WO2024139561A1 - Silicon carbide substrate of 8 inches or more, and low-stress machining method therefor - Google Patents

Abstract

The present invention relates to the field of crystalline materials. Provided are a silicon carbide substrate of 8 inches or more, and a low-stress machining method therefor. The silicon carbide substrate has a relative force not higher than 50. The machining method comprises the following steps: detecting a (0001) crystal face of a silicon carbide crystal ingot to obtain crystal face position information; then calculating an included angle between the crystal face position information and a first plane, and determining whether the included angle meets the requirement for a preset included angle, wherein the first plane always stays perpendicular to a first direction where a first laser beam is located; and applying vibration to a face to be stripped, so as to obtain a silicon carbide stripping film. Then, the stripping film is sequentially thinned, polished and cleaned to obtain the silicon carbide substrate of 8 inches or more. The silicon carbide substrate of 8 inches or more provided in the present invention solves the problems of high machining stress, excessive warpage and curvature, an overly high surface metal ion concentration, a poor hydrophilic effect, etc. of an existing silicon carbide substrate.

Description

A silicon carbide substrate larger than 8 inches and a low-stress processing method thereof Technical Field

The present invention relates to the field of crystal materials, and in particular to a silicon carbide substrate larger than 8 inches and a low-stress processing method thereof.

Background technique

With the development of the industry, the performance requirements for components are getting higher and higher, gradually approaching the physical limit of silicon materials. Due to its excellent physical properties, silicon carbide substrates have incomparable advantages over Si materials in the fields of high voltage, high frequency, and high temperature. Currently, they are widely used in power electronics, microwave radio frequency devices, and high-end lighting.

The Mohs hardness of silicon carbide crystal is 9.2, second only to diamond. Its physical and chemical properties are extremely stable. It is a typical hard and brittle material. Ultra-precision processing has always been a difficult problem faced by the industry. The current status of the industry is that domestic 6-inch is in the mass production stage, 8-inch is in the research and development stage, foreign 6-inch has been mass-produced, and 8-inch is in the small-batch stage. 8 inches is bound to be the trend of future development. At present, small-batch production of 8-inch substrates has been achieved internationally, and domestic substrate manufacturers are also conducting research and development of 8-inch silicon carbide substrates. As the size expands to 8 inches, processing problems become more prominent, which seriously restricts the industrialization development of substrates.

Existing substrates larger than 8 inches have problems such as large processing stress, excessive warpage (Sori) and bow (BOW), excessive surface metal ion concentration, and poor hydrophilic effect.

Summary of the invention

In order to solve the problems of large processing stress, excessive warping and bending, too high surface metal ion concentration and poor hydrophilic effect of existing silicon carbide substrates larger than 8 inches, the present invention provides a silicon carbide substrate larger than 8 inches and a low stress processing method thereof.

In a first aspect, the present invention provides a silicon carbide substrate larger than 8 inches, wherein the silicon carbide substrate has a relative stress not higher than 50.

In a second aspect, the present invention provides a low stress processing method for a silicon carbide substrate larger than 8 inches, the method comprising the following steps:

S01. Detect the (0001) crystal plane of the silicon carbide ingot to obtain crystal plane position information.

S02, calculating the angle value between the crystal plane position information and the first plane, and determining whether the angle value meets the requirement of a preset angle value, wherein the first plane is always perpendicular to the first direction where the first laser beam is located.

S03a. If the conditions are met, start the first laser beam to scan the silicon carbide ingot to form a peeling surface containing multiple cracks and extending along the first plane. S03b. If the conditions are not met, adjust the angle of the silicon carbide ingot and/or the angle of the first direction, and return to step S02 until the angle value meets the requirements of the preset angle value.

S04, applying vibration to the surface to be peeled off to obtain a silicon carbide peeling sheet.

S05. Thinning at least a portion of the peeling sheet to obtain a thinned sheet.

S06. Polishing the thinned sheet to obtain a polished sheet.

S07. Clean the polishing sheet to obtain a silicon carbide substrate.

Beneficial Effects

Compared with the prior art, the beneficial effects of the 8-inch or larger silicon carbide substrate of the present invention include at least one of the following:

(1) Compared with the prior art, the silicon carbide substrate of the present invention having a size of 8 inches or more has a smaller processing stress. For example, the relative stress does not exceed 30.

(2) Compared with the prior art, the silicon carbide substrate of the present invention has smaller processing stress and better flatness. For example, the SFQR index of the silicon carbide substrate is not higher than 2μm, Bow is less than 25μm, and Sori is less than 45μm.

(3) Compared with the prior art, the 8-inch or larger silicon carbide substrate of the present invention has smaller processing stress and is hydrophilic. For example, the hydrophilic contact angle is not higher than 10°.

(4) Compared with the prior art, the metal ion concentration on the surface of the silicon carbide substrate of 8 inches or larger in the present invention is low. For example, the metal ion concentration is not higher than 5×10 ¹⁰ ions/cm ² .

Compared with the prior art, the low stress processing method for silicon carbide substrates larger than 8 inches of the present invention has the following beneficial effects:

(5) Traditionally, mechanical cutting is used, including mortar multi-wire cutting and diamond wire multi-wire cutting. In terms of substrate quality, as the size increases, the longitudinal cutting contact area becomes larger and larger, and the cutting force per unit area that the abrasive can provide decreases, which will produce large deformation stress during the processing process. The processing stress will cause cracks in the subsequent processing process, as well as problems such as excessive bending and warping. In terms of processing efficiency, mortar cutting takes a long time and diamond wire cutting is short, both of which have the problem of low overall cutting efficiency. In addition, multi-wire cutting is a batch processing method and is difficult to automate. The laser stripping technology used in the present invention can realize automated processing. Laser stripping can reduce wafer processing stress, reduce the amount of shape change after epitaxy, increase the number of wafers produced per unit rod length, and increase the number of wafers produced per unit thickness of silicon carbide ingot by 30%. In addition, the efficiency of the laser stripping technology used in the present invention is increased by 2-3 times.

(6) For the subsequent thinning process, the conventional technology uses a multi-chip processing method, placing a batch of wafers on a grinding disc or polishing disc for batch processing, which cannot achieve precise control of a single wafer. The present invention uses a full single-chip processing method, which can be matched and designed according to the situation of the cutting disc, greatly improving the thickness uniformity. In addition, the thinning process of the present invention can improve the flatness of the silicon carbide substrate and reduce the SFQR index of the silicon carbide substrate.

(7) Compared with the conventional double-sided polishing of multiple wafers, the single-sided chemical mechanical polishing of the present invention can obtain a polished wafer with a roughness of no more than 0.1 nm.

(8) The conventional technology uses a tank-type multi-wafer cleaning method, which has the disadvantages of poor cleaning effect on nano-sized particles and particles with strong consolidation, which easily leads to the problem of particle agglomeration in the later stage and high surface metal ion concentration. The present invention adopts a single-wafer cleaning process, which makes the substrate surface extremely hydrophilic, has good cleaning effect and low surface metal ion concentration.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

FIG1 is a schematic diagram showing the SFQR of a silicon carbide substrate larger than 8 inches in Example 3 of the present invention;

FIG2 shows a Bow-Sori schematic diagram of a silicon carbide substrate of an inch or larger in Example 3 of the present invention;

FIG3 shows a processing technology roadmap of a conventional silicon carbide substrate;

FIG. 4 shows a processing technology roadmap of a silicon carbide substrate according to an embodiment of the present invention.

Detailed ways

In order to more clearly illustrate the overall concept of the present invention, a detailed description is given below in an exemplary manner in conjunction with the accompanying drawings.

In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

In addition, in the description of the present invention, it should be understood that the orientations or positional relationships indicated by terms such as "top", "bottom", "inside", "outside", "axial", "radial", and "circumferential" are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or a communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

In the present invention, unless otherwise clearly specified and limited, the first feature "on" or "under" the second feature may be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in an appropriate manner in any one or more embodiments or examples.

In an exemplary embodiment of the present invention, a silicon carbide substrate larger than 8 inches has a relative stress not higher than 50. For example, the relative stress of the silicon carbide substrate is not higher than 45; further, the relative stress of the silicon carbide substrate is 10-30; preferably, the relative stress of the silicon carbide substrate is 10-25. The silicon carbide substrate can be 8 inches or 12 inches.

Since it is difficult to measure the real stress directly, but the stress will affect the surface shape of the substrate and the changes in the surface shape before and after the epitaxy, the inventors found through many studies that a concept of relative stress can be introduced through the above parameters. The model is established by fitting and analyzing a large amount of data as follows:

Formula (1): S = [(A + B) / 2] + [(A _C + B _C ) * 2]

Where S is the relative stress, and the smaller the S value, the smaller the stress of the substrate. A—substrate Bow absolute value, B—substrate Sori value, _AC —absolute value of the change in Bow value before and after epitaxy, _BC —absolute value of the change in Sori value before and after epitaxy.

In an exemplary embodiment of the present invention, the SFQR of the silicon carbide substrate is not higher than 2μm, Bow is less than 25μm, Sori is less than 45μm, and the profile change before and after epitaxy is not higher than 10μm. The profile change before and after epitaxy is not higher than 10μm respectively means that the change of the Bow value before and after epitaxy is not higher than 10μm, and the change of the Sori value before and after epitaxy is not higher than 10μm.

In an exemplary embodiment of the present invention, the SFQR of the silicon carbide substrate may be 1-1.5 μm, Bow < 15 μm, Sori < 25 μm, and the profile change before and after epitaxy is no more than 8 μm. Preferably, the SFQR of the silicon carbide substrate is no more than 1 μm, Bow of the silicon carbide substrate is less than 10 μm, Sori < 15 μm, and the profile change before and after epitaxy is no more than 5 μm.

In the present invention, SFQR (Site flatness front least-squares range) refers to local flatness, which represents the maximum difference in thickness per unit square area. Bow refers to curvature, which represents the degree of concavity or convexity of the center of the wafer relative to the reference plane. Sori refers to the warpage of the front surface based on the least squares method, which represents the degree of deviation of the substrate as a whole relative to the mid-plane. In the present invention, the shape change before and after epitaxy refers to the change of Bow before and after epitaxy and the change of Sori before and after epitaxy.

In an exemplary embodiment of the present invention, the silicon carbide substrate has a hydrophilic surface with a contact angle of no more than 10°; preferably, the hydrophilic contact angle is no more than 5°. The hydrophilicity of the present invention refers to a contact angle of no more than 10°.

In an exemplary embodiment of the present invention, the surface metal ion concentration of the silicon carbide substrate is not higher than 5×10 ¹⁰ /cm ² , further, the surface metal ion concentration is not higher than 4×10 ¹⁰ /cm ² ; preferably, the surface metal ion concentration is not higher than 2×10 ¹⁰ /cm ² .

In an exemplary embodiment of the present invention, one surface of the silicon carbide substrate has a refractive index of 2.5-2.8; and the other surface of the silicon carbide substrate has a refractive index of 2.6-2.7.

In another exemplary embodiment of the present invention, the silicon carbide substrate is obtained by thinning, polishing and cleaning a laser cracking peeling sheet, and the relative stress of the laser cracking peeling sheet is 20~30. The size of the peeling sheet is not less than 8 inches, and the damage layer depth of the peeling sheet is not higher than 110μm; further, the damage layer depth of the peeling sheet is not higher than 90μm; preferably, the damage layer depth of the peeling sheet is 50~80μm. The Bow of the peeling sheet is less than 70μm, and the Sori is less than 120μm; further, the Bow of the peeling sheet is less than 40μm, and the Sori is less than 90μm. And the maximum value of the surface crack step height does not exceed 70% of the damage layer depth. The surface crack step height refers to the microcracks that will exist on the surface after peeling, and each microcrack extends along the cleavage plane. In this process, since each microcrack and the cleavage plane have an angle deviation, repeated crack steps are formed in the laser peeling direction.

In addition, the surface roughness of the thinned sheet obtained by thinning is not higher than 10nm, and further, the surface roughness of the thinned sheet is not higher than 7nm. The surface roughness of the polished sheet obtained by polishing is not higher than 0.2nm; further, the surface roughness of the polished sheet obtained by polishing is not higher than 0.1nm,

Among them, silicon carbide substrates larger than 8 inches are cut by laser monolithic stripping, and the laser monolithic stripping cutting includes setting the wavelength to 800-1200nm, the scanning interval to 0.5-5mm, the ultrasonic stripping frequency to 50-500KHZ and the scanning time to 10-40min.

The laser-stripped silicon carbide stripping sheet targeted by the present invention can be obtained by laser cracking and vibration stripping, for example, by steps S01 to S04, wherein:

S01, detecting the (0001) crystal plane of the silicon carbide ingot to obtain crystal plane position information;

S02, calculating the angle between the crystal plane position information and the first plane, and determining whether the angle meets the requirement of a preset angle, wherein the first plane is always perpendicular to the first direction where the first laser beam is located;

S03a, if satisfied, start the first laser beam to scan the silicon carbide ingot to form a to-be-peeled surface containing multiple cracks and extending along the first plane; S03b, if not satisfied, adjust the angle of the silicon carbide ingot and/or the angle of the first direction, and return to step S02 until the angle value meets the requirement of the preset angle value;

S04, applying vibration to the surface to be peeled off to obtain a silicon carbide peeling sheet.

The steps from S01 to S04 can also be described in detail as follows:

S01. Detect the (0001) crystal plane of the silicon carbide ingot to obtain crystal plane position information.

Specifically, the principle of Bragg diffraction can be used for crystal plane detection, that is, the surface crystal of silicon carbide is composed of crystal plane families A, B, and C with a plane spacing of d. When the laser beam is projected onto the silicon carbide crystal at a grazing angle α, the scattering of the lattice on crystal plane A and the scattering of the lattice on crystal planes B and C interfere with each other. For the laser scattered rays of the same layer, when the angle between the scattered rays and the crystal plane is equal to the grazing angle, the rays produce constructive interference in this direction. For the scattered rays of the same layer, when the angle between the scattered rays and the crystal plane is equal to the grazing angle, the rays produce constructive interference in this direction. For the scattered rays of different layers, when the optical path difference is an integer multiple of the wavelength, the scattered rays of each surface reinforce each other to form a very large light intensity. Using this principle, crystal plane detection is completed and crystal plane information is obtained.

S02, calculating the angle between the crystal plane position information and the first plane, and determining whether the angle meets the requirement of a preset angle, wherein the first plane is always perpendicular to the first direction where the first laser beam is located.

Specifically, the first plane is the plane of the silicon carbide ingot that is substantially perpendicular to the first laser beam. The first direction is the direction of irradiation of the first laser beam. The angle value is the angle between the (0001) crystal plane of the silicon carbide ingot and the first plane of the silicon carbide ingot. The preset angle value may be a determined value selected within the range of 0 to 10°, and further, the preset angle value may be a determined value selected within the range of 0.5 to 3.5° or 4.5 to 7°. For example, it may also be 0° or 4°. The requirement for the preset angle value may be equal to the preset angle value, or it may be within 10% of the preset angle value, for example, 4±0.1°.

S03a. If the conditions are met, start the first laser beam to scan the silicon carbide ingot to form a surface to be peeled that contains multiple cracks and extends along the first plane.

Specifically, if the angle between the (0001) crystal plane of the silicon carbide ingot and the first plane of the silicon carbide ingot is within the preset angle value range, the first laser beam is started to perform laser scanning on the silicon carbide ingot to form a surface to be peeled containing multiple cracks and extending along the first plane. The average output power of the first laser beam can be 0.8~3.5W, the wavelength can be 780~1100 nm, the scanning speed can be 300~700 mm/s, the scanning spacing can be 0.1~0.5 mm, the scanning time can be 10~40 min, and the number of scans can be 2~6 times.

S03b. If not, adjust the angle of the silicon carbide ingot and/or the angle of the first direction, and return to step S02 until the angle value meets the requirement of the preset angle value, and then perform step S03a.

Specifically, if the angle between the (0001) crystal plane of the silicon carbide ingot and the first plane of the silicon carbide ingot is not within the preset angle value range, the angle of the silicon carbide ingot can be adjusted, that is, the (0001) plane of the silicon carbide ingot can be adjusted, or the first direction of the first laser beam can be adjusted. After the adjustment, return to step S02, calculate the angle value, and determine whether it meets the preset angle value. If it does, enter S03a; if it does not, continue to adjust the angle value until the preset angle value is met.

S04. Apply vibration to the surface to be peeled off to obtain a silicon carbide peeling sheet.

Vibration is applied to the surface to be peeled in step S03a so that the surface to be peeled extends or breaks along the crack to obtain a peeling sheet. The vibration can be achieved by mechanical vibration, ultrasonic method, etc. For example, for the ultrasonic method, the frequency of the ultrasound can be 100-150 KHZ, the ultrasonic time can be 10-60 s, and the emission mode can be a continuous wave or a pulse wave.

The thickness of the silicon carbide peeling sheet obtained by the above processing method can be 100~1000μm. The size is not less than 8 inches, Bow≤60μm, Sori≤100μm, the damage layer depth is ≤100μm and the maximum height of the surface crack step does not exceed 70% of the damage layer depth.

In addition, in order to solve the problem of edge collapse, on the basis of the above steps S01 to S04, step S03 can be set to further include: when the angle value meets the requirements of the preset angle value, start the second laser beam to scan the silicon carbide ingot in the circumferential direction of the silicon carbide ingot, and ensure that the second direction of the second laser beam is always parallel to the first plane. The cracking direction of the first laser beam is perpendicular to the laser incident direction, while the cracking direction of the second laser beam is along the laser incident direction. This is to adjust the laser cracking direction by spot shaping. It is conducive to the peeling of the circumference of the edge of the silicon carbide ingot, and can further optimize the depth of the damaged layer and the depth of the surface step crack. The second laser head is configured to be able to be controlled in conjunction with the first laser head. The two laser heads peel the silicon carbide ingot successively. The first laser head generates a first laser beam to peel the area of the silicon carbide ingot except the circumferential edge, and the second laser head generates a second laser beam to peel the circumferential edge area of the silicon carbide ingot. The focus of the first laser beam and the position of the second laser beam should be controlled to ensure that the two generate cracks in the same plane. The second laser beam can optimize the depth of the damaged layer and the depth of the surface step crack by at least 10% compared with the result of peeling with only the first laser beam. The average output power of the second laser beam is 0.3 to 0.5 times the average output power parameter of the first laser beam, the wavelength is 780 to 1100 nm, the scanning speed is 0.3 to 0.5 times the scanning speed parameter of the first laser beam, the scanning spacing is 0.1 to 0.5 mm, the scanning time is 10 to 40 minutes, and the number of scans is 2 to 6 times.

Then, at least a portion of a single side of the single peeling sheet is thinned and/or at least a portion of another single side of the single peeling sheet is thinned to obtain a thinned sheet. The thinning includes a rough grinding process and a fine grinding process, and the roughness of the fine grinding process is less than the roughness of the rough grinding process. The thinned sheet is subjected to single-sheet single-side rough polishing, medium polishing, and fine polishing in sequence to obtain the desired polished sheet.

In addition, the silicon carbide substrate of the present invention having a size of 8 inches or more adopts single-chip single-sided chemical mechanical polishing, wherein the rough polishing adopts polyurethane and acidic alumina polishing liquid; the medium polishing adopts non-woven fabric and manganese oxide polishing liquid or non-woven fabric and alumina polishing liquid; and the fine polishing adopts damping cloth and alkaline silicon oxide polishing liquid.

Example 1

The present invention is an 8-inch silicon carbide substrate, the relative stress of the silicon carbide substrate is 16.8, the SFQR is 1.064μm, the Bow is 2.346μm, the Sori is 6.953μm, the Bow change before and after epitaxy is 1.269μm, and the Sori change before and after epitaxy is 4.789μm. The hydrophilic contact angle is 6°, and the surface metal ion concentration is less than 1.9×10 ¹⁰ /cm ^2. The refractive index of one surface of the silicon carbide substrate is 2.632, and the refractive index of the other surface is 2.673.

Example 2

The present invention is an 8-inch silicon carbide substrate, the relative stress of the silicon carbide substrate is 32.8, the SFQR is 1.211 μm, the Bow is 6.762 μm, the Sori is 14.865 μm, the Bow change before and after epitaxy is 3.281 μm, and the Sori change before and after epitaxy is 7.691 μm. The hydrophilic contact angle is 9°, and the surface metal ion concentration is less than 3.7×10 ¹⁰ /cm ^2. The refractive index of one surface of the silicon carbide substrate is 2.643, and the refractive index of the other surface is 2.695.

Example 3

The present invention is an 8-inch silicon carbide substrate, the relative stress of the silicon carbide substrate is 33.8, the SFQR is 1.395μm, the Bow is 8.256μm, the Sori is 13.314μm, the Bow change before and after epitaxy is 4.283μm, and the Sori change before and after epitaxy is 7.211μm. The hydrophilic contact angle is 10°, and the surface metal ion concentration is less than 2.7×10 ¹⁰ /cm ^2. The refractive index of one surface of the silicon carbide substrate is 2.643, and the refractive index of the other surface is 2.695. The SFQR schematic diagram of Example 3 is shown in reference to Figure 1. The Bow-Sori schematic diagram of the silicon carbide substrate is shown in reference to Figure 2.

Comparative Example 1

Comparative Example 1 is a performance test of an existing 8-inch silicon carbide substrate.

Table 1 Silicon carbide substrate performance table

	Size/inch	Relative stress	SFQR/μm	Bow/ μm	Sori/ μm	Bow epitaxial variation/μm	Sori epitaxial variation/μm	Contact angle/°	Ion concentration/pcs/ cm2
Example 1	8	16.8	1.064	2.346	6.953	1.269	4.789	6	＜1.9×10 10
Example 2	8	32.8	1.211	6.762	14.865	3.281	7.691	9	＜3.7×10 10
Example 3	8	33.8	1.395	8.256	13.314	4.283	7.211	10	＜2.7×10 10
Comparative Example 1	8	94.6	1.582	18.753	34.172	12.726	21.364	twenty three	＜1×10 12

As shown in Table 1, it can be seen from Example 1, Example 2, and Example 3 that the relative stress of the silicon carbide substrate of 8 inches or more of the present invention is not higher than 50, indicating that the processing stress of the present invention is low. In addition, while the processing stress of the present invention is low, it ensures that the substrate has good flatness, hydrophilicity, and low surface metal ion concentration.

Compared with comparative example 1, the relative stress of embodiment 1 is reduced by 82%, the SFQR is reduced by 0.52 μm, the Bow and Sori are significantly reduced, the change before and after epitaxy is significantly reduced, the contact angle is controlled within 10° and is hydrophilic, and the ion contamination concentration is reduced by two orders of magnitude.

Example 4

In an exemplary embodiment of the present invention, a low stress processing method for a silicon carbide substrate larger than 8 inches includes the following steps:

S01. Detect the (0001) crystal plane of the silicon carbide ingot to obtain crystal plane position information.

S02, calculating the angle value between the crystal plane position information and the first plane, and judging whether the angle value meets the requirement of the preset angle value, wherein the first plane is always perpendicular to the first direction where the first laser beam is located. The preset angle value can be a determined value selected in the range of 0 to 10, and further, the angle value is a determined value selected in the range of 0.5 to 3.5 or 4.5 to 7.

S03a, if satisfied, start the first laser beam to scan the silicon carbide ingot to form a peeling surface containing multiple cracks and extending along the first plane; S03b, if not satisfied, adjust the angle of the silicon carbide ingot and/or the angle of the first direction, and return to step S02 until the angle value meets the requirement of the preset angle value. The angle can be adjusted along the X direction and/or along the Y direction by the silicon carbide ingot angle adjustment mechanism. The X direction and the Y direction are in the same plane and perpendicular to each other. The average output power of the first laser beam is 0.8~3.5 W, the wavelength is 780~1100 nm, the scanning speed is 300~700 mm/s, the scanning spacing is 0.1~1 mm, the scanning time is 10~40 min, and the number of scans is 2~6 times.

S04, applying vibration to the surface to be peeled off to obtain a silicon carbide peeling sheet. For example, vibration can be applied by ultrasound, and the ultrasonic frequency can be 90~160KHz. The size of the silicon carbide peeling sheet is not less than 8 inches, and the thickness of the silicon carbide peeling sheet is 100~1000μm; further, the thickness of the silicon carbide peeling sheet is 200~700μm. The surface roughness of the peeling sheet is 10~50μm, the total thickness deviation (GBIR) is <20μm, Bow <100μm, Sori is <120μm, and the surface is evenly covered with microcracks in the direction of laser scanning; the depth of the damaged layer is ≤100μm and the maximum height of the surface crack step does not exceed 70% of the depth of the damaged layer. Further, the curvature (Bow) of the silicon carbide peeling sheet is 30~57μm, the warpage (Sori) is 50~97μm, the depth of the damaged layer is 60~95μm, and the maximum height of the surface crack step is 50~70% of the depth of the damaged layer.

In addition, in order to solve the problem of edge collapse, on the basis of the above steps S01 to S04, step S03 can be set to further include: when the angle value meets the requirements of the preset angle value, start the second laser beam to scan the silicon carbide ingot in the circumferential direction of the silicon carbide ingot, and ensure that the second direction of the second laser beam is always parallel to the first plane. The cracking direction of the first laser beam is perpendicular to the laser incident direction, while the cracking direction of the second laser beam is along the laser incident direction. This is to adjust the laser cracking direction by spot shaping. It is conducive to the peeling of the circumference of the edge of the silicon carbide ingot, and can further optimize the depth of the damaged layer and the depth of the surface step crack. The second laser head is configured to be able to be controlled in conjunction with the first laser head. The two laser heads peel the silicon carbide ingot successively. The first laser head generates a first laser beam to peel the area of the silicon carbide ingot except the circumferential edge, and the second laser head generates a second laser beam to peel the circumferential edge area of the silicon carbide ingot. The focus of the first laser beam and the position of the second laser beam should be controlled to ensure that the two generate cracks in the same plane. The second laser beam can optimize the depth of the damaged layer and the depth of the surface step crack by at least 10% compared with the result of peeling with only the first laser beam. The average output power of the second laser beam is 0.3 to 0.5 times the average output power parameter of the first laser beam, the wavelength is 780 to 1100 nm, the scanning speed is 0.3 to 0.5 times the scanning speed parameter of the first laser beam, the scanning spacing is 0.1 to 0.5 mm, the scanning time is 10 to 40 minutes, and the number of scans is 2 to 6 times.

S05, thinning at least a portion of the peeled sheet to obtain a thinned sheet. For example, the thinning process may include:

S51, thinning at least a portion of a single side of a single release sheet; and

S52, thinning at least a portion of the other single side of the single peeling sheet to obtain a thinned sheet. The S51 process and/or the S52 process include a sequential rough grinding process and a fine grinding process, the surface roughness of the fine grinding process is less than the surface roughness of the rough grinding process, the rough grinding wheel speed is higher than the fine grinding, the rough grinding feed speed is higher than the fine grinding, and the fine grinding wheel mesh number is higher than the rough grinding. For example, the feed speed can be set to 1~20μm/min, the grinding wheel speed can be set to 1000~2500rpm, and the grinding wheel mesh number can be set to 3000~30000 mesh during thinning. Further, the feed speed can be set to 5~15μm/min, the grinding wheel speed can be set to 1300~2000rpm, and the grinding wheel mesh number can be set to 5000~20000 mesh. Preferably, the feed speed can be set to 4~6μm/min, the grinding wheel speed can be set to 1500~1800rpm, and the grinding wheel mesh number can be set to 10000~15000 mesh.

The surface roughness of the thinned sheet is 1~10nm, GBIR is <5μm, Bow is <30μm, Sori is <60μm, and the surface is evenly covered with arc-shaped thinning marks in the direction of rotation of the grinding wheel.

S06, polishing the thinned sheet to obtain a polished sheet. The thinned sheet is polished i times in sequence to obtain the desired polished sheet; the roughness of the wafer obtained by the i-th polishing process is higher than that of the i+1-th polishing process, the hardness of the polishing pad required for the i-th polishing process is higher than that of the i+1-th polishing process, and the pH of the polishing liquid required for the i-th polishing process is lower than that of the i+1-th polishing process; wherein i is a natural number and traverses from 1 to n, and n is a natural number and is not less than 2. The particle size of the polishing liquid required for the i-th polishing process is smaller than the particle size of the polishing liquid required for the i+1-th polishing process. In this way, the surface roughness of the polished sheet obtained by tandem polishing is smaller. The substrate product obtained by further preparation is of higher quality.

For example, i can be 3, and the thinned sheet is polished three times in series, the first polishing is rough polishing to obtain the first polished wafer, the first polished wafer is polished again for the second time, the second polishing is medium polishing to obtain the second polished wafer; finally, the second polished wafer is finely polished for the third time to obtain the desired polished sheet. The hardness of the polishing pad required for the first polishing treatment is greater than the hardness of the polishing pad required for the second polishing treatment. For example, the rough polishing pad can be polyurethane, the hardness of the polyurethane is 85~95HA, the polishing liquid can be acidic alumina polishing liquid, pH2~5, and the particle size of the polishing liquid is 90~130nm. Preferably, pH3-4, the particle size of the polishing liquid is 100~120nm. The medium polishing pad is a non-woven fabric, the hardness of the non-woven fabric is 70~83HA, the polishing liquid is a neutral manganese oxide or neutral alumina polishing liquid; the pH value is 6~8, and the particle size of the polishing liquid is 65~85nm. The fine polishing pad is a damping cloth with a hardness of 55-68HA, the polishing liquid is an alkaline silicon oxide polishing liquid with a pH of 9-12, and a particle size of 35-62nm. The pH of the polishing liquid required for the first polishing process is less than that required for the second polishing process, and the pH of the polishing liquid required for the third polishing process is less than that required for the third polishing process. The removal rate of the first polishing is 3.5-5.5μm/h, the removal rate of the second polishing is 1-3μm/h, and the removal rate of the third polishing is 0.1-0.5μm/h. The thinned sheet is processed in accordance with the polishing process sequence, and the surface roughness of the polished sheet is gradually reduced. For example, the surface roughness of the polished wafer obtained by rough polishing is not higher than 0.3nm, the surface roughness of the polished wafer obtained by medium polishing is not higher than 0.2nm, and the surface roughness of the polished sheet obtained after fine polishing is not higher than 0.1nm.

Furthermore, the acidic alumina polishing liquid has a pH of 2-5, a concentration of 1-1.5%, a flow rate of 100-200 ml/min, a pressure of 300-500 g/cm ² applied to the wafer during polishing, and a rotation speed of 40-70 rpm during polishing. Preferably, the acidic alumina polishing liquid has a pH of 3-5, a concentration of 1.2-1.4%, a flow rate of 130-170 ml/min, a pressure of 350-450 g/cm ² , and a rotation speed of 50-60 rpm.

The neutral manganese oxide polishing liquid or neutral aluminum oxide polishing liquid has a pH value of 6-8, a concentration of 0.5-1%, a flow rate of 150-250 ml/min, a pressure of 200-400 g/cm ² , and a rotation speed of 30-60 rpm. Preferably, the neutral manganese oxide polishing liquid or neutral aluminum oxide polishing liquid has a pH value of 6-8, a concentration of 0.7-0.9%, a flow rate of 180-220 ml/min, a pressure of 250-350 g/cm ² , and a rotation speed of 40-50 rpm.

The fine polishing pad is a damping cloth, and the polishing liquid is an alkaline silicon oxide polishing liquid. The alkaline silicon oxide polishing liquid has a pH of 9-12, a concentration of 0.5-1%, a flow rate of 150-250 ml/min, a pressure of 200-400 g/cm ² , and a rotation speed of 30-60 rpm. Preferably, the alkaline silicon oxide polishing liquid has a pH of 10-11, a concentration of 0.7-0.9%, a flow rate of 180-220 ml/min, a pressure of 250-350 g/cm ² , and a rotation speed of 40-50 rpm.

S07, clean the polishing sheet in a single piece to obtain a silicon carbide substrate. The method includes using at least two of ozone water, hydrogen fluoride solution, ultrapure water and SC1 cleaning solution for cleaning. For example. Ozone water can be used for cleaning first and then ultrapure water; or ozone water can be used for cleaning for 10 to 30 seconds, ultrapure water for 5 to 20 seconds, hydrogen fluoride solution for cleaning for 10 to 30 seconds, ultrapure water for cleaning for 5 to 20 seconds, and SC1 for cleaning for 20 to 50 seconds in sequence. Or ozone water can be used for cleaning for 15 to 25 seconds, ultrapure water for cleaning for 10 to 15 seconds, hydrogen fluoride solution for cleaning for 15 to 25 seconds, ultrapure water for cleaning for 8 to 15 seconds, and SC1 for cleaning for 30 to 40 seconds in sequence. The ozone water concentration can be 10 to 50 ppm, and the HF concentration can be 1 to 10%. Further, the ozone water concentration can be 20 to 40 ppm, and the HF concentration can be 4 to 7%. The cleaned wafer is dried, for example, by high-speed spin drying for 10 to 30 seconds, but the present invention is not limited thereto. The 8-inch or larger silicon carbide substrate is obtained. The traditional method is to put a whole box (for example, 25 wafers) of wafers into a tank containing a cleaning solution for immersion, ultrasonication, heating, and other treatments to achieve cleaning. The present invention uses single-wafer cleaning for stronger cleaning capabilities.

The low stress processing flow of the silicon carbide substrate of the present invention is shown in FIG4. The silicon carbide substrate larger than 8 inches is a silicon carbide substrate not less than 8 inches, for example, a 10-inch silicon carbide substrate or a 12-inch silicon carbide substrate. However, the present invention is not limited thereto.

In the present invention, SFQR (Site flatness front least-squares range) refers to local flatness, which represents the maximum difference in thickness per unit square area. Bow refers to curvature, which represents the degree of concavity or convexity of the center of the wafer relative to the reference plane. Sori refers to the warpage of the front surface based on the least squares method, which represents the degree of deviation of the substrate as a whole relative to the mid-plane. In the present invention, the shape change before and after epitaxy refers to the change of Bow before and after epitaxy and the change of Sori before and after epitaxy.

Example 5

On the basis of Example 4, the low-stress processing method for silicon carbide substrates larger than 8 inches also includes grinding along the first plane the stripping area left on the silicon carbide ingot in step S04, and performing steps S01 to S04 again to obtain another silicon carbide stripping sheet; or after grinding along the first plane the stripping area left on the silicon carbide ingot in step S04, directly starting the first laser beam to scan the silicon carbide ingot again to form another surface to be stripped containing multiple cracks and extending along the first plane, and then performing step S04 to obtain another silicon carbide stripping sheet.

Example 6

On the basis of Example 4, step S03 of the low stress processing method for silicon carbide substrates larger than 8 inches further includes: when the angle value meets the requirement of the preset angle value, starting the second laser beam to scan the silicon carbide ingot in the circumferential direction of the silicon carbide ingot, and ensuring that the second direction where the second laser beam is located is always in the first plane. The average output power of the second laser beam is 0.8~3.5W, the wavelength is 780~1100nm, the scanning speed is 300~700mm/s, the scanning spacing is 0.1~1mm, the scanning time is 10~40min, and the number of scans is 2~6 times.

Example 7

Based on Example 4, the low-stress processing method for an 8-inch silicon carbide substrate comprises the following steps: subjecting a silicon carbide ingot to laser stripping and cutting, single-piece single-side thinning, single-piece single-side CMP, and single-piece cleaning in sequence to obtain the silicon carbide substrate larger than 8 inches. Specifically:

1. Laser single chip peeling and cutting

The laser single-chip peeling and cutting includes setting an average output power of 1.1W, a scanning interval of 0.12mm, a scanning speed of 300mm/s, a scanning number of 5 times, a scanning time of 20min, and a wavelength of 1064nm.

The ultrasonic stripping frequency was 100 KHZ and the ultrasonic time was 40 s.

2. Single-sided thinning

The single-sheet single-sided thinning includes rough grinding and fine grinding, wherein the rough grinding has an inclination angle of 0.1°, a grinding wheel mesh number of 4000, a feed speed of 12 μm/min, and a grinding wheel speed of 2000 rpm. The fine grinding has an inclination angle of -0.1°, a grinding wheel mesh number of 30000, a feed speed of 8 μm/min, and a grinding wheel speed of 1500 rpm.

3. Single-wafer single-sided CMP

The single-wafer single-sided CMP medium rough polishing adopts polyurethane and acidic aluminum oxide polishing liquid; the medium polishing adopts non-woven fabric and neutral manganese oxide polishing liquid; the fine polishing adopts damping cloth and alkaline silicon oxide polishing liquid.

Rough polishing: The silicon carbide thinning slice is firstly rough polished to obtain the first polished wafer, and the rough polishing polishing pad is made of polyurethane with a hardness of 90HA. The polishing liquid is an acidic alumina polishing liquid with an average particle size of 120nm. The acidic alumina polishing liquid has a pH of 3, a concentration of 1.2%, a flow rate of 120ml/min, a rotation speed of 60rpm, a pressure of 600g/ ^cm2 , and a polishing time of 10min.

Medium polishing: The first polished wafer is subjected to medium polishing to obtain the second polished wafer, wherein the medium polishing pad is made of non-woven fabric with a hardness of 82HA. The polishing liquid is a neutral manganese oxide polishing liquid with an average particle size of 80nm. The neutral manganese oxide polishing liquid has a pH value of 6.3, a concentration of 0.6%, a flow rate of 100ml/min, a rotation speed of 50rpm, a pressure of 500g/ ^cm2 , and a polishing time of 10min.

Fine polishing: The second polishing wafer is fine polished to obtain a silicon carbide polishing sheet, the fine polishing sheet uses a damping cloth with a hardness of 67HA. The polishing liquid is an alkaline silicon oxide polishing liquid, the average size of the polishing liquid particles is 60nm, the pH of the alkaline silicon oxide polishing liquid is 11, the concentration is 0.6%, the flow rate is 80ml/min, the pressure is 400g/ ^cm2 , the rotation speed is 40rpm, and the polishing time is 10min.

4. Single chip cleaning

The single-wafer cleaning is to sequentially clean the polishing wafer with ozone water for 12 seconds, ultrapure water for 8 seconds, hydrogen fluoride solution for 12 seconds, ultrapure water for 7 seconds, and SC1 for 22 seconds. The ozone water concentration is 12 ppm, and the HF concentration is 3%.

The cleaned wafer was spin-dried at high speed to obtain an 8-inch silicon carbide substrate. The performance characteristics of the relevant products are listed in Table 3.

Example 8

Based on Example 7, the difference is:

1. Laser single chip peeling and cutting

The laser single-chip peeling and cutting includes setting an average output power of 2.5W, a scanning interval of 0.18mm, a scanning speed of 500mm/s, a scanning number of 4 times, a scanning time of 30min, and a wavelength of 1064nm.

The ultrasonic stripping frequency was 120KHZ and the ultrasonic time was 30s.

2. Single-sided thinning

The single-sheet single-sided thinning includes rough grinding and fine grinding, the rough grinding has an inclination angle of 0.2°, a grinding wheel mesh number of 3500, a feed speed of 15 μm/min, and a grinding wheel speed of 2200 rpm. The fine grinding has an inclination angle of -0.23°, a grinding wheel mesh number of 25000, a feed speed of 10 μm/min, and a grinding wheel speed of 1700 rpm.

3. Single-wafer single-sided CMP

Rough polishing: The silicon carbide thinning slice is firstly rough polished to obtain the first polished wafer, and the rough polishing polishing pad is made of polyurethane with a hardness of 88HA. The polishing liquid is an acidic alumina polishing liquid with an average particle size of 110nm. The acidic alumina polishing liquid has a pH of 4, a concentration of 1.3%, a flow rate of 110ml/min, a pressure of 550g/ ^cm2 , a rotation speed of 55rpm, and a polishing time of 12min.

Medium polishing: The first polished wafer is subjected to medium polishing to obtain a second polished wafer. The medium polishing polishing pad is made of non-woven fabric with a hardness of 76HA. The polishing liquid is a neutral alumina polishing liquid with an average particle size of 70nm. The neutral alumina polishing liquid has a pH value of 6.9, a concentration of 0.6%, a flow rate of 100ml/min, a pressure of 450g/ ^cm2 , a rotation speed of 45rpm, and a polishing time of 12min.

Fine polishing: The second polishing wafer is fine polished to obtain a silicon carbide polishing sheet, the fine polishing sheet uses a damping cloth with a hardness of 65HA, the polishing liquid is an alkaline silicon oxide polishing liquid, the average particle size of the polishing liquid is 50nm, the alkaline silicon oxide polishing liquid has a pH of 11.5, a concentration of 0.8%, a flow rate of 80ml/min, a pressure of 350g/ ^cm2 , a rotation speed of 40rpm, and a polishing time of 12min.

4. Single chip cleaning

The single-wafer cleaning is to sequentially clean the polished wafer with ozone water for 17 seconds, ultrapure water for 12 seconds, hydrogen fluoride solution for 18 seconds, ultrapure water for 11 seconds, and SC1 for 33 seconds. The ozone water concentration is 14 ppm, and the HF concentration is 6%.

Example 9

Based on Example 7, the difference is:

1. Laser single chip peeling and cutting

The laser single-chip peeling and cutting includes setting an average output power of 3.2W, a scanning interval of 0.25mm, a scanning speed of 700mm/s, a scanning number of 3 times, a scanning time of 30min, and a wavelength of 1064nm.

The ultrasonic stripping frequency was 100 KHZ and the ultrasonic time was 20 s.

2. Single-sided thinning

The single-sheet single-sided thinning includes rough grinding and fine grinding, the rough grinding has an inclination angle of 0.3°, a grinding wheel mesh number of 3000, a feed speed of 20 μm/min, and a grinding wheel speed of 2500 rpm. The fine grinding has an inclination angle of -0.31°, a grinding wheel mesh number of 20000, a feed speed of 14 μm/min, and a grinding wheel speed of 2200 rpm.

3. Single-wafer single-sided CMP

Rough polishing: The silicon carbide thinned sheet is firstly rough polished to obtain the first polished wafer. The rough polishing polishing pad is made of polyurethane with a hardness of 85HA. The polishing liquid is an acidic alumina polishing liquid with an average particle size of 100nm. The acidic alumina polishing liquid has a pH of 4.5, a concentration of 1.4%, a flow rate of 110ml/min, a pressure of 500g/ ^cm2 , a rotation speed of 50rpm, and a polishing time of 15min.

Medium polishing: The first polished wafer is subjected to medium polishing to obtain a second polished wafer. The medium polishing polishing pad is made of non-woven fabric with a hardness of 73HA. The polishing liquid is a neutral manganese oxide polishing liquid with an average particle size of 70nm. The neutral manganese oxide polishing liquid has a pH value of 7.2, a concentration of 0.8%, a flow rate of 100ml/min, a pressure of 400g/ ^cm2 , a rotation speed of 40rpm, and a polishing time of 15min.

Fine polishing: The second polishing wafer is fine polished to obtain a silicon carbide polishing sheet. The fine polishing sheet uses a damping cloth with a hardness of 65HA. The polishing liquid is an alkaline silicon oxide polishing liquid with an average particle size of 40nm. The alkaline silicon oxide polishing liquid has a pH of 11.5, a concentration of 0.9%, a flow rate of 80ml/min, a pressure of 300g/ ^cm2 , a rotation speed of 35rpm, and a polishing time of 15min.

4. Single chip cleaning

The single wafer cleaning is carried out in sequence using ozone water cleaning for 22 seconds, ultrapure water cleaning for 17 seconds, hydrogen fluoride solution cleaning for 22 seconds, ultrapure water cleaning for 16 seconds, and SC1 cleaning for 43 seconds. The ozone water concentration is 24 ppm, and the HF concentration is 5%.

Comparative Example 2

The substrate is prepared using traditional technology.

The performance of the substrates obtained from the above-mentioned Example 7 to Comparative Example 2 was tested and the results are listed in Table 2.

Since it is difficult to measure the real stress directly, but the stress will affect the surface shape of the substrate and the changes in the surface shape before and after the epitaxy, the inventors found through many studies that a concept of relative stress can be introduced through the above parameters. The model is established by fitting and analyzing a large amount of data as follows:

Formula (1): S = [(A + B) / 2] + [(A _C + B _C ) * 2]

In formula (1), S is the relative stress. The smaller the S value, the smaller the stress of the substrate. A—substrate Bow absolute value, B—substrate Sori value, _AC —absolute value of the change of Bow value before and after epitaxy, _BC —absolute value of the change of Sori value before and after epitaxy.

Table 2 Substrate performance table

In summary, the laser stripping technology used in the present invention can realize automated processing, laser stripping can reduce the processing stress of the wafer, and the relative stress of the processing method of the present invention is not higher than 50. After many experiments, the applicant has reduced the change in the substrate epitaxy before and after the back-end profile by laser stripping cutting, single-chip single-sided thinning, single-chip single-sided CMP and single-chip cleaning. The change in the epitaxy before and after the back-end profile is not higher than 5μm, and the number of wafers produced per unit rod length can be increased, and the number of wafers produced per unit thickness of silicon carbide ingots is increased by 30%. In addition, the efficiency of the laser stripping technology used in the present invention is increased by 2-3 times. The prepared silicon carbide substrate has a Bow of no more than 10μm, a Sori of no more than 25μm, a maximum SFQR of no more than 1μm, a metal ion content on the surface of the silicon carbide substrate of no more than 5×10 ¹⁰ /cm ² , good hydrophilicity, and a contact angle of no more than 10°.

This invention is funded by the special fund of Taishan Industry Leading Talent Project.

The above description is only an embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims (20)

1. A silicon carbide substrate larger than 8 inches, characterized in that the relative stress of the silicon carbide substrate is not higher than 50.
2. The silicon carbide substrate according to claim 1 is characterized in that the relative stress of the silicon carbide substrate is 10~40; further, the relative stress of the silicon carbide substrate is 15~30.
3. The silicon carbide substrate according to claim 1 is characterized in that the SFQR of the silicon carbide substrate is not higher than 2μm, Bow is less than 25μm, Sori is less than 45μm, and the profile change before and after epitaxy is not higher than 10μm.
4. The silicon carbide substrate according to claim 3 is characterized in that the SFQR of the silicon carbide substrate is 1~1.5μm, Bow is less than 15μm, Sori is less than 25μm, and the shape change before and after epitaxy is not higher than 8μm; further, the SFQR of the silicon carbide substrate is not higher than 1μm, the Bow of the silicon carbide substrate is less than 10μm, Sori is less than 15μm, and the shape change before and after epitaxy is not higher than 5μm.
5. The silicon carbide substrate according to claim 1 is characterized in that the silicon carbide substrate is obtained by sequentially thinning, polishing and cleaning a laser cracking exfoliation sheet.
6. The silicon carbide substrate according to claim 5 is characterized in that the curvature is ≤60μm, the warpage is ≤100μm, the damage layer depth is ≤100μm and the maximum surface crack step height does not exceed 70% of the damage layer depth.
7. The silicon carbide substrate according to claim 5 is characterized in that the laser cracking exfoliation sheet is obtained by the following steps:

   S01, detecting the (0001) crystal plane of the silicon carbide ingot to obtain crystal plane position information;

   S02, calculating the angle between the crystal plane position information and the first plane, and determining whether the angle meets the requirement of a preset angle, wherein the first plane is always perpendicular to the first direction where the first laser beam is located;

   S03a, if satisfied, start the first laser beam to scan the silicon carbide ingot to form a to-be-peeled surface containing multiple cracks and extending along the first plane; S03b, if not satisfied, adjust the angle of the silicon carbide ingot and/or the angle of the first direction, and return to step S02 until the angle value meets the requirement of the preset angle value;

   S04, applying vibration to the surface to be peeled off to obtain a silicon carbide peeling sheet.
8. The silicon carbide substrate according to claim 1 is characterized in that the silicon carbide substrate has a hydrophilic surface with a contact angle not higher than 10°; further, the hydrophilic contact angle is not higher than 5°.
9. The silicon carbide substrate according to claim 1, characterized in that the surface metal ion concentration of the silicon carbide substrate is not higher than 5×10 ¹⁰ /cm ² , further, the surface metal ion concentration is not higher than 4×10 ¹⁰ /cm ² ; further, the surface metal ion concentration is not higher than 2×10 ¹⁰ /cm ² .
10. The silicon carbide substrate according to any one of claims 1 to 9 is characterized in that one surface of the silicon carbide substrate has a refractive index of 2.5~2.8; and the other surface of the silicon carbide substrate has a refractive index of 2.6~2.7.
11. A low stress processing method for silicon carbide substrates larger than 8 inches, characterized in that the processing method comprises the following steps:

    S01, detecting the (0001) crystal plane of the silicon carbide ingot to obtain crystal plane position information;

    S02, calculating the angle between the crystal plane position information and the first plane, and determining whether the angle meets the requirement of a preset angle, wherein the first plane is always perpendicular to the first direction where the first laser beam is located;

    S03a, if satisfied, start the first laser beam to scan the silicon carbide ingot to form a to-be-peeled surface containing multiple cracks and extending along the first plane; S03b, if not satisfied, adjust the angle of the silicon carbide ingot and/or the angle of the first direction, and return to step S02 until the angle value meets the requirement of the preset angle value;

    S04, applying vibration to the surface to be peeled off to obtain a silicon carbide peeling sheet;

    S05, thinning at least a portion of the peeling sheet to obtain a thinned sheet;

    S06, polishing the thinned sheet to obtain a polished sheet;

    S07. Clean the polishing sheet to obtain a silicon carbide substrate.
12. According to the low-stress processing method for silicon carbide substrates larger than 8 inches according to claim 11, it is characterized in that the processing method also includes grinding the stripping area left on the silicon carbide ingot in step S04 along the first plane, and performing steps S01 to S04 again to obtain another silicon carbide stripping sheet; or after grinding the stripping area left on the silicon carbide ingot in step S04 along the first plane, directly starting the first laser beam to scan the silicon carbide ingot again to form another surface to be stripped containing multiple cracks and extending along the first plane, and then performing step S04 to obtain another silicon carbide stripping sheet.
13. According to the low stress processing method for silicon carbide substrates larger than 8 inches in claim 11, it is characterized in that step S03 also includes: when the angle value meets the requirement of the preset angle value, starting the second laser beam to scan the silicon carbide ingot in a circumferential direction thereof, and ensuring that the second direction of the second laser beam is always within the first plane.
14. According to claim 11 or 13, the low-stress processing method for silicon carbide substrates larger than 8 inches is characterized in that the average output power of the first laser beam and/or the second laser beam is 0.8~2.0 W, the wavelength is 780~1100 nm, the scanning speed is 300~700 mm/s, the scanning spacing is 0.5~1 mm, the scanning time is 10~40 min, and the number of scans is 2~6 times.
15. According to claim 11, the low stress processing method for silicon carbide substrates larger than 8 inches is characterized in that the step S05 includes the following steps:

    S51, thinning at least a portion of a single side of a single release sheet; and

    S52, thinning at least a portion of the other single side of the single peeling sheet to obtain a thinned sheet.
16. According to the low-stress processing method for silicon carbide substrates larger than 8 inches according to claim 15, it is characterized in that the S51 process and/or the S52 process include a rough grinding process and a fine grinding process performed sequentially, and the surface roughness of the fine grinding process is smaller than the surface roughness of the rough grinding process.
17. The low-stress processing method for silicon carbide substrates larger than 8 inches according to claim 11 is characterized in that the S06 step is implemented by single-wafer single-sided CMP, including polishing the thinned slice in series i times in sequence; the roughness of the chip obtained by the i-th polishing treatment is higher than that of the i+1-th polishing treatment, the hardness of the polishing pad required for the i-th polishing treatment is greater than the hardness of the polishing pad required for the i+1-th polishing treatment, and the pH of the polishing liquid required for the i-th polishing treatment is less than the pH of the polishing liquid required for the i+1-th polishing treatment; wherein i is a natural number and traverses from 1 to n, and n is a natural number and is not less than 2.
18. According to the low stress processing method for silicon carbide substrates larger than 8 inches in size as described in claim 17, it is characterized in that i is 3; the laser-stripped silicon carbide thinning sheet is polished three times in sequence to obtain the desired polished sheet;

    The first polishing is rough polishing to obtain the first polished wafer; the second polishing is then carried out, and the second polished wafer is obtained through the intermediate polishing process; and finally the desired polished wafer is obtained through the third polishing and fine polishing process;

    The rough polishing pad is polyurethane, and the polishing liquid is acidic aluminum oxide polishing liquid; the medium polishing pad is non-woven fabric, and the polishing liquid is neutral manganese oxide or neutral aluminum oxide polishing liquid; the fine polishing pad is damping cloth, and the polishing liquid is alkaline silicon oxide polishing liquid.
19. According to the low-stress processing method for silicon carbide substrates larger than 8 inches according to claim 11, it is characterized in that the S07 step is implemented by single-wafer cleaning, including cleaning with at least two of ozone water, hydrogen fluoride solution, ultrapure water and SC1 cleaning solution.
20. According to the low-stress processing method for silicon carbide substrates larger than 8 inches according to claim 11, it is characterized in that Bow≤60μm, Sori≤100 μm, the damage layer depth≤100 μm and the maximum surface crack step height does not exceed 70% of the damage layer depth.