JP7567396B2 - Piezoelectric single crystal substrate and manufacturing method thereof - Google Patents

Description

The present invention relates to a piezoelectric single crystal substrate and a method for manufacturing the same.

Substrates obtained from single crystals are used as various materials. For example, piezoelectric 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) used in mobile communication devices to remove noise in electrical signals.

LT single crystals and LN single crystals are mainly manufactured by the Czochralski method. They 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 then heat-treated under soaking near the melting point to remove residual strain caused by thermal stress, and then subjected to a poling process to make it single-polarized. In other words, 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 still applied, and the voltage application is stopped and the crystal is cooled to room temperature. After the poling process, 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.

The procedure for processing a cylindrical single crystal ingot usually involves the following mechanical processes in that order: cylindrical grinding, slicing, beveling, lapping, and polishing. In some cases, an etching process is performed between the lapping and polishing processes. After going through the above-mentioned mechanical processes, a wafer-shaped single crystal substrate is manufactured from the single crystal ingot.

Conventionally, LT and LN single crystal substrates with a diameter of 150 mmφ or less have 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 11. In addition, a straight line portion shorter than the OF called an index flat (IF) 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.

However, when an OF or IF is provided on an 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 inevitably increases. Moreover, it has been found that when an LT or LN single crystal substrate with an OF or IF is processed by rotating it at high speed using a spin coater or the like in the device manufacturing process, problems occur due to the OF or IF being chipped. In other words, an LT or LN single crystal substrate with an OF or IF is naturally not a perfect circle on its periphery, and the OF or IF is chipped. When such an 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 to the rotor of the spin coater becomes detached or scattered at high speed, causing problems.

Therefore, instead of the single crystal substrate shown in Figure 11, which is formed with OF or IF, LT and LN single crystal substrates shown in Figure 12, which are formed with a V-shaped notch, were developed. These single crystal substrates have a notch cut into one end of the outer periphery of the single crystal substrate as a method of identifying crystal orientation in place of OF.

LT or LN single crystal substrates having a notch are processed, for example, by the following procedure 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 the temporary 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 temporary 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 the substrate is rotating to chamfer the edge 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 the notch formation position to form the notch. After the notch is formed, both the front and back surfaces are lapped using free abrasive grains in the lapping process, processing distortion is removed in the etching process, and then one side of the surface is mirror-polished in the polishing process.

In the case of a piezoelectric single crystal substrate as described above, in which the front side is mirror-polished but the back side is not, the front and back can be distinguished by visually checking the degree of polishing.

Patent No. 4151155

On the other hand, in recent years, SAW filters have become increasingly sophisticated. In these sophisticated SAW filters, the line width of the circuits drawn on the piezoelectric single crystal substrate has become more precise, and as a result, there has been a demand for the flatness of the piezoelectric single crystal substrate to be further improved in order to improve the accuracy of the line width when exposing the circuit pattern. 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 mirror-polished simultaneously. However, with such piezoelectric single crystal substrates with both sides mirror-polished, a problem has arisen in that it is not possible to distinguish between the front and back based on the degree of surface grinding.

Conventionally, the front and back of a single crystal substrate with OF and IF can be distinguished by the position of the IF based on the OF. Therefore, even in the case of a piezoelectric single crystal substrate with mirror polished surfaces on both sides, the OF and IF are always present, making it easy to distinguish the front and back (front and back surfaces) of the substrate.

On the other hand, when a notched single crystal substrate is mirror-polished on both sides, the appearance of the front and back sides is exactly the same, which creates the problem of being unable to distinguish between the front and back.

The present invention aims to provide a piezoelectric single crystal substrate and a method for manufacturing the same that can easily and reliably distinguish between the front and back sides of a piezoelectric single crystal substrate having a notch, and in particular, 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.

According to an aspect of the present invention, a piezoelectric single crystal substrate is provided in which the outer periphery is chamfered and has a notch on the outer periphery, the outer periphery has a transparent portion at a position that is asymmetric with the notch with respect to the center of the piezoelectric single crystal substrate, and the outer periphery is opaque except for the transparent portion.

The piezoelectric single crystal substrate of this embodiment may have mirror surfaces on both sides. The transparent portion may be a polished surface, and the opaque portion may be a beveled surface.

According to another aspect of the present invention, there is provided a method for manufacturing a piezoelectric single crystal substrate, which includes performing edge polishing on a thin plate of a piezoelectric single crystal having a beveled and notched outer periphery, in which a transparent portion is formed by edge polishing the thin plate at a position asymmetrical with respect to the notch with respect to the center of the thin plate, and performing polishing to mirror-polish the surface of the thin plate that has been edge polished.

The method for manufacturing a piezoelectric single crystal substrate according to the present invention may also include polishing both sides of the edge-polished thin plate to a mirror finish. The edge polishing may also include using abrasive grains of #1500 to #3000.

The piezoelectric single crystal substrate according to this embodiment can reliably distinguish between the front and back sides of a piezoelectric single crystal substrate having a notch, based on the relative positions of the notch and the transparent portion. In particular, the piezoelectric single crystal substrate according to this embodiment can reliably distinguish between the front and back sides of a substrate having a notch and mirror-polished on both sides, which was previously impossible to distinguish between by visual inspection. The single crystal substrate according to this embodiment can reliably distinguish between the front and back sides of a substrate, preventing the problem of the substrate being unable to be used as a material for a surface acoustic wave element or the like due to mistaking the front and back sides. Furthermore, the method for manufacturing a single crystal substrate according to this embodiment can manufacture the single crystal substrate of this embodiment.

1A and 1B are diagrams illustrating an example of a piezoelectric single crystal substrate according to an embodiment, in which 1A is a plan view, and 1B is a side view viewed in a direction A shown in 1A. 2 is a flowchart showing an example of a method for manufacturing a piezoelectric single crystal substrate according to an embodiment. FIG. 1 is a diagram showing an example of a cylindrical grinding process. 11A to 11C are diagrams illustrating an example of a groove forming step. 1A and 1B are views showing an example of a first marking step, in which FIG. 1A is a perspective view and FIG. FIG. 1 is a diagram illustrating an example of a slicing process. FIG. 11 is a cross-sectional view showing an example of a second marking step. 1A and 1B are diagrams showing an example of a bevel process, in which (A) shows the state in which the upper end of the outer periphery of a thin plate is beveled, and (B) and (C) are diagrams showing examples of the outer periphery of a thin plate after bevel processing, in which (B) is a side view and (C) is a plan view. FIG. 13 is a diagram illustrating an example of an edge polishing process. 1A to 1C are diagrams illustrating an example of a lapping process and a polishing process. FIG. 1 is a diagram showing an example of a conventional single crystal substrate with OF. FIG. 1 is a diagram showing an example of a conventional notched single crystal substrate. FIG. 2 is a diagram showing an example of an LT single crystal substrate.

Specific embodiments of the present invention are described in detail below. Note that the present invention is not limited to the following embodiments, and can be modified as appropriate without changing the gist of the present invention. Note that in each drawing, some or all of the drawings are shown schematically and the scale is changed as appropriate. In the following description, the expression "A to B" means "A or more and B or less."

As mentioned above, piezoelectric single crystal substrates are used as materials for surface acoustic wave elements (SAW filters). For example, SAW filters use LT single crystal substrates processed with a substrate principal surface orientation of about 42°RY or LN single crystal substrates processed with a principal surface orientation of about 128°RY. Here, for example, 42°RY is the direction rotated 42° from the Y axis to the Z axis direction in the Y-Z plane with the X axis as the rotation axis, as shown in FIG. 13. 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 a tilt in 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 single crystal substrates with OF or IF, the front and back can be distinguished by the position of the IF based on the OF. For this reason, even in the case of a piezoelectric single crystal substrate that has been mirror-polished on both sides, OF and IF always exist, making it easy to distinguish between the front and back sides of the substrate (the top and back surfaces).

However, as mentioned above, as substrates become larger in diameter, substrates with notches instead of OF or IF are becoming more common, but with substrates with notches, it can be difficult to distinguish between the front and back. In particular, with substrates with notches that are mirror-polished on both sides, it is impossible to determine the front and back.

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 viewed in the direction A shown in (A).

The piezoelectric single crystal substrate CPX (hereinafter sometimes abbreviated as "single crystal substrate") according to this embodiment is a piezoelectric single crystal substrate having a chamfered outer periphery 10 and a notch 11 in the outer periphery 10, characterized in that the outer periphery 10 has a transparent portion 12 at a position that is asymmetric with the notch 11 with respect to the center C of the single crystal substrate CPX, and the portion of the outer periphery 10 other than the transparent portion 12 is an opaque portion 13.

The piezoelectric single crystal used in the single crystal substrate CPX of this embodiment is a single crystal having piezoelectric properties, such as lithium tantalate (LT) single crystal (LT single crystal) or lithium niobate (LN) single crystal (LN single crystal).

The single crystal substrate CPX of this embodiment has a notch 11. The notch 11 is formed in the outer periphery 10 of the substrate in a direction of a predetermined crystal orientation. There are no particular limitations on the shape of the notch 11, and it may be any shape that is visually recognizable. The shape of the notch 11 may be, for example, a V-shaped or U-shaped cross-sectional shape. There are no particular limitations on the depth of the notch 11, but it is preferably 0.7 mm to 1.5 mm.

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 is beveled. The beveled shape is not particularly limited as long as the corners are beveled, and may be, for example, a beveled shape, an R shape, a curved shape, a tapered shape, or the like. The beveled shape is a process for forming the above-mentioned chamfered shape. The beveled portion is a grinding process using a grindstone or the like. The beveled portion becomes an opaque portion 13 that is a cloudy surface and not transparent. The degree of transparency of the opaque portion 13 includes a level that can be visually recognized as having a lower visible light transmittance than the transparent portion 12 described later, and does not have to be completely opaque. From the viewpoint of visibility, it is preferable that the opaque portion 13 has a low transparency (visible light transmittance).

In the single crystal substrate CPX of this embodiment, a transparent portion 12, which is a transparent region, is formed in part of the opaque portion of the outer periphery 10 of the single crystal substrate CPX. That is, the single crystal substrate CPX of this embodiment has a notch 11 and a transparent portion 12 in the outer periphery 10, and an opaque portion 13 in the portion of the outer periphery 10 other than the transparent portion 12.

The transparent portion 12 can be formed, for example, by performing a polishing process such as edge polishing, which will be described later. In other words, the transparent portion 12 may be a polished surface that has been subjected to a polishing process. When the transparent portion 12 is a polished surface, it can be easily performed compared to other methods of forming the transparent portion 12.

The position of the transparent portion 12 is not particularly limited as long as it is located in the outer peripheral portion 10 other than in the 180° direction P1 (see FIG. 1A) from the position of the notch 11, in other words, as long as the position of the transparent portion 12 is asymmetric with respect to the notch 11 with respect to the center C of the single crystal substrate CPX. With this configuration, the single crystal substrate CPX of this embodiment can easily distinguish between the front and back based on the positions of the notch 11 and the transparent portion 12.

As described above, the position of the transparent portion 12 is preferably close to the notch 11 from the viewpoint of visibility, because the front and back of the substrate are determined based on the position of the transparent portion 12 with respect to the notch 11. The position of the transparent portion 12 is preferably, for example, 1 cm to 3 cm away from the notch 11.

There are no particular limitations on the size (length) of the transparent portion 12, so long as it is visible. The length L1 of the transparent portion (see FIG. 1B) may be, for example, about 5 mm.

The transparency of the transparent portion 12 includes a level at which it is possible to visually recognize that the transparent portion 12 has a higher visible light transmittance than the opaque portion 13 described above, and it does not have to be completely transparent. From the viewpoint of ease of visibility, it is preferable that the transparent portion 12 has a high transparency (visible light transmittance).

As described above, the single crystal substrate CPX according to this embodiment is a piezoelectric single crystal substrate having a chamfered outer periphery 10 and a notch 11 on the outer periphery 10, and has a transparent portion 12 at a position that is asymmetric with the notch 11 with respect to the center C of the single crystal substrate CPX as a reference, and the portion of the single crystal substrate CPX other than the transparent portion 12 is an opaque portion 13. Note that the configuration other than the above in the single crystal substrate CPX of this embodiment is optional. The single crystal substrate CPX according to this embodiment can reliably distinguish the front and back of the single crystal substrate CPX having the notch 11 based on the relative positions of the notch 11 and the transparent portion 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 a notch 11 with both sides mirror-polished, which was previously 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 the substrate being unable to be used as a material for a surface acoustic wave element or the like due to the front and back being mistaken.

The state of the front or back surface of the single crystal substrate CPX is not particularly limited. For example, the front or back surface of the single crystal substrate CPX may 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 previously impossible to determine visually as described above, can be reliably determined, and the effect of the single crystal substrate CPX according to this embodiment becomes more pronounced. 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, and therefore, for example, confusion between the front and back surfaces during the manufacturing process can be prevented.

Next, a method for manufacturing a piezoelectric single crystal substrate according to this embodiment (hereinafter sometimes abbreviated as "method for manufacturing a single crystal substrate") will be described. The method for manufacturing a piezoelectric single crystal substrate according to this embodiment is a method for manufacturing a piezoelectric single crystal substrate, and includes performing edge polishing on a thin plate CP3 of a piezoelectric single crystal having a beveled and notched outer periphery 10 to form a transparent portion 12 at a position asymmetrical with respect to the notch 11 with respect to the center of the thin plate CP3 in the outer periphery 10, and performing polishing to mirror-polish the surface of the thin plate that has been edge polished. The method for manufacturing a single crystal substrate according to this embodiment is a method that can easily and reliably manufacture the single crystal substrate CPX of this embodiment described above.

An example of a method for manufacturing a single crystal substrate according to this embodiment will be described below. FIG. 2 is a flow chart showing an example of a method for manufacturing a single crystal substrate. Note that the method for manufacturing a single crystal substrate described below is only one example, and does not limit the method for manufacturing a single crystal substrate according to this embodiment. Furthermore, the matters described above for the single crystal substrate according to this embodiment can be applied to the method for manufacturing a single crystal substrate according to this embodiment, and the description thereof will be omitted or simplified as appropriate.

As shown in FIG. 2, the method for manufacturing a single crystal substrate in this embodiment includes a cylindrical grinding process S1, a groove forming process S2, a first marking process S3, a slicing process S4, a second marking process S5, a beveling process S6, an edge polishing process S7, a lapping process S8, and a polishing process S9.

(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, 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. 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.

(Groove forming step 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 polishing the side surface of the ingot C1 to form a groove.

The groove 14 is formed to extend in the direction of the central axis AX1 of the ingot C1. The groove 14 is formed at a position that indicates a predetermined crystal orientation and is used to identify the predetermined crystal orientation. The groove 14 is not removed by the beveling process S6 and remains, and is the part that will eventually become the notch 11 (see FIG. 1(A)) that will be used to identify the predetermined crystal orientation. The notch 11 is machined into its final shape by the beveling process S6 based on the shape of the groove 14. The depth of the groove 14 and the machining allowance in the beveling process S6 are adjusted so that the groove 14 is not removed by the beveling process S6 and becomes the notch 11 after the beveling process S6. In the case of an LT single crystal, the groove 14 is formed to indicate the crystal orientation in the +X direction shown in FIG. 13.

The cross-sectional shape of the groove 14 is preferably V-shaped as shown in FIG. 4. The cross-sectional shape of the groove 14 is not limited to V-shape and may be, for example, U-shaped. There is no particular limit to the depth of the groove 14, but it is preferable that it is, for example, 0.7 mm to 1.5 mm from the viewpoints of ease of recognition and processing loss.

(First marking step S3)
5A and 5B 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 surface (outer peripheral surface) of the ingot C1 in a portion that is asymmetric with the groove 14 with respect to the axis AX1 of the ingot C1.

The first mark M1 is formed on the outer periphery side of the bottom of the groove 14. 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 arranged at a position where θ is not 180° when the angle rotated around the central axis AX1 from the position of the groove 14 shown in FIG. 5B is θ. That is, the first mark M1 is arranged at a position asymmetrical with the groove 14 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 14 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 L2 (see FIG. 5B) from the groove 14 to the first mark M1 is 1 to 5 cm, since it is easy to determine the front and back. For example, in the example shown in FIG. 5B, the position of the first mark M1 relative to the groove 14 in the thin plate CP1 after the slicing process S4 described below 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 between 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.

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, application of paint with a pen, and 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), and YAG fourth harmonic laser (λ = 265 nm) can be used. In addition, for 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 marking by applying 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. When marking with a pen, there are no limitations on the position and size of the first mark M1, but for example, the first mark M1 may be formed by marking the side of the ingot C1 with a pen such as a marker, 2 cm away from the groove 14 in the clockwise direction, with a thickness of 5 mm.

(Slicing step S4)
FIG. 6 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 14 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 by a known wire saw device such as a multi-wire saw device. The groove 14 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 14 in the clockwise direction, if the position of the first mark M1 is in the clockwise direction with respect to the groove 14, it is the front side, and if it is in the counterclockwise direction, it is the back side, and it is easy to distinguish the front and back of the substrate.

(Second marking step S5)
FIG. 7 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 back surface of the thin plate CP1 sliced from the ingot C2. The second marking step S5 forms a thin plate CP2 in which the second mark M2 is 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 determined by the groove 14 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 visually recognized. For example, letters or symbols of about 5 mm square can be used.

The marking method in the second marking process S5 is not particularly limited, and for example, as in the first marking process described above, methods such as laser marker processing, blast processing, and application of paint with a pen can be used. Examples of the methods of laser marker processing, blast processing, and application of paint with a pen are similar to those in the first marking process, so their explanations are omitted. It is preferable that the marking in the second marking process S5 is performed so that the second mark M2 can be removed by surface polishing in the subsequent lapping process 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 process S8. For this reason, it is preferable that the marking in the second marking process S5 is performed by applying paint (ink) with a pen, since it is applied on the substrate, so there is no need to manage the depth, and the number of processing steps is small.

(Bevel process S6)
8(A) to (C) are diagrams showing an example of the bevel process S6, (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 bevel process S6 is a process of chamfering the outer periphery 10 of the thin plate CP2 on which the second mark M2 is formed, and removing the first mark M1. In the bevel process S6, the outer periphery of the thin plate CP2 is ground, and a notch 11 is machined at the position of the groove 14, and the bevel process S6 can obtain the thin plate CP3 in which the notch 11 shown in FIG. 8(C) is formed and the first mark M1 is removed.

The bevel process S6 can be performed using an apparatus similar to that used for conventional bevel processing. For example, as shown in FIG. 8(A), the bevel process S6 uses an apparatus in which a ring-shaped chamfering grindstone 32 is fixed to a groove on the peripheral surface of a core disk. In the bevel process S6, as shown in FIG. 8(A), the outer periphery 10 of the thin plate CP2 held on the substrate holding table 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 holding table 31 is lowered 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.

As described above, in the beveling process S6, the removal allowance is adjusted so as to remove the first mark M1. There are no particular restrictions on the removal allowance in the beveling process S6, but from the viewpoint of reducing losses due to processing, the smaller the removal allowance, the more preferable. When the first mark M1 is formed using the above-mentioned pen (paint, ink), this is preferable because it is easy and the removal allowance due to beveling can be reduced.

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

(Edge polishing step S7)
9 is a plan view showing an example of the edge polishing step S7. The edge polishing step S7 is a step of forming a transparent portion 12 at a position asymmetrical with respect to the notch 11 with respect to the center C of the thin plate CP3 in the outer peripheral portion 10 of the thin plate CP3 having been subjected to bevel processing and notch processing. In the edge polishing step S7 of this example, the transparent portion 12 is formed by partially performing edge polishing (edge polishing processing) on the side surface of the thin plate CP3 from which the first mark M1 has been removed by the beveling step S6, at a portion asymmetrical with respect to the notch 11 with respect to the center C of the thin plate CP3 (axis AX1 of the ingot C1). The edge polishing step S7 obtains a thin plate CP4 in which the transparent portion 12 is formed on the thin plate CP3. The thin plate CP4 includes the notch 11, the second mark M2, the transparent portion 12, and the opaque portion 13. The thin plate CP4 corresponds to the single crystal substrate CPX of the present embodiment described above.

The transparent portion 12 is formed at a position that allows the front and back of the substrate to be determined. For example, the transparent portion 12 is positioned at a position where θ is not 180° when the angle rotated from the position of the notch 11 around the center C of the thin plate CP4 (the central axis AX1 of the ingot C1). In other words, the transparent portion 12 is positioned asymmetrically with the notch 11 with respect to the center C of the thin plate CP4 (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 notch 11 and the transparent portion 12.

In the bevel process S6, the thin plate CP3 is subjected to chamfering such as taper processing and R surface processing. In the edge polishing process S7, a transparent portion 12 is formed by edge polishing a part of the circumference of the outer periphery of the thin plate CP3. The edge polishing is a polishing process. The outer periphery 10 becomes a polished surface by the edge polishing, and this polished surface becomes the transparent portion 12. There is no particular limitation on the method of edge polishing. For example, the edge polishing may be performed using a sheet-type edge polishing machine. The edge polishing is performed, for example, by bringing a rotating abrasive material 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. 9.

The position where the edge polishing is performed is not particularly limited as long as it is a position that is asymmetric with respect to the notch 11 with respect to the center C of the thin plate CP3 (the central axis AX1 of the ingot C1) (a position where θ is not 180° when the angle rotated from the position of the notch 11 around the center C of the thin plate CP3 is θ), but since the front and back are determined based on the position of the transparent part 12 (the position where the edge polishing was performed) with the notch 11 as the reference, a position close to the notch 11 is preferable. For example, a position 1 cm to 3 cm away from the notch 11 is preferable from the viewpoints of ease of processing and good visibility of the transparent part 12. The surface (end face) of the outer peripheral part 10 of the thin plate CP3 is a beveled surface that has been beveled, and is an opaque part 13 that is a cloudy surface and not transparent. In this edge polishing step S7, edge polishing is performed on a portion of the outer periphery 10 (opaque portion 13) of the thin plate CP3, so that the surface (portion, area) that has been subjected to edge polishing becomes transparent, forming the transparent portion 12. When forming the transparent portion 12, it is preferable to perform edge polishing using abrasive grains of #1500 to #3000 on an abrasive cloth 40. With the above abrasive grains, the transparent portion 12 can be formed more easily and reliably. The size L1 (length) of the transparent portion 12 may be large enough to be visible to the naked eye, for example, about 5 mm.

(Wrapping step S8)
FIG. 10 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 transparent portion 12 by edge polishing, and adjusting the surface shape and thickness. As described above, from the bevel step S6 to before the lapping step S8, the front and back of the substrate can be determined by the notch 11, the second mark M2 formed in the second marking step S5, and the transparent portion 12 formed in the edge polishing step S7. As a result, the lapping step S8 can be performed after determining the front and back 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.

After the lapping step S8, the surface shape and thickness of the substrate are adjusted, and a thin plate CP5 is obtained from which the second mark M2 has been deleted (removed). The thin plate CP5 has a notch 11, a transparent portion 12, and an opaque portion 13. The thin plate CP5 corresponds to the single crystal substrate CPX of the present embodiment described above. After the lapping step S8, the second mark M2 is deleted (removed), but the front and back of the substrate can be distinguished from each other based on the positional relationship (relative position) between the notch 11 and the transparent portion 12 formed in the edge polishing step S7.

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 the amount of etching is, for example, about 0.5 μm. Normally, even after the above-mentioned etching process is performed, there is no change in the transparent portion 12 (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).

(Polishing step S9)
The polishing step S9 is a step of polishing the thin plate that has been subjected to edge polishing to a mirror finish on the main surface F or both surfaces F, R (see FIG. 1(B)). The polishing step S9 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 CP5 whose surface shape and thickness have been adjusted by the lapping step S8, to obtain a thin plate CP6 having a notch 11, a transparent portion 12 and an opaque portion 13. The thin plate CP6 corresponds to the single crystal substrate CPX of this embodiment described above.

As described above, in the processes following the edge polishing process S7, the front and back of the substrate can be determined based on the positional relationship (relative position) between the notch 11 and the transparent portion 12 formed in the edge polishing process S7.

The polishing step S9 can be performed using a known single-sided polishing device or double-sided polishing device. A single-sided polishing device is, for example, a device in which the back surface of the thin plate is fixed to an upper platen, pressed against a lower platen to which an abrasive cloth is attached, abrasive liquid is supplied between the front surface of the thin platen and the abrasive cloth, and the thin platen and the abrasive cloth are rotated to mirror-finish the thin platen.

By the above-mentioned polishing step S9, the main surface F side or both surfaces of the substrate are mirror-polished to obtain a piezoelectric single crystal substrate CP6 (CPX) having a notch 11, a transparent portion 12, and an opaque portion 13, as shown in FIG. 10 (FIGS. 1(A) and (B)).

As described above, the method for manufacturing a single crystal substrate according to this embodiment is a method for manufacturing a piezoelectric single crystal substrate, and includes performing edge polishing on a piezoelectric single crystal thin plate CP3 having a beveled and notched outer periphery 10 to form a transparent portion 12 at a position asymmetrical with respect to the notch 11 with respect to the center of the thin plate CP3, and performing polishing to mirror-polish the surface of the thin plate CP4 (CP5) that has been edge polished. Note that in the single crystal substrate CPX of this embodiment, the configuration other than the above is optional. The method for manufacturing a single crystal substrate according to this embodiment can easily and reliably manufacture the single crystal substrate CPX of this embodiment.

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.

[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 groove (V groove) with a depth of 1 mm was provided in the +X direction of FIG. 13 on the cylindrically ground ingot, and a marking with a thickness of 5 mm was performed at a position 2 cm away from the V groove 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. Marking was performed with a marking 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 performed at the position of the V groove. After the bevel process, a #3000 diamond polishing cloth with a diameter of 38 mm and a length of 25 mm, rotating at 2500 rpm, was pressed against the V-groove at a position 2 cm clockwise using a sheet-type edge polishing machine with a pressure of 100 g for 20 seconds to perform edge polishing with a width of 5 mm to form a transparent part. In the lapping process, the front and back surfaces were polished by 25 μm 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.

When they were put into the device forming machine, all 80 sheets had devices formed on their front (main) surfaces, and not a single sheet was found with the front and back reversed.

[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 subjected to surface finishing at a 42° RY surface, 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 FIG. 13 on the cylindrically ground ingot, and a marking with a thickness of 5 mm was performed at a position 2 cm away from the V groove in the clockwise direction as 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 performed near the V groove on the front surface after slicing with a marker. 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.

When they were put into the device forming machine, 5 out of 80 sheets had devices formed on the reverse side, meaning 5 sheets had the wrong front and back.

The results of the above-mentioned examples and comparative examples confirm that the piezoelectric single crystal substrate according to this embodiment can reliably distinguish between the front and back of a piezoelectric single crystal substrate having a notch based on the relative positions of the notch and the transparent portion, and that it is possible to reliably distinguish between the front and back of a substrate even in the case of a substrate having a notch and mirror-polished on both sides, which was previously impossible to distinguish between by visual inspection.

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.

The present invention makes it possible to reliably distinguish between the front and back sides of a piezoelectric single crystal substrate having a notch, and prevents problems such as the substrate being unable to be used as a material for a surface acoustic wave element or the like due to mistaking the front and back sides. For example, it can prevent defects due to mistaking the front and back sides during the device formation process.

C1, C2: Piezoelectric single crystal ingot CP1 to CP5: Thin plate (piezoelectric single crystal thin plate)
CPX, CP4 to CP6: Piezoelectric single crystal substrate 10: Outer periphery 11: Notch 12: Transparent portion 13: Opaque portion

Claims (5)

A piezoelectric single crystal substrate having a chamfered outer periphery and a notch on the outer periphery,
a transparent portion is provided in the outer periphery at a position that is asymmetric with respect to the notch with respect to the center of the piezoelectric single crystal substrate;
In the outer periphery, a portion other than the transparent portion is an opaque portion,
The transparent portion is a portion that can be visually recognized as having a higher transmittance of visible light than the opaque portion . The piezoelectric single crystal substrate according to claim 1, wherein both sides of the piezoelectric single crystal substrate are mirror surfaces. the transparent portion is a polished surface,
3. The piezoelectric single crystal substrate according to claim 1, wherein the opaque portion is a beveled surface. A method for manufacturing a piezoelectric single crystal substrate, comprising the steps of:
performing edge polishing on a thin plate of a piezoelectric single crystal having an outer periphery that has been beveled and notched, in the outer periphery, at a position that is asymmetric with respect to the notch with respect to the center of the thin plate as a reference, to form a transparent portion;
and performing a polishing process to mirror-polish only the main surface or only both the main surface and the back surface of the thin plate that has been subjected to the edge polishing process. 5. The method for producing a piezoelectric single crystal substrate according to claim 4 , wherein the edge polishing is carried out using abrasive grains of #1500 to #3000.

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