Wafer Production Method

Abstract

To provide a generation method of a wafer, capable of preventing a separation layer from curving.SOLUTION: A generation method of a wafer, comprises: a preparation step of preparing a laser processing device; a Z-coordinate measurement step of measuring a height Z(X and Y) of an upper surface of an ingot 2 irradiated with a laser beam in accordance with an X-coordinate and a Y-coordinate where a separation layer to be formed is defined to be an X-Y flat surface; a calculation step of determining the Z-coordinate of a collector 48 by calculating a difference (Z(X and Y)-Z0) between the measured height Z(X and Y) and a Z-coordinate of the separation layer to be formed which is defined to be Z0; a separation layer formation step of forming the separation layer by operating X- axis movement means and Y- axis movement means of the laser processing device to relatively move holding means and the collector 48 in a X- axis direction and a Y- axis direction, and to move the collector 48 in a Z- axis direction on the basis of the Z-coordinate determined in the calculation step so as to position a focal point at the Z0; and a wafer separation step of separating the ingot 2 and the wafer from the separation layer.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a method for producing a wafer, in which a laser beam having a wavelength that is transparent to the ingot is focused inside the ingot from an end face of the ingot, the laser beam is irradiated onto the ingot to form a separation layer, and a wafer is produced from the separation layer. [Background technology]

[0002] Wafers, on whose surface multiple devices such as ICs and LSIs are formed, are divided along planned dividing lines and then separated into individual device chips using a dicing machine and laser processing machine. Each of the separated device chips is used in electrical equipment such as mobile phones and personal computers.

[0003] A Si (silicon) substrate on which a device is formed is formed by slicing a Si ingot to a thickness of about 1 mm using a cutting machine equipped with an inner diameter blade, a wire saw, etc., and then lapping and polishing the sliced ​​silicon ingot (see, for example, Patent Document 1).

[0004] Also, single crystal SiC (silicon carbide) substrates on which power devices, LEDs, etc. are formed are formed in the same manner. However, when cutting a SiC ingot with a wire saw and polishing the front and back surfaces to produce wafers, approximately half of the SiC ingot is wasted, which is uneconomical. Therefore, the applicant has proposed a technology in which the focal point of a laser beam that is transparent to single crystal SiC is positioned inside the SiC ingot, the laser beam is irradiated onto the SiC ingot, a separation layer is formed on the intended cutting surface, and the SiC ingot and wafer are separated along the intended cutting surface on which the separation layer is formed (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2000-94221 A [Patent Document 2] JP 2016-111143 A Summary of the Invention [Problem to be solved by the invention]

[0006] Although the technique disclosed in the above Patent Document 2 has enabled efficient production of wafers from an ingot, there is a problem in that the separation layer is slightly curved.

[0007] In view of the above, an object of the present invention is to provide a method for producing a wafer capable of preventing a separation layer from curving. [Means for solving the problem]

[0008] According to the present invention, there is provided the following wafer production method that solves the above problems: That is, the wafer production method includes positioning the focal point of a laser beam having a wavelength that is transparent to the ingot from an end face of the ingot inside the ingot, irradiating the ingot with the laser beam to form a separation layer, and producing a wafer from the separation layer, and includes a holding means for holding the ingot, a laser beam application means that has a condenser that can move the focal point in the Z-axis direction and irradiates the laser beam from the end face of the ingot held by the holding means, an X-axis movement means that moves the holding means and the condenser relatively in the X-axis direction, a Y-axis movement means that moves the holding means and the condenser relatively in the Y-axis direction, and a Z-coordinate measurement means that measures the height of the upper surface of the ingot. The Z coordinate measuring means is provided in pair on both sides of the condenser in the X-axis direction. A preparation process for preparing a laser processing device, and a height Z of the upper surface of the ingot to be irradiated with the laser beam, with the separation layer to be formed being the XY plane. (X、Y) a Z-coordinate measuring step of measuring the height Z of the separation layer to be formed by setting the Z-coordinate of the separation layer to Z0. (X、Y) The difference between (Z (X、Y)a separation layer forming step of operating the X-axis moving means and the Y-axis moving means to relatively move the holding means and the collector in the X-axis and Y-axis directions to move the collector in the Z-axis direction based on the Z coordinate determined in the calculation step, thereby positioning the focal point at Z0 and forming a separation layer; and a wafer separation step of separating an ingot and a wafer from the separation layer, wherein the Z-coordinate measuring step, the calculation step, and the separation layer forming step are performed in parallel.

[0009] Preferably, in the calculation step, when the numerical aperture of the objective lens of the condenser is NA(sinθ), the focal length of the objective lens is h, the refractive index of the ingot is n(sinθ / sinβ), and the Z coordinate of the objective lens is Z, the Z coordinate for positioning the objective lens is Z = h + (Z (X、Y) -Z0)(1-tanβ / tanθ) and calculate. The ingot is a SiC ingot, and the separation layer formation process preferably includes a processing feed step in which the holding means and the collector are processed and fed relatively in the X-axis direction, with the X-axis direction being a direction perpendicular to the direction in which the c-plane is inclined relative to the end face of the SiC ingot to form an off-angle, and an indexing feed step in which the holding means and the collector are indexed and fed relatively in the Y-axis direction. The ingot is a silicon ingot, and in the separation layer formation step, the crystal face (100) is set as an end face, and a direction parallel to the intersection line where the crystal face {100} and the crystal face {111} intersect is set. <110> It is preferable to include a processing feed step in which the holding means and the condenser are relatively processed and fed in the X-axis direction, with the direction

[0110] perpendicular to the intersection line being taken as the X-axis direction, and an indexing feed step in which the holding means and the condenser are relatively indexed and fed in the Y-axis direction. 。 Effect of the Invention

[0010] The wafer production method of the present invention is a wafer production method in which a focal point of a laser beam having a wavelength that is transparent to the ingot is positioned inside the ingot from an end face of the ingot, the laser beam is irradiated onto the ingot to form a separation layer, and a wafer is produced from the separation layer, and the method includes: a holding means for holding the ingot; a laser beam application means having a condenser that can move the focal point in the Z-axis direction and irradiating the laser beam from the end face of the ingot held by the holding means; an X-axis movement means for relatively moving the holding means and the condenser in the X-axis direction; a Y-axis movement means for relatively moving the holding means and the condenser in the Y-axis direction; and a Z-coordinate measurement means for measuring the height of the top face of the ingot. The Z coordinate measuring means is provided in pair on both sides of the condenser in the X-axis direction. A preparation process for preparing a laser processing device, and a height Z of the upper surface of the ingot to be irradiated with the laser beam, with the separation layer to be formed being the XY plane. (X、Y) a Z-coordinate measuring step of measuring the height Z of the separation layer to be formed by setting the Z-coordinate of the separation layer to Z0. (X、Y) The difference between (Z (X、Y) a separation layer forming step of operating the X-axis moving means and the Y-axis moving means to relatively move the holding means and the collector in the X-axis and Y-axis directions to move the collector in the Z-axis direction based on the Z coordinate determined in the calculation step, thereby positioning the focusing point at Z0 and forming a separation layer; and a wafer separation step of separating an ingot and a wafer from the separation layer, wherein the Z-coordinate measuring step, the calculation step, and the separation layer forming step are performed in parallel, so that a separation layer can be formed on an XY plane specified by the Z0 coordinate position, and curvature of the separation layer can be prevented. [Brief description of the drawings]

[0011] [Figure 1] (a) An oblique view of a SiC ingot, (b) a plan view of the SiC ingot shown in (a), and (c) a front view of the SiC ingot shown in (a). [Diagram 2] (a) Perspective view of a Si ingot, (b) Plan view of the Si ingot shown in (a). [Diagram 3] FIG. [Figure 4] FIG. 4 is a schematic diagram showing the configuration of the laser processing apparatus shown in FIG. 3. [Diagram 5] (a) An oblique view showing a state in which the SiC ingot shown in Figure 1 has been adjusted to a predetermined orientation in the Z-coordinate measurement process; (b) an oblique view showing a state in which the Si ingot shown in Figure 2 has been adjusted to a predetermined orientation in the Z-coordinate measurement process; (c) an oblique view showing a state in which the Si ingot shown in Figure 2 has been adjusted to another orientation in the Z-coordinate measurement process. [Figure 6] 1 is a table showing the measured data of the height Z(X, Y) of the top surface of the ingot. [Figure 7] Schematic diagram of a pulsed laser beam being irradiated onto an ingot through the collector objective lens. [Figure 8] (a) An oblique view showing the state in which a separation layer formation process is being performed on the SiC ingot shown in Figure 1, (b) a side view showing the state in which the separation layer formation process shown in (a) is being performed, and (c) a cross-sectional view of the SiC ingot on which a separation layer has been formed. [Figure 9] (a) An oblique view showing the state in which a separation layer formation process is being performed on the Si ingot shown in Figure 2, (b) a side view showing the state in which the separation layer formation process shown in (a) is being performed, and (c) a cross-sectional view of the Si ingot on which a separation layer has been formed. [Figure 10] FIG. 13 is a perspective view showing a state in which a wafer separation step is being performed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, preferred embodiments of the wafer production method of the present invention will be described with reference to the drawings.

[0013] FIG. 1 shows a cylindrical SiC (silicon carbide) ingot 2 that can be used in the wafer production method of the present invention. The SiC ingot 2 is formed of hexagonal single crystal SiC. The SiC ingot 2 has a circular first end face 4, a circular second end face 6 opposite to the first end face 4, a peripheral surface 8 located between the first end face 4 and the second end face 6, and a c-axis ( <0001> The first end face 4 has a c-plane ({0001} plane) perpendicular to the c-axis. At least the first end face 4 is flattened by grinding or polishing to such an extent that it does not prevent the incidence of a laser beam.

[0014] In the SiC ingot 2, the c-axis is inclined with respect to a perpendicular line 10 to the first end face 4, and an off angle α (for example, α=1, 3, or 6 degrees) is formed between the c-plane and the first end face 4. The direction in which the off angle α is formed is indicated by an arrow A in FIG. 1. In addition, a rectangular first orientation flat 12 and a second orientation flat 14, both of which indicate a crystal orientation, are formed on the peripheral surface 8 of the SiC ingot 2. The first orientation flat 12 is parallel to the direction A in which the off angle α is formed, and the second orientation flat 14 is perpendicular to the direction A in which the off angle α is formed. As shown in FIG. 1(b), when viewed from above, the length L2 of the second orientation flat 14 is shorter than the length L1 of the first orientation flat 12 (L2 <L1)。

[0015] The ingot that can be used in the wafer production method of the present invention is not limited to the SiC ingot 2, and may be, for example, a cylindrical Si (silicon) ingot 16 shown in FIG. 2. The Si ingot 16 has a circular first end face 18 with a crystal plane (100) as an end face, a circular second end face 20 opposite to the first end face 18, and a peripheral surface 22 located between the first end face 18 and the second end face 20. At least the first end face 18 is flattened by grinding or polishing to such an extent that it does not interfere with the incidence of a laser beam. A rectangular orientation flat 24 indicating a crystal orientation is formed on the peripheral surface 22 of the Si ingot 16. The orientation flat 24 is positioned so that the angle with respect to the intersection line 26 where the crystal plane {100} and the crystal plane {111} intersect is 45°.

[0016] In the illustrated embodiment, first, a preparation step is carried out to prepare a laser processing apparatus including a holding means for holding an ingot, a laser beam application means having a collector capable of moving the focal point in the Z-axis direction and applying a laser beam from an end face of the ingot held by the holding means, an X-axis movement means for relatively moving the holding means and the collector in the X-axis direction, and a Y-axis movement means for relatively moving the holding means and the collector in the Y-axis direction.

[0017] In the preparation step, for example, a laser processing device 28 shown in Fig. 3 may be prepared. The laser processing device 28 includes a holding means 30, a laser beam application means 32, an X-axis movement means 34, and a Y-axis movement means 36.

[0018] As shown in Fig. 3, the holding means 30 includes an X-axis movable plate 40 mounted on a base 38 so as to be movable in the X-axis direction, a Y-axis movable plate 42 mounted on the X-axis movable plate 40 so as to be movable in the Y-axis direction, a holding table 44 rotatably mounted on the upper surface of the Y-axis movable plate 42, and a motor (not shown) for rotating the holding table 44. Note that the X-axis direction is the direction indicated by the arrow X in Fig. 3, the Y-axis direction is the direction indicated by the arrow Y in Fig. 3 and is perpendicular to the X-axis direction, and the plane defined by the X-axis and Y-axis directions is substantially horizontal. Also, the direction indicated by the arrow Z in Fig. 3 is the up-down direction perpendicular to each of the X-axis and Y-axis directions.

[0019] In the holding means 30, the ingot is held on the upper surface of the holding table 44 via an appropriate adhesive (for example, an epoxy resin adhesive). Alternatively, a plurality of suction holes may be formed on the upper surface of the holding table 44, and a suction force may be generated on the upper surface of the holding table 44 to hold the ingot by suction.

[0020] Explaining with reference to Figures 3 and 4, the laser beam application means 32 includes a housing 46 (see Figure 3) extending upward from the upper surface of the base 38 and then extending substantially horizontally, an oscillator (not shown) incorporated in the housing 46, a collector 48 (see Figures 3 and 4) mounted on the underside of the tip of the housing 46 so as to be freely raised and lowered, and a lifting means 50 (see Figure 4) for raising and lowering the collector 48.

[0021] The oscillator oscillates a pulsed laser beam having a wavelength that is transparent to the ingot. As shown in FIG. 4, the condenser 48 has an objective lens 48a that condenses the pulsed laser beam oscillated by the oscillator onto the ingot held by the holding means 30. The lifting means 50 can be composed of, for example, a voice coil motor or a linear motor. In the laser beam application means 32, the condenser 48 is raised and lowered by the lifting means 50 to adjust the Z coordinate of the objective lens 48a, so that the focal point of the pulsed laser beam can be moved in the Z-axis direction. As shown in FIG. 3, an imaging means 52 that images the ingot held by the holding means 30 is attached to the lower surface of the tip of the housing 46, and a display means 54 that displays the image captured by the imaging means 52 is disposed on the upper surface of the housing 46.

[0022] Continuing the explanation with reference to Fig. 3, X-axis moving means 34 has a ball screw 56 connected to X-axis movable plate 40 and extending in the X-axis direction, and a motor 58 that rotates ball screw 56. X-axis moving means 34 converts the rotational motion of motor 58 into linear motion using ball screw 56 and transmits it to X-axis movable plate 40, and moves X-axis movable plate 40 in the X-axis direction relative to condenser 48 along guide rails 38a on base 38.

[0023] The Y-axis moving means 36 has a ball screw 60 connected to the Y-axis movable plate 42 and extending in the Y-axis direction, and a motor 62 that rotates the ball screw 60. The Y-axis moving means 36 converts the rotational motion of the motor 62 into linear motion using the ball screw 60 and transmits it to the Y-axis movable plate 42, and moves the Y-axis movable plate 42 in the Y-axis direction relative to the condenser 48 along the guide rail 40a on the X-axis movable plate 40.

[0024] The laser processing apparatus 28 further includes a Z coordinate measuring means 64 (see Figures 3 and 4) for measuring the height of the top surface of the ingot, a control means 66 (see Figure 4) for controlling the operation of the laser processing apparatus 28, and a separation means 68 (see Figure 3) for separating the ingot and the wafer from the separation layer.

[0025] A known laser type or ultrasonic type height measuring device can be used as the Z coordinate measuring means 64. In the illustrated embodiment, a pair of Z coordinate measuring means 64 is provided on both sides of the light collector 48 in the X-axis direction, but there may be only one Z coordinate measuring means 64. The control means 66, which may be composed of a computer, includes a central processing unit (CPU) that performs calculations according to a control program, a read-only memory (ROM) that stores the control program, etc., and a readable and writable random access memory (RAM) that stores calculation results, etc. (none of which are shown in the figure).

[0026] As shown in FIG. 3, the separation means 68 includes a rectangular parallelepiped casing 70 extending upward from the end of the guide rail 38a on the base 38, and an arm 72 extending in the X-axis direction from a base end attached to the casing 70 so as to be freely raised and lowered. The casing 70 has built-in arm elevating means (not shown) for raising and lowering the arm 72. A motor 74 is attached to the tip of the arm 72, and a suction piece 76 is connected to the lower surface of the motor 74 so as to be rotatable about an axis extending in the vertical direction. The suction piece 76 has a plurality of suction holes (not shown) formed on its lower surface, and is connected to the suction means (not shown) by a flow path. The suction piece 76 also has built-in ultrasonic vibration applying means (not shown) for applying ultrasonic vibration to the lower surface of the suction piece 76.

[0027] After carrying out the preparation process, the separation layer to be formed is set to the XY plane, and the height Z of the top surface of the ingot to be irradiated with the laser beam is set to (X、Y) A Z-coordinate measurement step is carried out to measure the above in accordance with the X- and Y-coordinates.

[0028] In the Z coordinate measurement step, first, an ingot (which may be a SiC ingot 2 or a Si ingot 16) is held on the upper surface of the holding table 44. Next, the ingot 2 (16) is imaged from above by the imaging means 52, and based on the image of the ingot 2 (16) captured by the imaging means 52, the holding table 44 is rotated and moved to adjust the orientation of the ingot 2 (16) to a predetermined orientation and to adjust the positional relationship between the Z coordinate measurement means 64 and the ingot 2 (16).

[0029] When adjusting the orientation of the ingot 2 (16) to a predetermined orientation, in the case of a SiC ingot 2, as shown in Fig. 5(a), the second orientation flat 14 is aligned to the X-axis direction to align the direction perpendicular to the direction A in which the off angle α is formed with the X-axis direction. In the case of a Si ingot 16, as shown in Fig. 5(b), the angle between the X-axis direction and the orientation flat 24 is adjusted to 45°, and the direction parallel to the intersection line 26 where the crystal plane {100} and the crystal plane {111} intersect is adjusted to align the direction perpendicular to the X-axis direction with the direction A in which the off angle α is formed with the X-axis direction. <110> Alternatively, in the case of a Si ingot 16, as shown in FIG. 5(c), the angle between the X-axis direction and the orientation flat 24 may be adjusted to 315°, and the direction

[0110] perpendicular to the intersection line 26 may be aligned with the X-axis direction.

[0030] Next, while the holding table 44 holding the ingot 2 (16) is being moved in the X-axis direction by the X-axis moving means 34, one of the pair of Z coordinate measuring means 64 is operated to measure the coordinates (X1, Y1), (X2, Y1), (X3, Y1), ..., (X m , Y1) of the upper surface (the first end surface 4 (18) in the illustrated embodiment) of the ingot 2 (16). (X1、Y1) , Z (X2、Y1) , Z (X3、Y1) , …, Z (Xm、Y1) The height of the upper surface of the ingot 2 (16) to be measured is the height of the upper surface of the ingot 2 (16) when the separation layer to be formed is set as the XY plane (reference plane).

[0031] Next, the holding table 44 is indexed and fed in the Y-axis direction by a predetermined pitch (Y2-Y1) by the Y-axis moving means 36, and then the Z-coordinate measuring means 64 is operated while moving the holding table 44 in the X-axis direction, and the coordinates (X1, Y2), (X2, Y2), (X3, Y2), ..., (X m , Y2) (X1、Y2) , Z (X2、Y2) , Z (X3、Y2) , …, Z (Xm、Y2)Then, measure the coordinate Y n up to a given pitch (Y n -Y n-1 ) while indexing and feeding the holding table 44 in the Y-axis direction, the height of the upper surface of the ingot 2 (16) is measured at multiple points along the X-axis direction, and the height Z of the upper surface of the ingot 2 (16) is measured at multiple points along the X-axis direction as shown in FIG. (X、Y) The data relating to the above is measured in correspondence with the X and Y coordinates, and the measured data is stored in the random access memory of the control means 64.

[0032] After the Z-coordinate measurement process is performed, the Z-coordinate of the separation layer to be formed is set to Z0, and the measured height Z (X、Y) The difference between (Z (X、Y) -Z0) to obtain the Z coordinate of the collector 48.

[0033] Referring to FIG. 7, in the calculation process of the illustrated embodiment, assuming that the numerical aperture of the objective lens 48a of the condenser 48 is NA (sin θ), the focal length of the objective lens 48a is h, the refractive index of the ingot 2 (16) is n (sin θ / sin β), and the Z coordinate of the objective lens 48a is Z, (Z (X、Y) -Z0)tanβ=[h-{Z-(Z (X、Y) -Z0)}]tanθ The above formula can be transformed into (Z (X、Y) -Z0)tanβ / tanθ=h-Z+(Z (X、Y) -Z0) Z = h + (Z (X、Y) -Z0)-(Z (X、Y) -Z0)tanβ / tanθ Z = h + (Z (X、Y) -Z0)(1-tanβ / tanθ) Equation (1) Then, the Z coordinate for positioning the objective lens 48a of the condenser 48 is determined by the above formula (1).

[0034] In the calculation process, the height Z of the top surface of the ingot 2 (16) measured in the Z coordinate measurement process is (X、Y) Based on the data about coordinates (X1, Y1) to (X m , Y n) to calculate the Z coordinate for positioning the objective lens 48a of the condenser 48. Then, m , Y n 7, the focal point FP of the pulsed laser beam LB can be positioned at Z0 by positioning the objective lens 48a of the collector 48 at the Z coordinate calculated in the calculation step. In addition, in Fig. 7, the focal position of the objective lens 48a in air is indicated by the symbol f(h).

[0035] After carrying out the calculation process, the X-axis moving means 34 and the Y-axis moving means 36 are operated to move the holding means 30 and the collector 48 relatively in the X-axis and Y-axis directions, and the collector 48 is moved in the Z-axis direction based on the Z coordinate obtained in the calculation process, thereby positioning the focusing point FP at Z0 and carrying out the separation layer formation process to form a separation layer.

[0036] The separation layer forming step will be described separately for the case where the separation layer forming step is performed on the SiC ingot 2 and the case where the separation layer forming step is performed on the Si ingot 16. First, the case where the separation layer forming step is performed on the SiC ingot 2 will be described with reference to FIG. 8. In the separation layer forming step, first, the positional relationship between the collector 48 and the SiC ingot 2 is adjusted, and the objective lens 48a of the collector 48 is positioned at the Z coordinate calculated in the calculation step. This positions the focal point FP (see FIG. 8(b)) of the pulsed laser beam LB at the Z coordinate (Z0) of the separation layer to be formed. As can be understood by referring to FIG. 8(a), in the separation layer forming step, as in the Z coordinate measurement step, the direction perpendicular to the direction A in which the off angle α is formed is aligned with the X-axis direction.

[0037] Next, the holding table 44 is processed and fed at a predetermined feed rate in the X-axis direction by the X-axis moving means 34, and the light collector 48 is moved in the Z-axis direction by the lifting means 50 based on the Z coordinate obtained in the calculation step, while the SiC ingot 2 is irradiated with a pulsed laser beam LB having a wavelength (e.g., 1064 nm) that is transparent to the SiC ingot 2 (processing and feeding step). As a result, the SiC is separated into Si (silicon) and C (carbon), and the next irradiated pulsed laser beam LB is absorbed by the previously formed C, so that the SiC is separated into Si and C in a chain reaction, and a separation zone 82 is formed in which a crack 80 extending isotropically along the c-plane extends from the portion 78 separated into Si and C.

[0038] In the processing feed step, objective lens 48a of collector 48 is positioned at the Z coordinate calculated in the calculation step, so that the focusing point FP of pulsed laser beam LB can be positioned at Z0 even when the height of the upper surface of SiC ingot 2 is not constant due to the presence of waviness on the upper surface of SiC ingot 2. Therefore, portion 78 of separation band 82 separated into Si and C is formed straight along the X-axis direction at the position of coordinate Z0.

[0039] Next, the Y-axis moving means 36 indexes and feeds the holding table 44 in the Y-axis direction by a predetermined indexing feed amount Li (indexing feed step). The indexing feed amount Li is a predetermined pitch (Y n -Y n-1 ) By alternately repeating the processing feed step and the indexing feed step, a separation layer 84 made up of a plurality of separation bands 82 and having reduced strength can be formed on the XY plane specified by the Z0 coordinate position.

[0040] It is preferable that the indexing feed amount Li does not exceed the width of the crack 80, and that adjacent cracks 80 in the Y-axis direction overlap each other in the vertical direction. This can further reduce the strength of the separation layer 84, making it easier to separate the wafers in the wafer separation process described below.

[0041] Next, a case where a separation layer forming process is performed on a Si ingot 16 will be described with reference to Fig. 9. In the separation layer forming process on a Si ingot 16, the objective lens 48a of the condenser 48 is also first positioned at the Z coordinate calculated in the calculation process. This positions the focusing point FP' (see Fig. 9(b)) of the pulsed laser beam LB' at the Z coordinate (Z0) of the separation layer to be formed. As can be understood by referring to Fig. 9(a), in the separation layer forming process on a Si ingot 16, as in the Z coordinate measurement process, the focusing point FP' (see Fig. 9(b)) of the pulsed laser beam LB' is positioned at the Z coordinate (Z0) of the separation layer to be formed. <110> is aligned with the X-axis direction. Alternatively, although not shown, the direction

[0110] perpendicular to the intersection line 26 may be aligned with the X-axis direction.

[0042] Next, the holding table 44 is processed and fed at a predetermined feed rate in the X-axis direction by the X-axis moving means 34, and the light collector 48 is moved in the Z-axis direction by the lifting means 50 based on the Z coordinate determined in the calculation step, while the Si ingot 16 is irradiated with a pulsed laser beam LB' having a wavelength (e.g., 1342 nm) that is transparent to the Si ingot 16 (processing and feeding step). This destroys the crystal structure of the silicon, and forms a separation zone 90 in which cracks 88 extend isotropically along the (111) plane from a portion 86 where the crystal structure is destroyed. The portion 86 in the separation zone 90 where the crystal structure is destroyed is formed straight along the X-axis at the position of the coordinate Z0.

[0043] In the illustrated embodiment, the direction is parallel to the intersection line 26 where the crystal plane {100} and the crystal plane {111} intersect. <110> The holding table 44 and the collector 48 are moved relative to each other in the direction perpendicular to the intersection line 26

[0110] , however, a separation band 90 similar to that described above is also formed when the holding table 44 and the collector 48 are moved relative to each other in the direction perpendicular to the intersection line 26

[0110] .

[0044] Next, the Y-axis moving means 36 indexes and feeds the holding table 44 in the Y-axis direction by a predetermined indexing feed amount Li' (indexing feed step). The indexing feed amount Li' is a predetermined pitch (Yn -Y n-1 ) By alternately repeating the processing feed step and the indexing feed step, a separation layer 92 having reduced strength and made up of a plurality of separation bands 90 can be formed on the XY plane specified by the Z0 coordinate position.

[0045] Although a small gap may be provided between the cracks 88 of adjacent separation bands 90 in the Y-axis direction, it is preferable to set the indexing feed amount Li' within a range not exceeding the width of the crack 88 so that adjacent separation bands 90 come into contact with each other. This allows adjacent separation bands 90 to be connected to each other, further reducing the strength of the separation layer 92, and makes it easier to separate the wafers in the wafer separation step described below.

[0046] After the separation layer forming step is performed, a wafer separation step is performed in which the ingot 2 (16) and the wafer are separated from the separation layer 84 (92).

[0047] With reference to FIG. 10, an example of separating the SiC ingot 2 and the wafer from the separation layer 84 will be described. In the wafer separation process, first, the holding table 44 is positioned below the suction piece 76 of the separation means 68 by the X-axis moving means 34. Next, the arm 72 is lowered to bring the lower surface of the suction piece 76 into close contact with the upper surface of the SiC ingot 2. Next, the suction means is operated to suction the lower surface of the suction piece 76 to the upper surface of the SiC ingot 2. Next, the ultrasonic vibration applying means is operated to apply ultrasonic vibration to the lower surface of the suction piece 76, and the motor 74 is used to rotate the suction piece 76. This allows the SiC ingot 2 and the wafer 94 to be separated from each other starting from the separation layer 84. After the wafer 94 is separated, the separation surface of the SiC ingot 2 and the separation surface of the wafer 94 are flattened by grinding or polishing. The same procedure is followed when separating the Si ingot 16 and the wafer from the separation layer 92.

[0048] As described above, according to the wafer production method of the illustrated embodiment, the separation layer 84 (92) can be formed on the XY plane specified by the Z0 coordinate position, and the separation layer 84 (92) can be prevented from curving. Moreover, because the separation layer 84 (92) is not curved, a wafer 94 with almost no waviness can be produced from the ingot 2 (16), and the work of removing waviness from the produced wafer 94 can be shortened or omitted.

[0049] In the illustrated embodiment, an example has been described in which the Z coordinate measurement step, the calculation step, and the separation layer formation step are performed separately, but the Z coordinate measurement step, the calculation step, and the separation layer formation step may be performed in parallel. That is, while the X-axis moving means 34 moves the holding table 44 to one side in the X-axis direction (for example, the left side in FIG. 4), the height Z of the upper surface of the ingot 2 (16) is measured by the Z coordinate measuring means 64 on the left side in FIG. (X、Y) (Z coordinate measurement process) and measure the height Z of the measured top surface (X、Y) may be used to determine the Z coordinate of the collector 48 (calculation step), and the laser beam may be irradiated onto the ingot 2 (16) while the collector 48 is moved in the Z-axis direction based on the calculated Z coordinate (separation layer formation step).

[0050] When the Z-coordinate measurement step, the calculation step, and the separation layer formation step are performed in parallel in this manner, it is preferable to provide Z-coordinate measurement means 64 on both sides of the collector 48 in the X-axis direction. This makes it possible to measure the height of the upper surface of the ingot 2 (16) before the collector 48 irradiates the ingot 2 (16) with a laser beam, regardless of whether the holding table 44 is moved to one side or the other side in the X-axis direction (left or right in FIG. 4). Therefore, when the Z-coordinate measurement means 64 are provided on both sides of the collector 48 in the X-axis direction, the holding table 44 can first be processed and fed to one side in the X-axis direction to form the separation layer 84 (92), and then indexed and fed, and then the holding table 44 can be processed and fed to the other side in the X-axis direction to form the separation layer 84 (92). In other words, the separation layer 84 (92) can be formed on both the forward and return passes, which improves productivity. [Explanation of symbols]

[0051] 2: SiC ingot 16:Si ingot 28: Laser processing equipment 30: Holding means 32: Laser beam irradiation means 34:X-axis movement means 36: Y-axis movement means 48: Concentrator 48a: Objective lens 84: Separation layer (SiC ingot) 92: Separation layer (Si ingot) α: Off angle A: The direction in which the off angle is formed

Claims

1. A method for producing a wafer, comprising: positioning a focal point of a laser beam having a wavelength that is transparent to the ingot from an end face of the ingot inside the ingot, irradiating the ingot with the laser beam to form a separation layer, and producing a wafer from the separation layer, a preparation step of preparing a laser processing device comprising: holding means for holding an ingot; laser beam application means having a condenser capable of moving a focal point in a Z-axis direction and applying a laser beam from an end face of the ingot held by the holding means; X-axis movement means for relatively moving the holding means and the condenser in an X-axis direction; Y-axis movement means for relatively moving the holding means and the condenser in a Y-axis direction; and Z-coordinate measurement means for measuring the height of an upper face of the ingot, the Z-coordinate measurement means being provided in pair on both sides of the condenser in the X-axis direction; The separation layer to be formed is the XY plane, and the height Z of the top surface of the ingot to be irradiated with the laser beam is （Ｘ、Ｙ） a Z-coordinate measuring step of measuring the X-coordinate and Y-coordinate by the Z-coordinate measuring means; The Z coordinate of the separation layer to be formed is Z ０ The measured height Z （Ｘ、Ｙ） The difference between （Ｘ、Ｙ） -Z ０ ) to obtain a Z coordinate of the collector; The X-axis moving means and the Y-axis moving means are operated to relatively move the holding means and the condenser in the X-axis direction and the Y-axis direction, and the condenser is moved in the Z-axis direction based on the Z coordinate obtained in the calculation step, thereby moving the condenser to the Z-axis direction. ０ a separation layer forming step of forming a separation layer at the position indicated by the arrow A; a wafer separation step of separating an ingot and a wafer from the separation layer; Including, A wafer producing method in which the Z coordinate measuring step, the calculation step, and the separation layer forming step are carried out in parallel.

2. In the calculation step, assuming that the numerical aperture of the objective lens of the condenser is NA (sin θ), the focal length of the objective lens is h, the refractive index of the ingot is n (sin θ / sin β), and the Z coordinate of the objective lens is Z, The Z coordinate for positioning the objective lens is: Z=h+(Z （Ｘ、Ｙ） -Z ０ )(1-tanβ / tanθ) The method for producing a wafer according to claim 1, wherein the above formula is obtained.

3. the ingot is a SiC ingot; 3. The method for producing a wafer according to claim 1 or 2, wherein the separation layer formation process includes a processing feed step in which the holding means and the collector are processed and fed relatively in the X-axis direction, with the X-axis direction being a direction perpendicular to the direction in which the c-plane is inclined relative to the end face of the SiC ingot to form an off-angle, and an indexing feed step in which the holding means and the collector are indexed and fed relatively in the Y-axis direction.

4. The ingot is a Si ingot, In the separation layer forming step, the crystal face (100) is set as an end face, 3. The wafer production method according to claim 1, further comprising: a processing feed step in which the holding means and the collector are relatively processed and fed in the X-axis direction, with the direction <110> parallel to the intersection line between the crystal plane {100} and the crystal plane {111} or the direction [110] perpendicular to the intersection line being the X-axis direction; and an indexing feed step in which the holding means and the collector are relatively indexed and fed in the Y-axis direction.

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