Wafer generation method and wafer generation apparatus

Abstract

The present invention provides a wafer generation method and a wafer generation apparatus that can generate a wafer having a desired thickness without individually detecting the height of the upper surface of an ingot. The wafer generation method generates a wafer from a semiconductor ingot, and the wafer generation method includes the following steps: a thermal stress wave generation step of irradiating a pulsed laser beam having a wavelength that is absorbent to the ingot onto the upper surface of the semiconductor ingot held by a chuck table to generate a thermal stress wave and causing the thermal stress wave to propagate inside the ingot; and a fracture layer formation step of irradiating a pulsed laser beam having a wavelength that is transmissive to the ingot onto the upper surface of the ingot at a time when the thermal stress wave generated in the thermal stress wave generation step reaches a position corresponding to the thickness of the wafer to be generated, based on the speed of sound corresponding to the material of the ingot, and generating absorption of the pulsed laser beam having a transmissive wavelength in a region where the band gap is narrowed due to the tensile stress of the thermal stress wave, thereby forming a fracture layer.

Description

Technical Field

[0001] The present invention relates to a wafer generation method for generating wafers from a semiconductor ingot and a wafer generation apparatus for generating wafers from a semiconductor ingot. Background Art

[0002] Devices such as ICs, LSIs, and LEDs are formed by laminating a functional layer on the front surface of a semiconductor wafer made of silicon, sapphire, etc. and dividing the wafer by a plurality of dividing predetermined lines intersecting with the functional layer.

[0003] Furthermore, the semiconductor wafer is divided into individual device chips by performing processing along the dividing predetermined lines of the semiconductor wafer using a cutting device or a laser processing device, and is thus used in electronic devices such as mobile phones and personal computers.

[0004] In addition, power devices, LEDs, etc. are formed by laminating a functional layer on the front surface of a wafer made of single crystal SiC, etc. and dividing the wafer by a plurality of dividing predetermined lines intersecting with the functional layer. In this way, a wafer on which devices are formed is usually generated by slicing a semiconductor ingot using a wire saw, and the front and back surfaces of the sliced wafer are polished to be finished into a mirror surface (for example, refer to Patent Document 1).

[0005] However, in the case of generating a wafer by cutting an ingot with a wire saw and polishing the front and back surfaces, 70% to 80% of the ingot is discarded, resulting in an uneconomical problem. In particular, in the case where the semiconductor ingot is a SiC ingot, the hardness of single crystal SiC is high, it is difficult to cut with a wire saw, the productivity is poor, and since the unit price of the SiC ingot is high, more efficient production of wafers is required. Therefore, the present applicant has proposed the following technology: positioning the focal point of a laser beam having a wavelength that is transmissive to single crystal SiC inside the SiC ingot and irradiating the ingot to form a separation layer on the cutting predetermined surface, thereby separating the wafer. (Refer to Patent Document 2).

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2000-094221

[0007] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2016-111143

[0008] However, in the case of accurately positioning the focal point of the laser beam inside the ingot and irradiating the ingot to form a separation layer for separating the wafer, it is necessary to accurately detect the height of the upper surface of the ingot. In addition, since the height of the upper surface of the ingot changes each time a wafer is generated, it is necessary to detect the height of the upper surface of the ingot each time one wafer is generated, resulting in a problem of poor productivity. Summary of the Invention

[0009] Accordingly, an object of the present invention is to provide a wafer generation method and a wafer generation apparatus capable of generating a wafer having a desired thickness without individually measuring the height of the upper surface of an ingot.

[0010] According to one aspect of the present invention, there is provided a wafer generation method for generating a wafer from a semiconductor ingot, the method including the steps of: a holding step of holding the semiconductor ingot on a chuck table; a thermal stress wave generation step of irradiating a pulse laser beam having a wavelength absorbable by the semiconductor ingot onto the upper surface of the semiconductor ingot held on the chuck table to generate a thermal stress wave and causing the thermal stress wave to propagate inside the semiconductor ingot; a fracture layer formation step of irradiating a pulse laser beam having a wavelength transmissive through the semiconductor ingot onto the upper surface of the semiconductor ingot at a time when the thermal stress wave generated in the thermal stress wave generation step reaches a position corresponding to the thickness of the wafer to be generated, at a speed of sound corresponding to the material of the semiconductor ingot, and causing absorption of the pulse laser beam having the transmissive wavelength in a region where the band gap is narrowed due to the tensile stress of the thermal stress wave, thereby forming a fracture layer; and a peeling step of peeling the wafer to be generated from the semiconductor ingot starting from the fracture layer.

[0011] Preferably, the wafer generation method further includes a planarization step of planarizing the peeling surface of the ingot after the peeling step.

[0012] According to another aspect of the present invention, there is provided a wafer generation apparatus for generating a wafer from a semiconductor ingot, the apparatus including: a chuck table for holding the semiconductor ingot; a thermal stress wave generation unit for irradiating a pulse laser beam having a wavelength absorbable by the semiconductor ingot onto the upper surface of the semiconductor ingot held on the chuck table to generate a thermal stress wave and causing the thermal stress wave to propagate inside the semiconductor ingot; and a fracture layer formation unit for irradiating a pulse laser beam having a wavelength transmissive through the semiconductor ingot onto the upper surface of the semiconductor ingot at a time when the thermal stress wave generated by the thermal stress wave generation unit reaches a position corresponding to the thickness of the wafer to be generated, at a speed of sound corresponding to the material of the semiconductor ingot, and causing absorption of the pulse laser beam having the transmissive wavelength in a region where the band gap is narrowed due to the tensile stress of the thermal stress wave, thereby forming a fracture layer.

[0013] Preferably, the wafer generation apparatus further includes a peeling unit for peeling the wafer from the fracture layer formed by the fracture layer formation unit.

[0014] According to the wafer generation method of the present invention, the thickness of the generated wafer can be controlled only by the propagation time without measuring the height of the upper surface of the ingot, the propagation time being based on the speed of sound corresponding to the material constituting the ingot, thereby improving productivity.

[0015] In addition, similar to the wafer generation method according to the present invention, the wafer generation apparatus can control the thickness of the generated wafer only by the propagation time without detecting the height of the upper surface of the ingot. The propagation time is based on the speed of sound corresponding to the material constituting the ingot, thereby improving the productivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is an overall perspective view of the wafer generation apparatus according to an embodiment of the present invention.

[0017] Figure 2 FIG. (a) shows a block diagram of an optical system of a laser beam irradiation unit provided in the Figure 1 illustrated wafer generation apparatus, Figure 2 and FIG. (b) is a cross-sectional view showing an enlarged part of the ingot when performing the thermal stress wave generation process and the fracture layer formation process.

[0018] Figure 3 is a perspective view showing an embodiment of the peeling process.

[0019] Figure 4 is a perspective view showing an embodiment of the planarization process.

[0020] REFERENCE SIGNS

[0021] 2: Wafer generation apparatus; 3: Base; 4: Holding unit; 18: X-axis direction movable plate; 20: Y-axis direction movable plate; 22: Chuck table; 5: Moving mechanism; 24: X-axis direction moving mechanism; 26: Y-axis direction moving mechanism; 6: Laser beam irradiation unit; 6A: First laser beam generation unit; 61: First laser beam generation unit; 611: First laser oscillator; 612: First attenuator; 62: Mirror; 6B: Second laser beam generation unit; 63: Second laser beam generation unit; 631: Second laser oscillator; 632: Second attenuator; 64: Delay unit; 6C: Laser beam introduction unit; 65: Dichroic mirror; 66: Mirror; 67: Indexing scanner; 68: Scanning scanner; 69: Condenser; 691: fθ lens; 7: Grinding unit; 7c: Grinding wheel; 7d: Grinding tool; 12: Imaging unit; 14: Display unit; 16: Peeling unit; 16a: Housing; 16b: Arm; 16c: Motor; 16d: Adsorption sheet; 50: Ingot; 52: Upper surface; 54: Lower surface; H1: Thermal stress wave generation unit; H2: Fracture layer formation unit. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, a wafer generation method according to an embodiment of the present invention and a wafer generation apparatus suitable for implementing the wafer generation method will be described in detail with reference to the drawings.

[0023] Figure 1 A perspective view showing the overall structure of the wafer generation apparatus 2 according to the present embodiment. The wafer generation apparatus 2 includes: a base 3; a holding unit 4 for holding a workpiece; a moving mechanism 5 for moving the holding unit 4; a laser beam irradiation unit 6 including a thermal stress wave generation unit and a fracture layer formation unit described later; a photographing unit 12; a display unit 14; a peeling unit 16; and a control unit (not shown).

[0024] The holding unit 4 includes: a rectangular X-axis movable plate 18 which is movably mounted on the base 3 in the X-axis direction; a rectangular Y-axis movable plate 20 which is movably mounted on the X-axis movable plate 18 along guide rails 18a, 18a in the Y-axis direction; and a cylindrical chuck table 22 which is rotatably provided on the upper surface of the Y-axis movable plate 20. In addition, the X-axis direction is Figure 1 the direction indicated by the arrow X in Figure 1 and the Y-axis direction is the direction indicated by the arrow Y in

[0025] perpendicular to the X-axis direction, and the XY plane is substantially horizontal. The moving mechanism 5 includes an X-axis moving mechanism 24 and a Y-axis moving mechanism 26. The X-axis moving mechanism 24 has: a ball screw 28 which extends in the X-axis direction on the base 3; and a motor 30 which is connected to one end of the ball screw 28. The nut portion (not shown) of the ball screw 28 is fixed to the lower surface of the X-axis movable plate 18. Moreover, the X-axis moving mechanism 24 converts the rotational motion of the motor 30 into a linear motion by the ball screw 28 and transmits it to the X-axis movable plate 18, causing the X-axis movable plate 18 to move forward and backward in the X-axis direction along the guide rails 3a, 3a on the base 3. The Y-axis moving mechanism 26 has: a ball screw 32 which extends in the Y-axis direction on the X-axis movable plate 18; and a motor 34 which is connected to one end of the ball screw 32. The nut portion of the ball screw 32 is formed on the lower surface side of the Y-axis movable plate 20. Moreover, the Y-axis moving mechanism 26 converts the rotational motion of the motor 34 into a linear motion by the ball screw 32 and transmits it to the Y-axis movable plate 20, causing the Y-axis movable plate 20 to move forward and backward in the Y-axis direction along the guide rail 18a on the X-axis movable plate 18. The moving mechanism 5 further includes a rotation mechanism (not shown) which has a motor built in the chuck table 22 and rotates the chuck table 22 relative to the Y-axis movable plate 20.

[0026] Inside the holding unit 4, a frame 36 is vertically provided. The frame 36 has a vertical wall portion 36a extending upward from the upper surface of the base 3 and a horizontal wall portion 36b extending substantially horizontally. An optical system of the laser light irradiation unit 6 is built in the horizontal wall portion 36b. The laser light irradiation unit 6 includes a thermal stress wave generation unit and a fracture layer formation unit of the present embodiment (which will be described in detail later). A condenser 69 constituting the laser light irradiation unit 6 is disposed on the lower surface of the front end of the horizontal wall portion 36b of the frame 36.

[0027] The photographing unit 12 is disposed on the lower surface of the front end of the horizontal wall portion 36b at a position spaced apart from the condenser 69 of the laser light irradiation unit 6 in the X-axis direction. The photographing unit 12 includes, as required: a normal photographing element (CCD) that photographs by visible light; an infrared irradiation unit that irradiates the workpiece with infrared rays; an optical system that captures the infrared rays irradiated by the infrared irradiation unit; and a photographing element (infrared CCD) or the like that outputs an electric signal corresponding to the infrared rays captured by the optical system. A display unit 14 that displays the image photographed by the photographing unit 12 is mounted on the upper surface of the horizontal wall portion 36b of the frame 36.

[0028] The peeling unit 16 includes: a rectangular parallelepiped-shaped outer shell 16a that extends upward from the terminal portions of the guide rails 3a, 3a on the base 3; and an arm 16b that extends in the X-axis direction from the base end supported by the outer shell 16a so as to be able to move up and down. An elevating unit (not shown) for elevating the arm 16b is built in the outer shell 16a. A motor 16c is disposed at the front end of the arm 16b. A disk-shaped adsorption sheet 16d that is rotatable about an axis extending in the vertical direction is connected to the lower surface of the motor 16c. A plurality of suction holes (not shown) are formed on the lower surface of the adsorption sheet 16d, and the adsorption sheet 16d is connected to a suction unit (not shown) via a flow path. In addition, an ultrasonic vibration imparting unit (not shown) for imparting ultrasonic vibration to the lower surface of the adsorption sheet 16d is built in the adsorption sheet 16d.

[0029] The control unit is composed of a computer and includes: a central processing unit (CPU) that performs arithmetic processing according to a control program; a read-only memory (ROM) that stores the control program and the like; and a random access memory (RAM) that can be read and written and stores the arithmetic results and the like. Moreover, the control unit is electrically connected to the moving mechanism 5, the laser light irradiation unit 6, the photographing unit 12, the display unit 14, and the peeling unit 16 to control the operations of the respective units.

[0030] In the present embodiment, the workpiece is Figure 1The cylindrical Si ingot (hereinafter simply referred to as the ingot) 50 shown has a circular upper surface 52 and a circular lower surface 54 on the opposite side of the upper surface 52.

[0031] Refer to Figure 2 FIG. (a) to explain the optical system of the laser beam irradiation unit 6 built in the horizontal wall portion 36b of the wafer generation apparatus 2.

[0032] Figure 2 The optical system of the laser beam irradiation unit 6 shown in FIG. (a) has: a first laser beam generation unit 6A that generates a first pulsed laser beam PL1 having a wavelength that is absorbent to the ingot 50 as the workpiece; a second laser beam generation unit 6B that generates a second pulsed laser beam PL2 having a wavelength that is transmissive to the ingot 50; and a laser beam introduction unit 6C that irradiates the upper surface 52 of the ingot 50 held by the holding unit 4 with the first pulsed laser beam PL1 generated by the first laser beam generation unit 6A and the second pulsed laser beam PL2 generated by the second laser beam generation unit 6B.

[0033] The first laser beam generation unit 6A of the present embodiment has: a first laser beam generation unit 61; and a reflecting mirror 62 that changes the optical path of the first pulsed laser beam PL1 emitted from the first laser beam generation unit 61. The first laser beam generation unit 61 has: a first laser oscillator 611 that emits a first pulsed laser beam PL1 having a wavelength of, for example, 355 nm; and a first attenuator 612 that adjusts the output of the first pulsed laser beam PL1 emitted from the first laser oscillator 611 to a desired output and emits it toward the reflecting mirror 62.

[0034] The second laser beam generation unit 6B has: a second laser beam generation unit 63; and a delay unit 64 that delays the second pulsed laser beam PL2 emitted from the second laser beam generation unit 63 by a desired time. The second laser beam generation unit 63 has: a second laser oscillator 631 that emits a second pulsed laser beam PL2 having a wavelength of, for example, 1064 nm; and a second attenuator 632 that adjusts and emits the output of the second pulsed laser beam PL2 emitted from the second laser oscillator 631. The second laser oscillator 631 is set to operate at the same repetition frequency as the above-described first laser oscillator 611 and emits the second pulsed laser beam PL2 at a timing synchronized with the first pulsed laser beam PL1. The delay unit 64 that delays the second pulsed laser beam PL2 emitted from the second laser oscillator 631 is realized, for example, by outputting the second pulsed laser beam PL2 via an optical fiber (not shown) having a length corresponding to the delayed time.

[0035] The laser light introduction unit 6C includes: a dichroic mirror 65 that reflects the first pulsed laser light PL1 reflected by the mirror 62 of the first laser light generation unit 6A and allows the second pulsed laser light PL2 guided from the second laser light generation unit 6B to pass through; a mirror 66 that changes the optical path of the light emitted from the dichroic mirror 65; a dividing scanner 67, which is constituted by, for example, an electric scanner, and divides the light reflected by the mirror 66 along the Y-axis direction on the chuck table 22; a scanning scanner 68, which is constituted by, for example, a resonant scanner, and scans the light reflected by the mirror 66 along the X-axis direction on the chuck table 22; and a condenser 69 that includes an fθ lens 691, and the fθ lens 691 condenses the light emitted from the scanning scanner 68 onto a predetermined position determined by the X-axis coordinate and the Y-axis coordinate on the upper surface 52 of the ingot 50 held by the chuck table 22 for irradiation. The first pulsed laser light PL1 and the second pulsed laser light PL2 guided to the dichroic mirror 65 are irradiated onto the same area on the chuck table 22.

[0036] The thermal stress wave generation unit H1 of the present invention is formed by the first laser light generation unit 6A and the laser light introduction unit 6C. The thermal stress wave generation unit H1 is a unit that irradiates the upper surface 52 of the ingot 50 held by the holding unit 4 with a pulsed laser light PL1 having a wavelength absorbable by the ingot 50 to generate a thermal stress wave, and propagates the thermal stress wave inside the ingot 50.

[0037] In addition, the fracture layer forming unit H2 of the present invention is formed by the second laser light generation unit 6B and the laser light introduction unit 6C. The fracture layer forming unit H2 is a unit that, at a predetermined time when the thermal stress wave generated on the upper surface 52 of the ingot 50 by the thermal stress wave generation unit H1 reaches a depth position (for example, a depth of 1 mm from the upper surface (52) of the ingot 50) corresponding to the thickness of the wafer W to be generated in the ingot 50 at the speed of sound corresponding to the material of the ingot 50, irradiates the second pulsed laser light PL2 having a wavelength transmissive to the ingot 50 from the upper surface 52 of the ingot 50, and generates absorption of the second pulsed laser light PL2 in a region where the band gap is narrowed due to the tensile stress of the thermal stress wave, thereby forming a fracture layer.

[0038] Refer to Figure 2 of (a) and Figure 2 of (b) for a more specific description of an embodiment of a wafer generation method for generating a wafer W from an ingot 50 that can be implemented using the above-described wafer generation apparatus 2.

[0039] When generating a wafer W with a desired thickness (1 mm) from an ingot 50, first, the ingot 50 is held on the chuck table 22 of the holding unit 4 (holding process). More specifically, an adhesive (e.g., an epoxy resin-based adhesive) is interposed between the upper surface of the chuck table 22 and the bottom surface 54 of the ingot 50, and the ingot 50 is fixed to the chuck table 22.

[0040] Next, when performing the thermal stress wave generation process and the fracture layer formation process, first, the moving mechanism 5 is actuated to move the chuck table 22 to directly below the imaging unit 12, and the ingot 50 is imaged by the imaging unit 12 to detect the position where processing should start (alignment process). Next, the moving mechanism 5 is controlled by a control unit (not shown) to position a specified processing start position on the upper surface 52 of the ingot 50 below the condenser 69.

[0041] Next, the thermal stress wave generation unit H1 is actuated to generate a first pulsed laser beam PL1 with a wavelength of 355 nm that is absorptive to the material of the ingot 50 (Si: silicon), and the first pulsed laser beam PL1 is irradiated to a specified position on the upper surface 52 of the ingot 50 via the laser beam introduction unit 6C (thermal stress wave generation process).

[0042] The laser beam irradiation conditions implemented in the above thermal stress wave generation process are as follows, for example. In addition, in the thermal stress wave generation process, the average output of the first pulsed laser beam PL1 adjusted by the first attenuator 612 of the thermal stress wave generation unit H1 is adjusted to a relatively low output to the following extent: Although the first pulsed laser beam PL1 is a laser beam absorptive to the ingot 50, ablation is not generated on the upper surface 52 of the ingot 50.

[0043] Wavelength: 355 nm

[0044] Repetition frequency: 50 kHz

[0045] Average output: 1 W

[0046] Pulse width: 100 ps or less

[0047] When the first pulsed laser beam PL1 is irradiated to the upper surface 52 of the ingot 50 through the above thermal stress wave generation process, the upper surface 52 of the ingot 50 is thermally excited, as Figure 2As shown in (b) thereof, the thermally induced stress wave generated by this thermal excitation propagates inside the ingot 50 as shown by N1→N2→N3 in the figure. The propagation speed of this thermally induced stress wave N1 to N3 is the speed of sound (9620 m / s) corresponding to the material (Si) constituting the ingot 50. The thermally induced stress waves N1 to N3 propagating in a semiconductor such as silicon are short-pulse tensile stress waves, and at the position where the tensile stress is applied, the bandgap is narrower than usual. That is, the region with a narrower bandgap propagates from the upper surface 52 toward the lower surface 54. Moreover, the fragmentation layer formation process implemented together with the above-described thermally induced stress wave generation process is implemented as described below.

[0048] When implementing the fragmentation layer formation process, the fragmentation layer formation unit H2 is operated, and the second pulsed laser beam PL2 having a wavelength (1064 nm) that is transmissive to the material (Si: silicon) constituting the ingot 50 is emitted from the second laser oscillator 631 in synchronization with the first laser oscillator 611 at the same repetition frequency (50 kHz). Next, the second pulsed laser beam PL2 is adjusted to a prescribed output by the second attenuator 632, and the second pulsed laser beam PL2 is output after being delayed by a prescribed time with respect to the first pulsed laser beam PL1 by the delay unit 64. This prescribed time delayed by the delay unit 64 of the second laser beam generation unit 6B is the time when the thermally induced stress wave generated on the upper surface 52 of the ingot 50 in the above-described thermally induced stress wave generation process reaches the depth position (1 mm) corresponding to the thickness of the wafer W to be generated at the speed of sound (9620 m / s) propagating inside the ingot 50. This prescribed time is 103.9 ns in the present embodiment. This second pulsed laser beam PL2 is irradiated onto the region of the upper surface 52 of the ingot 50 that is irradiated with the first pulsed laser beam PL1 via the laser beam introduction unit 6C.

[0049] The laser beam irradiation conditions implemented in the above-described fragmentation layer formation process are as follows, for example.

[0050] Wavelength: 1064 nm

[0051] Repetition frequency: 50 kHz

[0052] Average output: 10 W

[0053] Pulse width: 10 ns

[0054] When implementing the above-described thermally induced stress wave generation process and fragmentation layer formation process, the second pulsed laser beam PL2 irradiated by the fragmentation layer formation unit H2 is delayed by a prescribed time (103.9 ns) with respect to the first pulsed laser beam PL1. Thereby, as Figure 2As shown in (b), the first pulsed laser beam PL1 irradiates the upper surface 52 of the ingot 50 to form thermal stress waves (N1 to N3), which propagate at the speed of sound (propagation speed) corresponding to the material constituting the ingot 50. At a depth position P 1 mm from the upper surface 52, which is the thickness of the wafer W to be formed, a region with a narrowed bandgap is formed. In this region, the second pulsed laser beam PL2 is absorbed, and a destructive stress is applied to the ingot 50 to locally break the ingot 50.

[0055] As described above, the wafer generation apparatus 2 of the present embodiment includes a raster scanner 68 and a indexing scanner 67. The Figure 2 raster scanner 68 and the indexing scanner 67 shown in (a) are operated, and the first pulsed laser beam PL1 and the second pulsed laser beam PL2 are sequentially irradiated within a specified region defined by the X-axis coordinate and the Y-axis coordinate via the fθ lens 691. In the specified region, a fracture layer S is formed at a depth of 1 mm from the upper surface (52). Further, the moving mechanism 5 is operated to move the chuck table 22 in the X-axis direction and the Y-axis direction, and the regions of the ingot 50 where the first pulsed laser beam PL1 and the second pulsed laser beam PL2 are not irradiated are sequentially positioned in the region where the first pulsed laser beam PL1 and the second pulsed laser beam PL2 can be irradiated from the condenser 69. The above-described thermal stress wave generation process and fracture layer formation process are performed, and a fracture layer S is formed at a depth of 1 mm from the upper surface (52) of the ingot 50 over the entire region of the ingot 50.

[0056] Next, a peeling process of peeling the wafer W from the ingot 50 starting from the fracture layer S is performed. Hereinafter, with reference to Figure 1 and Figure 3 the steps of this peeling process will be described.

[0057] When performing the peeling process, first, the moving mechanism 5 is used to move the chuck table 22 below the adsorption plate 16d constituting the peeling unit 16. Next, the lifting unit (not shown) built in the housing 16a is operated to lower the arm 16b. As shown in Figure 3 , the ingot 50 is brought into close contact with the lower surface of the adsorption plate 16d. Next, an attracting unit (not shown) is operated to adsorb the lower surface of the adsorption plate 16d to the upper surface of the ingot 50. An ultrasonic vibration applying unit (not shown) is operated to apply ultrasonic vibration to the lower surface of the adsorption plate 16d, and the motor 16c is operated to rotate the adsorption plate 16d. As a result, the region on the upper surface side of the ingot 50 can be peeled off with the fracture layer S formed inside the ingot 50 as an interface, and thus a wafer W with a desired thickness (1 mm) can be generated. Thus, the peeling process is completed. After performing this peeling process, by performing the above-described thermal stress wave generation process, fracture layer formation process, and peeling process on the ingot 50 again, the wafer W can be repeatedly generated from the ingot 50.

[0058] According to the above-described embodiment, a first pulsed laser beam PL1 having a wavelength that is absorbable by the ingot 50 is irradiated onto the upper surface 52 of the ingot 50 to generate and propagate a thermal stress wave, and a second pulsed laser beam PL2 that is delayed by the time (103.9 ns) at which the thermal stress wave propagates to a position corresponding to the thickness of the wafer W to be formed is irradiated. Thereby, a fracture layer S can be formed at the position corresponding to the thickness (1 mm) of the wafer W to be formed, and thus the thickness of the wafer W can be controlled without detecting the height of the upper surface of the ingot 50, improving the productivity.

[0059] As described above, in the case where the peeling process is performed, the peeling surface of the ingot 50 after the wafer W is peeled, i.e., the new upper surface 52, becomes a rough surface due to the influence of the peeling layer S. Therefore, in the case of repeatedly forming the wafer W from the ingot 50, it is preferable to perform a planarization process for planarizing the new upper surface 52 of the ingot 50 after the wafer W is peeled.

[0060] To perform the planarization process for planarizing the upper surface 52 of the ingot 50, the ingot 50 having the upper surface 52 as the peeling surface is transferred to a separately prepared grinding device, and the upper surface 52 is ground and planarized. Alternatively, a grinding unit is provided in the above-described wafer forming device 2 to grind the upper surface 52 of the ingot 50. In the present embodiment, a grinding unit 7 (only a part is shown) as shown is provided on the base 3 of the wafer forming device 2, and a planarization process for planarizing the upper surface 52 of the ingot 50 is performed. Figure 4 The grinding unit 7 has: a main shaft 7a having a servo motor (not shown) and driven by the servo motor; a wheel mount 7b disposed at the lower end of the main shaft 7a; a grinding wheel 7c fixed to the wheel mount 7b; and a plurality of grinding tools 7d arranged in a ring shape on the lower surface of the grinding wheel 7c. The position of the grinding unit 7 in the grinding feed direction (vertical direction) is precisely controlled by a lifting unit (not shown).

[0061] When performing the planarization process, as

[0062] shown in Figure 4As shown, the chuck table 22 holding the ingot 50 is positioned below the grinding unit 7 described above. Next, by operating a rotation drive unit (not shown), the chuck table 22 is rotated in the direction indicated by the arrow at a rotation speed of, for example, 300 rpm, and by operating this servo motor, the grinding wheel 7c is rotated at a rotation speed of, for example, 6000 rpm. Next, by operating this lifting unit, the grinding unit 7 is lowered so that the grinding tool 7d contacts the upper surface 52 of the ingot 50, which is the peeling surface. After the grinding tool 7d contacts the upper surface 52 of the ingot 50, the grinding unit 7 is lowered at a prescribed grinding feed rate (for example, 0.1 μm / second). Thus, the upper surface 52 of the ingot 50 is planarized by the grinding tool 7d. After planarizing the upper surface 52 of the ingot 50 in this way, the above-described thermal stress wave generation process, damaged layer formation process, peeling process, and planarization process are performed again. By repeating such a wafer generation method, a plurality of wafers W are efficiently generated from the ingot 50. In addition, in the above-described embodiment, an example in which the planarization process is performed using the grinding unit 7 has been described, but the present invention is not limited thereto, and the planarization process may be performed using a polishing unit with a polishing pad.

[0063] The present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, the laser beam introduction unit 6C is shared by the thermal stress wave generation unit H1 and the damaged layer formation unit H2, and the first pulsed laser beam PL1 and the second pulsed laser beam PL2 are irradiated from the same direction, but it is not necessary to irradiate from the same direction. The laser beam introduction units may be provided in the thermal stress wave generation unit H1 and the damaged layer formation unit H2, and the first pulsed laser beam PL1 and the second pulsed laser beam PL2 may be irradiated from different angles.

Claims

1. A wafer generation method for generating a wafer from a semiconductor ingot, wherein, the wafer generation method has the following steps: a holding step of holding the semiconductor ingot on a chuck table; a thermal stress wave generation step of irradiating a pulsed laser beam having a wavelength absorbable by the semiconductor ingot onto the upper surface of the semiconductor ingot held by the chuck table to generate a thermal stress wave and causing the thermal stress wave to propagate inside the semiconductor ingot; a fracture layer formation step of irradiating a pulsed laser beam having a wavelength transmissive to the semiconductor ingot onto the upper surface of the semiconductor ingot at a time when the thermal stress wave generated in the thermal stress wave generation step reaches a position corresponding to the thickness of the wafer to be generated, and generating absorption of the pulsed laser beam having a transmissive wavelength in a region where the band gap is narrowed due to the tensile stress of the thermal stress wave, thereby forming a fracture layer; and a peeling step of peeling the wafer to be generated from the semiconductor ingot starting from the fracture layer.

2. The wafer generation method according to claim 1, wherein, the wafer generation method further has a planarization step of planarizing the peeling surface of the semiconductor ingot after the peeling step.

3. A wafer generation apparatus for generating a wafer from a semiconductor ingot, wherein, the wafer generation apparatus has: a chuck table for holding a semiconductor ingot; a thermal stress wave generation unit for irradiating a pulsed laser beam having a wavelength absorbable by the semiconductor ingot onto the upper surface of the semiconductor ingot held by the chuck table to generate a thermal stress wave and causing the thermal stress wave to propagate inside the semiconductor ingot; and a fracture layer formation unit for irradiating a pulsed laser beam having a wavelength transmissive to the semiconductor ingot onto the upper surface of the semiconductor ingot at a time when the thermal stress wave generated by the thermal stress wave generation unit reaches a position corresponding to the thickness of the wafer to be generated, and generating absorption of the pulsed laser beam having a transmissive wavelength in a region where the band gap is narrowed due to the tensile stress of the thermal stress wave, thereby forming a fracture layer.

4. The wafer generation apparatus according to claim 3, wherein, the wafer generation apparatus further has a peeling unit for peeling the wafer from the fracture layer formed by the fracture layer formation unit.

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