which the mark M1 has been removed is obtained.

[0051] The notch portion (first notch 11 and second notch 12) is formed by stopping the rotation of the thin plate CP2 with the outer periphery chamfered and processing the first groove 14a and the second groove 14b positions with a grindstone of a predetermined shape. When processing the first notch 11 (first groove 14a) and the second notch 12 (second groove 14b), one of them is processed with a grindstone having a different grit. It is preferable to use a high-grit grindstone as the grit of one of the grindstones. By using a high-grit grindstone, as described above, the surface conditions (surface roughness) of the first notch 11 and the second notch 12 can be formed to be different, and by visually checking the difference in surface roughness, it becomes possible to visually distinguish the front and back of the substrate (the first notch 11 and the second notch 12). Among them, by making the surface state of either the first notch 11 or the second notch 12 semitransparent (processing so as to reduce the surface roughness), the first notch 11 and the second notch 12 can be easily distinguished by visual inspection, and as a result, the front and back of the substrate can be easily distinguished. For example, the first groove 14a may be processed using a grindstone with a grit size of #800 to form the first notch 11, and the second groove 14b may be processed using a grindstone with a grit size of #1200 or more, preferably a grindstone with a grit size of #1500 or more and #2000 or less, to form the second notch 12. By making the grit size of the grindstone used to form the first notch 11 and the second notch 12 different, the surface state of the first notch 11 and the second notch 12 after processing changes, and the surface roughness can be formed to be different, and as a result, the first notch 11 and the second notch 12 can be easily distinguished by visual inspection (distinguishing the front and back of the substrate). By the above processing, a thin plate CP3 is obtained in which the second notch 12 has a surface roughness different from that of the first notch 11 and is formed with a notch that can be visually identified. This thin plate CP3 is included in the piezoelectric single crystal substrate CPX of the above-mentioned embodiment.

[0052] In the beveling process S5, as described above, the removal amount is adjusted so as to remove the mark M1. The removal amount in the beveling process S5 is not particularly limited, but from the viewpoint of reducing loss due to processing, the smaller the removal amount, the more preferable. When the 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.

[0053] (Wrapping process S6) 8 is a plan view showing an example of the lapping step S6 and the polishing step S7. The lapping step S6 is a step of polishing the thin plate CP3 obtained in the beveling step S5 to adjust the surface shape and thickness.

[0054] In this embodiment, in the beveling process S5 and subsequent processes, the front and back of the substrate can be distinguished by the first notch 11 and the second notch 12 formed in the beveling process. That is, in this embodiment, the beveling process S5 and subsequent processes can be performed after the front and back of the substrate can be easily distinguished by visual inspection.

[0055] The lapping step S6 can be performed after determining the front and back sides of the substrate. The lapping step S6 can be performed by a known lapping method. For example, the lapping step S6 can be performed using a double-sided lapping device. The conditions for the lapping step S6 are not particularly limited.

[0056] After the lapping step S6, a thin plate CP4 is obtained in which the surface shape and thickness of the substrate are adjusted. The thin plate CP4 has a first notch 11 and a second notch 12. The thin plate CP4 corresponds to the single crystal substrate CPX of the present embodiment described above.

[0057] After the lapping step S6, an etching step (etching treatment) 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 limitation on the amount of etching in the etching step, as long as the surface roughness of the first notch 11 and the second notch 12 is different and can be distinguished by visual inspection.

[0058] (Polishing process S7) The polishing step S7 is a step of polishing the thin plate CP4 that has been subjected to the lapping process to mirror-polish the main surface F or both surfaces F, R (see FIG. 1(B)). The polishing step S7 in this example is a step of mirror-polishing the main surface F or both surfaces (main surface F, back surface R) of the thin plate CP4 whose surface shape and thickness have been adjusted by the lapping step S6. The thin plate CP5 obtained by the polishing step S7 is a substrate having the above-mentioned first notch 11 and second notch 12, and having mirror-polished surfaces on both surfaces. This thin plate CP5 corresponds to the single crystal substrate CPX of this embodiment described above.

[0059] The polishing step S7 can be performed by using a known single-sided polishing device or double-sided polishing device. The single-sided polishing device is, for example, a device in which the back side of the thin plate is attached to a block, the block is fixed to the head of the single-sided polishing device, the lower side of the thin plate (the front side of the thin plate) is pressed against a lower surface plate to which an abrasive cloth is attached, an abrasive liquid is supplied between the front side of the thin plate and the abrasive cloth, and the thin plate and the abrasive cloth are rotated to mirror-finish one side of the thin plate.

[0060] As described above, the method for manufacturing a piezoelectric single crystal substrate of this embodiment includes forming a first notch 11 in the crystal orientation direction on the outer periphery of a piezoelectric single crystal thin plate having a beveled outer periphery with reference to the center of the thin plate, and forming a second notch 12 having a different surface roughness from that of the first notch 11 and capable of being visually identified at a position asymmetrical to the first notch 11. Note that in the method for manufacturing a piezoelectric single crystal substrate of this embodiment, configurations other than those described above are optional. According to the method for manufacturing a piezoelectric single crystal substrate of this embodiment, it is possible to easily and reliably distinguish the front and back of a piezoelectric single crystal substrate having a notch, and in particular, it is possible to provide a piezoelectric single crystal substrate and a method for manufacturing the same that can reliably distinguish the front and back of a piezoelectric single crystal substrate having a notch and both sides of which are mirror-polished. EXAMPLES

[0061] 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.

[0062] [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-shaped first groove 14a (V groove) with a depth of 1 mm was provided in the cylindrically ground ingot in the +X direction of FIG. 11, and a V-shaped second groove 14b (V groove) with a depth of 1 mm was provided at a position where θ1 is 20° when the angle rotated around the central axis AX1 from the position of the first groove 14a is θ1, and a marking with a thickness of 5 mm was made with a marker at a position 2 cm away from the second groove 14b in the clockwise direction as viewed from the surface. In the slicing process, the ingot was sliced ​​using a wire saw cutting device to obtain 80 thin plates with a thickness of 580 μm. In the beveling process, the ingot was ground to a diameter of 200.05 mmφ, and notch processing was performed at the positions of the first groove 14a and the second groove 14b. At this time, the first groove 14a was machined using a grindstone with a grit size of #800, and the second groove 14b was machined using a grindstone with a grit size of #1500, to form the first notch 11 and the second notch 12. The surface roughness of the first notch 11 was Ra 0.3 μm, and the surface roughness of the second notch 12 was Ra 0.05 μm. The surface state of the first notch 11 was opaque, and the second notch 12 was translucent and easy to see. In the lapping process, the front and back surfaces were each polished to a depth of 25 μm using GC#1000. In the etching process, etching was performed to a depth of 0.5 μm, and in the polishing process, the front and back surfaces were each mirror-polished to a depth of 15 μm. As a result of the above, a piezoelectric single crystal substrate CPX was obtained which had a first notch 11 and a second notch 12 at a position asymmetrical to the first notch 11, the second notch 12 having a different surface roughness than the first notch 11 and which was visually distinguishable.

[0063] When the obtained piezoelectric single crystal substrates were put into a CPX device formation apparatus, all 80 substrates had devices formed on their front surface (main surface), and not a single substrate was found to have the wrong front or back.

[0064] [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 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 cylindrically ground ingot in the +X direction of FIG. 11, and a marking with a thickness of 5 mm was made at a position 2 cm clockwise from the V groove when viewed from the front surface with a marker. In the slicing process, the ingot was sliced ​​using a wire saw cutting device to obtain 80 thin plates with a thickness of 580 μm. Marking was made with a marker near the V groove on the front surface after slicing. In the beveling process, the ingot was ground to a diameter of 200.05 mmφ, and notch processing was performed at the position of the V groove. 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 and back surfaces were mirror-polished by 15 μm each. As described above, a piezoelectric single crystal substrate was obtained.

[0065] When the obtained piezoelectric single crystal substrates were placed in a device forming apparatus, devices were formed on the reverse side of 5 out of 80 substrates, meaning that 5 substrates had the front and back sides reversed.

[0066] From the results of the above-mentioned examples and comparative examples, it is confirmed that the piezoelectric single crystal substrate of this embodiment allows the front and back of a piezoelectric single crystal substrate having a notch to be reliably distinguished from each other based on the relative positions of the first and second notches and the surface condition, and that even in the case of a substrate having a notch and mirror-polished on both sides, which was previously impossible to distinguish by visual inspection, the front and back of the substrate can be reliably distinguished.

[0067] 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]

[0068] According to the present invention, defects due to mistaken front and back mounting can be prevented in device manufacturing processes for notched double-side polished piezoelectric single crystal substrates. [Explanation of symbols]

[0069] C1, C2: Piezoelectric single crystal ingot CP1~CP2: Thin plate (piezoelectric single crystal thin plate) CPX, CP3 to CP5: Piezoelectric single crystal substrates 10: Outer periphery 11: First notch 12: Second notch 14: Groove 14a: First Groove 14b: Second Groove

Claims

1. A piezoelectric single crystal substrate having a chamfered outer periphery and a notch on the outer periphery, a first notch formed in the outer periphery in a crystal orientation direction with respect to the center of the piezoelectric single crystal substrate, and a second notch at a position asymmetrical with respect to the first notch; The second notch has a surface roughness different from that of the first notch and is visually distinguishable.

2. 2. The piezoelectric single crystal substrate according to claim 1, wherein the second notch forms an angle of 45[deg.] or less with the first notch and the center of the piezoelectric single crystal substrate as a reference.

3. 3. The piezoelectric single crystal substrate according to claim 1, wherein the second notch is semi-transparent.

4. 4. The piezoelectric single crystal substrate according to claim 1, wherein both surfaces of the piezoelectric single crystal substrate are mirror surfaces.

5. A method for manufacturing a piezoelectric single crystal substrate, comprising the steps of: a first notch is formed in a thin plate of a piezoelectric single crystal having a beveled outer periphery in a crystal orientation direction based on a center of the thin plate in the outer periphery; a second notch having a different surface roughness from the first notch and being visually distinguishable, at a position asymmetrical with respect to the first notch.

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