Wafer manufacturing methods

Abstract

[Problem] To provide a wafer manufacturing method that can efficiently manufacture wafers and eliminate the problem of uneconomical wafer manufacturing. [Solution] A wafer manufacturing method comprising: a first release layer forming step, wherein a laser beam of a wavelength having penetrability to a crystal ingot is positioned from the end face of the crystal ingot at a first depth for forming a large-diameter wafer to be manufactured and irradiated to form a first release layer; a second release layer forming step, wherein a laser beam of a focal point is positioned from the end face of the crystal ingot at a second depth smaller than the diameter of the crystal ingot and shallower than the first depth and irradiated to form a second release layer for manufacturing a small-diameter wafer; and a separation wall forming step, wherein a laser beam of a focal point is positioned at an annular region extending from the end face of the crystal ingot to the second release layer and irradiated to form an annular first separation wall corresponding to the outer periphery of the small-diameter wafer.

Description

Wafer manufacturing methods This invention relates to a method for manufacturing wafers. ICs, LSIs, and other components are formed by depositing functional layers on the front side of a wafer using materials such as silicon and sapphire, and then dividing the wafer by multiple predetermined dicing lines that intersect these functional layers. The wafer is then processed using a cutting device or a laser processing device to cut the predetermined dicing lines, resulting in individual component chips. These diced component chips are then used in electronic devices such as mobile phones and personal computers. Furthermore, power components, LEDs, etc., are formed by laminating a functional layer on the front side of a SiC wafer and dividing it by multiple predetermined dividing lines that intersect this functional layer. The wafers for forming elements, power elements, LEDs, etc., mentioned above are generally manufactured by slicing a crystal rod with a wire saw, and the front and back sides of the sliced ​​wafers are ground and mirror polished (for example, see Patent Document 1). However, if the crystal ingot is cut with a wire saw and both sides are ground to manufacture wafers, 70-80% of the crystal ingot will be discarded, which is uneconomical. In particular, SiC has high hardness, is difficult to cut with a wire saw, has poor manufacturability, and the unit price of the crystal ingot is high, posing challenges to the efficient manufacture of wafers. Therefore, the applicant in this case proposed a technology that focuses a laser beam of wavelength penetrating SiC onto the interior of a SiC crystal rod and irradiates it, forming a separation layer at a predetermined cutting surface and separating the wafer, thus avoiding waste of the crystal rod (see, for example, Patent Document 2). [Previous Art Documents] [Patent Documents] [Patent Document 1] Japanese Patent Application Publication No. 2000-094221 [Patent Document 2] Japanese Patent Application Publication No. 2016-111143 [Problem to be solved by the invention] However, even in the technology described in the aforementioned Patent Document 2, since the back side of the wafer is ground after forming multiple components on the front side of the wafer manufactured from the crystal rod and, for example, the thickness of 800 μm is polished to a thickness of 50 to 100 μm, a thickness of more than 700 μm is discarded, and the problem of uneconomicalness still remains. Therefore, the object of the present invention is to provide a wafer manufacturing method that can efficiently manufacture wafers and eliminate the problem of uneconomical wafer manufacturing. [Technical Means for Solving the Problem] According to one aspect of the present invention, a wafer manufacturing method is provided, which is a wafer manufacturing method for manufacturing wafers, and includes: a first release layer forming step, in which a focal point of laser light with a wavelength that has penetrability to a crystal rod is positioned from the end face of the crystal rod at a first depth for forming a large-diameter wafer to be manufactured and irradiated to form a first release layer; a second release layer forming step, in which a focal point of laser light is positioned from the end face of the crystal rod at a second depth that is smaller than the diameter of the crystal rod and shallower than the first depth and irradiated to form a second release layer for manufacturing a small-diameter wafer; a separation wall forming step, in which a focal point of laser light is positioned at an annular region from the end face of the crystal rod to the second release layer and irradiated to form an annular first separation wall corresponding to the outer periphery of the small-diameter wafer; and a wafer manufacturing step, in which the large-diameter wafer is peeled off from the first release layer and separated from the second release layer and the first separation wall to manufacture the small-diameter wafer. Preferably, the second release layer formed in the second release layer forming step is also formed in a region larger than the diameter of the small-diameter wafer to be manufactured and corresponding to the inner side of the annular reinforcement formed on the outer periphery of the large-diameter wafer to be manufactured. In the separation wall forming step, in addition to forming the first separation wall, an annular second separation wall is also formed along the inner periphery of the annular reinforcement. In the wafer manufacturing step, an annular wafer is also manufactured in the region sandwiched between the small-diameter wafer and the annular reinforcement. Preferably, the small-diameter wafer has a standardized diameter. Preferably, the wafer manufacturing method further comprises: a first alignment mark forming step, which forms, before or after the first release layer forming step, a first alignment mark required for forming a circuit on the large-diameter wafer to be manufactured, inside or outside the large-diameter wafer to be manufactured; and a second alignment mark forming step, which forms, before or after the second release layer forming step, a second alignment mark required for forming a circuit on the small-diameter wafer to be manufactured, inside or outside the small-diameter wafer to be manufactured. According to another aspect of the present invention, a method for manufacturing a wafer is provided, which is a method for manufacturing a wafer of wafers, and includes: a small-diameter release layer forming step, which involves positioning a focal point of laser light with a wavelength that is penetrable to a large-diameter wafer having multiple elements formed on its front side from the back side of the large-diameter wafer at a depth equivalent to the thickness of the small-diameter wafer to be manufactured, and irradiating it to form a small-diameter release layer in a region of the small-diameter wafer; a small-diameter separation wall forming step, which involves positioning a focal point of laser light in an annular region extending from the back side of the large-diameter wafer to the small-diameter release layer and irradiating it to form an annular small-diameter separation wall corresponding to the outer diameter of the small-diameter wafer; and a small-diameter wafer manufacturing step, which manufactures the small-diameter wafer from the small-diameter release layer and the small-diameter separation wall. Preferably, the small-diameter release layer formed in the small-diameter release layer formation step is also formed in a region larger than the diameter of the small-diameter wafer to be manufactured and corresponding to the inner side of the annular reinforcement formed on the outer periphery of the large-diameter wafer. In the small-diameter separation wall formation step, an annular small-diameter separation wall is formed not only on the outer periphery corresponding to the small-diameter wafer but also on the inner periphery corresponding to the annular reinforcement. In the wafer manufacturing step, in addition to manufacturing the small-diameter wafer, an annular wafer sandwiched between the small-diameter wafer and the annular reinforcement is also manufactured. Preferably, an alignment mark formation step is included, which is performed before or after the small-diameter release layer formation step, forming alignment marks required for circuit formation on the small-diameter wafer inside or outside the small-diameter wafer to be manufactured. [Effects of the Invention] According to the wafer manufacturing method of the present invention, small-diameter wafers with a diameter smaller than that of large-diameter wafers can be manufactured without waste. Furthermore, by applying the same wafer manufacturing method to the area where small-diameter wafers are manufactured, even smaller-diameter wafers can be manufactured, further reducing waste. Furthermore, according to the wafer manufacturing method of the present invention, it becomes possible to avoid grinding the back side of a large-diameter wafer on which multiple elements divided by intersecting predetermined dividing lines have been formed on the front side, and to irradiate laser light from the back side to form a small-diameter release layer, thereby manufacturing a small-diameter wafer with a smaller diameter in the area of ​​thickness that would otherwise be discarded, thus eliminating the problem of uneconomical production. Hereinafter, a wafer manufacturing method according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. Figure 1 shows an overall perspective view of a laser processing apparatus 1 suitable for implementing the wafer manufacturing method of this embodiment. The laser processing apparatus 1 comprises the following components: a base 2; a holding unit 3 disposed on the base 2 for holding the workpiece; a moving mechanism 4 for moving the holding unit 3 in the X-axis direction and the Y-axis direction orthogonal to the X-axis direction; a laser beam irradiation unit 6; an imaging unit 7 for performing alignment; and a wafer stripping unit 8. As shown in Figure 1, the holding unit 3 includes: a rectangular X-axis movable plate 31, which is movably mounted on the base 2 in the X-axis direction; a rectangular Y-axis movable plate 32, which is movably mounted on the X-axis movable plate 31 in the Y-axis direction; and a holding stage 33, which is disposed on the Y-axis movable plate 32 and is configured to rotate by having a pulse motor inside. The workpiece processed by the laser processing apparatus 1 shown in Figure 1 is the SiC ingot 10 shown in Figures 1 and 2(a). The moving mechanism 4 includes: an X-axis moving mechanism 41, which moves the stage 33 in the X-axis direction; and a Y-axis moving mechanism 42, which moves the stage 33 in the Y-axis direction. The X-axis moving mechanism 41 converts the rotational motion of the motor 43 into linear motion and transmits it to the movable plate 31 in the X-axis direction via a ball screw 44 whose end is supported by a bearing block 44a, causing the movable plate 31 in the X-axis direction to move along a pair of guide rails 2a, 2a arranged on the base 2 in the X-axis direction. The Y-axis moving mechanism 42 converts the rotational motion of the motor 45 into linear motion and transmits it to the movable plate 32 in the Y-axis direction via a ball screw 46, causing the movable plate 32 in the Y-axis direction to move along a pair of guide rails 35, 35 arranged on the movable plate 31 in the X-axis direction in the Y-axis direction. The laser processing apparatus 1 includes a frame 5 consisting of a vertical wall 5a and a horizontal wall 5b. The vertical wall 5a is erected on the side of the X-axis moving mechanism 41 and the Y-axis moving mechanism 42 on the base 2, and the horizontal wall 5b extends horizontally from the upper end of the vertical wall 5a. An optical system and a camera unit 7 are housed inside the horizontal wall 5b of the frame 5. The optical system constitutes the aforementioned laser beam irradiation unit 6. Although detailed descriptions are omitted, the optical system of the laser beam irradiation unit 6 includes: a laser oscillator that emits a laser beam LB of a desired wavelength; an attenuator that adjusts the output of the laser beam LB emitted from the laser oscillator; and a reflector that redirects the optical path of the laser beam LB to the side of a condenser 61 (not shown in the diagram). The repetition frequency, dot diameter, and average output of the laser beam LB irradiated from the laser beam irradiation unit 6 are controlled by a controller (not shown in the figure), and the focal point of the laser beam LB is controlled in a direction perpendicular to the upper surface of the holding stage 33, i.e., the holding surface (Z-axis direction in the figure). The wafer stripping unit 8 of this embodiment is disposed on the base 2 and is located near the end portion (bearing block 44a side) of the aforementioned guide rails 2a, 2a. The wafer stripping unit 8 includes: a stripping unit housing 81; a stripping unit arm 82, a portion of which is housed within the stripping unit housing 81 and supported to move in the Z-axis direction (vertical direction); a stripping pulse motor 83 disposed at the front end of the stripping unit arm 82; and a suction unit 84, rotatably supported by the stripping pulse motor 83 at the lower part of the stripping pulse motor 83, and having a plurality of suction holes on its lower surface. The stripping unit housing 81 includes a Z-axis movement mechanism (not shown) for controlling the movement of the stripping unit arm 82 in the Z-axis direction. The stripping unit housing 81 includes a Z-axis position detector (not shown) for detecting the Z-axis position of the stripping unit arm 82 and transmitting its position signal to the aforementioned controller. The aforementioned controller is constructed using a computer and includes: a central processing unit (CPU) that performs calculations according to the control program; read-only memory (ROM) that stores the control program, etc.; read-write random access memory (RAM) used to temporarily store detected values, calculation results, etc.; an input interface; and an output interface (detailed illustrations omitted). In addition to the aforementioned laser beam irradiation unit 6, the controller also connects to and controls the camera unit 7, the X-axis movement mechanism 41, the Y-axis movement mechanism 42, the wafer stripping unit 8, and the monitor 9, etc. The laser processing apparatus 1 described above generally has the same configuration as described above. The laser processing method of this embodiment implemented using the laser processing apparatus 1 will be described below. First, the first embodiment of the wafer manufacturing method of the present invention implemented using the laser processing apparatus 1 described above will be described below. In implementing this embodiment, a crystal ingot 10 as shown in Figures 1 and 2 is prepared. The crystal ingot 10 is made of SiC and is a hexagonal single crystal ingot with a diameter of 300 mm. The front surface 10a of the end face constituting the crystal ingot 10 is polished to a mirror finish by another polishing means. Thus, a large-diameter wafer 13 with a diameter of 300 mm and a small-diameter wafer 14 with a diameter of 200 mm are manufactured from the crystal ingot 10 (see also Figure 6). The diameters of the large-diameter wafer 13 and the small-diameter wafer 14 are standardized dimensions by means of the SEMI standard (SEMI (Semiconductor Equipment and Materials International) is a standard established for the purpose of unifying international industrial standards for the semiconductor industry). An orientation plane (hereinafter referred to as "orientation plane") 12 indicating the crystal orientation is formed on the crystal ingot 10. If the crystal ingot 10 has been prepared, it is placed on the upper surface of the holding stage 33 of the laser processing apparatus 1 and firmly fixed with adhesive, wax, etc. Next, the front side 10a of the crystal ingot 10 is photographed by the camera unit 7, and the height of the front side 10a and the alignment of the shape 10b of the crystal ingot 10 are detected. The information of the shape 10b and the height is stored in the controller. If the shape of the outer profile 10b of the front surface 10a of the crystal rod 10 and the height of the front surface 10a have been memorized in the controller, the holding stage 33 is rotated so that the direction shown by the straight section of the orientation plane 12 is aligned with the X-axis direction, and the holding stage 33 is moved in the X-axis direction and positioned directly below the concentrator 61 of the laser beam irradiation unit 6. Next, as shown in Figures 2(a) and 2(b), the focusing point P of the laser beam LB with a wavelength that has penetrability to the crystal rod 10 is positioned from the front surface 10a of the crystal rod 10 at a first depth (e.g., 800 μm) to form the large-diameter wafer 13 to be manufactured (see Figure 3(a)) and irradiated, while the crystal rod 10 is processed and fed in the X-axis direction to form the modified layer 100. If the modified layer 100 has already been formed, the laser beam LB is indexed and fed, for example, 400 μm in the Y-axis direction. At a position parallel to the previously formed modified layer 100, the focusing point P is positioned at the first depth, and the laser beam LB is irradiated while processing is performed in the X-axis direction to form the same modified layer 100. These steps are repeated to form multiple modified layers 100 along the entire area of ​​the front surface 10a of the crystal rod 10, thereby forming the first release layer 100A. The first release layer formation step of this embodiment is thus completed. Furthermore, the laser processing conditions in the first release layer formation step are as follows, for example. <Laser processing conditions for the first release layer formation step> Wavelength: 1064nm Average output: 7~16W Repetition frequency: 30kHz Pulse width: 3ns Processing feed rate: 165mm / s Defocus: 300μm (forming the first release layer 100A at a depth of 800μm from the front 10a) Furthermore, although details are omitted, the aforementioned crystal rod 10 is manufactured to include: a c-axis inclined at a predetermined angle α in a direction orthogonal to the straight portion of the orientation plane 12; and a c-plane orthogonal to the c-axis. The c-plane is inclined at the angle α relative to the front face 10a of the crystal rod 10. The angle α is, for example, 4°. Moreover, by performing the aforementioned first release layer formation step, a crack extends along the c-plane from the predetermined modified layer 100 toward the adjacent modified layer 100, thereby forming the first release layer 100A through the modified layer 100 and the crack. As described above, if the first release layer formation step has been performed, then the second release layer formation step described below shall be performed. As shown in Figure 3, in the second release layer formation step, the focal point P of the laser beam LB is positioned from the front side 10a of the end face constituting the crystal rod 10 at a second depth (e.g., 700 μm) that is smaller than the outer diameter of the large-diameter wafer 13 with the diameter of the crystal rod 10 (300 mm) and shallower than the first depth (800 μm) mentioned above, and is irradiated to form the second release layer 110A for manufacturing the small-diameter wafer 14. As shown in Figure 3(a), the area irradiated by the laser beam LB in the second lift-off layer formation step is defined by the outer periphery 14a, which manufactures a small-diameter wafer 14 with a diameter of 200 mm. This small-diameter wafer 14 is smaller than the large-diameter wafer 13, which uses the entire end face of the crystal rod 10 as the wafer manufacturing area. Furthermore, the outer periphery 14a shown in Figure 3(a) is an imaginary line and is not actually visible. The positional information of the outer periphery 14a is pre-memorized in the aforementioned controller. The small-diameter wafer 14 also forms an orientation plane 14b representing the crystal orientation, and the outer periphery 14a also includes a straight portion forming this orientation plane 14b. This orientation plane 14b is parallel to the orientation plane 12 formed on the crystal rod 10. In the second stripping layer formation step, based on the position information stored in the controller's outer periphery 14a, the concentrator 61 of the laser beam irradiation unit 6 is positioned on the outer periphery 14a of the front side 10a of the crystal rod 10. The focusing point P of the laser beam LB, which has a wavelength that can penetrate the crystal rod 10, is positioned at the second depth (700 μm). The modified layer 110 is formed while the crystal rod 10 is processed and fed in the X-axis direction. The beginning and end of the modified layer 110 are set on the aforementioned outer periphery 14a. If the modified layer 110 has been formed, the irradiation position of the laser beam LB is indexed and fed in the Y-axis direction, for example, by 400 μm. At a position parallel to the previously formed modified layer 110, the focusing point P is positioned at the second depth. The laser beam LB is irradiated while processing and feeding in the X-axis direction to form the same modified layer 110 as described above. These steps are repeated to form the modified layer 110 integrally within the area defined by the outer perimeter 14a described above. During the formation of this modified layer 110, similarly to the modified layer 100 described above, cracks extend between adjacent modified layers 110. Thus, as shown in FIG3(b), a second release layer 110A is formed by the modified layer 110 and the cracks, completing the second release layer formation step of this embodiment. Furthermore, the laser processing conditions in the second release layer formation step are, for example, as follows. <Laser processing conditions for the second release layer formation step> Wavelength: 1064nm Average output: 7-16W Repetition rate: 30kHz Pulse width: 3ns Processing feed rate: 165mm / s Defocus: 260μm (forming the second release layer 110A at a depth of 700μm from the front 10a) As described above, if the first release layer 100A and the second release layer 110A have been formed by the first release layer forming step and the second release layer forming step, then the separation wall forming step described below shall be performed. As shown in Figures 4(a) and 4(b), during the separation wall formation step, based on the information stored in the controller regarding the outer periphery 14a of the small-diameter wafer 14, the focus point P of the laser beam LB is positioned in the annular region defined by the outer periphery 14a and irradiated. The holding stage 33 is rotated in the direction indicated by arrow R1, thereby forming an annular first separation wall 120 along the outer periphery 14a. Furthermore, while forming the first separation wall 120 in the region of the orientation plane 14b on the outer periphery 14a, the rotation of the holding stage 33 is stopped and the X-axis movement mechanism 41 is operated to perform machining feed in the X-axis direction, thereby forming a linear first separation wall 120 in the orientation plane 14b. Furthermore, it is preferable to perform laser processing by varying the depth of the focal point P of the positioning laser beam LB multiple times in the vertical direction, thereby forming modified layers at multiple depth locations to manufacture the first separation wall 120. In this embodiment, the depth changes from the front surface 10a of the focal point P to 500 μm, 375 μm, 250 μm, and 125 μm, forming four modified layers along the outer periphery 14a, thereby completing the separation wall formation step of forming the first separation wall 120 in the annular region reaching the second peeling layer 110A. The laser processing conditions in this separation wall formation step are, for example, as follows. <Laser processing conditions for the separation wall formation step> Wavelength: 1064nm Average output: 7-16W Repetition rate: 30kHz Pulse width: 3ns Processing feed rate: 165mm / s Defocus: 200μm, 150μm, 100μm, 50μm (forming modified layers at depths of 500μm, 375μm, 250μm, and 125μm starting from front 10a) In the above description, although examples of sequentially performing the first release layer formation step, the second release layer formation step, and the separation wall formation step have been given, the present invention may also perform a first alignment mark formation step before or after the first release layer formation step. The first alignment mark formation step is to form alignment marks required when forming the circuit on the large-diameter wafer 13. As shown in FIG5(a), the alignment mark is, for example, an alignment mark 13a formed for a specific X-axis direction and Y-axis direction when forming the circuit on the large-diameter wafer 13. The large-diameter wafer 13 is manufactured by separating the wafer manufacturing steps described later after the first release layer 100A is formed by the first release layer formation step described above. As understood from FIG5(a), the alignment mark 13a is preferably formed at two points in a specific X-axis direction and two points in a specific Y-axis direction. In this embodiment, it is formed at a total of three locations. The alignment mark 13a is, for example, a mark formed inside the large-diameter wafer 13 by forming a modified layer according to the laser processing conditions in the aforementioned separation wall formation step, and is formed in the shape of a "+" when viewed from above. Furthermore, the alignment mark 13a is formed in a manner that does not obstruct the formation of circuits on the large-diameter wafer 13, near the outer periphery of the outer surface 10b and in the remaining area where no circuits are formed. While the first alignment mark formation step of the present invention can be performed before or after the first release layer formation step, it is preferable to perform it after the first release layer formation step in a manner that does not obstruct the formation of the first release layer 100A. Moreover, the alignment mark 13a formed by the first alignment mark formation step is not limited to the above-described form; for example, it can also be formed by positioning the focal point P of the laser beam LB on the front surface 10a of the ingot 10 and forming the alignment mark 13a by an ablation process. However, it is preferable to process at a depth to which the alignment mark 13a will not disappear due to subsequent grinding / polishing. Furthermore, a second alignment mark formation step can be performed before or after the second release layer formation step. This second alignment mark formation step forms alignment marks required for forming the circuit on the small-diameter wafer 14. These alignment marks are, for example, alignment marks 14c (see Figure 5(b)) formed for specific X-axis and Y-axis directions required for forming the circuit on the small-diameter wafer 14. The small-diameter wafer 14 is manufactured by separating the wafer fabrication steps described later after the second release layer 110A is formed by the aforementioned second release layer formation step. As shown in Figure 5(b), the alignment mark 14c, like the aforementioned alignment mark 13a, is preferably formed at at least three locations in specific X-axis and Y-axis directions. The alignment mark 14c is, for example, formed by processing according to the laser processing conditions performed in the aforementioned first alignment mark formation step, and is formed inside the small-diameter wafer 14 with a modified layer. Similarly, it is formed in a "+" shape, for example, when viewed from above. Furthermore, the alignment mark 14c is formed in a manner that does not obstruct the formation of circuits or the like on the small-diameter wafer 14, in the remaining peripheral area outside where no circuits or the like are formed. While the second alignment mark formation step of the present invention can be performed either before or after the second release layer formation step, it is preferred to perform it after the second release layer formation step in a manner that does not obstruct the formation of the second release layer 110A. The alignment mark 14c formed by the second alignment mark formation step of the present invention can also be formed similarly to the alignment mark 13a described above, by positioning the focus point P on the front surface 10a of the ingot 10 and forming the alignment mark 14c by ablation. By forming the alignment marks 13a and 14c by irradiating laser light LB in the above-described alignment mark formation step, it is not necessary to use additional equipment for forming alignment marks by exposure and etching, thereby improving productivity. As described above, if the first release layer formation step, the second release layer formation step, the separation wall formation step, the alignment mark formation step, etc. have been performed, then the wafer manufacturing steps described below shall be performed. As shown in Figure 6, the wafer manufacturing process involves the following steps: a large-diameter wafer 13 is peeled off starting from the first release layer 100A, and a small-diameter wafer 14 is manufactured by separating the wafer using the second release layer 110A and the first separation wall 120 as starting points. This wafer manufacturing process can be implemented, for example, using the wafer stripping unit 8 described in Figure 1. During the wafer manufacturing process, the holding stage 33 is moved by operating the moving mechanism 4 of the laser processing apparatus 1, positioning the front surface 10a of the ingot 10 directly below the suction cup 84 of the wafer stripping unit 8. Next, the suction cup 84 and the stripping unit arm 82 are lowered together by the Z-axis moving mechanism (not shown) built into the stripping unit housing 81, pressing against the front surface 10a of the ingot 10. Then, a negative pressure is created in the suction port of the suction cup 84 to adsorb the front surface 10a of the ingot 10. If the front side 10a has been adsorbed by the adsorber 84, the adsorber 84 is rotated by the pulse motor 83, thereby twisting the first release layer 100A and peeling off the large-diameter wafer 13, which is integral with the small-diameter wafer 14, from the ingot 10. If the large-diameter wafer 13 has been peeled off in this way, another peeling method is used to separate it from the second release layer 110A and the first separation wall 120 to manufacture the small-diameter wafer 14. Furthermore, as shown in FIG. 6, a thinning portion 13a is formed in the central region of the large-diameter wafer 13, and the thinning portion 13a is formed to a thickness of 100 μm by manufacturing the small-diameter wafer 14. Then, the front and back sides of the large-diameter wafer 13 and the small-diameter wafer 14 manufactured from the ingot 10 are ground and mirror-polished before circuit formation. The wafer manufacturing steps are completed by the above, and the wafer manufacturing method of the present invention is completed. According to the first embodiment described above, a small-diameter wafer 14 with a diameter of 200mm can be manufactured from a large-diameter wafer 13 with a diameter of 300mm manufactured from the ingot 10, without causing waste. Furthermore, by performing the same wafer manufacturing method as described above on the area where the small-diameter wafer 14 is manufactured, an even smaller diameter wafer of 150mm can be manufactured from the small-diameter wafer 14 with a diameter of 200mm, again without causing waste. As shown in Figure 6, in the wafer manufacturing method of this embodiment, a large-diameter wafer 13 and a small-diameter wafer 14 are formed from a crystal ingot 10, thereby making the front surface 10a of the crystal ingot 10 a rough surface. Therefore, when manufacturing the large-diameter wafer 13 and the small-diameter wafer 14 from the crystal ingot 10, another grinding means is used to grind and mirror polish the front surface 10a of the crystal ingot 10. The present invention is not limited to the first embodiment described above, but may also be the second embodiment described below. In the second embodiment, a crystal rod 10 identical to that in the first embodiment is prepared. As illustrated in FIG2, a first release layer formation step is performed, in which a first release layer 100A is formed at a first depth (e.g., 800 μm from the front side 10a) of the large-diameter wafer 13 to be manufactured. Next, as shown in FIG7(a), laser processing is performed during the second release layer formation step. The laser processing forms a modified layer 110' at the same second depth (700 μm) as the modified layer 110 in the region corresponding to the inner side of the inner periphery 11a of the annular reinforcement 11. The annular reinforcement 11 is formed along the outer periphery of the large-diameter wafer 13 to be manufactured, which is larger than the diameter of the small-diameter wafer 14 to be manufactured. As a result, as shown in FIG7(b), a second release layer 110'A is formed by the modified layer 110' and the elongation of the crack. Furthermore, the laser processing conditions for forming the second release layer 110'A are set to the same laser processing conditions as those for forming the modified layer 110 described above. If the second release layer formation step described above has been performed, as shown in Figures 8(a) and 8(b), in addition to the first separation wall 120 formed in the separation wall formation step described above, an annular second separation wall 130 is formed along the inner periphery 11a of the annular reinforcing portion 11. This second separation wall 130 is formed by using the same laser processing conditions and sequence as those performed when forming the first separation wall 120, and by positioning the focal point P of the laser beam LB from the front side 10a of the crystal rod 10 in the region of the inner periphery 11a of the annular reinforcing portion 11 and irradiating it, thereby forming the annular second separation wall 130 along the inner periphery 11a of the annular reinforcing portion 11. If the first release layer formation step, the second release layer formation step, and the separation wall formation step performed by the second embodiment described above have been implemented, then the wafer stripping unit 8 is used, and the wafer manufacturing steps are performed in a sequence substantially the same as that described in the first embodiment, thus completing the wafer manufacturing method of this embodiment. In this wafer manufacturing step, since the second release layer formation step and the separation wall formation step described above are performed, as shown in FIG9, in addition to manufacturing the large-diameter wafer 13' and the small-diameter wafer 14 having the annular reinforcing portion 11, an annular wafer 15 is also manufactured. The annular wafer 15 is formed from the area sandwiched between the annular reinforcing portions 11 of the small-diameter wafer 14 and the large-diameter wafer 13'. The large-diameter wafer 13' manufactured according to the second embodiment described above forms a thinned portion 13'a that is wider than the thinned portion 13a formed according to the first embodiment by separating the small-diameter wafer 14 and the annular wafer 15. Furthermore, although the thinned portion 13'a of the large-diameter wafer 13' achieves a thickness of 100 μm over a wider area by separating the small-diameter wafer 14 and the annular wafer 15, the processing becomes easier by forming the aforementioned annular reinforcing portion 11 and performing reinforcement. In addition, the annular wafer 15 formed according to this embodiment is discarded. Furthermore, a third embodiment of the wafer manufacturing method based on the present invention will be described. In the first and second embodiments described above, a large-diameter wafer 13 (or large-diameter wafer 13') and a small-diameter wafer 14 are manufactured from the ingot 10. However, according to this third embodiment, a small-diameter wafer can also be manufactured from the large-diameter wafer 20 shown in FIG. 10, which has a plurality of elements 22 formed on its front side 20a. Hereinafter, this third embodiment will be described. First, in implementing the third embodiment of the present invention, a large-diameter wafer 20 as shown on the right side of FIG10 is prepared. The large-diameter wafer 20 is, for example, a SiC wafer with a diameter of 300 mm and a thickness of 800 μm, and has multiple elements 22 formed on the front side 20a by multiple intersecting predetermined dividing lines 24. An orientation plane 20c indicating the crystal orientation is formed on the large-diameter wafer 20. If such a large-diameter wafer 20 has been prepared, a protective film T formed to the same size as the large-diameter wafer 20 is adhered to the front side 20a and integrated. Next, the large-diameter wafer 20 integrated with the protective film T is flipped over, with the back side 20b facing upward and the protective film T side facing downward, and is placed on the upper surface of the holding stage 33 of the laser processing apparatus 1, and fixed by an adhesive or the like. If the large-diameter wafer 20 has been fixed to the aforementioned holding stage 33, a small-diameter release layer formation step is performed, which is substantially the same as the second release layer formation step in the second embodiment described in FIG. 7. During this small-diameter release layer formation step, firstly, the large-diameter wafer 20 is photographed using the imaging unit 7 of the laser processing apparatus 1 to detect the shape of the large-diameter wafer 20 and the height of its back surface 20b. Next, as shown in FIG. 10, the wafer 20 is positioned directly below the concentrator 61 of the laser beam irradiation unit 6. Then, the focus point P of the laser beam LB, which has a wavelength that is penetrable to the SiC constituting the large-diameter wafer 20, is positioned from the back surface 20b of the large-diameter wafer 20 at a depth equivalent to the thickness of the small-diameter wafer 25 to be manufactured (e.g., 700 μm). Then, the laser beam LB is irradiated, and the aforementioned moving mechanism 4 is operated to form a modified layer identical to the modified layer 110 in the region corresponding to the inner side of the inner periphery 21a of the annular reinforcing portion 21. A small-diameter release layer 140, consisting of the modified layer and the elongated crack, is then formed. The annular reinforcing portion 21 is formed along the outer periphery of the large-diameter wafer 20, which is larger than the diameter of the small-diameter wafer 25 defined by the outer periphery 25a. Furthermore, the laser processing conditions for forming the small-diameter release layer 140 are set to the same laser processing conditions as those for the second release layer forming step of forming the modified layers 110 and 110'. If the above-described small-diameter release layer formation step has been performed, then the following steps are performed: a small-diameter separation wall formation step, in which the focus point of the laser beam LB is positioned at the annular region from the back surface 20b of the large-diameter wafer 20 to the small-diameter release layer 140 and irradiated, forming an annular small-diameter separation wall corresponding to the outer periphery 25a of the small-diameter wafer 25; and a small-diameter wafer manufacturing step, in which the small-diameter wafer 25 is manufactured from the small-diameter release layer 140 and the small-diameter separation wall. The small-diameter separation wall formation step is performed using the same laser processing conditions and sequence as the separation wall formation step described in FIG4 above. The small-diameter separation wall is formed on the outer periphery 25a in the same form as the first separation wall 120 described above. Detailed descriptions are omitted. Furthermore, in the small-diameter separation wall forming step of this third embodiment, an annular separation wall is also formed in the region corresponding to the inner periphery 21a of the annular reinforcing portion 21. The separation wall formed in the region corresponding to the inner periphery 21a of the annular reinforcing portion 21 is formed using the same laser processing conditions and sequence as the annular second separation wall 130 formed in the separation wall forming step of the second embodiment described above. Detailed explanations are omitted here. As described above, if the small-diameter release layer formation step and the small-diameter separation wall formation step have already been performed, the small-diameter wafer manufacturing step is performed in the same order as the wafer manufacturing steps in the first and second embodiments described above. As shown in FIG11, in addition to manufacturing the large-diameter wafer 20 having the annular reinforcing portion 21 and the small-diameter wafer 25 having the orientation plane 25b, an annular wafer 23 is also manufactured. The annular wafer 23 is formed from the region sandwiched between the small-diameter wafer 25 and the annular reinforcing portion 21 of the large-diameter wafer 20, and has the orientation plane 23a and the opening 23b. As described above, the thickness of the small-diameter wafer 25 is 700 μm, and a thinning portion 20d with a thickness of 100 μm is formed inside the annular reinforcing portion 21 of the large-diameter wafer 20. Furthermore, the annular wafer 23 formed by this embodiment is discarded. Although omitted in the above description, in the third embodiment, an alignment mark formation step may also be performed before or after the small-diameter release layer formation step. This alignment mark formation step involves forming the alignment marks required for circuit formation on the small-diameter wafer 25, either internally or externally. This alignment mark formation step forms the same alignment marks as the alignment mark 14c illustrated in FIG. 5(b) above, and achieves the same effect as the steps described above; detailed description is omitted here. According to the third embodiment described above, by irradiating laser light from the back side 20b of a large-diameter wafer 20 (300 mm in diameter) with multiple elements 22 divided by intersecting predetermined dividing lines 24 on the front side 20a without grinding the back side 20b, a small-diameter release layer 140 is formed, thereby enabling the manufacture of a small-diameter wafer 25 with a thickness of 700 μm and a diameter of 200 mm that would otherwise be discarded, thus solving the problem of uneconomical production. Furthermore, by including the alignment mark formation step performed by laser light LB as described above, the exposure and etching performed by a separate device to form the alignment marks is not required, as described above, thus improving productivity. 1: Laser processing device; 2: Base; 2a: Guide rail; 3: Holding unit; 31: Movable plate in the X-axis direction; 32: Movable plate in the Y-axis direction; 33: Holding stage; 4: Moving mechanism; 41: X-axis moving mechanism; 42: Y-axis moving mechanism; 5: Frame; 6: Laser beam irradiation unit; 61: Concentrator; 7: Camera unit; 8: Wafer lift-off unit; 81: Lift-off unit housing; 82: Lift-off unit arm; 83: Lift-off pulse motor; 84: Adsorber; 9: Monitor; 10: Crystal rod; 10a: Front view; 10b: Outer shape; 11: Annular reinforcement; 12: Orientation flat. 13: Large diameter wafer 13a: Alignment mark 14: Small diameter wafer 14a: Outer periphery 14b: Orientation plane 14c: Alignment mark 15: Ring wafer 20: Large diameter wafer 20a: Front side 20b: Back side 21: Ring reinforcement 22: Component 23: Ring wafer 24: Dividing line 25: Small diameter wafer 25a: Outline 100: Modified layer 100A: First release layer 110, 110': Modified layer 110A, 110'A: Second release layer 120: First separation wall 130: Second separation wall 140: Small diameter release layer Figure 1 is an overall perspective view of the laser processing apparatus. Figure 2(a) is a perspective view of an embodiment of the first release layer formation step, and Figure 2(b) is a side view of the embodiment shown in Figure 2(a). Figure 3(a) is a perspective view of an embodiment of the second release layer formation step, and Figure 3(b) is a side view of the embodiment shown in Figure 3(a). Figure 4(a) is a perspective view of an embodiment of the separation wall formation step, and Figure 4(b) is a side view of the embodiment shown in Figure 4(a). Figures 5(a) and 5(b) are perspective views of an embodiment of the alignment mark formation step. Figure 6 is a perspective view of an embodiment of the wafer manufacturing steps of the first embodiment. Figure 7(a) is a perspective view of an embodiment of the second release layer formation step of the second embodiment, and Figure 7(b) is a side view of the embodiment shown in Figure 7(a). Figure 8(a) is a perspective view of an embodiment of the separation wall formation step in the second embodiment, and Figure 8(b) is a side view of the embodiment shown in Figure 8(a). Figure 9 is a perspective view of an embodiment of the wafer fabrication step in the second embodiment. Figure 10 is a perspective view of an embodiment of the small-diameter lift-off layer formation step in the third embodiment. Figure 11 is a perspective view of an embodiment of the wafer fabrication step in the third embodiment. 33: Keep the platform 6: Laser beam irradiation unit 61: Concentrator 10: Crystal rod 10a: Front 12: Orientation flat 13: Large diameter wafers 14: Small diameter wafers 14a:Periphery 14b: Orientation Plane 100A: First peeling layer 110A: Second peeling layer 120: First separation wall LB: Laser Beam P: Location point R1: Arrow

Claims

1. A method for manufacturing a wafer, comprising: a first release layer forming step, wherein a laser beam of a wavelength having penetrability to a crystal ingot is positioned from the end face of the crystal ingot at a first depth for forming a large-diameter wafer to be manufactured and irradiated to form a first release layer; a second release layer forming step, wherein a laser beam of a wavelength having penetrability to a crystal ingot is positioned from the end face of the crystal ingot at a second depth smaller than the diameter of the crystal ingot and shallower than the first depth and irradiated to form a second release layer for manufacturing a small-diameter wafer; a separation wall forming step, wherein a laser beam of a laser beam is positioned at an annular region extending from the end face of the crystal ingot to the second release layer and irradiated to form an annular first separation wall corresponding to the outer periphery of the small-diameter wafer; and a wafer manufacturing step, wherein the large-diameter wafer is peeled off from the first release layer and separated from the second release layer and the first separation wall to manufacture the small-diameter wafer.

2. A method for manufacturing a wafer as described in claim 1, wherein, In the second release layer formation step, the second release layer is also formed in a region that is larger than the diameter of the small-diameter wafer to be manufactured and corresponds to the inner side of the annular reinforcement formed on the outer periphery of the large-diameter wafer to be manufactured. In the separation wall formation step, in addition to forming the first separation wall, an annular second separation wall is also formed along the inner periphery of the annular reinforcement. In the wafer manufacturing step, an annular wafer is also manufactured in the region sandwiched between the small-diameter wafer and the annular reinforcement.

3. A method for manufacturing a wafer as described in claim 1 or 2, wherein, This small-diameter wafer has a standardized diameter.

4. The wafer manufacturing method as described in claim 2, wherein, The ring-shaped wafer was discarded after it was manufactured.

5. A method for manufacturing a wafer as described in claim 1, wherein, Further comprising: a first alignment mark forming step, which forms, before or after the first release layer forming step, a first alignment mark required for forming circuits on the large-diameter wafer to be manufactured, inside or outside the large-diameter wafer to be manufactured; and a second alignment mark forming step, which forms, before or after the second release layer forming step, a second alignment mark required for forming circuits on the small-diameter wafer to be manufactured, inside or outside the small-diameter wafer to be manufactured.

6. A method for manufacturing a wafer, comprising: a small-diameter release layer forming step, wherein a laser beam of a wavelength with penetrability to a large-diameter wafer having multiple elements formed on its front side is positioned from the back side of the large-diameter wafer at a depth equivalent to the thickness of the small-diameter wafer to be manufactured, and irradiated to form a small-diameter release layer in a region of the small-diameter wafer; a small-diameter separation wall forming step, wherein a laser beam of a focal point is positioned in an annular region extending from the back side of the large-diameter wafer to the small-diameter release layer and irradiated to form an annular small-diameter separation wall corresponding to the outer diameter of the small-diameter wafer; and a small-diameter wafer manufacturing step, wherein the small-diameter wafer is manufactured from the small-diameter release layer and the small-diameter separation wall, wherein... In the small-diameter release layer formation step, the small-diameter release layer is also formed in a region that is larger than the diameter of the small-diameter wafer to be manufactured and corresponds to the inner side of the annular reinforcement formed on the outer periphery of the large-diameter wafer. In the small-diameter separation wall formation step, in addition to the outer periphery corresponding to the small-diameter wafer, an annular small-diameter separation wall is also formed on the inner periphery corresponding to the annular reinforcement. In the small-diameter wafer manufacturing step, in addition to manufacturing the small-diameter wafer, an annular wafer sandwiched between the small-diameter wafer and the annular reinforcement is also manufactured.

7. The wafer manufacturing method as described in claim 6, wherein, The ring-shaped wafer was discarded after it was manufactured.

8. A method for manufacturing a wafer as described in claim 6, wherein, It further includes: an alignment mark forming step, which forms alignment marks required for forming circuits on the small diameter wafer, either inside or outside the small diameter wafer to be manufactured, before or after the small diameter stripper layer forming step.

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