Laser stripping method and device for silicon carbide ingot

Abstract

The present invention provides a method and apparatus for laser stripping of silicon carbide ingots. The laser stripping method first focuses an ultrashort pulse laser beam at a set depth layer of the silicon carbide ingot, generates a cavity-modification region and a crack-modification region above the set depth layer, and scans to form a cavity-modification layer and a crack-modification layer. The focus of the short pulse laser beam is then moved a certain distance above the set depth layer, focusing the short pulse laser beam on the crack-modification region. This generates scattering perpendicular to the direction of the short pulse laser beam, causing cracks within the crack-modification region to grow laterally outward. Scanning is then performed to connect cracks within adjacent crack-modification regions through lateral growth. This method reduces the amount and length of cracks within the modified layer extending longitudinally along the silicon carbide ingot, increases the number and length of lateral crack growth, reduces cutting loss, and reduces waste.

Description

Technical Field

[0001] The present invention relates to the technical field of crystal ingots, and in particular to a laser stripping method and a device for a silicon carbide crystal ingot. Background Art

[0002] Among third-generation semiconductor materials, SiC (silicon carbide) features a wide bandgap, high breakdown electric field, high saturated electron drift velocity, and high thermal conductivity. It can be used in high-voltage environments exceeding 1200 volts, offering significant advantages in harsh environments. SiC substrate processing technology is a crucial foundation for device fabrication, and the quality and precision of its surface processing directly impact the quality of epitaxial thin films and the performance of its devices. Therefore, its applications require wafer surfaces to be ultra-smooth, defect-free, and damage-free, with surface roughness values reaching below the nanometer level.

[0003] However, SiC wafer processing is extremely difficult due to its high hardness, brittleness, excellent wear resistance, and extremely stable chemical properties. Ultra-precision machining of SiC single wafers involves the following steps: directional cutting, grinding (rough grinding and fine grinding), polishing (mechanical polishing), and ultra-precision polishing (chemical mechanical polishing).

[0004] Traditionally, sawing involves slicing SiC ingots along a specific orientation into thin wafers. Slicing SiC ingots into wafers with minimal warpage, uniform thickness, and low shear loss is crucial for subsequent grinding and polishing. Compared to traditional internal and external sawing, multi-wire sawing offers advantages such as high cutting speed, high machining precision, high efficiency, and a long lifespan, making it widely used for efficient wafer cutting. The multi-wire sawing process slices the ingot along a specific crystal orientation into flat, uniformly thick wafers no thicker than 1 mm, facilitating subsequent grinding. The basic principle is that a high-quality steel wire moves back and forth at high speed across the ingot surface. Diamond particles in the cutting fluid attached to the wire create intense friction against the ingot, causing the material to break and fall off the substrate, achieving the desired cutting effect. However, the disadvantage is high cutting wear. Due to the extreme hardness of silicon carbide, sawing it is challenging and subject to significant wear. The high cost and complex machining process contribute to the high cost of silicon carbide substrates, limiting their widespread application. In addition, the larger the chip size, the more difficult the corresponding crystal growth and processing technology is, while the manufacturing efficiency of downstream devices is higher and the unit cost is lower.

[0005] There is a technology in the prior art that uses lasers to cut silicon ingots. However, on the one hand, compared with silicon ingots, silicon carbide ingots are more hard, more brittle, more wear-resistant, and have extremely stable chemical properties. The existing laser cutting process cannot cut very thin wafers from silicon carbide ingots. On the other hand, in the existing laser cutting process of silicon ingots, laser modification is first used to form a modified layer at a certain thickness in the silicon ingot, and then the laser is used to heat the modified layer to make the cracks in the modified layer grow and spread, and then peeling is performed. In this process, the modified layer formed by laser modification is relatively thick. When the laser is subsequently used to heat the modified layer, the laser focus is focused on the modified layer. The height difference of the laser focus fluctuates greatly, and the focusing position of the laser focus is not well designed, causing the cracks in the modified layer to extend longer and more along the longitudinal direction of the silicon ingot, resulting in a large amount of cutting loss and a large amount of waste. Summary of the Invention

[0006] The present invention provides a laser stripping method and device for silicon carbide ingots, which reduces the amount and length of cracks in the modified layer extending longitudinally along the silicon carbide ingot, increases the number and length of transverse crack growth, reduces cutting loss thickness, and reduces waste.

[0007] In a first aspect, the present invention provides a laser lift-off method for a silicon carbide ingot, the laser lift-off method comprising:

[0008] Providing a silicon carbide ingot to be cut;

[0009] Focusing an ultrashort pulse laser beam at a set depth layer position of the silicon carbide ingot to generate a cavity modification forming region and a crack modification forming region above the set depth layer position, respectively; wherein the cavity modification forming region is located between the set depth layer position and the crack modification forming region;

[0010] Controlling the focus of an ultrashort pulse laser beam to scan a set depth layer of the silicon carbide ingot to form a cavity modified layer and a crack modified layer above the set depth layer, respectively; wherein the cavity modified layer is composed of a plurality of cavity modified forming regions, the crack modified layer is composed of a plurality of crack modified forming regions, and the cavity modified layer is located between the set depth layer and the crack modified layer;

[0011] Focusing the short-pulse laser beam on the crack modification formation area generates scattering perpendicular to the direction of the short-pulse laser beam, causing the cracks in the crack modification formation area to grow laterally outward;

[0012] Controlling the focus of the short pulse laser beam to scan the crack modified layer so that cracks in any adjacent crack modification formation areas in the crack modified layer are connected together through lateral growth;

[0013] A portion of the silicon carbide ingot is peeled off with the cracked modified layer as the interface to produce a wafer.

[0014] In the above scheme, an ultrashort pulse laser is first used to focus the ultrashort pulse laser beam at a set depth layer of the silicon carbide ingot, thereby generating a cavity modification formation region and a crack modification formation region above the set depth layer, respectively. The focus of the ultrashort pulse laser beam is then controlled to scan the set depth layer of the silicon carbide ingot to form the cavity modification layer and the crack modification layer. After the ultrashort pulse laser stealth cutting process, a short pulse laser is used to move the focus of the short pulse laser beam to a position above the set depth layer within a certain range, so that the focus of the short pulse laser beam is focused on the crack modification formation region. This allows the heat of the short pulse laser beam to act primarily on the crack modification formation region, generating scattering perpendicular to the direction of the short pulse laser beam, causing cracks in the crack modification formation region to grow laterally outward. The focus of the short pulse laser beam is then controlled to scan the crack modification layer so that cracks in any adjacent crack modification formation regions in the crack modification layer are connected by lateral growth.

[0015] Compared to existing laser silicon ingot cutting processes, the ultrashort pulse laser used in this process can generate a cavity-modification region and a crack-modification region above the set depth layer position of the ultrashort pulse laser beam focus. Through scanning, these two layers are formed, respectively, to refine and differentiate the modified layers in the existing technology. Subsequently, when using a short-pulse laser beam, the short-pulse laser beam is focused on the crack-modification region. The short-pulse laser beam focus is positioned above the ultrashort pulse laser beam focus, rather than at the same depth as in the existing technology. This generates scattering perpendicular to the direction of the short-pulse laser beam, causing cracks in the crack-modification region to grow laterally outward. Furthermore, through scanning, cracks in any adjacent crack-modification regions in the crack-modification layer are connected through lateral growth. That is, by subdividing the modified layer into a void modified layer and a crack modified layer, and then focusing the short pulse laser beam on the crack modified layer, the focal position of the short pulse laser beam is designed more accurately and reasonably, which not only makes the upper and lower height difference of the focus of the short pulse laser beam fluctuate less (because the upper and lower height difference of the crack modification forming area must be smaller than the upper and lower height difference of the modified layer composed of the crack modification forming area and the void modification forming area), but also optimizes the focus of the short pulse laser beam from focusing on the modified layer to focusing on the crack modified layer, optimizes the focal position of the short pulse laser beam, reduces the amount and length of the crack in the modified layer along the longitudinal extension of the silicon carbide ingot, and thus applies more laser energy to the lateral outward growth of the crack, which can increase the number and length of lateral crack growth, can cut thinner silicon carbide wafers, and also reduces the cutting loss thickness. More silicon carbide wafers can be cut from the same silicon carbide ingot, reducing waste.

[0016] In a specific embodiment, the ultrashort pulse laser beam is a picosecond pulse width laser beam or a femtosecond pulse width laser beam, and the wavelength of the ultrashort pulse laser beam is 500-1100nm, which is convenient for generating a better cavity modification forming area and a crack modification forming area above the focus of the ultrashort pulse laser beam.

[0017] In a specific embodiment, the short-pulse laser beam is a nanosecond pulse width laser beam, and the wavelength of the short-pulse laser beam is 500-1100nm, which is convenient for better reducing the amount and length of cracks in the modified layer extending longitudinally along the silicon carbide ingot, thereby applying more laser energy to the lateral outward growth of the cracks, increasing the number of lateral crack growth and the length of crack growth.

[0018] In a specific embodiment, the cavity modification forming region is located in the region 1-5um above the focus of the ultrashort pulse laser beam, and the crack modification forming region is located in the region 10-30um above the cavity modification forming region, so that the cavity modification forming region and the crack modification forming region are in different depth layers, and the cavity modification layer and the crack modification layer can be clearly distinguished.

[0019] In a specific embodiment, the focus of the short pulse laser beam is focused on the crack modification formation area to generate scattering perpendicular to the direction of the short pulse laser beam, so that the cracks in the crack modification formation area grow laterally outward, including: focusing the focus of the short pulse laser beam at the middle height position of the crack modification formation area to better optimize the focusing position of the short pulse laser beam.

[0020] In a specific embodiment, focusing the short pulse laser beam on the crack modification formation area to generate scattering perpendicular to the direction of the short pulse laser beam, so that the cracks in the crack modification formation area grow laterally outward, further comprising: adjusting the polarization state of the short pulse laser beam so that the electron propagation direction extends along the silicon carbide lattice direction of the silicon carbide ingot, generating scattering perpendicular to the direction of the short pulse laser beam, forming a 3-5° laterally growing crack, so as to better reduce the amount and length of the cracks in the modified layer along the longitudinal extension of the silicon carbide ingot, thereby applying more laser energy to the lateral outward growth of the cracks, and increasing the number of lateral crack growths and the crack growth length.

[0021] In a specific embodiment, controlling the focus of the ultrashort pulse laser beam to scan the set depth layer of the silicon carbide ingot includes: controlling the focus of the ultrashort pulse laser beam to scan the set depth layer of the silicon carbide ingot to produce multiple parallel first cutting paths, and the interval between any two adjacent first cutting paths is 20-45um, so as to facilitate the realization of a wider silicon carbide explosion point interval.

[0022] In a specific embodiment, controlling the focus of the short pulse laser beam to scan the crack modified layer includes: controlling the focus of the short pulse laser beam to scan multiple parallel second cutting paths in the crack modified layer, and each second cutting path is located directly above a first cutting path, thereby simplifying the scanning difficulty.

[0023] In a specific embodiment, controlling the focus of a short pulse laser beam to scan a plurality of parallel second cutting paths in the crack modification layer includes: controlling the focus of the short pulse laser beam to scan at each second cutting path for a number of times greater than or equal to three times, achieving connection of the burst point cracks by using a nanosecond laser beam for multiple processing and continuous heat injection, increasing the amount and length of lateral crack growth in the crack modification formation area, and making the cracks extending from adjacent second cutting paths connect together faster, thereby facilitating the separation of the silicon carbide ingot into multiple silicon carbide wafers through implicit crack induction growth.

[0024] In a second aspect, the present invention further provides a laser lift-off apparatus for silicon carbide ingots, comprising: a stage, an ultrashort pulse laser system, a first scanning system, a short pulse laser system, a second scanning system, and a lift-off system. The stage is used to hold the silicon carbide ingot to be cut. The ultrashort pulse laser system is used to provide an ultrashort pulse laser beam and focus the ultrashort pulse laser beam at a set depth layer of the silicon carbide ingot to generate a void-modified region and a crack-modified region above the set depth layer, respectively. The void-modified region is located between the set depth layer and the crack-modified region. The first scanning system is used to control the focus of the ultrashort pulse laser beam to scan the set depth layer of the silicon carbide ingot to generate a void-modified layer and a crack-modified layer above the set depth layer, respectively. The void-modified layer comprises multiple void-modified regions, and the crack-modified layer comprises multiple crack-modified regions, and the void-modified layer is located between the set depth layer and the crack-modified layer. The short-pulse laser system provides a short-pulse laser beam and focuses it on the crack-modification region, generating scattering perpendicular to the direction of the short-pulse laser beam, causing cracks within the crack-modification region to grow laterally outward. The second scanning system controls the focus of the short-pulse laser beam to scan across the crack-modification layer, connecting cracks within any adjacent crack-modification regions within the crack-modification layer through lateral growth. The stripping system strips a portion of the silicon carbide ingot, using the crack-modification layer as the interface, to produce a wafer.

[0025] In the above scheme, an ultrashort pulse laser is first used to focus the ultrashort pulse laser beam at a set depth layer of the silicon carbide ingot, thereby generating a cavity modification formation region and a crack modification formation region above the set depth layer, respectively. The focus of the ultrashort pulse laser beam is then controlled to scan the set depth layer of the silicon carbide ingot to form the cavity modification layer and the crack modification layer. After the ultrashort pulse laser stealth cutting process, a short pulse laser is used to move the focus of the short pulse laser beam to a position above the set depth layer within a certain range, so that the focus of the short pulse laser beam is focused on the crack modification formation region. This allows the heat of the short pulse laser beam to act primarily on the crack modification formation region, generating scattering perpendicular to the direction of the short pulse laser beam, causing cracks in the crack modification formation region to grow laterally outward. The focus of the short pulse laser beam is then controlled to scan the crack modification layer so that cracks in any adjacent crack modification formation regions in the crack modification layer are connected by lateral growth.

[0026] Compared to existing laser silicon ingot cutting processes, the ultrashort pulse laser used in this process can generate a cavity-modification region and a crack-modification region above the set depth layer position of the ultrashort pulse laser beam focus. Through scanning, these two layers are formed, respectively, to refine and differentiate the modified layers in the existing technology. Subsequently, when using a short-pulse laser beam, the short-pulse laser beam is focused on the crack-modification region. The short-pulse laser beam focus is positioned above the ultrashort pulse laser beam focus, rather than at the same depth as in the existing technology. This generates scattering perpendicular to the direction of the short-pulse laser beam, causing cracks in the crack-modification region to grow laterally outward. Furthermore, through scanning, cracks in any adjacent crack-modification regions in the crack-modification layer are connected through lateral growth. That is, by subdividing the modified layer into a void modified layer and a crack modified layer, and then focusing the short pulse laser beam on the crack modified layer, the focal position of the short pulse laser beam is designed more accurately and reasonably, which not only makes the upper and lower height difference of the focus of the short pulse laser beam fluctuate less (because the upper and lower height difference of the crack modification forming area must be smaller than the upper and lower height difference of the modified layer composed of the crack modification forming area and the void modification forming area), but also optimizes the focus of the short pulse laser beam from focusing on the modified layer to focusing on the crack modified layer, optimizes the focal position of the short pulse laser beam, reduces the amount and length of the crack in the modified layer along the longitudinal extension of the silicon carbide ingot, and thus applies more laser energy to the lateral outward growth of the crack, which can increase the number and length of lateral crack growth, can cut thinner silicon carbide wafers, and also reduces the cutting loss thickness. More silicon carbide wafers can be cut from the same silicon carbide ingot, reducing waste.

[0027] In one specific embodiment, the ultrashort pulse laser beam provided by the ultrashort pulse laser system is a picosecond pulse width laser beam or a femtosecond pulse width laser beam, and the wavelength of the ultrashort pulse laser beam is 500-1100 nm. The short pulse laser beam provided by the short pulse laser system is a nanosecond pulse width laser beam, and the wavelength of the short pulse laser beam is 500-1100 nm. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A flow chart of a laser lift-off method for a silicon carbide ingot provided in an embodiment of the present invention;

[0029] Figures 2 to 5 A schematic cross-sectional view of each step of a laser lift-off method for a silicon carbide ingot provided in an embodiment of the present invention;

[0030] Figure 6 A schematic structural diagram of a laser lift-off device for silicon carbide ingots provided in an embodiment of the present invention;

[0031] Figure 7 Based on Figure 6 A flow chart of a method for laser stripping of a silicon carbide ingot provided by a laser stripping device for a silicon carbide ingot;

[0032] Figure 8 An actual sample image of a cavity modification forming area and a crack modification forming area processed by an ultrashort pulse laser beam provided in an embodiment of the present invention.

[0033] Reference numerals:

[0034] 10-Silicon carbide ingot 21-Set depth layer 22-Void modified layer 23-Crack modified layer DETAILED DESCRIPTION

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in 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 making creative efforts shall fall within the scope of protection of the present invention.

[0036] To facilitate understanding of the laser lift-off method for silicon carbide ingots provided in an embodiment of the present invention, the following first describes an application scenario of the laser lift-off method provided in an embodiment of the present invention. This laser lift-off method is applied to the process of separating silicon carbide wafers from a silicon carbide ingot. The following describes the laser lift-off method for silicon carbide ingots in detail with reference to the accompanying drawings.

[0037] refer to Figures 1 to 5 The laser lift-off method for a silicon carbide ingot 10 provided in an embodiment of the present invention includes:

[0038] Step 10: Providing a silicon carbide ingot 10 to be cut;

[0039] Step 20: Focusing the ultrashort pulse laser beam at a predetermined depth layer 21 of the silicon carbide ingot 10 to generate a cavity modification region and a crack modification region above the predetermined depth layer 21; wherein the cavity modification region is located between the predetermined depth layer 21 and the crack modification region;

[0040] Step 30: Controlling the focus of the ultrashort pulse laser beam to scan the set depth layer 21 of the silicon carbide ingot 10 to form a void modified layer 22 and a crack modified layer 23 above the set depth layer 21, respectively; wherein the void modified layer 22 is composed of a plurality of void modified forming regions, and the crack modified layer 23 is composed of a plurality of crack modified forming regions, and the void modified layer 22 is located between the set depth layer 21 and the crack modified layer 23;

[0041] Step 40: Focusing the short pulse laser beam on the crack modification formation area to generate scattering perpendicular to the direction of the short pulse laser beam, so that the cracks in the crack modification formation area grow laterally outward;

[0042] Step 50: Control the focus of the short pulse laser beam to scan the crack modified layer 23 so that cracks in any adjacent crack modification areas in the crack modified layer 23 are connected together by lateral growth;

[0043] Step 60: Using the crack reformed layer 23 as an interface, a portion of the silicon carbide ingot 10 is peeled off to form a wafer.

[0044] In the above scheme, an ultrashort pulse laser is first used to focus the ultrashort pulse laser beam on the set depth layer 21 position of the silicon carbide ingot 10 to generate a cavity modification forming region and a crack modification forming region above the set depth layer 21 position, and the focus of the ultrashort pulse laser beam is controlled to scan the set depth layer 21 of the silicon carbide ingot 10 to form a cavity modification layer 22 and a crack modification layer 23. After ultrashort pulse laser stealth cutting processing, a short pulse laser is used to move the focus of the short pulse laser beam to a certain range above the set depth layer 21, so that the focus of the short pulse laser beam is focused on the crack modification formation area, so that the heat of the short pulse laser beam mainly acts on the crack modification formation area, generating scattering perpendicular to the direction of the short pulse laser beam, so that the cracks in the crack modification formation area grow laterally outward, and the focus of the short pulse laser beam is controlled to scan the crack modification layer 23, so that the cracks in any adjacent crack modification formation areas in the crack modification layer 23 are connected together through lateral growth.

[0045] Compared to existing laser silicon ingot cutting processes, the ultrashort pulse laser employed in this process can generate a cavity-modified formation region and a crack-modified formation region above a predetermined depth layer 21, where the ultrashort pulse laser beam is focused. Scanning then forms a cavity-modified layer 22 and a crack-modified layer 23, respectively, further refining and differentiating the modified layers used in existing techniques. Subsequently, when using a short-pulse laser beam, the short-pulse laser beam is focused on the crack-modified formation region. The short-pulse laser beam's focal point is positioned above the ultrashort pulse laser beam's focal point, rather than at the same depth as in existing techniques. This generates scattering perpendicular to the direction of the short-pulse laser beam, causing cracks within the crack-modified formation region to grow laterally outward. Furthermore, scanning connects cracks within any adjacent crack-modified formation regions within crack-modified layer 23 through lateral growth. That is, by subdividing the modified layer into a void modified layer 22 and a crack modified layer 23, and then focusing the short pulse laser beam on the crack modified layer 23, the focal position of the short pulse laser beam is more accurately and reasonably designed, not only reducing the vertical height difference of the focus of the short pulse laser beam (because the vertical height difference of the crack modified formation area must be smaller than the vertical height difference of the modified layer composed of the crack modified formation area and the void modified formation area), but also optimizing the focus of the short pulse laser beam on the modified layer to focus on the crack modified layer 23, optimizing the focal position of the short pulse laser beam, reducing the amount and length of cracks in the modified layer extending longitudinally along the silicon carbide ingot 10, thereby directing more laser energy to the lateral outward growth of the cracks, increasing the number and length of lateral crack growth, and being able to cut thinner silicon carbide wafers. It also reduces the cutting loss thickness, and more silicon carbide wafers can be cut from the same silicon carbide ingot 10, reducing waste. The above steps are described in detail below with reference to the accompanying drawings.

[0046] First, if Figure 3 and Figure 6 As shown, a silicon carbide ingot 10 to be cut is provided.

[0047] Next, refer to Figure 1 、 Figure 2 and Figure 8The ultrashort pulse laser beam is focused on the set depth layer 21 of the silicon carbide ingot 10 to generate a cavity modification formation region and a crack modification formation region above the set depth layer 21, respectively. The cavity modification formation region is located between the set depth layer 21 and the crack modification formation region. The intensity at the focal volume of the ultrashort pulse laser beam causes nonlinear absorption of the laser energy by the material through multiphoton ionization, tunnel ionization, and avalanche ionization. Due to nonlinear absorption, a microscopic, highly excited plasma is generated at the focal position. The microscopic size of the plasma varies depending on the crystal material, ranging from nanometers to submicrometers. Therefore, no large-scale material damage will occur in the direction of laser incidence.

[0048] The depth layer 21 set during the processing is specifically related to the thickness of the peeled wafer, the peeling loss thickness, etc. The focus of the ultrashort pulse laser beam can be accurately focused on the set depth layer 21 position of the silicon carbide ingot 10 by a three-axis galvanometer, an altimeter, etc. Figure 2 、 Figure 3 and Figure 8 The crack modification area and the cavity modification area generated above the set depth layer 21 occupy a certain thickness space. The size of the crack modification area and the cavity modification area is related to the energy of the ultrashort pulse laser beam. The size of the crack modification area and the cavity modification area increases with the increase of laser energy. Figure 2 and Figure 3 As shown, the cavity modification forming region can be located 1-5 μm above the focus of the ultrashort pulse laser beam, and the crack modification forming region can be located 10-30 μm above the cavity modification forming region, so that the cavity modification forming region and the crack modification forming region are at different depth layers, and the cavity modification layer 22 and the crack modification layer 23 can be clearly distinguished. When selecting an ultrashort pulse laser beam, the ultrashort pulse laser beam can be a picosecond pulse width laser beam or a femtosecond pulse width laser beam. In a more preferred embodiment, the wavelength of the ultrashort pulse laser beam can be controlled to be 500-1100 nm. Specifically, the wavelength of the ultrashort pulse laser beam can be any value between 500-1100 nm, such as 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1100 nm, etc. This facilitates the generation of a cavity modification forming region and a crack modification forming region with better effects above the focus of the ultrashort pulse laser beam.

[0049] Next, refer to Figure 1 and Figure 3, controlling the focus of the ultrashort pulse laser beam to scan the set depth layer 21 of the silicon carbide ingot 10, so as to form a cavity modification layer 22 and a crack modification layer 23 above the position of the set depth layer 21, respectively; wherein, the cavity modification layer 22 is composed of multiple cavity modification forming regions, the crack modification layer 23 is composed of multiple crack modification forming regions, and the cavity modification layer 22 is located between the set depth layer 21 and the crack modification layer 23.

[0050] Specifically, the focus of the ultrashort pulse laser beam can be controlled to scan the set depth layer 21 of the silicon carbide ingot 10 in a variety of ways to form a void modification layer 22 and a crack modification layer 23 in the silicon carbide ingot 10, respectively, so that the void modification in the void modification layer 22 is regionally spaced and filled with the void modification layer 22 area, and the crack modification in the crack modification layer 23 is regionally spaced and filled with the crack modification layer 23 area. For example, a spiral scanning method can be used, or a parallel and spaced scanning method can be used to form multiple cutting paths. For example, the focus of the ultrashort pulse laser beam can be controlled to scan multiple parallel first cutting paths at the set depth layer 21 of the silicon carbide ingot 10, and the interval between any two adjacent first cutting paths is 20-45 μm. Specifically, the interval between any two adjacent first cutting paths can be any value between 20-45 μm, such as 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, etc., to facilitate the realization of a wider silicon carbide explosion point interval. The distance between different focal points can also be made about 1-3 times the size of the crack modification area, so as to achieve a wider silicon carbide explosion point interval.

[0051] Next, refer to Figure 1 、 Figure 4 and Figure 5, focusing the short-pulse laser beam on the crack modification formation area, generating scattering perpendicular to the direction of the short-pulse laser beam, causing the cracks in the crack modification formation area to grow laterally outward. That is, the short-pulse laser moves upward relative to the focus position of the ultrashort-pulse laser, thereby focusing the short-pulse laser beam on the crack modification formation area. The above-mentioned void modification formation area is actually a modification area where voids have not yet formed. When the focused short-pulse laser beam that can penetrate the material is subsequently loaded, when the photon energy of the short-pulse laser beam is focused on the material, if the photon energy is high enough, the laser photons may directly break the chemical bonds of the sample, causing the volume of the local area to expand and explode rapidly. A sufficiently long short pulse width allows the photon energy to be immediately coupled to the silicon carbide lattice after being transferred to electrons. The photon energy will be converted into heat energy, causing the sample temperature to rise. As the temperature rises, the physical and chemical properties of the sample change further, the optical system coefficients change, and stress is generated inside the sample. As the pulse width increases, the stress continues to accumulate, breaking the chemical bonds in the crack-forming area created by the previous ultrashort pulse laser beam. The cracks formed between the carbon and silicon elements are then further guided to radiate outward.

[0052] It's important to explain that the longer pulse width of a short-pulse laser beam compared to an ultrashort-pulse laser beam is intended to increase the light dwell time, generating a greater thermal effect and thus extending the crack's growth. After multiple, continuous short-pulse laser irradiations—which can range from 1-3 to 3-5 times—the crack can grow horizontally to over 200 microns. Growth will vary depending on the material, type of material, doping, and laser parameters such as power, pulse width, and wavelength.

[0053] When the short pulse laser beam is focused on the crack modification area, scattering perpendicular to the direction of the short pulse laser beam is generated, so that the cracks in the crack modification area grow laterally outward, Figure 4 and Figure 5 , the polarization state of the short-pulse laser beam can be adjusted so that the electron propagation direction extends along the silicon carbide lattice direction of the silicon carbide ingot 10, generating scattering perpendicular to the direction of the short-pulse laser beam, and forming a 3-5° transverse growth crack, which is convenient for better reducing the amount and length of the cracks in the modified layer along the longitudinal extension of the silicon carbide ingot 10, thereby directing more laser energy to the lateral outward growth of the cracks, increasing the number of transverse crack growth and the crack growth length.

[0054] When a short-pulse laser beam is selected, the short-pulse laser beam can be a nanosecond pulse width laser beam. In a more preferred embodiment, the wavelength of the short-pulse laser beam can be 500-1100 nm. Specifically, the wavelength of the short-pulse laser beam can be any value between 500-1100 nm, such as 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1100 nm, etc. This facilitates better reduction of the amount and length of cracks in the modified layer that extend longitudinally along the silicon carbide ingot 10, thereby directing more laser energy to the lateral outward growth of the cracks, increasing the number and length of lateral crack growth.

[0055] When focusing the short-pulse laser beam on the crack modification area, generating scattering perpendicular to the direction of the short-pulse laser beam, and causing the cracks in the crack modification area to grow laterally outward, a more optimal approach is to focus the short-pulse laser beam at a height position midway within the crack modification area, further optimizing the focus position of the short-pulse laser beam. Of course, any approach that focuses the short-pulse laser beam on the crack modification area is within the scope of protection of this patent.

[0056] When the focus of the short pulse laser beam is moved upward relative to the focus of the ultrashort pulse laser beam, since the band gap of silicon carbide is approximately 3.2eV and the refractive index of the medium and air is 2.6, according to the law of refraction, when the laser head NA = 0.42, the incident angle of the laser when passing through the laser head is:

[0057] U1=sin(0.42)*180 / π=24.83°

[0058] The laser is refracted when passing through the sample surface, and its refraction angle is:

[0059] U2=sin(0.42 / 2.6)*180 / π=9.3°

[0060] Therefore, the magnification of the distance of the laser in the medium is:

[0061] A=tan(π*24.83 / 180) / tan(π*9.3 / 180)=2.83

[0062] Therefore, when the processing head moves along the Z axis from Z0 to Z1, the laser moves at a height of

[0063] h=2.83*(Z1-Z0)

[0064] The processing position of the short pulse laser relative to the ultrashort pulse laser can move the processing head on the Z axis by 3.88-12.36um. The average movement can be 8um, and the actual position movement is about 22um, which can achieve better results.

[0065] Next, refer to Figure 1 、 Figure 4 and Figure 5 , control the focus of the short pulse laser beam to scan the crack modification layer 23, so that the cracks in any adjacent crack modification forming areas in the crack modification layer 23 are connected together through lateral growth. The specific way of controlling the focus of the short pulse laser beam to scan the crack modification layer 23 is related to the way of controlling the focus of the ultrashort pulse laser beam to scan the set depth layer 21. For example, when the way of controlling the focus of the ultrashort pulse laser beam to scan the set depth layer 21 adopts a spiral scanning way, the way of controlling the focus of the short pulse laser beam to scan the crack modification layer 23 is also a spiral scanning way. When the way of controlling the focus of the ultrashort pulse laser beam to scan the set depth layer 21 adopts a method of multiple parallel first cutting paths, the way of controlling the focus of the short pulse laser beam to scan the crack modification layer 23 can be specifically: controlling the focus of the short pulse laser beam to scan multiple parallel second cutting paths in the crack modification layer 23, and each second cutting path is located directly above a first cutting path, thereby simplifying the scanning difficulty.

[0066] In addition, when controlling the focus of the short-pulse laser beam to scan multiple parallel second cutting paths in the crack modification layer 23, the focus of the short-pulse laser beam can be controlled to scan each second cutting path three or more times. By using the nanosecond laser beam for multiple processing and continuous heat injection to achieve the connection of the explosive point cracks, the amount and length of the lateral crack growth in the crack modification formation area are increased, and the cracks extending from adjacent second cutting paths are connected together more quickly, facilitating the separation of the silicon carbide ingot 10 into multiple silicon carbide wafers through the implicit crack induction growth method.

[0067] Next, refer to Figure 1 The crack modified layer 23 is used as the interface to peel off a portion of the silicon carbide ingot 10 to generate a wafer. Specifically, the method of peeling off a portion of the silicon carbide ingot 10 to generate a wafer using the crack modified layer 23 as the interface can be to use stretching, rotation, etc. to peel the wafer above the crack modified layer 23 from the silicon carbide ingot 10.

[0068] In addition, the following method can also be used to peel off a portion of the silicon carbide ingot 10 with the crack modification layer 23 as the interface to generate a wafer. The crack modification layer is cut by a diamond wire saw, and the crack modification layer is used as the interface to peel off a portion of the silicon carbide ingot to generate a silicon carbide wafer. The crack modification layer is formed at the predetermined depth layer by focusing the laser beam at a predetermined depth layer from the inside of the silicon carbide ingot and scanning. In the process of forming the crack modification layer, the energy density at the laser focus exceeds the silicon carbide ablation threshold, the material temperature rises suddenly, and the silicon carbide decomposes under high temperature conditions to generate amorphous silicon or single crystal silicon or a mixture of the two and carbon. The specific amorphous silicon and single crystal silicon are determined by the laser energy density. When the laser energy is large, single crystal silicon is generated, and when the laser energy is small, amorphous silicon is generated. Then, the crack modification layer is cut by a diamond wire saw, and the crack modification layer is used as the interface to peel off a portion of the silicon carbide ingot to generate a silicon carbide wafer. Since the materials of the crack modification layer are single crystal silicon, amorphous silicon and carbon, their hardness is much lower than that of silicon carbide. In the process of wire cutting the modified layer with a diamond wire saw, the wear of the diamond wire saw can be reduced, thereby reducing the loss of the diamond wire saw and reducing the difficulty of wire cutting. Therefore, a thinner diamond wire saw can be selected to reduce the loss of silicon carbide ingots and improve the slicing output rate of silicon carbide ingots. At the same time, the diamond wire saw cutting method is used, which is not easy to cause the silicon carbide wafer to break due to uneven force. That is, compared with the laser cutting + mechanical stripping method, the present application uses a diamond wire saw to cut the crack modification layer and peel off the silicon carbide wafer from the modified silicon carbide ingot without the need for mechanical stripping. This can avoid the phenomenon that the silicon carbide wafer may break due to uneven force during the mechanical stripping process, thereby improving the product yield and stripping efficiency.

[0069] After the silicon carbide wafer is stripped from the silicon carbide ingot and before it is ground, a step can be added in which the silicon carbide wafer is immersed in a chemical solution to etch the interface of the modified layer of the silicon carbide wafer. By using the chemical solution to etch the interface of the modified layer of the silicon carbide wafer, defects such as residual stress, dislocations, and cracks generated during the silicon carbide wafer stripping step can be removed. The interface of the modified layer of the silicon carbide wafer is then ground. Since there is no or little residual stress on the interface of the modified layer of the silicon carbide wafer at this time, the increase in defects during the grinding process is avoided. The phenomenon that the extrusion during the grinding process increases residual stress and thus causes continued crack growth can be slowed down. As a result, less material can be ground to completely remove the damaged layer, reducing ingot loss and improving wafer quality. In addition, the interface of the modified layer after chemical solution etching is more flat, which can reduce the difficulty of subsequent grinding and improve grinding efficiency.

[0070] In the various embodiments shown above, an ultrashort pulse laser is first used to focus the ultrashort pulse laser beam on a set depth layer 21 position of the silicon carbide ingot 10 to generate a cavity modification forming region and a crack modification forming region above the set depth layer 21 position, respectively, and the focus of the ultrashort pulse laser beam is controlled to scan the set depth layer 21 of the silicon carbide ingot 10 to form a cavity modification layer 22 and a crack modification layer 23. After ultrashort pulse laser stealth cutting processing, a short pulse laser is used to move the focus of the short pulse laser beam to a certain range above the set depth layer 21, so that the focus of the short pulse laser beam is focused on the crack modification formation area, so that the heat of the short pulse laser beam mainly acts on the crack modification formation area, generating scattering perpendicular to the direction of the short pulse laser beam, so that the cracks in the crack modification formation area grow laterally outward, and the focus of the short pulse laser beam is controlled to scan the crack modification layer 23, so that the cracks in any adjacent crack modification formation areas in the crack modification layer 23 are connected together through lateral growth.

[0071] Compared to existing laser silicon ingot cutting processes, the ultrashort pulse laser employed in this process can generate a cavity-modified formation region and a crack-modified formation region above a predetermined depth layer 21, where the ultrashort pulse laser beam is focused. Scanning then forms a cavity-modified layer 22 and a crack-modified layer 23, respectively, further refining and differentiating the modified layers used in existing techniques. Subsequently, when using a short-pulse laser beam, the short-pulse laser beam is focused on the crack-modified formation region. The short-pulse laser beam's focal point is positioned above the ultrashort pulse laser beam's focal point, rather than at the same depth as in existing techniques. This generates scattering perpendicular to the direction of the short-pulse laser beam, causing cracks within the crack-modified formation region to grow laterally outward. Furthermore, scanning connects cracks within any adjacent crack-modified formation regions within crack-modified layer 23 through lateral growth. That is, by subdividing the modified layer into a void modified layer 22 and a crack modified layer 23, and then focusing the short pulse laser beam on the crack modified layer 23, the focal position of the short pulse laser beam is designed more accurately and reasonably, which not only makes the upper and lower height difference of the focus of the short pulse laser beam fluctuate less (because the upper and lower height difference of the crack modification forming area must be smaller than the upper and lower height difference of the modified layer composed of the crack modification forming area and the void modification forming area), but also optimizes the focus of the short pulse laser beam on the modified layer to focus on the crack modified layer 23, optimizes the focal position of the short pulse laser beam, reduces the amount and length of the crack in the modified layer along the longitudinal extension of the silicon carbide ingot 10, and thus applies more laser energy to the lateral outward growth of the crack, which can increase the number and length of lateral crack growth, can cut out thinner silicon carbide wafers, and also reduces the cutting loss thickness. More silicon carbide wafers can be cut from the same silicon carbide ingot 10, reducing waste.

[0072] In addition, the embodiment of the present invention also provides a laser stripping device for silicon carbide ingots, referring to Figures 1 to 6 The laser lift-off apparatus includes a stage, an ultrashort pulse laser system, a first scanning system, a short pulse laser system, a second scanning system, and a lift-off system. The stage is used to hold the silicon carbide ingot 10 to be cut. The ultrashort pulse laser system is used to provide an ultrashort pulse laser beam and focus the ultrashort pulse laser beam on a set depth layer 21 of the silicon carbide ingot 10, thereby generating a cavity modification formation region and a crack modification formation region above the set depth layer 21, respectively; the cavity modification formation region is located between the set depth layer 21 and the crack modification formation region. The first scanning system is used to control the focus of the ultrashort pulse laser beam to scan the set depth layer 21 of the silicon carbide ingot 10, thereby forming a cavity modification layer 22 and a crack modification layer 23 above the set depth layer 21, respectively. The cavity modification layer 22 is composed of multiple cavity modification formation regions, and the crack modification layer 23 is composed of multiple crack modification formation regions, with the cavity modification layer 22 located between the set depth layer 21 and the crack modification layer 23. The short pulse laser system is used to provide a short pulse laser beam and focus the short pulse laser beam on the crack modification formation region, generating scattering perpendicular to the direction of the short pulse laser beam, causing cracks in the crack modification formation region to grow laterally outward. The second scanning system is used to control the focus of the short pulse laser beam to scan the crack modification layer 23, so that cracks in any adjacent crack modification formation regions in the crack modification layer 23 are connected by lateral growth. The stripping system is used to strip a portion of the silicon carbide ingot 10 using the crack modified layer 23 as an interface to generate a wafer.

[0073] like Figure 6 In the laser stripping device for a silicon carbide ingot shown, the first scanning system and the second scanning system can both be realized by a three-axis motion table, and the stage is fixed on the three-axis motion table. The ultrashort pulse laser system and the short pulse laser system can respectively use different lasers, and different laser systems can share some optical devices, and optical switches are set on different optical paths for switching. Among them, the ultrashort pulse laser beam provided by the above-mentioned ultrashort pulse laser system can be a picosecond pulse width laser beam or a femtosecond pulse width laser beam, and the wavelength of the ultrashort pulse laser beam can be 500-1100nm. The short pulse laser beam provided by the above-mentioned short pulse laser system can be a nanosecond pulse width laser beam, and the wavelength of the short pulse laser beam can be 500-1100nm. Reference Figure 6 , CCD cameras and light sources can also be set on different laser systems to observe the processing position in real time.

[0074] like Figure 7 Based on Figure 6The laser lift-off operation flow chart of the laser lift-off device for silicon carbide ingot is shown as follows. Figure 7 The operation flow shown can complete all the operation steps of any one of the laser lift-off methods shown above.

[0075] In the above scheme, an ultrashort pulse laser is first used to focus the ultrashort pulse laser beam on the set depth layer 21 position of the silicon carbide ingot 10 to generate a cavity modification forming region and a crack modification forming region above the set depth layer 21 position, and the focus of the ultrashort pulse laser beam is controlled to scan the set depth layer 21 of the silicon carbide ingot 10 to form a cavity modification layer 22 and a crack modification layer 23. After ultrashort pulse laser stealth cutting processing, a short pulse laser is used to move the focus of the short pulse laser beam to a certain range above the set depth layer 21, so that the focus of the short pulse laser beam is focused on the crack modification formation area, so that the heat of the short pulse laser beam mainly acts on the crack modification formation area, generating scattering perpendicular to the direction of the short pulse laser beam, so that the cracks in the crack modification formation area grow laterally outward, and the focus of the short pulse laser beam is controlled to scan the crack modification layer 23, so that the cracks in any adjacent crack modification formation areas in the crack modification layer 23 are connected together through lateral growth.

[0076] Compared to existing laser silicon ingot cutting processes, the ultrashort pulse laser employed in this process can generate a cavity-modified formation region and a crack-modified formation region above a predetermined depth layer 21, where the ultrashort pulse laser beam is focused. Scanning then forms a cavity-modified layer 22 and a crack-modified layer 23, respectively, further refining and differentiating the modified layers used in existing techniques. Subsequently, when using a short-pulse laser beam, the short-pulse laser beam is focused on the crack-modified formation region. The short-pulse laser beam's focal point is positioned above the ultrashort pulse laser beam's focal point, rather than at the same depth as in existing techniques. This generates scattering perpendicular to the direction of the short-pulse laser beam, causing cracks within the crack-modified formation region to grow laterally outward. Furthermore, scanning connects cracks within any adjacent crack-modified formation regions within crack-modified layer 23 through lateral growth. That is, by subdividing the modified layer into a void modified layer 22 and a crack modified layer 23, and then focusing the short pulse laser beam on the crack modified layer 23, the focal position of the short pulse laser beam is designed more accurately and reasonably, which not only makes the upper and lower height difference of the focus of the short pulse laser beam fluctuate less (because the upper and lower height difference of the crack modification forming area must be smaller than the upper and lower height difference of the modified layer composed of the crack modification forming area and the void modification forming area), but also optimizes the focus of the short pulse laser beam on the modified layer to focus on the crack modified layer 23, optimizes the focal position of the short pulse laser beam, reduces the amount and length of the crack in the modified layer along the longitudinal extension of the silicon carbide ingot 10, and thus applies more laser energy to the lateral outward growth of the crack, which can increase the number and length of lateral crack growth, can cut out thinner silicon carbide wafers, and also reduces the cutting loss thickness. More silicon carbide wafers can be cut from the same silicon carbide ingot 10, reducing waste.

[0077] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for laser lift-off of a silicon carbide ingot, characterized in that: include: Providing a silicon carbide ingot to be cut; focusing an ultrashort pulse laser beam at a set depth layer position of the silicon carbide ingot to generate a cavity modification forming region and a crack modification forming region above the set depth layer position, respectively; wherein the cavity modification forming region is located between the set depth layer position and the crack modification forming region; Controlling the focus of the ultrashort pulse laser beam to scan a set depth layer of the silicon carbide ingot to form a void modified layer and a crack modified layer above the set depth layer, respectively; wherein the void modified layer is composed of a plurality of the void modified forming regions, the crack modified layer is composed of a plurality of the crack modified forming regions, and the void modified layer is located between the set depth layer and the crack modified layer; Focusing a short pulse laser beam on the crack modification forming area to generate scattering perpendicular to the direction of the short pulse laser beam, so that the crack in the crack modification forming area grows laterally outward; Controlling the focus of the short pulse laser beam to scan the crack modified layer so that cracks in any adjacent crack modification forming regions in the crack modified layer are connected together by lateral growth; A portion of the silicon carbide ingot is peeled off with the crack reformed layer as an interface to produce a wafer.

2. The laser lift-off method according to claim 1, wherein: The ultrashort pulse laser beam is a picosecond pulse width laser beam or a femtosecond pulse width laser beam, and the wavelength of the ultrashort pulse laser beam is 500-1100 nm.

3. The laser lift-off method according to claim 1, wherein: The short pulse laser beam is a nanosecond pulse width laser beam, and the wavelength of the short pulse laser beam is 500-1100 nm.

4. The laser lift-off method according to claim 1, wherein: The cavity modification forming region is located in a region 1-5 μm above the focus of the ultrashort pulse laser beam, and the crack modification forming region is located in a region 10-30 μm above the cavity modification forming region.

5. The laser lift-off method according to claim 4, wherein: The step of focusing the short pulse laser beam on the crack modification forming area to generate scattering perpendicular to the direction of the short pulse laser beam so as to cause the cracks in the crack modification forming area to grow laterally outward includes: The short pulse laser beam is focused at a middle height position of the crack modification formation region.

6. The laser lift-off method according to claim 1, wherein: The step of focusing the short pulse laser beam on the crack modification forming region to generate scattering perpendicular to the direction of the short pulse laser beam so that the crack in the crack modification forming region grows laterally outwards further comprises: The polarization state of the short pulse laser beam is adjusted so that the electron propagation direction extends along the silicon carbide lattice direction of the silicon carbide ingot, generating scattering perpendicular to the direction of the short pulse laser beam and forming a 3-5° transverse growth crack.

7. The laser lift-off method according to claim 1, wherein: Controlling the focus of the ultrashort pulse laser beam to scan the silicon carbide ingot at a set depth layer includes: The focus of the ultrashort pulse laser beam is controlled to scan a plurality of parallel first cutting streets at a set depth layer of the silicon carbide ingot, and the interval between any two adjacent first cutting streets is 20-45 μm.

8. The laser lift-off method according to claim 7, wherein: The controlling the focus of the short pulse laser beam to scan the crack modified layer includes: The focus of the short pulse laser beam is controlled to scan a plurality of parallel second cutting lines on the crack modified layer, and each second cutting line is located directly above one of the first cutting lines.

9. The laser lift-off method according to claim 8, wherein: The step of controlling the focus of the short pulse laser beam to scan a plurality of parallel second cutting paths in the crack modified layer comprises: The focus of the short pulse laser beam is controlled to scan at each second cutting street for a number of times greater than or equal to three times.

10. A laser lift-off device for silicon carbide ingots, characterized in that: include: a stage for holding the silicon carbide ingot to be cut thereon; an ultrashort pulse laser system, configured to provide an ultrashort pulse laser beam, and focus the ultrashort pulse laser beam at a set depth layer position of the silicon carbide ingot, so as to generate a cavity modification forming region and a crack modification forming region above the set depth layer position, respectively; wherein the cavity modification forming region is located between the set depth layer position and the crack modification forming region; a first scanning system, configured to control the focus of the ultrashort pulse laser beam to scan a set depth layer of the silicon carbide ingot, so as to form a void modified layer and a crack modified layer above the set depth layer, respectively; wherein the void modified layer is composed of a plurality of the void modified forming regions, the crack modified layer is composed of a plurality of the crack modified forming regions, and the void modified layer is located between the set depth layer and the crack modified layer; a short pulse laser system for providing a short pulse laser beam and focusing the short pulse laser beam on the crack modification forming area to generate scattering perpendicular to the direction of the short pulse laser beam, so that the cracks in the crack modification forming area grow laterally outward; a second scanning system for controlling the focus of the short pulse laser beam to scan the crack modified layer so that cracks in any adjacent crack modification forming areas in the crack modified layer are connected together by lateral growth; The stripping system is used to strip a portion of the silicon carbide ingot using the crack modified layer as an interface to generate a wafer.

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