SiC wafer manufacturing method and SiC wafer manufacturing apparatus

Abstract

A SiC wafer manufacturing method for manufacturing a SiC wafer (108) from a SiC ingot (82) having an end face (84), the SiC wafer manufacturing method comprising: a verification step of applying a test laser beam to the SiC ingot (82) in a predetermined area in a state where the focal point of the test laser beam is set to a predetermined depth inside the SiC ingot (82) from the end face (84) of the SiC ingot (82), the predetermined depth corresponding to the thickness of the SiC wafer (108) to be manufactured, and the test laser beam having a transmission wavelength for SiC, to thereby form a plurality of test separation layers (96) inside the SiC ingot (82) at the predetermined depth, each of the test separation layers (96) having a modified test portion (98),where SiC is decomposed into Si and C and test cracks (100) extend from the modified test section (98) along a c-plane in the SiC ingot (82), wherein it is verified whether the test cracks (100) have been properly formed or not;after performing the verification step, a separation layer formation step comprising applying a laser beam (LB) to the SiC ingot (82) in a state in which the focal point (FP) of the laser beam (LB) is set from the end face (84) of the SiC ingot (82) to the predetermined depth inside the SiC ingot (82), wherein the predetermined depth corresponds to the thickness of the SiC wafer (108) to be produced and the laser beam (LB) has a transmission wavelength for SiC, whereby a separation layer (106) is formed at the predetermined depth inside the SiC ingot (82), wherein the Separating layer (106) has a modified section (102) where SiC is decomposed into Si and C,and cracks (104) extend from the modified portion (102) along the c-plane in the SiC ingot (82); and after performing the separation layer formation step, a separation step comprising separating the SiC wafer (108) from the SiC ingot (82) along the separation layer (106), wherein the verification step includes the steps of varying the power of the test laser beam to thereby form a plurality of test separation layers (96) under different power settings of the test laser beam, the test separation layers (96) being arranged along a plurality of parallel lines and each formed under the same power conditions, and setting the power of the laser beam to a minimum power that was capable of properly forming the test cracks.

Description

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

[0001] The present invention relates to a SiC wafer manufacturing method for manufacturing a SiC wafer from a SiC ingot and also to a SiC wafer manufacturing apparatus for carrying out the SiC wafer manufacturing method. DESCRIPTION OF THE RELATED PRIOR ART

[0002] Various devices, such as integrated circuits (ICs), large-scale integrations (LSIs), and light-emitting diodes (LEDs), are formed by forming a functional layer on the front side of a wafer made of Si (silicon) or Al2O3 (sapphire) and dividing this functional layer into a plurality of separate regions along a plurality of division lines. Furthermore, power devices or optical devices, such as LEDs, are formed by forming a functional layer on the front side of a SiC wafer made of single-crystal SiC (silicon carbide) and dividing this functional layer into a plurality of separate regions along a plurality of division lines.The separation lines of such a wafer containing these components are processed by a processing device, such as a dicing device and a laser processing device, to thereby separate the wafer into a plurality of individual component chips, each containing the components. The resulting component chips are used in a wide variety of electronic equipment, such as mobile phones and personal computers.

[0003] Generally, the wafer on which the components are to be formed is manufactured by cutting a cylindrical ingot with a wire saw. Both sides of the wafer cut from the ingot are polished to a mirror finish (see, for example, Japanese Unexamined Patent Application Laid-Open No. 2000-94221A). However, when the ingot is cut by the wire saw and both sides of each SiC wafer cut from the ingot are polished to obtain the product, a large proportion (70% to 80%) of the ingot becomes scrap, causing the problem of poor economic efficiency. In particular, a SiC ingot has high hardness, and it is therefore difficult to cut the SiC ingot with the wire saw. Accordingly, a considerable amount of time is required to cut the SiC ingot, resulting in a reduction in productivity.Furthermore, since a SiC ingot has a high unit price, there is the problem of efficiently producing a SiC wafer from a SiC ingot using this state of the art technology.

[0004] The present applicant has proposed a technique for solving this problem (see, for example, Japanese Unexamined Patent Application Laid-Open No. 2016-111143 A). This technique includes the steps of setting the focal point of a laser beam having a transmission wavelength for SiC single crystal to the interior of the SiC ingot, then applying the laser beam to the SiC ingot while scanning the laser beam along the SiC ingot, thereby forming a separation layer in a cutting plane previously set inside the SiC ingot, and then breaking the SiC ingot along the cutting plane where the separation layer with a reduced strength has been formed, thereby separating a SiC wafer from the SiC ingot.

[0005] In addition, DE 10 2018 202 984 A1 discloses an inspection method for a semiconductor ingot in which modified layers parallel to an upper surface of the ingot and cracks extending from each modified layer are previously formed as a separation starting point.The inspection method includes a light application step of applying light from a light source to the upper surface of the ingot, the light being incident on the upper surface at a predetermined angle of incidence, a projected image formation step of reflecting the light at the upper surface of the ingot to obtain reflected light and then forming a projected image from the reflected light, the projected image showing the prominence of the asperities generated on the upper surface of the ingot due to the formation of the modified layers and the cracks inside the ingot, an imaging step of acquiring the projected image to form a captured image, and a determination step of comparing the acquired image with predetermined conditions to determine the condition of the modified layers and the cracks. SUMMARY OF THE INVENTION

[0006] However, there is a problem that if the height of the SiC ingot is reduced by repeatedly separating a SiC wafer, a change in the crystal structure in the cutting plane is caused, and it is difficult to properly form the separation layer along the cutting plane under the initial processing conditions. Furthermore, since the crystal structure in the SiC ingot varies from one ingot to another, there is a case where the processing conditions for properly forming the separation layer for initially separating the SiC wafer from the SiC ingot may vary from one ingot to another. Accordingly, when the SiC ingot to be processed is changed, there is a case where the separation layer cannot be properly formed along the cutting plane under the previous processing conditions.

[0007] It is therefore an object of the present invention to provide a SiC wafer manufacturing method that can properly form the separation layer along the cutting plane even when the height of the SiC ingot is reduced by repeating the cutting of SiC wafers, causing a change in the crystal structure in the cutting plane, or even when the SiC ingot to be processed is changed, causing a change in the crystal structure in the cutting plane. Another object of the present invention is to provide a SiC wafer manufacturing apparatus for carrying out the SiC wafer manufacturing method mentioned above.

[0008] According to one aspect of the present invention, there is provided a SiC wafer manufacturing method for manufacturing a SiC wafer from a SiC ingot having an end face, the SiC wafer manufacturing method comprising: a verification step of applying a test laser beam to the SiC ingot in a predetermined region in the state where the focal point of the test laser beam is set at a predetermined depth inside the SiC ingot from the end face of the SiC ingot, the predetermined depth corresponding to the thickness of the SiC wafer to be manufactured, and the test laser beam having a transmission wavelength for SiC, to thereby form a plurality of test separation layers at the predetermined depth inside the SiC ingot, each of the test separation layers having a modified test portion,where SiC is decomposed into Si and C, and test cracks extend from the modified test portion along a c-plane in the SiC ingot, verifying whether the test cracks have been properly formed; after performing the verification step, a separation layer forming step comprising applying a laser beam to the SiC ingot in the state where the focal point of the laser beam is set at a predetermined depth inside the SiC ingot from the end face of the SiC ingot, the predetermined depth corresponding to the thickness of the SiC wafer to be produced, and the test laser beam having a transmission wavelength for SiC, to thereby form a separation layer at the predetermined depth inside the SiC ingot, the separation layer having a modified portion,where SiC is decomposed into Si and C and cracks extend from the modified portion along the c-plane in the SiC ingot; and after performing the separation layer formation step, a separation step comprising separating the SiC wafer from the SiC ingot along the separation layer, wherein the verification step includes the steps of changing the power of the test laser beam to thereby form a plurality of test separation layers under different power settings of the test laser beam, the test separation layers being arranged along a plurality of parallel lines and each formed under the same power conditions, and setting the power of the laser beam to a minimum power capable of properly forming the test cracks.

[0009] Preferably, the verification step is performed again after the initial execution of the separation step and before the next execution of the separation step.

[0010] In accordance with another aspect of the present invention, there is provided a SiC wafer manufacturing apparatus for manufacturing a SiC wafer from a SiC ingot having an end face, the SiC wafer manufacturing apparatus comprising: a laser beam application unit for applying a laser beam to the SiC ingot in the state where the focal point of the laser beam is set at a predetermined depth inside the SiC ingot from the end face of the SiC ingot, the predetermined depth corresponding to the thickness of the SiC wafer to be manufactured, and the laser beam having a transmission wavelength for SiC, to thereby form a separation layer at the predetermined depth inside the SiC ingot, the separation layer having a modified portion,where SiC is decomposed into Si and C, and cracks extend from the modified portion along a c-plane in the SiC ingot; a separating unit for separating a SiC wafer from the SiC ingot along the separation layer; and a verification unit configured to apply a test laser beam to the SiC ingot in a predetermined region in the state where the focal point of the test laser beam is set to the predetermined depth inside the SiC ingot from the end face of the SiC ingot, before the laser beam is applied by the laser beam application unit, wherein the predetermined depth corresponds to the thickness of the SiC wafer to be produced, and the test laser beam has a transmission wavelength for SiC, thereby forming a plurality of test separation layers inside the SiC ingot at the predetermined depth, each of the test separation layers having a modified test portion,where SiC is decomposed into Si and C and test cracks extend from the modified test section along the c-plane in the SiC ingot, verifying whether the test cracks have been properly formed or not, and the verification unit performs verification by changing the power of the test laser beam to thereby form the plurality of test separation layers under different power settings of the test laser beam, the test separation layers being arranged along a plurality of parallel lines and each formed under the same power conditions, and setting the power of the laser beam to a minimum power that was capable of properly forming the test cracks.

[0011] Preferably, the verification unit includes a light-emitting element for applying light to the test separation layer formed in the SiC ingot, a camera for imaging the test separation layer, and a determination section for determining whether the power of the test laser beam is a power at which the test cracks of the test separation layer are properly formed or not, in accordance with whether the brightness of an image obtained by the camera falls within a limit range or not.Preferably, the determining section performs binarization processing for the image to obtain a binary image, and then determines whether or not the ratio between a black area and a white area in the binary image falls within a predetermined range, wherein, when the ratio between the black area and the white area falls within the predetermined range, the determining section determines that the power of the test laser beam is a power at which the test cracks are properly formed.

[0012] According to the SiC wafer manufacturing method of the present invention, the following effect can be exhibited. Even if the height of the SiC ingot is reduced by repeating the separation of SiC wafers, causing a change in the crystal structure in the cutting plane, or even if the SiC ingot to be processed is replaced, causing a change in the crystal structure in the cutting plane, the separation layer can be properly formed along the cutting plane.

[0013] According to the SiC wafer manufacturing apparatus of the present invention, the verification unit is provided to adjust the laser beam power to a power at which the test cracks are properly formed in the separation layer after verifying the result of changing the laser beam power. Even if the height of the SiC ingot is reduced due to repeated cutting of SiC wafers, causing a change in the crystal structure in the cutting plane, or even if the SiC ingot to be processed is changed, causing a change in the crystal structure in the cutting plane, the separation layer can be properly formed along the cutting plane.

[0014] The above and other objects, features and advantages of the present invention and the mode for carrying them into effect will become more apparent and the invention itself will be best understood by studying the following description and appended claims with reference to the attached drawings which show a preferred embodiment of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a SiC wafer manufacturing apparatus in accordance with a preferred embodiment of the present invention; Fig. 2A is a side view of a SiC ingot; Fig. 2B is a plan view of the Fig. SiC ingots shown in Figure 2A; Fig. 3A is a perspective view illustrating an application process of a test laser beam to the SiC ingot during a verification step; Fig. Figure 3B is an enlarged sectional view showing the Fig. 3A; Fig. 4 is an enlarged partial sectional side view illustrating an imaging process of the SiC ingot by using a camera during the verification step; The Fig. 5A to 5D are schematic plan views of images obtained by the camera in the case where the power of the laser beam is changed to form a plurality of different separation layers; Fig. 6A is a perspective view illustrating a separation layer forming step; Fig. 6B is an enlarged sectional view showing the Fig. 6A illustrates the separation layer formation step; Fig. 7 is a perspective view illustrating a separation step; and Fig. 8 is a perspective view showing a forming step of a flat surface. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0015] A preferred embodiment of the SiC wafer manufacturing method and apparatus in accordance with the present invention will now be described with reference to the drawings. The SiC wafer manufacturing apparatus in accordance with this preferred embodiment will first be described with reference to Fig. 1. Referring to Fig. 1 shows a SiC wafer manufacturing apparatus 2, which includes a holding unit 4, a laser beam application unit 6, an X-movement mechanism 8, a Y-movement mechanism 10, a separation unit 12, and a verification unit 14. The holding unit 4 serves to hold a SiC ingot.The laser beam application unit 6 serves to apply a laser beam to the SiC ingot in the state where the focal point of the laser beam is set from an end surface of the SiC ingot to a predetermined depth inside the SiC ingot, the predetermined depth corresponding to the thickness of a SiC wafer to be manufactured, and the laser beam has a transmission wavelength for SiC, to thereby form a separation layer inside the SiC ingot at the predetermined depth, the separation layer having a modified portion where SiC is decomposed into Si (silicon) and C (carbon), and cracks extending from the modified portion along a c-plane in the SiC ingot. The X-movement mechanism 8 serves to move the holding unit 4 and the laser beam application unit 6 in the X-direction (feed direction) shown in FIG. Fig. 1 is represented by an arrow X, relative to each other. The Y-movement mechanism 10 serves to move the holding unit 4 and the laser beam application unit 6 in the Y-direction (division direction) shown in Fig. 1, represented by an arrow Y, relative to each other. The separation unit 12 serves to separate the SiC wafer from the SiC ingot along the separation layer.The verification unit 14 is for applying a test laser beam to the SiC ingot in a predetermined area in the state where the focal point of the test laser beam is set to the predetermined depth from the end surface of the SiC ingot inside the SiC ingot, this predetermined depth corresponding to the thickness of the SiC wafer to be manufactured and the test laser beam has a transmission wavelength for SiC, to thereby form a test separation layer at the predetermined depth inside the SiC ingot, this test separation layer having a modified test portion where SiC is decomposed into Si and C and test cracks extend from the modified test portion along the c-plane in the SiC ingot, thereby verifying whether the test cracks have been properly formed.The X direction represented by the arrow X and the Y direction represented by the arrow Y are perpendicular to each other and define a substantially horizontal plane as an XY plane.

[0016] As in Fig. 1, the SiC wafer manufacturing apparatus 2 includes a base 16 having a substantially horizontal upper surface. The holding unit 4 includes an X-movable plate 18 mounted on the base 16 so as to be movable in the X direction, a Y-movable plate 20 mounted on the X-movable plate 18 so as to be movable in the Y direction, a circular holding table 22 rotatably mounted on the upper surface of the Y-movable plate 20, and a holding table motor (not shown) for rotating the holding table 22.

[0017] The laser beam application unit 6 includes a housing 24 having an inverted L-shape. The housing 24 is configured with a vertical portion extending vertically upward from the upper surface of the base 16 and a horizontal portion extending substantially horizontally from the upper end of the vertical portion toward a position above the holding unit 4. The laser beam application unit 6 further includes an unillustrated laser generating unit incorporated in the housing 24, a focusing means 26 mounted on the lower surface of the housing 24 at a front end portion thereof, and an unillustrated focal point position adjusting means for adjusting the vertical position of the laser beam focal point.The laser generating unit includes a laser oscillator (not shown) for generating a pulsed laser beam and a power controller (not shown) for controlling the power of the pulsed laser beam generated by the laser oscillator. The focusing means 26 includes a focusing lens (not shown) for focusing the pulsed laser beam generated by the laser oscillator. The focal point position adjusting means may be configured to include a ball screw connected to the focusing means 26 so as to extend in a vertical direction and a motor for rotating this ball screw, thereby adjusting the vertical position of the focal point of the pulsed laser beam generated by the laser oscillator.

[0018] The X-movement mechanism 8 includes a ball screw 28 extending along the upper surface of the base 16 in the X direction, and a motor 30 for rotating the ball screw 28. The ball screw 28 is provided with a nut member (not shown) connected to the X-movable plate 18. When the ball screw 28 is rotated by the motor 30, a rotational motion of the motor 30 is accordingly converted into a linear motion by the ball screw 28, and this linear motion is transmitted to the X-movable plate 18, so that the X-movable plate 18 is moved in the X direction along a pair of guide rails 16a provided on the upper surface of the base 16. Consequently, the X-movable plate 18 can be relatively fed with respect to the laser beam application unit 6 in the X direction. The X-movable plate 18 is slidably mounted on the guide rails 16a extending in the X direction.

[0019] The Y-movement mechanism 10 includes a ball screw 32 extending along the upper surface of the X-movable plate 18 in the Y direction, and a motor 34 for rotating the ball screw 32. The ball screw 32 is provided with a nut member (not shown) connected to the Y-movable plate 20. When the ball screw 32 is rotated by the motor 34, a rotational motion of the motor 34 is accordingly converted into a linear motion by the ball screw 32, and this linear motion is transmitted to the Y-movable plate 20, so that the Y-movable plate 20 is moved in the Y direction along a pair of guide rails 18a provided on the upper surface of the X-movable plate 18. Consequently, the Y-movable plate 20 can be further moved or indexed in the Y direction with respect to the laser beam application unit 6.The Y-movable plate 20 is slidably mounted on the guide rails 18a extending in the Y direction.

[0020] The separating unit 12 includes a housing 36 which, as shown in Fig. 1, near the left ends of the guide rails 16a, an arm 38 is provided on the base 16, which has a base end movably supported on the housing 36 in the vertical direction and extends from the base end in the X direction, and an unillustrated arm lifting means for moving the arm 38 in the vertical direction. The arm lifting means may be configured to include a ball screw connected to the arm 38 and extending in the vertical direction, and a motor for rotating this ball screw. A motor 40 is connected to the front end of the arm 38, and a suction member 42 is connected to the lower surface of the motor 40 so that it is rotatable about its vertical axis. A plurality of unillustrated suction holes are formed on the lower surface of the suction member 42. These suction holes of the suction member 42 are connected to an unillustrated suction means for generating a vacuum.Furthermore, the suction element 42 includes an unillustrated ultrasonic vibration applying means for applying an ultrasonic vibration to the lower surface of the suction element 42.

[0021] The verification unit 14 includes a light-emitting element 44 for applying light to the test separation layer formed in the SiC ingot, a camera 46 for imaging the test separation layer, and a determination section 48 for determining whether the power of the test laser beam is a power at which the test cracks of the test separation layer are properly formed or not, in accordance with whether the brightness of an image captured by the camera 46 falls within a limit range. The camera 46 is mounted at its front end portion on the lower surface of the housing 24 so as to be spaced apart from the focusing means 26 in the X direction. The light-emitting element 44 may be configured as an LED lamp. The light-emitting element 44 is attached to a lower end portion of the camera 46.

[0022] A control unit 50 is electrically connected to the camera 46, and data about the image obtained by the camera 46 is transmitted to the control unit 50. The control unit 50 is configured by a computer. Although not shown, this computer includes a central processing unit (CPU) for calculating in accordance with a control program or the like, a read-only memory (ROM) that previously stores the control program, a random access memory (RAM) for storing calculation results, and the like. The determination section 48 of the verification unit 14 is previously stored as a control program in the read-only memory of the control unit 50. In addition, a control section 52 for controlling the power control of the laser beam application unit 6 is also previously stored as a control program in the read-only memory of the control unit 50.In addition, a monitor 54 for displaying the image obtained by the camera 46 is provided on the upper surface of the housing 24.

[0023] The SiC wafer manufacturing apparatus 2 in this preferred embodiment includes, as shown in Fig. 1, further includes a grinding unit 56 for grinding the upper surface of the SiC ingot held by the holding unit 4. The grinding unit 56 includes a fixed vertical wall 58 connected to the housing 24, a vertically movable platen 60 mounted on the front surface of the fixed vertical wall 58, and a lifting means 62 for moving the movable platen 60 in the vertical direction.

[0024] The lifting means 62 includes a ball screw 64 extending along the front surface of the vertical wall 58 in the vertical direction, and a motor 66 for rotating the ball screw 64. The ball screw 64 is provided with a nut member (not shown) connected to the movable plate 60. When the ball screw 64 is rotated by the motor 66, a rotational movement of the motor 66 is accordingly converted into a linear movement by the ball screw 64, and this linear movement is transmitted to the movable plate 60, so that the movable plate 60 is moved in the vertical direction along a pair of guide rails 58a provided on the front surface of the vertical wall 58. That is, the movable plate 60 is slidably mounted on the guide rails 58a extending in the vertical direction perpendicular to the X direction and the Y direction.

[0025] A support member 68 is fixed to the front surface of the movable plate 60 so that it protrudes in the Y direction. A spindle 70 is supported on the support member 68 so that it is rotatable about a vertical axis. A spindle motor 72 for rotating the spindle 70 is mounted on the upper surface of the support member 68. Referring to the Fig. 1 and Fig. 8, a disc-shaped wheel mount 74 is fixed to the lower end of the spindle 70, and an annular grinding wheel 78 is fixed to the lower surface of the wheel mount 74 by bolts 76. A plurality of grinding elements 80 are fixed to the lower surface of the grinding wheel 78 so as to be arranged in a ring shape at predetermined intervals along the outer circumference of the grinding wheel 78.

[0026] The Fig. 2A and Fig. 2B illustrate a SiC ingot 82 formed from SiC. The SiC ingot 82 has a substantially cylindrical shape. That is, the SiC ingot 82 has a substantially circular first end surface 84, a substantially circular second end surface 86 opposite the first end surface 84, a substantially cylindrical surface 88 formed to connect the first end surface 84 and the second end surface 86, a c-axis ( <0001> -direction) and a c-plane ({0001}-plane) perpendicular to the c-axis.

[0027] In the SiC ingot 82, the c-axis is inclined relative to a normal 90 to the first end surface 84 by a deviation angle α (for example, α = 1°, 3°, or 6°). The deviation angle α is formed between the c-plane and the first end surface 84. The formation direction of the deviation angle α (i.e., the inclination direction of the c-axis) is indicated in the Fig. 2A and Fig. 2B by an arrow A. Furthermore, the cylindrical surface 88 of the SiC ingot 82 is formed with a first orientation plane 92 and a second orientation plane 94, which are perpendicular when viewed from the side and serve to indicate a crystal orientation. As shown in Fig. 2B, the first alignment plane 92 is parallel to the formation direction A of the deviation angle α, and the second alignment plane 94 is perpendicular to the formation direction A of the deviation angle α. As further shown in Fig. 2B, the length L2 of the second alignment plane 94 is set shorter than the length L1 of the first alignment plane 92 (L2 <L1) .

[0028] The SiC wafer manufacturing method according to this preferred embodiment will now be described for the case of using the above-described SiC wafer manufacturing apparatus 2. First, the SiC ingot 82 is fixed to the upper surface of the holding table 22 by using a suitable adhesive (for example, an epoxy resin adhesive) in the state where the second end surface 86 of the SiC ingot 82 is directed downward. That is, the adhesive is interposed between the second end surface 86 of the SiC ingot 82 and the upper surface of the holding table 22. Alternatively, a plurality of suction holes may be formed on the upper surface of the holding table 22, and suction force may be applied to the upper surface of the holding table 22 through these suction holes, thereby holding the SiC ingot 82 to the upper surface of the holding table 22 via negative pressure.

[0029] After holding the SiC ingot 82 on the upper surface of the holding table 22, a verification step is carried out in such a way that a test laser beam is applied to the SiC ingot 82 in a predetermined area in the state in which the focal point of the test laser beam is set from an end surface of the SiC ingot 82 (that is, in this preferred embodiment, the first end surface 84) to a predetermined depth inside the SiC ingot 82, this predetermined depth corresponding to the thickness of the SiC wafer to be manufactured and the test laser beam has a transmission wavelength for SiC, to thereby form a test separation layer inside the SiC ingot 82 at this predetermined depth, the test separation layer having a modified test portion where SiC is decomposed into Si and C and test cracks extend from the modified test portion along the c-plane in the SiC ingot 82 and in which verified becomes,whether the test cracks have been properly formed or not.

[0030] In the verification step, the SiC ingot 82 is first imaged using the camera 46 positioned above the SiC ingot 82. Thereafter, the holding table 22 is moved and rotated according to an image of the SiC ingot 82 obtained by the camera 46 by operating the X-movement mechanism 8, the Y-movement mechanism 10, and the holding table motor, to thereby position an edge portion of the SiC ingot 82 (i.e., a peripheral edge portion of the SiC wafer produced from the SiC ingot 82, with no components formed in this peripheral edge portion) directly under the focusing means 26. Further, the second alignment plane 94, as shown in Fig. 3A, aligned parallel to the X direction, so that the direction perpendicular to the formation direction A of the deviation angle α is aligned parallel to the X direction and the formation direction A of the deviation angle α is aligned parallel to the Y direction.

[0031] Thereafter, the focusing means 26 is moved in the vertical direction by operating the focal point position adjusting means in order to set the focal point FP (see Fig. 3B) of a pulsed laser beam LB from the first end surface 84 of the SiC ingot 82 to a predetermined depth, this predetermined depth corresponding to the thickness of a SiC wafer to be produced. Thereafter, the pulsed laser beam LB, which has a transmission wavelength for SiC, is guided by actuating the X-movement mechanism 8 while moving the holding table 22 at a predetermined feed speed in the X-direction, as shown in FIGS. Fig. 3A and Fig. 3B, is applied to the SiC ingot 82 from the focusing means 26, wherein the X direction is parallel to the direction perpendicular to the formation direction A of the deviation angle α. As a result, a test separation layer 96 for use in the verification step is formed in the peripheral region at the predetermined depth inside the SiC ingot 82. The test separation layer 96 is formed in the peripheral region within approximately 2 mm from the peripheral edge of the SiC ingot 82. This peripheral region of the SiC ingot 82 corresponds to the peripheral edge region of the SiC wafer where no devices are formed. Accordingly, in the subsequent formation of devices on the SiC wafer made from the SiC ingot 82, it is not possible for the test separation layer 96 to reduce the quality of the devices.

[0032] When forming the test separation layer 96 during the verification step, the power control of the laser beam application unit 6 is controlled by the control section 52 of the control unit 50 to thereby change the power of the pulsed laser beam LB at appropriate time intervals during the application of the pulsed laser beam LB to the SiC ingot 82. Accordingly, a plurality of test separation layers 96 are formed under different power conditions of the pulsed laser beam LB. In particular, in this preferred embodiment, as shown in Fig. As shown in Figure 3B, a test separation layer 96a is formed by setting the power of the pulsed laser beam LB to 4 watts, a test separation layer 96b is formed by setting the power of the pulsed laser beam LB to 5 watts, a test separation layer 96c is formed by setting the power of the pulsed laser beam LB to 6 watts, and a test separation layer 96d is formed by setting the power of the pulsed laser beam LB to 7 watts. The power settings and the number of the plurality of separation layers 96 can be arbitrarily selected.

[0033] Thereafter, the Y-movement mechanism 10 is actuated to move the holding table 22 by a predetermined pitch amount Li in the Y-direction, thereby relatively further moving the SiC ingot 82 with respect to the focal point FP by the predetermined pitch amount Li in the Y-direction parallel to the formation direction A of the deviation angle α. Thereafter, the application of the pulsed laser beam LB and the pitching and further moving processes are repeated an appropriate number of times, thereby, as shown in Fig. 3A, a plurality of test separation layers 96 are formed under different power settings of the pulsed laser beam LB. These test separation layers 96 are arranged along a plurality of parallel lines spaced apart from each other by the pitch Li in the Y direction, each line extending in the X direction. The test separation layers 96, which are adjacent to each other in the Y direction parallel to the formation direction A of the deviation angle α, are formed under the same power conditions.

[0034] Afterwards, light, as in Fig. 4, from the light-emitting element 44 onto the test separation layers 96a to 96d at an inclination angle with respect to a vertical direction, and the test separation layers 96a to 96d are imaged or recorded by the camera 46. The Fig. 5A to 5D represent images P1 to P4 of the test separation layers 96a to 96d, respectively. In particular, Fig. 5A shows the image P1 of the plurality of test separation layers 96a adjacent to each other in the direction A. Fig. 5B illustrates the image P2 of the plurality of test separation layers 96b adjacent to each other in the direction A. Fig. 5C illustrates image P3 of the plurality of test separation layers 96c adjacent to each other in direction A. Fig. 5D illustrates the image P4 of the plurality of separation layers 96d adjacent to each other in the direction A. As in Fig. 5A, each test separation layer 96a is constructed from a modified test section 98a in which SiC is decomposed into Si and C, and test cracks 100a extend isotropically from the modified test section 98a along the c-plane. Similarly, each test separation layer 96b, as shown in Fig. 5B, constructed from a modified test section 98b and test cracks 100b. As shown in Fig. 5D, each test separation layer 96c is constructed from a modified test section 98c and test cracks 100c. As shown in Fig. 5B, each test separation layer 96d is composed of a modified test section 98d and test cracks 100d. Specifically, the pulsed laser beam LB is initially applied to the SiC ingot 82 to thereby decompose SiC into Si and C. Thereafter, the pulsed laser beam LB is next applied to the SiC ingot 82 and absorbed by the previously generated C. Consequently, with the movement of the holding table 22 in the X direction, SiC is decomposed into Si and C in a chain reaction manner, thereby forming each modified section 98a, as shown in Fig. 5A, is formed linearly extending in the X-direction.

[0035] As in Fig. 5A, the test cracks 100a of the test separation layers 96a that are adjacent in the direction A do not overlap in the direction A. As shown in Fig. 5B, the test cracks 100b of the test separation layers 96b, which are adjacent to each other in the direction A, do not overlap each other in the direction A. As shown in Fig. 5C, the test cracks 100c of the test separation layers 96c, which are adjacent to each other in the direction A, overlap in the direction A. As shown in Fig. 5D, the test cracks 100d of the test release layers 96d that are adjacent to each other in the direction A overlap in a similar manner in the direction A.

[0036] In the event that the cracks of the separation layers adjacent to each other in the direction A do not overlap each other in the direction A, it is difficult to separate the SiC wafer from the SiC ingot 82 along the separation layers. In the event that the cracks of the separation layers adjacent to each other in the direction A overlap in the direction A, the SiC wafer can be easily separated from the SiC ingot 82 along the separation layers. However, if the power of the pulsed laser beam LB is too high, the cracks may be excessively generated along the c-plane, which is inclined relative to the first end surface 84 of the SiC ingot 82.As a result, when separating the SiC wafer from the SiC ingot 82 and then grinding a separation surface of the SiC ingot 82 and a separation surface of the SiC wafer to thereby flatten these separation surfaces, the amount of grinding of the SiC ingot 82 and the SiC wafer is increased, causing an increase in material loss. To address this problem, in the verification step according to this preferred embodiment, the power of the pulsed laser beam LB is set to a minimum power as a power (for example, 6 watts in this preferred embodiment) capable of overlapping the test cracks of the test separation layers adjacent to each other in the direction A, as the power at which the cracks of the separation layers to be formed later are properly formed.

[0037] As described above, when adjusting the power of the pulsed laser beam LB during the verification step, the area of ​​the test cracks 100a of each test separation layer 96a in the A direction can be checked via the image P1. Similarly, the area of ​​the test cracks 100b of each test separation layer 96b in the A direction can be checked via the image P2, the area of ​​the test cracks 100c of each test separation layer 96c in the A direction can be checked via the image P3, and the area of ​​the test cracks 100d of each test separation layer 96d in the A direction can be checked via the image P4.However, in this preferred embodiment, the determining section 48 of the verification unit 14 can determine whether or not the power of the pulsed laser beam LB is a power at which the test cracks are properly formed, in accordance with whether or not the brightness of each of the images P1 to P4 obtained by the camera 46 falls within a limit range.

[0038] The determination section 48 receives data on the images P1 to P4 obtained by the camera 46. Afterward, the determination section 48 performs binarization processing on the images P1 to P4. When the images P1 to P4 are subjected to binarization processing, the area where the test cracks 100a to 100d are formed becomes mainly white, whereas the area where the test cracks 100a to 100d are not formed and the modified portions 98a to 98d where SiC is decomposed into Si and C become mainly black. Consequently, the determination section 48 generates a binary image from each of the images P1 to P4.When the ratio between the black area and the white area in each binary image falls within a predetermined range (for example, when the proportion of the black area falls within a range of 30% to 40% and the proportion of the white area falls within a range of 60% to 70%, that is, the ratio between the black area and the white area falls within a range of 3:7 to 4:6), the determining section 48 determines that the test cracks have been properly formed, and that the power of the pulsed laser beam LB in this case is an appropriate power at which the test cracks are properly formed.

[0039] The area to be subjected to binarization processing in the image obtained by the camera 46 may, for example, be in the case of Fig. 5A can be set in the following manner. In the formation direction A of the deviation angle α, the range from the uppermost modified portion 98a to the lowermost modified portion 98a can be set, whereas in the direction perpendicular to the formation direction A of the deviation angle α, any range including the test separation layers formed under the same power settings can be set. Furthermore, the ratio between the black area and the white area in the binary image for the case of forming the separation layer can be determined in advance through an experiment by setting the power at which the cracks are properly formed.

[0040] After performing the verification step, a separation layer forming step is performed in such a manner that the pulsed laser beam LB having a transmission wavelength for SiC is applied to the SiC ingot 82 in the state where the focal point FP of the pulsed laser beam LB is set to a predetermined depth from the top surface of the SiC ingot 82 (for example, from the first end surface 84 in this embodiment) inside the SiC ingot 82, this predetermined depth corresponding to the thickness of the SiC wafer to be manufactured, whereby a separation layer is formed at this predetermined depth inside the SiC ingot 82, the separation layer being composed of a modified portion where SiC is decomposed into Si and C, and cracks extending from this modified portion along the c-plane in the SiC ingot 82.The power of the pulsed laser beam LB during the separation layer formation step is the same as the power (for example, 6 watts in this preferred embodiment) set in the verification step.

[0041] In the separation layer formation step, first, in accordance with the image of the SiC ingot 82 obtained by the camera 46 in the verification step, a positional relationship between the SiC ingot 82 and the focusing means 26 is set on an XY plane. The orientation of the SiC ingot 82 is set in a similar manner to that set in the verification step. That is, the direction perpendicular to the formation direction A of the deviation angle α is aligned parallel to the X direction, and the formation direction A of the deviation angle α is aligned parallel to the Y direction (see Fig. 6A).

[0042] Thereafter, the focal point FP of the pulsed laser beam LB is adjusted from the first end face 84 of the SiC ingot 82 to a predetermined depth inside the SiC ingot 82, which predetermined depth corresponds to the thickness of the SiC wafer to be produced. Thereafter, the pulsed laser beam LB, which has a transmission wavelength for SiC, is directed as shown in Fig. 6A, by operating the X-movement mechanism 8 while moving the holding table 22 in the X-direction at a predetermined feed speed from the focusing means 26, the SiC ingot 82 is applied, with the X-direction being parallel to the direction perpendicular to the formation direction A of the deviation angle α. As a result, a band-shaped separation layer 106 is formed inside the SiC ingot 82 to the predetermined depth so as to extend in the X-direction. The separation layer 106 is composed of a modified portion 102 where SiC is decomposed into Si and C, and cracks 104 extending isotropically from the modified portion 102 along the c-plane. Specifically, the pulsed laser beam LB is initially applied to the SiC ingot 82 to thereby decompose SiC into Si and C. The pulsed laser beam LB is then applied to the SiC ingot 82 and absorbed by the previously generated C.Consequently, with the movement of the holding table 22 in the X direction, SiC is decomposed into Si and C in a chain reaction manner to thereby linearly form the modified portion 102 extending in the X direction.

[0043] Thereafter, the Y-moving mechanism 10 is actuated to move the holding table 22 by a predetermined pitch amount Li in the Y direction, thereby further moving the SiC ingot 82 with respect to the focal point FP by the predetermined pitch amount Li in the Y direction parallel to the formation direction A of the deviation angle α. Thereafter, the application of the pulsed laser beam LB and the pitching process are alternately repeated, thereby forming a plurality of modified portions 102 spaced from each other by the pitch amount Li in the formation direction A of the deviation angle α, each modified portion 102 extending continuously in the direction perpendicular to the formation direction A of the deviation angle α. Further, cracks 104 extend isotropically from each modified portion 102 along the c-plane.The grading amount Li in the interface formation step is the same as the grading amount Li in the verification step.

[0044] In this preferred embodiment, the verification step is performed before performing the separation layer formation step, thereby adjusting the power of the pulsed laser beam LB to a power at which the cracks 104 are properly formed. Accordingly, the cracks 104 of the separation layers 106, which are adjacent to each other in the formation direction A of the deviation angle α, overlap as shown in Fig. 6B, in the direction A (the Y direction). In this way, the separation layer forming step is carried out to form the plurality of separation layers 106 from the first end surface 84 of the SiC ingot 82 to a predetermined depth (in a cutting plane) inside the SiC ingot 82. This predetermined depth corresponds to the thickness of the SiC wafer to be manufactured, and each separation layer 106 is composed of the modified portion 102 and the cracks 104, and each separation layer 106 has a reduced strength that allows the SiC wafer to be separated from the SiC ingot 82. The plurality of separation layers 106 are formed inside the SiC ingot 82 at the same depth to form a planar separation layer.

[0045] After performing the separation layer formation step, a separation step is performed to separate the SiC wafer from the SiC ingot 82 along the planar separation layer composed of the plurality of separation layers 106. In the separation step, the X-movement mechanism 8 is actuated to move the holding table 22 to the position directly below the suction member 42 of the separation unit 12. Thereafter, the arm lifting means in the separation unit 12 is actuated to lower the arm 38 until the lower surface of the suction member 42 comes into close contact with the first end surface 84 of the SiC ingot 82, which, as shown in Fig. 7, is held on the upper surface of the holding table 22. Thereafter, the suction means is actuated to hold the first end surface 84 of the SiC ingot 82 to the lower surface of the suction element 42 via suction force. Thereafter, the ultrasonic vibration applying means in the separation unit 12 is actuated to apply ultrasonic vibration to the lower surface of the suction element 42, and at the same time, the motor 40 is actuated to rotate the suction element 42. Accordingly, an external force is exerted on the planar separation layer composed of the plurality of separation layers 106, so that a SiC wafer 108 as shown in Fig. 7, along the planar separation layer constructed from the plurality of separation layers 106, the SiC ingot 82 can be separated.

[0046] After performing the separation step, a flat surface forming step is performed in which the upper surface of the SiC ingot 82 (which is shown in Fig. 8) is ground to thereby flatten the parting surface 110 of the SiC ingot 82. In the flat surface forming step, first, the X-movement mechanism 8 is actuated to move the holding table 22 to the position below the grinding wheel 78 (the grinding elements 80) of the grinding unit 56. Thereafter, the holding table 22 is, as shown in Fig.8, the holding table motor rotates counterclockwise at a predetermined speed (for example, 300 revolutions per minute) as viewed from above. Similarly, the spindle 70 is rotated counterclockwise at a predetermined speed (for example, 6000 revolutions per minute) as viewed from above by the spindle motor 72. Thereafter, the spindle 70 is lowered by the lifting means 62 until the grinding elements 80 come into contact with the parting surface 110 of the SiC ingot 82. Thereafter, the spindle 70 is further lowered at a predetermined feed speed (for example, 0.1 μm / s). Accordingly, the parting surface 110 of the SiC ingot 82 is ground by the grinding elements 80 to form a flat surface with such flatness that the incidence of the pulsed laser beam LB is not obstructed in a subsequent step.

[0047] After performing the flat surface forming step, the verification step, the separation layer forming step, the separation step, and the flat surface forming step are all repeated, thereby manufacturing a plurality of SiC wafers 108 from the SiC ingot 82. Preferably, the verification step is performed each time the separation layer is formed. That is, the verification step is preferably performed after performing the separation step and before the next separation step. However, after the first execution of the verification step and the separation step, the number of repetitions of the verification step may be selected to be smaller than the number of repetitions of the separation step. For example, the verification step may be performed once after the separation step has been repeated five times.

[0048] According to the above preferred embodiment, the verification step is performed to adjust the power of the pulsed laser beam LB to a power at which the cracks 104 are properly formed in each separation layer 106 after verifying the result of changing the power of the pulsed laser beam LB. Accordingly, even if the height of the SiC ingot 82 decreases due to the repetition of cutting the SiC wafer 108, causing a change in the crystal structure in the cutting plane, or even if the SiC ingot 82 to be processed is replaced, causing a change in the crystal structure in the cutting plane, each separation layer 106 can be properly formed along the cutting plane.

[0049] The verification step and the interface formation step can be performed, for example, under the following processing conditions. The width of the modified portion and the crack area (i.e., the length of each crack extending from the modified portion) mentioned above are those in the formation direction A of the deviation angle α. Wavelength of the pulsed laser beam: 1064 nm Repetition frequency: 120 kHz Average power: 4 to 10 watts Pulse width: 4 ns Numerical aperture (NA) of the focusing lens: 0.65 Feeding speed: 900 mm / s Graduation amount: 400 to 500 µm Width of the modified section: 10 µm Crack area: 250 µm

[0050] The present invention is not limited to the details of the preferred embodiment described above. The scope of the invention is defined by the appended claims, and all changes and modifications that fall within the equivalent scope of the claims are therefore included in the invention.

Claims

[1] A SiC wafer manufacturing method for manufacturing a SiC wafer (108) from a SiC ingot (82) having an end face (84), the SiC wafer manufacturing method comprising: a verification step comprising applying a test laser beam to the SiC ingot (82) in a predetermined area in a state in which the focal point of the test laser beam is set to a predetermined depth inside the SiC ingot (82) from the end face (84) of the SiC ingot (82), wherein the predetermined depth corresponds to the thickness of the SiC wafer (108) to be produced and the test laser beam has a transmission wavelength for SiC, to thereby form a plurality of test separation layers (96) inside the SiC ingot (82) at the predetermined depth, wherein each of the test separation layers (96) has a modified test portion (98) where SiC is decomposed into Si and C and test cracks (100) extend from the modified test portion (98) along a c-plane in the SiC ingot (82), wherein it is verified whether the test cracks (100) have been properly trained or not; after performing the verification step, a separation layer formation step comprising applying a laser beam (LB) to the SiC ingot (82) in a state in which the focal point (FP) of the laser beam (LB) is set from the end face (84) of the SiC ingot (82) to the predetermined depth inside the SiC ingot (82), wherein the predetermined depth corresponds to the thickness of the SiC wafer (108) to be produced and the laser beam (LB) has a transmission wavelength for SiC, whereby a separation layer (106) is formed at the predetermined depth inside the SiC ingot (82), wherein the separation layer (106) has a modified portion (102) where SiC is decomposed into Si and C, and cracks (104) extend from the modified portion (102) along the c-plane in the SiC ingot (82); and after carrying out the separation layer formation step, a separation step comprising separating the SiC wafer (108) from the SiC ingot (82) along the separation layer (106), wherein the verification step includes the steps of varying the power of the test laser beam to thereby form a plurality of test separation layers (96) under different power settings of the test laser beam, the test separation layers (96) being arranged along a plurality of parallel lines and each formed under the same power conditions, and setting the power of the laser beam to a minimum power that was capable of properly forming the test cracks. [2] The SiC wafer manufacturing method according to claim 1, wherein the verification step is performed again after the initial execution of the separating step and before the next execution of the separating step. [3] SiC wafer manufacturing apparatus (2) for manufacturing a SiC wafer (108) from a SiC ingot (82) having an end face (84), the SiC wafer manufacturing apparatus (2) comprising: a laser beam application unit (6) configured to apply a laser beam (LB) to the SiC ingot (82) in a state in which the focal point (FP) of the laser beam (LB) is set from the end face (84) of the SiC ingot (82) to a predetermined depth inside the SiC ingot (82), wherein the predetermined depth corresponds to the thickness of the SiC wafer (108) to be produced and the laser beam (LB) has a transmission wavelength for SiC, to thereby form a separation layer (106) at the predetermined depth inside the SiC ingot (82), wherein the separation layer (106) has a modified portion (102) where SiC is decomposed into Si and C, and cracks (104) extend from the modified portion (102) along a c-plane in the SiC ingot (82); a separation unit (12) for separating the SiC wafer (108) from the SiC ingot (82) along the separation layer (106); and a verification unit configured to apply a test laser beam to the SiC ingot (82) in a predetermined area in a state in which the focal point of the test laser beam is set from the end face (84) of the SiC ingot (82) to the predetermined depth inside the SiC ingot (82), prior to the application of the laser beam (LB) by the laser beam application unit (6), wherein the predetermined depth corresponds to the thickness of the SiC wafer (108) to be produced, and the test laser beam has a transmission wavelength for SiC, to thereby form a plurality of test separation layers (96) inside the SiC ingot (82) at the predetermined depth, wherein each of the test separation layers (96) has a modified test portion (98) where SiC is decomposed into Si and C, and test cracks (100) extend from the modified test portion (98) along the c-plane in the SiC ingot (82), verifyingwhether the test cracks (100) have been properly formed or not;, wherein the verification unit is further configured to perform verification by changing the power of the test laser beam to thereby form the plurality of test separation layers (96) under different power settings of the test laser beam, the test separation layers (96) being arranged along a plurality of parallel lines and each formed under the same power conditions, and setting the power of the laser beam to a minimum power that was capable of properly forming the test cracks (100). [4] The SiC wafer manufacturing apparatus (2) according to claim 3, wherein the verification unit (14) comprises a light-emitting element (44) for applying light to the test separation layer (96) formed in the SiC ingot (82), a camera (46) for imaging the test separation layer (96), and a determination section (48) for determining whether the power of the test laser beam is a power at which the test cracks (100) of the test separation layer (96) are properly formed or not, in accordance with whether the brightness of an image (P) obtained by the camera (46) falls within a boundary range or not. [5] The SiC wafer manufacturing apparatus (2) according to claim 4, wherein the determining section (48) performs binarization processing for the image (P) to obtain a binary image, and then determines whether or not the ratio between a black area and a white area in the binary image falls within a predetermined range, wherein, when the ratio between the black area and the white area falls within the predetermined range, the determining section (48) determines that the power of the test laser beam is a power at which the test cracks (100) are properly formed.

Images