Small face area detection method and detection device, wafer generation method and laser processing device

Abstract

The present invention provides a method and device for detecting a small face area, as well as a method for generating a wafer and a laser processing device. The method for detecting a small face area is a method for detecting a small face area of ​​a SiC crystal ingot that can detect a small face area and a non-small face area. The method for detecting a small face area includes the following steps: a fluorescence brightness detection step, irradiating an excitation light (EL) of a specified wavelength to a SiC crystal ingot (84) from the upper surface of the SiC crystal ingot (84), and detecting the inherent fluorescence brightness of SiC; and a coordinate setting step, setting an area where the fluorescence brightness is above a specified value in the fluorescence brightness detection step as a non-small face area (100), and setting an area where the fluorescence brightness is lower than a specified value as a small face area (98), and setting the coordinates of the boundary between the small face area (98) and the non-small face area (100).

Description

Technical Field

[0001] The present invention relates to a method and device for detecting a facet region of a SiC ingot, a method for generating a SiC wafer from a SiC ingot, and a laser processing device for forming a peeling layer on a SiC ingot. Background Art

[0002] IC, LSI, LED and other devices are formed by stacking functional layers on the front of a wafer made of Si (silicon), Al2O3 (sapphire) and the like and dividing the functional layers by a plurality of intersecting predetermined dividing lines. In addition, power devices, LEDs and the like are formed by stacking functional layers on the front of a wafer made of hexagonal single crystal SiC (silicon carbide) and dividing the functional layers by a plurality of intersecting predetermined dividing lines. The predetermined dividing lines are processed by a cutting device or a laser processing device to divide the wafer with the device formed thereon into individual device chips, and the device chips obtained by the division are used in electrical equipment such as mobile phones and personal computers.

[0003] The wafers that form the device are usually produced by thinly cutting a cylindrical ingot using a wire saw. The front and back of the cut wafer are polished to a mirror finish (see, for example, Patent Document 1). However, when the ingot is cut with a wire saw and the front and back of the cut wafer are polished, most of the ingot (70 to 80%) is discarded, which is uneconomical. In particular, SiC ingots are difficult to cut with a wire saw due to their high hardness, which takes a considerable amount of time, so the productivity is poor, and the unit price of the ingot is high, which poses a problem in efficiently generating wafers.

[0004] Therefore, the inventors have proposed the following technology: positioning the focal point of a laser beam having a wavelength that is transmissive to hexagonal single crystal SiC inside a SiC ingot, irradiating the SiC ingot with the laser beam to form a peeling layer on a predetermined cutting surface, and peeling a SiC wafer from the SiC ingot along the predetermined cutting surface on which the peeling layer is formed (see, for example, Patent Document 2).

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2000-94221

[0008] Patent Document 2: Japanese Patent Application Publication No. 2016-111143 Summary of the invention

[0009] Problems to be solved by the invention

[0010] However, sometimes there are regions called small faces with different crystal structures inside the SiC ingot. Compared with the non-small face regions, the small face regions have a higher refractive index and a higher energy absorption rate. Therefore, there is the following problem: the position and completion of the peeling layer formed inside the SiC ingot by irradiation of laser light are uneven, and the chip has a step difference between the small face region and the non-small face region.

[0011] Therefore, an object of the present invention is to provide a method for detecting a facet region of a SiC ingot, which is capable of detecting both a facet region and a non-facet region.

[0012] Another object of the present invention is to provide a device for detecting a facet region of a SiC ingot, which is capable of detecting a facet region and a non-facet region.

[0013] Another object of the present invention is to provide a method for producing a wafer, which is capable of producing a wafer without a step difference between a small facet region and a non-small facet region.

[0014] Still another object of the present invention is to provide a laser processing apparatus capable of producing a wafer having no step difference between a facet region and a non-facet region.

[0015] Means for solving problems

[0016] According to one embodiment of the present invention, there is provided a method for detecting a small face area, which is a method for detecting a small face area of ​​a SiC ingot, wherein the method comprises the following steps: a fluorescence brightness detection step, in which an excitation light of a specified wavelength is irradiated on the SiC ingot from the upper surface of the SiC ingot to detect the fluorescence brightness inherent in SiC; and a coordinate setting step, in which an area in which the fluorescence brightness in the fluorescence brightness detection step is greater than a specified value is set as a non-small face area, an area in which the fluorescence brightness is lower than the specified value is set as a small face area, and the coordinates of the boundary between the small face area and the non-small face area are set.

[0017] According to another aspect of the present invention, there is provided a method for producing a wafer, which produces a SiC wafer from a SiC ingot, wherein the method comprises the following steps: a flat surface forming step, in which the upper surface of the SiC ingot is ground to form a flat surface; a fluorescence brightness detecting step, in which the SiC ingot is irradiated with excitation light of a specified wavelength from the upper surface of the SiC ingot to detect the fluorescence brightness inherent to SiC; a coordinate setting step, in which a direction perpendicular to a direction in which a c-plane is inclined with respect to the upper surface of the SiC ingot to form an offset angle is set as an X-axis, and a direction perpendicular to the X-axis is set as a Y-axis, in which an area with a fluorescence brightness above a specified value in the fluorescence brightness detection step is set as a non-small face area, and an area with a fluorescence brightness below the specified value is set as a small face area, and the X-coordinate and Y-coordinate of a boundary between the small face area and the non-small face area are set; and a processing feed step, in which a laser beam having a wavelength that is transparent to SiC is converged by a condenser to obtain a coordinate. The focal point is positioned at a depth from the upper surface of the SiC ingot that is equivalent to the thickness of the wafer to be generated, and the SiC ingot is irradiated with the laser light while the SiC ingot and the focal point are processed and fed relative to each other in the X-axis direction, so that SiC is separated into Si and C and a strip-shaped peeling layer is formed in which cracks extend along the c-plane; a graduated feeding step is performed to feed the SiC ingot and the focal point relative to each other in the Y-axis direction, and strip-shaped peeling layers are arranged in parallel in the Y-axis direction; and a peeling step is performed to peel the wafer to be generated from the peeling layer, in which the wafer to be generated is peeled off from the peeling layer, and in the processing and feeding step, based on the X-coordinate and Y-coordinate of the boundary between the small face area and the non-small face area set by the coordinate setting step, the energy of the laser light when the small face area is irradiated with the laser light is increased relative to the energy of the laser light when the non-small face area is irradiated with the laser light and the position of the condenser, and the position of the condenser is increased.

[0018] According to another embodiment of the present invention, there is provided a detection device for a small face area, which is a detection device for a small face area of ​​a SiC ingot, wherein the device comprises: a fluorescence brightness detection component, which irradiates the SiC ingot with excitation light of a specified wavelength from the upper surface of the SiC ingot to detect the fluorescence brightness inherent in SiC; and a coordinate setting component, which sets an area where the fluorescence brightness detected by the fluorescence brightness detection component is above a specified value as a non-small face area, sets an area where the fluorescence brightness is lower than the specified value as a small face area, and sets the coordinates of the boundary between the small face area and the non-small face area.

[0019] According to another embodiment of the present invention, there is provided a laser processing device for forming a peeling layer on a SiC ingot, wherein the device comprises: a holding table for holding the SiC ingot; a fluorescence brightness detection component for irradiating the SiC ingot with excitation light of a specified wavelength from the upper surface of the SiC ingot to detect the fluorescence brightness inherent to SiC; a coordinate setting component for setting a direction orthogonal to a direction in which a c-plane is inclined relative to the upper surface of the SiC ingot to form a deviation angle as an X-axis, setting a direction orthogonal to the X-axis as a Y-axis, setting an area in which the fluorescence brightness detected by the fluorescence brightness detection component is greater than a specified value as a non-small face area, setting an area in which the fluorescence brightness is lower than the specified value as a small face area, and setting the X-coordinate and Y-coordinate of a boundary between the small face area and the non-small face area; and a laser light irradiation unit including a condenser. The device positions the focal point of the laser light having a wavelength that is transparent to SiC at a depth from the upper surface of the SiC ingot that is equivalent to the thickness of the wafer to be generated, and irradiates the SiC ingot with the laser light, so that the SiC is separated into Si and C and a peeling layer is formed in which the cracks extend along the c-plane; an X-axis feeding mechanism, which causes the holding worktable and the condenser to perform processing feeding relative to each other in the X-axis direction; a Y-axis feeding mechanism, which causes the holding worktable and the condenser to perform indexing feeding relative to each other in the Y-axis direction; and a control unit, which increases the energy of the laser light when irradiating the small face area with the laser light based on the X-coordinate and Y-coordinate of the boundary between the small face area and the non-small face area, relative to the energy of the laser light when irradiating the non-small face area with the laser light and the position of the condenser, and increases the position of the condenser.

[0020] Effects of the Invention

[0021] According to the facet region detection method of the present invention, the boundary between the facet region and the non-facet region can be detected. Therefore, based on the data of the detected facet region and the non-facet region, the processing conditions for irradiating the SiC crystal ingot with laser light can be appropriately controlled, and a wafer without a step difference between the facet region and the non-facet region can be generated.

[0022] According to the wafer production method of the present invention, the position and finish of the peeling layer formed in the facet region and the non-facet region can be made uniform, and a wafer with no step difference between the facet region and the non-facet region can be produced.

[0023] According to the small face area detection device of the present invention, the processing conditions for irradiating the SiC ingot with laser light can be appropriately controlled based on the data of the detected small face area and non-small face area, and a chip with no step difference between the small face area and the non-small face area can be generated.

[0024] According to the laser processing apparatus of the present invention, the position and finish of the separation layer formed in the facet region and the non-facet region can be made uniform, and a wafer with no step difference between the facet region and the non-facet region can be generated. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a perspective view of a laser processing device according to an embodiment of the present invention.

[0026] Figure 2 yes Figure 1 Schematic diagram of the fluorescence brightness detection component shown.

[0027] Figure 3 Graphs showing the relationship between the fluorescence wavelength and the brightness of the facet region and the non-facet region when the excitation light wavelength is 370 nm and 273 nm.

[0028] Figure 4 It is a perspective view showing a state where a flat surface forming step is performed.

[0029] Figure 5 (a) is the front view of SiC ingot. Figure 5 (b) is a top view of the SiC ingot.

[0030] Figure 6 It is a perspective view showing a state where a fluorescence brightness detection step is performed.

[0031] Figure 7 (a) is a schematic diagram of an image of a SiC ingot taken during the fluorescence brightness detection process. Figure 7 (b) is a table of X-coordinates and Y-coordinates of the boundary between the small face region and the non-small face region set in the coordinate setting step.

[0032] Figure 8 (a) is a perspective view showing a state in which a processing feed process is performed. Figure 8 (b) is a cross-sectional view showing a state where a processing feed step is performed.

[0033] Fig. 9 is a cross-sectional view showing a peeling layer formed inside a SiC ingot.

[0034] Fig.10 It is a perspective view showing a state where a peeling process is performed. DETAILED DESCRIPTION

[0035] The following describes preferred embodiments of the small face area detection method and detection device, as well as the wafer generation method and laser processing device of the present invention with reference to the accompanying drawings.

[0036] First refer to Figure 1The laser processing device according to the embodiment of the present invention is described. The laser processing device, which is generally represented by the symbol 2, includes at least: a holding unit 4, which holds the SiC ingot; a fluorescence brightness detection component 6, which irradiates the SiC ingot with excitation light of a specified wavelength from the upper surface of the SiC ingot to detect the fluorescence brightness inherent in SiC; a coordinate setting component 8, which sets the area with fluorescence brightness detected by the fluorescence brightness detection component 6 as a non-small face area, sets the area with fluorescence brightness lower than the specified value as the small face area, and sets the X-coordinate and Y-coordinate of the boundary between the small face area and the non-small face area; and a laser light irradiation unit 12, which includes a condenser 10, which The condenser 10 positions the focal point of the laser beam having a wavelength that is transparent to SiC at a depth from the upper surface of the SiC ingot that is equivalent to the thickness of the wafer to be generated, irradiates the SiC ingot with the laser beam, separates SiC into Si and C, and forms a peeling layer with cracks extending along the c-plane; an X-axis feed mechanism 14, which causes the holding unit 4 and the condenser 10 to perform processing feed relative to each other in the X-axis direction; a Y-axis feed mechanism 16, which causes the holding unit 4 and the condenser 10 to perform indexing feed relative to each other in the Y-axis direction; and a control unit 18, which controls the operation of the laser processing device 2. It should be noted that the X-axis direction is Figure 1 The direction indicated by the arrow X in the middle, the Y axis direction is Figure 1 The direction indicated by the arrow Y is a direction perpendicular to the X-axis direction. In addition, the plane defined by the X-axis direction and the Y-axis direction is substantially horizontal.

[0037] like Figure 1 As shown, the holding unit 4 includes: an X-axis movable plate 22 mounted on a base 20 so as to be freely movable along the X-axis direction; a Y-axis movable plate 24 mounted on the X-axis movable plate 22 so as to be freely movable along the Y-axis direction; a holding worktable 26 mounted on the upper surface of the Y-axis movable plate 24 so as to be freely rotatable; and a holding worktable motor (not shown) for rotating the holding worktable 26.

[0038] Reference Figure 1 and Figure 2 The fluorescence brightness detection member 6 is described. The fluorescence brightness detection member 6 of this embodiment is provided in a frame 28 extending upward from the upper surface of the base 20 and then extending substantially horizontally, and includes a housing 30 attached to the lower surface of the front end of the frame 28. Figure 2As shown, the fluorescence brightness detection component 6 includes: a light source 32, which oscillates an excitation light EL of a specified wavelength (for example, 370nm) with a low output (for example, 0.1W) that does not perform laser processing on the SiC ingot; a dichroic mirror 34, which reflects the excitation light EL of the specified wavelength oscillated by the light source 32, and transmits light of wavelengths other than a first specified wavelength range (for example, 365 to 375nm) including the above-mentioned specified wavelength; a focusing lens 36, which converges the excitation light EL reflected by the dichroic mirror 34 and irradiates it to the SiC ingot; a bandpass filter 38, which transmits light in a second specified wavelength range (for example, 395 to 430nm); and a photodetector 40, which detects the brightness of the light that has passed through the bandpass filter 38.

[0039] In this embodiment, if Figure 2 As shown, the light source 32, the dichroic mirror 34, the focusing lens 36 and the bandpass filter 38 are arranged in the housing 30. In addition, although not shown in the figure, the fluorescence brightness detection member 6 includes a focal point position adjustment member for adjusting the vertical position of the focal point of the excitation light EL by raising and lowering the housing 30, and the focal point position adjustment member can be composed of a ball screw connected to the housing 30 and extending in the vertical direction, and a motor for rotating the ball screw.

[0040] The excitation light EL oscillated by the light source 32 is reflected by the dichroic mirror 34 and guided to the focusing lens 36, where it is converged and irradiated to the SiC ingot. When the excitation light EL is irradiated to the SiC ingot, fluorescence (radiated light) FL containing a wavelength different from the wavelength of the excitation light EL (for example, about 410 nm) is emitted from the SiC ingot. The fluorescence FL passes through the focusing lens 36 and the dichroic mirror 34, and then only the fluorescence FL in the second predetermined wavelength region passes through the bandpass filter 38, and the brightness of the fluorescence FL that passes through the bandpass filter 38 is detected by the photodetector 40. In addition, in the fluorescence brightness detection component 6, the excitation light EL of a predetermined wavelength is irradiated to the SiC ingot from the upper surface of the SiC ingot while the SiC ingot and the shell 30 are relatively moved, thereby detecting the brightness of the SiC-specific fluorescence FL on the entire upper surface of the SiC ingot.

[0041] like Figure 2As shown, the coordinate setting component 8 is electrically connected to the photodetector 40 of the fluorescence brightness detection component 6, and the data of the fluorescence brightness of each part of the SiC ingot detected by the photodetector 40 is input into the coordinate setting component 8. Furthermore, in the coordinate setting component 8, the direction perpendicular to the direction in which the c-plane is inclined relative to the upper surface of the SiC ingot to form a deviation angle is set as the X-axis, the direction perpendicular to the X-axis is set as the Y-axis, the area where the fluorescence brightness detected by the fluorescence brightness detection component 6 is above a specified value is set as the non-small face area, the area where the fluorescence brightness is lower than the specified value is set as the small face area, and the X-coordinate and Y-coordinate of the boundary between the small face area and the non-small face area are set. It should be noted that the X-axis and Y-axis used by the coordinate setting component 8 are the same as Figure 1 The X-axis direction and the Y-axis direction shown above are substantially the same.

[0042] Here, the predetermined value of brightness which is a criterion for distinguishing the facet region from the non-facet region by the coordinate setting means 8 is described. When the SiC ingot is irradiated with light having a wavelength of 370 nm or a wavelength of 273 nm as the excitation light EL, Figure 3 As shown, at any wavelength, the peak brightness appears when the wavelength of the fluorescence FL emitted from the SiC ingot is around 410nm. Figure 3 It is understood that the peak brightness of the small face area and the non-small face area when the wavelength of the excitation light EL is 370nm is different from the peak brightness of the small face area and the non-small face area when the wavelength of the excitation light EL is 273nm. Therefore, the prescribed value of the brightness, which serves as a criterion for distinguishing the small face area from the non-small face area, is set according to the wavelength of the excitation light EL so that it is between the peak brightness of the small face area and the peak brightness of the non-small face area. The prescribed value can be about the middle value of the peak brightness of the small face area and the peak brightness of the non-small face area. For example, when the wavelength of the excitation light EL is 370nm, the peak brightness of the small face area is about 48A.U. (refer to Figure 3 The peak brightness of the non-facet area is about 65A.U. (refer to Figure 3 ), so the specified value can be set to about 55 to 58 A.U. In addition, when the wavelength of the excitation light EL is 273nm, the peak brightness of the small face area is about 28 A.U. (refer to Figure 3 The peak brightness of the non-facet area is about 40A.U. (refer to Figure 3 The thick dotted line in the figure shows the specified value, so the specified value can be set to about 33 to 35 A.U.

[0043] like Figure 1As shown, the condenser 10 of the laser beam irradiation unit 12 and the housing 30 of the fluorescent brightness detection member 6 are installed on the lower surface of the front end of the frame 28 at a distance in the X-axis direction. In addition, although not shown in the figure, the laser beam irradiation unit 12 includes: a laser oscillator that oscillates a pulse laser with a wavelength that is transparent to SiC; an attenuator that adjusts the output of the pulse laser beam emitted from the laser oscillator; and a focal point position adjustment member that raises and lowers the condenser 10 to adjust the vertical position of the focal point of the pulse laser beam. The focal point position adjustment member can be configured to include a ball screw connected to the condenser 10 and extending in the vertical direction, and a motor that rotates the ball screw.

[0044] Furthermore, in the laser beam irradiation unit 12, the condenser 10 is raised and lowered by a focal point position adjustment component, and the focal point of the pulsed laser beam having a wavelength that is transmissive to SiC is positioned at a depth equivalent to the thickness of the wafer to be generated from the upper surface of the SiC ingot held in the holding unit 4. Thereafter, the pulsed laser beam emitted by the laser oscillator and whose output is adjusted by the attenuator is converged by the condenser 10 and irradiated onto the SiC ingot, thereby forming a peeling layer with reduced strength inside the SiC ingot.

[0045] like Figure 1 As shown, the X-axis feed mechanism 14 includes: a ball screw 42 connected to the X-axis movable plate 22 and extending in the X-axis direction; and a motor 44 connected to one end of the ball screw 42. In addition, the X-axis feed mechanism 14 converts the rotational motion of the motor 44 into a linear motion by using the ball screw 42 and transmits it to the X-axis movable plate 22, so that the X-axis movable plate 22 moves forward and backward relative to the condenser 10 along the guide rail 20a on the base 20 in the X-axis direction.

[0046] The Y-axis feed mechanism 16 includes a ball screw 46 connected to the Y-axis movable plate 24 and extending in the Y-axis direction, and a motor 48 connected to one end of the ball screw 46. The Y-axis feed mechanism 16 converts the rotational motion of the motor 48 into a linear motion by the ball screw 46 and transmits the linear motion to the Y-axis movable plate 24, so that the Y-axis movable plate 24 moves forward and backward relative to the condenser 10 along the guide rail 22a on the X-axis movable plate 22 in the Y-axis direction.

[0047] The control unit 18 is electrically connected to the coordinate setting member 8, and the X-coordinate and Y-coordinate of the boundary between the facet region and the non-facet region set by the coordinate setting member 8 are input to the control unit 18. Furthermore, in the control unit 18, based on the X-coordinate and Y-coordinate of the boundary between the facet region and the non-facet region, the energy of the laser beam when irradiating the facet region with the laser beam and the position of the condenser 10 are increased, and the position of the condenser 10 is increased, relative to the energy of the laser beam when irradiating the non-facet region with the laser beam. It should be noted that the control unit 18 and the coordinate setting member 8 may be composed of separate computers or may be composed of a single computer.

[0048] In this embodiment, if Figure 1 As shown, the laser processing device 2 further includes: a shooting unit 50 for shooting the SiC ingot held in the holding unit 4; a display unit 52 for displaying the image shot by the shooting unit 50; a grinding unit 54 for grinding the upper surface of the SiC ingot held in the holding unit 4; and a stripping mechanism 56 for stripping the chip to be generated from the stripping layer of the SiC ingot held in the holding unit 4.

[0049] The imaging unit 50 is mounted on the lower front end of the housing 28 and is disposed between the housing 30 of the fluorescence brightness detection member 6 and the condenser 10 of the laser beam irradiation unit 12. In addition, the display unit 52 is disposed on the upper surface of the housing 28.

[0050] The grinding unit 54 includes: a housing 58 mounted on the side of the frame 28 so as to be freely movable in the Y-axis direction; a housing moving mechanism 60 for moving the housing 58 in the Y-axis direction; an arm 62 extending in the Y-axis direction from a base end supported by the housing 58 so as to be freely liftable; an arm lifting member (not shown) for lifting the arm 62; and a spindle housing 64 mounted on the front end of the arm 62.

[0051] A spindle motor (not shown) is built into the spindle housing 64, and the spindle motor rotatably supports a spindle 66 extending in the vertical direction and rotates the spindle 66. Figure 4 To explain, a disc-shaped grinding wheel mount 68 is fixed to the lower end of the spindle 66, and an annular grinding wheel 72 is fixed to the lower surface of the grinding wheel mount 68 by bolts 70. A plurality of grinding tools 74 arranged annularly at intervals in the circumferential direction are fixed to the outer peripheral portion of the lower surface of the grinding wheel 72.

[0052] like Figure 1As shown, the peeling mechanism 56 includes: a housing 76 disposed at the terminal end of the guide rail 20a on the base 20; an arm 78 extending in the X-axis direction from the base end supported by the housing 76 so as to be freely liftable; and an arm lifting member (not shown) for lifting and lowering the arm 78. A motor 80 is attached to the front end of the arm 78, and an adsorption sheet 82 is connected to the lower surface of the motor 80 so as to be freely rotatable around an axis extending in the vertical direction. A plurality of suction holes (not shown) are formed on the lower surface of the adsorption sheet 82, and the adsorption sheet 82 is connected to the suction member (not shown). In addition, an ultrasonic vibration imparting member (not shown) for imparting ultrasonic vibration to the lower surface of the adsorption sheet 82 is built into the adsorption sheet 82.

[0053] Figure 5 84 is a SiC ingot made of SiC. The SiC ingot 84 is formed into a cylindrical shape as a whole, and has a circular first end face 86, a circular second end face 88 on the opposite side of the first end face 86, a peripheral surface 90 located between the first end face 86 and the second end face 88, and a c-axis ( <0001> direction), and the c-plane ({0001} plane) that is orthogonal to the c-axis.

[0054] In the SiC crystal ingot 84, the c-axis is inclined relative to the perpendicular line 92 of the first end face 86, and the c-plane and the first end face 86 form an offset angle α (for example, α=1, 3, 6 degrees). Figure 5 The direction in which the deviation angle α is formed is indicated by arrow A. In addition, a rectangular first orientation plane 94 and a second orientation plane 96 are formed on the peripheral surface 90 of the SiC crystal ingot 84 to indicate the crystal orientation. The first orientation plane 94 is parallel to the direction A in which the deviation angle α is formed, and the second orientation plane 96 is orthogonal to the direction A in which the deviation angle α is formed. Figure 5 As shown in (b), when viewed from above, the length L2 of the second orientation plane 96 is shorter than the length L1 of the first orientation plane 94 (L2 <L1)。

[0055] In addition, the SiC ingot 84 shown in the figure is mainly formed of hexagonal single crystal SiC, but a small face region 98 having a different crystal structure is partially present. The small face region 98 is formed in a columnar shape from the first end face 86 to the second end face 88 of the SiC ingot 84, and has the same shape as kintaro in the thickness direction (up and down direction) of the SiC ingot 84. It should be noted that the non-small face region other than the small face region 98 is represented by the symbol 100.

[0056] Next, an embodiment of the wafer production method of the present invention is described. Here, a wafer production method using the above-mentioned laser processing device 2 is described. In this embodiment, first, the SiC ingot 84 is fixed to the upper surface of the holding table 26 by a suitable adhesive (e.g., an epoxy resin adhesive). It should be noted that a plurality of suction holes can be formed on the upper surface of the holding table 26, and a suction force is generated on the upper surface of the holding table 26 to attract and hold the SiC ingot 84.

[0057] After SiC ingot 84 is fixed to holding table 26 , a flat surface forming step is performed to grind the upper surface of SiC ingot 84 to form a flat surface, except when the upper surface of SiC ingot 84 is already flat.

[0058] In the flat surface forming step, first, the holding table 26 is positioned below the grinding wheel 72 of the grinding unit 54. Figure 4 As shown, the holding table 26 is rotated at a predetermined rotation speed (e.g., 300 rpm) counterclockwise as viewed from above. In addition, the spindle 66 is rotated at a predetermined rotation speed (e.g., 6000 rpm) counterclockwise as viewed from above. Then, the arm 62 is lowered by the arm lifting member so that the grinding tool 74 contacts the upper surface of the SiC ingot 84 (the first end surface 86 in this embodiment). Thereafter, the arm 62 is lowered at a predetermined grinding feed speed (e.g., 0.1 μm / s). Thus, the upper surface of the SiC ingot 84 can be ground to form a flat surface to a degree that does not hinder the incidence of the laser beam.

[0059] After the flat surface forming step is performed, a fluorescence brightness detection step is performed to irradiate SiC ingot 84 with excitation light EL of a predetermined wavelength from the upper surface of SiC ingot 84 to detect the fluorescence brightness inherent to SiC.

[0060] In the fluorescence brightness detection process, first, the holding table 26 is positioned below the imaging unit 50, and the SiC ingot 84 is imaged from the upper surface by the imaging unit 50. Next, based on the image of the SiC ingot 84 captured by the imaging unit 50, the holding table 26 is moved and rotated by the X-axis feed mechanism 14, the Y-axis feed mechanism 16, and the holding table motor, thereby adjusting the orientation of the SiC ingot 84 to a predetermined orientation, and adjusting the positions of the SiC ingot 84 and the housing 30 of the fluorescence brightness detection member 6 on the XY plane. When the orientation of the SiC ingot 84 is adjusted to a predetermined orientation, as shown in FIG. Figure 6 As shown, by aligning the second orientation flat 96 with the X-axis direction, the direction orthogonal to the direction A formed with the deviation angle α is aligned with the X-axis direction, and the direction A formed with the deviation angle α is aligned with the Y-axis direction.

[0061] Next, the housing 30 is raised and lowered by the light-converging point position adjustment member, and the light-converging point of the excitation light EL is positioned at a suitable position (e.g., the first end face 86) of the SiC crystal ingot 84. Next, while the holding table 26 is moved in the X-axis direction (in the direction orthogonal to the direction A forming the deviation angle α) by the X-axis feed mechanism 14, the SiC crystal ingot 84 is irradiated with the excitation light EL of a predetermined wavelength (e.g., 370 nm) and of a low output (e.g., 0.1 W) that does not cause laser processing to the SiC crystal ingot 84. In this way, as Figure 2 As shown, fluorescence (radiated light) FL having a wavelength different from that of the excitation light EL (e.g., about 410 nm) is emitted from the SiC ingot 84. After the fluorescence FL passes through the condenser lens 36 and the dichroic mirror 34, only the fluorescence FL in the second predetermined wavelength range (e.g., 395 to 430 nm) passes through the bandpass filter 38, and the brightness of the fluorescence FL that passes through the bandpass filter 38 is detected by the photodetector 40.

[0062] Next, the holding table 26 is moved by the Y-axis feeding mechanism 16, so that the SiC crystal ingot 84 is indexed and fed relative to the focal point of the excitation light EL in the Y-axis direction consistent with the direction A where the deviation angle α is formed. Thereafter, by alternately and repeatedly irradiating the excitation light EL and indexing, the brightness of the fluorescence FL of each of the micro areas obtained by dividing the first end surface 86 of the SiC crystal ingot 84 as a whole into a grid of appropriate size in the X-axis direction and the Y-axis direction is associated with the X-coordinate and the Y-coordinate for detection. The data of the brightness of the fluorescence FL detected by the light detector 40 is transmitted to the coordinate setting member 8 in association with the X-coordinate and the Y-coordinate.

[0063] The coordinate setting process is implemented by using the coordinate setting member 8. In this coordinate setting process, the direction A perpendicular to the direction A in which the c-plane is inclined with respect to the upper surface of the SiC crystal ingot 84 (the first end face 86 in this embodiment) to form a deviation angle α is set as the X-axis, and the direction perpendicular to the X-axis is set as the Y-axis. In this fluorescence brightness detection process, the area where the brightness of the fluorescence FL is above a specified value (for example, 55 to 58 A.U. when the wavelength of the excitation light EL is 370nm) is set as the non-small face area 100, and the area where the brightness of the fluorescence FL is lower than the specified value is set as the small face area 98, and the X-coordinate and Y-coordinate of the boundary between the small face area 98 and the non-small face area 100 are set. In the coordinate setting process of this embodiment, as shown in FIG. Figure 7As shown, based on the data of the brightness of the fluorescent light FL transmitted by the light detector 40 of the fluorescent light brightness detection member 6, the X-coordinate and Y-coordinate of the multiple points (e.g., 24 points from point a to point x) at the boundary of the facet region 98 and the non-facet region 100 are set by the coordinate setting member 8. The data of the X-coordinate and Y-coordinate of the multiple points at the boundary of the facet region 98 and the non-facet region 100 set by the coordinate setting member 8 are transmitted to the control unit 18. It should be noted that, in the coordinate setting process, the X-coordinate and Y-coordinate of the entire facet region 98 may be set, and the X-coordinate and Y-coordinate of the entire non-facet region 100 may be set, and these may be transmitted to the control unit 18.

[0064] After the coordinate setting process is implemented, the processing feed process is implemented, and the focal point obtained by converging the laser light with a wavelength that is transparent to SiC using the condenser 10 is positioned at a depth from the upper surface of the SiC crystal ingot 84 equivalent to the thickness of the chip to be generated. While irradiating the SiC crystal ingot 84 with laser light, the SiC crystal ingot 84 and the focal point are processed and fed relative to each other in the X-axis direction, and the SiC is separated into Si and C and a strip-shaped peeling layer is formed in which cracks extend along the c-plane.

[0065] In the processing feeding process, first, based on the image of the SiC ingot 84 captured by the imaging unit 50 in the fluorescence brightness detection process, the holding table 26 is moved in the X-axis direction and the Y-axis direction, thereby adjusting the positions of the SiC ingot 84 and the condenser 10 on the XY plane. Next, the condenser 10 is raised and lowered by the condenser position adjustment member, and the condenser 10 is moved to the non-facet area 100 (see FIG. 1 ). Figure 8 (b)) is positioned at a depth from the upper surface of the SiC ingot 84 corresponding to the thickness of the wafer to be produced. Figure 8 As shown in (a), while the holding table 26 is moved in the X-axis direction (in the direction orthogonal to the direction A forming the deviation angle α) at ​​a predetermined feed speed, a pulsed laser beam LB having a wavelength that is transparent to SiC is irradiated from the condenser 10 to the SiC ingot 84. Fig. 9 As shown, with the irradiation of pulse laser light LB, SiC is separated into Si (silicon) and C (carbon), and the next irradiated pulse laser light LB is absorbed by the previously formed C to cause SiC to be separated into Si and C in a chain reaction, and a crack 104 is formed along the X-axis direction, and a band-shaped peeling layer 106 extends isotropically along the c-plane from the part 102 where SiC is separated into Si and C.

[0066] Furthermore, in such a processing feed process, based on the X-coordinate and Y-coordinate of the facet region 98 and the non-facet region 100 set in the coordinate setting process, the laser beam irradiation unit 12 is controlled by the control unit 18 so that the energy of the pulsed laser beam LB when irradiating the facet region 98 is increased and the position of the condenser 10 is increased relative to the energy of the pulsed laser beam LB and the position of the condenser 10 when irradiating the non-facet region 100. In the case where the refractive index of the facet region 98 is higher than that of the non-facet region 100, by performing the control as described above, as shown in FIG. Figure 8 As shown in (b), the depths of the focal points FP in the facet region 98 and the non-facet region 100 can be made substantially the same, and the depths of the peeling layer 106 formed in the facet region 98 and the non-facet region 100 can be made substantially uniform. In addition, although the facet region 98 has a higher energy absorption rate than the non-facet region 100, by increasing the energy of the pulsed laser beam LB irradiated to the facet region 98 compared to the energy of the pulsed laser beam LB irradiated to the non-facet region 100, the completion of the peeling layer 106 formed in the facet region 98 and the non-facet region 100 can be made uniform.

[0067] Such a processing feeding step can be performed under the following processing conditions, for example. It should be noted that the defocusing described below refers to the amount of movement of the condenser 10 from the state where the focal point FP of the pulsed laser beam LB is positioned on the upper surface of the SiC ingot 84 toward the upper surface of the SiC ingot 84 .

[0068] (Non-facet area: refractive index 2.65)

[0069]

[0070] (Small face area: refractive index 2.79)

[0071]

[0072] In addition, a step of indexing and feeding is performed to index and feed the SiC ingot 84 and the focusing point FP relative to each other in the Y-axis direction, and to arrange the strip-shaped peeling layer 106 in parallel in the Y-axis direction. Figure 8 (a) and Fig. 9) The SiC crystal ingot 84 is indexed and fed relative to the focal point FP in the Y-axis direction while repeating the above-mentioned processing and feeding steps. As a result, strip-shaped peeling layers 106 extending in the X-axis direction can be arranged side by side in the Y-axis direction inside the SiC crystal ingot 84. In addition, by setting the indexing feed amount Li to a range not exceeding the width of the crack 104 and making the cracks 104 of the peeling layers 106 adjacent in the Y-axis direction overlap each other when viewed from the top and bottom, the wafer can be easily peeled in the following peeling step.

[0073] After the processing feeding step and the indexing feeding step are performed to generate a plurality of strip-shaped peeling layers 106 on the SiC crystal ingot 84, a peeling step is performed to peel off the wafer to be generated from the peeling layer 106. In the peeling step, the holding table 26 is first moved to below the suction piece 82 of the peeling mechanism 56. Then, the arm 78 is lowered by the arm lifting member, as shown in FIG. Fig.10 As shown, the lower surface of the suction sheet 82 is brought into close contact with the first end surface 86 of the SiC crystal ingot 84. Next, the suction member is operated to cause the lower surface of the suction sheet 82 to be attracted to the first end surface 86 of the SiC crystal ingot 84. Next, the ultrasonic vibration imparting member is operated to impart ultrasonic vibration to the lower surface of the suction sheet 82, and the suction sheet 82 is rotated by the motor 80. In this way, the SiC wafer 108 to be produced can be peeled off from the peeling layer 106.

[0074] In addition, the above-mentioned flat surface forming step is performed on the SiC ingot 84 from which the SiC wafer 108 is peeled to flatten the peeled surface, and then the processing feeding step, the indexing feeding step, and the peeling step are repeated, thereby making it possible to produce a plurality of SiC wafers 108 from the SiC ingot 84. With regard to the fluorescence brightness detection step and the coordinate setting step, since the facet region 98 is formed in a columnar shape from the upper surface to the lower surface of the SiC ingot 84 and has the same shape like a kintaro in the thickness direction, the fluorescence brightness detection step and the coordinate setting step only need to be performed when the first SiC wafer 108 is produced from the SiC ingot 84, and these steps do not need to be performed when the second and subsequent SiC wafers 108 are produced.

[0075] As described above, in the present embodiment, the position and finish of the peeling layer 106 formed in the facet region 98 and the non-facet region 100 can be made uniform, so that the SiC wafer 108 without a step difference between the facet region 98 and the non-facet region 100 can be generated. Therefore, there is no need to estimate the step difference between the facet region 98 and the non-facet region 100 and peel the SiC wafer 108 thicker, and efficiency can be achieved.

[0076] It should be noted that, in the above-mentioned present embodiment, an example of assembling the fluorescence brightness detection member 6 and the coordinate setting member 8 into the laser processing device 2 is described, but these members may not be assembled into the laser processing device 2. That is, the fluorescence brightness detection member 6 and the coordinate setting member 8 may be components of a detection device for a small face area including at least the fluorescence brightness detection member 6 and the coordinate setting member 8. And the detection device for a small face area including at least the fluorescence brightness detection member 6 and the coordinate setting member 8 may be used to implement a detection method for a small face area including at least the above-mentioned fluorescence brightness detection process and the coordinate setting process. Thus, the small face area 98 and the non-small face area 100 of the SiC crystal ingot 84 can be detected, so that the processing conditions for irradiating the SiC crystal ingot 84 with the pulsed laser beam LB can be appropriately controlled based on the data of the detected small face area 98 and the non-small face area 100, and a SiC wafer 108 without a step difference between the small face area 98 and the non-small face area 100 can be generated.

[0077] Explanation of symbols

[0078] 2: Laser processing equipment

[0079] 4: Keep unit

[0080] 6: Fluorescence brightness detection component

[0081] 8: Coordinate setting component

[0082] 10: Concentrator

[0083] 12: Laser beam irradiation unit

[0084] 14: X-axis feed mechanism

[0085] 16: Y-axis feed mechanism

[0086] 18: Control unit

[0087] 84: SiC ingot

[0088] 98: Small area

[0089] 100: Non-faceted area

[0090] 102: SiC is separated into Si and C parts

[0091] 104: Crack

[0092] 106: Peeling Layer

[0093] 108: SiC wafer

[0094] EL: Excitation light

[0095] FL: Fluorescence

Claims

1. A method for detecting a small face area, which is a method for detecting a small face area of ​​a SiC ingot, wherein: The method comprises the following steps: a fluorescence brightness detection step of irradiating the SiC ingot with excitation light of a predetermined wavelength from the upper surface of the SiC ingot to detect the fluorescence brightness inherent to SiC; and In the coordinate setting process, the direction perpendicular to the direction in which the c-plane is inclined relative to the upper surface of the SiC crystal ingot to form a deviation angle is set as the X-axis, and the direction perpendicular to the X-axis is set as the Y-axis. In the fluorescence brightness detection process, the area where the fluorescence brightness is above a specified value is set as the non-small face area, and the area where the fluorescence brightness is lower than the specified value is set as the small face area, and the X-coordinate and Y-coordinate of the small face area and the non-small face area are set.

2. A method for producing a wafer, which produces a SiC wafer from a SiC ingot, wherein: The method comprises the following steps: a flat surface forming step of grinding the upper surface of the SiC ingot to form a flat surface; a fluorescence brightness detection step of irradiating the SiC ingot with excitation light of a predetermined wavelength from the upper surface of the SiC ingot to detect the fluorescence brightness inherent to SiC; a coordinate setting step, setting a direction perpendicular to the direction in which the c-plane is inclined relative to the upper surface of the SiC crystal ingot to form an offset angle as an X-axis, setting a direction perpendicular to the X-axis as a Y-axis, setting a region in which the fluorescence brightness is greater than a specified value in the fluorescence brightness detection step as a non-small face region, and setting a region in which the fluorescence brightness is less than the specified value as a small face region, and setting an X-coordinate and a Y-coordinate of a boundary between the small face region and the non-small face region; In a processing and feeding step, a light-converging point obtained by converging a laser beam having a wavelength that is transparent to SiC by using a concentrator is positioned at a depth from the upper surface of the SiC ingot that is equivalent to the thickness of a wafer to be generated, and while irradiating the SiC ingot with the laser beam, the SiC ingot and the light-converging point are processed and fed relative to each other in the X-axis direction, so that SiC is separated into Si and C and a strip-shaped peeling layer is formed in which cracks extend along the c-plane; A step of indexing and feeding the SiC ingot and the light-converging point relative to each other in the Y-axis direction, and arranging strip-shaped peeling layers in parallel in the Y-axis direction; as well as a peeling step of peeling off the wafer to be produced from the peeling layer; In the processing feed process, based on the X-coordinate and Y-coordinate of the boundary between the small face area and the non-small face area set by the coordinate setting process, the energy of the laser beam when irradiating the non-small face area with the laser beam is increased, and the position of the condenser is increased relative to the energy of the laser beam when irradiating the non-small face area with the laser beam.

3. A detection device for a small face area, which is a detection device for a small face area of ​​a SiC crystal ingot, wherein: The device has: a fluorescence brightness detection member for irradiating the SiC ingot with excitation light of a predetermined wavelength from the upper surface of the SiC ingot to detect the fluorescence brightness inherent to SiC; and A coordinate setting member, which sets a direction perpendicular to a direction in which a c-plane is inclined relative to an upper surface of a SiC crystal ingot to form a deviation angle as an X-axis, sets a direction perpendicular to the X-axis as a Y-axis, sets an area in which a fluorescence brightness detected by the fluorescence brightness detection member is greater than a specified value as a non-small face area, sets an area in which a fluorescence brightness is lower than the specified value as a small face area, and sets the X-coordinate and Y-coordinate of the small face area and the non-small face area.

4. A laser processing device for forming a peeling layer on a SiC ingot, wherein: The device has: A holding table for holding the SiC ingot; a fluorescence brightness detection member for irradiating the SiC ingot with excitation light of a predetermined wavelength from the upper surface of the SiC ingot to detect the fluorescence brightness inherent to SiC; a coordinate setting member, which sets a direction perpendicular to the direction in which the c-plane is inclined with respect to the upper surface of the SiC crystal ingot to form an off angle as an X-axis, sets a direction perpendicular to the X-axis as a Y-axis, sets a region where the fluorescence brightness detected by the fluorescence brightness detection member is greater than a specified value as a non-small face region, sets a region where the fluorescence brightness is less than the specified value as a small face region, and sets an X-coordinate and a Y-coordinate of a boundary between the small face region and the non-small face region; a laser beam irradiation unit including a condenser that positions a focal point of a laser beam having a wavelength that is transparent to SiC at a depth from an upper surface of the SiC ingot corresponding to the thickness of a wafer to be produced, irradiates the SiC ingot with the laser beam, separates the SiC into Si and C, and forms a peeling layer in which cracks extend along the c-plane; An X-axis feeding mechanism enables the holding table and the condenser to perform processing feeding relative to each other in the X-axis direction; A Y-axis feeding mechanism, which enables the holding table and the condenser to perform indexing feeding relative to each other in the Y-axis direction; as well as A control unit increases the energy of the laser beam when irradiating the small face area with the laser beam, and raises the position of the condenser based on the X and Y coordinates of the boundary between the small face area and the non-small face area, relative to the energy of the laser beam when irradiating the non-small face area with the laser beam and the position of the condenser.

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