JP7639280B2 - Manufacturing method of piezoelectric single crystal substrate - Google Patents

Description

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

Substrates obtained from single crystals are used as various materials. For example, piezoelectric single crystal substrates (hereinafter sometimes abbreviated as "single crystal substrates") such as lithium tantalate single crystal substrates (LT single crystal substrates) obtained from lithium tantalate (LT) single crystals and lithium niobate single crystal substrates (LN single crystal substrates) obtained from lithium niobate (LN) single crystals are used as materials for surface acoustic wave elements (SAW filters) 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. An etching process may also be 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 10. In addition, a straight line portion called an index flat (IF), which is shorter than the OF, is 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 10, which is formed with OF or IF, LT and LN single crystal substrates shown in Figure 11, 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 provisional notch when the ingot is sliced). In the slicing process, the ingot is sliced into a disk-shaped substrate using free abrasive grains with a wire saw. In the beveling process, the substrate with the provisional notch formed in the slicing process is held on a rotatable substrate grinding stage, and the stage is brought close to a rotating grindstone while rotating the substrate to chamfer the edge 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.

Patent No. 4151155

SAW filters use LT single crystal substrates processed with a substrate principal surface orientation of approximately 42°RY and LN single crystal substrates processed with a substrate principal surface orientation of approximately 128°RY. Here, for example, 42°RY is a 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 Figure 11, a substrate processed perpendicular to such an orientation is called a substrate with a principal surface orientation of 42°RY. Such LT and LN single crystal substrates have a tilt in the crystal axis and only surfaces with a specified crystal orientation are used, so it is necessary to distinguish between 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 example, single crystal substrates with OFs and IFs are manufactured by attaching a temporary OF of approximately the same length as the OF to be formed in the beveling process in the desired crystal orientation in the cylindrical grinding process, and a temporary IF of approximately the same length as the IF to be formed in the beveling process, and then forming a wafer-shaped single crystal substrate in the slicing process, and then chamfering the edge in the beveling process to obtain the desired edge shape, and forming the OF and IF based on the temporary OF and temporary IF. Therefore, since the OF and IF are always present in the single crystal substrate in the wafer shape after the slicing process, it is easy to distinguish the front and back of the substrate (front and back surfaces).

On the other hand, after a notched single crystal substrate is made into a wafer-shaped single crystal substrate in the slicing process, it only has a temporary notch or a notch formed in the beveling process on the outer periphery, making it difficult to distinguish between the front and back sides until the front side is mirror-polished on one side in the polishing process. This means that the front and back sides can sometimes be mistaken for each other in the slicing, beveling, lapping, etching, and polishing processes. If the front and back sides are mistaken for each other in the slicing, beveling, lapping, etching, and polishing processes, the back side is mirror-polished in the polishing process, resulting in the problem that a substrate with the wrong front and back sides cannot be used as a surface acoustic wave element.

The present invention aims to provide a method for reliably determining the front and back sides of a notched piezoelectric single crystal substrate during the manufacturing process up to the polishing process.

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

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

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

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 peripheral end of a thin plate is beveled, and (B) and (C) are diagrams showing examples of the outer peripheral end 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."

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

Therefore, in the manufacturing method of the single crystal substrate of this embodiment, a second mark is formed on at least one of the front or back surfaces of a thin plate sliced from an ingot of a piezoelectric single crystal having a groove that becomes a notch and a first mark that is removed in the beveling process formed on the side surface, and a third mark is formed on the outer periphery of the substrate after the beveling process. According to this manufacturing method, the front and back can be distinguished from each other by the positional relationship of the groove (notch) and the first mark on the outer periphery of the substrate before the beveling process in the slicing process and the beveling process, and the front and back can be distinguished from each other by the second mark on the front or back surface made in the slicing process after the beveling process in the beveling process, and the front and back of the substrate can be distinguished from each other by the positional relationship of the groove (notch) and the third mark (the part where the edge polishing was applied) on the outer periphery of the substrate from the lapping process to before the polishing process in the polishing process. In addition, the main surface (front surface) is a mirror surface after the polishing process, so the front and back can be distinguished. As described above, with this invention, it is possible to distinguish between the front and back sides in all processes, eliminating the risk of accidentally polishing the back side to a mirror finish in the polishing process due to the front and back sides being mistaken for each other, and eliminating the problem of being unable to use the device as a surface acoustic wave element due to the front and back sides being mistaken for each other.

An example of a method for manufacturing a piezoelectric single crystal substrate according to this embodiment (hereinafter, abbreviated as a method for manufacturing a single crystal substrate) will be described in detail below. FIG. 1 is a flow chart showing an example of a method for manufacturing a single crystal substrate. The method for manufacturing a single crystal substrate according to this embodiment is a method for manufacturing a piezoelectric single crystal substrate having a notch used to identify a specific crystal orientation, and 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, as shown in FIG. 1.

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

(Cylindrical grinding process S1)
2 is a diagram showing an example of the cylindrical grinding step S1. The cylindrical grinding step S1 is a step of performing cylindrical grinding on the side (cylindrical side, 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)
3 is a perspective view showing an example of the groove forming step S2. The groove forming step S2 is a step of forming a predetermined groove 10 in the side surface of the ingot C1 that has been subjected to cylindrical grinding. The groove 10 can be formed by a known method such as polishing the side surface of the ingot C1 to form a groove.

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

As shown in FIG. 3, the cross-sectional shape of the groove 10 is preferably V-shaped. However, the cross-sectional shape of the groove 10 is not limited to V-shape and may be, for example, U-shaped.

The depth of the groove 10 is not particularly limited, but is preferably 0.7 mm to 1.5 mm, for example, from the standpoint of ease of recognition and reduction in processing loss.

(First marking step S3)
4A and 4B 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 10 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 10. The first mark M1 is formed at a position where the front and back of the substrate can be determined. For example, the first mark M1 is arranged at a position where θ is not 180° when the angle rotated around the central axis AX1 from the position of the groove 10 shown in FIG. 4B is θ. That is, the first mark M1 is arranged at a position asymmetrical with the groove 10 with respect to the central axis AX1 of the ingot C1. This makes it possible to determine the front and back of the substrate from the positional relationship (relative position) between the groove 10 and the first mark M1. When the above θ is 180°, it becomes difficult to determine the front and back of the substrate from the slicing step S4 to the second marking step S5 described later. The position of the first mark M1 is not particularly limited, but it is preferable that the distance L1 (see FIG. 4B) from the groove 10 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. 4B, the position of the first mark M1 relative to the groove 10 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 pen, with a thickness of 5 mm, at a position 2 cm clockwise from the groove 10.

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

(Second marking step S5)
FIG. 6 is a diagram showing an example of the second marking step S5. The second marking step S5 is a step of forming a second mark M2 on at least one of the front surface (main surface) and 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 10 formed in the thin plate CP1 and the first mark M1. The position, size, and shape of the second mark M2 are not particularly limited as long as they can be 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)
7(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 peripheral end of the thin plate is beveled (beveling process), (B) and (C) are diagrams showing an example of the outer peripheral end 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 peripheral end E 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 peripheral portion of the thin plate CP2 is ground, and a notch 13 is processed at the position of the groove 10, and the bevel process S6 can obtain the thin plate CP3 in which the notch 13 shown in FIG. 7(C) is formed and the first mark M1 is removed.

The bevel process S6 can be performed using an apparatus similar to that used in conventional beveling. For example, as shown in FIG. 7(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. 7(A), the outer peripheral end E 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)
8 is a plan view showing an example of the edge polishing step S7. In the edge polishing step S7, a third mark M3 is formed by partially performing edge polishing (edge polishing processing) on a portion of the side surface of the thin plate CP3 from which the first mark M1 has been removed in the beveling step S6 that is asymmetric with the groove 10 with respect to the axis AX1 (center of the substrate) of the ingot C1. The edge polishing step S7 obtains a thin plate CP4 in which the third mark M3 is formed on the thin plate CP3. The thin plate CP4 includes a notch 13, a second mark M2, and a third mark M3.

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

In the bevel process S6, the thin plate CP3 is tapered or R-faced. In the edge polishing process S7, a part of the circumference of the outer periphery of the thin plate CP3 is edge polished to form a third mark M3. There are no particular limitations on the method of edge polishing. For example, the edge polishing may be performed using a sheet-feed edge polishing machine. The edge polishing is performed, for example, by bringing a rotating abrasive 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. 8(A).

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

(Wrapping step S8)
FIG. 9 is a plan view showing an example of the lapping step S8 and the polishing step S9. The lapping step S8 is a step of polishing the thin plate CP4 having the third mark M3 and edge polished to adjust the surface shape and thickness. As described above, from the bevel step S6 to before the lapping step S8, the front and back of the substrate can be determined by the notch 13, the second mark M2 formed in the second marking step S5, and the third mark M3 formed in the edge polishing step S7. As a result, the lapping step S8 can be performed after determining the front and back 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 process 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 13 and a third mark M3. After the lapping process S8, the second mark M2 is deleted (removed), but the front and back of the substrate can be determined based on the positional relationship (relative position) between the notch 13 and the third mark M3 formed in the edge polishing process 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, for example, the amount of etching is about 0.5 μm. Normally, even after the above-mentioned etching process is performed, there is no change in the third mark M3 (the portion where the edge polishing is performed), so even after the etching step is performed, it is easy to determine the front and back of the substrate (thin plate).

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

The polishing step S9 is a single-sided polishing step in which the surface on the main surface F side of the thin plate CP5 after the lapping step S8 is mirror-polished (polished). The polishing step S9 can be performed using a known single-sided polishing device. The 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 plate and the abrasive cloth, and the thin plate and the abrasive cloth are rotated to mirror-polish the thin plate.

By the above-mentioned polishing step S9, the surface on the main surface F side is mirror-polished to obtain a piezoelectric single crystal substrate CPX having a notch 13 and a third mark M3, as shown in FIG. 9.

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

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

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

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 in the +X direction as shown in FIG. 3 was provided on the cylindrically ground ingot at a position corresponding to the +X direction in FIG. 12, and a marking with a thickness of 5 mm was performed with a marker at a position 2 cm away from the V groove in the clockwise direction as viewed from the surface (main surface). In the slicing process, the ingot was sliced using a wire saw cutting device to obtain 80 substrates with a thickness of 580 μm. Marking was performed with a marker near the V groove on the surface after slicing. In the beveling process, the ingot was ground to a diameter of 200.05 mmφ, and a notch was 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 from the V-groove with a pressure of 100 g for 20 seconds to perform edge polishing to a width of 5 mm. The edge-polished portion was transparent. In the lapping process, the front and back surfaces were polished to 25 μm each using GC#1000. In the etching process, etching was performed to 0.5 μm, and the front surface was mirror-polished to 30 μm in the polishing process.

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

[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. The ingot was subjected to surface finishing at a 42° RY surface, and cylindrically ground to a diameter of 201 mmφ. A V groove with a depth of 1 mm was provided in the +X direction as shown in FIG. 3 at a position corresponding to the +X direction in FIG. 12 on the cylindrically ground ingot, and a marking with a thickness of 5 mm was performed with a marker at a position 2 cm away from the V groove in the clockwise direction as viewed from the front surface (main surface). In the slicing process, the ingot was sliced using a wire saw cutting device to obtain 80 substrates with a thickness of 580 μm. In the beveling process, the ingot was ground to a diameter of 200.05 mmφ, and 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 using GC#1000. In the etching process, etching was performed by 0.5 μm, and in the polishing process, the front surface was mirror-polished by 30 μm.

Using an oscilloscope to determine the front and back of the boards based on the waveform pattern when the sides were touched, it was confirmed that the backs of five of the 80 boards were mirror-polished.

[Comparative Example 2]
A lithium tantalate single crystal 36° RY grown ingot with a diameter of 210 mm was prepared as a piezoelectric single crystal. The ingot was subjected to surface finishing at a 42° RY plane, and cylindrically ground to a diameter of 201 mmφ. A V-shaped groove with a depth of 1 mm in the +X direction as shown in FIG. 3 was provided in the cylindrically ground ingot at a position corresponding to the +X direction in FIG. 12. In the slicing process, the ingot was sliced using a wire saw cutting device to obtain 80 substrates with a thickness of 580 μm. In the beveling process, the ingot was ground to a diameter of 200.05 mmφ, and 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 surface was mirror-polished by 30 μm.

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

The results of the above examples and comparative examples confirm that the method for manufacturing a piezoelectric single crystal substrate of this embodiment can reliably distinguish the front and back of the substrate during all manufacturing steps in the manufacturing process of a piezoelectric single crystal substrate having a notch.

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 method for manufacturing a piezoelectric single crystal substrate according to this embodiment makes it possible to reliably determine the front and back sides of the substrate in all manufacturing processes, eliminating the risk of mistaking the front side (main surface) for the back side and mirror-polishing the back side in the polishing process. This eliminates the problem of being unable to use the substrate as a surface acoustic wave element due to mistaking the front side (main surface) for the back side.

C1, C2: Piezoelectric single crystal ingot CP1 to CP5: Thin plate (piezoelectric single crystal thin plate)
CPX: Piezoelectric single crystal substrate 10: Groove 13: Notch M1: First mark M2: Second mark M3: Third mark AX1: Central axis

Claims (5)

A method for manufacturing a piezoelectric single crystal substrate having a notch used for identifying a predetermined crystal orientation, comprising the steps of:
a groove forming step of forming a groove that will become the notch and that extends in the axial direction of the ingot on a side surface of the cylindrically ground piezoelectric single crystal ingot;
a first marking step of forming a first mark on a side surface of the ingot in a portion asymmetric with respect to an axis of the ingot relative to the groove;
a slicing step of slicing the ingot in which the groove and the first mark are formed into a thin plate;
a second marking step of forming a second mark on at least one surface of the thin plate sliced from the ingot;
a beveling process for beveling an outer peripheral edge of the thin plate on which the second mark is formed, thereby removing the first mark;
an etch-polishing step of partially performing edge polishing on a portion of the side surface of the thin plate from which the first mark has been removed that is asymmetric with the groove with respect to the axis of the ingot to form a third mark;
a lapping process for polishing the thin plate to which the edge polishing has been applied, and adjusting the surface shape and thickness;
a polishing step of mirror-polishing a main surface side of the thin plate whose surface shape and thickness have been adjusted to obtain a piezoelectric single crystal substrate having the notch and the third mark. The method for manufacturing a piezoelectric single crystal substrate according to claim 1, wherein the first mark and the second mark are formed with paint. The method for manufacturing a piezoelectric single crystal substrate according to claim 1 or 2, wherein the first marking step and the second marking step each include forming the first mark and the second mark using a pen. 4. The method for producing a piezoelectric single crystal substrate according to claim 1, wherein the edge polishing is performed using abrasive grains of #1500 to #3000. The method for manufacturing a piezoelectric single crystal substrate according to any one of claims 1 to 4, wherein the third mark is more transparent on the side surface of the thin plate than the portion other than the third mark.

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