Wafer manufacturing method and processing apparatus

Abstract

The invention provides a wafer manufacturing method and a wafer processing apparatus, which can reduce the time required for manufacturing an upper limit of wafers from each ingot while processing a plurality of ingots in parallel at the same time. In a planarization step included in a series of steps for manufacturing a wafer from an ingot, the ingot is ground until the thickness of the ingot is thinner than the thickness of the ingot at the time when the series of steps are started, the thickness of the ingot is obtained by adding the finished thickness of the wafer, the assumed thickness of the separation layer, and the distribution thickness. The distribution thickness is obtained by dividing the remaining thickness of the ingot by a number obtained by subtracting 1 from the upper limit number of wafers that can be manufactured from the ingot.

Description

Technical Field

[0001] The present invention relates to a wafer manufacturing method for manufacturing three or more wafers from an ingot and a processing device used in the manufacturing method. Background Art

[0002] Semiconductor device chips are generally manufactured using wafers made of single crystals such as silicon (Si), silicon carbide (SiC), gallium nitride (GaN), lithium tantalate (LiTaO3:LT), or lithium niobate (LiNbO3:LN). The wafers are manufactured by, for example, cutting out an ingot using a wire saw.

[0003] However, the cutting margin when a wafer is cut from an ingot using a wire saw is about 300 μm, which is relatively large. In addition, fine concave-convex surfaces are formed on the front of the wafer cut in this way, and the wafer is bent as a whole (the wafer is warped). Therefore, when using the wafer to manufacture chips, it is necessary to grind, etch and / or polish the front of the wafer to flatten the front.

[0004] In this case, the amount of raw materials used as wafers is about 2 / 3 of the total amount of the ingot. That is, when wafers are cut out of the ingot and the front surface of the wafer is flattened, about 1 / 3 of the total amount of the ingot is discarded. Therefore, when wafers are manufactured using a wire saw in this way, productivity is low.

[0005] In view of this, a method for manufacturing a wafer from an ingot using a laser beam having a wavelength that is transmitted through the raw material of the ingot has been proposed (for example, see Patent Document 1). Specifically, in this method, first, the laser beam is irradiated onto the ingot so that a focal point of the laser beam is positioned inside the ingot, while the focal point and the ingot are moved relative to each other.

[0006] Thus, a separation layer including a modified portion and cracks extending from the modified portion is formed inside the ingot. Then, in this method, an external force is applied to the ingot in such a way as to further extend the cracks. As a result, the ingot is separated at the separation layer to produce a wafer.

[0007] In addition, when a wafer is manufactured from an ingot in this way, separation layers remain on the ingot and the wafer respectively (separation layer remaining on the ingot side and separation layer remaining on the wafer side). Therefore, in the above-mentioned wafer manufacturing method, the ingot and the wafer are respectively flattened by grinding the ingot and the wafer respectively to remove the separation layer remaining on the ingot side and the separation layer remaining on the wafer side.

[0008] Patent Document 1: Japanese Patent Application Publication No. 2019-12765

[0009] When the above-mentioned wafer manufacturing method is repeated, an ingot having a thickness slightly smaller than the thickness required for manufacturing two wafers may remain. In this case, the final wafer is manufactured by grinding the ingot for a long time until the finished thickness of the wafer is reached.

[0010] However, when processing a plurality of ingots simultaneously and in parallel while manufacturing an upper limit number of wafers from each ingot, the long grinding process to manufacture the final wafer from each ingot may become a bottleneck. That is, in this case, the processing of other ingots may be stopped for a long time while grinding a specific ingot to manufacture the final wafer. Summary of the invention

[0011] In view of this, an object of the present invention is to provide a wafer manufacturing method and a processing device used in the manufacturing method, which can reduce the time required for manufacturing an upper limit number of wafers from each ingot while processing a plurality of ingots simultaneously and in parallel.

[0012] According to one aspect of the present invention, a method for manufacturing a wafer is provided, wherein a series of steps including a separation layer forming step, a separation step, and a flattening step are repeatedly performed to manufacture three or more wafers from an ingot, wherein the separation layer forming step forms a separation layer inside the ingot, the separation step separates the ingot at the separation layer after the separation layer forming step to manufacture the wafer, and the flattening step removes the residual separation layer remaining on the ingot side of the ingot and the residual separation layer remaining on the wafer side of the wafer after the separation step to flatten the ingot and the wafer, respectively, wherein the method for manufacturing a wafer has the following calculation step: before manufacturing three or more wafers from the ingot, referring to the initial thickness of the ingot, the finished thickness of the wafer, and the set thickness of the separation layer The upper limit number of the wafers that can be manufactured from the ingot and the remaining thickness of the ingot are calculated, and in the separation layer forming step, the laser beam is irradiated to the ingot in such a manner that a focal point of a laser beam having a wavelength that passes through the raw material of the ingot is positioned at a predetermined depth from the front surface of the ingot, while the focal point and the ingot are moved relative to each other, thereby forming the separation layer, and in the flattening step, the ingot is ground until it becomes thinner than the thickness of the ingot at the beginning of the series of steps by a thickness obtained by adding the finished thickness, the imagined thickness and the allocated thickness, the allocated thickness being obtained by dividing the remaining thickness by a number obtained by subtracting 1 from the upper limit number, and the wafer is ground until it becomes the finished thickness.

[0013] Furthermore, it is preferred that the prescribed depth is a depth corresponding to a first thickness obtained by adding the finished thickness and the thickness of the residual separation layer on the wafer side. Alternatively, it is preferred that the prescribed depth is a depth corresponding to a second thickness obtained by adding the finished thickness, the thickness of the residual separation layer on the wafer side, and the allocated thickness. Alternatively, it is preferred that the prescribed depth is a depth that is longer than the first thickness obtained by adding the finished thickness and the thickness of the residual separation layer on the wafer side and shorter than the second thickness obtained by adding the first thickness and the allocated thickness.

[0014] According to another aspect of the present invention, a processing device is provided for manufacturing more than three chips from an ingot, wherein the processing device comprises: a laser processing unit for forming a separation layer inside the ingot; a separation unit for separating the ingot at the separation layer to manufacture the chip; a flattening unit for removing the residual separation layer remaining on the ingot side of the ingot to flatten the ingot; and a controller for controlling the laser processing unit, the separation unit and the flattening unit so as to repeat a series of steps including forming the separation layer, separating the ingot and flattening the ingot according to a number obtained by subtracting 1 from an upper limit number of the chips that can be manufactured from the ingot, the controller comprising: a memory for storing an initial thickness of the ingot, a finished thickness of the chip and an assumption of the separation layer thickness; and a processor for calculating the upper limit number of sheets and the remaining thickness of the ingot with reference to the initial thickness, the finished thickness and the assumed thickness, the processor controlling the laser processing unit so as to irradiate the laser beam to the ingot in a manner such that a focal point of the laser beam having a wavelength of a raw material passing through the ingot is positioned at a predetermined depth from the front face of the ingot, while the focal point and the ingot are moved relative to each other, thereby forming the separation layer, and the processor controlling the flattening unit so as to grind the ingot until it becomes thinner than the thickness of the ingot at the time of starting the series of steps by a thickness obtained by adding the finished thickness, the assumed thickness and a distributed thickness, the distributed thickness being obtained by dividing the remaining thickness by a number obtained by subtracting 1 from the upper limit number of sheets.

[0015] In the present invention, in a flattening step included in a series of steps for manufacturing a chip from an ingot (specifically, flattening of the ingot), the ingot is ground until it becomes thinner than the thickness of the ingot at the start of the series of steps by a thickness obtained by adding the finished thickness of the chip, the assumed thickness of the separation layer, and the allocated thickness, wherein the allocated thickness is obtained by dividing the remaining thickness of the ingot by a number obtained by subtracting 1 from the upper limit number of chips that can be manufactured from the ingot.

[0016] Then, when this series of steps is repeated, an ingot having a thickness that is greater than the minimum thickness of the ingot required for manufacturing the final chip (specifically, the thickness obtained by adding the finished thickness of the chip and the thickness of the residual separation layer on the ingot side) and less than the thickness obtained by adding the minimum thickness of the ingot required for manufacturing the final chip and the allocated thickness is provided to the final flattening step.

[0017] In this case, the time required to grind the ingot to the finished thickness of the wafer to produce the final wafer is shortened. Therefore, by applying the present invention as a method for processing a plurality of ingots simultaneously and in parallel while producing an upper limit number of wafers from each ingot, the grinding of the ingot for producing the final wafer from each ingot does not become a bottleneck, and the time required can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 (A) is a perspective view schematically showing an example of an ingot, Figure 1 (B) is a schematic diagram showing Figure 1 (A) is a side view of the ingot shown.

[0019] Figure 2 It is a schematic diagram showing the Figure 1 (A) and Figure 1 (B) is a flow chart of an example of a method for manufacturing three or more wafers from an ingot.

[0020] Figure 3 It is schematically shown in Figure 2 A side view of parameters referenced in calculation steps included in the wafer manufacturing method shown.

[0021] Figure 4 It is schematically shown Figure 2 A perspective view showing a state of a separation layer forming step included in a wafer manufacturing method shown.

[0022] Figure 5 (A) is a schematic diagram showing Figure 2 A partially enlarged cross-sectional view of an ingot after a separation layer forming step included in the wafer manufacturing method shown in FIG. Figure 5 (B) is a schematic diagram showing Figure 2 A plan view of an ingot after a separation layer forming step included in the wafer manufacturing method is shown.

[0023] Figure 6 (A) and Figure 6 (B) are schematically shown Figure 2 The figure is a side view showing a state of a separation step included in the wafer manufacturing method.

[0024] Figure 7It is schematically shown Figure 2 A perspective view showing a wafer manufacturing method including a non-final planarization step.

[0025] Figure 8 is a schematic diagram showing the Figure 1 (A) and Figure 1 (B) is a block diagram of an example of a processing apparatus for manufacturing three or more wafers from the ingot shown.

[0026] Fig. 9 is a schematic diagram showing the Figure 1 (A) and Figure 1 (B) is a block diagram of another example of a processing apparatus for manufacturing three or more wafers from an ingot.

[0027] Description of symbols

[0028] 2: Laser processing device; 4: Chuck table; 6: Laser beam irradiation unit; 8: Head; 10: Shell; 11: Ingot (11a: front, 11b: back) (11c: c-axis, 11d: vertical line, 11e: c-plane); 12: Shooting unit; 13: Primary orientation plane; 14: Separation device; 15: Secondary orientation plane; 16: Chuck table; 17: Modification unit; 18: Separation unit; 19: Crack; 20: Suction plate; 21: Separation layer; 22: Vertical direction moving mechanism; 23: Wafer (23a: one surface ); 24: grinding device; 26: chuck table; 28: grinding unit; 30: spindle; 32: mounting seat; 34: grinding wheel; 36: base; 38: grinding tool; 40: processing device; 42: laser processing part; 44: separation part; 46: flattening part; 48: controller; 50: processor; 52: memory; 54: processing device; 56: laser processing part (56a: sub-controller); 58: separation part (58a: sub-controller); 60: flattening part (60a: sub-controller); 62: main controller. DETAILED DESCRIPTION

[0029] Embodiments of the present invention will be described with reference to the drawings. Figure 1 (A) is a perspective view schematically showing an example of an ingot, Figure 1 (B) is a schematic diagram showing Figure 1 (A) is a side view of the ingot shown. Figure 1 (A) and Figure 1 Ingot 11 shown in (B) is made of, for example, a single crystal of SiC, and has a cylindrical shape including a front surface 11 a and a back surface 11 b that are substantially parallel to each other.

[0030] The ingot 11 is produced by epitaxial growth. In order to reduce lattice defects formed inside, the ingot 11 is produced in such a way that the c-axis 11c of SiC is slightly inclined relative to the perpendicular line 11d of the front surface 11a and the back surface 11b. For example, the angle (deviation angle) α formed by the c-axis 11c and the perpendicular line 11d is 1° to 6° (typically 4°).

[0031] In addition, two flat portions for indicating the crystal orientation of SiC, namely, a primary orientation plane 13 and a secondary orientation plane 15, are formed on the side surface of the ingot 11. The primary orientation plane 13 is longer than the secondary orientation plane 15. In addition, the secondary orientation plane 15 is formed as an intersection line where a plane parallel to the c-plane 11e of SiC intersects the front surface 11a or the back surface 11b.

[0032] In addition, the ingot 11 may use a single crystal of a material other than SiC (e.g., Si, GaN, LT, or LN, etc.) as a raw material. In addition, one or both of the primary orientation plane 13 and the secondary orientation plane 15 may not be provided on the side surface of the ingot 11, and a cutout (notch) for indicating the crystal orientation of the raw material constituting the ingot 11 may be formed instead of them.

[0033] Figure 2 The flowchart schematically shows an example of a wafer manufacturing method for manufacturing three or more wafers from an ingot 11. In short, in this method, a series of steps for separating and flattening the ingot 11 by the number (n-1) obtained by subtracting 1 from the upper limit number n (n is a natural number greater than or equal to 3) of wafers that can be manufactured from the ingot 11 are repeatedly performed, thereby manufacturing n wafers from the ingot 11.

[0034] Furthermore, in this method, the removal of the excess thickness (i.e., the thickness exceeding the thickness required to manufacture n wafers) of the ingot 11 is not concentrated in a series of steps implemented to manufacture the final wafer, but is distributed in a series of steps implemented (n-1) times.

[0035] Specifically, in this method, in each series of steps, the thickness of the ingot 11 is reduced by the thickness obtained by adding the minimum thickness of the ingot 11 that decreases as the chip is manufactured (specifically, the thickness obtained by adding the finished thickness of the chip described later and the assumed thickness of the separation layer) and the distributed thickness (specifically, the thickness obtained by dividing the remaining thickness by (n-1)).

[0036] exist Figure 2 In the wafer manufacturing method shown, first, the upper limit number n of wafers that can be manufactured from the ingot 11 and the remaining thickness of the ingot 11 are calculated with reference to previously known parameters (calculation step S1). Figure 3 : is a side view schematically showing the parameters referred to in the calculation step S1.

[0037] In the calculation step S1, reference is made to the initial thickness T0 of the ingot 11, the finished thickness T1 of the chip (i.e., the thickness of the chip after flattening in the non-final flattening step S5 and the final flattening step S6 described later), and the assumed thickness T2 of the separation layer (i.e., the thickness of the separation layer assumed to be formed inside the ingot 11 in the separation layer forming step S2 described later).

[0038] Specifically, in this method, ingot 11 is separated into a number (n-1) obtained by subtracting 1 from the upper limit number n of wafers that can be produced from ingot 11. Therefore, initial thickness T0 of ingot 11 becomes a value that satisfies the following inequalities (1) and (2).

[0039] T0>n×T1+(n-1)×T2-(1)

[0040] T0<(n+1)×T1+n×T2…(2)

[0041] Furthermore, when the above inequalities (1) and (2) are modified, it can be seen that the upper limit number n of wafers that can be manufactured from the ingot 11 is a natural number that satisfies the following inequality (3).

[0042]

[0043] Furthermore, if the upper limit number n of wafers that can be manufactured from the ingot 11 is calculated, the remaining thickness T3 of the ingot 11 expressed by the following mathematical formula (4) can also be calculated.

[0044] T3=T0-{n×T1+(n-1)×T2}…(4)

[0045] Furthermore, if the upper limit number n of wafers that can be manufactured from ingot 11 and remaining thickness T3 of ingot 11 are calculated, the distributed thickness ΔT of ingot 11 expressed by the following mathematical formula (5) can also be calculated.

[0046]

[0047] For example, if the initial thickness T0 of the ingot 11 is 20 mm (20,000 μm), the finished thickness T1 of the wafer is 350 μm, and the assumed thickness T2 of the separation layer is 80 μm, the upper limit number n of wafers that can be manufactured from the ingot 11 is 46, and the remaining thickness T3 of the ingot 11 is 300 μm. In this case, the allocated thickness ΔT of the ingot 11 is 6.67 μm.

[0048] After the calculation step S1 , a separation layer is formed inside the ingot 11 (separation layer forming step S2 ). Figure 4 : is a perspective view schematically showing the separation layer forming step S2. Figure 4 The X-axis direction and the Y-axis direction shown are directions perpendicular to each other on a horizontal plane, and the Z-axis direction is a direction (vertical direction) perpendicular to the X-axis direction and the Y-axis direction.

[0049] The separation layer forming step S2 is performed in the laser processing device 2. The laser processing device 2 includes a chuck table 4 having a circular holding surface substantially parallel to a horizontal plane and capable of holding the ingot 11 on the holding surface.

[0050] The chuck table 4 is connected to a suction mechanism (not shown). The suction mechanism includes, for example, an ejector. When the suction mechanism is operated, suction acts on the space near the holding surface of the chuck table 4. Therefore, when the suction mechanism is operated with the ingot 11 placed on the holding surface, the ingot 11 is held on the holding surface of the chuck table 4.

[0051] In addition, the chuck table 4 is connected to a rotating mechanism (not shown). The rotating mechanism includes, for example, a pulley and a motor, etc. When the rotating mechanism is operated, the chuck table 4 rotates with a straight line along the Z-axis direction passing through the center of the holding surface as a rotation axis.

[0052] A head 8 of the laser beam irradiation unit 6 is provided above the chuck table 4. The head 8 is provided at the front end of a cylindrical housing 10 extending in the Y-axis direction. The head 8 houses an optical system such as a condenser lens and a reflector, and the housing 10 houses an optical system such as a reflector and / or a lens.

[0053] The base end of the housing 10 is connected to a moving mechanism. The moving mechanism includes, for example, a ball screw and a motor, etc. When the moving mechanism is operated, the head 8 and the housing 10 move along the X-axis direction, the Y-axis direction, and / or the Z-axis direction.

[0054] In addition, the laser beam irradiation unit 6 has a laser oscillator (not shown) that generates a laser beam having a wavelength (e.g., 1064 nm) that is transmitted through the raw material of the ingot 11. The laser oscillator has a laser medium such as Nd:YAG. When the laser beam is generated by the laser oscillator, the laser beam is emitted toward the holding surface side of the chuck table 4 via an optical system housed in the housing 10 and the head 8.

[0055] Furthermore, a photographing unit 12 capable of photographing the holding surface side of the chuck table 4 is provided on the side of the housing 10. The photographing unit 12 includes, for example, a light source such as an LED (Light Emission Diode), an objective lens, a CCD (Charge Coupled Device) image sensor, or a CMOS (Complementary Metal Oxide Semiconductor) image sensor, and other photographing elements.

[0056] When the separation layer forming step S2 is performed in the laser processing device 2, first, the ingot 11 is placed on the holding surface of the chuck table 4 in such a manner that the front surface 11a faces upward. Next, the suction mechanism is operated in such a manner that the ingot 11 is held on the chuck table 4. Next, based on the image of the front surface 11a of the ingot 11 formed by the imaging unit 12, etc., the rotation mechanism rotates the chuck table 4 so that the secondary orientation plane 15 is parallel to the X-axis direction.

[0057] Next, the moving mechanism moves the head 8 and the housing 10 in the X-axis direction and / or the Y-axis direction so that the region of the ingot 11 slightly inside the secondary orientation plane 15 is positioned in the X-axis direction when viewed from the head 8 in a plan view. Next, the moving mechanism moves the head 8 and the housing 10 in the Z-axis direction so that the focal point of the laser beam emitted from the head 8 is positioned at a predetermined depth from the front surface 11a of the ingot 11.

[0058] In addition, the prescribed depth is set with reference to the parameters known in advance. Specifically, the prescribed depth is set to be greater than the first thickness and less than the second thickness, wherein the first thickness is the thickness obtained by adding the finished thickness T1 of the wafer and the thickness of the separation layer remaining on the wafer after the wafer is separated from the ingot 11 (the separation layer remaining on the wafer side), and the second thickness is the thickness obtained by adding the first thickness and the distribution thickness ΔT of the ingot 11. In addition, regarding the thickness of the separation layer remaining on the wafer side, in short, it is a thickness corresponding to the thickness obtained by subtracting the thickness of the separation layer remaining on the ingot 11 (the separation layer remaining on the ingot side) after the wafer is separated from the ingot 11 from the assumed thickness T2 of the separation layer.

[0059] Next, while emitting a laser beam from the head 8, the head 8 and the housing 10 are moved in the X-axis direction by the moving mechanism so that the focal point where the laser beam converges passes from one end to the other end in the X-axis direction of the ingot 11. That is, while irradiating the ingot 11 with the laser beam, the focal point where the laser beam converges and the ingot 11 are relatively moved along the intersection line where the surface parallel to the c-plane 11e of the raw material (here, SiC) of the ingot 11 intersects the front surface 11a.

[0060] Next, the moving mechanism moves the head 8 and the housing 10 along the Y-axis direction so that the head 8 is located in the X-axis direction when viewed from above from an area slightly away from the secondary orientation plane 15 than the area already irradiated with the laser beam. Next, the ingot 11 is irradiated with the laser beam as described above again.

[0061] Then, the movement of the head 8 and the housing 10 along the Y-axis direction and the irradiation of the ingot 11 with the laser beam are repeated until the irradiation of the laser beam to the region of the ingot 11 farthest from the secondary orientation plane 15 is completed. Thus, the separation layer forming step S2 is completed.

[0062] Figure 5 (A) is a partially enlarged cross-sectional view schematically showing the ingot 11 after the separation layer forming step S2, Figure 5 (B) is a plan view schematically showing the ingot 11 after the separation layer forming step S2. In the separation layer forming step S2, a modified portion 17 in which the crystal structure of the raw material of the ingot 11 (here, SiC) is disturbed is formed inside the ingot 11 with the focal point where the laser beam converges as the center.

[0063] In addition, when the modified portion 17 is formed inside the ingot 11, the volume of the ingot 11 expands and internal stress is generated in the ingot 11. The crack 19 extends from the modified portion 17 to relieve the internal stress. In addition, the crack 19 mainly extends along the c-plane 11e. As a result, a separation layer 21 including a plurality of modified portions 17 and cracks 19 extending from the plurality of modified portions 17 is formed inside the ingot 11.

[0064] After separation layer forming step S2 , ingot 11 is separated at separation layer 21 to produce wafers (separation step S3 ). Figure 6 (A) and Figure 6 (B) are side views schematically showing the separation step S3. The separation step S3 is implemented in the separation device 14. The separation device 14 has a chuck table 16, and the chuck table 16 has Figure 4 The chuck table 4 shown is of the same construction.

[0065] The chuck table 16 is connected to a table-side suction mechanism (not shown). The table-side suction mechanism includes, for example, a vacuum pump. When the table-side suction mechanism is operated, suction acts on the space near the holding surface of the chuck table 16. Therefore, when the table-side suction mechanism is operated with the ingot 11 placed on the holding surface, the ingot 11 is held on the holding surface of the chuck table 16.

[0066] A separation unit 18 is provided above the chuck table 16. The separation unit 18 has a suction plate 20 having a plurality of suction ports formed on the lower surface. The plurality of suction ports are connected to a separation unit side suction mechanism such as a vacuum pump via a suction path formed inside the suction plate 20. When the separation unit side suction mechanism is operated, suction acts on the space near the lower surface of the suction plate 20.

[0067] In addition, the upper part of the suction plate 20 is connected to a vertical direction moving mechanism 22. The vertical direction moving mechanism 22 includes, for example, an air cylinder, etc. When the vertical direction moving mechanism 22 is operated, the suction plate 20 moves in the vertical direction.

[0068] When the separation step S3 is performed in the separation device 14, first, in a state where the chuck table 16 and the suction plate 20 are sufficiently separated, the ingot 11 having the separation layer 21 formed therein is placed on the holding surface of the chuck table 16 with the front surface 11a facing upward. Next, the table-side suction mechanism is operated so as to hold the ingot 11 on the chuck table 16.

[0069] Next, the vertical direction moving mechanism is moved so that the lower surface of the suction plate 20 contacts the front surface 11a of the ingot 11 (see Figure 6 The suction plate 20 is lowered in the manner of (A)). Next, the separation unit side suction mechanism is operated so as to suck the front surface 11a side of the ingot 11 upward.

[0070] Next, the vertical direction moving mechanism separates the suction plate 20 from the chuck table 16 (see Figure 6 The suction plate 20 is raised in the manner of (B). At this time, tensile stress acts on the ingot 11, and the cracks 19 included in the separation layer 21 are further extended.

[0071] As a result, the ingot 11 is separated at the separation layer 21, and the ingot 11 having the ingot-side residual separation layer on the front surface 11a side of the ingot 11 and the wafer 23 having the wafer-side residual separation layer on one surface side are manufactured. In addition, the front surface 11a of the ingot 11 and the one surface of the wafer 23 each have a concavo-convex shape reflecting the distribution of the modified portion 17 and the crack 19 in the separation layer 21. Thus, the separation step S3 is completed.

[0072] Moreover, if the ingot 11 has not been separated (n-1) times (step S4: No), the ingot 11 is ground until it reaches a specified thickness, thereby removing the residual separation layer on the ingot side and flattening the ingot 11, and the wafer is ground until it reaches a finished thickness T1, thereby removing the residual separation layer on the wafer side and flattening the wafer 23 (non-final flattening step S5).

[0073] In addition, the specified thickness is a thickness that is thinner than the thickness of the ingot 11 at the moment when a series of steps including the separation layer forming step S2, the separation step S3, and the non-final flattening step S5 are started (i.e., the moment when the separation layer forming step S2 is started) by adding the finished thickness T1 of the chip 23, the assumed thickness T2 of the separation layer 21, and the allocated thickness ΔT of the ingot 11.

[0074] Figure 7 2 is a perspective view schematically showing the state of the non-final flattening step S5. The non-final flattening step S5 is implemented in the grinding device 24. The grinding device 24 has a chuck table 26, and the chuck table 26 has a holding surface on which the wafer 23 can be held, and the holding surface is in a shape equivalent to the side surface of a cone whose center protrudes slightly more than the outer edge.

[0075] The chuck table 26 is connected to a suction mechanism. The suction mechanism includes an ejector or the like. When the suction mechanism is operated, suction acts on the space near the holding surface of the chuck table 26. Therefore, when the suction mechanism is operated with the ingot 11 or the wafer 23 placed on the holding surface, the ingot 11 or the wafer 23 is held on the holding surface of the chuck table 26.

[0076] The chuck table 26 is connected to a horizontal direction moving mechanism. The horizontal direction moving mechanism includes, for example, a ball screw and a motor, etc. When the horizontal direction moving mechanism is operated, the chuck table 26 moves in the horizontal direction.

[0077] The chuck table 26 is connected to a rotation mechanism (not shown). The rotation mechanism includes, for example, a pulley and a motor, etc. When the rotation mechanism is operated, the chuck table 26 rotates about a straight line passing through the center of the holding surface as a rotation axis.

[0078] A measuring unit (not shown) is provided near the chuck table 26 . The measuring unit includes, for example, a contact or non-contact thickness measuring device, etc. The measuring unit can measure the thickness of the ingot 11 or the wafer 23 held on the holding surface of the chuck table 26 .

[0079] A grinding unit 28 is provided above the chuck table 26. The grinding unit 28 includes a main shaft 30 whose upper end is connected to a motor. A disc-shaped mounting seat 32 is provided at the lower end of the main shaft 30, and a grinding wheel 34 is mounted on the mounting seat 32.

[0080] The grinding wheel 34 has an annular base 36 and a plurality of grinding stones 38 discretely arranged along the circumferential direction of the base 36. The lower surfaces of the plurality of grinding stones 38 are arranged at substantially the same height, and their lower surfaces serve as grinding surfaces for grinding the ingot 11 and the wafer 23.

[0081] Furthermore, the main shaft 30 is connected to a vertical direction moving mechanism. The vertical direction moving mechanism includes, for example, a ball screw and a motor, etc. Furthermore, when the vertical direction moving mechanism is operated, the main shaft 30, the mounting seat 32, and the grinding wheel 34 move in the vertical direction.

[0082] When the non-final flattening step S5 is performed in the grinding device 24, for example, the SiC ingot 11 is ground until the above-mentioned predetermined thickness is reached, and then the wafer 23 is ground until the finished thickness T1 is reached. In this case, first, the ingot 11 is placed on the holding surface of the chuck table 26 with the front surface 11a facing upward, while the chuck table 26 and the grinding wheel 34 are sufficiently separated in the horizontal direction and the vertical direction, respectively.

[0083] Next, the suction mechanism is operated so that the chuck table 26 holds the ingot 11. Next, the horizontal movement mechanism moves the chuck table so that the center of the holding surface of the chuck table 26 overlaps with the trajectory of the plurality of grinding tools 38 when the grinding wheel 34 and the spindle 30 are rotated together in the vertical direction.

[0084] Next, the rotating mechanism is operated to rotate the chuck table 26, and the motor connected to the upper end of the main shaft 30 is operated to rotate the grinding wheel 34. Next, the main shaft 30, the mounting seat 32, and the grinding wheel 34 are lowered so that the grinding surface of any one of the plurality of grinding tools 38 comes into contact with the front surface 11a of the ingot 11.

[0085] Thus, the grinding of the ingot 11 is started. Then, the grinding is continued (ie, the grinding wheel 34 is lowered while both the chuck table 26 and the grinding wheel 34 are rotated) until the thickness of the ingot 11 measured by the measuring unit reaches the predetermined thickness.

[0086] When the grinding of the ingot 11 is completed, the rotation of both the chuck table 26 and the grinding wheel 34 is stopped, and the horizontal moving mechanism and the vertical moving mechanism are operated so that the chuck table 26 and the grinding wheel 34 are sufficiently separated in the horizontal direction and the vertical direction, respectively.

[0087] Next, the wafer 23 is ground in the same steps as the above steps until the finished thickness T1 is reached. Thus, the non-final planarization step S5 is completed. In addition, in the non-final planarization step S5, one of the grinding of the ingot 11 and the grinding of the wafer 23 may be performed in a grinding device different from the grinding device 24. In this case, the grinding of the ingot 11 and the wafer 23 can be performed in parallel.

[0088] In addition, the thickness of the ingot 11 removed in the non-final flattening step S5 and the thickness of the wafer 23 vary depending on the above-mentioned specified depth (i.e., the distance between the focal point of the laser beam irradiated to the ingot 11 in the separation layer forming step S2 and the front surface 11a of the ingot 11).

[0089] Specifically, in a case where the specified depth is a depth corresponding to the above-mentioned first thickness (i.e., the thickness obtained by adding the finished thickness T1 of the chip and the thickness of the residual separation layer on the chip side), the thickness of the ingot 11 removed in the non-final flattening step S5 corresponds to the thickness obtained by adding the thickness of the residual separation layer on the ingot side and the allocated thickness ΔT of the ingot 11, and further, the thickness of the chip 23 removed in the non-final flattening step S5 corresponds to the thickness of the residual separation layer on the chip side.

[0090] In this case, even if crack 19 unexpectedly extends long toward back surface 11 b of ingot 11 in separation layer forming step S2 and separation step S3 , crack 19 is prevented from remaining in ingot 11 , thereby increasing the possibility of flattening ingot 11 .

[0091] In addition, in a case where the specified depth is a depth corresponding to the above-mentioned second thickness (i.e., the thickness obtained by adding the above-mentioned first thickness and the allocated thickness ΔT of the ingot 11), the thickness of the ingot 11 removed in the non-final flattening step S5 corresponds to the thickness of the residual separation layer on the ingot side, and in addition, the thickness of the chip 23 removed in the non-final flattening step S5 corresponds to the thickness obtained by adding the thickness of the residual separation layer on the chip side and the allocated thickness ΔT of the ingot 11.

[0092] In this case, even if the crack 19 unexpectedly extends long toward the front surface 11 a of the ingot 11 in the separation layer forming step S2 and the separation step S3 , the crack 19 is prevented from remaining in the wafer 23 , thereby increasing the possibility of flattening the wafer 23 .

[0093] In addition, when the specified depth is longer than the above-mentioned first thickness and shorter than the above-mentioned second thickness, the thickness of the ingot 11 removed in the non-final flattening step S5 corresponds to the thickness obtained by adding the thickness of the residual separation layer on the ingot side and the allocated thickness ΔT of the ingot 11 multiplied by (k / k+1) (k is a positive real number), and the thickness of the chip 23 removed in the non-final flattening step S5 corresponds to the thickness obtained by adding the thickness of the residual separation layer on the chip side and the allocated thickness ΔT of the ingot 11 multiplied by (1 / k+1).

[0094] In this case, even if the crack 19 accidentally extends to a certain extent toward both the front side 11a and the back side 11b of the ingot 11 in the separation layer forming step S2 and the separation step S3, the crack 19 will not remain in both the ingot 11 and the wafer 23, thereby increasing the possibility of flattening both the ingot 11 and the wafer 23.

[0095] After the non-final planarization step S5, the separation layer formation step S2 and the separation step S3 are performed again. Furthermore, the non-final planarization step S5, the separation layer formation step S2 and the separation step S3 are repeated in sequence until the ingot 11 is separated (n-1) times.

[0096] Then, if the ingot 11 has been separated (n-1) times (step S4: yes), the ingot 11 and the wafer 23 are ground separately until they reach the finished thickness T1, thereby removing the remaining separation layers (i.e., the residual separation layer on the ingot side or the residual separation layer on the wafer side) and flattening the ingot and the wafer (2 wafers) (final flattening step S6).

[0097] In addition, the thickness of the ingot 11 at the moment when a series of steps including the separation layer forming step S2, the separation step S3 and the final flattening step S6 are started (i.e., the moment when the last separation layer forming step S2 is started) corresponds to the thickness obtained by adding twice the thickness T1 of the chip 23, the assumed thickness T2 of the separation layer 21 and the allocated thickness ΔT of the ingot 11.

[0098] In addition, the thickness of the ingot 11 at the moment of starting the final flattening step S6 is greater than the minimum thickness of the ingot 11 required for manufacturing the final chip 23 (specifically, the thickness obtained by adding the finished thickness T1 of the chip 23 and the thickness of the residual separation layer on the ingot side), and is less than the thickness obtained by adding the minimum thickness of the ingot 11 required for manufacturing the final chip 23 and the allocated thickness ΔT.

[0099] The final planarization step S6 is performed in the same manner as the non-final planarization step S5 described above. Therefore, a detailed description of the final planarization step S6 is omitted here. Then, when the final planarization step S6 is completed, the production of n wafers 23 from the ingot 11 is completed. That is, the process is completed. Figure 2 The wafer manufacturing method is shown.

[0100] exist Figure 2In the chip manufacturing method shown, in a non-final flattening step S5 included in a series of steps for manufacturing a chip 23 from an ingot 11, the ingot 11 is ground until the ingot 11 becomes thinner than the thickness of the ingot 11 at the moment of starting the series of steps by a thickness obtained by adding the finished thickness T1 of the chip 23, the assumed thickness T2 of the separation layer 21, and the allocated thickness ΔT of the ingot 11, wherein the allocated thickness ΔT is obtained by dividing the remaining thickness T3 of the ingot 11 by the number (n-1) obtained by subtracting 1 from the upper limit number n of chips 23 that can be manufactured from the ingot 11.

[0101] Then, when this series of steps is repeated, an ingot 11 having a thickness greater than the minimum thickness of the ingot 11 required for manufacturing the final chip 23 (specifically, the thickness obtained by adding the finished thickness T1 of the chip 23 and the thickness of the residual separation layer on the ingot side) and less than the thickness obtained by adding the minimum thickness of the ingot 11 required for manufacturing the final chip 23 and the allocated thickness ΔT is provided to the final flattening step S6.

[0102] In this case, the time required to grind the ingot 11 to the finished thickness T1 of the wafer 23 and manufacture the final wafer 23 is shortened. Figure 2 The wafer manufacturing method shown is a method for manufacturing an upper limit number n of wafers 23 from each ingot 11 while processing a plurality of ingots 11 simultaneously and in parallel. Grinding of the ingot 11 for manufacturing the final wafer 23 from each ingot 11 does not become a bottleneck, and the time required can be reduced.

[0103] The above contents are one embodiment of the present invention, and the present invention is not limited to the above contents. For example, in the present invention, a measurement step for measuring the initial thickness T0 of the ingot 11 may be performed before the calculation step S1.

[0104] In addition, in the present invention, an ultrasonic applying step of applying ultrasonic waves to the front surface 11a side of the ingot 11 may be performed after the separation layer forming step S2 and before the separation step S3. In this case, in the ultrasonic applying step, the cracks 19 included in the separation layer 21 extend, thereby facilitating the separation of the ingot 11 in the separation step S3.

[0105] Furthermore, the present invention may be a processing device for manufacturing three or more wafers 23 from the ingot 11 . Figure 8 1 is a block diagram schematically showing an example of such a processing device. Figure 8 The processing device 40 shown includes a laser processing unit 42 , a separation unit 44 , a flattening unit 46 , and a controller 48 .

[0106] The laser processing part 42 has, for example, Figure 4The laser processing device 2 shown in FIG. 4 is similar in structure to the laser processing device 2 shown in FIG. Therefore, in the laser processing unit 42 , the separation layer 21 can be formed inside the ingot 11 as described above.

[0107] The separation portion 44 has, for example, Figure 6 The structure is the same as that of the separating device 14 shown in the figure. Therefore, in the separating unit 44, the ingot 11 can be separated at the separation layer 21 to produce the wafer 23 as described above.

[0108] The flattened portion 46 has, for example, Figure 7 Therefore, in the flattening section 46, as described above, the ingot 11 and the wafer 23 can be flattened by removing the ingot side residual separation layer and the wafer side residual separation layer respectively.

[0109] In addition, only the ingot 11 may be flattened in the flattening section 46. In this case, a flattening section different from the flattening section 46 may be provided in the processing device 40, and the wafer 23 may be flattened in the other flattening section. Alternatively, in this case, the wafer 23 may be flattened in a device different from the processing device 40 (for example, a grinding device).

[0110] The controller 48 has a processor 50 and a memory 52. ​​The processor 50 is composed of, for example, a CPU (Central Processing Unit) etc. In addition, the memory 52 is composed of, for example, a volatile memory such as a DRAM (Dynamic Random Access Memory) or an SRAM (Static Random Access Memory) and a non-volatile memory such as an SSD (Solid State Drive) (NAND flash memory) or an HDD (Hard Disk Drive) (magnetic storage device).

[0111] The memory 52 stores data and programs used by the processor 50. Examples of the data include the initial thickness T0 of the ingot 11, the finished thickness T1 of the wafer 23, the assumed thickness T2 of the separation layer 21, the thickness of the separation layer remaining on the ingot side, and the thickness of the separation layer remaining on the wafer side. In addition, examples of the programs include a program for implementing the processing in the processing device 40. Figure 2 The procedure of the wafer manufacturing method is shown.

[0112] The processor 50 uses the data stored in the memory 52 and reads out and executes the program stored in the memory 52. ​​For example, the processor 50 refers to the initial thickness T0 of the ingot 11 stored in the memory 52, and reads out the program for implementing the process from the memory 52. Figure 2 The procedure of the wafer manufacturing method shown is performed.

[0113] Specifically, when the processing device 40 is implemented Figure 2 When the method for manufacturing the chip shown is used, first, referring to the initial thickness T0 of the ingot 11, the finished thickness T1 of the chip 23, and the assumed thickness T2 of the separation layer 21 stored in the memory 52, the processor 50 calculates the upper limit number n of chips that can be manufactured from the ingot 11 and the remaining thickness T3 of the ingot 11 (calculation step S1).

[0114] Then, the processor 50 stores the calculated upper limit number n of wafers that can be manufactured from the ingot 11 and the remaining thickness T3 of the ingot 11 in the memory 52. ​​In addition, the processor 50 may also calculate the allocated thickness ΔT of the ingot 11 with reference to the upper limit number n of wafers that can be manufactured from the ingot 11 and the remaining thickness T3 of the ingot 11, and store it in the memory 52.

[0115] If the calculation step S1 is completed, the processor 50 controls the laser processing unit 42, the separation unit 44 and the flattening unit 46 in a manner that repeats a series of steps including the formation of the separation layer 21 (separation layer formation step S2), the separation of the ingot 11 (separation step S3) and the flattening of the ingot 11 (non-final flattening step S5 or final flattening step S6) by the number (n-1) obtained by subtracting 1 from the upper limit number n of wafers 23 that can be manufactured from the ingot 11.

[0116] In addition, in the processing device of the present invention, not all processing units (specifically, laser processing unit, separation unit and flattening unit) may be controlled by one controller, but a controller may be provided for each processing unit, and each processing unit may be controlled by a separate controller. Fig. 9 This is a block diagram schematically showing an example of a processing device in which a controller is provided for each processing unit.

[0117] Fig. 9 The processing device 54 shown in the figure has: a laser processing unit 56, which has a sub-controller 56a; a separation unit 58, which has a sub-controller 58a; a flattening unit 60, which has a sub-controller 60a; and a main controller 62. In other words, in addition to the fact that the controller 48 is divided into the sub-controllers 56a, 58a, 60a and the main controller 62, the processing device 54 has the same Figure 8 The processing device 40 shown is constructed in the same manner.

[0118] The laser processing part 56 includes, for example, Figure 4The laser processing device 2 shown in the figure has a sub-controller 56a including a processor and a memory in addition to the same components. The memory stores, for example, data and programs required for forming the separation layer 21 in the laser processing unit 56 (separation layer forming step S2).

[0119] For example, the separation portion 58 is Figure 6 The separator 14 shown has the same components as those of the separator 14, and further has a sub-controller 58a including a processor and a memory. The memory stores, for example, data and programs required for separating the ingots 11 in the separator 58 (separation step S3).

[0120] For example, the planarization portion 60 has Figure 7 The grinding device 24 shown in the figure has the same components as the components thereof, and further has a sub-controller 60a including a processor and a memory. The memory stores, for example, data and programs required for flattening the ingot 11 and the wafer 23 in the flattening section 60 (non-final flattening step S5 and final flattening step S6).

[0121] In addition, in the flattening section 60, only the ingot 11 may be flattened. In this case, a flattening section different from the flattening section 60 may be provided in the processing device 54, and the wafer 23 may be flattened in the other flattening section. Alternatively, in this case, the wafer 23 may be flattened in a device different from the processing device 54 (for example, a grinding device).

[0122] The main controller 62 has a processor and a memory. In addition, the memory stores, for example, the initial thickness T0 of the ingot 11, the finished thickness T1 of the wafer 23, the assumed thickness T2 of the separation layer 21, the thickness of the separation layer remaining on the ingot side, and the thickness of the separation layer remaining on the wafer side. In addition, the main controller 62 is connected to the sub-controllers 56a, 58a, and 60a via a wired or wireless communication line.

[0123] In the processing device 54, the calculation step S1 is implemented by the main controller 62. Specifically, referring to the initial thickness T0 of the ingot 11, the finished thickness T1 of the wafer 23, and the assumed thickness T2 of the separation layer 21 stored in the memory of the main controller 62, the processor of the main controller 62 calculates the upper limit number n of wafers that can be manufactured from the ingot 11 and the remaining thickness T3 of the ingot 11.

[0124] Then, the processor of the main controller 62 sends data necessary for determining the above-mentioned predetermined depth (i.e., the distance between the focal point of the laser beam irradiated to the ingot 11 in the separation layer forming step S2 and the front surface 11a of the ingot 11) to the sub-controller 56a. In addition, the data includes, for example, data necessary for calculating the finished thickness T1 of the wafer, the thickness of the residual separation layer on the wafer side, and the allocated thickness ΔT of the ingot 11 (specifically, the upper limit number n of wafers that can be manufactured from the ingot 11 and the remaining thickness T3 of the ingot 11).

[0125] The processor of the main controller 62 sends data necessary for determining the predetermined thickness to the sub-controller 60a. The data includes data necessary for calculating the finished thickness T1 of the wafer 23, the assumed thickness T2 of the separation layer 21, and the distributed thickness ΔT of the ingot 11.

[0126] In addition, the processor of the main controller 62 may calculate the allocated thickness ΔT of the ingot 11 in addition to the upper limit number n of wafers that can be manufactured from the ingot 11 and the remaining thickness T3 of the ingot 11. In this case, the processor of the main controller 62 may send the allocated thickness ΔT of the ingot 11 itself to the sub-controllers 56a, 60a instead of the data required for calculating the allocated thickness ΔT of the ingot 11.

[0127] When the calculation step S1 in the main controller 62 is completed, the main controller 62 sends a signal to the sub-controller 56a to instruct the formation of the separation layer 21 in the laser processing unit 56 (separation layer formation step S2). Figure 4 When the separation layer forming step S2 is completed with the same components as the components of the laser processing device 2 shown, the sub-controller 56a sends a signal indicating this to the main controller 62.

[0128] When the main controller 62 receives a signal from the sub-controller 56a, the main controller 62 sends a signal to the sub-controller 58a to instruct the sub-controller 58a to separate the ingot 11 in the separation unit 58 (separation step S3). Figure 6 When the separation step S3 is completed by the same components as the components of the separation device 14 shown, the sub-controller 58a sends a signal indicating this to the main controller 62.

[0129] If the main controller 62 receives a signal from the sub-controller 58a, the main controller 62 sends a signal to the sub-controller 60a to instruct the sub-controller 60a to perform flattening of the ingot 11 in the flattening section 60 (not the final flattening step S5). Figure 7If the non-final flattening step S5 is completed using the same components as the components of the grinding device 24 shown, the sub-controller 60a sends a signal indicating this to the main controller 62.

[0130] Furthermore, the sending and receiving of signals between the sub-controllers 56a, 58a, 60a and the main controller 62 is repeated until a signal indicating that the separation step S3 is completed is received from the sub-controller 58a in the main controller 62, which is a number (n-1) obtained by subtracting 1 from the upper limit number n of chips 23 that can be manufactured from the ingot 11.

[0131] Then, if the main controller 62 receives the signal from the sub-controller 58a according to the number (n-1), the main controller 62 sends a signal to the sub-controller 60a to instruct the flattening section 60 to flatten the ingot 11 (final flattening step S6). Then, if the sub-controller 60a controls the Figure 7 When the final flattening step S6 is completed with the same components as those of the grinding device 24 shown, the sub-controller 60a sends a signal indicating this to the main controller 62.

[0132] In addition, additional components may be provided in the processing devices 40 and 54. For example, a measuring unit for measuring the initial thickness T0 of the ingot 11 may be provided in the processing devices 40 and 54. In addition, a conveying unit for conveying the ingot 11 into any one of the laser processing unit 42, the laser processing unit 56, the separation unit 44, the separation unit 58, and the flattening unit 46 and the flattening unit 60 or conveying the ingot 11 out of any one of them may be provided in the processing devices 40 and 54.

[0133] In addition, the structure and method etc. which concern on the said embodiment can be implemented with appropriate modification unless it deviates from the scope of the objective of this invention.

Claims

1. A method for manufacturing a wafer, comprising repeatedly performing a series of steps including a separation layer forming step, a separation step, and a flattening step, thereby manufacturing three or more wafers from an ingot, wherein the separation layer forming step forms a separation layer inside the ingot, the separation step separates the ingot at the separation layer after the separation layer forming step to manufacture the wafer, and the flattening step removes the ingot-side residual separation layer remaining on the ingot and the wafer-side residual separation layer remaining on the wafer after the separation step to flatten the ingot and the wafer, respectively, wherein: The wafer manufacturing method comprises the following calculation steps: before manufacturing three or more wafers from the ingot, referring to the initial thickness of the ingot, the finished thickness of the wafer and the assumed thickness of the separation layer, calculating the upper limit number of wafers that can be manufactured from the ingot and the remaining thickness of the ingot; In the separation layer forming step, the separation layer is formed by irradiating the ingot with a laser beam having a wavelength that passes through a raw material of the ingot so that a focal point thereof is positioned at a predetermined depth from the front surface of the ingot, while the focal point and the ingot are relatively moved. In the flattening step, the ingot is ground until it becomes thinner than the thickness of the ingot at the start of the series of steps by a thickness obtained by adding the finished thickness, the assumed thickness and the allocated thickness, the allocated thickness being the remaining thickness divided by a number obtained by subtracting 1 from the upper limit number of sheets, and the chip is ground until it reaches the finished thickness.

2. The method for manufacturing a wafer according to claim 1, wherein: The predetermined depth is a depth corresponding to a first thickness obtained by adding the finished thickness and the thickness of the residual separation layer on the wafer side.

3. The method for manufacturing a wafer according to claim 1, wherein: The predetermined depth is a depth corresponding to a second thickness obtained by adding the finished thickness, the thickness of the wafer-side residual separation layer, and the allocated thickness.

4. The method for manufacturing a wafer according to claim 1, wherein: The predetermined depth is a depth that is longer than a first thickness obtained by adding the finished thickness to the thickness of the wafer-side residual separation layer and is shorter than a second thickness obtained by adding the first thickness to the allocated thickness.

5. A processing apparatus for producing three or more wafers from an ingot, wherein: The processing device has: a laser processing section for forming a separation layer inside the ingot; A separation part, which is used to separate the ingot at the separation layer to manufacture the wafer; a flattening section for removing a residual separation layer remaining on the ingot side of the ingot to flatten the ingot; as well as a controller for controlling the laser processing unit, the separation unit, and the flattening unit so as to repeatedly perform a series of steps including forming the separation layer, separating the ingot, and flattening the ingot according to a number obtained by subtracting 1 from an upper limit number of the wafers that can be manufactured from the ingot, The controller features: a memory for storing the initial thickness of the ingot, the finished thickness of the wafer, and the assumed thickness of the separation layer; as well as a processor for calculating the upper limit number of sheets and the remaining thickness of the ingot with reference to the initial thickness, the finished thickness, and the assumed thickness, The processor controls the laser processing unit so as to irradiate the ingot with the laser beam in such a manner that a focal point of the laser beam having a wavelength that passes through the raw material of the ingot is positioned at a predetermined depth from the front surface of the ingot, while the focal point and the ingot are moved relative to each other, thereby forming the separation layer. Furthermore, the processor controls the flattening section to grind the ingot until it becomes thinner than the thickness of the ingot at the moment of starting the series of steps by a thickness obtained by adding the finished thickness, the assumed thickness, and the allocated thickness, wherein the allocated thickness is obtained by dividing the remaining thickness by a number obtained by subtracting 1 from the upper limit number of sheets.

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