A method and device for producing wafers by laser stripping of SiC ingot

Abstract

The present invention relates to a wafer generation method, and in particular to a method and device for generating wafers by laser stripping of SiC ingots. The method adjusts the rotation angle of the SiC ingot and the scanning direction of the laser beam so that the scanning direction of the laser beam deviates from a specific angle range relative to the main cutting edge, thereby improving the formation of the modified layer and the propagation path of the crack, reducing the residual wafer defects, and improving the qualified rate of finished products.

Description

Technical Field

[0001] The present invention relates to a wafer production method, and in particular to a method and device for producing a wafer by laser stripping of a SiC crystal ingot. Background Art

[0002] In the manufacture of modern semiconductor and optoelectronic devices, SiC (silicon carbide) wafers have become an important material due to their superior physical properties, such as high thermal conductivity, high electron mobility and high temperature resistance. However, the traditional SiC wafer cutting method mainly relies on wire cutting technology, which has significant inefficiency and material waste when processing SiC materials with higher hardness.

[0003] Wire cutting technology usually uses a metal wire with a diameter of about 100 to 300 microns to slice SiC ingots in a sawing manner. This method not only requires a long processing time, but also results in up to 70% to 80% material waste. Especially for SiC ingots with high Mohs hardness, the time-consuming problem in the cutting process is more prominent, thus limiting the possibility of large-scale production and application.

[0004] In recent years, laser processing technology has been introduced into the cutting process of SiC wafers. By adjusting the power, wavelength and focal position of the laser, a modified layer and cracks can be formed inside the SiC ingot, thereby achieving efficient cutting of the wafer. Compared with traditional mechanical cutting methods, laser processing has the advantages of non-contact, high precision and strong controllability. By forming a modified layer in the SiC ingot, it is easier to peel the wafer along a predetermined cutting path. For example, the following technology is recorded in Japanese Patent Gazette No. 2013-49161: The focal point of a laser beam with a wavelength that is transparent to SiC is positioned inside the SiC ingot and irradiated, and a modified layer and cracks are formed on the predetermined cutting surface, and an external force is applied to cut the wafer along the predetermined cutting surface formed with the modified layer and cracks, thereby separating the wafer from the ingot.

[0005] In order to clearly explain the technical solution of this application, the following are defined: Figure 1 and Figure 5 upper side, lower side, left side, right side, front side and rear side shown, Figure 4 Left side, right side, front side and back side shown.

[0006] like Figure 1 In this method, there is an angle (e.g. 4°) between the cleavage plane of SiC and the crystal surface. The intersection line between the two is Ideally, the laser is directed along Crystalline scanning shows that the depth of the modified layer is the most stable. However, in actual processing, it is difficult to confirm The actual laser scanning path will generally follow path ① or path ② depending on the crystal direction. Figure 2Display path ①, path ② and Schematic diagram of the right side view of the vertical section inside the SiC crystal. Figure 3 As shown in the figure, when the laser scans along path ①, the crack will gradually extend upward along the cleavage plane, but will not extend infinitely; after reaching a certain height, the crack height will drop back due to the laser energy density dropping below the modification threshold; due to the uneven doping concentration in various parts of the ingot, some areas will have defective areas a extending upward. The defect is located on one side of the wafer after peeling, which may cause the wafer to remain defective when it is ground to the specified thickness and fail to meet the requirements.

[0007] The applicant found that if Figure 3 As shown in the figure, the laser scans along path ②, and the crack will gradually extend downward along the cleavage plane, but it will not extend indefinitely; after reaching a certain depth, the crack height will rise again because the laser energy density drops below the modification threshold; due to the uneven doping concentration in various parts of the ingot, some areas will have defective areas b extending downward. The defect is located on one side of the ingot after stripping, which may lead to an increase in the amount of ingot grinding. Compared with unqualified wafers, the increase in the amount of ingot grinding has a smaller impact. At the same time, since the light absorption of the material increases with depth, the defect a extends more upward and the defect b extends less downward. Summary of the invention

[0008] In order to solve the above-mentioned technical problems, the purpose of the present invention is to provide a method for generating wafers by laser peeling of SiC ingots. The method adjusts the rotation angle of the SiC ingot or the incident angle of the laser beam so that the scanning direction of the laser beam deviates from a specific angle range relative to the main cutting edge, thereby improving the formation of the modified layer and the propagation path of the cracks, reducing the residual wafer defects and improving the qualified rate of finished products.

[0009] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0010] A method for producing a wafer by laser stripping of a SiC ingot comprises the following steps:

[0011] 1) forming a modified layer parallel to the first surface of the SiC ingot from the first surface, the modified layer being formed by irradiating the ingot with a modifying laser beam and positioning the focal point of the modifying laser beam at a depth from the first surface corresponding to the thickness of the wafer to be generated;

[0012] 2) After the modified layer is formed, a crack is extended from the modified layer to the cleavage plane of the SiC ingot so as to peel the SiC wafer from the ingot along the crack;

[0013] The SiC ingot has a main cutting edge that is originally perpendicular to the scanning direction of the modifying laser beam. The rotation angle of the SiC ingot and the scanning direction of the modifying laser beam are adjusted. When the scanning direction of the modifying laser beam is from back to front, the scanning direction of the modifying laser beam deviates clockwise relative to the main cutting edge, and the deviation angle is between 1° and 15°; when the scanning direction of the modifying laser beam is from front to back, the scanning direction of the modifying laser beam deviates counterclockwise relative to the main cutting edge, and the deviation angle is between 1° and 15°.

[0014] Preferably, the method comprises the following steps:

[0015] 1) forming a bottom layer parallel to a first surface of a SiC crystal ingot, the bottom layer being formed by irradiating the ingot with a bottom-forming laser beam having a first power and positioning a focal point of the bottom-forming laser beam at a first depth from the first surface corresponding to the thickness of a wafer to be generated;

[0016] 2) After forming the base layer, corresponding to the position of the base layer, use the modifying laser beam to further position the focal point of the modifying laser beam at a second deeper depth of the ingot, and form a modified layer at the first depth; adjust the rotation angle of the SiC crystal ingot and the scanning direction of the modifying laser beam, when the scanning direction of the modifying laser beam is from back to front, the scanning direction of the modifying laser beam deviates clockwise relative to the main cutting edge, and the deviation angle is between 1° and 15°; when the scanning direction of the modifying laser beam is from front to back, the scanning direction of the modifying laser beam deviates counterclockwise relative to the main cutting edge, and the deviation angle is between 1° and 15°.

[0017] 3) After the modified layer is formed, a crack is extended from the modified layer to the cleavage plane of the SiC ingot so as to peel the SiC wafer from the ingot along the crack.

[0018] In the above technical solution, a low-energy bottom-building laser beam is used to process the bottom layer inside the ingot in advance ( Figure 6 The bottoming depth can be kept consistent by controlling the bottoming energy, point spacing, pulse width and other parameters. Then, a second laser beam with a larger power than the first power is used to process the modified layer again along path ②. The bottom layer blocks the laser modified layer from continuing to propagate downward along the cleavage plane, which ultimately makes the peeling layer depth more stable.

[0019] Preferably, the bottom layer can be processed by multi-spot laser processing to increase the bottom width, which can more effectively prevent the laser modified layer from extending into the interior of the ingot.

[0020] Preferably, the deviation angle of the scanning direction of the modifying laser beam relative to the main cutting edge is between 5° and 10°.

[0021] Preferably, the wavelength of the bottom-building laser beam is transparent to the SiC ingot.

[0022] Preferably, the modified laser beam is irradiated on the area of ​​the base layer to induce the formation of a modified layer through multi-photon absorption and to cause cracks to propagate along the cleavage plane.

[0023] Preferably, in the wafer peeling step, an external force is applied to the SiC crystal ingot so that the wafer is separated from the ingot at the separation starting point of the reformed layer and the crack.

[0024] Preferably, the modifying laser beam has a second power greater than the first power.

[0025] Preferably, the bottom-building laser beam control parameters are as follows:

[0026] Wavelength: 1000~1100 nm;

[0027] Pulse width: 0.0001~20ns;

[0028] Focus spot diameter: 0.5~3μm;

[0029] Numerical aperture (NA) of the condenser lens: 0.4~0.9.

[0030] As a further preferred embodiment, the control parameters of the bottom-building laser beam are as follows:

[0031] Wavelength: 1000~1100nm;

[0032] Repetition frequency: 90~110kHz;

[0033] Average power: 0.8~1.2 W;

[0034] Pulse width: 0.0001~0.0005ns;

[0035] Focus spot diameter: 1.5~2μm;

[0036] Numerical aperture (NA) of the condenser lens: 0.6~0.7.

[0037] Preferably, the control parameters of the modified laser beam are as follows:

[0038] Wavelength: 1000~1100 nm;

[0039] Pulse width: 0.0001~20ns;

[0040] Focus spot diameter: 0.5~10μm;

[0041] Numerical aperture (NA) of the condenser lens: 0.4~0.9.

[0042] As a further preferred embodiment, the control parameters of the modified laser beam are as follows:

[0043] Wavelength: 1000~1100nm;

[0044] Repetition frequency: 90~110 kHz;

[0045] Average power: 2.7~3.3 W;

[0046] Pulse width: 15~20ns;

[0047] Focus spot diameter: 1.5~2μm;

[0048] Numerical aperture (NA) of the condenser lens: 0.6~0.7.

[0049] Furthermore, the present invention also discloses a device for implementing the method, which adjusts the rotation angle of the SiC ingot and the scanning direction of the modifying laser beam. When the scanning direction of the modifying laser beam is from back to front, the scanning direction of the modifying laser beam deviates clockwise relative to the main cutting edge, and the deviation angle is between 1° and 15°; when the scanning direction of the modifying laser beam is from front to back, the scanning direction of the modifying laser beam deviates counterclockwise relative to the main cutting edge, and the deviation angle is between 1° and 15°.

[0050] The present invention has the following technical effects due to the adoption of the above technical solution:

[0051] 1. Improve the quality of the modified layer

[0052] By controlling the scanning direction of the modified laser beam so that it has a specific deviation angle (between 1° and 15°) relative to the main cutting edge of the SiC ingot, the formation of the modified layer can be effectively controlled. This control can reduce the overlap between the modified layers and ensure the uniformity and consistency of the modified layer, thereby improving the quality of the modified layer. This precise formation of the modified layer makes the subsequent wafer peeling more controllable and effective.

[0053] 2. Improve the controllability of crack propagation

[0054] By adjusting the scanning direction and incident angle of the laser beam, the propagation path of the crack between the modified layers can be controlled. By setting the deviation angle, the extension direction of the crack can be optimized so that it propagates along the cleavage plane. This optimized crack propagation path helps to form a clear and controllable stripping path in the SiC ingot, thereby achieving high-precision stripping of the wafer and reducing the risk of residual defects and breakage of the wafer caused by uneven crack propagation during the stripping process.

[0055] 3. Increase the efficiency and yield of wafer production

[0056] The multi-step modified layer formation method, combined with laser beams of different powers and parameters, can accurately control the formation depth and position of each modified layer. This can effectively improve the efficiency of wafer stripping and reduce unnecessary processing steps. At the same time, by accurately controlling the formation of modified layers and cracks, the generation of defects and flaws can be reduced, significantly improving the yield of the wafer. This high-efficiency and high-yield generation method is particularly important in industrial production.

[0057] 4. Reduce material waste and production costs

[0058] By optimizing laser beam parameters (such as wavelength, pulse width, focal spot diameter, numerical aperture, etc.) and scanning direction, the present invention can significantly reduce material waste during processing. The precise control of the modified layer and cracks enables the maximum utilization of raw materials when peeling the wafer from the SiC ingot, reducing material waste caused by over-processing and misoperation. This improvement in material utilization directly reduces production costs and is of great significance for large-scale industrial applications.

[0059] 5. Improve the processing quality of the chip surface

[0060] By controlling the scanning direction of the laser beam and other parameters of laser processing, microscopic defects on the surface and inside of the wafer, such as microcracks and increased surface roughness, can be reduced. A more stable modified layer and crack formation process can provide a smoother peeling surface, which is of great significance for subsequent wafer processing (such as grinding, polishing) and applications (such as semiconductor device manufacturing).

[0061] In summary, the present invention realizes comprehensive optimization of the SiC wafer production process from modified layer formation, crack propagation to wafer peeling through innovative laser beam control methods and modified layer formation strategies, significantly improves production efficiency, material utilization and product quality, and has broad industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 It is the principle diagram of path ① and path ② of the present invention.

[0063] Figure 2 It is the right view of path ① and path ② of the present invention.

[0064] Figure 3 Schematic diagram of the modified layer formed by the scanning direction of the laser beam used for path ① and path ② modification.

[0065] Figure 4 This is a scanning direction diagram of the laser beam processed in Example 1 and Example 2 of the present invention.

[0066] Figure 5 , Figure 6 This is the schematic diagram of the processing of Example 2. DETAILED DESCRIPTION

[0067] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0068] Example 1

[0069] Step 1: Formation of modified layer

[0070] The SiC ingot was fixed on a support table with the first surface facing upward and aligned with the incident path of the laser beam. The ingot was irradiated with a reforming laser beam (wavelength 1064 nm).

[0071] The focal point of the reforming laser beam was adjusted so as to be positioned at a depth of 390 μm from the first surface of the SiC ingot, which depth corresponds to a reference depth of the thickness of the wafer to be generated.

[0072] The control parameters of the modified laser beam were set as follows: pulse width 20 ns, focal spot diameter 2 μm, numerical aperture (NA) 0.7, repetition frequency 100 kHz, and average power 3 W.

[0073] Adjust the rotation angle of the SiC ingot and the scanning direction of the modified laser beam. When the scanning direction of the modified laser beam is from back to front, the scanning direction of the modified laser beam is deviated by 7° clockwise relative to the main cutting edge; when the scanning direction of the modified laser beam is from front to back, the scanning direction of the modified laser beam is deviated by 7° counterclockwise relative to the main cutting edge to ensure that the deviation angle is within the optimized angle range. The crystal ingot is scanned from left to right relative to the modified laser beam at a feed speed of 60mm / s to form a uniform modified layer, and cracks propagating along the cleavage plane are formed on both sides thereof.

[0074] Step 2: Wafer peeling

[0075] After the modified layer and cracks are formed, external force is applied by mechanical means to extend the cracks along the cleavage plane, thereby finally achieving the peeling of the SiC wafer from the ingot.

[0076] Example 2

[0077] Step 1: Formation of the base layer

[0078] The SiC ingot is fixed on a supporting table with its first surface facing upward and aligned with the incident path of the laser beam. The ingot is irradiated with a bottoming laser beam (wavelength 1064 nm) having a first power.

[0079] The focal point of the bottom forming laser beam was adjusted to be positioned at a depth of 390 μm from the first surface of the SiC ingot, which depth corresponds to a reference depth of the thickness of the wafer to be generated.

[0080] The control parameters of the bottom-forming laser beam were set as follows: pulse width 0.0003 ns, focal spot diameter 2 μm, numerical aperture (NA) 0.7, repetition frequency 100 kHz, and average power 1 W.

[0081] The ingot is scanned relative to the bottoming laser beam from left to right at a feed speed of 60 mm / s to form a uniform bottom layer.

[0082] Step 2: Formation of modified layer

[0083] After the base layer is formed, the SiC ingot is further processed using a reforming laser beam (wavelength 1064 nm) having a second power. The power of the reforming laser beam is greater than that of the base layer laser beam.

[0084] The focal point of the reforming laser beam is adjusted to be positioned at a depth of 5 μm deeper than the first depth, that is, 395 μm. This depth increases the spot size of the reforming laser beam at the first substrate to improve the propagation efficiency of the crack.

[0085] The control parameters of the modified laser beam are: pulse width 20ns, focal spot diameter 2μm, numerical aperture (NA) 0.7, repetition frequency 100kHz, and average power 3W.

[0086] Adjust the rotation angle of the SiC ingot and the scanning direction of the modified laser beam. When the scanning direction of the modified laser beam is from back to front, the scanning direction of the modified laser beam is deviated by 7° clockwise relative to the main cutting edge; when the scanning direction of the modified laser beam is from front to back, the scanning direction of the modified laser beam is deviated by 7° counterclockwise relative to the main cutting edge to ensure that the deviation angle is within the optimized angle range. The crystal ingot is scanned from left to right relative to the modified laser beam at a feed speed of 60mm / s to form a modified layer with the same depth as the base layer, and cracks propagating along the cleavage plane are formed on both sides thereof.

[0087] Step 3: Wafer peeling

[0088] After the modified layer and the cracks are formed, an external force is applied by a mechanical device so that the cracks extend along the modified layer, thereby finally achieving the peeling of the SiC wafer from the ingot.

[0089] Comparative Example 1

[0090] The processing is carried out in the scanning direction of the laser beam according to path ① in the background technology, and other technical features are as shown in Example 1.

[0091] Comparative Example 2

[0092] According to the background technology The laser beam is processed in the scanning direction, and other technical features are as shown in Example 1.

[0093] In the technical solutions of the embodiment and the comparative example, the laser processing depth of all the crystal ingots is the same, that is, the theoretical focal depth of the light beam inside the crystal ingot is ensured to be the same;

[0094] In the technical solutions of the embodiment and the comparative example, all wafers were polished to a target thickness of 350um, and a microscope was used to observe whether there were any residual processing defects such as laser marks and cracks inside the wafers;

[0095] In the technical solutions of the embodiment and the comparative example, if there are still processing defects remaining when the wafer is polished to the target thickness of 350um, it will no longer be polished, and it will be recorded in the number of unqualified wafer traces remaining;

[0096] In the technical solutions of the embodiments and comparative examples, all the peeled ingots need to be polished until the laser marks, cracks and other processing defects disappear, and the chip consumption at this time is recorded as the chip consumption when the ingot is polished clean;

[0097] In the technical solutions of the embodiments and comparative examples, the total removal amount = the wafer consumption when the ingot is polished clean - the target thickness of the wafer after polishing;

[0098] In the technical solutions of the embodiments and comparative examples, the qualified rate = the number of unqualified wafers with residual wafer marks ÷ the number of processed wafers.

[0099] The processing effect statistics are shown in Table 1.

[0100] Table 1 Statistical data of processing effect

[0101]

[0102] The above is a description of the embodiments of the present invention. Through the above description of the disclosed embodiments, professionals and technicians in the field can implement or use the present invention. Various modifications to these embodiments will be apparent to professionals and technicians in the field. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown in this article, but will conform to the widest range consistent with the principles and novelties disclosed herein.

Claims

1. A method for laser stripping of a SiC ingot to generate a wafer, comprising the following steps: 1) forming a modified layer parallel to the first surface of the SiC ingot from the first surface, the modified layer being formed by irradiating the ingot with a modifying laser beam and positioning the focal point of the modifying laser beam at a depth from the first surface corresponding to the thickness of the wafer to be generated; 2) After the modified layer is formed, a crack is extended from the modified layer to the cleavage plane of the SiC ingot so as to peel the SiC wafer from the ingot along the crack; The invention is characterized in that the SiC ingot has a main cutting edge which is originally perpendicular to the scanning direction of the modified laser beam, and the rotation angle of the SiC ingot and the scanning direction of the modified laser beam are adjusted; when the scanning direction of the modified laser beam is from back to front, the scanning direction of the modified laser beam is deviated clockwise relative to the main cutting edge, and the deviation angle is between 1° and 15°; when the scanning direction of the modified laser beam is from front to back, the scanning direction of the modified laser beam is deviated counterclockwise relative to the main cutting edge, and the deviation angle is between 1° and 15°; the laser is deviated along the The crystal path is scanned so that the crack gradually extends toward the side of the ingot along the cleavage plane.

2. The method according to claim 1, characterized in that The method comprises the following steps: 1) forming a bottom layer parallel to a first surface of a SiC crystal ingot, the bottom layer being formed by irradiating the ingot with a bottom-forming laser beam having a first power and positioning a focal point of the bottom-forming laser beam at a first depth from the first surface corresponding to the thickness of a wafer to be generated; 2) After forming the base layer, corresponding to the position of the base layer, using the modified laser beam to further position the focal point of the modified laser beam at a deeper second depth of the ingot, and forming a modified layer at the first depth; adjusting the rotation angle of the SiC ingot and the scanning direction of the modified laser beam, when the scanning direction of the modified laser beam is from back to front, the scanning direction of the modified laser beam is deviated clockwise relative to the main cutting edge, and the deviation angle is between 1° and 15°; when the scanning direction of the modified laser beam is from front to back, the scanning direction of the modified laser beam is deviated counterclockwise relative to the main cutting edge, and the deviation angle is between 1° and 15°; 3) After the modified layer is formed, a crack is extended from the modified layer to the cleavage plane of the SiC ingot so as to peel the SiC wafer from the ingot along the crack.

3. The method according to claim 1 or 2, characterized in that: The deviation angle of the scanning direction of the modifying laser beam relative to the main cutting edge is between 5° and 10°.

4. The method according to claim 2, characterized in that: The wavelength of the bottom-building laser beam is transparent to the SiC crystal ingot.

5. The method according to claim 2, characterized in that: The modified laser beam is irradiated on the area of ​​the base layer to induce the formation of a modified layer through multi-photon absorption and to make cracks propagate along the cleavage plane.

6. The method according to claim 2, characterized in that In the wafer peeling step, the wafer is separated from the SiC ingot at the separation starting point of the reformed layer and the crack by applying an external force to the ingot.

7. The method according to claim 2, characterized in that The reforming laser beam has a second power greater than the first power.

8. The method according to claim 2, characterized in that: The bottoming laser beam control parameters are as follows: Wavelength: 1000~1100nm; Repetition frequency: 90~110kHz; Average power: 0.8~1.2 W; Pulse width: 0.0001~0.0005ns; Focus spot diameter: 1.5~2μm; Numerical aperture (NA) of the condenser lens: 0.6~0.

7.

9. The method according to claim 2, characterized in that: The control parameters of the modified laser beam are as follows: Wavelength: 1000~1100nm; Repetition frequency: 90~110 kHz; Average power: 2.7~3.3 W; Pulse width: 15~20ns; Focus spot diameter: 1.5~2μm; Numerical aperture (NA) of the condenser lens: 0.6~0.

7.

10. A device for implementing the method according to any one of claims 1 to 9, characterized in that: The equipment adjusts the rotation angle of the SiC ingot and the scanning direction of the modifying laser beam. When the scanning direction of the modifying laser beam is from back to front, the scanning direction of the modifying laser beam deviates clockwise relative to the main cutting edge, and the deviation angle is between 1° and 15°; when the scanning direction of the modifying laser beam is from front to back, the scanning direction of the modifying laser beam deviates counterclockwise relative to the main cutting edge, and the deviation angle is between 1° and 15°.

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