Wafer manufacturing method

Abstract

The present invention provides a wafer manufacturing method that allows for the reliable formation of a separation layer in the outer peripheral region of the workpiece, capable of discharging gases generated inside the workpiece during laser processing, while simultaneously reducing the power of the irradiated laser beam. [Solution] The wafer manufacturing method comprises a holding step S1 in which an ingot 11 which is a nitride or oxide semiconductor is held; a first separation layer formation step S2 in which a laser beam is irradiated onto the outer peripheral region A1 of the ingot 11 to form a separation layer 15; a second separation layer formation step S3 in which a laser beam is irradiated onto the inner region A2 of the ingot 11 after the first separation layer formation step S2 to form a separation layer 15; 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. In the first separation layer formation step S2, a laser beam is irradiated such that the output at the outer position in the outer peripheral region A1 is higher than the output at the inner position.

Description

Technical Field

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

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 gallium nitride (GaN) ingot to form a modified layer and a separation layer including cracks extending from the modified layer inside the ingot, and then a plate-like object is peeled off from the ingot to generate a wafer.

[0003] I When performing laser processing on a GaN ingot, the bond between gallium atoms and nitrogen atoms is broken, and nitrogen gas is generated inside the ingot. Due to this nitrogen gas, abnormal volume expansion occurs inside the ingot in the radial direction inside the separation layer, and the ingot may be damaged. In Patent Document 1, a method of forming a discharge port for nitrogen gas by irradiating a laser beam to the outer peripheral region of the ingot to form a separation layer exposed at the outermost peripheral edge of the ingot is described.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In order to surely form a separation layer exposed at the outermost peripheral edge of the workpiece, it is necessary to irradiate a high-power laser beam. Then, the load on the manufactured wafer increases, and problems such as processing defects and an increase in material loss occur.

[0006] The present invention provides a wafer manufacturing method that allows for the reliable formation of a separation layer in the outer peripheral region of a workpiece, capable of discharging gases generated inside the workpiece during laser processing, while simultaneously reducing the power of the irradiated laser beam. [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 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 involves irradiating the outer peripheral region of the workpiece with the laser beam such that the output at the outer position in the outer peripheral region of the workpiece is higher than the output at the inner 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 irradiated laser beam. [Brief explanation of the drawing]

[0009] [Figure 1]Figure 1 is a perspective view showing a laser processing apparatus. [Figure 2] Figure 2 is a diagram illustrating the laser beam irradiation mechanism. [Figure 3] Figure 3 illustrates a modified example of a laser beam irradiation mechanism. [Figure 4] Figure 4 is an example of a flowchart for a wafer manufacturing method. [Figure 5] Figure 5 is a top view of an ingot, showing an example of a separation layer formed in the outer peripheral region of the ingot during the first separation layer formation step, indicated by a dashed line. [Figure 6] Figure 6 shows an example of laser processing by the first separation layer formation step. [Figure 7] Figure 7 shows a first modified example of laser processing by the first separation layer formation step. [Figure 8] Figure 8 shows a second modified example of laser processing using the first separation layer formation step. [Figure 9] Figure 9 is a photograph of the outer periphery of an ingot when a laser beam is irradiated such that the output at the inner position in the outer periphery of the ingot is lower than the output at the outer position. [Figure 10] Figure 10 is a photograph of the outer region of an ingot when a high-power laser beam is uniformly irradiated onto the outer region. [Figure 11] Figure 11 illustrates the second separation layer formation step. [Figure 12] Figure 12 is a diagram illustrating the separation step. [Modes for carrying out the invention]

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

[0011] [Laser processing equipment] FIG. 1 is a perspective view showing a 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 that controls 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 including 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. 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 including a ball screw 62 and a pulse motor 64.

[0015] On the second slide block 6, a holding table 10 is mounted. 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 the column 12.

[0017] Figure 2 is a diagram illustrating the laser beam irradiation mechanism 8. As shown in Figures 1 and 2, the laser beam irradiation mechanism 8 comprises 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, 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 output adjustment unit 81 adjusts the output of the laser beam to a predetermined power. The adjusted laser beam is reflected by the mirror 87 of the concentrator 84, and then the focusing point is positioned by the focusing lens 88 and irradiated into the ingot 11 (an example of a workpiece) fixed to the holding table 10.

[0020] The ingot 11 is formed from a nitride or oxide semiconductor material, such as gallium nitride, gallium oxide, or silicon nitride. 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 surface to which the laser beam is irradiated.

[0021] The control unit 14 controls each of the above-described components of 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 a processor such as a CPU (Central Processing Unit). The storage unit has memory such as an HDD (Hard Disk Drive), ROM (Read Only Memory), and 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 each of the above-described components via the input / output interface according to the calculation results, thereby controlling each of the components of the laser processing apparatus 1.

[0022] As shown in Figure 2, the laser processing apparatus 1 forms a separation layer 15 inside the ingot 11, which 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 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] Note that the laser beam irradiation mechanism 8 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 beam shaping unit 83 in addition to the laser oscillator 80 and the output adjustment unit 81.

[0024] The beam shaping unit 83 can, for example, branch the laser beam into multiple beams in a predetermined direction at predetermined intervals, as shown in the figure, or shape the laser beam so that the focal point extends in a predetermined direction (for example, an elliptical shape). This makes it possible to enlarge the modified region and the region where cracks are formed with a single laser beam irradiation.

[0025] [Wafer manufacturing method] Next, an embodiment of the wafer manufacturing method of the present invention will be described.

[0026] Figure 4 is a flowchart of one embodiment of a wafer manufacturing method. The wafer manufacturing method 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 laser beam is irradiated onto the outer peripheral region A1 of the ingot 11 to form a separation layer 15; a second separation layer formation step S3 in which, after the first separation layer formation step S2, a laser beam is irradiated onto the inner region A2 of the ingot 11 to form a separation layer 15; and a separation step S4 in which a plate-like material is separated from the ingot 11 as a wafer W, starting from the separation layer 15 formed by the first separation layer formation step S2 and the second separation layer formation step S3. Each of these steps is performed by a control unit 14.

[0027] (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.

[0028] (First separation layer formation step) As mentioned above, since the ingot 11 is made of a nitride or oxide semiconductor material, when laser processing is performed by the laser processing device 1, 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 ingot 11 will be damaged during laser processing.

[0029] To prevent damage caused by this gas expansion, as shown in Figure 5, the first separation layer formation step S2 first irradiates the outer peripheral region A1 of the ingot 11 with a laser beam to form a separation layer 15 (dashed line) exposed on the outermost edge 11c of the ingot 11. Here, the outer peripheral region A1 of the ingot 11 is the region from the outermost edge 11c of the ingot 11 to a predetermined distance (for example, about 100 μm to 200 μm) inward. The outermost edge 11c of the ingot 11 is the side surface of the ingot 11.

[0030] More specifically, in the first separation layer formation step S2, a pulsed laser beam having a wavelength that penetrates the ingot 11 is positioned at a predetermined depth from the surface 11a and irradiated onto the outer peripheral region A1 of the ingot 11 held in the holding step S1, thereby forming a separation layer 15 on the outer peripheral region A1 of the ingot 11.

[0031] This allows for the formation of a separation layer 15 exposed on the outermost edge 11c of the ingot 11, i.e., a gas outlet, which enables the discharge of gas generated inside the ingot 11.

[0032] By the way, in order to reliably form the separation layer 15 exposed on the outermost edge 11c, it is necessary to irradiate it with a high-power laser beam. However, if a high-power laser beam is irradiated all over the outer peripheral region A1 of the ingot 11, the load on the manufactured wafer W will increase, leading to problems such as processing defects and increased material loss.

[0033] Therefore, in the first separation layer formation step S2, the output adjustment unit 81 of the laser beam irradiation mechanism 8 adjusts the output of the laser beam irradiated onto the outer peripheral region A1 of the ingot 11 so that it differs between the outer and inner positions in the outer peripheral region A1. Specifically, in the first separation layer formation step S2, the laser beam is irradiated onto the outer peripheral region A1 such that the output at the outer position in the outer peripheral region A1 is higher than the output at the inner position. The outer position of the outer peripheral region A1 is a position close to the outermost edge 11c of the ingot 11, and the inner position is a position closer to the inner region A2 of the ingot 11 than the outer position.

[0034] Figure 6 shows an example of laser processing performed in the first separation layer formation step S2. Figure 6 shows an enlarged view of a portion of the outer peripheral region A1 of the ingot 11. In Figure 6, the separation layer 15 is simplified and shown with a dashed line (the same applies to Figures 7 and 8, which will be described later).

[0035] In the example shown in Figure 6, the first separation layer formation step S2 forms the separation layer 15 by sequentially irradiating the laser beam from the inner position to the outer position of the outer peripheral region A1. Specifically, the first separation layer formation step S2 positions the focal point of the laser beam at position P1, which is included in the inner position of the outer peripheral region A1, and repeatedly irradiates the ingot 11 along its circumferential direction. Subsequently, the first separation layer formation step S2 similarly irradiates positions P2 to P5 in the outer peripheral region A1 with the laser beam while varying the output. Alternatively, the first separation layer formation step S2 may form the separation layer 15 by sequentially irradiating the laser beam from the outer position to the inner position, in the opposite direction to the example in Figure 6.

[0036] The first separation layer formation step S2 increases the output of the laser beam from the inner position to the outer position in the outer peripheral region A1 of the ingot 11, for example, in a linear relationship. For example, if the output of the laser beam at position P5 is 100%, the outputs at positions P1 to P5 are set to 20%, 40%, 60%, 80%, and 100%, respectively.

[0037] The mode of change in the laser beam output from the inner position to the outer position is not limited to a linear increase in output, but may also be a nonlinear gradual increase in output (e.g., 10%, 20%, 35%, 60%, 100%) or a stepwise increase in output (e.g., 20%, 20%, 60%, 60%, 100%).

[0038] Thus, in the first separation layer formation step S2, the laser beam is irradiated such that the output at the outer position in the outer peripheral region A1 is higher than the output at the inner position, so that the separation layer 15 exposed on the outermost edge 11c of the ingot 11 can be reliably formed. Furthermore, in the first separation layer formation step S2, the output of the laser beam at the inner position in the outer peripheral region A1 of the ingot 11 is lower than that at the outer position. Therefore, compared to the case where a high-power laser beam is uniformly irradiated onto the outer peripheral region A1, the laser beam output can be reduced, and processing defects due to excessive output can be suppressed.

[0039] Here, it is preferable that the output of the laser beam irradiated to the inner position in the outer peripheral region A1 in the first separation layer formation step S2 is close to the output of the laser beam irradiated to the inner region A2 in the second separation layer formation step S3.

[0040] Specifically, it is preferable that the output of the laser beam irradiated to the inner position in the outer peripheral region A1 in the first separation layer formation step S2 is equal to the output of the laser beam irradiated to the inner region A2 in the second separation layer formation step S3. The output in the inner region A2 does not need to be as high as the output in the outer peripheral region A1, and by making the output at the inner position in the outer peripheral region A1 (specifically position P1) equal to the output in the inner region A2, the output of the laser beam can be reduced. Furthermore, the boundary between the outer peripheral region A1 and the inner region A2 of the ingot 11 can be processed well.

[0041] Furthermore, the output of the laser beam irradiated to the inner position in the outer region A1 during the first separation layer formation step S2 may be less than the output of the laser beam irradiated to the inner region A2 during the second separation layer formation step S3. This also produces the same effects as described above.

[0042] Figure 7 shows a first modified example of laser processing by the first separation layer formation step S2. Figure 7(a) is a schematic diagram of the laser processing of the ingot 11 viewed from the side, and Figure 7(b) is an enlarged view of a part of the outer peripheral region A1 of the ingot 11. In the first modified example, laser processing is performed using the modified laser beam irradiation mechanism 8 shown in Figure 3.

[0043] In the first modified example, the focal point of the laser beam irradiated in the first separation layer formation step S2 has a shape (for example, an elliptical shape) that extends in the direction from the inner position to the outer position in the outer peripheral region A1 of the ingot 11. The first separation layer formation step S2 repeatedly irradiates the ingot 11 along the circumferential direction with this laser beam.

[0044] In the first modified example, the first separation layer formation step S2 involves irradiating the outer peripheral region A1 with a laser beam such that the output at the outer position in the outer peripheral region A1 is higher than the output at the inner position. The manner in which the output of the laser beam changes from the inner position to the outer position can be in various ways, as in the embodiments described above.

[0045] According to the first modified example, a single laser beam irradiation allows for laser processing from the inner position to the outer position in the outer peripheral region A1 of the ingot 11.

[0046] Figure 8 shows a second modified example of laser processing by the first separation layer formation step S2. Figure 8(a) is a schematic diagram of the laser processing of the ingot 11 viewed from the side, and Figure 8(b) is an enlarged view of a part of the outer peripheral region A1 of the ingot 11. In the second modified example as well, laser processing is performed using the modified laser beam irradiation mechanism 8 shown in Figure 3.

[0047] In the second modified example, the focal point of the laser beam irradiated in the first separation layer formation step S2 is branched into multiple points in the direction from the inner position to the outer position in the outer peripheral region A1 of the ingot 11. The first separation layer formation step S2 repeatedly irradiates the ingot 11 along its circumferential direction with this laser beam.

[0048] In the second modified example, the first separation layer formation step S2 irradiates the outer peripheral region A1 with a laser beam such that the output at the outer position in the outer peripheral region A1 is higher than the output at the inner position. The manner in which the output of the laser beam changes from the inner position to the outer position can be in various ways, as in the embodiments described above.

[0049] According to the second modified example, a single laser beam irradiation allows for laser processing from the inner position to the outer position in the outer peripheral region A1 of the ingot 11.

[0050] Next, referring to Figures 9 and 10, we will explain the experimental results for the case where the laser beam is irradiated such that the output at the inner position in the outer peripheral region A1 of the ingot 11 is lower than the output at the outer position (Figure 9), and the case where a high-power laser beam is uniformly irradiated onto the outer peripheral region A1 (Figure 10).

[0051] In all experiments, a GaN ingot 11 was used. In all experiments, a laser processing apparatus 1 equipped with the modified laser beam irradiation mechanism 8 described above was used, and laser processing was performed by splitting the laser beam's focusing point into multiple points (in this case, 10 branches) as in the second modified example described above.

[0052] In the experimental example shown in Figure 9, the output of the laser beam at the outermost focusing position was set to 100%, and the output at the innermost focusing position was set to 10%, with the output being increased linearly by 10% in increments from there outward. As shown in Figure 9, it can be seen that a separation layer 15 is uniformly formed in the outer peripheral region A1 of the ingot 11 from the outer position to the inner position.

[0053] In the experimental example shown in Figure 10, a region of processing defects is formed near the inner position of the outer peripheral region A1. This is presumed to be due to excessive output from the irradiated laser beam, which caused abnormal cracks. Furthermore, it is observed that the separation layer 15 is not sufficiently formed at the outer position of the outer peripheral region A1.

[0054] Thus, in the first separation layer formation step S2, by irradiating the laser beam such that the output at the outer position in the outer peripheral region A1 is higher than the output at the inner position, the separation layer 15 exposed on the outermost edge 11c of the ingot 11 can be reliably formed, and processing defects can be suppressed.

[0055] (Second separation layer formation step) Figure 11 illustrates the second separation layer formation step S3. In the second separation layer formation step S3, a separation layer 15 is formed in the inner region A2 of the ingot 11 after the first separation layer formation step S2.

[0056] More specifically, in the second separation layer formation step S3, after the first separation layer formation step S2, the laser beam is irradiated onto the inner region A2 of the ingot 11 with the laser beam focusing point positioned at a predetermined depth from the surface 11a of the ingot 11, thereby forming a separation layer 15 in the inner region A2. For example, in the second separation layer formation step S3, the ingot 11 is processed and fed so that the focusing 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 processed and fed so that the focusing 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, and this process is repeated. As a result, a separation layer 15 is formed inside the ingot 11.

[0057] 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 of the ingot 11 in the outer peripheral region A1. Therefore, damage to the ingot 11 due to abnormal volume expansion of the gas during laser processing can be suppressed.

[0058] (Separation step) Figure 12 illustrates the separation step S4. Figure 12(a) shows the state in which ultrasound is being applied to the ingot 11, and Figure 12(b) shows the state in which the wafer W is being separated from the ingot 11.

[0059] 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 from the ingot 11, and a moving mechanism 100 that moves the ultrasonic oscillation unit 91 and the separation unit 96 in a horizontal direction.

[0060] 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.

[0061] 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 includes ball screws connected to the moving pieces 110 and 120, and a motor that rotates the ball screws.

[0062] The ultrasonic oscillation unit 91 includes an ultrasonic transducer 92 that 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 ultrasonic transducer 92, a transducer lifting mechanism 94 that adjusts the vertical position of the ultrasonic transducer 92, and a nozzle lifting mechanism 95 that adjusts 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, or ball screws and motors, etc.

[0063] The ultrasonic transducer 92 has an end face 92a facing the surface 11a of the ingot 11. The ultrasonic transducer 92 is positioned by the transducer lifting mechanism 94 so that a small gap is created between the end face 92a and the surface 11a of the ingot 11.

[0064] 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.

[0065] 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 for adjusting the vertical position of the suction pad 97. The pad lifting mechanism 98 may be composed of an air cylinder, or a ball screw and motor, etc.

[0066] 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.

[0067] 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.

[0068] As described above, in the wafer manufacturing method of this embodiment, the laser beam irradiated when forming the separation layer 15 in the outer peripheral region A1 of the ingot 11 can be reduced in power. This makes it possible to suppress processing defects of the ingot 11 in the first separation layer formation step S2, and as a result, the quality of the manufactured wafer W can be improved.

[0069] Although one embodiment of the present invention has been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to this embodiment. 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 embodiment may be combined in any way without departing from the spirit of the invention.

[0070] 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.

[0071] 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.

[0072] (1) A method for manufacturing a wafer (wafer W) that is thinner than a workpiece (ingot 11, wafer W) which is a semiconductor of nitride or oxide, A holding step (holding step S1) for holding the workpiece, A first separation layer formation step (first separation layer formation step S2) is performed by irradiating the outer peripheral region (outer peripheral region A1) of the workpiece held in the holding step with a pulsed laser beam having a wavelength that penetrates the workpiece, with the focal point of the laser beam positioned at a predetermined depth from the surface, thereby forming a separation layer (separation layer 15) in 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 (inner region A2) of the workpiece that is inside the outer peripheral region, 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 involves irradiating the outer peripheral region of the workpiece with the laser beam such that the output at the outer position in the outer peripheral region of the workpiece is higher than the output at the inner position. A method for manufacturing wafers.

[0073] According to (1), the first separation layer formation step irradiates the laser beam such that the output at the outer position in the outer peripheral region of the workpiece is higher than the output at the inner position, thereby reliably forming a separation layer exposed at the outermost edge of the workpiece and allowing gas generated inside the workpiece to be discharged to the outside. In addition, since the output of the laser beam in the first separation layer formation step is lower at the inner position in the outer peripheral region of the workpiece than at the outer position, the laser beam can be reduced in power, thereby suppressing processing defects due to excessive power.

[0074] (2) A method for manufacturing a wafer as described in (1), The output of the laser beam irradiated to the inner position in the outer peripheral region in the first separation layer formation step is equal to or less than the output of the laser beam irradiated to the inner region in the second separation layer formation step. A method for manufacturing wafers.

[0075] According to (2), the output of the laser beam irradiated to the inner position in the outer peripheral region of the workpiece can be reduced. In addition, the boundary between the outer peripheral region and the inner region of the workpiece can be processed smoothly.

[0076] (3) A method for manufacturing a wafer as described in (1) or (2), The focal point of the laser beam irradiated in the first separation layer formation step has a shape that extends in the direction from the inner position toward the outer position. A method for manufacturing wafers.

[0077] According to (3), a single laser beam irradiation allows for laser processing from the inner position to the outer position in the outer peripheral region of the workpiece.

[0078] (4) A method for manufacturing a wafer as described in (1) or (2), The focal point of the laser beam irradiated in the first separation layer formation step is divided into multiple points in the direction from the inner position toward the outer position. A method for manufacturing wafers.

[0079] According to (4), a single laser beam irradiation allows for laser processing from the inner position to the outer position in the outer peripheral region of the workpiece. [Explanation of Symbols]

[0080] 11. Ingot (workpiece) 15 Separation layer A1 Outer perimeter area A2 inner area S1 Holding step S2 First separation layer formation step S3 Second separation layer formation step S4 Separation Step W wafer

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 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 separation step includes separating a plate-like object 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 involves irradiating the outer peripheral region of the workpiece with the laser beam such that the output at the outer position in the outer peripheral region of the workpiece is higher than the output at the inner position. A method for manufacturing wafers.

2. A method for manufacturing a wafer according to claim 1, The output of the laser beam irradiated to the inner position in the outer peripheral region in the first separation layer formation step is equal to or less than the output of the laser beam irradiated to the inner region in the second separation layer formation step. A method for manufacturing wafers.

3. A method for manufacturing a wafer according to claim 1 or 2, The focal point of the laser beam irradiated in the first separation layer formation step has a shape that extends in the direction from the inner position toward the outer position. A method for manufacturing wafers.

4. A method for manufacturing a wafer according to claim 1 or 2, The focal point of the laser beam irradiated in the first separation layer formation step is divided into multiple points in the direction from the inner position toward the outer position. A method for manufacturing wafers.

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