JP7655036B2 - Cutting Method - Google Patents

Description

The present invention relates to a cutting method, for example, a method for cutting lithium niobate and lithium tantalate.

Conventionally, a method using a wire saw machine has been known as a method for cutting cylindrical crystal ingots of lithium niobate (LN) or lithium tantalate (LT) manufactured by the Czochralski method into wafers in order to manufacture substrates for surface acoustic wave elements used in surface acoustic wave devices and the like. For example, the cutting method using a wire saw machine described in Patent Document 1 uses a wire saw machine having three main shaft rollers, grooves formed on the outer periphery of the main shaft rollers at a pitch that matches the target wafer thickness, and a single saw wire is wound around the grooves of the main shaft rollers to form a wire row consisting of multiple saw wires.

Then, the main shaft roller is rotated to run the wire saw, and the main table to which the crystal ingot is fixed is operated to press the crystal ingot against the wire row, cutting it into multiple wafers at the same time.

JP 2001-1248 A

In recent years, substrates for surface acoustic wave elements have become larger and thinner. As a result, the probability of wafer-shaped workpieces cracking during the process of cutting a crystal ingot into wafers is increasing due to vibrations caused by the cutting process and contact between the cut wafer-shaped workpieces. In order to prevent cracking of large-diameter, thin substrates, a method can be considered in which the process of cutting the crystal ingot into wafers with a wire saw is stopped halfway through, and a reinforcing plate is attached to cover all of the cut areas of the crystal ingot to fix the cut areas. This makes it possible to prevent the cut wafer-shaped workpieces from cracking due to vibration or from cracking due to contact between adjacent wafer-shaped workpieces.

However, once processing was stopped, the wire saw would shift in the thickness direction of the wafer-shaped workpiece (perpendicular to the cut surface), forming steps on the surface of the wafer-shaped workpiece obtained from a workpiece such as a crystal ingot, which could result in a deterioration in the flatness of the surface of the wafer-shaped workpiece made from the crystal ingot.

The present invention therefore aims to provide a cutting method for cutting a workpiece into wafers that can suppress the occurrence of cracks in the wafer-shaped workpiece and can suppress deterioration of the flatness of the surface of the wafer-shaped workpiece caused by the wire saw shifting while cutting the workpiece.

The cutting method of the present invention is a cutting method in which a wire array, which is a running plurality of saw wires, is pressed parallel to the side of a workpiece to cut the workpiece into a wafer shape. The workpiece before cutting is held by a first workpiece holding plate that is in contact with the wire array before the workpiece is cut and holds the side of the workpiece across both ends, and a second workpiece holding plate that is in contact with the wire array after the workpiece is cut and holds the side of the workpiece across both ends. The cutting method includes a first cutting step in which the first workpiece holding plate is cut but the workpiece is not cut, an attachment step in which a reinforcing plate that holds all of the cut portions of the first workpiece holding plate and reinforces the first workpiece holding plate is attached to the first workpiece holding plate after the first cutting step and before the workpiece is cut, and a second cutting step in which the workpiece is cut with the wire array after the attachment step.

In the cutting method of the present invention, the first workpiece holding plate and the second workpiece holding plate may be arranged parallel to the cutting direction by the wire array in the following order: first workpiece holding plate, work, second workpiece holding plate.

In the cutting method of the present invention, the wire row may be a row of multiple identical saw wires arranged at equal intervals and run at the same speed.

In the cutting method of the present invention, in the first cutting step and the second cutting step, the multiple saw wires may all be pressed against the workpiece with the same pressure to cut it.

In the cutting method of the present invention, the workpiece may be cylindrical.

In the cutting method of the present invention, the workpiece may be a crystalline ingot of lithium tantalate or lithium niobate.

The cutting method of the present invention, in a cutting method for cutting a workpiece into wafers, can suppress the occurrence of cracks in the wafer-shaped workpiece and also suppress deterioration of the flatness of the surface of the wafer-shaped workpiece caused by the wire saw shifting while cutting the workpiece.

FIG. 2 is a side view showing a schematic diagram of a wire saw device used in the cutting method according to one embodiment of the present invention. 2A is an enlarged perspective view showing a main portion E in a cutting process in the wire saw device shown in FIG. 1 , and FIG. 2B is an enlarged perspective view showing a cutting fluid supply unit 30 a. 1A and 1B are schematic diagrams showing a state in which a first work holding plate 92 is attached to a crystalline ingot L, in which (A) is a side view and (B) is a perspective view. 4A and 4B are schematic diagrams showing the state in which the first work holding plate 92 has been cut by the first cutting process, in which (A) is a side view and (B) is a cross-sectional view showing the first work holding plate 92 and multiple saw wires W at the cross section taken along the line G-G in FIG. 4A. 11A and 11B are schematic diagrams showing the crystalline ingot L, the first workpiece holding plate 92, the reinforcing plate 93, and the saw wire W after the mounting process, in which (A) is a side view and (B) is a perspective view. 5(A) is a schematic cross-sectional view showing a first work holding plate 92, a reinforcing plate 93, and a plurality of saw wires W in a cross section taken along the line J-J of FIG. 1 is a schematic side view showing the crystalline ingot L, the first work holding plate 92, the reinforcing plate 93, and the saw wire W during cutting of the crystalline ingot L in the second cutting step. FIG. 1 is a schematic side view illustrating a method for cutting a crystal ingot L in Comparative Example 1. FIG. 1A and 1B are schematic cross-sectional views for explaining a method of cutting a crystalline ingot L in Comparative Example 2, in which (A) is the state before cutting begins, (B) is the state after cutting of the crystalline ingot L has been temporarily stopped, and (C) is a diagram showing the state after a first work holding plate 92 has been attached to the crystalline ingot L after cutting has been temporarily stopped.

A cutting method according to one embodiment of the present invention will be described with reference to the drawings. The cutting method of this embodiment is a cutting method in which a wire array, which is a running plurality of saw wires, is pressed parallel to the side of a workpiece to cut the workpiece into a wafer shape. The workpiece before the start of cutting is held by a first workpiece holding plate that is in contact with the wire array before the workpiece is cut and holds the side of the workpiece across both ends, and a second workpiece holding plate that is in contact with the wire array after the workpiece is cut and holds the side of the workpiece across both ends. The cutting method includes a first cutting step in which the first workpiece holding plate is cut but the workpiece is not cut, an attachment step in which a reinforcing plate that holds all of the cut parts of the first workpiece holding plate and reinforces the first workpiece holding plate is attached to the first workpiece holding plate after the first cutting step and before the workpiece is cut, and a second cutting step in which the workpiece is cut with the wire array after the attachment step.

The shape and material of the workpiece, which is the object to be cut by the cutting method of this embodiment, are not particularly limited as long as it can be cut with a saw wire. The material of the workpiece can be, for example, metal, glass, ceramic, resin, polystyrene foam, wood, etc., and hard materials, particularly lithium niobate (LN), lithium tantalate (LT), silicon carbide (SiC), sapphire, etc., can be suitably used as the workpiece. In addition, wafers obtained from LN and LT crystal ingots can be used, for example, as substrates for surface acoustic wave elements used in surface acoustic wave devices, etc.

The shape of the workpiece may be, for example, cylindrical, prismatic, or other columnar, and a cylindrical workpiece with a part of its side surface made flat may also be used. That is, the cutting method of this embodiment may be applied to a crystal ingot in which an orientation flat is formed on a cylindrical crystal ingot manufactured by the Czochralski method or the like. This embodiment will be described using, as an example, a crystal ingot L in which an orientation flat is formed on a cylindrical crystal ingot as the workpiece.

The size of the workpiece is not particularly limited. When a crystal ingot is used as the workpiece, its size can be, for example, 6 or 8 inches in diameter and 50 to 100 mm in length. The thickness of the wafer to be cut into is not particularly limited, and can be, for example, 200 μm to 1000 μm.

Figure 1 is a schematic diagram of a wire saw device 100, which is an example of a wire saw device used in the cutting method of this embodiment. Also, Figure 2 (A) is an enlarged perspective view of a main part E in the cutting process, surrounded by a dotted line, of the wire saw device 100 shown in Figure 1, and Figure 2 (B) is an enlarged perspective view of a cutting fluid supply unit 30a, which will be described later.

[Wiresaw device and cutting method]
First, the configuration of the wire saw device 100 and the operation of the device when cutting the crystalline ingot L will be described.

The wire saw device 100 of this embodiment is a multi-wire saw device using the down-cut method. That is, the crystalline ingot L, which is the workpiece, is positioned above the saw wire used for cutting, and the crystalline ingot L is lowered from above toward the saw wire and pressed against the saw wire, thereby cutting the crystalline ingot L. The cutting method of the present invention can also be applied to a wire saw device using an up-cut method in which the ingot is positioned below the saw wire and the workpiece is raised to cut it. In addition, in the cutting method of the present invention, the crystalline ingot L may be moved toward the saw wire, or the saw wire may be moved toward the crystalline ingot L.

The wire saw device 100 includes a tank 10, a pump 20 for pumping cutting fluid, a cutting fluid supply unit 30, piping 40 connecting the tank 10, the pump 20, and the cutting fluid supply unit 30, a cutting fluid recovery section 50, a base 60 for holding a crystal ingot L, a pair of rollers 70 around which the saw wire W is stretched, a new wire bobbin 80a for supplying new wire for the saw wire W, and a recovery bobbin 80b for recovering the saw wire W. As shown in FIG. 1, in the wire saw device 100, the rollers 70, the recovery section 50, and the tank 10 are arranged in a substantially vertically aligned line so that the cutting fluid can be recovered more efficiently.

The wire saw device 100 also includes a control unit (not shown) that controls the operation of the device. The control unit has a CPU (central processing unit), memory, and storage. Programs are stored in advance in the storage, and the CPU reads and executes the programs. The CPU executes the programs to control the operation of each component of the wire saw device.

The material of each component that constitutes the wire saw device 100 can be appropriately selected depending on the physical properties of the workpiece (crystal ingot L) and the cutting fluid.

The cutting method of the workpiece using the wire saw device can be broadly divided into a free abrasive method, in which the workpiece is cut by supplying cutting fluid containing abrasive grains, depending on the method of supplying the abrasive grains to the workpiece, and a fixed abrasive method, in which the workpiece is cut by polishing while moving a wire saw with abrasive grains such as diamond fixed by electroplating or adhesive in the linear direction. The cutting method in the present invention is not particularly limited, and an appropriate method may be selected according to the material of the workpiece, for example. In this embodiment, the free abrasive method is used. Wires such as piano wires can be used as the saw wire W. In addition, abrasive grains such as diamond can be used as the abrasive grains used in the cutting fluid. In addition, the wire diameter of the wire and the grain size of the abrasive grains can be appropriately selected according to the material forming the crystal ingot L, the cutting thickness, etc.

The tank 10 is for storing cutting fluid. The tank 10 is, for example, cylindrical, and a pipe 40 is connected to the side wall 11 of the tank 10 to supply the cutting fluid stored in the tank 10, and a recovery section 50 is connected to the top surface 12 of the tank 10 to recover the cutting fluid.

The pump 20 pumps up the cutting fluid stored in the tank 10. The pump 20 supplies the cutting fluid from the tank 10 to the cutting fluid supply unit 30 via the piping 40. The flow rate of the cutting fluid pumped by the pump 20 can be, for example, about 50 L/min to 150 L/min.

The cutting fluid supply unit 30 supplies cutting fluid between the saw wire W and the crystal ingot L. As shown in Figs. 1 and 2, the cutting fluid supply unit 30 is composed of cutting fluid supply units 30a and 30b, each of which is provided above a pair of rollers 70 (described later). As shown in Figs. 2(A) and (B), the cutting fluid supply unit 30a includes a main body 31 provided such that its longitudinal direction is aligned with the longitudinal direction of the rollers 70a and 70b, a connection portion 32 with the piping 40, and a discharge portion 33 that supplies cutting fluid between the saw wire W and the crystal ingot L. The cutting fluid supply unit 30b has a structure similar to that of the cutting fluid supply unit 30a.

The main body 31 is formed longer than the longitudinal dimension of the rollers 70a and 70b so that cutting fluid can be supplied between all the saw wires W hung between the rollers 70a and 70b and the crystal ingot. In addition, the discharge section 33 has a plurality of holes 33a formed in a line in the longitudinal direction on the side of the main body, as shown in FIG. 2(B). Since the wire saw device 100 is provided with two cutting fluid supply units, when the flow rate of the cutting fluid is 100 L/min, the cutting fluid can be discharged evenly from the cutting fluid supply units 30a and 30b at 50 L/min each. Note that the cutting fluid may not be discharged evenly from the cutting fluid supply units 30a and 30b by changing the supply amount to the cutting fluid supply units 30a and 30b or the configuration of the cutting fluid supply units 30a and 30b.

The piping 40 connects the tank 10, the pump 20, and the cutting fluid supply unit 30. The piping 40 has a piping body 41, a Y-shaped connector 42 that connects the piping body 41 to the hose 43, and two hoses 43 that are connected to the piping body 41 via the connector 42. Note that in FIG. 1, the hose 43 that connects the piping body 41 to the cutting fluid supply unit 30a is omitted.

The recovery section 50 is formed in a funnel shape, and has an inverted cone-shaped main body 51, a cylindrical wall 52 standing upright from the top of the main body 51, and a cylindrical foot 53 extending downward from the tip of the cone shape of the main body. The recovery section 50 is also provided to cover the entire area below the roller 70, and the lower end of the foot 53 is connected to the upper surface 12 of the tank. This allows the entire amount of cutting fluid supplied between the crystal ingot L and the saw wire W to be recovered without leakage, and the cutting fluid can be returned to the tank 10.

The pedestal 60 is for holding the crystal ingot L. The pedestal 60 has a holding portion 61 for holding the crystal ingot L fixed to the pedestal body 62, a pedestal body 62 for fixing the crystal ingot L via a second work holding plate 91, and a driving means (not shown). The crystal ingot L can be fixed to the pedestal body 62 by being held by the second work holding plate 91 that holds the side of the crystal ingot L over both ends of the crystal ingot L with an adhesive. The adhesive for fixing the crystal ingot L can be selected according to the second work holding plate 91 and the crystal ingot L, and an adhesive such as an epoxy resin adhesive can be used. In addition, the pedestal 60 is configured to be movable up and down by a driving means (not shown), and the crystal ingot L can be pressed against the wire row described later.

In addition, when a planar orientation flat is formed on the outer peripheral surface of the crystal ingot L, the second work holding plate 91 can be made flat and the orientation flat can be attached and fixed to the base body 62 side so that the crystal ingot L can be easily held. In the case where an orientation flat is not formed and the crystal ingot is cylindrical, the second work holding plate 91 can be fixed in a shape corresponding to the side shape of the crystal ingot. In addition, since the second work holding plate 92 is a member that contacts the wire row after cutting the crystal ingot L, the material of the second work holding plate 91 is not particularly limited, and may be a hard material or a material (e.g., glass, resin, etc.) that can be cut by the saw wire W like the first work holding plate 92 described later.

The pair of rollers 70 consists of rollers 70a and 70b. Rollers 70a and 70b are cylindrical and have a guide groove (not shown) formed in a spiral shape along the circumferential direction of rollers 70a and 70b. A saw wire W for cutting the crystal ingot L is hung between rollers 70a and 70b along the guide groove.

The saw wire W is wound around the guide grooves of the rollers 70a and 70b, and is stretched between the rollers 70a and 70b to form a wire row with multiple wires arranged at a predetermined interval in the longitudinal direction of the rollers 70a and 70b. The crystal ingot is cut thinner by a kerf loss of about several tens of μm than the interval between adjacent saw wires W in the wire row (dimension P in FIG. 2), so the interval between the guide grooves arranged in the longitudinal direction of the rollers 70a and 70b can be set to a desired thickness dimension for cutting the crystal ingot, taking into account the kerf loss. In FIG. 2, the saw wire W is wound around the rollers 70a and 70b four times, but the drawing is a schematic diagram of the device, and the number of turns, intervals, etc. can be changed as appropriate according to the size of the crystal ingot, the thickness to be cut, and the number of sheets.

For example, when cutting a cylindrical crystal ingot L to the same thickness, the wire row is preferably a row of multiple identical saw wires arranged at equal intervals and run at the same speed. In the first cutting process and second cutting process of this embodiment described below, it is preferable to press the multiple saw wires against the crystal ingot L with the same pressure to cut the crystal ingot L. In the wire saw device 100 of this embodiment, the multiple saw wires W are arranged at equal intervals, run at the same speed, and are all pressed against the crystal ingot L with the same pressure.

The new wire bobbin 80a is a cylindrical bobbin around which new saw wire W is wound, and rotates in the direction of arrow C in FIG. 1 to pay out the saw wire W in the direction of arrow A, thereby supplying new wire to the roller 70. The recovery bobbin 80b is a cylindrical bobbin around which the saw wire W used in cutting the crystal ingot is wound, and rotates in the direction of arrow D in FIG. 1 to wind up the saw wire W in the direction of arrow A, thereby recovering the saw wire W.

As described above, the cutting fluid is stored in the tank 10, pumped up by the pump 20, and supplied to the cutting fluid supply units 30a and 30b through the piping 40. The cutting fluid is then supplied from the discharge section 33 of the cutting fluid supply units 30a and 30b to between the crystal ingot L and the section where the wire row of the saw wire W is formed. Finally, the cutting fluid is dripped toward the recovery section and returned to the tank 10.

When the cutting process of the wire saw device begins, the new wire bobbin 80a, the recovery bobbin 80b, and the rollers 70a and 70b rotate. As a result, the new wire of the saw wire W is unwound from the new wire bobbin 80a in the direction of arrow A and wound onto the recovery bobbin 80b. At this time, the saw wire W forming the wire row travels in the direction of arrow A. The traveling speed of the saw wire W can be set appropriately according to the crystal ingot L. After the saw wire W is completely wound onto the recovery bobbin 80b, the saw wire W may be made to travel in the opposite direction to the direction of arrow A and used again for cutting.

As the saw wire W travels, the base 60 holding the crystalline ingot L is lowered in the direction of arrow B in Figure 1, so that the side of the crystalline ingot L is pressed parallel to the wire row. By pressing the crystalline ingot L against the traveling wire row, the crystalline ingot L is cut into intervals corresponding to the distance between adjacent saw wires W in the wire row. In this manner, the crystalline ingot L is cut into wafers by the wire saw device 100.

[Cutting method]
Next, each step of the cutting method of this embodiment will be described with reference to the drawings. Here, FIG. 3 is a schematic diagram showing a state in which the first workpiece holding plate 92 is attached to the crystal ingot L before the start of cutting, (A) is a side view, and (B) is a perspective view. FIG. 4 is a schematic diagram showing a state in which the first workpiece holding plate 92 is cut by the first cutting step, (A) is a side view, and (B) is a cross-sectional view showing the first workpiece holding plate 92 and multiple saw wires W in the cross section of the arrow G-G line in FIG. 4(A). FIG. 5 is a schematic diagram showing the crystal ingot L, the first workpiece holding plate 92, the reinforcing plate 93, and the saw wires W after the attachment step, (A) is a side view, and (B) is a perspective view. FIG. 6 is a schematic cross-sectional view showing the first workpiece holding plate 92, the reinforcing plate 93, and multiple saw wires W in the cross section of the arrow J-J line in FIG. 5(A). 7 is a schematic side view showing the crystalline ingot L, the first workpiece holding plate 92, the reinforcing plate 93, and the saw wire W during cutting of the crystalline ingot L in the second cutting step. The saw wire W is omitted in FIGS. 3(B) and 5(B). The dotted lines Q in FIGS. 3(B) and 5(B) indicate the planned cutting positions for cutting the crystalline ingot L into wafers with the saw wire W. In FIGS. 4, 5, and 7, the arrow F indicates the cutting direction of the workpiece by the wire saw device 100, and the first workpiece holding plate 92 and the crystalline ingot L are cut in that order. In the following description, the dimensions of the members are exemplified when cutting a crystalline ingot L having a diameter of 8 inches.

(First cutting process)
As shown in Fig. 3 and Fig. 4, the first cutting step is a step of cutting the first work holding plate 92 with a wire row, without cutting the crystalline ingot L, which is the work. That is, the first cutting step is a step of cutting the first work holding plate 92 to the middle of the thickness direction (the state of Fig. 4), or cutting to the boundary position between the first work holding plate 92 and the crystalline ingot L (a position where the first work holding plate 92 is cut all the way in the thickness direction, but the crystalline ingot L is not cut). Below, a method of cutting the first work holding plate 92 to the middle of the thickness direction in the first cutting step will be described by way of example.

3, the first workpiece holding plate 92 is a member that is cut in contact with the wire row before the crystal ingot L and holds the side of the crystal ingot L over both ends of the crystal ingot L. For example, the first workpiece holding plate 92 can have the same length as the crystal ingot L. In addition, in the present embodiment, the first workpiece holding plate 92 has a curved surface that is attached to the cylindrical crystal ingot L and matches the surface shape of the crystal ingot L, and the opposite surface is flat. In addition, the thickness of the first workpiece holding plate 92 can be about 13 mm at the thinnest point (T1 in FIG. 5A) when the crystal ingot L has a diameter of 8 inches, for example. In addition, the material of the first workpiece holding plate 92 is not particularly limited, and can be formed of, for example, a resin material or glass. In addition, the first workpiece holding plate 92 can be attached to the crystal ingot L using an adhesive such as an epoxy resin adhesive.

The position where the first workpiece holding plate 92 is attached is not particularly limited. For example, in this embodiment, the crystal ingot L, the first workpiece holding plate 92, and the second workpiece holding plate 91 are arranged in the following order: first workpiece holding plate 91, workpiece crystal ingot L, second workpiece holding plate 92, parallel to the cutting direction (arrow F in FIG. 4) by the wire array.

The specific steps of the first cutting process are as follows. As shown in FIG. 3, first, the first workpiece holding plate 92 is attached to the crystal ingot L before cutting begins. Then, the crystal ingot L with the first workpiece holding plate 92 attached is lowered (in the direction of arrow B in FIG. 1) and the saw wire W is pressed against it, cutting the first workpiece holding plate 92 up to the middle of its thickness direction. The dimension by which the first workpiece holding plate 92 is cut in the first cutting process (dimension H in FIGS. 4 and 5) is, for example, about 5 mm; in other words, if the thinnest point of the first workpiece holding plate 92 is 13 mm, the dimension to the crystal ingot L can be 8 mm.

By the first cutting process, the first workpiece holding plate 92 is cut at intervals corresponding to the intended cutting position Q, for example, in the case shown in Figures 3 and 5, at four locations. After the first cutting process, as shown in Figures 4 (A) and (B), a groove 921 is formed in the first workpiece holding plate 92, and the saw wire W is positioned at the innermost portion 921a of the groove.

(Installation process)
Next, an attachment step is performed. The attachment step is a step performed after the first cutting step and before the second cutting step of cutting the crystal ingot L, and is a step of attaching a reinforcing plate 93 to the first work holding plate 92 to hold all of the cut portions of the first work holding plate 92 and reinforce the first work holding plate 92. In the attachment step, cutting with the wire saw may be stopped, or the first work holding plate may be attached while the machine is still in operation. In this step, if it is necessary to ensure safety, it is preferable to temporarily stop cutting with the wire saw.

The reinforcing plate 93 is a flat member attached so as to cover the entire portion of the first workpiece holding plate 92 cut by the saw wire W, and may have, for example, approximately the same dimensions as the first workpiece holding plate 92. The thickness of the reinforcing plate 93 (T2 in FIG. 5A) may be, for example, approximately 19 mm, and the width of the reinforcing plate 93 (T3 in FIG. 5A) may be, for example, approximately 70 mm. The material of the reinforcing plate 93 is not particularly limited, and may be made of, for example, a resin material or glass. The reinforcing plate 93 may be attached to the first workpiece holding plate 92 using an adhesive such as an epoxy resin adhesive.

By attaching the reinforcing plate 93 to the first workpiece holding plate 92 in the mounting process, all of the areas of the first workpiece holding plate 92 that were cut in the first cutting process are covered and held in place, as shown in FIG. 6.

In this embodiment, the position where the reinforcing plate 93 is attached is the rear side of the first work holding plate 92 in the cutting direction F, but is not particularly limited as long as the cut portions of the first work holding plate 92 can be kept at a constant distance. The position where the reinforcing plate 93 is attached may be the same position as the first work holding plate 92 in the cutting direction F, for example.

(Second cutting process)
Next, a second cutting step is performed. As shown in Fig. 7, the second cutting step is a step of cutting the crystalline ingot L with a wire array after the mounting step. The crystalline ingot L to which the first workpiece holding plate 92 and the reinforcing plate 93 are attached is lowered in the direction of arrow B in Fig. 1, and the crystalline ingot L is cut following the first workpiece holding plate 92, so that the crystalline ingot L can be cut into wafers.

This completes the cutting method of this embodiment. The resulting wafer-shaped workpiece of crystal ingot L is then processed by beveling, polishing, cleaning, and other processes to become wafers.

(Compared to conventional cutting methods)
In the conventional cutting method, in order to prevent the cut substrate from cracking, the cutting process is stopped once while cutting the crystal ingot into wafers with a wire saw, and a reinforcing plate is attached to cover the cut parts of the crystal ingot to fix the cut parts. However, although this method prevents the cut parts from cracking due to vibration or the adjacent wafer-shaped workpieces from contacting each other and cracking, the wire saw is displaced in the thickness direction of the wafer-shaped workpiece (perpendicular to the cut surface) at the point where the cutting process is stopped, and a step is formed in the obtained wafer-shaped workpiece, which deteriorates the flatness.

In the cutting method of this embodiment, by attaching a reinforcing plate 93 to the first workpiece holding plate 92 cut in the first cutting step to reinforce it, the workpieces are connected to each other in a wafer-like shape by the reinforcing plate 93, and the distance between the cut wafer-like workpieces is kept constant. Therefore, in the second cutting step, it is possible to suppress the cut wafer-like workpiece from being broken by vibration or the adjacent wafer-like workpieces from coming into contact and breaking. Therefore, it is possible to suppress the occurrence of cracks in the wafer-like workpiece of the crystal ingot. Furthermore, in the cutting method of this embodiment, since it is not the crystal ingot L but the first workpiece holding plate 92 that is cut in the first cutting step, even if the wire saw is shifted in the thickness direction of the wafer-like workpiece (the longitudinal direction of the crystal ingot), it is the first workpiece holding plate 92 that forms a step. Therefore, no step is formed on the surface of the wafer-like workpiece obtained from the crystal ingot L, and deterioration of the flatness of the wafer-like workpiece can be suppressed.

The present invention is not limited to the above-described embodiment, and other configurations that can achieve the object of the present invention are also included in the present invention.

Although the best configurations and methods for implementing the present invention have been disclosed above, the present invention is not limited thereto. That is, the present invention has been described mainly with respect to specific embodiments, but those skilled in the art can make various modifications to the above-described embodiments in terms of shape, material, quantity, and other detailed configurations without departing from the scope of the technical idea and purpose of the present invention. Therefore, the descriptions limiting the shapes, materials, etc. disclosed above are provided as examples to facilitate understanding of the present invention, and do not limit the present invention. Therefore, descriptions of the names of components that have some or all of the limitations on the shapes, materials, etc. removed are included in the present invention.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples in any way.

In this embodiment, a single crystal ingot of lithium tantalate (hereinafter sometimes referred to as "LT") was cut using the wire saw device 100 described above to obtain a wafer-shaped workpiece of the single crystal ingot.

[Preparation of crystal ingot]
First, a single crystal ingot of LT was produced as a general crystal ingot for wafers. A cylindrical LT single crystal having a diameter of 8 inches and a length of 60 mm was grown by the Czochralski method using a raw material with a congruent composition.

This single crystal ingot of LT was subjected to heat treatment to remove thermal distortion and poling to make it a single polarization, after which the outer periphery was ground and the surface was shaped to 42° RY (Rotated Y axis). This resulted in the single crystal ingot of LT to be cut.

Next, the LT single crystal ingot was machined and then set in the wire saw device. The ingot was attached to a second workpiece holder plate with an epoxy resin adhesive in the +x direction, and fixed to the base. The LT single crystal ingot used for cutting was cylindrical with a diameter of 8 inches and a length of 60 mm, and was cut to an average thickness of 580 μm (570 μm to 600 μm) per piece, yielding 76 wafer-like workpieces. Note that a piano wire with a wire diameter of 0.14 mm was used as the saw wire, and cutting was performed while supplying cutting fluid containing free abrasive grains (GC#1000).

[Cutting process]
The above-mentioned crystal ingot was subjected to cutting processing in Example 1, Comparative Example 1, and Comparative Example 2.
Example 1
In Example 1, the crystalline ingot was cut using the cutting method of the above-mentioned embodiment. That is, first, as a first cutting step, a first workpiece holding plate was attached to the side of the crystalline ingot held by the wire saw device, and the first workpiece holding plate was cut 5 mm in the thickness direction. Also, the wire saw was held at the cutting position. Furthermore, as an attachment step, a reinforcing plate was attached to the first workpiece holding plate that had been cut halfway, to hold and reinforce all of the cut portions of the first workpiece. Finally, as a second cutting step, the first workpiece holding plate and the crystalline ingot were cut again from the position where the wire saw was held in the first cutting step, and the crystalline ingot was cut into a wafer shape.

(Comparative Example 1)
In Comparative Example 1, the crystalline ingot was held only by the second workpiece holding plate without using the first workpiece holding plate and the reinforcing plate, and the crystalline ingot was cut into wafers. That is, as shown in Fig. 8, the crystalline ingot L before cutting was attached to the wire saw device by the second workpiece holding plate 91 and cut in the direction of the arrow F. The other conditions were the same as those in Example 1.

(Comparative Example 2)
9 is a diagram showing the cutting process in Comparative Example 2. In Comparative Example 2, the crystalline ingot L was held only by the second workpiece holding plate 91 without using the first workpiece holding plate and the reinforcing plate (FIG. 9(A)), and then the crystalline ingot L was cut by 5 mm in the direction of the arrow F, and then the cutting was stopped (FIG. 9(B)). Furthermore, the wire saw was held at the position where the cutting was stopped (stop position), and as shown in FIG. 9(C), the first workpiece holding plate 92 was attached so as to cover the cut position of the crystalline ingot L, and the wire saw device was operated again to cut the crystalline ingot L into wafers.

[Evaluation of wafer-like workpieces and evaluation results]
The 76 wafer-like workpieces obtained in Example 1, Comparative Example 1, and Comparative Example 2 were visually observed for cracks in the wafer-like workpieces and for the presence or absence of steps formed on the surfaces of the wafer-like workpieces. The results are shown in Table 1.

In Comparative Example 1, which did not use the first workpiece holding plate or reinforcing plate, cracks occurred in 43 out of 76 wafer-shaped workpieces. In addition, because the cutting process of the crystal ingot was not stopped midway, no steps were observed.

In Comparative Example 2, in which the crystal ingot was cut by 5 mm, the first workpiece holding plate was attached, and the crystal ingot was cut again, cracks occurred in only two of the 76 wafer-shaped workpieces, and the occurrence of cracks was significantly suppressed compared to Comparative Example 1. However, the occurrence of a step of about 20 μm was confirmed on the surface of the wafer-shaped workpiece. The position where the step was formed was the position (stop position) where cutting with the wire saw was stopped to attach the first workpiece holding plate, and when comparing the part cut before stopping (Lb in FIG. 9(C)) and the part cut after the first workpiece holding plate was attached (La in FIG. 9(C)) with the stop position as the boundary, the cut was shifted by 20 μm in the thickness direction.

In Example 1, cracks occurred in only two of the 76 wafer-shaped workpieces, which significantly reduced the occurrence of cracks compared to Comparative Example 1, in which no fixing plate was used, and no steps were observed, unlike Comparative Example 2, in which the first cutting process was not performed.

As shown in the embodiment of the present invention, by performing the first cutting step, the attachment step, and the second cutting step, it has been shown that it is possible to suppress the occurrence of cracks in the wafer-shaped workpiece of the crystal ingot, and to suppress the deterioration of the flatness of the surface of the wafer-shaped workpiece of the crystal ingot due to the misalignment of the wire saw during cutting of the crystal ingot.

100 Wire saw device 91 Second workpiece holding plate 92 First workpiece holding plate 93 Reinforcement plate W Saw wire L Crystal ingot (workpiece)

Claims (6)

A cutting method for cutting a workpiece into wafers by pressing a wire row having a plurality of running saw wires against a side surface of the workpiece in parallel, the method comprising the steps of:
Before cutting begins, the workpiece is held by a first workpiece holding plate that contacts the wire array before the workpiece is cut and holds the side surface of the workpiece across both ends, and a second workpiece holding plate that contacts the wire array after the workpiece is cut and holds the side surface of the workpiece across both ends,
The cutting method includes:
a first cutting step of cutting the first workpiece holding plate with the wire array but not cutting the workpiece;
a mounting step of mounting a reinforcing plate to the first work holding plate after the first cutting step and before cutting the work, the reinforcing plate holding all of the cut portions of the first work holding plate and reinforcing the first work holding plate;
a second cutting step of cutting the workpiece with the wire array after the attaching step;
A cutting method comprising: The cutting method according to claim 1, wherein the workpiece, the first workpiece holding plate, and the second workpiece holding plate are arranged in the order of the first workpiece holding plate, the workpiece, and the second workpiece holding plate, parallel to the cutting direction by the wire array. The cutting method according to claim 1 or 2, wherein the wire row is a row of multiple identical saw wires arranged at equal intervals and run at the same speed. The cutting method according to any one of claims 1 to 3 , wherein in the first cutting step and the second cutting step, the plurality of saw wires are all pressed against the workpiece with the same pressure to cut the workpiece. The cutting method according to any one of claims 1 to 4, wherein the workpiece is cylindrical. The cutting method according to any one of claims 1 to 5, wherein the workpiece is a crystalline ingot of lithium tantalate or lithium niobate.

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