JP7643181B2 - Piezoelectric single crystal substrate and its manufacturing method - 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 (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 sequential mechanical processes of cylindrical grinding, slicing, beveling, lapping, and polishing. Etching 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, single crystal substrates with a diameter of 150 mm or less have had a straight line portion called an orientation flat (OF) at a specified position on the outer circumference to identify the crystal orientation, as shown in Figure 9. In addition, a straight line portion called an index flat (IF), which is shorter than the OF, has been provided to determine the front and back sides during the processing process and to determine the front and back sides of double-sided mirror-finished substrates.

However, it has become clear that providing OFs and IFs in single crystal substrates with a diameter of more than 150 mm reduces the effective area when devices are cut out of the substrate, and that larger diameter single crystal substrates inevitably increase in weight. Furthermore, when single crystal substrates with OFs and IFs are processed by rotating them at high speed using a spin coater or the like in the device manufacturing process, problems occur due to the OFs and IFs being chipped. In other words, single crystal substrates with OFs and IFs are naturally not perfectly circular on the periphery, and the OFs and IFs are chipped. When such a single crystal substrate with a chipped periphery is rotated at high speed using a spin coater or the like, an unbalanced load is generated, which causes problems such as the single crystal substrate vacuum-adsorbed to the rotor of the spin coater becoming detached or scattering due to the high speed rotation.

Therefore, instead of the single crystal substrate shown in Figure 9, which is formed with OF or IF, the single crystal substrate shown in Figure 10, which is formed with a V-shaped notch, was developed. This single crystal substrate has 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.

A single crystal substrate having a notch is processed, for example, by the following procedure as described in Patent Document 1. In the cylindrical grinding process, the surface of the single crystal is cylindrically ground to process it into a cylindrical single crystal ingot (ingot), and a V-shaped groove is formed in a specific direction on the side of the ingot (this groove becomes 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 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 is 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 the circuit pattern is exposed. 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 of the substrate (front and back surfaces).

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

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

According to another aspect of the present invention, there is provided a method for manufacturing a piezoelectric single crystal substrate, which includes forming a first notch in the crystal orientation direction on the outer periphery of a thin plate of a piezoelectric single crystal having a beveled outer periphery, with the center of the thin plate as a reference, and forming a second notch in a position asymmetrical with the first notch, the second notch having a different surface roughness from the first notch and being visually distinguishable.

The present invention provides 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 mirror-polished on both sides.

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 of the present invention. 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 marking process, in which FIG. 1A is a perspective view and FIG. FIG. 1 is a diagram illustrating an example of a slicing process. 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. 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. 11. A substrate processed perpendicular to such an orientation is called a substrate with a principal surface orientation of 42°RY. Such 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 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 single crystal substrate (the front 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 the case of 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 peripheral portion 10 and a notch 11 on the outer peripheral portion 10, and is characterized in that the outer peripheral portion 10 has a first notch 11 formed in the crystal orientation direction with respect to the center of the piezoelectric single crystal substrate CPX as a reference, and a second notch 12 at a position asymmetrical to the first notch 11, and the second notch 12 has a different surface roughness from the first notch 11 and is visually distinguishable.

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

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

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

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

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

The first notch 11 and the second notch 12 have different surface roughness and are visually distinguishable. The outer periphery 10 of the single crystal substrate CPX is beveled to have a chamfered shape (see FIG. 1B).

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

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

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

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

As described above, the single crystal substrate CPX according to this embodiment has a first notch 11 formed in the crystal orientation direction with respect to the center C of the piezoelectric single crystal substrate CPX in the outer periphery 10, and a second notch 12 at a position asymmetrical to the first notch 11, and the second notch 12 has a different surface roughness from the first notch 11 and is visually distinguishable. In the single crystal substrate CPX of this embodiment, the configuration other than the above is optional. The single crystal substrate CPX according to this embodiment can reliably distinguish the front and back of the single crystal substrate CPX based on the relative positions and surface condition of the first notch 11 and the second notch 12. In particular, the single crystal substrate CPX according to this embodiment can reliably distinguish the front and back of the substrate even in a substrate with both sides mirror-polished, which was previously impossible to distinguish visually. 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, mistakes between the front and back surfaces during the manufacturing process can be prevented.

An example of a method for manufacturing a single crystal substrate of 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 of this embodiment. Furthermore, the matters described in the above-mentioned single crystal substrate of this embodiment are applicable to the method for manufacturing a single crystal substrate of this embodiment, and the description will be omitted or simplified as appropriate. Furthermore, the matters described in the above-mentioned method for manufacturing a single crystal substrate of this embodiment are also applicable to the above-mentioned single crystal substrate of this embodiment.

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 marking process S3, a slicing process S4, a beveling process S5, a lapping process S6, and a polishing process S7.

(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 forming a groove by grinding the side surface of the ingot C1.

The groove 14 is formed so as to extend in the direction of the central axis AX1 of the ingot C1. The groove 14 is formed in two places, the first groove 14a which becomes the first notch 11, and the second groove 14b which becomes the second notch 12. The first groove 14a is formed at a position which indicates a predetermined crystal orientation and is used to identify the predetermined crystal orientation. The second groove 14b is formed at a position which is asymmetric with the first groove 14a. There is no particular limitation on the position of the second groove 14b, as long as it is at a position other than 180° from the position of the first groove 14a, in other words, as long as the position of the second groove 14b is at a position which is asymmetric with the first groove 14a with respect to the center AX1 of the single crystal C2. It is preferable that the position of the second groove 14b is formed so that the angle θ1 between the first groove 14a and the center AX1 of the single crystal is 45° or less. Furthermore, it is more preferable that the second groove 14b is located on the circumference (on the outer periphery 10) 1 to 3 cm away from the first groove 14a.

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

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

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

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

There is no particular limitation on the method of forming (marking) the mark M1. For example, the 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 S5, so it is preferable to perform the 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, for example. When marking with a pen, there are no limitations on the position and size of the mark M1, but for example, the mark M1 may be formed by marking the side of the ingot C1 with a pen such as a marker to a thickness of 5 mm at a position 2 cm clockwise away from the second groove 14b.

(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 first groove 14a, the second groove 14b and the 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 thin plate CP1 formed by the slicing step S4 has the first groove 14a, the second groove 14b and the mark M1 formed therein. This allows the thin plate CP1 formed by the slicing step S4 to identify the front and back of the substrate. For example, when marking is performed using a pen (paint, ink) or the like at a position 2 cm away from the second groove 14b in the clockwise direction, the mark M1 is the front side when the mark M1 is in the clockwise direction relative to the second groove 14b, and the mark M1 is the back side when the mark M1 is in the counterclockwise direction, and it is easy to distinguish the front and back of the substrate.

(Bevel process S5)
7(A) to (C) are diagrams showing an example of the bevel process S5, (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 S5 is a process in which the outer periphery 10 of the thin plate CP1 is chamfered to form the first notch 11 and the second notch 12, and the mark M1 is removed. In the bevel process S5, the outer periphery 10 of the thin plate CP1 is ground, and the first notch 11 and the second notch 12 are formed at the positions of the first groove 14a and the second groove 14b. By the bevel process S5, the thin plate CP3 in which the first notch 11 and the second notch 12 shown in FIG. 7(C) are formed and the mark M1 is removed can be obtained. The thin plate CP3 is included in the single crystal substrate CPX of the present embodiment described above.

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

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

In the beveling process S5, as described above, the removal allowance is adjusted so as to remove the mark M1. There are no particular restrictions on the removal allowance in the beveling process S5, but from the viewpoint of reducing losses due to processing, the smaller the removal allowance, the more preferable it is. When the 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.

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

In this embodiment, in the bevel process S5 and subsequent steps, the front and back of the substrate can be determined by the first notch 11 and the second notch 12 formed in the bevel process. In other words, in this embodiment, the bevel process S5 and subsequent steps can be performed after the front and back of the substrate can be easily determined by visual inspection.

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

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

After the lapping step S6, an etching step (etching treatment) may be performed as necessary. The etching step is a step for removing processing distortion. The etching step is, for example, chemical etching using acid. There is no particular limit to the amount of etching in the etching step, so long as the surface roughness of the first notch 11 and the second notch 12 is different and can be distinguished by visual inspection.

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

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

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

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 surface and cylindrically ground to a diameter of 201 mmφ. A V-shaped first groove 14a (V groove) with a depth of 1 mm was provided in the cylindrically ground ingot in the +X direction of FIG. 11, and a V-shaped second groove 14b (V groove) with a depth of 1 mm was provided at a position where θ1 is 20° when the angle rotated around the central axis AX1 from the position of the first groove 14a is θ1, and a marking with a thickness of 5 mm was performed with a marker at a position 2 cm away from the second groove 14b in the clockwise direction as viewed from the surface. In the slicing process, 80 thin plates with a thickness of 580 μm were obtained by slicing using a wire saw cutting device. In the beveling process, the ingot was ground to a diameter of 200.05 mmφ, and notch processing was performed at the positions of the first groove 14a and the second groove 14b. At this time, the first groove 14a was machined using a grindstone with a grit size of #800, and the second groove 14b was machined using a grindstone with a grit size of #1500, to form the first notch 11 and the second notch 12. The surface roughness of the first notch 11 was Ra 0.3 μm, and the surface roughness of the second notch 12 was Ra 0.05 μm. The surface state of the first notch 11 was opaque, and the second notch 12 was translucent and easy to see. In the lapping process, the front and back surfaces were 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. As a result of the above, a piezoelectric single crystal substrate CPX was obtained which had a first notch 11 and a second notch 12 at a position asymmetrical with respect to the first notch 11, the second notch 12 having a different surface roughness than the first notch 11 and which was visually distinguishable.

When the obtained piezoelectric single crystal substrates were placed in a CPX device formation device, all 80 substrates had devices formed on their front surface (main surface), and not a single substrate 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 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. 11 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 using GC#1000. In the etching process, etching was performed by 0.5 μm, and in the polishing process, the front and back surfaces were mirror-polished by 15 μm each. As described above, a piezoelectric single crystal substrate was obtained.

When the obtained piezoelectric single crystal substrates were placed in a device formation device, five out of 80 substrates had devices formed on the back side, meaning five substrates had the front and back reversed.

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 first and second notches and the surface condition, 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 visually.

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 prevent defects caused by mistaking the front and back during device processing of notched double-sided polished piezoelectric single crystal substrates.

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

Claims (5)

A piezoelectric single crystal substrate having a chamfered outer periphery and a notch on the outer periphery,
a first notch formed in the outer periphery in a crystal orientation direction with respect to the center of the piezoelectric single crystal substrate, and a second notch at a position asymmetrical with respect to the first notch;
The second notch has a surface roughness different from that of the first notch and is visually distinguishable. The piezoelectric single crystal substrate according to claim 1, wherein the second notch forms an angle of 45° or less with the first notch relative to the center of the piezoelectric single crystal substrate. The piezoelectric single crystal substrate according to claim 1 or 2, wherein the second notch is translucent. The piezoelectric single crystal substrate according to any one of claims 1 to 3, wherein both sides of the piezoelectric single crystal substrate are mirror surfaces. A method for manufacturing a piezoelectric single crystal substrate, comprising the steps of:
a first notch is formed in a thin plate of a piezoelectric single crystal having a beveled outer periphery in a crystal orientation direction based on a center of the thin plate in the outer periphery;
a second notch having a different surface roughness from the first notch and being visually distinguishable, at a position asymmetrical with respect to the first notch.

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