CN114473188A - Laser processing method and device for stripping wafer - Google Patents
Laser processing method and device for stripping wafer Download PDFInfo
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- CN114473188A CN114473188A CN202210315631.7A CN202210315631A CN114473188A CN 114473188 A CN114473188 A CN 114473188A CN 202210315631 A CN202210315631 A CN 202210315631A CN 114473188 A CN114473188 A CN 114473188A
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- 238000003672 processing method Methods 0.000 title claims abstract description 14
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 claims abstract description 233
- 229910010271 silicon carbide Inorganic materials 0.000 claims abstract description 233
- 239000013078 crystal Substances 0.000 claims abstract description 131
- 238000000034 method Methods 0.000 claims abstract description 33
- 230000008569 process Effects 0.000 claims abstract description 24
- 230000002093 peripheral effect Effects 0.000 claims description 6
- 230000004048 modification Effects 0.000 abstract description 11
- 238000012986 modification Methods 0.000 abstract description 11
- 230000001133 acceleration Effects 0.000 abstract description 10
- 235000012431 wafers Nutrition 0.000 description 37
- 229910052751 metal Inorganic materials 0.000 description 16
- 239000002184 metal Substances 0.000 description 16
- 238000010586 diagram Methods 0.000 description 6
- 239000000463 material Substances 0.000 description 5
- 230000000694 effects Effects 0.000 description 4
- 230000008859 change Effects 0.000 description 3
- 230000003287 optical effect Effects 0.000 description 3
- 239000004065 semiconductor Substances 0.000 description 3
- 238000004026 adhesive bonding Methods 0.000 description 2
- 229910003460 diamond Inorganic materials 0.000 description 2
- 239000010432 diamond Substances 0.000 description 2
- 238000000926 separation method Methods 0.000 description 2
- 239000002699 waste material Substances 0.000 description 2
- 229910002601 GaN Inorganic materials 0.000 description 1
- JMASRVWKEDWRBT-UHFFFAOYSA-N Gallium nitride Chemical compound [Ga]#N JMASRVWKEDWRBT-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 239000003822 epoxy resin Substances 0.000 description 1
- 230000005307 ferromagnetism Effects 0.000 description 1
- 239000003292 glue Substances 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 230000001678 irradiating effect Effects 0.000 description 1
- 239000004570 mortar (masonry) Substances 0.000 description 1
- 229920000647 polyepoxide Polymers 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
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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
- B23K26/08—Devices involving relative movement between laser beam and workpiece
- B23K26/0823—Devices involving rotation of the workpiece
-
- 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
-
- 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
- B23K26/36—Removing material
- B23K26/40—Removing material taking account of the properties of the material involved
- B23K26/402—Removing material taking account of the properties of the material involved involving non-metallic material, e.g. isolators
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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
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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
- B23K26/70—Auxiliary operations or equipment
- B23K26/702—Auxiliary equipment
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Abstract
The invention relates to the technical field of laser processing, and discloses a laser processing method and a laser processing device for peeling a wafer, wherein the laser processing method and the laser processing device comprise the following steps: providing a silicon carbide ingot, and rotating the silicon carbide ingot at a predetermined rotation speed; laser irradiation of the inside of the silicon carbide ingot in a radial direction of the silicon carbide ingot at a predetermined rate during the rotation to form a modified layer at a predetermined depth inside the silicon carbide ingot; according to the invention, the silicon carbide crystal ingot is scanned to form the modified layer by rotating the silicon carbide crystal ingot and moving the laser scanning line, the movement track of laser modification is not a reciprocating broken line in the crystal any more, so that the time wasted by acceleration and deceleration of a motor in the movement process of the broken line is reduced, the processing efficiency is improved, the inner part and the edge of the crystal are processed in regions by two laser heads respectively, the modified layers in the inner part and the edge are positioned on the same horizontal plane, and the thickness consistency in the wafer is ensured.
Description
Technical Field
The invention relates to the technical field of laser processing, in particular to a laser processing method and device for peeling a wafer.
Background
Because the third-generation semiconductor represented by silicon carbide, diamond and gallium nitride has the characteristics of wider forbidden bandwidth, higher thermal conductivity, higher radiation resistance, higher electron saturation drift rate and the like, various devices prepared by taking the third-generation semiconductor as a substrate are more suitable for being applied to the industries of 5G communication, new energy and power electronics. However, the materials have extremely high hardness, so that the processing of the materials is very difficult, the traditional semiconductor wafer separation method, such as mortar cutting, diamond wire cutting and the like, has the phenomena of long time consumption and serious material waste when the wafers are processed, and the invention patent 'CN 110010519A' proposes that pulse laser is focused in an ingot, a modified layer is formed at the focus, and then the wafers are separated from the modified layer, so that the method not only can improve the processing efficiency, but also can greatly reduce the material waste.
However, the conventional laser processing platform, such as patent "CN 110010519A", is usually an XY two-axis linear motion platform, and when such a platform is used to perform scanning processing on the end face of a generally cylindrical ingot, the platform needs to perform reciprocating linear motion by frequent acceleration and deceleration to complete the processing of the whole end face, which is the processing path in the conventional mode as shown in fig. 2; in the whole processing process, the time of platform acceleration and deceleration occupies a large part, and meanwhile, frequent acceleration and deceleration can also cause the instability of the processed crystal ingot on the platform due to inertia, so that the depth of a laser focus in the crystal ingot is influenced, the height of a formed modified layer is inconsistent, and the thickness uniformity of a wafer is poor; the laser energy may be insufficient or excessive in the acceleration and deceleration section, which affects the modification degree of the modified layer and the success rate of the subsequent wafer separation.
Disclosure of Invention
The invention aims to solve the problem of poor effect caused by scanning and processing of a crystal ingot by a traditional laser processing platform, and provides a laser processing method and a device for peeling a wafer.
In order to achieve the above object, the present invention provides a laser processing method for peeling a wafer, comprising the steps of:
providing a silicon carbide ingot, and rotating the silicon carbide ingot at a predetermined rotation speed;
during the rotation, the laser unit moves along the radius direction of the silicon carbide crystal ingot at a preset speed and performs laser irradiation on the inside of the silicon carbide crystal ingot so as to form a modified layer at a preset depth in the inside of the silicon carbide crystal ingot, wherein the scanning track of the laser irradiation is a spiral line or a plurality of concentric circles with different radii.
Optionally, the laser unit comprises at least one laser head, and the control unit controls the at least one laser head to perform linear feed motion or linear uniform motion along the radial direction of the silicon carbide ingot from the center of the silicon carbide ingot to the outer side of the silicon carbide ingot or from the outer side of the silicon carbide ingot to the center of the silicon carbide ingot at a predetermined rate;
when the laser unit comprises at least two laser heads, the at least two laser heads are arranged at intervals along the radius direction of the silicon carbide crystal ingot and respectively irradiate different inner and outer areas on the surface of the silicon carbide crystal ingot so as to realize irradiation of the whole surface of the silicon carbide crystal ingot, wherein in the process that the at least two laser heads irradiate different areas on the surface of the silicon carbide crystal ingot, corresponding focusing depths are set according to the light refractive indexes corresponding to the different areas, so that the heights of modified layers formed by irradiation of the different inner and outer areas of the silicon carbide crystal ingot are consistent.
Optionally, the method further includes: the properties of the modified layers formed by irradiation of different areas inside and outside the silicon carbide ingot are consistent by adjusting the laser intensity, the laser irradiation frequency, the spot size, the pulse width and the like of at least two laser heads in different areas inside and outside the silicon carbide ingot.
Optionally, the diameter of a light spot formed by laser irradiation in the silicon carbide crystal ingot is 10-50 um, the distance between adjacent scanning lines in a scanning track of the laser irradiation is the diameter of the light spot or is smaller than the diameter of the light spot, and the overlapping rate of the light spots formed by the laser irradiation is 0-50%.
Optionally, the method further includes: when the laser unit irradiates on the surfaces of different areas in the center and the periphery of the silicon carbide crystal ingot, the performance of the modified layer formed by irradiation in the center and the periphery of the silicon carbide crystal ingot is consistent by controlling the rotating speed of the silicon carbide crystal ingot and/or the laser irradiation frequency and the focusing depth.
The present invention also provides a laser processing apparatus for peeling a wafer, comprising: the device comprises a servo motor, a laser unit and a control unit;
the control unit controls the servo motor to drive the silicon carbide crystal ingot to rotate according to a preset rotating speed;
the control unit controls the laser unit to do linear motion along the radius direction of the silicon carbide crystal ingot at a preset speed during rotation, and performs laser irradiation on the inside of the silicon carbide crystal ingot during the linear motion so as to form a modified layer at a preset depth inside the silicon carbide crystal ingot, wherein the scanning track of the laser irradiation is a spiral line or a plurality of concentric circles with different radii.
Optionally, the laser unit comprises at least one laser head, and the control unit controls the at least one laser head to perform linear feed motion or linear uniform motion along the radial direction of the silicon carbide ingot from the center of the silicon carbide ingot to the outer side of the silicon carbide ingot or from the outer side of the silicon carbide ingot to the center of the silicon carbide ingot at a predetermined rate;
when the laser unit comprises at least two laser heads, the at least two laser heads are arranged at intervals along the radius direction of the silicon carbide crystal ingot and respectively irradiate different inner and outer areas on the surface of the silicon carbide crystal ingot so as to realize irradiation of the whole surface of the silicon carbide crystal ingot, wherein in the process that the at least two laser heads irradiate different areas on the surface of the silicon carbide crystal ingot, corresponding focusing depths are set according to the light refractive indexes corresponding to the different areas, so that the heights of modified layers formed by irradiation of the different inner and outer areas of the silicon carbide crystal ingot are consistent.
Optionally, the method further includes: the properties of the modified layers formed by irradiation of different areas inside and outside the silicon carbide ingot are consistent by adjusting the laser intensity, the laser irradiation frequency, the spot size and the pulse width of at least two laser heads in different areas inside and outside the silicon carbide ingot.
Optionally, the laser device further comprises a guide rail, and the control unit controls the laser unit to move linearly along the guide rail along the radial direction of the silicon carbide crystal ingot at a predetermined speed.
Optionally, the method further includes: when the laser unit irradiates on the surfaces of different areas in the center and the periphery of the silicon carbide crystal ingot, the properties of the modified layer formed by irradiation in the center and the periphery of the silicon carbide crystal ingot are consistent by controlling the rotating speed and/or the laser irradiation frequency of the silicon carbide crystal ingot.
The invention has the beneficial effects that: the laser head does slow linear motion through the rotary worktable, the motion is more stable, a more flat and uniform modified layer is formed by the motion track of a concentric circle or a spiral line, so that a better surface type wafer can be obtained, the motion track of laser modification is not a reciprocating broken line in a crystal any more, the time wasted by acceleration and deceleration of a motor in the broken line motion process is reduced, and the processing efficiency and the stability are improved; in addition, through the cooperative work of at least two laser heads, the outer periphery and the inner part of the crystal ingot can adopt different laser process conditions, the laser focusing position deviation caused by the edge effect of the crystal can be compensated, the modified layers of the inner part and the edge of the crystal ingot are ensured to be positioned on the same horizontal plane, and the in-chip consistency of the thickness of the wafer is ensured.
Drawings
Fig. 1 is a schematic structural view of a laser processing apparatus for peeling a wafer according to an embodiment of the present invention when there is one laser head.
Fig. 2 is a schematic diagram of a laser scanning movement track of a conventional laser processing apparatus.
Fig. 3 is a schematic diagram of a laser scanning motion track of a laser processing apparatus for peeling a wafer according to an embodiment of the present invention when the laser head performs a linear feed motion when there is one laser head.
Fig. 4 is a schematic diagram of a laser scanning motion track of a laser processing apparatus for peeling a wafer according to an embodiment of the present invention when the laser head performs a linear uniform motion when there is one laser head.
Fig. 5 is a schematic view showing the change of the rotation speed of the silicon carbide ingot when the laser pulse frequency is fixed when the laser head performs a linear feed motion in the laser processing apparatus for peeling a wafer according to the embodiment of the present invention.
Fig. 6 is a schematic diagram showing the change of the laser pulse frequency when the rotation speed of the silicon carbide ingot is fixed when the laser head performs a linear feed motion in the laser processing apparatus for peeling a wafer according to the embodiment of the present invention.
Fig. 7 is a schematic structural view of a laser processing apparatus for peeling a wafer according to an embodiment of the present invention when there are two laser heads.
Fig. 8 is a schematic view of scanning areas of a first laser head and a second laser head when the number of the laser heads is two in the laser processing apparatus for peeling a wafer according to the embodiment of the present invention.
FIG. 9a is a schematic view showing the difference in depth between the modified layers in the inner region and the edge region when the laser head scans the silicon carbide ingot according to the laser processing apparatus for peeling a wafer in accordance with the embodiment of the present invention.
FIG. 9b is a schematic view of the laser processing apparatus for peeling a wafer according to the embodiment of the present invention, when the two laser heads scan the silicon carbide ingot, the depth of the inner and edge modified regions of the silicon carbide ingot is consistent.
FIG. 10 is a schematic diagram of the reason why the laser processing apparatus for peeling the wafer according to the embodiment of the present invention causes the inconsistency of the heights of the inner and edge modified regions of the silicon carbide when the number of the laser heads is one.
FIG. 11 is a schematic diagram of a laser processing method for peeling a wafer according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 11, the present embodiment provides a technical solution: a laser processing method for peeling a wafer, comprising the steps of:
step S100, providing a silicon carbide crystal ingot, and rotating the silicon carbide crystal ingot according to a preset rotating speed;
a step S200 of irradiating laser light to the inside of the silicon carbide ingot in a radial direction of the silicon carbide ingot at a predetermined rate during rotation to form a modified layer at a predetermined depth inside the silicon carbide ingot; wherein, the scanning track for laser irradiation is a spiral line or a plurality of concentric circles with different radiuses.
The diameter of a light spot formed by laser irradiation in the silicon carbide crystal ingot is 10-50 um, the distance between adjacent scanning lines in a scanning track for laser irradiation is the diameter of the light spot or is smaller than the diameter of the light spot, and the overlapping rate of the light spots formed by laser irradiation is 0-50%.
The laser unit comprises at least one laser head, and the control unit controls the at least one laser head to perform linear feed motion or linear uniform motion along the radial direction of the silicon carbide ingot from the center of the silicon carbide ingot to the outer side of the silicon carbide ingot or from the outer side of the silicon carbide ingot to the center of the silicon carbide ingot at a predetermined rate;
when the laser unit comprises at least two laser heads, the at least two laser heads are arranged at intervals along the radius direction of the silicon carbide crystal ingot and respectively irradiate different inner and outer areas on the surface of the silicon carbide crystal ingot so as to realize irradiation of the whole surface of the silicon carbide crystal ingot, wherein in the process that the at least two laser heads irradiate different areas on the surface of the silicon carbide crystal ingot, corresponding focusing depths are set according to the light refractive indexes corresponding to the different areas, so that the heights of modified layers formed by irradiation of the different inner and outer areas of the silicon carbide crystal ingot are consistent.
Further, the method also comprises the following steps: the performance of the modified layer formed by irradiation of different areas inside and outside the silicon carbide ingot is consistent by adjusting the laser intensity, the laser irradiation frequency, the spot size, the pulse width and the like of at least two laser heads in different areas inside and outside the silicon carbide ingot, wherein the performance of the modified layer comprises the height of the modified layer.
In the embodiment, a more flat and uniform modified layer can be formed by the movement track of a concentric circle or a spiral line, so that a wafer with a better surface shape can be obtained, the movement track of laser modification is not a reciprocating broken line in the crystal any more, the time wasted by acceleration and deceleration of a motor in the broken line movement process is reduced, and the processing efficiency is improved; and the motion state of the silicon carbide crystal ingot is more stable under the rotation motion, so that the problems of unstable crystal fixation and non-uniform laser energy caused by acceleration and deceleration can be avoided.
Based on the same inventive concept, the present embodiment further provides a technical solution: a laser processing apparatus for peeling a wafer, comprising: the device comprises a servo motor, a laser unit and a control unit;
the control unit controls the servo motor to drive the silicon carbide crystal ingot to rotate according to a preset rotating speed;
the control unit controls the laser unit to make a linear motion along the radius direction of the silicon carbide crystal ingot fixed on the fixing unit at a preset speed during the rotation, and performs laser irradiation on the inside of the silicon carbide crystal ingot during the linear motion so as to form a modified layer at a preset depth inside the silicon carbide crystal ingot, wherein the scanning track of the laser irradiation is a spiral line or a plurality of concentric circles with different radiuses.
As shown in fig. 1, the fixing unit comprises a rotary table 101 and a metal chuck 102, wherein the metal chuck 102 is used for fixing a silicon carbide ingot 103, wherein the silicon carbide ingot can be fixed on the metal disc with ferromagnetism by gluing or wax sticking, wherein the gluing can be performed by using epoxy resin glue for bonding, the silicon carbide ingot and the metal chuck are fixed in concentric circles, the deviation of the total thickness of the surface of the silicon carbide ingot after bonding is TTV <10um, and the concentricity of the silicon carbide ingot and the metal chuck can be ensured by a positioning pin; the rotary worktable 101 is used for fixing the metal chuck 102, the rotary worktable 101 is provided with an electromagnet, the metal chuck is fixed on the rotary worktable 101 through the electromagnetic attraction mode of the electromagnet, wherein, the metal chuck is placed with the rotary worktable in a concentric circle position, and the concentricity of the metal chuck and the rotary worktable can be ensured through mechanical positioning.
The control unit controls the servo motor 100 to drive the rotary table 101 to rotate according to a preset rotating speed, the rotating speed is adjustable from 50RPM to 5000RPM, and the silicon carbide crystal ingot 103 is adsorbed on the rotary table 101 through the metal chuck 102 and also moves in a rotating mode according to the preset rotating speed.
The laser processing apparatus for peeling off a wafer of the present embodiment further includes a guide rail, and the control unit controls the laser unit to linearly move along the guide rail at a predetermined rate in a radial direction of the silicon carbide ingot fixed to the fixing unit.
The laser unit comprises at least one laser head, the control unit controls the at least one laser head to perform linear feeding motion or linear uniform motion along the radius direction of the silicon carbide crystal ingot fixed on the fixing unit from the center of the silicon carbide crystal ingot to the outer side of the silicon carbide crystal ingot or from the outer side of the silicon carbide crystal ingot to the center of the silicon carbide crystal ingot according to a preset speed, wherein when the laser unit comprises at least two laser heads, the at least two laser heads are arranged at intervals along the radius direction of the silicon carbide crystal ingot fixed on the fixing unit and respectively scan different areas of the surface of the silicon carbide crystal ingot so as to realize scanning of the whole surface of the silicon carbide crystal ingot, the scanning efficiency is improved, and in addition, the at least two laser heads perform irradiation on different areas of the surface of the silicon carbide crystal ingot, setting corresponding focusing depths according to the corresponding optical refractive indexes of different areas, so that the heights of modified layers formed by irradiation in different areas inside and outside the silicon carbide crystal ingot are consistent; specifically, when the laser unit irradiates on the surfaces of different areas in the center and the periphery of the silicon carbide crystal ingot, the rotation speed of the silicon carbide crystal ingot and/or the laser irradiation frequency and the focusing depth are controlled, so that the properties of the modified layer formed by irradiation in the center and the periphery of the silicon carbide crystal ingot are consistent.
As an embodiment, as shown in fig. 1, the laser unit includes a laser head 104, the linear motion includes a linear feeding motion or a linear uniform motion, during the rotation of the silicon carbide ingot 103, the control unit controls the guide rails to drive the laser heads 104 to make a straight feed motion or a straight uniform motion along the radius direction of the silicon carbide ingot fixed on the fixing unit from the center of the silicon carbide ingot to the outer side of the silicon carbide ingot or from the outer side of the silicon carbide ingot to the center of the silicon carbide ingot at a predetermined rate, and the laser head moves linearly while the laser beam continuously provides laser pulses according to the pulse frequency (1 KHz-500 KHz), and the laser pulses are focused at a certain set depth in the silicon carbide crystal ingot to modify the material to form a modified layer.
When linear feeding motion is carried out, the feeding speed is adjustable from 0.01-1.0 mm/step/sec, the rotating speed of the silicon carbide crystal ingot and the feeding speed of the laser head are cooperated with each other, so that the distance between scanned laser spots on a motion track is consistent, the linear feeding motion can be carried out in a mode of changing the rotating speed of the silicon carbide crystal ingot by fixing the laser pulse frequency, or in a mode of changing the rotating speed of the silicon carbide crystal ingot by fixing the rotating speed of the silicon carbide crystal ingot by changing the laser pulse frequency; specifically, the method comprises the following steps: when the laser pulse frequency is fixed, the circular motion track is short near the center of the silicon carbide crystal ingot, the silicon carbide crystal ingot is subjected to a faster rotating speed, the circular motion track is long near the outer side of the silicon carbide crystal ingot, the silicon carbide crystal ingot is subjected to a slower rotating speed, the rotating speed is gradually increased from low to high when the servo motor is started, and the laser head can scan from the outer side of the silicon carbide crystal ingot to the center of the silicon carbide crystal ingot along the radial direction at the fixed laser pulse frequency, and the rotating speed of the 6-inch silicon carbide crystal ingot changes from the outer side of the silicon carbide crystal ingot to the center of the silicon carbide crystal ingot when the fixed laser pulse frequency is 50KHz as shown in figure 5; when the rotation speed of the silicon carbide ingot is fixed, the system needs to wait for the rotation speed of the silicon carbide ingot to be stabilized at a preset value, then the laser head scans from the center of the silicon carbide ingot to the outer side of the silicon carbide ingot along the radius direction or scans from the outer side of the silicon carbide ingot to the center of the silicon carbide ingot along the radius direction, the pulse frequency of the laser is set to be low at a position close to the center, and the pulse frequency of the laser is set to be high at a position far from the center, as shown in fig. 6, when the rotation speed of the 6-inch silicon carbide ingot is fixed to be 200RPM, the change of the laser pulse frequency from the center of the silicon carbide ingot to the outer side of the silicon carbide ingot is realized.
When performing the linear feeding motion, the laser head is fed a certain distance from the outer side of the silicon carbide ingot to the center of the silicon carbide ingot every time the silicon carbide ingot rotates, until the laser head moves to the center of the silicon carbide ingot, or the laser head is fed a certain distance from the center of the silicon carbide ingot to the outer side of the silicon carbide ingot, until the laser head moves to the outer side of the silicon carbide ingot, the scanning of the whole end face is completed, the motion track of the laser head on the silicon carbide ingot is the motion track composed of a plurality of concentric circles with different radiuses as shown in fig. 3, and the distances between the adjacent concentric circles are the same.
When the laser head performs linear uniform motion, the rate of the uniform motion of the laser head is adjustable from 0.01-1.0 mm/sec, the rotating speed of the silicon carbide crystal ingot and the moving speed of the laser head are cooperated with each other, so that the distance between the scanned laser spots on the motion track is consistent, the laser motion can be performed in a mode of changing the rotating speed of the silicon carbide crystal ingot by fixing the laser pulse frequency, and can also be performed in a mode of changing the laser pulse frequency by fixing the rotating speed of the silicon carbide crystal ingot; and when the silicon carbide ingot rotates, the laser head makes uniform linear motion from the center of the silicon carbide ingot to the outer side of the silicon carbide ingot until the laser head moves to the outer side of the silicon carbide ingot, or the laser head makes uniform linear motion from the outer side of the silicon carbide ingot to the center of the silicon carbide ingot until the laser head moves to the center of the silicon carbide ingot to complete scanning of the whole end face, the motion track of the laser head on the silicon carbide ingot is a spiral line as shown in fig. 4, and the intervals between the adjacent spiral lines are the same.
As an improvement of the above embodiment, the laser unit includes at least two laser heads, the at least two laser heads are arranged at intervals along the radial direction of the silicon carbide ingot fixed on the fixing unit, the control unit controls the guide rail to drive the at least two laser heads to perform linear feeding motion or linear uniform motion along the radial direction of the silicon carbide ingot fixed on the fixing unit from the center of the silicon carbide ingot to the outer side of the silicon carbide ingot or from the outer side of the silicon carbide ingot to the center of the silicon carbide ingot at a predetermined rate, respectively scan different regions of the surface of the silicon carbide ingot to realize scanning of the entire surface of the silicon carbide ingot, wherein the at least two laser heads are set with corresponding focusing depths according to the corresponding light refractive indexes of the different regions during irradiation of the different regions of the surface of the silicon carbide ingot, not only improves the processing efficiency, but also ensures that the modified layers formed by irradiation in different areas inside and outside the silicon carbide crystal ingot have the same height.
Further, the method also comprises the following steps: the properties of the modified layers formed by irradiation of different areas inside and outside the silicon carbide ingot are consistent by adjusting the laser intensity, the laser irradiation frequency, the spot size, the pulse width and the like of at least two laser heads in different areas inside and outside the silicon carbide ingot.
For example, as shown in fig. 7, the laser unit comprises two laser heads, namely a first laser head 104a and a second laser head 104b, which are arranged in parallel along the radius direction of the silicon carbide ingot fixed on the fixing unit, wherein the first laser head 104a is responsible for scanning the annular area of the edge of the silicon carbide crystal, and the second laser head 104b is responsible for scanning the circular area inside the silicon carbide crystal, but in other embodiments, the two laser heads may be arranged not in parallel but in a staggered manner, but still one laser head is aligned with the outer edge of the silicon carbide ingot, the other laser head is located inside the silicon carbide ingot, the first laser head and the second laser head are arranged in parallel along the radius direction, and scanning is performed in regions, so as to realize scanning of the whole end face of the silicon carbide ingot, as shown in fig. 8, the scanning regions of the two laser heads correspond to each other, wherein the first laser head 104a correspondingly scans a first scanning region a, which is an edge ring region of the silicon carbide crystal, and the second laser head 104b correspondingly scans a second scanning region b, which is an inner circle region of the silicon carbide crystal, wherein different focusing depths are set due to different optical refractive indexes of the first scanning region and the second scanning region, so as to ensure that the obtained modified layers are consistent.
In particular, fig. 9a and 9b further illustrate the advantages of using two laser heads for processing. When only one laser head processes the whole silicon carbide ingot, in order to maintain the stability of the processing, the laser head 104 adopts the same focusing depth, and scans from the inner part to the outer periphery or from the outer periphery to the inner part, and as shown in fig. 9a, the problem that the heights of the edge modification layer and the inner modification layer are not consistent can occur; fig. 10 further illustrates the reason for the inconsistent height of the modified layer, because of the large refractive index difference between the inner region and the peripheral air of the silicon carbide crystal, the media around the laser focusing spot of the inner region are all silicon carbide, while one side of the laser focusing spot of the edge region is silicon carbide, the refractive index is n-2.654, the other side is air, and the refractive index is n-1, which results in different refraction effects of the optical path, causes the inconsistency of the focusing depth at the inner side and the edge of the crystal, and finally forms the modified regions with two different depths. When two laser heads are adopted, the second laser head 104b processes the second scanning area b, namely the inner circular area, and the first laser head 104a processes the second scanning area a, namely the peripheral annular area, as shown in fig. 9b, the height difference between the edge and the inner modified area caused by the refractive index difference can be compensated through the setting of different focusing depths of the two laser heads, so that the height of the inner modified layer and the edge is consistent, and the thickness uniformity in the processed wafer surface is ensured.
During processing, when the rotating speed of the silicon carbide crystal ingot reaches a preset rotating speed, the first laser heads and the second laser heads are arranged at intervals along the radial direction of the silicon carbide crystal ingot fixed on the fixing unit, and do linear feed motion or linear uniform motion integrally along the radial direction of the silicon carbide crystal ingot from the center of the silicon carbide crystal ingot to the outer side of the silicon carbide crystal ingot or from the outer side of the silicon carbide crystal ingot to the center of the silicon carbide crystal ingot at different laser pulse frequencies and different laser focusing depths respectively, one laser head is responsible for scanning the outer periphery, and the other laser head is responsible for a larger inner area, namely completing the scanning of the whole surface of the silicon carbide crystal ingot.
When the scanning of the whole end face is completed, namely the laser modification of one wafer is completed, a modified layer is formed, the wafer after the laser modification is stripped from the upper part of the silicon carbide ingot in a vacuum adsorption mode, and then the upper surface of the stripped silicon carbide ingot is ground, specifically: demagnetizing the rotary workbench, taking away the metal chuck, keeping the state that the silicon carbide ingot is adhered to the metal chuck, and grinding the upper surface of the silicon carbide ingot on a grinding workbench/working position to reduce the roughness of the upper surface of the silicon carbide ingot to be within 50 nm; then the metal chuck and the rest silicon carbide crystal ingot are electromagnetically adsorbed on the rotary worktable, so that the metal chuck and the rotary worktable are arranged in concentric circles, and the next silicon carbide crystal wafer is subjected to laser modification and stripping; when the thickness of the silicon carbide crystal ingot is not enough to peel one silicon carbide crystal ingot, demagnetizing the rotary worktable, taking away the metal chuck of the tool, carrying out off-line degumming removal on the residual part, and then placing the next metal chuck adhered with the silicon carbide crystal ingot to peel the next silicon carbide crystal wafer.
In this embodiment, the rotation scanning process and the linear scanning process are compared by setting specific laser parameters and motion parameters, see table 1, in which the processing efficiency of the two processing modes of the rotation scanning process and the linear scanning process is compared, and it is obvious that the time consumption of the rotation scanning process is much smaller than that of the linear scanning process no matter whether the wafer process is a wafer process with a diameter of 100mm (4 inches) or a wafer process with a diameter of 150mm (6 inches).
TABLE 1
The invention provides a novel laser processing device for stripping crystal ingots, which is different from the traditional device in that the crystal ingots are fixed on a rotating processing platform, the silicon carbide crystal ingots rotate along with a workbench at a certain rotating speed, and the laser heads perform linear feed motion or uniform linear motion along the linear direction of the silicon carbide crystal ingots, so that the laser heads cooperatively complete the scanning of the whole circular end face of the crystal.
According to the invention, the rotary worktable rotates, the laser head moves linearly at a low speed, the movement is more stable, and a more flat and uniform modified layer is formed by the movement track of a concentric circle or a spiral line, so that a better surface type wafer can be obtained, the movement track of laser modification is not a reciprocating broken line in a crystal any more, the time wasted by acceleration and deceleration of a motor in the broken line movement process is reduced, and the processing efficiency is improved; the motion state of the silicon carbide crystal ingot is more stable under the rotation motion, and the problems of unstable crystal fixation and non-uniform laser energy caused by acceleration and deceleration can be avoided; furthermore, two laser heads are adopted to work cooperatively, and different laser process conditions can be adopted on the periphery and the inside of the crystal ingot, so that the laser focusing position deviation caused by the edge effect of the crystal can be compensated, the modified layers in the inner part and the edge of the crystal ingot are ensured to be positioned on the same horizontal plane, and the in-chip consistency of the thickness of the wafer is ensured.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to limit the present invention, and those skilled in the art can make variations and modifications of the present invention without departing from the spirit and scope of the present invention by using the methods and technical contents disclosed above.
Claims (10)
1. A laser processing method for peeling a wafer, comprising the steps of:
providing a silicon carbide ingot, and rotating the silicon carbide ingot at a predetermined rotation speed;
during the rotation, the laser unit moves along the radius direction of the silicon carbide crystal ingot at a preset speed and performs laser irradiation on the inside of the silicon carbide crystal ingot so as to form a modified layer at a preset depth in the inside of the silicon carbide crystal ingot, wherein the scanning track of the laser irradiation is a spiral line or a plurality of concentric circles with different radii.
2. The laser processing method for peeling a wafer as set forth in claim 1, wherein the laser unit includes at least one laser head, and the control unit controls the at least one laser head to make a straight feed motion or a straight uniform motion along a radius direction of the silicon carbide ingot from a center of the silicon carbide ingot to an outer side of the silicon carbide ingot or from the outer side of the silicon carbide ingot to the center of the silicon carbide ingot at a predetermined rate;
when the laser unit comprises at least two laser heads, the at least two laser heads are arranged at intervals along the radius direction of the silicon carbide crystal ingot and respectively irradiate different inner and outer areas on the surface of the silicon carbide crystal ingot so as to realize irradiation of the whole surface of the silicon carbide crystal ingot, wherein in the process that the at least two laser heads irradiate different areas on the surface of the silicon carbide crystal ingot, corresponding focusing depths are set according to the light refractive indexes corresponding to the different areas, so that the heights of modified layers formed by irradiation of the different inner and outer areas of the silicon carbide crystal ingot are consistent.
3. The laser processing method for peeling off a wafer as claimed in claim 2, further comprising: the properties of the modified layers formed by irradiation of different areas inside and outside the silicon carbide ingot are consistent by adjusting the laser intensity, the laser irradiation frequency, the spot size and the pulse width of at least two laser heads in different areas inside and outside the silicon carbide ingot.
4. The laser processing method for peeling off a wafer as set forth in claim 1, wherein a spot diameter formed by laser irradiation inside the silicon carbide ingot is 10 to 50 μm, a pitch between adjacent scanning lines in a scanning track of the laser irradiation is the spot diameter or less, and a spot overlapping ratio formed by the laser irradiation is 0 to 50%.
5. The laser processing method for peeling off a wafer as set forth in claim 1, wherein properties of the modified layer formed by irradiation in the center and peripheral regions of the silicon carbide ingot are made uniform by controlling the rotation speed of the silicon carbide ingot and/or the laser irradiation frequency when the laser unit irradiates the surfaces in the center and peripheral regions of the silicon carbide ingot.
6. A laser processing apparatus for peeling a wafer, comprising: the device comprises a servo motor, a laser unit and a control unit;
the control unit controls the servo motor to drive the silicon carbide crystal ingot to rotate according to a preset rotating speed;
the control unit controls the laser unit to do linear motion along the radius direction of the silicon carbide crystal ingot at a preset speed during rotation, and performs laser irradiation on the inside of the silicon carbide crystal ingot during the linear motion so as to form a modified layer at a preset depth inside the silicon carbide crystal ingot, wherein the scanning track of the laser irradiation is a spiral line or a plurality of concentric circles with different radii.
7. The laser processing apparatus for peeling off a wafer as set forth in claim 6, wherein the laser unit comprises at least one laser head, and the control unit controls the at least one laser head to make a straight-line feeding motion or a straight-line uniform motion along a radius direction of the silicon carbide ingot from a center of the silicon carbide ingot to an outer side of the silicon carbide ingot or from the outer side of the silicon carbide ingot to the center of the silicon carbide ingot at a predetermined rate;
when the laser unit comprises two laser heads, the two laser heads are arranged at intervals along the radius direction of the silicon carbide crystal ingot and respectively irradiate different inner and outer areas on the surface of the silicon carbide crystal ingot so as to realize irradiation of the whole surface of the silicon carbide crystal ingot, wherein in the process that at least two laser heads irradiate different areas on the surface of the silicon carbide crystal ingot, corresponding focusing depths are set according to the light refractive indexes corresponding to the different areas, so that the heights of modified layers formed by irradiation of the different areas inside and outside the silicon carbide crystal ingot are consistent.
8. The laser processing apparatus for peeling off a wafer as claimed in claim 7, further comprising: the properties of the modified layers formed by irradiation of different areas inside and outside the silicon carbide ingot are consistent by adjusting the laser intensity, the laser irradiation frequency, the spot size and the pulse width of at least two laser heads in different areas inside and outside the silicon carbide ingot.
9. The laser processing apparatus for peeling a wafer as set forth in claim 6, further comprising a guide rail, wherein the control unit controls the laser unit to make a linear movement along the guide rail at a predetermined rate in a radial direction of the silicon carbide ingot.
10. The laser processing apparatus for peeling off a wafer as set forth in claim 6, wherein properties of the modified layer formed by irradiation in the center and peripheral regions of the silicon carbide ingot are made uniform by controlling the rotation speed of the silicon carbide ingot and/or the laser irradiation frequency when the laser unit irradiates the surfaces in the center and peripheral regions of the silicon carbide ingot.
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| CN115770946A (en) * | 2022-12-09 | 2023-03-10 | 苏州龙驰半导体科技有限公司 | Wafer cutting method |
| CN115808134A (en) * | 2023-02-02 | 2023-03-17 | 通威微电子有限公司 | Silicon carbide crystal surface curvature measuring system and method |
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| WO2021192853A1 (en) * | 2020-03-24 | 2021-09-30 | 東京エレクトロン株式会社 | Substrate processing method and substrate processing apparatus |
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| CN112005341A (en) * | 2018-04-27 | 2020-11-27 | 东京毅力科创株式会社 | Substrate processing system and substrate processing method |
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