Cutting method

Abstract

To provide a cutting method capable of suppressing occurrence of cracks in a wafer-like workpiece and suppressing deterioration in flatness of the surface of the workpiece due to displacement of a wire saw during cutting of the workpiece.SOLUTION: In a workpiece cutting method using a plurality of saw wires W, a workpiece L before start of cutting is held by a first workpiece holding plate 92 which is brought into contact with a wire row and cut before the workpiece is cut, and holds the side surface of the workpiece over both the ends of the workpiece, and a second workpiece holding plate 91 which is brought into contact with the wire row and cut after the cutting, and holds the side surface of the workpiece over both the ends of the workpiece. The cutting method includes a first cutting step for cutting the first workpiece holding plate by the wire row without cutting the workpiece, an attaching step of holding the whole cut portion of the first workpiece holding plate and attaching a reinforcing plate 93 for reinforcing the first workpiece holding plate to the first workpiece holding plate after the first cutting step and before cutting the work, and a second cutting step of cutting the workpiece with the wire row after the attaching step.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a cutting method, for example, a method for cutting lithium niobate or lithium tantalate. [Background technology]

[0002] Conventionally, a method using a wire saw machine has been known as a method for cutting a cylindrical crystal ingot of lithium niobate (LN), lithium tantalate (LT), or the like, manufactured by the Czochralski method, into wafers in order to manufacture a surface acoustic wave element substrate used in a surface acoustic wave device, etc. 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 matching the target wafer thickness, and a wire row consisting of multiple saw wires, with one saw wire wound around the groove of the main shaft rollers.

[0003] The main shaft roller is then rotated to run the wire saw, and the main table to which the crystalline ingot is fixed is operated to press the crystalline ingot against the wire row, thereby cutting it into multiple wafers at the same time. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2001-1248 A Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, the diameter of the substrate for surface acoustic wave devices has been increased and the thickness of the substrate has been reduced. Accordingly, in the process of cutting a crystal ingot into wafers, the probability of the wafer-shaped workpiece cracking due to vibrations during cutting or contact between the cut wafer-shaped workpieces is increasing. In order to prevent cracking of the large diameter and thin plate substrate, a method is considered in which the process of cutting the crystal ingot into wafers with a wire saw is stopped once in the middle of the process, and a reinforcing plate is attached to cover all the cut parts of the crystal ingot to fix the cut parts. This makes it possible to prevent the cut wafer-shaped workpiece from cracking due to vibration or from cracking due to contact between adjacent wafer-shaped workpieces.

[0006] However, once processing was stopped, the wire saw would shift in the thickness direction of the wafer-like workpiece (the direction perpendicular to the cut surface), resulting in the formation of steps on the surface of the wafer-like 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-like workpiece made from the crystal ingot.

[0007] Therefore, an object of the present invention is to provide a cutting method for cutting a workpiece into wafers, which can suppress the occurrence of cracks in the wafer-like workpiece and can suppress deterioration of the flatness of the surface of the wafer-like workpiece due to the wire saw shifting during cutting of the workpiece. [Means for solving the problem]

[0008] The cutting method of the present invention is a cutting method in which a wire array, on which a plurality of saw wires are run, is pressed parallel to a side of a workpiece to cut the workpiece into wafers, wherein the workpiece before cutting begins is held by a first work holding plate which contacts the wire array before the workpiece and is cut, and which holds the side of the workpiece across both ends of the workpiece, and a second work holding plate which contacts the wire array after the workpiece is cut and holds the side of the workpiece across both ends of the workpiece, and the cutting method includes a first cutting step in which the first work holding plate is cut with the wire array, but the workpiece is not cut, an attachment step in which, after the first cutting step and before the workpiece is cut, a reinforcing plate is attached to the first work holding plate to hold all of the cut portions of the first work holding plate and reinforce the first work holding plate, and a second cutting step in which the workpiece is cut with the wire array after the attachment step.

[0009] 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 order of the first workpiece holding plate, the work, and the second workpiece holding plate.

[0010] In the cutting method of the present invention, the wire row may be a row in which a plurality of identical saw wires are arranged at equal intervals and run at the same speed.

[0011] In the cutting method of the present invention, in the first cutting step and the second cutting step, the plurality of saw wires may all be pressed against the workpiece with the same pressure to cut the workpiece.

[0012] In the cutting method of the present invention, the workpiece may be cylindrical.

[0013] In the cutting method of the present invention, the workpiece may be a crystal ingot of lithium tantalate or lithium niobate. Effect of the Invention

[0014] 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-like workpiece and also suppress the deterioration of the flatness of the surface of the wafer-like workpiece due to the wire saw shifting while cutting the workpiece. [Brief description of the drawings]

[0015] [Figure 1] 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. [Diagram 2] 2 is an enlarged perspective view showing (A) a main portion E in a cutting process and (B) a cutting fluid supply unit 30a in the wire saw device shown in FIG. 1. FIG. [Diagram 3] 1A and 1B are schematic diagrams showing a state in which a first work holding plate 92 is attached to a crystalline ingot L, where (A) is a side view and (B) is a perspective view. [Figure 4] 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 along the arrow GG line in FIG. 4A. [Diagram 5] 1A and 1B 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 step, where (A) is a side view and (B) is a perspective view. [Figure 6] 5(A) is a schematic cross-sectional view taken along the line JJ of FIG. 5(A), showing a first work holding plate 92, a reinforcing plate 93, and a plurality of saw wires W. FIG. [Figure 7] 1 is a schematic side view showing the crystalline ingot L, a first work holding plate 92, a reinforcing plate 93, and a saw wire W during cutting of the crystalline ingot L in a second cutting step. [Figure 8] 1 is a schematic side view illustrating a method for cutting a crystal ingot L in Comparative Example 1. FIG. [Figure 9]11A and 11B are schematic cross-sectional views illustrating a method for 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. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] A cutting method according to an 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 plurality of running saw wires, is pressed parallel to a side surface of a workpiece to cut the workpiece into a wafer shape, and 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 surface 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 surface of the workpiece across both ends, and the cutting method includes a first cutting step in which the first workpiece holding plate is cut but 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 by the wire array after the attachment step.

[0017] The shape and material of the workpiece, which is the cutting object of 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 applied as the workpiece. In addition, wafers obtained from crystal ingots of LN and LT can be used as substrates for surface acoustic wave elements used in surface acoustic wave devices, etc.

[0018] The shape of the workpiece may be, for example, a columnar shape, such as a cylindrical shape or a rectangular columnar shape, and a cylindrical workpiece with a part of the 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 by taking, as an example, a crystal ingot L in which an orientation flat is formed on a cylindrical crystal ingot as the workpiece.

[0019] The size of the workpiece is not particularly limited. When a crystal ingot is used as the workpiece, the size of the workpiece may be, for example, 6 or 8 inches in diameter and 50 to 100 mm in length. The thickness of the workpiece to be cut into wafers is not particularly limited, and may be, for example, 200 μm to 1000 μm.

[0020] Fig. 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 the present embodiment. Fig. 2(A) is an enlarged perspective view of a main part E in cutting processing, surrounded by a dotted line, of the wire saw device 100 shown in Fig. 1, and Fig. 2(B) is an enlarged perspective view of a cutting fluid supply unit 30a, which will be described later.

[0021] [Wire saw 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.

[0022] The wire saw device 100 of this embodiment is a multi-wire saw device of the down-cut type. 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 that adopts an up-cut type 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.

[0023] The wire saw device 100 includes a tank 10, a pump 20 for pumping up 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 a saw wire W is stretched, a new wire bobbin 80a for supplying a 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.

[0024] 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, thereby controlling the operation of each component of the wire saw device.

[0025] The material of each part constituting the wire saw device 100 can be appropriately selected depending on the physical properties of the crystal ingot L, which is the workpiece, and the cutting fluid.

[0026] The cutting method of the workpiece using the wire saw device is roughly divided into a free abrasive method, which cuts the workpiece by supplying a cutting fluid containing abrasive grains, and a fixed abrasive method, which cuts the workpiece by polishing while feeding a wire saw with abrasive grains such as diamonds fixed by electroplating or adhesive in a linear direction, depending on the method of supplying abrasive grains to the workpiece. 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 diamonds 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.

[0027] The tank 10 is for storing cutting fluid. The tank 10 is, for example, cylindrical, and a piping 40 for supplying the cutting fluid stored in the tank 10 is connected to a side wall 11 of the tank 10, and a recovery unit 50 for recovering the cutting fluid is connected to an upper surface 12 of the tank 10.

[0028] 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 up by the pump 20 can be, for example, about 50 L / min to 150 L / min.

[0029] The cutting fluid supply unit 30 supplies cutting fluid between the saw wire W and the crystalline ingot L. As shown in FIG. 1 and FIG. 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 FIG. 2(A) and (B), the cutting fluid supply unit 30a includes a main body 31 provided such that the longitudinal direction of the cutting fluid supply unit 30a 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 crystalline ingot L. The cutting fluid supply unit 30b has a structure similar to that of the cutting fluid supply unit 30a.

[0030] The main body 31 is formed longer than the longitudinal dimension of the rollers 70a, 70b so that the cutting fluid can be supplied between all the saw wires W hung between the rollers 70a, 70b and the crystal ingot. In addition, the discharge part 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, 30b at 50 L / min each. Note that the cutting fluid may not be discharged evenly from the cutting fluid supply units 30a, 30b by changing the supply amount to the cutting fluid supply units 30a, 30b or the configuration of the cutting fluid supply units 30a, 30b.

[0031] The piping 40 connects the tank 10, the pump 20, and the cutting fluid supply unit 30. The piping 40 has a piping main body 41, a Y-shaped connecting part 42 that connects the piping main body 41 and the hose 43, and two hoses 43 connected to the piping main body 41 via the connecting part 42. Note that in Fig. 1, the hose 43 that connects the piping main body 41 and the cutting fluid supply unit 30a is omitted.

[0032] The recovery section 50 is formed in a funnel shape, and has an inverted cone-shaped main body 51, a cylindrical wall section 52 standing upward from the upper part of the main body 51, and a cylindrical foot section 53 extending downward from the tip of the cone-shaped main body. The recovery section 50 is also provided so as to cover the entire lower part of the roller 70, and the lower end of the foot section 53 is connected to the upper surface 12 of the tank. This allows the cutting fluid supplied between the crystal ingot L and the saw wire W to be recovered in its entirety without leakage, and the cutting fluid to be returned to the tank 10.

[0033] The pedestal 60 is for holding the crystalline ingot L. The pedestal 60 has a holding part 61 for holding the crystalline ingot L fixed to the pedestal body 62, a pedestal body 62 for fixing the crystalline ingot L via a second work holding plate 91, and a driving means (not shown). The crystalline 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 crystalline ingot L across both ends of the crystalline ingot L with an adhesive. The adhesive for fixing the crystalline ingot L can be selected according to the second work holding plate 91 and the crystalline 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 crystalline ingot L can be pressed against a wire row described later.

[0034] In addition, when a planar orientation flat is formed on the outer peripheral surface of the crystalline 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 as to easily hold the crystalline ingot L. In the case where no orientation flat is formed and the crystalline ingot is cylindrical, the second work holding plate 91 can be fixed in a shape corresponding to the side shape of the crystalline ingot. In addition, since the second work holding plate 92 is a member that contacts the wire array after cutting the crystalline 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.

[0035] The pair of rollers 70 is composed of rollers 70a and 70b. The rollers 70a and 70b are cylindrical and have a guide groove (not shown) formed in a spiral shape along the circumferential direction of the rollers 70a and 70b. A saw wire W for cutting the crystal ingot L is hung between the rollers 70a and 70b along the guide groove.

[0036] 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 in which a plurality of wires are arranged at a predetermined interval in the longitudinal direction of the rollers 70a and 70b. Since the crystal ingot is cut thinner by a kerf loss of about several tens of μm than the interval (dimension P in FIG. 2) between the adjacent saw wires W in the wire row, the interval between the guide grooves arranged in the longitudinal direction of the rollers 70a and 70b can be set to an interval that takes into account the kerf loss in the desired thickness dimension for cutting the crystal ingot. 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. are appropriately changed according to the size of the crystal ingot, the thickness to be cut, and the number of sheets.

[0037] For example, when cutting a cylindrical crystalline ingot L to the same thickness, the wire row is preferably a row in which a plurality of identical saw wires are arranged at equal intervals and run at the same speed. In the first cutting step and the second cutting step of this embodiment described later, it is preferable to press the plurality of saw wires against the crystalline ingot L with the same pressure to cut the crystalline ingot L. In the wire saw device 100 of this embodiment, the plurality of saw wires W are arranged at equal intervals, run at the same speed, and are all pressed against the crystalline ingot L with the same pressure.

[0038] The new wire bobbin 80a is a cylindrical bobbin around which a new wire of the saw wire W is wound, and rotates in the direction of the arrow C in Fig. 1 to pay out the saw wire W in the direction of the arrow A, thereby supplying the new wire to the roller 70. The recovery bobbin 80b is a cylindrical bobbin around which the saw wire W used in cutting a crystal ingot is wound, and rotates in the direction of the arrow D in Fig. 1 to take up the saw wire W in the direction of the arrow A, thereby recovering the saw wire W.

[0039] 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. Furthermore, the cutting fluid is supplied from the discharge parts 33 of the cutting fluid supply units 30a and 30b to between the crystal ingot L and the part where the wire row of the saw wire W is formed. Finally, the cutting fluid is dripped toward the recovery part and returned to the tank 10.

[0040] In addition, when the cutting process of the wire saw device starts, the new wire bobbin 80a, the recovery bobbin 80b, and the rollers 70a, 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 the arrow A and wound around the recovery bobbin 80b. At this time, the saw wire W forming the wire row travels in the direction of the arrow A. The traveling speed of the saw wire W can be appropriately set according to the crystal ingot L. After the saw wire W is completely wound around the recovery bobbin 80b, the saw wire W may be made to travel in the opposite direction to the direction of the arrow A and used again for cutting.

[0041] As the saw wire W travels, the base 60 holding the crystalline ingot L is lowered in the direction of arrow B in Fig. 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 intervals 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.

[0042] [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 taken along the line GG 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 taken along the line JJ in FIG. 5(A). FIG. 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 in the middle of cutting the crystalline ingot L in the second cutting step. The saw wire W is omitted in FIG. 3(B) and FIG. 5(B). The dotted line Q in FIG. 3(B) and FIG. 5(B) indicates a planned cutting position for cutting the crystalline ingot L into a wafer shape with the saw wire W. In FIG. 4, FIG. 5, and FIG. 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.

[0043] (1st cutting process) As shown in Figures 3 and 4, the first cutting step is a step in which the first work holding plate 92 is cut with a wire row, but the crystalline ingot L, which is the work, is not cut. That is, the first cutting step is a step in which the first work holding plate 92 is cut partway in the thickness direction (the state in Figure 4), or cut up 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 partway in the thickness direction in the first cutting step will be described by way of example.

[0044] As shown in FIG. 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 across 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 first workpiece holding plate 92 in this embodiment, the surface that is attached to the cylindrical crystal ingot L is curved to match 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. 5(A)) 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.

[0045] The position where the first work holding plate 92 is attached is not particularly limited. For example, in this embodiment, the crystal ingot L, the first work holding plate 92, and the second work holding plate 91 are arranged in the order of the first work holding plate 91, the work crystal ingot L, and the second work holding plate 92, parallel to the cutting direction (arrow F in FIG. 4) by the wire array.

[0046] The specific procedure of the first cutting step is as follows. As shown in Fig. 3, first, a first workpiece holding plate 92 is attached to the crystal ingot L before cutting begins. Then, the crystal ingot L to which the first workpiece holding plate 92 is 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 step (dimension H in Figs. 4 and 5) is, for example, about 5 mm, that is, when the thinnest part of the first workpiece holding plate 92 is 13 mm, the dimension to the crystal ingot L can be 8 mm.

[0047] By the first cutting step, the first work holding plate 92 is cut at intervals corresponding to the intended cutting positions Q, for example, four positions in the case shown in Figures 3 and 5. After the first cutting step, as shown in Figures 4(A) and (B), a groove 921 is formed in the first work holding plate 92, and the saw wire W is positioned in the innermost portion 921a of the groove.

[0048] (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, which holds all of the cut portions of the first work holding plate 92 and reinforces 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.

[0049] The reinforcing plate 93 is a flat member attached so as to cover the entire portion of the first work holding plate 92 cut by the saw wire W, and may have, for example, substantially the same dimensions as the first work holding plate 92. The thickness of the reinforcing plate 93 (T2 in FIG. 5(A)) may be, for example, about 19 mm, and the width of the reinforcing plate 93 (T3 in FIG. 5(A)) may be, for example, about 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 work holding plate 92 using an adhesive such as an epoxy resin adhesive.

[0050] In the attachment step, the reinforcing plate 93 is attached to the first work holding plate 92, so that all the areas of the first work holding plate 92 that have been cut in the first cutting step are covered and held, as shown in FIG.

[0051] In this embodiment, the reinforcing plate 93 is attached to the first workpiece holding plate 92. However, this is not particularly limited as long as the cut portions of the first work holding plate 92 can be kept at a constant distance from each other. 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.

[0052] (2nd 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.

[0053] This completes the slicing method of the present embodiment. The obtained wafer-shaped product of the crystalline ingot L is then subjected to post-processing such as beveling, polishing, and cleaning to become wafers.

[0054] (Compared to conventional cutting methods) In the conventional cutting method, in order to prevent cracking of the cut substrate, a method has been considered in which cutting is stopped once in the middle of cutting the crystal ingot into wafers with a wire saw, and a reinforcing plate is attached to cover all 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 cracking due to contact between adjacent wafer-shaped workpieces, the wire saw may shift in the thickness direction of the wafer-shaped workpiece (perpendicular to the cut surface) at the point where cutting is stopped, resulting in the formation of steps in the obtained wafer-shaped workpiece and a deterioration in flatness.

[0055] 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 crystalline ingot. Furthermore, in the cutting method of this embodiment, since it is not the crystalline 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 crystalline 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 crystalline ingot L, and deterioration of the flatness of the wafer-like workpiece can be suppressed.

[0056] It should be noted that 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.

[0057] In addition, the best configurations and methods for implementing the present invention are disclosed in the above description, but 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 illustrative descriptions to facilitate understanding of the present invention, and do not limit the present invention, so descriptions of the names of components that are free of some or all of the limitations on the shapes, materials, etc. are included in the present invention. EXAMPLES

[0058] 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.

[0059] In this embodiment, a single crystal ingot of lithium tantalate (hereinafter, sometimes referred to as "LT") was used as the cutting target, and the single crystal ingot was cut using the above-mentioned wire saw device 100 to obtain a wafer-shaped workpiece of the single crystal ingot.

[0060] [Preparation of crystal ingots] First, we produced a single crystal ingot of LT as a general crystal ingot for wafers. Using a raw material with a congruent composition, we grew a cylindrical LT single crystal with a diameter of 8 inches and a length of 60 mm by the Czochralski method.

[0061] This LT single crystal ingot was subjected to heat treatment to remove thermal distortion and poling to make it a single polarization, after which the outer circumference was ground to obtain a 42° RY (Rotated Y axis) surface. This resulted in the LT single crystal ingot to be cut.

[0062] Next, the shape of the LT single crystal ingot was processed and then set in the wire saw device. The +x direction of the ingot was attached to a second workpiece holder plate using an epoxy resin adhesive and fixed to the pedestal. The LT single crystal ingot used for cutting had a cylindrical shape 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 to obtain 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).

[0063] [Cutting] 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 crystal 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 crystal 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 crystal ingot were cut again from the position where the wire saw was held in the first cutting step, and the crystal ingot was cut into a wafer shape.

[0064] 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 of Example 1.

[0065] Comparative Example 2 Fig. 9 is a diagram showing a 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.

[0066] [Evaluation of wafer-like processed products 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.

[0067] [Table 1]

[0068] In Comparative Example 1, in which the first workpiece holding plate and the reinforcing plate were not used, cracks occurred in 43 out of 76 wafer-shaped workpieces. In addition, since the cutting process of the crystal ingot was not stopped midway, the occurrence of steps was not confirmed.

[0069] 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 attaching the first workpiece holding plate (La in FIG. 9(C)) with the stop position as the boundary, the cut was shifted by 20 μm in the thickness direction.

[0070] In Example 1, cracks occurred in only two of the 76 wafer-like 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.

[0071] It has been shown that by performing the first cutting step, the attachment step, and the second cutting step as in the embodiment which is an exemplary aspect of the present invention, it is possible to suppress the occurrence of cracks in the wafer-shaped workpiece of the crystalline ingot, and also to suppress the deterioration of the flatness of the surface of the wafer-shaped workpiece of the crystalline ingot due to the shifting of the wire saw during cutting of the crystalline ingot. [Explanation of symbols]

[0072] 100 Wire saw device 91 Second work holding plate 92 First work holding plate 93 Reinforcement plate W Saw Wire L Crystal ingot (work)

Claims

1. 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:

2. The cutting method according to claim 1 , wherein the workpiece, the first workpiece holding plate, and the second workpiece holding plate are arranged parallel to the cutting direction by the wire array in the order of the first workpiece holding plate, the workpiece, and the second workpiece holding plate.

3. 3. The cutting method according to claim 1, wherein the wire row is a row in which a plurality of identical saw wires are arranged at equal intervals and run at the same speed.

4. 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.

5. The cutting method according to any one of claims 1 to 4, wherein the workpiece is cylindrical.

6. The cutting method according to any one of claims 1 to 5, wherein the workpiece is a crystal ingot of lithium tantalate or lithium niobate.

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