CN114589421A - Method for processing SiC ingot and laser processing device - Google Patents

Method for processing SiC ingot and laser processing device Download PDF

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Publication number
CN114589421A
CN114589421A CN202011414819.4A CN202011414819A CN114589421A CN 114589421 A CN114589421 A CN 114589421A CN 202011414819 A CN202011414819 A CN 202011414819A CN 114589421 A CN114589421 A CN 114589421A
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CN
China
Prior art keywords
sic ingot
processing
laser beam
axis direction
reflected light
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Pending
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CN202011414819.4A
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Chinese (zh)
Inventor
平田和也
田畑晋
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Disco Corp
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Disco Corp
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Priority to CN202011414819.4A priority Critical patent/CN114589421A/en
Publication of CN114589421A publication Critical patent/CN114589421A/en
Pending legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/50—Working by transmitting the laser beam through or within the workpiece
    • B23K26/53—Working by transmitting the laser beam through or within the workpiece for modifying or reforming the material inside the workpiece, e.g. for producing break initiation cracks
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/03—Observing, e.g. monitoring, the workpiece
    • B23K26/032—Observing, e.g. monitoring, the workpiece using optical means
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/064—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms
    • B23K26/0643—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms comprising mirrors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/08—Devices involving relative movement between laser beam and workpiece
    • B23K26/083—Devices involving movement of the workpiece in at least one axial direction
    • B23K26/0853—Devices involving movement of the workpiece in at least in two axial directions, e.g. in a plane
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/08—Devices involving relative movement between laser beam and workpiece
    • B23K26/0869—Devices involving movement of the laser head in at least one axial direction
    • B23K26/0876—Devices involving movement of the laser head in at least one axial direction in at least two axial directions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
    • B24B27/00—Other grinding machines or devices
    • B24B27/0076—Other grinding machines or devices grinding machines comprising two or more grinding tools
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
    • B24B7/00—Machines or devices designed for grinding plane surfaces on work, including polishing plane glass surfaces; Accessories therefor
    • B24B7/10—Single-purpose machines or devices
    • B24B7/16—Single-purpose machines or devices for grinding end-faces, e.g. of gauges, rollers, nuts, piston rings
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
    • B24B7/00—Machines or devices designed for grinding plane surfaces on work, including polishing plane glass surfaces; Accessories therefor
    • B24B7/20—Machines or devices designed for grinding plane surfaces on work, including polishing plane glass surfaces; Accessories therefor characterised by a special design with respect to properties of the material of non-metallic articles to be ground
    • B24B7/22—Machines or devices designed for grinding plane surfaces on work, including polishing plane glass surfaces; Accessories therefor characterised by a special design with respect to properties of the material of non-metallic articles to be ground for grinding inorganic material, e.g. stone, ceramics, porcelain
    • B24B7/228—Machines or devices designed for grinding plane surfaces on work, including polishing plane glass surfaces; Accessories therefor characterised by a special design with respect to properties of the material of non-metallic articles to be ground for grinding inorganic material, e.g. stone, ceramics, porcelain for grinding thin, brittle parts, e.g. semiconductors, wafers

Abstract

The invention provides a method for processing a SiC ingot and a laser processing device, wherein the method for processing the SiC ingot can form a proper stripping belt in the SiC ingot at any height. The method for processing the SiC ingot comprises the following steps: a separation band forming step of positioning a converging point of a processing laser beam having a wavelength that is transparent to the SiC ingot at a depth corresponding to a thickness of a wafer to be produced, and irradiating the SiC ingot with the processing laser beam to form a band-shaped separation band composed of cracks; a reflected light detection step of irradiating the separation zone with an inspection laser beam having a wavelength which is transmissive to the SiC ingot and is reflected at the crack of the separation zone, and detecting the intensity of the reflected light reflected at the crack; and a processing laser beam output adjustment step of adjusting the output of the processing laser beam so that the intensity of the reflected light detected in the reflected light detection step falls within a predetermined range.

Description

Method for processing SiC ingot and laser processing device
Technical Field
The present invention relates to a method of processing a SiC ingot and a laser processing apparatus.
Background
IC. The devices such as LSI and LED are made of Si (silicon) and Al2O3A functional layer is laminated on the front surface of a wafer as a raw material such as sapphire and is divided by a plurality of intersecting planned dividing lines. Further, a power device, an LED, or the like is formed by stacking a functional layer on the front surface of a wafer made of single crystal SiC (silicon carbide) as a raw material and dividing the functional layer by a plurality of intersecting planned dividing lines. The wafer on which the devices are formed is divided into device chips by processing the lines to be divided by a cutting device or a laser processing device, and the divided device chips are used in electronic devices such as mobile phones and personal computers.
A wafer on which devices are formed is generally produced by thinly cutting a cylindrical semiconductor ingot by a wire saw. The cut wafer is finished into a mirror surface by polishing the front and back surfaces (see, for example, patent document 1). However, when the front and back surfaces of the cut wafer are polished by cutting the semiconductor ingot with a wire saw, most (70 to 80%) of the semiconductor ingot is discarded, which is not economical. In particular, the SiC ingot has a high hardness, is difficult to cut by a wire saw, and requires a considerable time, so that the productivity is poor, and the semiconductor ingot has a high unit price, which is a problem in efficiently producing wafers.
Therefore, the present applicant has proposed the following techniques: a method for separating a wafer from an SiC ingot includes positioning a converging point of a laser beam having a wavelength that is transparent to single crystal SiC inside the SiC ingot, irradiating the SiC ingot with the laser beam, forming a separation zone on a predetermined cutting plane, and separating the wafer from the SiC ingot along the predetermined cutting plane on which the separation zone is formed (see, for example, patent document 2).
Patent document 1: japanese patent laid-open No. 2000-94221
Patent document 2: japanese patent laid-open publication No. 2016-111143
However, since the crystal structure becomes uniform as the SiC ingot grows, it is necessary to increase the energy of the laser beam irradiated to the SiC ingot when the exfoliation band is formed in the first growing portion, as compared with the case where the exfoliation band is formed in the last growing portion, and there is a problem that the energy of the laser beam for forming an appropriate exfoliation band differs depending on the height (axial position) of the SiC ingot.
Disclosure of Invention
Accordingly, an object of the present invention is to provide a method and a laser processing apparatus for processing a SiC ingot, which can form an appropriate separation zone in the SiC ingot at an arbitrary height.
According to an aspect of the present invention, there is provided a method of processing a SiC ingot, including the steps of: a strip forming step of forming a strip-shaped strip by processing and feeding the SiC ingot and a light-converging point of processing laser light having a wavelength that is transparent to the SiC ingot in the X-axis direction while positioning the light-converging point at a depth corresponding to a thickness of a wafer to be produced, the strip forming step being performed such that a direction perpendicular to a direction in which an off angle is formed by an end face and a C-face of the SiC ingot is an X-axis direction, the C-face being inclined with respect to the end face of the SiC ingot, the direction perpendicular to the X-axis direction being a Y-axis direction, and the SiC ingot being processed and fed so as to face the light-converging point in the X-axis direction, the strip extending along the C-face at a portion where a crack is separated from SiC into Si and C; an index feeding step of indexing the SiC ingot and the light converging point in the Y axis direction so as to be opposed to each other and arranging the peeling tape in parallel in the Y axis direction; a reflected light detection step of irradiating the separation zone with an inspection laser beam having a wavelength which is transmissive to the SiC ingot and is reflected at the crack of the separation zone, and detecting an intensity of the reflected light reflected at the crack; and a processing laser beam output adjustment step of adjusting the output of the processing laser beam so that the intensity of the reflected light detected in the reflected light detection step falls within a predetermined range.
Preferably, the method of processing an SiC ingot further includes the following step of forming a flat surface: before the release tape forming step, the end face of the SiC ingot is ground to form a flat surface.
According to another aspect of the present invention, there is provided a laser processing apparatus for forming a delaminated tape in a SiC ingot, the laser processing apparatus including: a chuck table for holding a SiC ingot; a laser beam irradiation unit including a condenser that irradiates the SiC ingot with a processing laser beam having a wavelength that is transmissive to the SiC ingot, the condenser being positioned at a condensing point of the processing laser beam at a depth corresponding to a thickness of a wafer to be produced, the laser beam irradiation unit forming a ribbon-shaped peeling tape in which a portion where a crack is separated from SiC into Si and C extends along a C-plane, the X-axis direction being a direction perpendicular to a direction in which a deviation angle is formed between the C-plane and the C-plane of the SiC ingot, the C-plane being inclined with respect to the end surface of the SiC ingot held by the chuck table, and the Y-axis direction being a direction perpendicular to the X-axis direction; an X-axis feeding mechanism which carries out processing feeding on the chuck worktable and the condenser relatively in the X-axis direction; a Y-axis feeding mechanism for indexing the chuck table and the condenser in the Y-axis direction; a reflected light detection unit that irradiates the peeling tape with an inspection laser beam having a wavelength that is transmissive to the SiC ingot and that is reflected at a crack in the peeling tape, and detects an intensity of reflected light that is reflected at the crack; and a control unit that adjusts the output of the processing laser beam so that the intensity of the reflected light detected by the reflected light detection unit is within a predetermined range.
According to the method for processing a SiC ingot of the present invention, an appropriate separation zone can be formed in the SiC ingot at any height.
According to the laser processing apparatus of the present invention, as in the case of the SiC ingot processing method, an appropriate separation zone can be formed in the SiC ingot at an arbitrary height.
Drawings
Fig. 1 is a perspective view of a laser processing apparatus according to an embodiment of the present invention.
Fig. 2 is a block diagram showing a part of the structure of the laser processing apparatus shown in fig. 1.
Fig. 3 (a) is a front view of the SiC ingot, and fig. 3 (b) is a plan view of the SiC ingot.
Fig. 4 is a perspective view showing a state where the flat surface forming step is performed.
Fig. 5 (a) is a perspective view showing a state where a release tape forming process is performed, and fig. 5 (b) is a cross-sectional view showing a state where the release tape forming process is performed.
Fig. 6 is a perspective view showing a state where the reflected light detection step is performed.
Fig. 7 is a perspective view showing a state where the peeling step is performed.
Description of the reference symbols
2: a laser processing device; 4: a holding unit; 6: a condenser; 8: a laser beam irradiation unit; 10: an X-axis feed mechanism; 12: a Y-axis feed mechanism; 14: a reflected light detection unit; 16: a control unit; 86: SiC ingots; 100: SiC into Si and C fractions; 102: cracking; 104: stripping the tape; 106: a wafer; LB 1: a pulsed laser beam for machining; LB 2: the inspection is performed with pulsed laser light.
Detailed Description
Preferred embodiments of a method for processing a SiC ingot and a laser processing apparatus according to the present invention will be described below with reference to the drawings.
First, a laser processing apparatus according to an embodiment of the present invention will be described with reference to fig. 1. The laser machining device, generally designated by the reference numeral 2, comprises at least: a holding unit 4 that holds a SiC ingot; a laser beam irradiation unit 8 having a condenser 6, the condenser 6 positioning a condensing point of a processing laser beam having a wavelength that is transparent to the SiC ingot at a depth corresponding to a thickness of a wafer to be produced and irradiating the SiC ingot with the laser beam, the laser beam irradiation unit 8 forming a strip-shaped separation zone in which a portion where a crack is separated from SiC into Si (silicon) and C (carbon) extends along a C-plane; an X-axis feed mechanism 10 that feeds the holding unit 4 and the condenser 6 to the X-axis direction; a Y-axis feed mechanism 12 that index-feeds the holding unit 4 and the condenser 6 in the Y-axis direction; a reflected light detection unit 14 that irradiates the delaminated tape with an inspection laser beam having a wavelength that is transmissive to the SiC ingot and that is reflected at a crack in the delaminated tape, and detects the intensity of the reflected light that is reflected at the crack; and a control unit 16 (see fig. 2) that adjusts the output of the processing laser beam so that the intensity of the reflected light detected by the reflected light detection unit 14 falls within a predetermined range. The X-axis direction is a direction indicated by an arrow X in fig. 1, and the Y-axis direction is a direction indicated by an arrow Y in fig. 1, and is a direction perpendicular to the X-axis direction. The plane defined by the X-axis direction and the Y-axis direction is substantially horizontal.
As shown in fig. 1, the holding unit 4 includes: an X-axis movable plate 20 mounted on the base 18 to be movable in the X-axis direction; a Y-axis movable plate 22 mounted on the X-axis movable plate 20 to be movable in the Y-axis direction; a circular holding table 24 rotatably mounted on the upper surface of the Y-axis movable plate 22; and a holding table motor (not shown) for rotating the holding table 24.
The laser beam irradiation unit 8 includes a housing 26 extending upward from the upper surface of the base 18 and then extending substantially horizontally. As shown in fig. 2, the housing 26 incorporates therein: a laser oscillator 28 that oscillates a processing pulse laser beam having a wavelength that is transparent to the SiC ingot; an attenuator 30 that adjusts the output of the processing pulsed laser beam LB1 emitted from the laser oscillator 28; and a mirror 32 that reflects the processing pulse laser beam LB1 whose output has been adjusted by the attenuator 30 and guides the reflected beam to the condenser 6.
As shown in fig. 1, the condenser 6 of the laser light irradiation unit 8 is mounted on the front end lower surface of the housing 26. The laser beam irradiation unit 8 includes a focal point position adjustment unit (not shown). The focal point position adjusting means may be configured to include, for example, a ball screw connected to the condenser 6 and extending in the vertical direction and a motor for rotating the ball screw, and adjust the vertical position of the focal point of the processing pulse laser beam LB1 emitted from the oscillator 28.
The c-plane is inclined with respect to the end face of the SiC ingot held by the holding unit 4, a direction perpendicular to a direction forming an off-angle between the end face and the c-plane of the SiC ingot is an X-axis direction, a direction perpendicular to the X-axis direction is a Y-axis direction, and the condenser 6 irradiates the SiC ingot with the processing pulse laser beam LB1 by positioning a condensing point of the processing pulse laser beam LB1 having a wavelength that is transparent to the SiC ingot at a depth corresponding to the thickness of the wafer to be produced.
As shown in fig. 1, an imaging unit 3 for imaging the SiC ingot held by the holding unit 4 is attached to the front end lower surface of the housing 26 at a distance 4 from the condenser 6 in the X-axis direction. Further, a display unit 36 that displays an image captured by the imaging unit 34 is disposed on the upper surface of the housing 26.
The X-axis feed mechanism 10 includes: a ball screw 38 extending in the X-axis direction along the upper surface of the base 18; and a motor 40 that rotates the ball screw 38. The nut portion (not shown) of the ball screw 38 is coupled to the X-axis movable plate 20. The X-axis feed mechanism 10 converts the rotational motion of the motor 40 into linear motion by the ball screw 38 and transmits the linear motion to the X-axis movable plate 20, thereby feeding the X-axis movable plate 20 along the guide rail 18a on the base 18 in the X-axis direction relative to the condenser 6.
The Y-axis feed mechanism 12 includes: a ball screw 42 extending in the Y-axis direction along the upper surface of the X-axis movable plate 20; and a motor 44 that rotates the ball screw 42. The nut portion (not shown) of the ball screw 42 is coupled to the Y-axis movable plate 22. The Y-axis feed mechanism 12 converts the rotational motion of the motor 44 into linear motion by the ball screw 42 and transmits the linear motion to the Y-axis movable plate 22, thereby indexing and feeding the Y-axis movable plate 22 along the guide rail 20a on the X-axis movable plate 20 relative to the condenser 6 in the Y-axis direction.
Continuing with the description of fig. 1, the reflected light detection unit 14 includes a light emitter 46 and a light receiver 48, and the light emitter 46 and the light receiver 48 are both mounted on the lower surface of the front end of the housing 26. The light emitter 46 includes: a laser oscillator (not shown) that oscillates a pulse laser for inspection having a wavelength that is transparent to the SiC ingot and that is reflected at a crack of the separation zone; and an irradiator (not shown) for irradiating the SiC ingot with the inspection pulse laser beam LB2 emitted from the laser oscillator. The light receiver 48 may be constituted by a photodiode or the like.
The light emitter 46 and the light receiver 48 are both movable in the X-axis direction, the Y-axis direction, and the vertical direction, and are configured so that the angle of the light emitter 46 and the angle of the light receiver 48 (both angles with respect to the end face of the SiC ingot) can be changed. This makes it possible to adjust the incident angle θ of the inspection pulse laser beam LB2 with respect to the end face of the SiC ingot, and to adjust the position of the light receiving surface of the light receiver 48 in the optical path of the inspection pulse laser beam LB2 reflected at the crack of the separation zone (see fig. 6).
The control unit 16, which is constituted by a computer, includes: a Central Processing Unit (CPU) for performing arithmetic processing according to a control program; a Read Only Memory (ROM) that stores a control program and the like; and a readable and writable Random Access Memory (RAM) (both not shown) for storing the operation result and the like.
As shown in fig. 2, the control unit 16 is electrically connected to the light receiver 48, and a signal relating to the intensity of the reflected light detected by the light receiver 48 is transmitted from the light receiver 48 to the control unit 16. The control unit 16 is also electrically connected to the attenuator 30 of the laser beam irradiation unit 8. The control unit 16 controls the attenuator 30 based on the intensity of the reflected light transmitted from the light receiver 48, and adjusts the output of the processing pulse laser beam LB1 such that the intensity of the reflected light detected by the light receiver 48 is within a predetermined range (for example, within a range of 1V to 1.2V in the voltage signal output from the light receiver 48).
The predetermined range is a range in which the separation zone can be appropriately formed inside the SiC ingot and the wafer can be appropriately separated from the SiC ingot, and is appropriately set according to the results of experiments performed in advance and the like. If the intensity of the reflected light is less than the lower limit of the predetermined range, there is a possibility that the crack of the separation zone does not grow sufficiently, and the wafer cannot be appropriately separated from the SiC ingot. Therefore, when the intensity of the reflected light is less than the lower limit of the predetermined range, the control unit 16 controls the attenuator 30 to increase the output of the processing pulse laser beam LB1 so that the intensity of the reflected light falls within the predetermined range.
On the other hand, when the intensity of the reflected light detected by the light receiver 48 exceeds the upper limit value of the predetermined range, although the wafer can be appropriately peeled from the SiC ingot, cracks of the peeling tape grow more than necessary, and the amount of grinding when the peeled surface of the SiC ingot and the peeled surface of the wafer are ground and flattened after the wafer is peeled from the SiC ingot increases, and the loss of the raw material increases. Therefore, when the intensity of the reflected light exceeds the upper limit of the predetermined range, the control unit 16 controls the attenuator 30 to decrease the output of the processing pulse laser beam LB1 so that the intensity of the reflected light falls within the predetermined range.
As shown in fig. 1, the laser processing apparatus 2 of the present embodiment further includes: a peeling unit 50 that peels the wafer from the SiC ingot with the peeling tape as a starting point; and a grinding unit 52 that grinds an end face of the SiC ingot to form the end face into a flat surface.
The peeling unit 50 includes: a housing 54 disposed at the terminal end of the guide rail 18a on the base 18; an arm 56 extending in the X-axis direction from a base end supported to be movable up and down on the housing 54; and an arm lifting unit (not shown) that lifts and lowers the arm 56. The arm lifting unit may be configured to include a ball screw coupled to the arm 56 and extending in the vertical direction, and a motor for rotating the ball screw. A motor 58 is attached to the front end of the arm 56, and a suction piece 60 is connected to the lower surface of the motor 58 so as to be rotatable about an axis extending in the vertical direction. A plurality of suction holes (not shown) are formed in the lower surface of the suction sheet 60, and the suction sheet 60 is connected to a suction unit (not shown). The suction sheet 60 incorporates an ultrasonic vibration applying unit (not shown) for applying ultrasonic vibration to the lower surface of the suction sheet 60.
The grinding unit 52 includes: a mounting wall 62 connected to the housing 26; a lifting plate 64 mounted on one surface of the mounting wall 62 to be lifted and lowered; and a lifting unit 66 for lifting the lifting plate 64. The lifting unit 66 includes a ball screw 68 extending in the vertical direction along one surface of the mounting wall 62, and a motor 70 for rotating the ball screw 68. The nut portion (not shown) of the ball screw 68 is coupled to the lifting plate 64. In the elevating unit 66, the rotational motion of the motor 70 is converted into linear motion by the ball screw 68 and transmitted to the elevating plate 64, and the elevating plate 64 is elevated along the guide rail 62a attached to one surface of the mounting wall 62.
A support wall 72 protruding in the Y-axis direction is fixed to one surface of the rising and lowering plate 64. The spindle 74 is supported rotatably about an axis extending in the vertical direction on the support wall 72, and a spindle motor 76 for rotating the spindle 74 is mounted on the upper surface of the support wall 72. Referring to fig. 1 and 4, a disc-shaped grinding wheel mounting seat 78 is fixed to the lower end of the main shaft 74, and an annular grinding wheel 82 is fixed to the lower surface of the grinding wheel mounting seat 78 by a bolt 80. A plurality of grinding stones 84 are fixed to the outer peripheral edge of the lower surface of the grinding wheel 82 at circumferentially spaced intervals and arranged in a ring shape.
A cylindrical SiC ingot 86 formed of SiC is shown in fig. 3. The SiC ingot 86 has: a first end face 88 of circular shape; a second end face 90 of circular shape located on the opposite side of the first end face 88; a peripheral surface 92 located between the first 88 and second 90 end surfaces; a c-axis (<0001> direction) from the first end face 88 to the second end face 90; and the c plane ({0001} plane) perpendicular to the c axis.
In SiC ingot 86, the c-plane is inclined with respect to first end surface 88 (the c-axis is inclined with respect to perpendicular 94 to first end surface 88), and first end surface 88 and the c-plane form an off-angle α (for example, α is 1 degree, 3 degrees, or 6 degrees). The direction in which the deviation angle alpha will be formed is shown by arrow a in fig. 3. Further, a first orientation flat 96 and a second orientation flat 98, both of which have a rectangular shape and show crystal orientation, are formed on the circumferential surface 92 of the SiC ingot 86. The first orientation plane 96 is parallel to the direction a forming the deviation angle α and the second orientation plane 98 is perpendicular to the direction a forming the deviation angle α. As shown in fig. 3 (b), the length L2 of the second orientation plane 98 is shorter than the length L1 of the first orientation plane 96 (L2< L1) as viewed from above.
Next, a preferred embodiment of the method for processing an SiC ingot according to the present invention will be described, and here, a method for processing an SiC ingot using the laser processing apparatus 2 will be described. In the SiC ingot processing method of the present embodiment, first, the SiC ingot 86 is fixed to the upper surface of the holding table 24 with the second end surface 90 facing downward and with a suitable adhesive (for example, an epoxy adhesive). Further, a plurality of suction holes may be formed in the upper surface of the holding table 24, and the SiC ingot 86 may be sucked and held by generating a suction force on the upper surface of the holding table 24.
After SiC ingot 86 is fixed to holding table 24, a flat surface forming step is performed to grind the end surface of SiC ingot 86 to form a flat surface, except when the end surface of SiC ingot 86 is already formed flat.
In the flat surface forming step, first, the holding table 24 is positioned below the grinding wheel 82 of the grinding unit 52 by the X-axis feed mechanism 10. Next, as shown in fig. 4, the holding table 24 is rotated counterclockwise at a predetermined rotational speed (for example, 300rpm) when viewed from above by the holding table motor. The spindle 74 is rotated counterclockwise at a predetermined rotational speed (for example, 6000rpm) when viewed from above by the spindle motor 76. Next, the main shaft 74 is lowered by the lifting means 66, and the grinding whetstone 84 is brought into contact with the first end surface 88 of the SiC ingot 86. Thereafter, the spindle 74 is lowered at a predetermined grinding feed rate (e.g., 0.1 μm/s). This can grind the first end surface 88 of the SiC ingot 86 to form a flat surface to an extent that does not interfere with incidence of the laser beam.
After the SiC ingot 86 is held by the upper surface of the holding table 24, a strip forming step is performed in which a direction perpendicular to a direction a in which an off-angle α is formed by an end surface of the SiC ingot 86 and a C-plane inclined with respect to the end surface of the SiC ingot 86 and a direction perpendicular to the X-axis direction is set as an X-axis direction, a converging point of a processing pulse laser beam LB1 having a wavelength transparent to the SiC ingot 86 is positioned at a depth corresponding to a thickness of a wafer to be produced, the SiC ingot 86 is irradiated with the processing pulse laser beam LB1, and the SiC ingot 86 and the converging point are relatively processed and fed in the X-axis direction to form a strip-shaped strip in which a portion where a crack is separated from SiC into Si and C extends along the C-plane.
In the separation tape forming step, first, the SiC ingot 86 is imaged by the imaging unit 34 from above the SiC ingot 86. Next, based on the image of the SiC ingot 86 captured by the imaging unit 34, the holding table 24 is moved and rotated by the X-axis feeding mechanism 10, the Y-axis feeding mechanism 12, and the holding-table motor, whereby the orientation of the SiC ingot 86 is adjusted to a predetermined orientation, and the position of the SiC ingot 86 and the condenser 6 on the XY plane is adjusted. When the orientation of SiC ingot 86 is adjusted to a predetermined orientation, second orientation flat 98 is aligned with the X-axis direction, the direction perpendicular to direction a forming off-angle α is aligned with the X-axis direction, and direction a forming off-angle α is aligned with the Y-axis direction, as shown in fig. 5 (a).
Next, the condenser 6 is moved up and down by the converging point position adjusting means, and the converging point FP1 (see fig. 5 b) of the processing pulse laser beam LB1 is positioned at a depth corresponding to the thickness of the wafer to be produced from the first end surface 88 of the SiC ingot 86. Next, while the holding table 24 is being fed by the X-axis feed mechanism 10 at a predetermined processing feed speed in the X-axis direction (corresponding to the direction perpendicular to the direction a forming the off-angle α), the SiC ingot 86 is irradiated with a processing pulsed laser beam LB1 having a wavelength that is transparent to the SiC ingot 86 from the condenser 6. As a result, SiC is separated into Si and C by irradiation with the processing pulse laser beam LB1, SiC is sequentially separated into Si and C by absorption of the processing pulse laser beam LB1 that has been irradiated by the C that has been formed, and a separation zone 104 in which a portion 100 where the crack 102 is separated from SiC into Si and C extends along the C-plane is formed along the X-axis direction, as shown in fig. 5 (b).
Such a release tape forming step can be performed under the following conditions, for example. The defocus described below is a movement amount when the condenser 6 is moved toward the upper surface of the SiC ingot 86 from a state in which the focal point FP1 of the processing pulse laser beam LB1 is positioned on the upper surface of the SiC ingot 86.
Wavelength of processing pulse laser beam: 1064nm
Average output: 7W to 16W
Repetition frequency: 30kHz
Pulse width: 3ns
Processing feed speed: 165mm/s
Defocusing: 188 μm
Position of the strip from the upper surface of the SiC ingot: 500 μm
While the separation tape forming step is performed, the following reflected light detection step is performed: the peeling tape 104 is irradiated with an inspection laser beam having a wavelength which is transmissive to the SiC ingot 86 and is reflected at the crack 102 of the peeling tape 104, and the intensity of the reflected light reflected at the crack 102 is detected.
Referring to fig. 6, in the reflected light detection step, the converging point FP2 of the inspection pulse laser beam LB2 irradiated from the light emitter 46 is positioned at the crack 102 of the separation zone 104 formed by irradiation of the processing pulse laser beam LB 1. When adjusting the position of the light emitter 46, the incident angle θ of the inspection pulse laser beam LB2 with respect to the first end face 88 of the SiC ingot 86 is preferably set to the brewster angle. Thus, in the inspection pulse laser beam LB2 irradiated onto the SiC ingot 86, the ratio of incidence of the light on the inside of the SiC ingot 86 without being reflected by the first end surface 88 of the SiC ingot 86 is increased, and therefore, the detection accuracy of the reflected light reflected by the crack 102 of the separation zone 104 formed inside the SiC ingot 86 can be improved. The light receiving surface of the light receiver 48 is positioned in the optical path of the reflected light of the inspection pulse laser beam LB2 reflected at the crack 102 of the separation tape 104.
While the holding table 24 is being fed in the X-axis direction, the SiC ingot 86 is irradiated with the processing pulse laser beam LB1 to form the release tape 104, and the crack 102 of the formed release tape 104 is irradiated with the inspection pulse laser beam LB 2. In this way, the reflected light of the inspection pulse laser beam LB2 reflected at the crack 102 of the peeling tape 104 is detected by the light receiver 48, and a signal relating to the intensity of the reflected light detected by the light receiver 48 is transmitted to the control unit 16.
Such a reflected light detection step can be performed under the following conditions, for example.
Wavelength of the inspection pulse laser beam: 1064nm
Average output: 0.1W
Repetition frequency: 10kHz
Pulse width: 10ns
Processing feed speed: 165mm/s
Further, while the separation tape forming step and the reflected light detecting step are performed, the following processing laser beam output adjusting step is performed: the output of the processing pulse laser beam LB1 is adjusted so that the intensity of the reflected light detected in the reflected light detection step falls within a predetermined range. That is, the peeling tape 104 is formed by irradiation of the processing pulse laser beam LB1, and the output of the processing pulse laser beam LB1 is adjusted while irradiating the crack 102 of the formed peeling tape 104 with the inspection pulse laser beam LB2 and detecting the reflected light of the inspection pulse laser beam LB 2.
In the processing laser beam output adjustment step, the control unit 16 controls the attenuator 30 to adjust the output of the processing pulsed laser beam LB1 so that the intensity of the reflected light detected by the light receiver 48 falls within a predetermined range. When the intensity of the reflected light detected by the light receiver 48 is less than the lower limit of the predetermined range, the output of the processing pulse laser beam LB1 is increased to, for example, about 1W to 6W. On the other hand, when the intensity of the reflected light detected by the light receiver 48 exceeds the upper limit value of the predetermined range, the output of the processing pulse laser beam LB1 is reduced to, for example, about 1W to 6W.
Next, an index feeding step is performed to index the SiC ingot 86 and the converging point FP1 in the Y-axis direction, and the release tape 104 is disposed side by side in the Y-axis direction. In the index feeding step, the holding table 24 is moved by the Y-axis feeding mechanism 12, and the SiC ingot 86 is index-fed relative to the converging point FP1 by a predetermined index feed amount Li in the Y-axis direction that coincides with the direction a in which the off angle α is formed.
By alternately repeating the above-described release tape forming step and index feed, the release tape 104 extending in the X-axis direction is provided in the Y-axis direction at intervals of a predetermined index feed amount Li, as shown in fig. 5. The wafer is easily peeled in the peeling step described below by setting the index feed amount Li within a range not exceeding the width of the crack 102 and overlapping the cracks 102 of the peeling tape 104 adjacent to each other in the Y-axis direction when viewed from the top-bottom direction. After the output of the processing pulse laser beam LB1 is adjusted so that the intensity of the reflected light falls within a predetermined range, the reflected light detection step and the processing laser beam output adjustment step may not be performed at the same depth position of the SiC ingot 86.
After a plurality of the separation zones 104 are formed inside the SiC ingot 86 (at a depth corresponding to the thickness of the wafer to be grown), a separation step is performed to separate the wafer from the SiC ingot 86 starting from the separation zones 104.
In the peeling step, first, the holding table 24 is positioned below the suction sheet 60 of the peeling unit 50 by the X-axis feed mechanism 10. Next, the arm 56 is lowered by the arm raising and lowering means, and as shown in fig. 7, the lower surface of the suction piece 60 is brought into close contact with the first end surface 88 of the SiC ingot 86. Next, the suction unit is operated to cause the lower surface of the suction sheet 60 to be sucked to the first end surface 88 of the SiC ingot 86. Next, the ultrasonic vibration applying means is operated to apply ultrasonic vibration to the lower surface of the suction sheet 60, and the suction sheet 60 is rotated by the motor 58. This enables the wafer 106 to be peeled from the peeling tape 104.
After the peeling step is performed, the flat surface forming step, the peeling tape forming step, the reflected light detecting step, the processing laser beam output adjusting step, the index feeding step, and the peeling step as described above are repeated, whereby a plurality of wafers 106 can be produced from the SiC ingot 86.
As described above, in the present embodiment, the intensity of the reflected light reflected by the crack 102 is detected by irradiating the crack 102 of the delaminated tape 104 with the inspection pulse laser beam LB2, and the output of the processing pulse laser beam LB1 is adjusted so that the intensity of the detected reflected light falls within a predetermined range, and therefore, an appropriate delaminated tape 104 can be formed at any height in the SiC ingot 86.
In the present embodiment, the separation tape forming step, the reflected light detecting step, and the processing laser beam output adjusting step are performed simultaneously, but these steps may be performed separately. That is, the separation tape forming step may be performed, the reflected light detecting step may be performed, and the processing laser beam output adjusting step may be performed.

Claims (3)

1. A method for processing a SiC ingot, wherein,
the method for processing the SiC ingot comprises the following steps:
a strip forming step of forming a strip-shaped strip by processing and feeding the SiC ingot and a light-converging point in a direction perpendicular to a direction in which an off-angle is formed by an end face of the SiC ingot and a C-face, the C-face being inclined with respect to the end face of the SiC ingot, the direction perpendicular to the X-axis direction being a Y-axis direction, the SiC ingot being irradiated with processing laser light having a wavelength that is transparent to the SiC ingot while the light-converging point of the processing laser light is positioned at a depth corresponding to a thickness of a wafer to be produced, the SiC ingot and the light-converging point being opposed to each other in the X-axis direction, the strip extending along the C-face at a portion where a crack is separated from SiC into Si and C;
an index feeding step of indexing the SiC ingot and the light converging point in the Y axis direction so as to be opposed to each other and arranging the peeling tape in parallel in the Y axis direction;
a reflected light detection step of irradiating the separation zone with an inspection laser beam having a wavelength which is transmissive to the SiC ingot and is reflected at the crack of the separation zone, and detecting an intensity of the reflected light reflected at the crack; and
and a processing laser beam output adjustment step of adjusting the output of the processing laser beam so that the intensity of the reflected light detected in the reflected light detection step falls within a predetermined range.
2. The method of processing an SiC ingot according to claim 1, wherein,
the method for processing the SiC ingot further includes the following flat surface forming step: before the release tape forming step, the end face of the SiC ingot is ground to form a flat surface.
3. A laser processing apparatus for forming a release tape in a SiC ingot, wherein,
the laser processing device comprises:
a chuck table for holding a SiC ingot;
a laser beam irradiation unit including a condenser that irradiates the SiC ingot with a processing laser beam having a wavelength that is transmissive to the SiC ingot, the condenser being positioned at a condensing point of the processing laser beam at a depth corresponding to a thickness of a wafer to be produced, the laser beam irradiation unit forming a ribbon-shaped peeling tape in which a portion where a crack is separated from SiC into Si and C extends along a C-plane, the X-axis direction being a direction perpendicular to a direction in which a deviation angle is formed between the C-plane and the C-plane of the SiC ingot, the C-plane being inclined with respect to the end surface of the SiC ingot held by the chuck table, and the Y-axis direction being a direction perpendicular to the X-axis direction;
an X-axis feed mechanism that feeds the chuck table and the condenser in the X-axis direction;
a Y-axis feeding mechanism for indexing the chuck table and the condenser in the Y-axis direction;
a reflected light detection unit that irradiates the peeling tape with an inspection laser beam having a wavelength that is transmissive to the SiC ingot and that is reflected at a crack in the peeling tape, and detects an intensity of reflected light that is reflected at the crack; and
and a control unit that adjusts the output of the processing laser beam so that the intensity of the reflected light detected by the reflected light detection unit falls within a predetermined range.
CN202011414819.4A 2020-12-07 2020-12-07 Method for processing SiC ingot and laser processing device Pending CN114589421A (en)

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CN202011414819.4A CN114589421A (en) 2020-12-07 2020-12-07 Method for processing SiC ingot and laser processing device

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Application Number Priority Date Filing Date Title
CN202011414819.4A CN114589421A (en) 2020-12-07 2020-12-07 Method for processing SiC ingot and laser processing device

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Publication Number Publication Date
CN114589421A true CN114589421A (en) 2022-06-07

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