Wafer generation method

Abstract

To provide a wafer manufacturing method that can efficiently manufacture wafers and can solve such a problem that wafer manufacturing is uneconomical.SOLUTION: A wafer manufacturing method includes: a first peel-off layer forming step of forming a first peel-off layer by applying a laser beam having a wavelength transmittable through an ingot while positioning a focus spot of the laser beam at a first depth from an end face of the ingot for fabricating a larger-diameter wafer to be fabricated; a second peel-off layer forming step of forming a second peel-off layer for fabricating a smaller-diameter wafer by applying the laser beam while positioning the focus spot of the laser beam at a second depth which is smaller than a diameter of the ingot and shallower than the first depth, from the end face of the ingot; a separating wall forming step of forming an annular first separating wall along an outer periphery of the smaller-diameter wafer by applying the laser beam while positioning the focused spot of the laser beam on an annular area extending from the end face of the ingot to the second peel-off layer; and a wafer manufacturing step of manufacturing the wafer by peeling off the larger-diameter wafer from the first peel-off layer and separating the smaller-diameter wafer from the second peel-off layer and the first separating wall.SELECTED DRAWING: Figure 4

Description

Technical Field

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

Background Art

[0002] A plurality of devices such as ICs and LSIs are formed by laminating a functional layer on the surface of a wafer made of silicon, sapphire, etc. and partitioning by a planned division line. Then, the planned division line of the wafer is processed by a cutting device or a laser processing device, and divided into individual device chips, which are used in electrical devices such as mobile phones and personal computers.

[0003] Also, power devices, LEDs, etc. are formed by laminating a functional layer on the surface of a wafer made of SiC and partitioning by a planned division line.

[0004] The wafers on which the above-mentioned devices, power devices, LEDs, etc. are formed are generally generated by slicing an ingot with a wire saw, and the front and back surfaces of the sliced wafer are polished to be finished into a mirror surface (see, for example, Patent Document 1).

[0005] However, when an ingot is cut with a wire saw and the front and back surfaces are polished to generate a wafer, 70 to 80% of the ingot is discarded, which is uneconomical. In particular, SiC has a problem in efficiently generating a wafer because it has a high hardness, is difficult to cut with a wire saw, has poor productivity, and has a high unit price of the ingot.

[0006] Therefore, the applicant has proposed a technique of irradiating a condensing point of a laser beam having a wavelength permeable to SiC inside a SiC ingot, forming a separation layer on a planned cutting surface, and separating the wafer, thereby eliminating waste of the ingot (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0007] [Patent Document 1] Japanese Patent Publication No. 2000-094221 [Patent Document 2] Japanese Patent Publication No. 2016-111143 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, even in the technology described in Patent Document 2 mentioned above, after forming multiple devices on the surface of a wafer produced from an ingot, the back surface of the wafer is ground down to finish it from, for example, a thickness of 800 μm to 50-100 μm. As a result, more than 700 μm of thickness is wasted, and the problem of uneconomical practices remains.

[0009] The present invention has been made in view of the above facts, and its main technical problem is to provide a wafer manufacturing method that can efficiently produce wafers and solve the problem that wafer manufacturing is uneconomical. [Means for solving the problem]

[0010] To solve the above-mentioned main technical problems, the present invention provides a wafer manufacturing method for manufacturing a wafer, comprising: a first delamination layer formation step of positioning the focal point of a laser beam with a wavelength that is transparent to an ingot at a first depth to form a large-diameter wafer to be manufactured from the end face of the ingot and irradiating it to form a first delamination layer; a second delamination layer formation step of positioning the focal point of a laser beam at a second depth smaller than the diameter of the ingot and shallower than the first depth from the end face of the ingot and irradiating it to form a second delamination layer to manufacture a small-diameter wafer; a separation wall formation step of positioning the focal point of a laser beam in an annular region extending from the end face of the ingot to the second delamination layer and irradiating it to form an annular first separation wall corresponding to the outer circumference of the small-diameter wafer; and a wafer manufacturing step of delaminating the large-diameter wafer from the first delamination layer and separating the small-diameter wafer from the second delamination layer and the first separation wall to manufacture the wafer.

[0011] In the second delamination layer formation step, the second delamination layer is formed in a region corresponding to the inside of the annular reinforcing portion formed on the outer peripheral region of the large-diameter wafer to be formed, which is larger than the diameter of the small-diameter wafer to be formed. In the separation wall formation step, in addition to the first separation wall, an annular second separation wall is formed along the inner circumference of the annular reinforcing portion. In the wafer production step, it is preferable to also produce a ring-shaped wafer in the region sandwiched between the small-diameter wafer and the annular reinforcing portion. Furthermore, it is preferable that the small-diameter wafer has a standardized diameter. In addition, the ring-shaped wafer may be discarded.

[0012] The process may include a first alignment mark formation step for forming alignment marks on the inside or outside of a large-diameter wafer to be produced before or after the first delamination layer formation step, which are necessary for forming circuits on the wafer, and a second alignment mark formation step for forming alignment marks on the inside or outside of a small-diameter wafer to be produced before or after the second delamination layer formation step, which are necessary for forming circuits on the wafer,

[0013] Furthermore, according to the present invention, a wafer generation method for generating a wafer comprises: a small diameter delamination layer formation step of positioning a focal point of a laser beam with a wavelength that is transparent to a large diameter wafer on which a plurality of devices are formed on the surface, at a depth corresponding to the thickness of the small diameter wafer to be generated from the back surface of the large diameter wafer, and irradiating it to form a small diameter delamination layer in the region of the small diameter wafer; a small diameter separation wall formation step of positioning a focal point of a laser beam in an annular region reaching from the back surface of the large diameter wafer to the small diameter delamination 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 generation step of generating the small diameter wafer from the small diameter delamination layer and the small diameter separation wall. In the small-diameter peel layer formation process, the small-diameter peel layer is formed in a region corresponding to the inside of the annular reinforcement portion formed in the outer peripheral region of the large-diameter wafer, which is larger than the diameter of the small-diameter wafer to be produced. In the small-diameter separation wall formation process, an annular small-diameter separation wall is formed not only on the outer peripheral region corresponding to the small-diameter wafer, but also on the inner peripheral region corresponding to the annular reinforcement portion. In the small-diameter wafer production process, in addition to the small-diameter wafer, a ring-shaped wafer sandwiched between the small-diameter wafer and the annular reinforcement portion is also produced. A method for generating wafers is provided.

[0014] ApplicableThe ring-shaped wafer may be discarded. Furthermore, the process may include an alignment mark formation step in which alignment marks necessary for forming circuits on the small-diameter wafer to be produced before or after the small-diameter peel layer formation step are formed, either internally or externally. [Effects of the Invention]

[0015] The wafer production method of the present invention comprises: a first delamination layer formation step of positioning the focal point of a laser beam with a wavelength that is transparent to the ingot at a first depth to form a large-diameter wafer to be produced from the end face of the ingot and irradiating it to form a first delamination layer; a second delamination layer formation step of positioning the focal point of a laser beam at a second depth that is smaller than the diameter of the ingot and shallower than the first depth from the end face of the ingot and irradiating it to form a second delamination layer to produce a small-diameter wafer; and from the end face of the ingot The process includes a separation wall formation step, in which a laser beam is focused and irradiated to an annular region reaching the delamination layer to form an annular first separation wall corresponding to the outer circumference of the small-diameter wafer, and a wafer generation step, in which the large-diameter wafer is delaminated from the first delamination layer and the small-diameter wafer is separated from the second delamination layer and the first separation wall. As a result, small-diameter wafers with a smaller diameter than the large-diameter wafer can be produced from the large-diameter wafer produced from the ingot, thus eliminating waste. Furthermore, by performing the same wafer generation method as described above on the region where the small-diameter wafer is produced, it is possible to produce even smaller-diameter wafers, further reducing waste.

[0016] In addition, the method for generating a wafer according to the present invention includes a small-diameter separation layer forming step of positioning the focal point of a laser beam having a wavelength that is transparent to a large-diameter wafer on which a plurality of devices are formed on the surface at a depth corresponding to the thickness of a small-diameter wafer to be generated from the back surface of the large-diameter wafer and irradiating the focal point to form a small-diameter separation layer in the region of the small-diameter wafer; a small-diameter separation wall forming step of positioning the focal point of the laser beam in an annular region reaching the small-diameter separation layer from the back surface of the large-diameter wafer and irradiating the focal point to form an annular small-diameter separation wall corresponding to the outer diameter of the small-diameter wafer; and a small-diameter wafer generating step of generating the small-diameter wafer from the small-diameter separation layer and the small-diameter separation wall. In the small-diameter peel layer formation step, the small-diameter peel layer is formed in a region corresponding to the inside of an annular reinforcing portion formed in the outer peripheral region of a large-diameter wafer, which is larger than the diameter of the small-diameter wafer to be produced. In the small-diameter separation wall formation step, an annular small-diameter separation wall is formed not only on the outer peripheral region corresponding to the small-diameter wafer, but also on the inner peripheral region corresponding to the annular reinforcing portion. In the small-diameter wafer production step, in addition to the small-diameter wafer, a ring-shaped wafer sandwiched between the small-diameter wafer and the annular reinforcing portion is also produced. Since it is configured in this way, it is possible to form a small-diameter separation layer by irradiating a laser beam from the back surface without grinding the back surface of a large-diameter wafer on which a plurality of devices have already been partitioned by a dicing line and formed on the surface, and to generate a small-diameter wafer with a small diameter in a region of the thickness that was supposed to be discarded, thus solving the problem of inefficiency.

Brief Description of the Drawings

[0017] [Figure 1] It is an overall perspective view of a laser processing apparatus. [Figure 2] (a) A perspective view showing an embodiment of the first separation layer forming step, (b) A side view of the embodiment shown in (a). [Figure 3] (a) A perspective view showing an embodiment of the second separation layer forming step, (b) A side view of the embodiment shown in (a). [Figure 4] (a) A perspective view showing an embodiment of the separation wall forming step, (b) A side view of the embodiment shown in (a). [Figure 5] It is a perspective view showing an embodiment of an alignment mark forming step. [Figure 6] It is a perspective view showing an embodiment of a wafer generating step of the first embodiment. [Figure 7] (a) A perspective view showing an embodiment of the second separation layer forming step of the second embodiment, (b) A side view of the embodiment shown in (a). [Figure 8](a) Perspective view showing an embodiment of the separation wall forming step of the second embodiment, and (b) Side view of the embodiment shown in (a). [Figure 9] Perspective view showing an embodiment of the wafer generation step of the second embodiment. [Figure 10] Perspective view showing an embodiment of the small-diameter separation layer forming step of the third embodiment. [Figure 11] Perspective view showing an embodiment of the wafer generation step of the third embodiment.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of a method for generating a wafer configured based on the present invention will be described in detail with reference to the accompanying drawings.

[0019] FIG. 1 shows an overall perspective view of a laser processing apparatus 1 suitable for carrying out the method for generating a wafer of the present embodiment. The laser processing apparatus 1 includes a base 2, holding means 3 disposed on the base 2 for holding a workpiece, moving means 4 for moving the holding means 3 in the X-axis direction and in the Y-axis direction orthogonal to the X-axis direction, laser beam irradiation means 6, and imaging means 7 for performing alignment, and wafer peeling means 8.

[0020] As shown in FIG. 1, the holding means 3 includes a rectangular X-axis direction movable plate 31 mounted on the base 2 so as to be movable in the X-axis direction, a rectangular Y-axis direction movable plate 32 mounted on the X-axis direction movable plate 31 so as to be movable in the Y-axis direction, and a holding table 33 disposed on the Y-axis direction movable plate 32 and configured to be rotatable by including a pulse motor inside. The workpiece processed by the laser processing apparatus 1 shown in FIG. 1 is a SiC ingot 10 shown in FIGS. 1 and 2(a).

[0021] The moving means 4 includes an X-axis moving means 41 that moves the holding table 33 in the X-axis direction and a Y-axis moving means 42 that moves the holding table 33 in the Y-axis direction. The X-axis moving means 41 converts the rotational motion of the motor 43 into linear motion via a ball screw 44 whose end is supported by a bearing block 44a and transmits it to the X-axis movable plate 31, moving the X-axis movable plate 31 in the X-axis direction along a pair of guide rails 2a, 2a arranged on the base 2 along the X-axis direction. The Y-axis moving means 42 converts the rotational motion of the motor 45 into linear motion via a ball screw 46 and transmits it to the Y-axis movable plate 32, moving the Y-axis movable plate 32 in the Y-axis direction along a pair of guide rails 35, 35 arranged on the X-axis movable plate 31 along the Y-axis direction.

[0022] The laser processing apparatus 1 includes a frame 5 consisting of a vertical wall portion 5a erected to the side of the X-axis moving means 41 and Y-axis moving means 42 on the base 2, and a horizontal wall portion 5b extending horizontally from the upper end of the vertical wall portion 5a. The optical system constituting the laser beam irradiation means 6 and the imaging means 7 are housed inside the horizontal wall portion 5b of the frame 5. Details are omitted, but the optical system of the laser beam irradiation means 6 includes an 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 oscillator, and a reflective mirror that converts the optical path of the laser beam LB toward the concentrator 61 equipped with a concentrating lens (not shown). Control means (not shown) control the repetition frequency, spot diameter, and average output of the laser beam LB emitted from the laser beam irradiation means 6, and also control the focal point position of the laser beam LB in a direction perpendicular to the holding surface, which is the upper surface of the holding table 33 (Z-axis direction in the figure).

[0023] The wafer peeling means 8 of this embodiment is disposed on a stationary base 2 and is installed near the end of the guide rails 2a, 2a (on the bearing block 44a side). The wafer peeling means 8 comprises a peeling unit case 81, a peeling unit arm 82 which is partially housed within the peeling unit case 81 and supported to be movable in the Z-axis direction (vertical direction), a peeling pulse motor 83 disposed at the tip of the peeling unit arm 82, and a suction means 84 located below the peeling pulse motor 83 which is rotatably supported by the peeling pulse motor 83 and has a plurality of suction holes on its lower surface. The peeling unit case 81 is equipped with a Z-axis moving means (not shown) for controlling the movement of the peeling unit arm 82 in the Z-axis direction. The peeling unit case 81 is equipped with a Z-axis position detection means (not shown) for detecting the position of the peeling unit arm 82 in the Z-axis direction, and the position signal is sent to the control means described above.

[0024] The control means described above is composed of a computer and includes a central processing unit (CPU) that performs calculations according to a control program, a read-only memory (ROM) for storing the control program and the like, a read-write random access memory (RAM) for temporarily storing detected values, calculation results, etc., and an input interface and an output interface (details are not shown in the illustration). In addition to the laser beam irradiation means 6 described above, the control means is connected to and controls an imaging means 7, an X-axis moving means 41, a Y-axis moving means 42, a wafer peeling means 8, a display means 9, etc.

[0025] The laser processing apparatus 1 described above has a configuration that is generally as described above, and the laser processing method of this embodiment, which is carried out using the laser processing apparatus 1, will be described below.

[0026] First, a first embodiment of the wafer production method of the present invention, which is carried out using the laser processing apparatus 1 described above, will be explained below.

[0027] In carrying out this embodiment, an ingot 10 shown in Figures 1 and 2 is prepared. The ingot 10 is a hexagonal single crystal ingot made of SiC with a diameter of 300 mm. The surface 10a that constitutes the end face of the ingot 10 is polished to a mirror finish by a separate polishing means. From this ingot 10, a large-diameter wafer 13 with a diameter of 300 mm and a small-diameter wafer 14 with a diameter of 200 mm are produced (see also Figure 6). The diameters of the large-diameter wafer 13 and the small-diameter wafer 14 are dimensions specified by SEMI standards (standards established by SEMI (Semiconductor Equipment and Materials International) with the aim of unifying international industrial standards for the semiconductor industry). An orientation flat (hereinafter referred to as "orientation flat") 12 indicating the crystal orientation is formed on the ingot 10.

[0028] Once the above-mentioned ingot 10 is prepared, the ingot 10 is placed on the upper surface of the holding table 33 of the laser processing apparatus 1 and firmly fixed with a bonding agent, wax, etc. Next, the imaging means 7 is used to image the surface 10a of the ingot 10 and perform alignment to detect the height of the surface 10a and the shape of the outer shape 10b of the ingot 10, and the information of the shape of the outer shape 10b and its height is stored in the control means described above.

[0029] Once the shape of the outer shape 10b of the surface 10a of the ingot 10 and the height of the surface 10a are stored in the control means, the holding table 33 is rotated to align the direction indicated by the straight portion of the orientation flat 12 with the X-axis direction, and the holding table 33 is moved in the X-axis direction to position it directly below the concentrator 61 of the laser beam irradiation means 6. Next, as shown in Figures 2(a) and (b), the focal point P of the laser beam LB, which has a wavelength that is transparent to the ingot 10, is positioned at a first depth (for example, 800 μm) from the surface 10a of the ingot 10 to form the large-diameter wafer 13 (see Figure 3(a)) to be generated, and the ingot 10 is irradiated to form the modified layer 100 while the ingot 10 is processed and fed in the X-axis direction. Once the modified layer 100 is formed, the irradiation position of the laser beam LB is advanced by, for example, 400 μm in the Y-axis direction to position the focal point P at the first depth parallel to the previously formed modified layer 100, and the laser beam LB is irradiated while processing in the X-axis direction to form a similar modified layer 100. By repeating these steps, multiple modified layers 100 are formed over the entire surface 10a of the ingot 10, thereby forming the first peel layer 100A. This completes the first peel layer formation step of this embodiment. The laser processing conditions in the first peel layer formation step are, for example, as follows.

[0030] <Laser processing conditions for the first delamination layer formation process> Wavelength: 1064nm Average output: 7~16W Repetition frequency: 30kHz Pulse width: 3ns Machining feed rate: 165 mm / s Defocus: 300 μm (Forms a first delamination layer 100A at a depth of 800 μm from the surface 10a)

[0031] Although details are omitted here, the ingot 10 described above is manufactured to have a c-axis inclined at a predetermined off-angle α in a direction perpendicular to the straight portion of the orientation flat 12, and a c-plane perpendicular to the c-axis. The c-plane is inclined at the off-angle α with respect to the surface 10a of the ingot 10. The off-angle α is, for example, 4°. Then, by carrying out the first delamination layer formation process described above, a crack extends along the c-plane from a predetermined modified layer 100 toward an adjacent modified layer 100, and the modified layer 100 and the crack form the first delamination layer 100A.

[0032] As described above, once the first delamination layer formation step has been carried out, the second delamination layer formation step, which will be described below, is performed.

[0033] In the second delamination layer formation step, as shown in Figure 3, the focal point P of the laser beam LB is positioned and irradiated from the surface 10a constituting the end face of the ingot 10 to a second depth (for example, 700 μm) which is smaller than the diameter of the ingot 10 (300 mm) and shallower than the first depth (800 μm) described above, to form a second delamination layer 110A that generates a small diameter wafer 14.

[0034] In the second delamination layer formation step, the region irradiated by the laser beam LB is defined by the outer circumference 14a, which generates a small-diameter wafer 14 with a diameter of 200 mm, smaller than the large-diameter wafer 13 whose wafer generation region covers the entire end face of the ingot 10, as shown in Figure 3(a). Note that the outer circumference 14a shown in Figure 3(a) is a virtual line and is not actually visible. The position information of the outer circumference 14a is stored in advance in the control means described above. An orientation flat 14b indicating the crystal orientation is also formed on the small-diameter wafer 14, and the outer circumference 14a includes a straight section that forms the orientation flat 14b. The orientation flat 14b is parallel to the orientation flat 12 formed on the ingot 10. In the second delamination layer formation step, based on the position information of the outer circumference 14a stored in the control means, the focuser 61 of the laser beam irradiation means 6 is positioned on the outer circumference 14a on the surface 10a of the ingot 10, and the focal point P of the laser beam LB, which has a wavelength that is transparent to the ingot 10, is positioned at the second depth (700 μm). The modified layer 110 is formed while the ingot 10 is processed and fed in the X-axis direction. The start and end points for forming the modified layer 110 are set on the outer circumference 14a as described above. Once the modified layer 110 is formed, the irradiation position of the laser beam LB is advanced by, for example, 400 μm in the Y-axis direction, and the focal point P is positioned at the second depth parallel to the previously formed modified layer 110. The laser beam LB is then irradiated while the ingot 10 is processed and fed in the X-axis direction to form a modified layer 110 in the same manner as above. These steps are repeated to form the modified layer 110 over the entire area defined by the outer circumference 14a as described above. When forming this modified layer 110, cracks extend between adjacent modified layers 110, similar to the modified layer 100 described above. As a result, as shown in Figure 3(b), a second peeling layer 110A is formed by the modified layer 110 and the cracks, and the second peeling layer formation step of this embodiment is completed. The laser processing conditions in the second peeling layer formation step are, for example, as follows. ru.

[0035] <Laser processing conditions for the second delamination layer formation process> Wavelength: 1064nm Average output: 7~16W Repetition frequency: 30kHz Pulse width: 3ns Machining feed rate: 165 mm / s Defocus: 260 μm (A second delamination layer 110A is formed at a depth of 700 μm from the surface 10a)

[0036] As described above, once the first peeling layer 100A and the second peeling layer 110A have been formed by the first peeling layer formation step and the second peeling layer formation step, the separation wall formation step described below is carried out.

[0037] When performing the separation wall formation process, based on the information of the outer circumference 14a of the small-diameter wafer 14 stored in the control means, as shown in Figures 4(a) and (b), the focal point P of the laser beam LB is positioned and irradiated in the annular region defined by the outer circumference 14a, and the holding table 33 is rotated in the direction indicated by the arrow R1 to form an annular first separation wall 120 along the outer circumference 14a. When forming the first separation wall 120 in the region of the orientation flat 14b on the outer circumference 14a, the rotation of the holding table 33 is stopped and the X-axis moving means 41 is activated to feed the wafer in the X-axis direction, thereby forming a linear first separation wall 120 on the orientation flat 14b. Furthermore, the first separation wall 120 is preferably formed by performing laser processing by changing the depth at which the focal point P of the laser beam LB is positioned multiple times in the vertical direction, thereby forming modified layers at multiple depth positions. In this embodiment, the separation wall formation process is completed by changing the depth from the surface 10a of the focal point P to 500 μm, 375 μm, 250 μm, and 125 μm, forming four modified layers along the outer circumference 14a, thereby forming the first separation wall 120 in an annular region reaching the second peeling layer 110A. The laser processing conditions in the separation wall formation process are, for example, as follows.

[0038] <Laser processing conditions for the separation wall formation process> Wavelength: 1064nm Average output: 7~16W Repetition frequency: 30kHz Pulse width: 3ns Machining feed rate: 165 mm / s Defocus: 200 μm, 150 μm, 100 μm, 50 μm (Modified layers are formed at depths of 500 μm, 375 μm, 250 μm, and 125 μm from surface 10a)

[0039] In the above description, an example was given in which the first delamination layer formation step, the second delamination layer formation step, and the separation wall formation step are carried out in order. However, in the present invention, a first alignment mark formation step may be carried out before or after the first delamination layer formation step to form alignment marks necessary for forming a circuit on the large-diameter wafer 13. As shown in Figure 5(a), the alignment marks are, for example, alignment marks 13a that are formed to specify the X-axis direction and Y-axis direction necessary for forming a circuit on the large-diameter wafer 13 that is separated and generated by the wafer generation step described later, after the first delamination layer 100A has been formed by the first delamination layer formation step described above. As can be seen from Figure 5(a), it is preferable that the alignment marks 13a are formed at two points that specify the X-axis direction and two points that specify the Y-axis direction, and in this embodiment, they are formed at a total of three locations. The alignment mark 13a is formed by creating a modified layer inside the large-diameter wafer 13 using processing conditions similar to the laser processing conditions in the separation wall formation process described above, for example, so as to be in the shape of a "+" in plan view. Furthermore, the alignment mark 13a is formed near the outer shape 10b in the outer peripheral excess area where circuits are not formed, so as not to interfere with the formation of circuits or the like on the large-diameter wafer 13. The first alignment mark formation process of the present invention can be performed before or after the first delamination layer formation process, but it is preferable to perform it after the first delamination layer formation process so as not to interfere with the formation of the first delamination layer 100A. Moreover, the alignment mark 13a formed by the first alignment mark formation process is not limited to the above-described form, and for example, the alignment mark 13a may be formed by positioning the focal point P of the laser beam LB on the surface 10a of the ingot 10 and forming the alignment mark 13a by ablation processing. However, in that case, it is preferable to machine to a depth such that the alignment mark 13a does not disappear due to subsequent grinding and polishing processes.

[0040] Furthermore, a second alignment mark formation step may be performed before or after the second delamination layer formation step to form alignment marks necessary for forming circuits on the small-diameter wafer 14. These alignment marks are, for example, alignment marks 14c (see Figure 5(b)) formed on the small-diameter wafer 14, which is separated and produced by the wafer production step described later, after the second delamination layer 110A is formed by the second delamination layer formation step described above, in order to specify the X-axis direction and Y-axis direction necessary for forming circuits on the small-diameter wafer 14. As shown in Figure 5(b), it is preferable that the alignment marks 14c are formed in a total of three locations, similar to the alignment marks 13a described above, so as to specify the X-axis direction and Y-axis direction. The alignment mark 14c is formed in the interior of the small-diameter wafer 14 using a modified layer, for example, by processing conditions similar to those used in the first alignment mark formation step described above. Similar to the above, it is formed, for example, in the shape of a "+" in plan view. Furthermore, the alignment mark 14c is formed in the outer peripheral excess area where circuits are not formed, so as not to interfere with the formation of circuits on the small-diameter wafer 14. The second alignment mark formation step of the present invention can be performed either before or after the second delamination layer formation step, but it is preferable to perform it after the second delamination layer formation step so as not to interfere with the formation of the second delamination layer 110A. The alignment mark 14c formed by the second alignment mark formation step of the present invention may be formed by ablation processing, similar to the alignment mark 13a described above, by positioning a focusing point P on the surface 10a of the ingot 10. By forming the alignment marks 13a and 14c using the alignment mark formation process described above, which involves irradiating with a laser beam LB, it is not necessary to form the alignment marks by exposure and etching using a separate device, thereby improving productivity.

[0041] As described above, once the first delamination layer formation process, the second delamination layer formation process, the separation wall formation process, the alignment mark formation process, etc., are carried out, the wafer production process described below is performed.

[0042] The wafer production process, as shown in Figure 6, involves peeling off a large-diameter wafer 13 starting from the first peeling layer 100A described above, and separating and producing a small-diameter wafer 14 starting from the second peeling layer 110A and the first separation wall 120 described above. This wafer production process can be carried out, for example, by using the wafer peeling means 8 described with reference to Figure 1. When carrying out the wafer production process, the holding table 33 is moved by operating the moving means 4 of the laser processing apparatus 1 to position the surface 10a of the ingot 10 directly below the adsorption means 84 of the wafer peeling means 8. Next, the adsorption means 84 is lowered together with the peeling unit arm 82 by the Z-axis moving means (not shown) built into the peeling unit case 81 and pressed against the surface 10a of the ingot 10. Next, negative pressure is generated in the suction hole of the adsorption means 84 to adsorb the surface 10a of the ingot 10.

[0043] Once the surface 10a is adsorbed by the adsorption means 84, the adsorption means 84 is rotated by the pulse motor 83 to generate a twist in the first delamination layer 100A, thereby delaminating the large-diameter wafer 13, which is integrated with the small-diameter wafer 14, from the ingot 10. After the large-diameter wafer 13 has been delaminated in this way, the small-diameter wafer 14 is separated and produced from the second delamination layer 110A and the first separation wall 120 using a separate delamination means. As shown in Figure 6, a thinned portion 13a with a thickness of 100 μm is formed in the central region of the large-diameter wafer 13 due to the production of the small-diameter wafer 14. The front and back surfaces of the large-diameter wafer 13 and the small-diameter wafer 14 produced from the ingot 10 are polished to a mirror finish before circuit formation. With this, the wafer production process is completed, and the wafer production method of the present invention is completed.

[0044] According to the first embodiment described above, a small-diameter wafer 14 with a diameter of 200 mm can be produced from a large-diameter wafer 13 with a diameter of 300 mm generated from an ingot 10, thereby eliminating waste. Furthermore, by applying the same wafer production method as described above to the region where the small-diameter wafer 14 is produced, it is possible to produce an even smaller wafer of 150 mm from the small-diameter wafer 14 with a diameter of 200 mm, thereby further reducing waste.

[0045] As shown in Figure 6, when the wafer manufacturing method of this embodiment is carried out to form a large-diameter wafer 13 and a small-diameter wafer 14 from the ingot 10, the surface 10a of the ingot 10 becomes rough. Therefore, when the large-diameter wafer 13 and the small-diameter wafer 14 are produced from the ingot 10 next, the surface 10a of the ingot 10 is polished to a mirror finish using a separate polishing means.

[0046] The present invention is not limited to the first embodiment described above, but may also be the second embodiment described below.

[0047] In the second embodiment, an ingot 10 similar to that of the first embodiment described above is prepared, and as explained with reference to Figure 2, a first delamination layer formation step is performed to form a first delamination layer 100A at a first depth (for example, 800 μm from the surface 10a) for forming the large-diameter wafer 13 to be produced. Next, when performing the second delamination layer formation step described above, as shown in Figure 7(a), laser processing is performed to form a modified layer 110' at a second depth (700 μm) similar to that of the modified layer 110, in the entire region corresponding to the inside of the inner circumference 11a of the annular reinforcement portion 11 formed along the outer peripheral region of the large-diameter wafer 13 to be produced, which is larger than the diameter of the small-diameter wafer 14 to be produced. As a result, a second delamination layer 110'A is formed as shown in Figure 7(b) due to the extension of the modified layer 110' and cracks. Furthermore, the laser processing conditions for forming the second peel layer 110'A are set to the same laser processing conditions as those for forming the modified layer 110 described above.

[0048] If the second delamination layer formation step described above is performed, as shown in Figures 8(a) and (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 circumference 11a of the annular reinforcement portion 11. The second separation wall 130 is formed using the same laser processing conditions and procedures as when the first separation wall 120 was formed. The focusing point P of the laser beam LB is positioned on the inner circumference 11a region of the annular reinforcement portion 11 and irradiated from the surface 10a of the ingot 10 to form an annular second separation wall 130 along the inner circumference 11a.

[0049] Once the first delamination layer formation step, the second delamination layer formation step, and the separation wall formation step according to the second embodiment described above have been performed, the wafer production step is carried out using the wafer delamination means 8 in substantially the same procedure as described in the first embodiment, thereby completing the wafer production method of this embodiment. In this wafer production step, since the second delamination layer formation step and the separation wall formation step described above have been performed, as shown in Figure 9, in addition to the large-diameter wafer 13' and the small-diameter wafer 14 having the annular reinforcing portion 11, a ring-shaped wafer 15 formed in the region sandwiched between the small-diameter wafer 14 and the annular reinforcing portion 11 of the large-diameter wafer 13' is also produced.

[0050] In the second embodiment described above, the large-diameter wafer 13' produced has a thinner portion 13'a that is wider than the thinned portion 13a formed in the first embodiment, achieved by separating the small-diameter wafer 14 and the ring-shaped wafer 15. Furthermore, the thinned portion 13'a of the large-diameter wafer 13' achieves a thickness of 100 μm over a wide area due to the separation of the small-diameter wafer 14 and the ring-shaped wafer 15, and is reinforced by the formation of the annular reinforcement portion 11 described above, making it easier to handle during processing. The ring-shaped wafer 15 formed in this embodiment is discarded.

[0051] Furthermore, a third embodiment relating to a wafer production 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 were produced from an ingot 10. However, according to this third embodiment, it is also possible to produce a small-diameter wafer from a large-diameter wafer 20 on which a plurality of devices 22 shown in Figure 10 are formed on the surface 20a. This third embodiment will be described below.

[0052] First, in carrying out the third embodiment of the present invention, a large-diameter wafer 20 shown on the right side of Figure 10 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 is a wafer on which multiple devices 22 are partitioned by division lines 24 and formed on the surface 20a. An orientation flat 20c indicating the crystal orientation is formed on the large-diameter wafer 20. Once such a large-diameter wafer 20 is prepared, a protective tape T formed to the same dimensions as the large-diameter wafer 20 is attached to the surface 20a to form an integral part. Next, the large-diameter wafer 20 integrated with the protective tape T is inverted so that the back surface 20b faces upward and the protective tape T side faces downward, and placed on the upper surface of the holding table 33 of the laser processing apparatus 1 described above and fixed with adhesive or the like.

[0053] Once the large-diameter wafer 20 is fixed to the holding table 33 described above, a small-diameter peel-off layer formation process is carried out that is substantially the same as the second peel-off layer formation process in the second embodiment, as explained with reference to Figure 7. When carrying out this small-diameter peel-off layer formation process, first, the large-diameter wafer 20 is imaged by the imaging means 7 of the laser processing apparatus 1 to detect the shape of the large-diameter wafer 20 and the height of the back surface 20b. Next, as shown in Figure 10, the wafer 20 is positioned directly below the concentrator 61 of the laser beam irradiation means 6. Then, the focal point P of the laser beam LB, which has a wavelength that is transparent to the SiC constituting the large-diameter wafer 20, is positioned at a depth (for example, 700 μm) corresponding to the thickness of the small-diameter wafer 25 to be generated from the back surface 20b of the large-diameter wafer 20. Then, the laser beam LB is irradiated and the moving means 4 is operated to form a modified layer similar to the modified layer 110 described above in the entire region corresponding to the inside of the inner circumference 21a of the annular reinforcing portion 21, which is formed along the outer peripheral region of the large-diameter wafer 20 and is larger than the diameter of the small-diameter wafer 25 defined by the outer circumference 25a, thereby forming a small-diameter peel layer 140 consisting of the modified layer and elongated cracks. The laser processing conditions when forming the small-diameter peel layer 140 are set to the same laser processing conditions as the second peel layer formation step in which the modified layers 110 and 110' described above are formed.

[0054] After the small-diameter delamination layer formation process described above is performed, the focal point of the laser beam LB is positioned and irradiated to an annular region extending from the back surface 20b of the large-diameter wafer 20 to the small-diameter delamination layer 140, thereby forming a small-diameter separation wall corresponding to the outer circumference 25a of the small-diameter wafer 25. A small-diameter wafer generation process is then performed to generate the small-diameter wafer 25 from the small-diameter delamination layer 140 and the small-diameter separation wall. The small-diameter separation wall formation process is performed using the same laser processing conditions and procedures as the separation wall formation process described based on Figure 4 described above, and the small-diameter separation wall is formed on the outer circumference 25a in the same form as the first separation wall 120 described above. A detailed explanation is omitted.

[0055] Furthermore, in the small-diameter separation wall formation step of this third embodiment, an annular separation wall is also formed in the region corresponding to the inner circumference 21a of the annular reinforcing portion 21. The separation wall formed in the region corresponding to the inner circumference 21a of the annular reinforcing portion 21 is formed by the same laser processing conditions and procedures as the annular second separation wall 130 formed in the separation wall formation step of the second embodiment described above, and a detailed explanation is omitted.

[0056] As described above, once the small-diameter peel layer formation process and the small-diameter separation wall formation process are carried out, the small-diameter wafer production process is carried out in the same procedure as the wafer production process of the first and second embodiments described above, so that as shown in Figure 11, in addition to the large-diameter wafer 20 having an annular reinforcement portion 21 and the small-diameter wafer 25 having an orientation flat 25b, a ring-shaped wafer 23 is also produced, which is formed in the region sandwiched between the small-diameter wafer 25 and the annular reinforcement portion 21 of the large-diameter wafer 20 and has an orientation flat 23a and an opening 23b. As described above, the thickness of the small-diameter wafer 25 is 700 μm, and a thinned portion 20d with a thickness of 100 μm is formed inside the annular reinforcement portion 21 of the large-diameter wafer 20. The ring-shaped wafer 23 formed in this embodiment is discarded.

[0057] Although omitted in the above description, in the third embodiment as well, an alignment mark formation step may be performed before or after the small-diameter peel layer formation step to form alignment marks on the inside or outside of the small-diameter wafer 25, which are necessary for forming circuits. This alignment mark formation step is a step to form alignment marks similar to the alignment marks 14c described based on Figure 5(b) above, and has the same effects as described above, so a detailed explanation is omitted.

[0058] According to the third embodiment described above, a large-diameter wafer 20 with a diameter of 300 mm has already been partitioned by division lines 24 and formed on the surface 20a of the wafer. Without grinding the back surface 20b of the wafer 20 with a diameter of 300 mm, a small-diameter peel layer 140 can be formed by irradiating the back surface 20b with a laser beam to form a small-diameter peel layer 140, and a small-diameter wafer 25 with a diameter of 200 mm can be produced with a thickness of 700 μm that would otherwise be discarded. This eliminates the problem of uneconomical production. Furthermore, by including an alignment mark formation process performed by a laser beam LB as described above, it is not necessary to perform exposure and etching with a separate device to form alignment marks, as described above, thus improving productivity. [Explanation of Symbols]

[0059] 1: Laser processing equipment 2: Base 2a, 2a: Guide rail 3: Holding means 31:X-axis movable plate 32: Y-axis movable plate 33: Holding Table 4: Means of transportation 41:X-axis movement means 42: Y-axis movement means 5:Frame body 6: Laser beam irradiation means 61: Light concentrator 7: Imaging means 8: Wafer peeling method 81: Peeling Unit Case 82: Peeling Unit Arm 83: Pulse motor for stripping 84: Adsorption means 9:Display means 10: Ingot 10a: End surface (top surface) 10b:Outline 11: Ring-shaped reinforcement section 12: Orientation Flat (OriFura) 13: Large diameter wafer 13a: Alignment marks 14: Small diameter wafer 14a: Outer perimeter 14b: Original Flag 14c: Alignment Mark 15: Ring-shaped wafer 20: Large diameter wafer 20a: Surface 20b: Back side 21: Ring-shaped reinforcement section 22: Device 23: Ring-shaped wafer 24: Planned division line 25: Small diameter wafer 25a: External shape 100: Modified layer 100A: First delamination layer 110, 110': Modified layer 110A, 110'A: Second delamination layer 120:First dividing wall 130:Second separation wall 140: Small diameter delamination layer

Claims

1. A method for generating a wafer, A first delamination layer formation step involves positioning the focal point of a laser beam with a wavelength that is transparent to the ingot at a first depth from the end face of the ingot to form a large-diameter wafer, and irradiating it to form a first delamination layer. A second delamination layer formation step involves positioning the focal point of a laser beam at a second depth smaller than the diameter of the ingot and shallower than the first depth from the end face of the ingot, and irradiating it to form a second delamination layer that generates a small-diameter wafer. A separation wall formation step involves positioning the focal point of a laser beam in an annular region extending from the end face of the ingot to the second delamination layer and irradiating it to form an annular first separation wall corresponding to the outer circumference of the small-diameter wafer. A wafer production step in which the large-diameter wafer is peeled off from the first peeling layer and the small-diameter wafer is separated from the second peeling layer and the first separation wall to produce a wafer, A method for generating a wafer comprising the above.

2. The second delamination layer formed in the second delamination layer formation step is also formed in a region corresponding to the inside of the annular reinforcing portion formed in the outer peripheral region of the large-diameter wafer to be formed, which is larger than the diameter of the small-diameter wafer to be formed. In the separation wall formation process, in addition to the first separation wall, a second annular separation wall is formed along the inner circumference of the annular reinforcing portion. The wafer manufacturing method according to claim 1, wherein the wafer manufacturing step also involves manufacturing a ring-shaped wafer in the region sandwiched between the small-diameter wafer and the annular reinforcement portion.

3. The wafer manufacturing method according to claim 1 or 2, wherein the small-diameter wafer has a standardized diameter.

4. The wafer production method according to claim 2, wherein the ring-shaped wafer is discarded.

5. A first alignment mark formation step, which forms alignment marks on the inside or outside of a large-diameter wafer that is to be produced before or after the first delamination layer formation step, which are necessary for forming a circuit on the wafer. A second alignment mark formation step, which involves forming alignment marks on the inside or outside of a small-diameter wafer that is to be produced before or after the second delamination layer formation step, which are necessary for forming a circuit on the wafer. A method for producing a wafer according to claim 1, comprising:

6. A method for generating a wafer, A small-diameter peel layer formation step involves positioning the focal point of a laser beam with a wavelength that is transparent to a large-diameter wafer on which multiple devices are formed on the surface of the large-diameter wafer at a depth corresponding to the thickness of the small-diameter wafer to be generated from the back surface of the large-diameter wafer and irradiating it to form a small-diameter peel layer in the region of the small-diameter wafer, A small-diameter separation wall formation step involves positioning the focal point of a laser beam in an annular region extending from the back surface of the large-diameter wafer to the small-diameter delamination layer and irradiating it to form an annular small-diameter separation wall corresponding to the outer diameter of the small-diameter wafer, A small-diameter wafer production step for generating a small-diameter wafer from the small-diameter peel layer and the small-diameter separation wall, It includes and is composed of, In the small-diameter peel layer formation process, the small-diameter peel layer is also formed in a region corresponding to the inside of the annular reinforcement portion formed in the outer peripheral region of the large-diameter wafer, which is larger than the diameter of the small-diameter wafer to be produced. In the small-diameter separation wall formation process, an annular small-diameter separation wall is formed not only on the outer circumference corresponding to the small-diameter wafer, but also on the inner circumference corresponding to the annular reinforcement portion. A wafer manufacturing method comprising the process of manufacturing a small-diameter wafer, wherein in addition to the small-diameter wafer, a ring-shaped wafer sandwiched between the small-diameter wafer and the annular reinforcing portion is also manufactured.

7. The method for producing a wafer according to claim 6, wherein the ring-shaped wafer is discarded.

8. The wafer production method according to claim 6, further comprising an alignment mark formation step of forming alignment marks on the inside or outside of a small-diameter wafer to be produced before or after the small-diameter peel layer formation step, which are necessary for forming a circuit on the wafer.

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