CN115555736A

CN115555736A - Method and device for stripping silicon carbide crystal ingot by laser

Info

Publication number: CN115555736A
Application number: CN202211322500.8A
Authority: CN
Inventors: 侯煜; 李曼; 张喆; 石海燕; 张昆鹏; 文志东; 张紫辰
Original assignee: Institute of Microelectronics of CAS
Current assignee: Institute of Microelectronics of CAS
Priority date: 2022-10-26
Filing date: 2022-10-26
Publication date: 2023-01-03

Abstract

The invention provides a method and a device for stripping a silicon carbide crystal ingot by laser. And then the short pulse laser beam is focused on the cavity modification forming region after transmitting the second end surface of the silicon carbide crystal ingot, and is scattered and propagated in the cavity modification forming region, so that the heat of the short pulse laser beam acts on the cavity modification forming region, the cracks in the crack modification forming region grow outwards in the transverse direction, and the cracks in the adjacent cavity modification forming regions in the cavity modification layer are connected together through the transverse growth by scanning. The amount and the length of the crack in the modification layer along the longitudinal extension of the silicon carbide crystal ingot are reduced, the number of the transverse crack growth and the crack growth length are increased, the cutting loss thickness is reduced, and the waste is reduced.

Description

Method and device for stripping silicon carbide crystal ingot by laser

Technical Field

The invention relates to the technical field of silicon carbide crystal ingots, in particular to a method and a device for peeling a silicon carbide crystal ingot by laser.

Background

In the third generation semiconductor materials, siC (silicon carbide) has the characteristics of large forbidden band width, high breakdown electric field, high saturated electron drift velocity, large thermal conductivity and the like, and can be applied to high-voltage environments of more than 1200 volts, so that the SiC has obvious advantages in severe environments. The SiC substrate processing technology is an important basis for manufacturing devices, the quality and precision of surface processing directly affect the quality of an epitaxial film and the performance of the devices, and therefore the application of the SiC substrate processing technology requires that the surface of a wafer is ultra-smooth, free of defects and free of damage, and the roughness value of the surface of the wafer is below a nanometer level.

However, the processing of SiC wafers is very difficult due to the high hardness, high brittleness, good wear resistance and extremely stable chemical properties of SiC crystals. The ultra-precision machining process of the SiC single crystal wafer mainly comprises the following steps according to the machining sequence: directional cutting, grinding (rough grinding, fine grinding), polishing (mechanical polishing), and ultra-precision polishing (chemical mechanical polishing).

In the traditional method, cutting is a process of cutting the SiC crystal bar into crystal slices along a certain direction. The SiC crystal bar is cut into wafers with small warpage, uniform thickness and low cutting loss, and is vital to subsequent grinding and polishing. Compared with the traditional internal circle and external circle cutting, the multi-line cutting has the advantages of high cutting speed, high processing precision, high efficiency, long service life and the like, and is widely applied to the high-efficiency cutting of wafers. The multi-wire cutting process is to cut the crystal ingot into cutting pieces with thickness not more than 1mm, flat surface and uniform thickness according to a certain crystal direction, so as to facilitate the subsequent grinding processing. The basic principle is that a high-quality steel wire moves back and forth on the surface of an ingot at a high speed, and diamond particles in cutting fluid attached to the steel wire generate violent friction on the ingot, so that the material is cracked and falls off from the surface of a matrix, and the cutting effect is achieved. The disadvantages are high cutting abrasion, and high processing difficulty and much abrasion when cutting the silicon carbide due to the extremely high hardness of the silicon carbide. The high cost of silicon carbide substrates due to the expensive time and complex processing techniques limits the amount of silicon carbide that can be used. In addition, the larger the wafer size, the greater the difficulty of the growth and processing techniques of the corresponding crystal, and the higher the manufacturing efficiency and lower the unit cost of downstream devices.

There are techniques in the prior art for cutting silicon ingots using a laser. On the one hand, however, silicon carbide ingots have the characteristics of high hardness, high brittleness, good wear resistance and extremely stable chemical properties compared with silicon ingots, and very thin wafers cannot be cut from the silicon carbide ingots by the existing laser cutting process. On the other hand, in the conventional process of cutting a silicon ingot by laser, a modified layer is formed at a position with a certain thickness in the silicon ingot by laser modification, then the modified layer is heated by the laser to grow and diffuse cracks in the modified layer, and then stripping is performed. In the process, the thickness of the modified layer formed by modifying the laser is thicker, the laser focus is focused in the modified layer when the modified layer is heated by the laser subsequently, the fluctuation of the height difference of the laser focus is larger, the focusing position of the laser focus is not well designed, the cracks in the modified layer are longer and more along the longitudinal direction of the silicon ingot, so that the cutting loss and the thickness are more, and a large amount of waste is caused.

Disclosure of Invention

The invention provides a method and a device for stripping a silicon carbide crystal ingot by laser, which can reduce the amount and the length of cracks in a modifying layer expanding along the longitudinal direction of the silicon carbide crystal ingot, increase the number of transverse crack growth and the growth length of the cracks, reduce the cutting loss thickness and reduce the waste.

In a first aspect, the present invention provides a method of laser cleaving a silicon carbide ingot, the silicon carbide ingot to be cut having opposing first and second end faces. The method for stripping the silicon carbide crystal ingot by the laser comprises the following steps:

after transmitting the ultrashort pulse laser beam through the first end surface of the silicon carbide crystal ingot to be cut, focusing the ultrashort pulse laser beam at the position of a set depth layer of the silicon carbide crystal ingot to respectively generate a cavity modification forming region and a crack modification forming region above the position of the set depth layer; wherein, the cavity modification forming region is positioned between the position of the set depth layer and the crack modification forming region;

controlling the ultrashort pulse laser beam to penetrate through the first end face, then focusing on a set depth layer of the silicon carbide crystal ingot and scanning on the set depth layer so as to form a cavity modified layer and a crack modified layer above the set depth layer respectively; the crack modifying layer consists of a plurality of crack modifying forming regions, and the cavity modifying layer is positioned between the set depth layer and the crack modifying layer;

after transmitting the short pulse laser beam through the second end surface of the silicon carbide crystal ingot, focusing the short pulse laser beam on the cavity modification forming region, and scattering and propagating the short pulse laser beam in the cavity modification forming region to enable the crack in the cavity modification forming region to grow outwards in the transverse direction;

controlling the short pulse laser beam to penetrate through the second end surface, then focusing on the cavity modified layer and scanning on a set depth layer so as to enable cracks in any adjacent cavity modified forming region in the cavity modified layer to be connected together through transverse growth;

and taking the hollow modified layer as an interface to strip part of the silicon carbide crystal ingot to generate the silicon carbide wafer.

In the above scheme, an ultrashort pulse laser beam is first used, and is focused on a set depth layer position of a silicon carbide ingot after penetrating through a first end face 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, and the focus of the ultrashort pulse laser beam is controlled to scan on the set depth layer of the silicon carbide ingot, so as to form a cavity modification layer and a crack modification layer. After the ultrashort pulse-level laser stealth cutting processing, short pulse-level laser with slightly wider pulse width is adopted, short pulse laser beams penetrate through the second end face of the silicon carbide crystal ingot and are focused on the cavity modification forming region and are scattered and propagated in the cavity modification forming region, so that the heat of the short pulse laser beams mainly acts on the cavity modification forming region, cracks in the crack modification forming region grow outwards in the transverse direction, and the focus of the short pulse laser beams is controlled to scan on the cavity modification layer, so that cracks in any adjacent cavity modification forming region in the cavity modification layer are connected together through the transverse growth.

Compared with the existing process for cutting the silicon ingot by adopting the laser, the adopted ultrashort pulse laser can respectively generate a cavity modification forming region and a crack modification forming region above the position of the set depth layer where the focus of the ultrashort pulse laser beam is located after penetrating through the first end face of the silicon carbide crystal ingot, and respectively form a cavity modification layer and a crack modification layer through scanning, so that the modification layers in the prior art are refined and distinguished. And then, when the short pulse laser beam is adopted, the short pulse laser beam penetrates through the second end surface of the silicon carbide crystal ingot and then is focused on the cavity modifying and forming region, the focal position of the short pulse laser beam is above the focal position of the ultrashort pulse laser beam instead of the same depth position in the prior art, so that the short pulse laser beam can scatter and propagate in the cavity modifying and forming region, cracks in the cavity modifying and forming region grow outwards in the transverse direction, and the cracks in any adjacent cavity modifying and forming region in the cavity modifying layer are connected together through the transverse growth through scanning. Since the short pulse laser beam is incident on the cavity modification forming region of the silicon carbide ingot through the second end surface, it is not necessary to transmit the crack modification forming region above the cavity modification forming region, so that the influence of the crack in the crack modification forming region on the scattering of the short pulse laser beam can be prevented, the laser energy concentration ratio can be improved, and the heating efficiency and the crack extension efficiency of the cavity modification forming region can be improved. In addition, in the process of focusing the short pulse laser beam on the cavity modification forming region and heating the cavity modification forming region, the crack modification forming region can stop the growth of the crack, so that the upward growth length of the crack in the cavity modification forming region can be limited to a region below the crack modification forming region, the longitudinal growth length of the crack can be limited to a small height range, the crack extension efficiency is improved, the longitudinal extension degree of the crack is reduced to the greatest extent, and the slice loss is reduced to the greatest extent. The modified layer is divided into a cavity modified layer and a crack modified layer through thinning, then a short pulse laser beam penetrates through the second end surface of the silicon carbide crystal ingot and is focused on the cavity modified layer, the focal position of the short pulse laser beam is designed more accurately and reasonably, the fluctuation of the vertical height difference of the focal point of the short pulse laser beam is small (the vertical height difference of the cavity modified forming region is certainly smaller than the vertical height difference of the modified layer formed by the crack modified forming region and the cavity modified forming region), the focal point of the short pulse laser beam is focused on the modified layer and is optimized to be focused on the cavity modified layer, the crack modified forming region on the modified layer blocks the vertical upward growth of cracks in the cavity modified forming region, the length of the vertical growth of the cracks is limited in a smaller height range, the focusing position of the short pulse laser beam is optimized, the amount and the length of the cracks in the modified layer which expand along the longitudinal direction of the silicon carbide crystal ingot are reduced, so that more laser energy acts on the horizontal outward growth of the cracks, the number of the horizontal crack growth and the growth length of the silicon carbide crystal ingot can be cut, thinner silicon carbide crystal ingot can be cut, and more waste of the silicon carbide crystal ingot can be reduced.

In a specific implementation mode, the thickness of the silicon carbide crystal ingot to be cut is not more than 5mm, the distance between the set depth layer and the first end surface and the distance between the set depth layer and the second end surface are both 2-3 mm, the difficulty and the energy dissipation of focusing on the cavity modification forming region after the short pulse laser beam is transmitted from the second end surface of the silicon carbide crystal ingot are both considered, and the larger energy dissipation is prevented.

In a specific embodiment, the pulse width of the short pulse laser beam is more than 50ns, and the wavelength of the short pulse laser beam is 500-1100nm, so that the amount and the length of the crack in the modifying layer extending along the longitudinal direction of the silicon carbide crystal ingot can be reduced better, the laser energy is applied to the transverse direction of the crack to grow outwards, and the number of the transverse crack growth and the crack growth length are increased.

In one embodiment, the ultrashort pulse laser beam has a pulse width of 243fs-900fs and a wavelength of 500-1100nm, so as to further improve the modifying effect of the cavity modification forming region and the crack modification forming region generated above the focal point of the ultrashort pulse laser beam.

In one specific embodiment, the method for propagating a short pulse laser beam through a second end surface, focusing the short pulse laser beam on a cavity modifying formation region, and scattering and propagating the short pulse laser beam in the cavity modifying formation region to grow a crack in the cavity modifying formation region laterally outward includes: and adjusting the polarization state of the short pulse laser beam to expand the electron propagation direction along the silicon carbide crystal lattice direction of the silicon carbide crystal ingot to form 3-5-degree transverse growth cracks, so that the amount and length of the cracks in the modifying layer extending along the longitudinal direction of the silicon carbide crystal ingot are reduced better, more laser energy is applied to the transverse direction of the cracks to grow outwards, and the number of the transverse crack growth and the crack growth length are increased.

In one embodiment, controlling the focus of the ultrashort pulse laser beam to scan a set depth layer of the silicon carbide ingot comprises: and controlling the focus of the ultrashort pulse laser beam to scan a plurality of parallel first cutting channels on a set depth layer of the silicon carbide crystal ingot, wherein the interval between any two adjacent first cutting channels is 10-25um. Controlling the focal point of the short pulse laser beam to scan the cavity modifying layer includes: and the focus of the short pulse laser beam is controlled to scan a plurality of parallel second cutting channels on the cavity modifying layer, and each second cutting channel is positioned right above one first cutting channel, so that the silicon carbide explosion point interval with the proper width can be conveniently set, and the scanning difficulty is simplified.

In one embodiment, controlling the focal point of the short pulse laser beam to scan a plurality of parallel second scribe lines on the hole modifying layer includes: the number of times of scanning the focus of the short pulse laser beam at each second cutting channel is controlled to be more than or equal to three times, the connection of the explosion point cracks is realized by adopting the short pulse laser beam to process continuous heat injection for multiple times, the transverse growth amount and length of the cracks in the crack modification forming region are improved, the cracks extending out of the adjacent second cutting channels are connected together more quickly, and the aim of separating the silicon carbide crystal ingot into a plurality of silicon carbide crystal wafers is fulfilled conveniently by a concealed cutting crack induced growth mode.

In a second aspect, the present invention also provides an apparatus for laser stripping a silicon carbide ingot to be cut, the silicon carbide ingot having opposed first and second end faces. The device for laser stripping of the silicon carbide ingot comprises: the system comprises an object stage, an ultrashort pulse laser system, a first scanning system, a short pulse laser system, a second scanning system and a stripping system. Wherein the stage is used for fixing the silicon carbide crystal ingot to be cut. The ultrashort pulse laser system is used for focusing an ultrashort pulse laser beam at a set depth layer position of the silicon carbide crystal ingot after the ultrashort pulse laser beam penetrates through the first end face of the silicon carbide crystal ingot to be cut so as to respectively generate a cavity modification forming region and a crack modification forming region above the set depth layer position; wherein the cavity modifying formation region is located between the predetermined depth layer position and the crack modifying formation region. The first scanning system is used for controlling the ultrashort pulse laser beam to be focused on a set depth layer of the silicon carbide crystal ingot and scanned on the set depth layer after the ultrashort pulse laser beam penetrates through the first end face, so that a cavity modified layer and a crack modified layer are respectively formed above the set depth layer; 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. The short pulse laser system is used for transmitting a short pulse laser beam through the second end surface of the silicon carbide crystal ingot, focusing the short pulse laser beam on the cavity modification forming region, scattering and propagating the short pulse laser beam in the cavity modification forming region, and enabling cracks in the cavity modification forming region to grow outwards in the transverse direction. And the second scanning system is used for controlling the short pulse laser beam to be focused on the cavity modified layer and scan the cavity modified layer at a set depth layer after the short pulse laser beam penetrates through the second end surface, so that cracks in any adjacent cavity modified forming region in the cavity modified layer are connected together through transverse growth. The peeling system is used for peeling off a part of the silicon carbide ingot to produce a silicon carbide wafer with the hollow modified layer as an interface.

In the above scheme, an ultrashort pulse laser beam is first used, and is focused on a set depth layer position of a silicon carbide ingot after penetrating through a first end face 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, and the focus of the ultrashort pulse laser beam is controlled to scan on the set depth layer of the silicon carbide ingot, so as to form a cavity modification layer and a crack modification layer. After the ultrashort pulse level laser stealth cutting processing, short pulse level laser with slightly wide pulse width is adopted, short pulse laser beams penetrate through the second end face of the silicon carbide crystal ingot and then are focused on the cavity modification forming region and are scattered and propagated in the cavity modification forming region, so that heat of the short pulse laser beams mainly acts on the cavity modification forming region, cracks in the crack modification forming region grow outwards in the transverse direction, and the focus of the short pulse laser beams is controlled to scan on the cavity modification layer, so that cracks in any adjacent cavity modification forming region in the cavity modification layer are connected together through the transverse growth.

In one embodiment, both the ultrashort pulse laser system and the short pulse laser system are disposed above the stage. The apparatus for laser stripping a silicon carbide ingot further comprises: and a clamping and overturning mechanism for clamping and overturning the silicon carbide crystal ingot held on the object stage so that the first end face or the second end face of the silicon carbide crystal ingot faces upwards. When the ultrashort pulse laser system and the short pulse laser system are both arranged above the objective table, the clamping and overturning mechanism can be additionally arranged, after ultrashort pulse laser beams emitted by the ultrashort pulse laser system penetrate through the first end face of the silicon carbide crystal ingot to generate a crack modification layer and a cavity modification layer in the silicon carbide crystal ingot, the silicon carbide crystal ingot is overturned through the clamping and overturning mechanism, the second end face of the silicon carbide crystal ingot faces upwards, the short pulse laser beams emitted by the short pulse laser system can penetrate through the second end face of the silicon carbide crystal ingot to be focused on a cavity modification forming region, crack expansion and extension are carried out, and automatic operation efficiency is improved.

In a particular embodiment, the stage holds the silicon carbide ingot to be cut by holding the sidewall of the silicon carbide ingot so that both the first end face and the second end face of the silicon carbide ingot are free of obstructions. The ultra-short pulse laser system and the short pulse laser system are respectively arranged above and below the objective table. The stage is fixed by holding the side wall of the silicon carbide ingot, so that the first end face and the second end face of the silicon carbide ingot are not shielded by the stage. And the ultrashort pulse laser system can be arranged on one side of the first end surface of the silicon carbide crystal ingot, so that the ultrashort pulse laser beam emitted by the ultrashort pulse laser system passes through the first end surface to process the interior of the silicon carbide crystal ingot. The short pulse laser system may be disposed on the second end face side of the silicon carbide ingot, and the short pulse laser beam emitted therefrom may be caused to penetrate the second end face to process the inside of the silicon carbide ingot without turning the silicon carbide ingot upside down.

Drawings

FIG. 1 is a flow chart of a method of laser cleaving a silicon carbide ingot in accordance with an embodiment of the present invention;

fig. 2 to 6 are schematic sectional structural views illustrating steps in a method for laser lift-off of a silicon carbide ingot according to an embodiment of the present invention, wherein fig. 3 is a diagram of an actual sample of a hole modification formation region and a crack modification formation region processed by using an ultrashort pulse laser beam according to an embodiment of the present invention;

FIG. 7 is a schematic view of the structure of an apparatus for laser stripping a silicon carbide ingot according to an embodiment of the present invention;

FIG. 8 is a flowchart for performing laser lift-off of a silicon carbide ingot based on the apparatus for laser lift-off of a silicon carbide ingot of FIG. 7;

FIG. 9 is a schematic structural view of another apparatus for laser exfoliation of a silicon carbide ingot according to an embodiment of the present invention;

fig. 10 is a schematic diagram illustrating optical path transmission when an ultra-short pulse laser beam and a short pulse laser beam are respectively operated based on the apparatus for stripping a silicon carbide ingot provided in fig. 9.

Reference numerals:

10-silicon carbide ingot 21-set depth layer 22-void modified layer 23-crack modified layer

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In order to facilitate understanding of the method for laser stripping a silicon carbide ingot provided by the embodiment of the invention, an application scenario of the method for laser stripping a silicon carbide ingot provided by the embodiment of the invention is firstly explained, wherein the method for laser stripping a silicon carbide ingot is applied to a process of stripping a silicon carbide wafer from the silicon carbide ingot, wherein the silicon carbide ingot to be cut is in a prism or cylinder shape and is provided with a first end face and a second end face which are opposite, the first end face can be a front face of the silicon carbide ingot, and the second end face is a back face of the silicon carbide ingot; the first end face may also be a back face of the silicon carbide ingot and the second end face is a front face of the silicon carbide ingot. The method for laser peeling the silicon carbide ingot is described in detail below with reference to the accompanying drawings.

Referring to fig. 1 to 5, a method for laser peeling a silicon carbide ingot according to an embodiment of the present invention includes:

step10: after transmitting an ultrashort pulse laser beam through a first end face of a silicon carbide crystal ingot 10 to be cut, focusing the ultrashort pulse laser beam at a position of a set depth layer 21 of the silicon carbide crystal ingot 10 to respectively generate a cavity modification forming region and a crack modification forming region above the position of the set depth layer 21; wherein the cavity modification forming region is located between the position of the set depth layer 21 and the crack modification forming region;

step20: controlling the ultrashort pulse laser beam to penetrate through the first end face, focusing on the set depth layer 21 of the silicon carbide crystal ingot 10, and scanning on the set depth layer 21 to form a cavity modified layer 22 and a crack modified layer 23 above the position of the set depth layer 21; wherein the cavity modified layer 22 is composed of a plurality of cavity modified forming regions, the crack modified layer 23 is composed of a plurality of crack modified forming regions, and the cavity modified layer 22 is located between the set depth layer 21 and the crack modified layer 23;

step30: transmitting a short pulse laser beam through the second end surface of the silicon carbide ingot 10, focusing the short pulse laser beam on the cavity modification forming region, and scattering and propagating the short pulse laser beam in the cavity modification forming region to enable the crack in the cavity modification forming region to grow outwards in the transverse direction;

step40: after the short pulse laser beam is controlled to penetrate through the second end face, the short pulse laser beam is focused on the cavity modified layer 22 and is scanned on the set depth layer 21, so that cracks in any adjacent cavity modified forming area in the cavity modified layer 22 are connected together through transverse growth;

step50: a silicon carbide wafer is grown by peeling off a part of the silicon carbide ingot 10 with the hollow modified layer 22 as an interface.

In the above scheme, an ultrashort pulse laser beam is first used, and is focused on the position of the set depth layer 21 of the silicon carbide ingot 10 after passing through the first end face of the silicon carbide ingot 10, so as to generate a cavity modified formation region and a crack modified formation region above the position of the set depth layer 21, and the focus of the ultrashort pulse laser beam is controlled to scan the set depth layer 21 of the silicon carbide ingot 10, so as to form a cavity modified layer 22 and a crack modified layer 23. After the ultrashort pulse level laser stealth cutting processing, short pulse level laser with a slightly wider pulse width is adopted, short pulse laser beams penetrate through the second end face of the silicon carbide crystal ingot 10 and then are focused on the cavity modification forming region, and the short pulse laser beams are scattered and propagated in the cavity modification forming region, so that the heat of the short pulse laser beams mainly acts on the cavity modification forming region, cracks in the crack modification forming region grow outwards in the transverse direction, and the focus of the short pulse laser beams is controlled to scan on the cavity modification layer 22, so that the cracks in any adjacent cavity modification forming region in the cavity modification layer 22 are connected together through the transverse growth.

Compared with the existing process for cutting silicon ingots by using laser, the adopted ultrashort pulse laser can penetrate through the first end face of the silicon carbide crystal ingot 10, respectively generate a cavity modification forming region and a crack modification forming region above the position of the set depth layer 21 where the focus of the ultrashort pulse laser beam is located, and respectively form a cavity modification layer 22 and a crack modification layer 23 through scanning, so that the modification layers in the prior art are refined and distinguished. Then, when a short pulse laser beam is used, the short pulse laser beam is transmitted through the second end surface of the silicon carbide ingot 10 and focused on the cavity modifying formation region, and the focal position of the short pulse laser beam is located above the focal position of the ultrashort pulse laser beam, not at the same depth position as in the prior art, so that the short pulse laser beam scatters and propagates in the cavity modifying formation region, cracks in the cavity modifying formation region grow laterally outward, and the cracks in any adjacent cavity modifying formation region in the cavity modifying layer 22 are connected together by lateral growth through scanning. Since the short pulse laser beam is incident on the cavity modifying formation region of the silicon carbide ingot 10 through the second end surface, it is not necessary to transmit the crack modifying formation region above the cavity modifying formation region, and therefore, the influence of the crack in the crack modifying formation region on the scattering of the short pulse laser beam can be prevented, the laser energy concentration ratio can be increased, and the heating efficiency and the crack extension efficiency of the cavity modifying formation region can be increased. In addition, in the process of focusing the short pulse laser beam on the cavity modification forming region and heating the cavity modification forming region, the crack modification forming region can stop the growth of the crack, so that the upward growth length of the crack in the cavity modification forming region can be limited to a region below the crack modification forming region, the longitudinal growth length of the crack can be limited to a small height range, the crack extension efficiency is improved, the longitudinal extension degree of the crack is reduced to the greatest extent, and the slice loss is reduced to the greatest extent. The modified layer is divided into a cavity modified layer 22 and a crack modified layer 23 by thinning, then a short pulse laser beam penetrates through the second end surface of the silicon carbide crystal ingot 10 and is focused on the cavity modified layer 22, the focal position of the short pulse laser beam is designed more accurately and reasonably, the fluctuation of the vertical height difference of the focal point of the short pulse laser beam is small (the vertical height difference of the cavity modified forming region is smaller than the vertical height difference of the modified layer formed by the crack modified forming region and the cavity modified forming region together), the focal position of the short pulse laser beam is optimized to be focused on the modified layer 22, the crack modified forming region on the modified layer blocks the crack in the cavity modified forming region from growing upwards longitudinally, the length of the crack growing longitudinally is limited in a smaller height range, the focusing position of the laser beam is optimized, the amount and the length of the crack in the modified layer expanding longitudinally along the silicon carbide crystal ingot 10 are reduced, more laser energy is applied to the crack to grow outwards, the number of the transverse direction and the crack growth and the short pulse laser beam can cut the silicon carbide crystal ingot 10, and the waste of the same silicon carbide crystal ingot can be reduced. The above steps will be described in detail with reference to the accompanying drawings.

First, referring to fig. 1, 2 and 3, an ultrashort pulse laser beam is focused on a set depth layer 21 of a silicon carbide ingot 10 after passing through a first end face of the silicon carbide ingot 10 to be cut, so as to generate a cavity modification forming region and a crack modification forming region above the set depth layer 21; the cavity modifying region is located between the position of the set depth layer 21 and the crack modifying region. The intensity at the focal volume of the ultrashort pulse laser beam causes nonlinear absorption of laser energy by the material through multiphoton ionization, tunneling ionization, and avalanche ionization. Because of the nonlinear absorption, the focal position produces highly excited plasmas of very small size, which can vary from nanometer to submicron size for different crystal materials. And thus large-sized material damage in the laser incident direction is not generated.

The depth layer 21 is set during the processing process, and specifically relates to the thickness of the peeled wafer, the thickness of the peeling loss, and the like. The focus of the ultrashort pulse laser beam can be accurately focused on the position of the set depth layer 21 of the silicon carbide crystal ingot 10 through a triaxial galvanometer, a height gauge and the like.

As shown in fig. 2 to 4, the crack modifying formation region and the cavity modifying formation region generated above the position of the set depth layer 21 both occupy a certain thickness space, the sizes of the crack modifying formation region and the cavity modifying formation region are related to the energy of the ultrashort pulse laser beam, and the sizes of the crack modifying formation region and the cavity modifying formation region both increase with the increase in the laser energy. As shown in fig. 2 to 4, the cavity modification forming region may be located in a region 1 to 5um above the focal point of the ultrashort pulse laser beam, and the crack modification forming region may be located in a region 10 to 30um above the cavity modification forming region, so that the cavity modification forming region and the crack modification forming region are located at different depth layers, and the cavity modification layer 22 and the crack modification layer 23 can be clearly distinguished.

When the ultrashort pulse laser beam is selected, the ultrashort pulse laser beam can be a subpicosecond pulse width laser beam, a picosecond pulse width laser beam or a femtosecond pulse width laser beam, and a cavity modification forming region and a crack modification forming region with better effect can be conveniently generated above the focus of the ultrashort pulse laser beam. For example, the pulse width of the ultrashort pulse laser beam may be set to any value between 243fs and 900fs, and the modifying effect of the cavity modifying region and the crack modifying region generated above the focal point of the ultrashort pulse laser beam is further improved. In a more preferred embodiment, the wavelength of the ultrashort pulse laser beam can be controlled to be 500-1100nm, and specifically, the wavelength of the ultrashort pulse laser beam can be 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, 1100nm, and any value between 500-1100nm. The cavity modification forming region and the crack modification forming region with better effect can be generated above the focus of the ultrashort pulse laser beam.

In addition, in a more preferred embodiment, the thickness of the silicon carbide ingot 10 to be cut may be made not more than 5mm, and the depth layer 21 may be set at a distance of 2 to 3mm from both the first end face and the second end face. So that the length of a transmission path in the silicon carbide crystal ingot 10 is between 2 and 3mm when the ultrashort pulse laser beam is focused to the set depth layer 21; when the short pulse laser beam is focused on the cavity modifying region through the second end surface, the propagation path length in the silicon carbide ingot 10 may be 2 to 3 mm. The difficulty and energy dissipation of the second end surface of the silicon carbide crystal ingot 10, which is focused on the cavity modification forming region after transmitting the short pulse laser beam, are both considered, and the occurrence of larger energy dissipation is prevented. That is, when the thickness of the silicon carbide ingot 10 to be cut is greater than 5mm, a plurality of thinner silicon carbide ingots 10 may be cut out of a thicker silicon carbide ingot 10 by multiple cutting. Thereafter, a satisfactory silicon carbide wafer is sliced from a relatively thin silicon carbide ingot 10 using the method illustrated herein.

Next, referring to fig. 1 and 4, 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 modified layer 22 and a crack modified layer 23 above the position of the set depth layer 21, respectively; the cavity modified layer 22 is composed of a plurality of cavity modified forming regions, the crack modified layer 23 is composed of a plurality of crack modified forming regions, and the cavity modified layer 22 is located between the set depth layer 21 and the crack modified layer 23.

Specifically, the mode of controlling the focus of the ultrashort pulse laser beam to scan the set depth layer 21 of the silicon carbide ingot 10 may adopt various modes, so as to form the cavity modified layer 22 and the crack modified layer 23 in the silicon carbide ingot 10, respectively, so that the cavity modified in the cavity modified layer 22 forms a region of the cavity modified layer 22 in an interval mode, and the crack modified in the crack modified layer 23 forms a region of the crack modified layer 23 in an interval mode. For example, a spiral scanning mode may be adopted, and a mode of scanning a plurality of cutting tracks at parallel intervals may also be adopted. Illustratively, the focus of the ultrashort pulse laser beam can be controlled to scan a plurality of parallel first cutting channels on the set depth layer 21 of the silicon carbide ingot 10, and the interval between any two adjacent first cutting channels can be 10-25um, specifically, the interval between any two adjacent first cutting channels can be any value between 10-25um such as 10um, 15um, 20um, 25um, and the like, and the characteristics that the size of the cavity modification forming region is smaller than that of the crack modification forming region and the crack growth range is lower are considered, so that the interval between adjacent cavity modification forming regions is properly reduced, the difficulty of transverse growth and connection of subsequent cracks is simplified, the silicon carbide explosion point interval with proper width is conveniently set, the slicing efficiency is improved, and the scanning difficulty is simplified.

Next, referring to fig. 1, 5 and 6, a short pulse laser beam is transmitted through the second end surface of the silicon carbide ingot 10, focused on the cavity reformed formation region, and scatteringly propagates in the cavity reformed formation region, thereby growing a crack in the cavity reformed formation region laterally outward. The pulse width of the short pulse laser beam is larger than that of the ultrashort pulse laser beam, and the pulse width of the short pulse laser beam does not reach the nanosecond pulse width degree and is in the subnanosecond wavelength level of picosecond magnitude. That is, the focus position of the short pulse laser relative to the focus position of the ultra-short pulse laser shifts up to a certain extent. Further, the short pulse laser beam is incident on the cavity reformed formation region in the silicon carbide ingot 10 from the second end surface of the silicon carbide ingot 10, and does not need to pass through the crack reformed formation region above the cavity reformed formation region, whereby the influence of the crack in the crack reformed formation region on the scattering of the short pulse laser beam can be prevented, the laser energy concentration ratio can be increased, and the heating efficiency and the crack extension efficiency for the cavity reformed formation region can be increased. The scattering property of the focused focal spot of the laser in the cavity modification forming region is realized by the laser self-scattering property of free ions after the laser passes through the crack modification region through the short pulse laser beam in the cavity modification forming region, and the laser is scattered and propagated in the cavity modification forming region to drive the crack of the cavity modification forming region to grow.

Early laser machining Process, 10 ^-15 The laser energy of s pulse width order is absorbed in the material, and for different action materials (conductors, semiconductors, insulators and the like), the essence of the laser is that the laser introduces the free electron distribution of a non-equilibrium state, and the energy is transferred through the interaction between electrons, crystal lattices and phonons. The plasma was then in subpicosecond (10) ^-9 s) is initiated, with an inherent process of evaporation and melting, in which the energy and the transfer rate between the crystal lattices are related to the intrinsic properties of the material, and the material begins to change its phase state at this stage as the laser energy continues to act. After which the impinging radiation is generated, which process exists over a large time span (typically occurring at 10) ^-12 s to 10 ^-3 s) the thermal effect of the material gradually dominates the main factor, thereby creating a thermal front and an evaporation front resulting in a gradual increase of the back momentum, with the concomitant occurrence of weaker secondary radiative processes. The processing method shown in this step of the patent is taken from the initial stage of the material starting to produce the heat effect, and the heat accumulation effect is produced.

The cavity modifying forming region is actually a modifying region, no cavity is formed, when a focused short pulse laser beam capable of transmitting enough material is subsequently loaded, when the photon energy of the short pulse laser beam is focused on the material and the photon energy is high enough, the laser photon can directly break off the chemical bond of the sample, so that the volume of the local region is rapidly expanded and exploded. The short pulse width is long enough so that the photon energy, after being transferred to the electrons, can be coupled into the silicon carbide lattice immediately and the photon energy will be converted into thermal energy, resulting in an increase in the temperature of the sample. When the temperature rises, the physicochemical property of the sample further changes, the coefficient of the optical system changes and enables the inside of the sample to generate stress, and the stress is continuously superposed along with the extension of the pulse width, after the chemical bond in the cavity modification forming region processed by the previous ultrashort pulse laser beam is broken, the cracks between the carbon element and the silicon element which are respectively formed further guide the outward radiation.

It should be explained that the pulse width broadening of the short pulse laser beam is expected to have more light dwell time and generate more thermal effect than that of the ultrashort pulse laser beam, so that the crack grows longer, after multiple continuous irradiation of the short pulse laser beam, the multiple irradiation can be 1-3 times or 3-5 times, and the crack can grow in the horizontal direction by more than 200 microns. The growth will be different according to the material, the material type, the doping injection condition, the power pulse width wavelength of different laser parameters, etc.

When the short pulse laser beam is selected, the short pulse laser beam can be a subnanosecond laser beam, and the number and the length of the transverse growth of cracks are increased. For example, the pulse width of the short pulse laser beam may be any value greater than 50ns to facilitate better reduction in the amount and length of crack propagation in the modifying layer along the longitudinal direction of silicon carbide ingot 10, thereby imparting more laser energy to the lateral outward growth of cracks and increasing the number of lateral crack growth and the crack growth length. In a more preferred embodiment, the short pulse laser beam may have a wavelength of 500 to 1100nm, and specifically, the short pulse laser beam may have a wavelength of 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, 1100nm, or any value between 500 and 1100nm. Facilitating a better reduction in the amount and length of crack propagation in the modified layer in the longitudinal direction of silicon carbide ingot 10, thereby imparting more laser energy to the lateral outward growth of cracks and increasing the number of lateral crack growths and the crack growth length.

When the focus of the short pulse laser beam is focused on the cavity modifying formation region, in a more preferable mode, the focus of the short pulse laser beam can be focused at a position 1-4.5um higher than the focus of the ultrashort pulse laser beam, so that the focus position of the short pulse laser beam can be better optimized. It is understood that any method of focusing the focal point of the short pulse laser beam on the cavity modifying formation region is within the scope of the present patent application.

In addition, the control of the explosion energy diffusion direction of the cavity modification formation region can be realized by controlling the polarization state of the short pulse laser beam, and the crack growth at a certain angle of the explosion point of the short pulse laser beam can also be realized. In the process of focusing the short pulse laser beam on the cavity modifying formation region through the second end face of the silicon carbide crystal ingot 10 and scattering and propagating in the cavity modifying formation region to enable the crack in the cavity modifying formation region to grow transversely outwards, the polarization state of the short pulse laser beam can be adjusted to enable the electron propagation direction to expand along the silicon carbide crystal lattice direction of the silicon carbide crystal ingot 10 to form a transverse growth crack of 3-5 degrees, so that the amount and the length of the crack in the modifying layer expanding along the longitudinal direction of the silicon carbide crystal ingot 10 can be reduced better, the laser energy is more acted on the transverse outwards growth of the crack, and the number of transverse crack growth and the crack growth length are increased. For example, the polarization state of the short pulse laser beam can be adjusted so that the growth direction of the laterally grown crack is at an angle of 3-5 ° with respect to the direction of the scribe line.

Next, referring to fig. 1, 5 and 6, after the short pulse laser beam is controlled to transmit through the second end surface, the short pulse laser beam is focused on the cavity modified layer 22 and scanned on the set depth layer 21, so that the cracks in any adjacent cavity modified formation region in the cavity modified layer 22 are connected together by lateral growth. Specifically, the mode of controlling the scanning of the focal point of the short-pulse laser beam on the cavity modifying layer 22 is related to the mode of controlling the scanning of the focal point of the ultra-short-pulse laser beam on the set depth layer 21. For example, when the spiral scanning method is adopted to control the focus of the ultrashort pulse laser beam to scan the set depth layer 21, the spiral scanning method is also adopted to control the focus of the short pulse laser beam to scan the cavity-modified layer 22. When the mode of controlling the focus of the ultrashort pulse laser beam to scan in the set depth layer 21 adopts a mode of a plurality of parallel first cutting channels, the mode of controlling the focus of the second short pulse laser beam to scan in the cavity modified layer 22 may specifically be: the focus of the short pulse laser beam is controlled to scan a plurality of parallel second cutting channels on the hollow modified layer 22, and each second cutting channel is located right above one first cutting channel, so that the scanning difficulty is simplified.

In addition, when the focus of the short pulse laser beam is controlled to scan a plurality of parallel second cutting channels on the cavity modified layer 22, the number of times that the focus of the short pulse laser beam is scanned at each second cutting channel can be controlled to be more than or equal to three times, the shot crack connection is realized by adopting the multiple processing continuous heat injection of the short pulse laser beam, the transverse growth amount and length of the crack in the crack modified forming region are improved, the cracks extending from the adjacent second cutting channels are connected together more quickly, and the aim of separating the silicon carbide crystal ingot 10 into a plurality of silicon carbide wafers through the implicit cutting crack induced growth mode is fulfilled.

Next, referring to fig. 1, a silicon carbide wafer is grown by peeling off a part of silicon carbide ingot 10 with hollow modified layer 22 as an interface. Specifically, in a mode of peeling off a part of the silicon carbide ingot 10 to produce a silicon carbide wafer with the hollow modified layer 22 as an interface, a wafer above the hollow modified layer 22 may be peeled off from the silicon carbide ingot 10 by means of stretching, rotation, or the like.

Further, a grown wafer may be peeled from a part of the silicon carbide ingot 10 with the hollow modified layer 22 as an interface. And performing line cutting on the hole modified layer by using a diamond wire saw, and taking the hole modified layer as an interface to strip part of the silicon carbide crystal ingot to generate the silicon carbide wafer. A void modification layer is formed at a predetermined depth layer location by first focusing a laser beam at the predetermined depth layer from the interior of the silicon carbide ingot and scanning. In the process of forming the cavity modified layer, the energy density at the laser focus exceeds the ablation threshold of the silicon carbide, the temperature of the material rises suddenly, the silicon carbide is decomposed under the high-temperature condition, and amorphous silicon or monocrystalline silicon or a mixture of the amorphous silicon and the monocrystalline silicon and carbon are generated, wherein the specific amorphous silicon and the monocrystalline silicon are determined by the energy density of the laser. When the laser energy is large, monocrystalline silicon is produced, and when the laser energy is small, amorphous silicon is produced. And then, carrying out wire cutting on the hole modified layer by adopting a diamond wire saw, taking the hole modified layer as an interface, and stripping a part of the silicon carbide crystal ingot to generate the silicon carbide wafer. Because the materials of the cavity modified layer are monocrystalline silicon, amorphous silicon and carbon, the hardness of the cavity modified layer is much lower than that of silicon carbide, and the abrasion of the diamond wire saw can be reduced in the process of adopting the diamond wire saw to carry out wire cutting on the cavity modified layer, so that the loss of the diamond wire saw is reduced, and the wire cutting difficulty is reduced. Therefore, a thinner diamond wire saw can be selected, the loss of the silicon carbide crystal ingot is reduced, and the slicing yield of the silicon carbide crystal ingot is improved. Meanwhile, the cutting mode of the diamond wire saw is adopted, so that the silicon carbide wafer is not easy to crack due to uneven stress. Compared with a laser cutting and mechanical stripping method, the method has the advantages that the diamond wire saw is used for cutting the cavity modified layer, the silicon carbide wafer is stripped from the modified silicon carbide crystal ingot, a mechanical stripping mode is not needed, the phenomenon that the silicon carbide wafer is cracked due to uneven stress in the mechanical stripping process can be avoided, and the product yield and the stripping efficiency are improved.

After the silicon carbide wafer is peeled from the silicon carbide ingot, before the silicon carbide wafer is polished, a step of immersing the silicon carbide wafer in a chemical solution to etch the interface of the modified layer of the silicon carbide wafer may be added, and the interface of the modified layer of the silicon carbide wafer is etched by using the chemical solution, whereby defects such as residual stress, dislocation, and crack generated in the silicon carbide wafer peeling step can be removed. And then grinding the modified layer interface of the silicon carbide wafer, wherein no residual stress or less residual stress exists on the modified layer interface of the silicon carbide wafer, so that defect increment of a grinding process is avoided, the phenomenon that the residual stress is increased due to extrusion of the grinding process so as to cause continuous growth of cracks can be relieved, a damaged layer can be completely removed by grinding less materials, the ingot loss is reduced, and the quality of the wafer is improved. And the modified layer interface corroded by the chemical solution has better flatness, the subsequent grinding difficulty can be reduced, and the grinding efficiency is improved.

In the above-described embodiments, the ultrashort pulse laser beam is first used, and then the ultrashort pulse laser beam is focused on the position of the set depth layer 21 of the silicon carbide ingot 10 after passing through the first end surface of the silicon carbide ingot 10, so as to generate the cavity modified formation region and the crack modified formation region above the position of the set depth layer 21, and the focus of the ultrashort pulse laser beam is controlled to scan the set depth layer 21 of the silicon carbide ingot 10, so as to form the cavity modified layer 22 and the crack modified layer 23. After the ultrashort pulse level laser stealth cutting processing, short pulse level laser with a slightly wider pulse width is adopted, short pulse laser beams penetrate through the second end face of the silicon carbide crystal ingot 10 and then are focused on the cavity modification forming region, and the short pulse laser beams are scattered and propagated in the cavity modification forming region, so that the heat of the short pulse laser beams mainly acts on the cavity modification forming region, cracks in the crack modification forming region grow outwards in the transverse direction, and the focus of the short pulse laser beams is controlled to scan on the cavity modification layer 22, so that the cracks in any adjacent cavity modification forming region in the cavity modification layer 22 are connected together through the transverse growth.

Compared with the existing process for cutting silicon ingots by using laser, the adopted ultrashort pulse laser can penetrate through the first end face of the silicon carbide crystal ingot 10, respectively generate a cavity modification forming region and a crack modification forming region above the position of the set depth layer 21 where the focus of the ultrashort pulse laser beam is located, and respectively form a cavity modification layer 22 and a crack modification layer 23 through scanning, so that the modification layers in the prior art are refined and distinguished. Then, when a short pulse laser beam is used, the short pulse laser beam is transmitted through the second end surface of silicon carbide ingot 10 and focused on the cavity modified formation region, and the focal point of the short pulse laser beam is located above the focal point of the ultrashort pulse laser beam, rather than at the same depth position as in the prior art, so that the short pulse laser beam scatters and propagates in the cavity modified formation region, cracks in the cavity modified formation region grow laterally outward, and cracks in any adjacent cavity modified formation regions in cavity modified layer 22 are connected together by lateral growth through scanning. Since the short pulse laser beam is incident on the cavity modifying formation region of the silicon carbide ingot 10 through the second end surface, it is not necessary to transmit the crack modifying formation region above the cavity modifying formation region, and therefore, the influence of the crack in the crack modifying formation region on the scattering of the short pulse laser beam can be prevented, the laser energy concentration ratio can be increased, and the heating efficiency and the crack extension efficiency of the cavity modifying formation region can be increased. In addition, in the process of focusing the short pulse laser beam on the cavity modification forming region and heating the cavity modification forming region, the crack modification forming region can stop the growth of the crack, so that the upward growth length of the crack in the cavity modification forming region can be limited to a region below the crack modification forming region, the longitudinal growth length of the crack can be limited to a small height range, the crack extension efficiency is improved, the longitudinal extension degree of the crack is reduced to the greatest extent, and the slice loss is reduced to the greatest extent. The modified layer is divided into a cavity modified layer 22 and a crack modified layer 23, then the short pulse laser beam is focused on the cavity modified layer 22 after penetrating through the second end surface of the silicon carbide crystal ingot 10, the focal point position of the short pulse laser beam is designed more accurately and reasonably, the fluctuation of the height difference between the upper part and the lower part of the focal point of the short pulse laser beam is small (because the height difference between the upper part and the lower part of the cavity modified forming region is certainly smaller than the height difference between the upper part and the lower part of the modified layer formed by the crack modified forming region and the cavity modified forming region), the focal point of the short pulse laser beam is focused on the modified layer to be focused on the cavity modified layer 22, the crack modified forming region on the modified layer blocks the crack in the cavity modified forming region from growing upwards in the longitudinal direction, the length of the crack growing in the longitudinal direction is limited in a smaller height range, the focusing position of the laser beam is optimized, the amount and the length of the crack expanding along the longitudinal direction of the silicon carbide crystal ingot 10 are reduced, so that more laser energy is applied to the crack growing outwards in the transverse direction of the crack, the silicon carbide crystal ingot, the number of the transverse direction growing and the crack growing and the thickness of the silicon carbide crystal ingot is reduced, and the silicon wafer is more wasted.

In addition, the embodiment of the invention also provides a device for stripping the silicon carbide crystal ingot by laser, wherein the silicon carbide crystal ingot 10 to be cut is provided with a first end face and a second end face which are opposite. The device for laser stripping of the silicon carbide ingot comprises: the system comprises an object stage, an ultrashort pulse laser system, a first scanning system, a short pulse laser system, a second scanning system and a stripping system. Wherein the stage is used to hold a silicon carbide ingot 10 to be cut. The ultrashort pulse laser system is used for focusing an ultrashort pulse laser beam at the position of a set depth layer 21 of the silicon carbide crystal ingot 10 after the ultrashort pulse laser beam penetrates through the first end face of the silicon carbide crystal ingot 10 to be cut so as to respectively generate a cavity modification forming region and a crack modification forming region above the position of the set depth layer 21; the cavity modifying region is located between the position of the set depth layer 21 and the crack modifying region. The first scanning system is used for controlling the ultrashort pulse laser beam to be focused on the set depth layer 21 of the silicon carbide crystal ingot 10 after penetrating through the first end surface and scanning the set depth layer 21 so as to form a cavity modified layer 22 and a crack modified layer 23 above the position of the set depth layer 21 respectively; the cavity modified layer 22 is composed of a plurality of cavity modified forming regions, the crack modified layer 23 is composed of a plurality of crack modified forming regions, and the cavity modified layer 22 is located between the set depth layer 21 and the crack modified layer 23. The short pulse laser system is configured to transmit a short pulse laser beam through the second end surface of the silicon carbide ingot 10, focus the short pulse laser beam on the cavity modifying formation region, and scatter and propagate the short pulse laser beam in the cavity modifying formation region, so that a crack in the cavity modifying formation region grows laterally outward. The second scanning system is used for controlling the short pulse laser beam to pass through the second end surface, then focus on the cavity modified layer 22 and scan on the set depth layer 21, so that cracks in any adjacent cavity modified forming region in the cavity modified layer 22 are connected together through lateral growth. The peeling system is used to peel off a portion of the silicon carbide ingot 10 to produce a silicon carbide wafer with the hollow modified layer 22 as an interface.

In the different laser peeling apparatuses for silicon carbide crystal ingot as shown in fig. 7 and 9, the first scanning system and the second scanning system can be realized by a three-axis moving table, and the object stage is fixed on the three-axis moving table. The ultra-short pulse laser system and the short pulse laser system can respectively adopt different lasers. For the parameter setting manner of the ultrashort pulse laser beam provided by the ultrashort pulse laser system, reference may be made to the description of the relevant part of the method for peeling off the silicon carbide crystal ingot by the laser, and details are not repeated here. The parameter setting manner of the short pulse laser beam provided by the short pulse laser system can refer to the description of the relevant part of the method for laser stripping silicon carbide crystal ingot, and is not repeated herein. Referring to fig. 8, a CCD camera and a light source may also be provided on a different laser system to observe the condition of the processing position in real time.

Referring to fig. 7, both the ultra-short pulse laser system and the short pulse laser system may be disposed above the stage. As shown in fig. 7, at this time, the apparatus for laser peeling the silicon carbide ingot may further include: and a holding and inverting mechanism for holding and inverting silicon carbide ingot 10 held on the stage so that the first end face or the second end face of silicon carbide ingot 10 faces upward. When the ultrashort pulse laser system and the short pulse laser system are both arranged above the objective table, a clamping and overturning mechanism can be additionally arranged, and after the ultrashort pulse laser beam emitted by the ultrashort pulse laser system penetrates through the first end face of the silicon carbide crystal ingot 10 to generate a crack modified layer 23 and a hollow modified layer 22 in the silicon carbide crystal ingot 10, the silicon carbide crystal ingot 10 is overturned through the clamping and overturning mechanism, so that the second end face of the silicon carbide crystal ingot 10 faces upwards. Then the short pulse laser system adopts a vibrating mirror focusing method, a telecentric flat field lens with a long focal depth is adopted as a focusing mirror, the lens with the long focal depth can enable a large amount of energy to act on the position of the cavity modification forming region with a larger focal point, namely, the short pulse laser beam emitted by the short pulse laser system can be focused on the cavity modification forming region through the second end surface of the silicon carbide crystal ingot 10, so that the position generates more heat effect, the crack grows longer and expands, the short pulse laser beam continuously irradiates the short pulse laser beam for 3 to 5 times for many times, the crack can grow more than 200 microns in the horizontal direction, and the growth can be different according to different materials, material types, doping injection conditions, different laser parameter power pulse width wavelengths and the like. By the mode, the automatic operation efficiency can be improved. As shown in fig. 8, which is a flowchart of a laser slicing operation mode of the apparatus for laser peeling a silicon carbide ingot shown in fig. 7, all the operation steps of any one of the laser slicing methods shown above can be completed according to the operation flowchart shown in fig. 8.

In this case, the focus position of the ultrashort pulse laser beam and the focus position of the short pulse laser beam may be determined as follows. According to the actual machining position H, when the laser head NA =0.42, the incident angle of the laser light generated by the laser head is:

U1＝sin(0.42)*180/π＝24.83°

the laser generates refraction through the surface of the sample, and the refraction angle is as follows:

U2＝sin(0.42/2.6)*180/π＝9.3°

therefore, the magnification of the distance of the laser in the medium is:

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

therefore, when the laser is focused at a certain position H in the sample, the movement distance of the laser head through the Z axis is as follows:

L＝H/2.83

referring to fig. 9 and 10, the stage may hold silicon carbide ingot 10 by holding the side wall of silicon carbide ingot 10 to be cut so that the first and second end faces of silicon carbide ingot 10 are free from obstruction. In this case, as shown in fig. 9 and 10, the ultra-short pulse laser system and the short pulse laser system may be disposed above and below the stage, respectively. At this time, the stage is fixed by holding the side wall of silicon carbide ingot 10, so that the first end face and the second end face of silicon carbide ingot 10 are not shielded by the stage. Further, the ultrashort pulse laser system may be disposed at a first end surface side of the silicon carbide ingot 10 such that the ultrashort pulse laser beam emitted therefrom passes through the first end surface to process the inside of the silicon carbide ingot 10. A short pulse laser system may be disposed on the side of the second end face of silicon carbide ingot 10 to process the inside of silicon carbide ingot 10 through the second end face by emitting a short pulse laser beam without turning over silicon carbide ingot 10. Specifically, as shown in fig. 9 and 10, the ultrashort pulse laser system may be disposed above the stage, and the short pulse laser system may be disposed below the stage. Of course, it is also possible to have the ultrashort pulse laser system disposed below the stage and the short pulse laser system disposed above the stage.

In a specific implementation, as shown in fig. 9 and 10, an aperture of a through hole may be formed below the stage, after the ultrashort pulse laser beam is processed along the cutting path, another short pulse laser beam is rapidly triggered after being delayed by a position according to a position trigger mode, and each point emits 3-5 times of pulses to act on a cavity modification formation region formed after the previous ultrashort pulse is processed, so as to expand a crack. The method can save processing time, and the processing positions Z1 and Z2 of the two beams of laser are processed integrally and can move simultaneously. The positions of the two axes are mainly to ensure that the ultrashort pulse laser and the short pulse laser are respectively focused at the lower (1-3 um) position and the upper (3-5 um) position of the set height of the target silicon carbide wafer. By adopting the method, the crystal ingot can be rapidly processed to realize the growth connection of the internal cracks of the crystal ingot.

Compared with the existing process for cutting silicon ingots by using laser, the adopted ultrashort pulse laser can penetrate through the first end face of the silicon carbide crystal ingot 10, respectively generate a cavity modification forming region and a crack modification forming region above the position of the set depth layer 21 where the focus of the ultrashort pulse laser beam is located, and respectively form a cavity modification layer 22 and a crack modification layer 23 through scanning, so that the modification layers in the prior art are refined and distinguished. Then, when a short pulse laser beam is used, the short pulse laser beam is transmitted through the second end surface of the silicon carbide ingot 10 and focused on the cavity modifying formation region, and the focal position of the short pulse laser beam is located above the focal position of the ultrashort pulse laser beam, not at the same depth position as in the prior art, so that the short pulse laser beam scatters and propagates in the cavity modifying formation region, cracks in the cavity modifying formation region grow laterally outward, and the cracks in any adjacent cavity modifying formation region in the cavity modifying layer 22 are connected together by lateral growth through scanning. Since the short pulse laser beam is incident on the cavity modifying formation region of the silicon carbide ingot 10 through the second end surface, it is not necessary to transmit the crack modifying formation region above the cavity modifying formation region, and therefore, the influence of the crack in the crack modifying formation region on the scattering of the short pulse laser beam can be prevented, the laser energy concentration ratio can be increased, and the heating efficiency and the crack extension efficiency of the cavity modifying formation region can be increased. In addition, in the process of focusing the short pulse laser beam on the cavity modification forming region and heating the cavity modification forming region, the crack modification forming region can stop the growth of the crack, so that the upward growth length of the crack in the cavity modification forming region can be limited to a region below the crack modification forming region, the longitudinal growth length of the crack can be limited to a small height range, the crack extension efficiency is improved, the longitudinal extension degree of the crack is reduced to the greatest extent, and the slice loss is reduced to the greatest extent. The modified layer is divided into a cavity modified layer 22 and a crack modified layer 23 by thinning, then a short pulse laser beam penetrates through the second end surface of the silicon carbide crystal ingot 10 and is focused on the cavity modified layer 22, the focal position of the short pulse laser beam is designed more accurately and reasonably, the fluctuation of the vertical height difference of the focal point of the short pulse laser beam is small (the vertical height difference of the cavity modified forming region is smaller than the vertical height difference of the modified layer formed by the crack modified forming region and the cavity modified forming region together), the focal position of the short pulse laser beam is optimized to be focused on the modified layer 22, the crack modified forming region on the modified layer blocks the crack in the cavity modified forming region from growing upwards longitudinally, the length of the crack growing longitudinally is limited in a smaller height range, the focusing position of the laser beam is optimized, the amount and the length of the crack in the modified layer expanding longitudinally along the silicon carbide crystal ingot 10 are reduced, more laser energy is applied to the crack to grow outwards, the number of the transverse direction and the crack growth and the short pulse laser beam can cut the silicon carbide crystal ingot 10, and the waste of the same silicon carbide crystal ingot can be reduced.

The above description is only for the specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method of laser cleaving a silicon carbide ingot, the silicon carbide ingot to be cut having opposing first and second end faces, the method comprising:

after transmitting the first end face, ultra-short pulse laser beams are focused at a set depth layer position of a silicon carbide crystal ingot to be cut so as to respectively generate a cavity modification forming region and a crack modification forming region above the set depth layer position; wherein the cavity modifying formation region is located between the set depth layer position and the crack modifying formation region;

after the ultrashort pulse laser beam penetrates through the first end face, focusing the ultrashort pulse laser beam on a set depth layer of the silicon carbide crystal ingot and scanning the ultrashort pulse laser beam on the set depth layer so as 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 the cavity modification forming regions, the crack modified layer is composed of a plurality of the crack modification forming regions, and the cavity modified layer is located between the set depth layer and the crack modified layer;

after transmitting the short pulse laser beam through the second end surface, focusing the short pulse laser beam on the cavity modification forming region, and scattering and propagating the short pulse laser beam in the cavity modification forming region to enable the crack in the cavity modification forming region to grow outwards in the transverse direction;

after the short pulse laser beam is controlled to penetrate through the second end face, the short pulse laser beam is focused on the cavity modification layer and is scanned on the set depth layer, so that cracks in any adjacent cavity modification forming area in the cavity modification layer are connected together through transverse growth;

and taking the hollow modification layer as an interface to strip a part of the silicon carbide crystal ingot to generate a silicon carbide wafer.

2. The method of claim 1, wherein the silicon carbide ingot to be cut has a thickness of no greater than 5mm and the set depth layer is between 2 and 3mm from each of the first and second end faces.

3. The method according to claim 1, wherein the pulse width of the short pulse laser beam is 50ns or more, and the wavelength of the short pulse laser beam is 500 to 1100nm.

4. The method of claim 1, wherein the ultra-short pulse laser beam has a pulse width of 243fs-900fs and a wavelength of 500-1100nm.

5. The method according to claim 1, wherein said transmitting a short pulse laser beam through said second end surface, focusing on said hole modifying formation region, and scattering and propagating in said hole modifying formation region to grow a crack in said hole modifying formation region laterally outward comprises:

and adjusting the polarization state of the short pulse laser beam to expand the electron propagation direction along the silicon carbide crystal lattice direction of the silicon carbide crystal ingot to form a transverse growth crack of 3-5 degrees.

6. The method of claim 1, wherein the controlling the focus of the ultrashort pulse laser beam to scan at a set depth layer of the silicon carbide ingot comprises:

controlling the focus of the ultrashort pulse laser beam to scan a plurality of parallel first cutting channels on a set depth layer of the silicon carbide crystal ingot, wherein the interval between any two adjacent first cutting channels is 10-25um;

the controlling of the focal point of the short pulse laser beam to scan at the hole modifying layer includes:

and controlling the focus of the short pulse laser beam to scan a plurality of parallel second cutting channels on the cavity modification layer, wherein each second cutting channel is positioned right above one first cutting channel.

7. The method of claim 6, wherein said controlling the focal point of the short pulse laser beam to scan a plurality of parallel second streets across the hole modifying layer comprises:

and controlling the number of times that the focal point of the short pulse laser beam scans at each second cutting track to be more than or equal to three.

8. An apparatus for laser cleaving a silicon carbide ingot, the silicon carbide ingot to be cut having opposing first and second end faces, the apparatus comprising:

the object stage is used for fixing the silicon carbide crystal ingot to be cut;

the ultrashort pulse laser system is used for focusing an ultrashort pulse laser beam at a set depth layer position of a silicon carbide crystal ingot to be cut after the ultrashort pulse laser beam penetrates through the first end face so as to respectively generate a cavity modification forming region and a crack modification forming region above the set depth layer position; wherein the cavity modifying formation region is located between the set depth layer position and the crack modifying formation region;

the first scanning system is used for controlling the ultrashort pulse laser beam to be focused on a set depth layer of the silicon carbide crystal ingot and scan the set depth layer after the ultrashort pulse laser beam penetrates through the first end face, so that a cavity modified layer and a crack modified layer are respectively formed above the set depth layer; wherein the cavity modified layer is composed of a plurality of the cavity modification forming regions, the crack modified layer is composed of a plurality of the crack modification forming regions, and the cavity modified layer is located between the set depth layer and the crack modified layer;

the short pulse laser system is used for focusing a short pulse laser beam on the cavity modification forming region after the short pulse laser beam penetrates through the second end surface, and scattering and propagating in the cavity modification forming region to enable a crack in the cavity modification forming region to grow outwards in a transverse direction;

the second scanning system is used for controlling the short pulse laser beam to be focused on the cavity modification layer and scan on the set depth layer after the short pulse laser beam penetrates through the second end surface, so that cracks in any adjacent cavity modification forming region in the cavity modification layer are connected together through transverse growth;

and the stripping system is used for stripping a part of the silicon carbide crystal ingot to generate a silicon carbide wafer by taking the hollow modification layer as an interface.

9. The apparatus of claim 8, wherein the ultra-short pulse laser system and the short pulse laser system are both disposed above the stage;

the device further comprises: a clamping and overturning mechanism for clamping and overturning the silicon carbide ingot held on the stage so that the first end face or the second end face of the silicon carbide ingot faces upward.

10. The apparatus of claim 8, wherein the stage holds the silicon carbide ingot to be cut by gripping a sidewall of the silicon carbide ingot such that both the first end face and the second end face of the silicon carbide ingot are unobstructed;

the ultra-short pulse laser system and the short pulse laser system are respectively arranged above and below the objective table.