Wafer manufacturing process and detection process for a processing feed direction

Abstract

Wafer fabrication process comprising producing a wafer (88) from a cylindrical SiC single-crystal ingot (60) having a circular top surface (64) and a cylindrical circumferential surface (62) with a first alignment plane (68) and a second alignment plane (70) that is shorter than the first alignment plane (68) and perpendicular to the first alignment plane (68), wherein the cylindrical SiC single-crystal ingot (60) has a c-axis inclined from a vertical axis (72) perpendicular to the circular top surface (64) in the direction of the second alignment plane (70) and an angle of deviation formed between a c-plane perpendicular to the c-axis and the top surface (64), wherein the wafer fabrication process comprises: a detection step for a processing feed direction with a confirmation as to whether a direction in which the c-axis is inclined and the second alignment plane (70) are perpendicular to each other or not and a detection of a processing feed direction perpendicular to the direction (A) in which the c-axis is inclined; a formation step for a region of reduced strength (82) comprising positioning the focal point of a laser beam from the circular upper surface (64) at a depth in the cylindrical SiC single-crystal ingot (60), the depth corresponding to the thickness of a wafer (88) to be produced, and, while moving the cylindrical SiC single-crystal ingot (60) and the focal point relative to the processing feed direction, which was detected in the processing feed direction detection step, irradiating the cylindrical SiC single-crystal ingot (60) with a laser beam having a wavelength that transmits SiC, thereby forming a straight region of reduced strength (82) consisting of a modified layer (84) parallel to the circular upper surface (64) and cracks (86) extending from the modified layer (84) at a depth along the c-plane,which corresponds to the thickness of the wafer to be produced (88); , a peeling plane formation step comprising forming a peeling plane in the cylindrical SiC single-crystal ingot by repeatedly performing the formation step for a region of reduced strength (82) at predetermined intervals in a direction perpendicular to the processing feed direction; and after the peeling plane formation step a wafer manufacturing step with a production of a wafer (88) from the cylindrical SiC single crystal ingot (60) by peeling off a section of the cylindrical SiC single crystal ingot (60) from the peeling plane, which serves as an interface; where the acquisition step includes one processing feed direction: a scanning step comprising performing a scanning irradiation to position the focal point of a laser beam from the circular upper surface (64) at a predetermined depth in the cylindrical SiC single-crystal ingot (60) and, while moving the cylindrical SiC single-crystal ingot (60) and the focal point relative to each other, irradiating the cylindrical SiC single-crystal ingot (60) with a laser beam having a wavelength that transmits SiC along a direction parallel to the second alignment plane (70) and a plurality of directions inclined clockwise and counterclockwise by respective predetermined angles to the second alignment plane (70) in order to form a plurality of scanned straight regions of reduced strength (74) in the cylindrical SiC single-crystal ingot (60),wherein each of the sampled straight areas of reduced strength (74) is composed of a modified layer (76) parallel to the circular upper surface (64) and cracks (78) extending from the modified layer (76) along at least one c-plane, and , a determination step involving the acquisition of respective images of the sampled straight areas of reduced strength (74) with an imaging means (12), measuring the number of nodes (80) that are present per unit length in each of the sampled straight areas of reduced strength (74) in one of their images, and determining a direction in which the sampled straight area of ​​reduced strength (74), where the measured number of nodes (80) is zero, extends, as the processing feed direction.

Description

BACKGROUND OF THE INVENTIONField of the invention

[0001] The present invention relates to a wafer manufacturing method comprising manufacturing a wafer from a SiC single crystal ingot and a processing feed direction detecting method comprising detecting a processing feed direction perpendicular to the direction in which a c-axis is inclined at the time of manufacturing a wafer from the SiC single crystal ingot. Description of the related prior art

[0002] Components such as integrated circuits (ICs), large-scale integration circuits (LSIs), light-emitting diodes (LEDs), etc., are manufactured by depositing functional layers on the top surface of a wafer made of Si (silicon), Al2O3 (sapphire), or similar materials, and defining the functional layer along projected dividing lines. Power devices, LEDs, etc., are manufactured by depositing functional layers on the top surface of a wafer made of SiC (silicon carbide) single crystal and defining the functional layer along projected dividing lines. The wafers are cut into individual components along the projected dividing lines by a cutter or a laser processing device. These components are used in a wide variety of electronic devices, such as mobile phones, personal computers, etc.

[0003] Generally, a wafer on which components are to be formed is produced by cutting a cylindrical ingot into a thin piece with a wire saw. The upper and lower surfaces of the produced wafer are polished to a mirror finish (see Japanese Unexamined Patent Application No. 2000-94221A). One problem with cutting an ingot into a wafer with a wire saw and polishing the upper and lower surfaces of the wafer is that it is not economical, as the majority of the ingot (70 to 80%) must be discarded. In particular, SiC single-crystal ingots are very hard and pose a productivity problem because cutting them with a wire saw is difficult to perform and requires a significant amount of time, incurs high costs, and represents an obstacle to efficient wafer production.

[0004] A technology for applying a laser beam with a wavelength that transmits SiC to a SiC ingot while maintaining a focal point in the SiC ingot, thereby forming a modified layer in a projected cutting plane in the SiC ingot, and cutting the SiC ingot along the projected cutting plane where the modified layer has been formed, thus producing a wafer from the SiC ingot has been proposed (see Japanese Unexamined Patent Application Publication No. 2013-49161A). However, producing wafers from a SiC ingot suffers from poor economics because a number of adjacent modified layers must be formed in the SiC ingot.

[0005] Furthermore, US 2008 / 0 008 641 A1 discloses a semiconductor crystal and the associated growth method. The crystal includes a seed portion and a growth portion on the seed portion. The seed portion and the growth portion form a substantially rectangular cylindrical single crystal of silicon carbide. A seed surface defines an interface between the growth portion and the seed portion, wherein the seed surface is substantially parallel to the end faces of the rectangular cylindrical crystal and is inclined with respect to a crystal plane of the single crystal.

[0006] DE 10 2015 113 919 A1, on the other hand, relates to a manufacturing method for a substrate from an ingot, wherein the method performs a crack formation process along an interface between a first section of the ingot and a second section of the ingot. The crack formation process forms the crack by irradiating the ingot with pulsed laser light, the focal point of which is positioned at the interface. For crack formation, an impurity concentration or the material of the first section and the second section differ from each other.

[0007] However, none of these documents addresses the machining feed direction when cutting the ingot or its determination. SUMMARY OF THE INVENTION

[0008] It is an object of the present invention to provide a wafer manufacturing method that can improve productivity.

[0009] Another object of the present invention is to provide a detection method for a processing feed direction that enables to carry out the wafer manufacturing process, which can improve productivity.

[0010] According to one aspect of the present invention, a wafer manufacturing method is provided comprising manufacturing a wafer from a cylindrical SiC single-crystal ingot having a cylindrical peripheral surface with a first alignment plane and a second alignment plane that is shorter than the first alignment plane and perpendicular to the first alignment plane, and a circular top surface, wherein the cylindrical SiC single-crystal ingot has a c-axis inclined from a vertical axis perpendicular to the circular top surface toward the second alignment plane, and a deviation angle formed between a c-plane perpendicular to the c-axis and the top surface. The wafer manufacturing method includes: a processing feed direction detection step of confirming whether a direction in which the c-axis is inclinedand the second alignment plane are perpendicular to each other or not, and detecting a machining feed direction perpendicular to the direction in which the c-axis is inclined; a reduced-strength region forming step comprising: positioning the focal point of a laser beam at a depth from the circular top surface in the cylindrical SiC single-crystal ingot, the depth corresponding to the thickness of a wafer to be produced, and, while relatively moving the cylindrical SiC single-crystal ingot and the focal point in the machining feed direction detected in the machining feed direction detecting step, irradiating the cylindrical SiC single-crystal ingot with a laser beam having a wavelength that transmits SiC, thereby forming a straight reduced-strength region composed of a modified layer parallel to the circular top surface and cracks,which extend from the modified layer along the c-plane to a depth corresponding to the thickness of the wafer to be produced; a peeling plane formation step comprising forming a peeling plane in the cylindrical SiC single-crystal ingot by repeatedly performing the reduced-strength region formation step at predetermined intervals in a direction perpendicular to the processing feed direction; and a wafer manufacturing step after the peeling plane formation step comprising manufacturing a wafer from the cylindrical SiC single-crystal ingot by peeling a portion of the cylindrical SiC single-crystal ingot from the peeling plane,which serves as an interface. The processing feed direction detection step includes: a scanning step of performing scanning irradiation to position the focal point of a laser beam at a predetermined depth from the circular top surface in the cylindrical SiC single-crystal ingot, and while moving the cylindrical SiC single-crystal ingot and the focal point relative to each other, irradiating the cylindrical SiC single-crystal ingot with a laser beam having a wavelength that transmits SiC along a direction parallel to the second alignment plane and a plurality of directions inclined clockwise and counterclockwise by respective predetermined angles from the second alignment plane, thereby forming a plurality of scanned straight reduced-strength regions in the cylindrical SiC single-crystal ingot.wherein each of the scanned straight reduced strength regions is composed of a modified layer parallel to the circular upper surface and cracks extending from the modified layer along at least one c-plane; and a determining step comprising capturing respective images of the scanned straight reduced strength regions with an imaging means, measuring the number of nodes present per unit length in each of the scanned straight reduced strength regions in one of their images, and determining a direction in which the scanned straight reduced strength region, in which the measured number of nodes is zero, extends as the machining feed direction.

[0011] In accordance with another aspect of the present invention, there is provided a processing feed direction detection method comprising detecting a processing feed direction in manufacturing a wafer from a cylindrical SiC single-crystal ingot having a cylindrical peripheral surface with a first alignment plane and a second alignment plane that is shorter than the first alignment plane and perpendicular to the first alignment plane, and a circular top surface, wherein the cylindrical SiC single-crystal ingot has a c-axis inclined from a vertical axis perpendicular to the circular top surface toward the second alignment plane and a deviation angle,which is formed between a c-plane perpendicular to the c-axis and the top surface. The machining feed direction detection method includes: a scanning step of performing scanning irradiation to position the focal point of a laser beam at a predetermined depth from the circular top surface in the cylindrical SiC single-crystal ingot, and while moving the cylindrical SiC single-crystal ingot and the focal point relative to each other, irradiating the cylindrical SiC single-crystal ingot with a laser beam having a wavelength that transmits SiC along a direction parallel to the second alignment plane and a plurality of directions inclined clockwise and counterclockwise by respective predetermined angles from the second alignment plane, thereby forming a plurality of scanned straight reduced-strength regions in the cylindrical SiC single-crystal ingot.wherein each of the scanned straight reduced strength regions is composed of a modified layer parallel to the circular upper surface and cracks extending from the modified layer along at least one c-plane; and a determining step comprising capturing respective images of the scanned straight reduced strength regions with an imaging means, measuring the number of nodes present per unit length in each of the scanned straight reduced strength regions in one of their images, and determining a direction in which the scanned straight reduced strength region, where the measured number of nodes is zero, extends as the machining feed direction.

[0012] The wafer manufacturing method according to the present invention is capable of producing a wafer with a desired thickness by peeling a portion of the SiC single-crystal ingot from the peeling plane, which serves as a boundary plane. Wafers can be efficiently produced from the SiC single-crystal ingot. The amount of wafer material that must be discarded is reduced. Wafers can be produced from the SiC single-crystal ingot with improved productivity.

[0013] The machining feed direction detection method according to the present invention determines a direction in which the scanned straight region of reduced strength, where the measured node count is zero, extends as the machining feed direction. Consequently, the machining feed direction is set perpendicular to the direction in which the c-axis is tilted. Therefore, a high-quality pull-off plane for producing wafers from the SiC single-crystal ingot can be reliably formed.

[0014] The above and other objects, features and advantages of the present invention and the manner in which they are carried out will become more apparent and the invention will be best understood by studying the following description and appended claims with reference to the attached drawings which show a preferred embodiment of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a laser processing apparatus; Fig. 2 is a block diagram showing an electrical layout of the Fig. 1 shows the laser processing device shown; Fig. 3A is a plan view of a SiC single crystal ingot; Fig. Figure 3B is a front side view of the SiC single crystal ingot; Fig. 4A is a side view, partly in section, showing the manner in which a scanning step of a machining feed direction detecting step is performed on the SiC single crystal ingot; Fig. 4B is a perspective view showing the manner in which the scanning step is performed on the SiC single crystal ingot; Fig. 5A is a plan view of the SiC single crystal ingot on which the scanning step has been performed; Fig. Figure 5B is a schematic view of a plurality of scanned reduced strength regions; Fig. 6 is a perspective view showing the manner in which a peeling plane forming step is carried out on the SiC single crystal ingot; Fig. 7A is a plan view of the SiC single crystal ingot on which the peeling plane forming step has been performed; Fig. 7B is a partial sectional view of the SiC single crystal ingot on which the pull-off plane forming step has been performed; and Fig. 8 is a perspective view showing the manner in which a wafer manufacturing step is carried out. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0015] A wafer manufacturing method and a processing feed direction detection method in accordance with a preferred embodiment of the present invention will be described below with reference to the drawings. First, a Fig. 1 and Fig. 2 shown laser processing device 2 and a in the Fig. 3A and Fig. 3B shown hexagonal SiC single crystal ingot 60 used in the processes. As in Fig. 1, a laser processing apparatus 2 comprises a base table 4, a holding means 6 for holding a workpiece, a moving means 8 for moving the holding means 6, a laser beam applying means 10, an imaging means 12, a display means 14, a peeling means 16, and a control means 18.

[0016] The holding means 6 includes a rectangular X-direction movable plate 20 mounted on the base table 4 for movement in X directions, a rectangular Y-direction movable plate 22 mounted on the X-direction movable plate 20 for movement in Y directions, and a cylindrical chuck table 24 rotatably mounted on an upper surface of the Y-direction movable plate 23. The X directions refer to the directions indicated by the arrow X in Fig. 1, and the Y directions refer to the directions indicated by the arrow Y in Fig. 1 and are perpendicular to the X directions. The X and Y directions together define a plane that is essentially a horizontal plane.

[0017] The moving means 8 includes an X-direction moving means 26, a Y-direction moving means 28, and a rotation means (not shown). The X-direction moving means 26 has a ball screw 30 extending above the base table 4 in the X directions, and a motor 32 coupled to one end of the ball screw 30. The ball screw 30 is fixed to a lower surface of the X-direction movable plate 20 via a thread of a nut (not shown). When the motor 32 is energized, the ball screw 30 converts a rotational motion of the motor 32 into a linear motion and transmits the linear motion to the X-direction movable plate 20, which selectively moves the X-direction movable plate 20 in one or the other of the X directions along a pair of guide rails 4a on the base table 4.The Y-direction moving means 28 includes a ball screw 34 extending above the X-direction movable plate 20 in the Y directions, and a motor 36 coupled to one end of the ball screw 34. The ball screw 34 is threadably secured to a lower surface of the Y-direction movable plate 22 with a nut (not shown). When the motor 36 is energized, the ball screw 34 converts a rotational motion of the motor 36 into a linear motion and transmits the linear motion to the Y-direction movable plate 22, which selectively moves the Y-direction movable plate 22 in one or the other of the Y directions along a pair of guide rails 20a on the X-direction movable plate 20. The rotating means includes a motor (not shown) housed in the chuck table 24.Under power, the motor rotates the clamping table 24 around its own axis with respect to the plate 22 which is movable in the Y direction.

[0018] The laser beam application means 10 includes a frame 38 mounted on an upper surface of the base table 4 and having a substantially horizontally extending cantilever arm, a pulsed laser beam oscillation means (not shown) housed in the frame 38, a beam condenser 40 disposed on a lower surface of the distal end of the cantilever arm of the frame 38, and a focal point position adjustment means (not shown). The pulsed laser beam oscillation means includes a pulsed laser beam oscillator, output power adjustment means for adjusting the output power of a pulsed laser beam, and adjustment means for adjusting a repetition frequency of the pulsed laser beam. These components of the pulsed laser beam oscillation means have been omitted from the illustration.The beam condenser 40 has a condenser lens (not shown) for condensing a pulsed laser beam emitted from the pulsed laser beam oscillating means.

[0019] The imaging means 12 is mounted on the lower surface of the distal end of the cantilever arm of the frame 38 and spaced apart in the X-direction from the beam condenser 40. The imaging means 12 includes a conventional imaging means (charged coupled device (CCD)) for capturing visible light images, an infrared radiation application means for applying infrared radiation to a workpiece, an optical system for receiving the infrared radiation applied by the infrared radiation application means, and an imaging device (infrared CCD) for outputting an electrical signal representing the infrared radiation captured by the optical system. These components of the imaging means 12 have been omitted from the illustration. The display means 14, which displays images captured by the imaging means 12, is mounted on an upper surface of the distal end of the cantilever arm of the frame 38.

[0020] The peeling means 16 includes a housing 42 mounted on the base table 4 and extending upward from ends of the guide rails 4a, and an arm 44 extending from the housing 42 along the X-directions. The arm 44 has a proximal end coupled to the housing 42 for movement in the Z-directions. The Z-directions refer to directions indicated by the arrow Z in Fig. 1, and are perpendicular to the X and Y directions. The housing 42 accommodates therein a Z-direction moving means (not shown) for selectively moving the arm 44 in one or the other of the Z directions. A motor 46 is mounted at the distal end of the arm 44. A disc-shaped suction member 48 is coupled to a lower surface of the motor 46 for rotation about an axis along the Z directions. The suction member 48 has a plurality of suction holes (not shown) defined in a lower surface (suction surface) thereof and connected to a suction means (not shown) through fluid passages (not shown). The suction member 48 accommodates therein a not-shown ultrasonic vibration applying means for applying ultrasonic vibrations to the lower surface of the suction member 48.

[0021] As in Fig. 2, the control means 18 comprising a computer includes a central processing unit (CPU) 50 for executing machining operations in accordance with a control program, a read-only memory (ROM) 52 for storing the control program, etc., and a random access memory (RAM) 54 that enables data to be written to and read from, for storing the results of the machining operations, etc. The control means 18 is electrically connected to the moving means 8, the laser beam applying means 10, the imaging means 12, the display means 14, and the peeling means 16, and controls these means.

[0022] The Fig. 3A and Fig. 3B show a hexagonal SiC single-crystal ingot 60, hereinafter referred to as "ingot 60," having a cylindrical shape with a cylindrical peripheral surface 62 and circular upper and lower surfaces 64 and 66. The peripheral surface 62 includes a rectangular first alignment plane 68 and a rectangular second alignment plane 70, which indicate crystal orientations. Viewed in the direction of a vertical axis 72 perpendicular to the upper surface 64, the length L2 of the second alignment plane 70 is smaller than the length L1 of the first alignment plane 68 (L2 < L1). The first alignment plane 68 and the second alignment plane 70 are perpendicular to each other. The ingot 60 has a c-axis (

[0001] direction) extending from the vertical axis 72 toward the second alignment plane 70, i.e.the direction in which the c-axis is inclined as indicated by arrow A, and has a deviation angle alpha formed between a c-plane ({0001} plane) perpendicular to the c-axis and the top surface 64. On the hexagonal SiC single-crystal ingot 60, the second orientation plane 70 is normally formed perpendicular to the direction A in which the c-axis is inclined.

[0023] Now, a wafer manufacturing method and a processing feed direction detection method including detecting a processing feed direction at the time of manufacturing a wafer using the laser processing apparatus 2 and the ingot 60 will be described below. First, the ingot 60 is Fig. 1, secured to the chuck table 24 with an adhesive, for example an epoxy resin adhesive, which is inserted between the lower surface 66 of the ingot 60 and the upper surface of the chuck table 24.

[0024] After the ingot 60 has been secured to the chuck table 24, an alignment step is performed. During the alignment step, the moving means 8 moves the chuck table 24 under the imaging means 12, and the imaging means 12 captures an image of the ingot 60. Then, based on the image of the ingot 60 captured by the imaging means 12, the first alignment plane 68 and the second alignment plane 70 are acquired. The moving means 8 then moves and rotates the chuck table 24 to position the ingot 60 in alignment with the beam condenser 40. Thereafter, the focal point position adjusting means moves the beam condenser 40 in the Z directions to adjust the focal point of a pulsed laser beam to a position in the ingot 60 spaced apart from the upper surface 64 of the ingot 60 by a predetermined depth, that is, a position at a depth corresponding to the thickness of a wafer to be manufactured.

[0025] The alignment step is followed by a machining feed direction detection step, which confirms whether the direction A in which the c-axis is inclined is perpendicular to the second alignment plane 70 or not, and detects a machining feed direction that is perpendicular to the direction A in which the c-axis is inclined at the time a wafer is produced from the ingot. The machining feed direction detection step includes a scanning step and a determination step. In the scanning step, as shown in the Fig. 4A, Fig. 4B and Fig. 5A, scanning irradiation is performed such that, while the chuck table 24 is moved by the X-direction moving means 26 in the X directions at a predetermined machining feed speed, the beam condenser 40 irradiates the ingot 60 with a pulsed laser beam having a wavelength that transmits SiC, to thereby form a scanned straight reduced strength region 74 in the ingot 60 parallel to the upper surface 64 thereof.Specifically, the scanning irradiation is performed a plurality of times when the beam condenser 40 scans the upper surface 64 of the ingot 60 along a direction parallel to the second alignment plane 70 and a plurality of directions inclined clockwise and counterclockwise by respective predetermined angles of, for example, 0.5° from the second alignment plane 70, while the moving means 8 moves and rotates the chuck table 24, thereby forming a plurality of scanned straight reduced-strength regions 74 in the ingot 60. The scanning irradiation is performed under the following processing conditions: Laser beam wavelength: 1064 nm Repetition frequency: 80 kHz Average output power: 3.2 W Pulse duration: 3 ns Focal spot diameter: 10 µm Numerical aperture of the condenser lens (NA): 0.65 Machining feed speed: 150 mm / s Defocus: 90 µm

[0026] The defocus referred to above represents a distance by which the beam condenser 40 moves toward the top surface 64 of the ingot 60 from the position where the focal point of the pulsed laser beam is positioned at the top surface 64.

[0027] In the detection step for a machining feed direction, the scanning step is followed by the determination step. In the determination step, the clamping table 24 is moved by the moving means 8 below the imaging means 12, and the imaging means 12 takes an image of each of the scanned reduced strength regions 74. As shown in Fig. 5B, each of the sampled regions of reduced strength 74 is composed of a modified layer 76 and cracks 78 that propagate from the modified layer 76 along the c-plane on both sides of the modified layer 76. In the Fig. 5A and Fig. 5B, the scanned reduced strength region 74 formed parallel to the second alignment plane 70 is used as a reference (0°). Those scanned reduced strength regions 74 that are inclined clockwise from the scanned reference reduced strength region 74, as seen on the upper surface 64, are indicated by respective angles with a "-" sign, and those scanned reduced strength regions 74 that are inclined counterclockwise from the scanned reference reduced strength region 74, as seen on the upper surface 64, are indicated by respective angles with a "+" sign. The images captured by the imaging means 12 are displayed on the screen of the display means 14.The number of nodes 80 present per unit length, such as 10 mm, in each of the scanned reduced strength regions 74 is counted in the displayed images, and the direction in which the scanned reduced strength region 74 extends where the number of nodes 80 is zero, ie, the direction indicated by the angle of -3° in the illustrated embodiment, is determined as the machining feed direction.

[0028] The machining feed direction thus determined extends absolutely perpendicular to the c-axis of the ingot 60. Although the second alignment plane 70 should be formed particularly parallel to the machining feed direction, it was actually formed with a deviation of 3° from the machining feed direction.The inventor of the present invention has found that the scanned reduced strength region 74 extending parallel to the machining feed direction is continuous and free of nodes 80, while the modified layer 76 and the cracks 78 are formed on the same c-plane, whereas those scanned reduced strength regions 74 not extending parallel to the machining feed direction have nodes 80 formed due to defects caused in the modified layer 76 and the cracks 78 because the focal point of the laser beam moves across two c-planes that are adjacent to each other at the atomic level.Since the direction in which the scanned reduced strength region 74 extends where the number of nodes 80 is zero is determined as a machining feed direction in the machining feed direction detecting step, it is possible to confirm whether or not the direction A in which the c-axis is inclined and the second alignment plane 70 are perpendicular to each other and to detect a machining feed direction that is absolutely perpendicular to the direction A in which the c-axis is inclined.

[0029] After the detection step for a machining feed direction is performed, a peeling plane formation step is performed. In the peeling plane formation step, the moving means 8 moves and rotates the chuck table 24 to align the direction viewed from the upper surface 64, which is inclined by 3° from the second alignment plane 70, with the X directions, and to position the ingot 60 and the beam condenser 40 in alignment with each other. Then, the focal point position adjusting means moves the beam condenser 40 in the Z directions to adjust the focal point of a pulsed laser beam to a position at a depth from the upper surface 64, the depth corresponding to the thickness of a wafer to be produced. Then, a reduced strength region formation process is performed. In the reduced strength region formation process, the beam condenser 40 irradiates, as shown in Fig. 6, the ingot 60 is irradiated with a pulsed laser beam having a wavelength that transmits SiC while the chuck table 24 is moved by the X-direction moving means 26 at a predetermined feed speed in the X directions, thereby forming a straight reduced-strength region 82 in the ingot 60. Specifically, the reduced-strength region forming process is performed multiple times at predetermined intervals in the direction A in which the c-axis is inclined by causing the Y-direction moving means 28 to incrementally feed the chuck table 24 in one of the Y directions. The peeling plane forming step is performed under the following processing conditions: Laser beam wavelength: 1064 nm Repetition frequency: 80 kHz Average output power: 3.2 W Pulse duration: 3 ns Focal spot diameter: 10 µm Numerical aperture of the condenser lens (NA): 0.65 Graduation distance: 500 µm Machining feed speed: 150 mm / s Defocus: 90 µm

[0030] As in the Fig. 7A and Fig. As shown in Figure 7B, each of the reduced strength regions 82 formed in the reduced strength region formation process to a depth corresponding to the thickness of a wafer to be manufactured is composed of a modified layer 84 and cracks 86. Since the reduced strength regions 82 extend parallel to the top surface 64, the modified layers 84 of the reduced strength regions 82 are positioned on the same c-plane. As each of the modified layers 84 is formed in the ingot 60, the cracks 86 propagate from the modified layer 84 along the c-plane on both sides of the modified layer 84. The length of the crack 86 propagating on one side of each modified layer 84 is approximately 250 μm, so the length Lc of the cracks 86 on both sides of the modified layer 84 is approximately 500 μm.Thus, when the pitch Li in the peeling plane forming step in the Y directions as described above is about 500 µm, a peeling plane is formed in the ingot 60 to a depth corresponding to the thickness of a wafer to be manufactured.

[0031] The peel plane formation step is followed by a wafer manufacturing step. In the wafer manufacturing step, the moving means 8 moves the chuck table 24 under the suction member 48, and the Z-direction moving means lowers the arm 44 until the lower surface of the suction member 48, as shown in Fig.8, is brought into close contact with the upper surface of the ingot 60. Then, the suction means is actuated to develop negative pressure in the suction holes in the suction means 48, thereby allowing the lower surface of the suction member 48 to attract the upper surface of the ingot 60 under suction. Thereafter, the ultrasonic vibration applying means is actuated to apply ultrasonic vibrations to the lower surface of the suction member 48, and the motor 46 is energized to rotate the suction member 48 about its own axis. At this time, a disc-shaped portion of the ingot 60, attracted to the suction member 48, is peeled off as a wafer 88 with a desired thickness from the peeling surface serving as an interface. Consequently, the wafer 88 is efficiently manufactured from the ingot 60.After the wafer 88 is produced, the exposed upper surface of the ingot 60 is polished by a polishing agent (not shown) on the base table 4, and the peel plane forming step and the wafer manufacturing step are performed again on the ingot 60, so that a plurality of wafers can be manufactured from the ingot 60. Accordingly, the amount of ingot material that must be discarded when manufacturing a wafer from the ingot 60 is reduced, and wafers can be manufactured from the ingot 60 with improved productivity. Since the process feed direction detection step for producing the first wafer 88 has been performed, the process feed direction detection step does not need to be repeated on the same ingot 60 for manufacturing subsequent wafers therefrom.

[0032] The present invention is not limited to the details of the embodiment described above. The scope of the invention is defined by the appended claims, and all changes and modifications that fall within the equivalent scope of the claims are therefore included in the invention.

Claims

[1] A wafer manufacturing method comprising producing a wafer (88) from a cylindrical SiC single-crystal ingot (60) having a circular upper surface (64) and a cylindrical peripheral surface (62) with a first alignment plane (68) and a second alignment plane (70) that is shorter than the first alignment plane (68) and perpendicular to the first alignment plane (68), the cylindrical SiC single-crystal ingot (60) having a c-axis inclined from a vertical axis (72) perpendicular to the circular upper surface (64) toward the second alignment plane (70), and a deviation angle formed between a c-plane perpendicular to the c-axis and the upper surface (64), the wafer manufacturing method comprising: a machining feed direction detecting step of confirming whether or not a direction in which the c-axis is inclined and the second alignment plane (70) are perpendicular to each other and detecting a machining feed direction perpendicular to the direction (A) in which the c-axis is inclined; a reduced strength region formation step (82) comprising positioning the focal point of a laser beam from the circular upper surface (64) at a depth in the cylindrical SiC single-crystal ingot (60), the depth corresponding to the thickness of a wafer (88) to be produced, and while relatively moving the cylindrical SiC single-crystal ingot (60) and the focal point in the processing feed direction detected in the processing feed direction detection step, irradiating the cylindrical SiC single-crystal ingot (60) with a laser beam having a wavelength that transmits SiC, thereby forming a straight reduced strength region (82) composed of a modified layer (84) parallel to the circular upper surface (64) and cracks (86) extending from the modified layer (84) at a depth along the c-plane,which corresponds to the thickness of the wafer (88) to be produced;, a pulling plane forming step comprising forming a pulling plane in the cylindrical SiC single-crystal ingot by repeatedly performing the reduced strength region forming step (82) at predetermined intervals in a direction perpendicular to the machining feed direction; and after the peeling plane forming step, a wafer manufacturing step comprising manufacturing a wafer (88) from the cylindrical SiC single crystal ingot (60) by peeling a portion of the cylindrical SiC single crystal ingot (60) from the peeling plane serving as an interface; wherein the step of detecting a machining feed direction includes: a scanning step comprising performing scanning irradiation to position the focal point of a laser beam from the circular upper surface (64) at a predetermined depth in the cylindrical SiC single-crystal ingot (60) and, while moving the cylindrical SiC single-crystal ingot (60) and the focal point relative to each other, irradiating the cylindrical SiC single-crystal ingot (60) with a laser beam having a wavelength that transmits SiC along a direction parallel to the second alignment plane (70) and a plurality of directions inclined clockwise and counterclockwise by respective predetermined angles to the second alignment plane (70), thereby forming a plurality of scanned straight reduced-strength regions (74) in the cylindrical SiC single-crystal ingot (60),wherein each of the scanned straight regions of reduced strength (74) is constructed from a modified layer (76) parallel to the circular upper surface (64) and cracks (78) extending from the modified layer (76) along at least one c-plane, and, a determining step comprising taking respective images of the scanned straight reduced strength regions (74) with an imaging means (12), measuring the number of nodes (80) present per unit length in each of the scanned straight reduced strength regions (74) in one of its images, and determining a direction in which the scanned straight reduced strength region (74) where the measured number of nodes (80) is zero extends as a machining feed direction. [2] A method for detecting a machining feed direction, comprising detecting a machining feed direction in manufacturing a wafer (88) from a cylindrical SiC single-crystal ingot (60) having a circular upper surface (64) and a cylindrical peripheral surface (62) with a first alignment plane (68) and a second alignment plane (70) that is shorter than the first alignment plane (68) and perpendicular to the first alignment plane (68), wherein the cylindrical SiC single-crystal ingot (60) has a c-axis inclined from a vertical axis (72) perpendicular to the circular upper surface (64) toward the second alignment plane (70), and a deviation angle formed between a c-plane perpendicular to the c-axis and the upper surface (64), the method comprising: a scanning step comprising performing scanning irradiation to position the focal point of a laser beam from the circular upper surface (64) at a predetermined depth in the cylindrical SiC single-crystal ingot (60) and, while moving the cylindrical SiC single-crystal ingot (60) and the focal point relative to each other, irradiating the cylindrical SiC single-crystal ingot (60) with a laser beam having a wavelength that transmits SiC along a direction parallel to the second alignment plane (70) and a plurality of directions inclined to the second alignment plane (70) by respective predetermined angles in the clockwise and counterclockwise directions, thereby forming a plurality of scanned straight reduced-strength regions (74) in the cylindrical SiC single-crystal ingot (60),wherein each of the scanned straight regions of reduced strength (74) is constructed from a modified layer (76) parallel to the circular upper surface (64) and cracks (78) extending from the modified layer (76) along at least one c-plane; and, a determining step comprising taking respective images of the scanned straight reduced strength regions (74) with an imaging means (12), measuring the number of nodes (80) present per unit length in each of the scanned straight reduced strength regions (74) in one of its images, and determining a direction in which the scanned straight reduced strength region (74) where the measured number of nodes is zero extends as a machining feed direction.

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