Wafer manufacturing method

Abstract

The present invention provides a wafer manufacturing method that reliably forms a separation layer capable of discharging gas generated inside the workpiece in the outer peripheral region of the workpiece, while reducing the power of the laser beam irradiated during the formation of the separation layer. [Solution] A wafer manufacturing method comprises a holding step S1 of holding an ingot 11; a first separation layer formation step S2 of forming a separation layer 15 in the outer peripheral region of the ingot 11 by irradiating the outer peripheral region of the ingot 11 with a laser beam; a second separation layer formation step S3 of forming a separation layer 15 in the inner region of the ingot 11 by irradiating the inner region of the ingot 11 with a laser beam; and a separation step S4 of separating the wafer W from the ingot 11. The first separation layer formation step S2 includes an inner processing step S21 of forming a separation layer 15 at an inner position in the outer peripheral region, and an outer processing step S22 of forming a separation layer 15 at a position outside the inner position.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a wafer.

Background Art

[0002] As a method for generating a wafer such as a semiconductor, Patent Document 1 describes a method in which a laser beam having a wavelength with permeability is condensed and irradiated from the surface side of a hexagonal single crystal ingot to form a separation starting point including a modified layer inside the ingot and cracks extending from the modified layer, and then a plate-like object is peeled off from the ingot to generate a wafer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When laser processing as described in Patent Document 1 is performed on a nitride or oxide semiconductor ingot, gas may be generated inside the ingot. When this gas expands, the manufactured wafer may be damaged during laser processing.

[0005] Therefore, a method of forming a gas discharge port by first irradiating a laser beam to the outer peripheral region of the ingot to form a separation layer exposed at the outermost peripheral edge (outer peripheral surface) of the ingot during laser processing can be considered. However, in order to surely form the separation layer exposed at the outermost peripheral edge, it is necessary to irradiate a high-power laser beam, and there is a problem that the load on the manufactured wafer is large.

[0006] The present invention provides a wafer manufacturing method that reliably forms a separation layer capable of discharging gas generated inside the workpiece in the outer peripheral region of the workpiece, while reducing the power of the laser beam irradiated during the formation of the separation layer. [Means for solving the problem]

[0007] The present invention A method for manufacturing a wafer, which involves producing a wafer thinner than the workpiece from a workpiece that is a nitride or oxide semiconductor, A holding step for holding the back surface of the workpiece, A first separation layer formation step involves irradiating the outer peripheral region of the workpiece held in the holding step with a pulsed laser beam having a wavelength that penetrates the workpiece, by positioning the focal point of the laser beam at a predetermined depth from the surface, thereby forming a separation layer in the outer peripheral region of the workpiece. A second separation layer formation step is performed, in which, after the first separation layer formation step, the laser beam is irradiated onto an inner region of the workpiece that is inside the outer peripheral region of the workpiece, with the focal point of the laser beam positioned at a predetermined depth from the surface, thereby forming a separation layer in the inner region of the workpiece. The process includes a separation step in which a plate-like object is separated from the workpiece as a wafer, starting from the separation layer formed by the first separation layer formation step and the second separation layer formation step, The first separation layer formation step is, An internal processing step in which the separation layer is formed at a position inside the outermost edge of the outer peripheral region, The process includes, after the internal processing step, an external processing step in which the separation layer is formed at a position outside the internal position. [Effects of the Invention]

[0008] According to the present invention, a separation layer capable of discharging gas generated inside the workpiece during laser processing can be reliably formed in the outer peripheral region of the workpiece, while simultaneously reducing the power output of the laser beam irradiated during the formation of the separation layer. [Brief explanation of the drawing]

[0009] [Figure 1] This is a perspective view showing laser processing apparatus 1. [Figure 2] This is a diagram illustrating the laser beam irradiation mechanism 8 of the laser processing apparatus 1. [Figure 3] This is a diagram illustrating a modified example of the laser beam irradiation mechanism 8. [Figure 4] This is a flowchart illustrating one embodiment of a wafer manufacturing method. [Figure 5] This is a top view of the ingot 11, showing the inner processing line L1 and outer processing line L2, which are formed in the first separation layer formation step S2, with dashed lines. [Figure 6] This figure illustrates the inner processing step S21 and outer processing step S22 of the first separation layer formation step S2. [Figure 7] This figure illustrates the separation layer 15 formed in the outer peripheral region of the ingot 11 by the inner processing step S21 and outer processing step S22 of the first separation layer formation step S2. [Figure 8] This is a diagram illustrating the second separation layer formation step S3. [Figure 9] This is a schematic side view of the separation device 9, showing the state in which ultrasonic waves are being applied to the ingot 11 by the ultrasonic oscillation unit 91. [Figure 10] This is a schematic side view of the separation device 9, showing the state in which the wafer W is separated from the ingot 11 by the separation unit 96. [Figure 11] This figure illustrates a modified example 1 of the first separation layer formation step S2. [Figure 12] This figure illustrates a modified example 2 of the first separation layer formation step S2. [Modes for carrying out the invention]

[0010] Hereinafter, an embodiment of the method for manufacturing a wafer according to the present invention will be described based on the accompanying drawings. First, the laser processing apparatus 1 used in the method for manufacturing a wafer will be described.

[0011] (Laser Processing Apparatus) FIG. 1 is a perspective view showing the laser processing apparatus 1. In the following description, the X-axis direction is one direction in the horizontal plane. The Y-axis direction is a direction orthogonal to the X-axis direction in the horizontal plane. The Z-axis direction is a direction orthogonal to the X-axis direction and the Y-axis direction.

[0012] The laser processing apparatus 1 of the present embodiment includes a base 2, a first slide block 4 mounted on the base 2 so as to be movable in the Y-axis direction, a second slide block 6 mounted above the first slide block 4 so as to be movable in the X-axis direction, a holding table 10 provided on the second slide block 6, a column 12 erected on the base 2, a laser beam irradiation mechanism 8 attached to the column 12, and a control unit 14 for controlling the laser processing apparatus 1.

[0013] The first slide block 4 is configured to be movable along a pair of guide rails 48 in the indexing direction, that is, the Y-axis direction, by an indexing feed mechanism 46 composed of a ball screw 42 and a pulse motor 44.

[0014] Above the first slide block 4, a second slide block 6 is mounted so as to be movable in the X-axis direction. That is, the second slide block 6 is configured to be movable along a pair of guide rails 68 in the processing feed direction, that is, the X-axis direction, by a processing feed mechanism 66 composed of a ball screw 62 and a pulse motor 64.

[0015] A holding table 10 is mounted on the second slide block 6. The holding table 10 is movable in the X-axis direction and the Y-axis direction by the processing feed mechanism 66 and the indexing feed mechanism 46, and is configured to be rotatable by a motor housed in the second slide block 6.

[0016] A column 12 is erected on the base 2, and a laser beam irradiation mechanism 8 is attached to this column 12.

[0017] Figure 2 is a diagram illustrating the laser beam irradiation mechanism 8 of the laser processing apparatus 1. As shown in Figures 1 and 2, the laser beam irradiation mechanism 8 consists of a laser beam generation unit 82 housed in a casing 13 and a light concentrator (laser head) 84 attached to the tip of the casing 13. An imaging unit 86 having a microscope and a camera is attached to the tip of the casing 13 adjacent to the light concentrator 84.

[0018] The laser beam generation unit 82 includes a laser oscillator 80 that emits a YAG laser or a YVO4 laser, and an output adjustment unit 81. Although not specifically shown in the figures, the laser oscillator 80 has a Brewster window, and the laser beam emitted from the laser oscillator 80 is a linearly polarized laser beam.

[0019] The pulsed laser beam, adjusted to a predetermined power by the output adjustment unit 81 of the laser beam generation unit 82, is reflected by the mirror 87 of the concentrator 84, and then the focusing point is positioned by the focusing lens 88 inside the ingot 11, which is an example of a workpiece fixed to the holding table 10, and irradiated.

[0020] The ingot 11 is a nitride or oxide semiconductor, such as a gallium nitride, gallium oxide, or silicon nitride ingot. The ingot 11 is not limited to a single crystal ingot, but may also be a polycrystalline ingot. The ingot 11 has a surface 11a and a back surface 11b opposite to the surface 11a. The surface 11a of the ingot 11 is polished to a mirror finish because it is the irradiation surface for the laser beam. The thickness of the ingot 11 is, for example, 0.35 mm to 100 mm.

[0021] The control unit 14 controls each of the above-mentioned components of the laser processing apparatus 1 to cause the laser processing apparatus 1 to perform various processes on the workpiece. The control unit 14 is a computer that includes a control unit that performs various calculations, a storage unit having a storage medium, and an input / output interface (not shown) that controls the input and output of data to and from the inside and outside of the control unit 14. The control unit includes, for example, a microprocessor such as a CPU (Central Processing Unit). The storage unit has memory such as an HDD (Hard Disk Drive), ROM (Read Only Memory), or RAM (Random Access Memory). The control unit performs various calculations based on a predetermined program stored in the storage unit. The control unit outputs various control signals to the above-mentioned components via the input / output interface according to the calculation results, thereby controlling the laser processing apparatus 1.

[0022] As shown in Figure 2, the laser processing apparatus 1 configured in this way forms a separation layer 15 inside the ingot 11 that includes multiple modified regions and cracks extending from the modified regions. When forming the separation layer 15, the laser processing apparatus 1 positions the focal point of a laser beam having a wavelength that penetrates the ingot 11 held by the holding table 10 (for example, a wavelength of 1064 nm) at a position deeper than the surface 11a of the ingot 11, and forms the modified regions and cracks by focusing and irradiating the laser beam from the surface 11a of the ingot 11.

[0023] The laser beam irradiation mechanism 8 of the laser processing apparatus 1 is not limited to the configuration described above. Figure 3 is a diagram illustrating a modified version of the laser beam irradiation mechanism 8. In the modified version of the laser beam irradiation mechanism 8, the laser beam generation unit 82 further includes a branching unit 83 in addition to the laser oscillator 80 and the output adjustment unit 81. The branching unit 83 branches the laser beam, whose output has been adjusted by the output adjustment unit 81, into multiple beams (for example, 5) at predetermined intervals in a predetermined direction within the XY plane. For example, by branching the laser beam into multiple beams, multiple modified regions and cracks can be formed at once.

[0024] (Wafer manufacturing method) Next, an embodiment of the wafer manufacturing method of the present invention will be described.

[0025] Figure 4 is a flowchart of one embodiment of a method for manufacturing a wafer W. The method for manufacturing a wafer W includes: a holding step S1 in which the back surface 11b of the ingot 11 is held; a first separation layer formation step S2 in which a pulsed laser beam having a wavelength that penetrates the ingot 11 is irradiated onto the outer peripheral region of the ingot 11 held in the holding step S1 by positioning the focal point of the laser beam at a predetermined depth from the surface 11a and irradiating the laser beam; a second separation layer formation step S3 in which, after the first separation layer formation step S2, the laser beam is irradiated onto the inner region of the ingot 11, which is inside the outer peripheral region of the ingot 11, with the focal point of the laser beam positioned at a predetermined depth from the surface 11a, thereby forming a separation layer 15 on the inner region of the ingot 11; and a separation step S4 in which a plate-like object is separated from the ingot 11 as a wafer W, starting from the separation layer 15 formed in the first separation layer formation step S2 and the second separation layer formation step S3. Each of these steps is performed by the control unit 14.

[0026] (Holding step) In the holding step S1, the back surface 11b of the ingot 11 is held by the holding table 10, as shown in Figures 2 and 3.

[0027] (First separation layer formation step) As mentioned above, since the ingot 11 is a nitride or oxide semiconductor, when laser processing is performed using the laser processing apparatus 1, gas (for example, nitrogen gas or oxygen gas) is generated inside the ingot 11 (specifically in the modified region and cracks). If this gas expands, there is a risk that the wafer W being manufactured will be damaged during laser processing.

[0028] Therefore, the first separation layer formation step S2 first irradiates the outer peripheral region of the ingot 11 with a laser beam to form a separation layer 15 exposed at the outermost edge of the ingot 11. This forms a gas outlet at the outermost edge of the ingot 11. Here, the outer peripheral region of the ingot 11 is the region from the outermost edge of the ingot 11 to a position a predetermined distance (for example, about 200 μm) inward from the outermost edge. The outermost edge of the ingot 11 is the side surface 11c of the ingot 11.

[0029] In this embodiment, the first separation layer formation step S2 includes an inner processing step S21 in which the separation layer 15 is formed at a position inside the outermost edge of the outer peripheral region, and an outer processing step S22 in which the separation layer 15 is formed at a position outside the inner position after the inner processing step S21.

[0030] Figure 5 is a top view of the ingot 11, showing the internal processing line L1 where the internal processing step S21 is performed and the external processing line L2 where the external processing step S22 is performed, indicated by dashed lines. Figure 6 is a diagram illustrating the internal processing step S21 and the external processing step S22.

[0031] In the internal processing step S21, a laser beam is irradiated at the position of the internal processing line L1, forming a separation layer 15 along the entire circumference of the outermost edge of the ingot 11 at the position of the internal processing line L1. In the external processing step S22, after the internal processing step S21, a laser beam is irradiated at the position of the external processing line L2, forming a separation layer 15 along the entire circumference of the outermost edge of the ingot 11 at the position of the external processing line L2. The irradiation position of the laser beam is adjusted by control by the control unit 14.

[0032] Figure 7 illustrates the separation layer 15 formed on the outer periphery of the ingot 11 by the internal processing step S21 and the external processing step S22. When the separation layer 15 is formed by irradiating the position of the internal processing line L1 with a laser beam in the internal processing step S21, the gas generated in the separation layer 15 expands. In the external processing step S22, the stress caused by the gas that expanded inside the separation layer 15 of the internal processing line L1 is used to expose the separation layer 15 of the external processing line L2 to the side surface 11c of the ingot 11.

[0033] If the first separation layer formation step S2 includes only the external processing step S22, then in order to reliably form the separation layer 15 exposed on the side surface 11c of the ingot 11, the laser beam irradiated in the first separation layer formation step S2 must be set to a high power, which would place a heavy load on the manufactured wafer W.

[0034] On the other hand, the first separation layer formation step S2 of this embodiment includes an internal processing step S21 and an external processing step S22 performed after the internal processing step S21. When forming the separation layer 15 at the position of the external processing line L2 in the external processing step S22, the stress caused by the expansion of gas generated in the separation layer 15 of the internal processing line L1 is used to expose the separation layer 15 of the external processing line L2 to the side surface 11c of the ingot 11. Therefore, even when irradiating with a laser beam of lower power compared to the laser beam output when the first separation layer formation step S2 includes only the external processing step S22, the separation layer 15 exposed on the side surface 11c of the ingot 11 can be reliably formed, and the gas generated inside the ingot 11 during the formation of the separation layer 15 can be reliably discharged to the outside.

[0035] Incidentally, in the example illustrated in Figures 6 and 7, the laser beam emitted from the laser processing apparatus 1 was not split into multiple beams. However, by using the modified laser processing apparatus 1 shown in Figure 3, the inner processing step S21 and the outer processing step S22 may be performed by splitting the emitted laser beam into multiple beams and irradiating the ingot 11 with them. This makes it possible to increase the processing speed of the inner processing step S21 and the outer processing step S22.

[0036] (Second separation layer formation step) Figure 8 illustrates the second separation layer formation step S3. In the second separation layer formation step S3, after the first separation layer formation step S2, a separation layer 15 is formed in the inner region of the ingot 11, which is inside the outer peripheral region. For example, in the second separation layer formation step S3, the ingot 11 is processed and fed so that the focal point moves from one end to the other along the X-axis direction to form a modified region and cracks along the X-axis direction, and then indexed and fed by a predetermined amount in the Y-axis direction, and then the process of processing and feeding so that the focal point moves from the other end to the one end along the X-axis direction to form a modified region and cracks along the X-axis direction is repeated. As a result, a separation layer 15 is formed inside the ingot 11.

[0037] The gas generated during the second separation layer formation step S3 is discharged to the outside of the ingot 11 from the separation layer 15 exposed on the side surface 11c of the ingot 11 in the outer region.

[0038] (Separation device and separation step) Figures 9 and 10 are schematic side views of the separation device 9. Figure 9 shows the state in which ultrasound is being applied to the ingot 11, and Figure 10 shows the state in which the wafer W is being separated from the ingot 11.

[0039] The separation device 9 includes a cylindrical holding table 90 that holds the ingot 11 with its surface 11a facing upwards, an ultrasonic oscillation unit 91 that applies ultrasonic waves to the ingot 11, a separation unit 96 that separates the wafer W (see Figure 10) from the ingot 11, and a moving mechanism 100 that moves the ultrasonic oscillation unit 91 and the separation unit 96 in the horizontal direction.

[0040] The holding table 90 holds the ingot 11, for example, via an epoxy resin adhesive, or holds the ingot 11 by suction force generated by a suction source (not shown). The holding table 90 is also rotatable about an axis that passes through its radial center and extends vertically.

[0041] The moving mechanism 100 has a rectangular opening 101 that extends horizontally, and a moving piece 110 that supports the ultrasonic oscillation unit 91 and a moving piece 120 that supports the separation unit 96 are provided to move along the opening 101. Although not shown in the figures, the moving mechanism 100 is composed of a ball screw connected to the moving pieces 110 and 120, and a motor that rotates the ball screw.

[0042] As shown in Figure 9, the ultrasonic oscillation unit 91 includes an ultrasonic transducer 92 having an end face 92a facing the surface 11a of the ingot 11 held on the holding table 90, which applies ultrasonic waves to the ingot 11; a liquid supply nozzle 93 that supplies liquid (e.g., pure water) between the surface 11a of the ingot 11 and the end face 92a of the ultrasonic transducer 92; a transducer lifting mechanism 94 extending downward from the lower surface of the movable piece 110 to adjust the vertical position of the ultrasonic transducer 92; and a nozzle lifting mechanism 95 extending downward from the lower surface of the movable piece 110 to adjust the vertical position of the liquid supply nozzle 93. The transducer lifting mechanism 94 and the nozzle lifting mechanism 95 are composed of air cylinders, ball screws and motors, etc. The dashed arrows in Figure 9 indicate the flow of liquid ejected from the liquid supply nozzle 93.

[0043] The ultrasonic transducer 92 is positioned by the transducer lifting mechanism 94 so that a small gap (e.g., 0.6 mm) is created between the end face 92a and the surface 11a of the ingot 11. The ultrasonic waves applied to the ingot 11 have a frequency of, for example, 20 kHz to 50 kHz.

[0044] The liquid supply nozzle 93 continuously supplies liquid into the gap between the end face 92a of the ultrasonic transducer 92 and the surface 11a of the ingot 11 while applying ultrasonic waves to the ingot 11, thereby forming a liquid layer WL. The ultrasonic waves irradiated from the ultrasonic transducer 92 are transmitted to the ingot 11 through the liquid layer WL, causing cracks in the separation layer 15 formed in the ingot 11 to extend. This reduces the strength of the separation layer 15.

[0045] The separation unit 96 includes a suction pad 97 for suction and holding the wafer W to be separated from the ingot 11, and a pad lifting mechanism 98 that extends downward from the lower surface of the movable piece 120 and adjusts the vertical position of the suction pad 97. The pad lifting mechanism 98 is composed of an air cylinder, or a ball screw and motor, etc.

[0046] As shown in Figure 10, after ultrasonic waves are applied to the entire surface 11a of the ingot 11, the moving pieces 110 and 120 move, and the suction pad 97 moves to a position opposite the ingot 11 held on the holding table 90. Then, the separation unit 96 separates the plate-like material including the surface 11a of the ingot 11 as a wafer W by adsorbing the surface 11a of the ingot 11 onto the suction pad 97 and moving the suction pad 97 upward.

[0047] The first separation layer formation step S2, the second separation layer formation step S3, and the separation step S4 described above are repeated to produce multiple wafers W from the ingot 11.

[0048] (Variation 1) Figure 11 is a diagram illustrating a modified example 1 of the first separation layer formation step S2. As shown in Figure 11, in modified example 1 of the first separation layer formation step S2, the inner processing step S21 and the outer processing step S22 are performed consecutively. Specifically, after performing the inner processing step S21, the laser beam irradiation is continued, and the process moves from the end of the inner processing line L1 to the beginning of the outer processing line L2, and the outer processing step S22 is performed immediately. According to this modified example 1, the processing time of the first separation layer formation step S2 can be shortened.

[0049] (Modification 2) Figure 12 is a diagram illustrating a modified example 2 of the first separation layer formation step S2. As shown in Figure 12, in the modified example 2 of the first separation layer formation step S2, the inner processing step S21 and the outer processing step S22 are not performed on the entire circumference at once, but rather the inner processing step S21 and the outer processing step S22 are repeated in multiple steps.

[0050] Specifically, the inner processing line L1 and the outer processing line L2 are divided into multiple sections in the circumferential direction. The laser processing apparatus 1 irradiates a laser beam onto the position of the first divided inner processing line L1_1 to form a separation layer 15 along the divided inner processing line L1_1 ((1) Inner processing step S21). Subsequently, the laser processing apparatus 1 irradiates a laser beam onto the position of the divided outer processing line L2_1, which is parallel to the outer circumference of the divided inner processing line L1_1, to form a separation layer 15 along the divided outer processing line L2_1 ((2) Outer processing step S22). Subsequently, the laser processing apparatus 1 irradiates a laser beam onto the position of the divided inner processing line L1_2, which is adjacent to the first processed divided inner processing line L1_1, to form a separation layer 15 along the divided inner processing line L1_2 ((3) Inner processing step S21). Thereafter, the outer processing step S22 and the inner processing step S21 are repeated for circumferentially adjacent processing lines. Even with this modified example 2, the same effects as the above-described embodiment and modified example 1 can be obtained.

[0051] Although one embodiment of the present invention and its modifications have been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to these embodiments. It is clear to those skilled in the art that various modifications or alterations can be conceived within the scope of the claims, and these are also understood to naturally fall within the technical scope of the present invention. Furthermore, the components of the above embodiments may be combined in any way without departing from the spirit of the invention.

[0052] For example, the wafer manufacturing method of the embodiment described above was explained using the case where the workpiece is an ingot 11 as an example, but it is not limited to this, and for example the workpiece may be a wafer W. That is, by performing the wafer manufacturing method of the embodiment described above on a single wafer W, a single wafer W may be further divided into multiple wafers.

[0053] This specification includes at least the following: The components and other elements corresponding to those in the embodiments described above are shown in parentheses as examples, but are not limited thereto.

[0054] (1) A method for manufacturing a wafer (wafer W) that is thinner than a workpiece (ingot 11) which is a semiconductor of nitride or oxide, A holding step (holding step S1) for holding the back surface (back surface 11b) of the workpiece, A first separation layer formation step (first separation layer formation step S2) is performed by irradiating the outer peripheral region of the workpiece held in the holding step with a pulsed laser beam having a wavelength that penetrates the workpiece, with the focal point positioned at a predetermined depth from the surface (surface 11a) and the laser beam irradiated, thereby forming a separation layer (separation layer 15) on the outer peripheral region of the workpiece. After the first separation layer formation step, a second separation layer formation step (second separation layer formation step S3) is performed, in which the laser beam is irradiated onto an inner region of the workpiece that is inside the outer peripheral region of the workpiece, with the focal point of the laser beam positioned at a predetermined depth from the surface, thereby forming a separation layer in the inner region of the workpiece. The process includes a separation step (separation step S4) in which a plate-like object is separated from the workpiece as a wafer, starting from the separation layer formed by the first separation layer formation step and the second separation layer formation step, The first separation layer formation step is, An internal processing step (internal processing step S21) is performed to form the separation layer at a position inside the outermost edge of the outer peripheral region (internal processing line L1, divided internal processing line), The process includes, after the internal processing step, an external processing step (external processing step S22) in which the separation layer is formed at an external position (external processing line L2, divided external processing line) that is external to the internal position, A method for manufacturing wafers.

[0055] According to (1), the first separation layer formation step includes an internal processing step and an external processing step performed after the internal processing step. Therefore, when forming the separation layer in the external processing step, the stress caused by the expansion of gas generated in the internal separation layer can be utilized. Thus, even when irradiated with a low-power laser beam, a separation layer exposed at the outermost edge of the workpiece can be reliably formed, and gas generated inside the workpiece can be reliably discharged to the outside.

[0056] (2) A method for manufacturing a wafer as described in (1), The outer processing step is generated by irradiating the laser beam in the inner processing step, and utilizes the stress caused by the gas that expands inside the separation layer at the inner position to expose the separation layer at the outer position to the side surface (side surface 11c) of the workpiece. A method for manufacturing wafers.

[0057] According to (2), even when irradiated with a low-power laser beam, a separation layer exposed at the outermost edge of the workpiece can be reliably formed, and gas generated inside the workpiece can be discharged to the outside.

[0058] (3) A method for manufacturing a wafer as described in (1) or (2), The internal processing step involves irradiating the internal position (internal processing line L1) with the laser beam, and forming the separation layer at the internal position along the entire circumference of the outermost edge. The outer processing step involves irradiating the outer position (outer processing line L2) with the laser beam after the inner processing step, and forming the separation layer at the outer position along the entire circumference of the outermost edge. A method for manufacturing wafers.

[0059] According to (3), since the separation layer is formed along the entire circumference of the outermost edge in the inner processing step before the outer processing step is performed, the processing speed of the first separation layer formation step can be increased.

[0060] (4) A method for manufacturing a wafer as described in (3), The internal machining step and the external machining step are performed in succession. A method for manufacturing wafers.

[0061] According to (4), the processing time for the first separation layer formation step can be shortened. [Explanation of Symbols]

[0062] 11. Ingot (workpiece) 11a surface 11b Back side 11c side 15 Separation layer W wafer L1 Internal machining line (internal position in the outer peripheral area) L2 Outside processing line (outside position of outer peripheral area) S1 Holding step S2 First separation layer formation step S21 Inner Machining Step S22 External machining step S3 Second separation layer formation step S4 Separation Step

Claims

1. A method for manufacturing a wafer, which involves producing a wafer thinner than the workpiece from a workpiece that is a nitride or oxide semiconductor, A holding step for holding the back surface of the workpiece, A first separation layer formation step involves irradiating the outer peripheral region of the workpiece, which is held in the holding step, with a pulsed laser beam having a wavelength that penetrates the workpiece, by positioning the focal point of the laser beam at a predetermined depth from the surface, thereby forming a separation layer in the outer peripheral region of the workpiece. A second separation layer formation step is performed, in which, after the first separation layer formation step, the laser beam is irradiated onto an inner region of the workpiece that is inside the outer peripheral region of the workpiece, with the focal point of the laser beam positioned at a predetermined depth from the surface, thereby forming a separation layer in the inner region of the workpiece. The process includes a separation step in which a plate-like object is separated from the workpiece as a wafer, starting from the separation layer formed by the first separation layer formation step and the second separation layer formation step, The first separation layer formation step is, An internal processing step in which the separation layer is formed at a position inside the outermost edge of the outer peripheral region, The process includes, after the internal processing step, an external processing step in which the separation layer is formed at a position outside the internal position, A method for manufacturing wafers.

2. A method for manufacturing a wafer according to claim 1, The outer processing step is generated by irradiating the laser beam in the inner processing step, and utilizes the stress caused by the gas that expands inside the separation layer at the inner position to expose the separation layer at the outer position to the side surface of the workpiece. A method for manufacturing wafers.

3. A method for manufacturing a wafer according to claim 1 or 2, The internal processing step involves irradiating the internal position with the laser beam and forming the separation layer at the internal position along the entire circumference of the outermost edge. The outer processing step involves irradiating the outer position with the laser beam after the inner processing step, thereby forming the separation layer at the outer position along the entire circumference of the outermost edge. A method for manufacturing wafers.

4. A method for manufacturing a wafer according to claim 3, The internal machining step and the external machining step are performed in succession. A method for manufacturing wafers.

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