A silicon carbide substrate of 8 inches or more

Abstract

The application provides a silicon carbide substrate with a size of more than 8 inches, and relates to the field of crystal materials. The silicon carbide substrate has a relative stress of not more than 50. The silicon carbide substrate with a size of more than 8 inches solves the problems of the existing silicon carbide substrate, such as large processing stress, excessive warping and bending, excessively high surface metal ion concentration, and poor hydrophilic effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of crystal materials, in particular to an 8-inch or more silicon carbide substrate. BACKGROUND

[0002] With the development of the industry, the performance requirements for components are getting higher and higher, gradually approaching the physical limit of silicon material. Silicon carbide substrate has incomparable advantages in high voltage, high frequency, high temperature and other fields due to its excellent physical properties compared with Si material. It is currently widely used in power electronics, microwave radio frequency devices and high-end lighting fields.

[0003] The Mohs hardness of silicon carbide crystal is 9.2, second only to diamond, and its physical and chemical properties are stable. It is a typical hard and brittle material, and ultra-precision machining has always been a problem faced by the industry. At present, the industry status is that domestic 6-inch is in the stage of increasing production, 8-inch is in the stage of research and development, foreign 6-inch has been mass-produced, and 8-inch is in the stage of small batch production. 8-inch is the inevitable trend of future development. At present, small batch production of 8-inch substrate has been realized internationally, and domestic substrate manufacturers are also developing 8-inch silicon carbide substrate. With the expansion of the size to 8 inches, the processing problem is more prominent, which seriously restricts the industrialization development of the substrate.

[0004] The existing 8-inch or more substrate has the problems of large processing stress, excessive warpage (Sori) and bending (BOW), high surface metal ion concentration and poor hydrophilic effect. SUMMARY

[0005] In order to solve the problems of large processing stress, excessive warpage and bending, high surface metal ion concentration and poor hydrophilic effect of the existing 8-inch or more silicon carbide substrate.

[0006] The present application provides an 8-inch or more silicon carbide substrate, which has a relative stress of not more than 50.

[0007] Compared with the prior art, the beneficial effects of the present application include at least one of the following contents:

[0008] (1) Compared with the prior art, the 8-inch or more silicon carbide substrate of the present application has smaller processing stress. For example, the relative stress is not more than 30.

[0009] (2) Compared with the prior art, the 8-inch or more silicon carbide substrate of the present application has smaller processing stress and better flatness. For example, the silicon carbide substrate SFQR index is not higher than 2pm, Bow < 25pm, and Sori < 45pm.

[0010] (3) Compared with the prior art, the 8-inch or above silicon carbide substrate has smaller processing stress and hydrophilicity. For example, the hydrophilic contact angle is not higher than 10°.

[0011] (4) Compared with the prior art, the 8-inch or above silicon carbide substrate has low metal ion concentration on the surface. For example, the metal ion concentration is not higher than 5×10 10 / cm 2 . BRIEF DESCRIPTION OF DRAWINGS

[0012] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the application. In the drawings:

[0013] Figure 1 SFQR diagram of the 8-inch or above silicon carbide substrate in the embodiment 3 of the application is shown;

[0014] Figure 2 Bow-Sori diagram of the 8-inch or above silicon carbide substrate in the embodiment 3 of the application is shown. DETAILED DESCRIPTION

[0015] In order to more clearly illustrate the overall concept of the application, the following will be described in detail with reference to the accompanying drawings.

[0016] In the following description, a lot of specific details are set forth in order to facilitate a thorough understanding of the application, however, the application can also be implemented in other ways different from those described herein, therefore, the protection scope of the application is not limited by the specific embodiments disclosed below.

[0017] In addition, in the description of the application, it should be understood that the terms "top", "bottom", "inner", "outer", "axial", "radial", "circumferential" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore, it cannot be understood as a limitation of the application.

[0018] In the present application, unless specifically defined and limited otherwise, the terms "mounting", "connecting", "connecting", "fixing" and the like should be understood broadly, for example, it can be fixed connection, or detachable connection, or integrated; it can be mechanical connection, or electrical connection, or communication; it can be directly connected, or indirectly connected through intermediate medium, or the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0019] In the present application, unless specifically defined and limited otherwise, the first feature is "on" or "under" the second feature, which can be direct contact between the first and second features, or indirect contact between the first and second features through an intermediate medium. In the description of the present application, the description of the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present application, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples.

[0020] In one exemplary embodiment of the present application, the 8-inch or more silicon carbide substrate has a relative stress of not more than 50. For example, the relative stress of the silicon carbide substrate is not more 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, 12 inches.

[0021] Since the true stress is difficult to measure directly, but the stress will affect the surface shape of the substrate and the change of the surface shape before and after the substrate is epitaxied, the inventors have found through repeated research that a relative stress concept is introduced through the above parameters. A model is established by fitting analysis of a large amount of data as follows:

[0022] Formula (1): S=[ (A+B) / 2]+ [ (A C +B C )*2]

[0023] Wherein, S is the relative stress, the smaller the value of S represents the smaller the stress of the substrate. A—substrate Bow absolute value, B—substrate Sori value, A C —change of Bow value before and after epitaxy absolute value, B C —change of Sori value before and after epitaxy absolute value.

[0024] In one exemplary embodiment of the present application, the silicon carbide substrate has a SFQR of no more than 2 μm, a Bow of less than 25 μm, a Sori of less than 45 μm, and a front-to-back surface profile variation of no more than 10 μm. The front-to-back surface profile variation of no more than 10 μm refers to a Bow variation of no more than 10 μm and a Sori variation of no more than 10 μm.

[0025] In one exemplary embodiment of the present application, the silicon carbide substrate has a SFQR of 1 to 1.5 μm, a Bow of less than 15 μm, a Sori of less than 25 μm, and a front-to-back surface profile variation of no more than 8 μm. Preferably, the silicon carbide substrate has a SFQR of no more than 1 μm, a Bow of less than 10 μm, a Sori of less than 15 μm, and a front-to-back surface profile variation of no more than 5 μm.

[0026] In the present application, SFQR (Site flatness front least-squares range) refers to local flatness, representing the maximum difference in thickness within a unit planar area. Bow refers to the degree of curvature, representing the concave or convex degree of the wafer center relative to a reference plane. Sori refers to the warping of the front surface based on the least squares method, representing the deviation degree of the substrate as a whole relative to the median plane. In the present application, the front-to-back surface profile variation refers to the Bow variation and the Sori variation before and after epitaxy.

[0027] In one exemplary embodiment of the present application, 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°. In the present application, the hydrophilicity refers to a contact angle of no more than 10°.

[0028] In one exemplary embodiment of the present application, the silicon carbide substrate has a surface metal ion concentration of no more than 5 x 10 10 cm 2 -1; further, the surface metal ion concentration is no more than 4 x 10 10 cm 2 -1; preferably, the surface metal ion concentration is no more than 2 x 10 10 cm 2 -1.

[0029] In one exemplary embodiment of the present application, one surface of the silicon carbide substrate has a refractive index of 2.5 to 2.8; the other surface of the silicon carbide substrate has a refractive index of 2.6 to 2.7.

[0030] In another exemplary embodiment of the present application, the silicon carbide substrate is obtained by thinning, polishing and cleaning a laser-induced cleavage wafer, and the laser-induced cleavage wafer has a relative stress of 20-30. The size of the wafer is not less than 8 inches, and the damage layer depth of the wafer is not higher than 110 μm; further, the damage layer depth of the wafer is not higher than 90 μm; preferably, the damage layer depth of the wafer is 50-80 μm. The Bow of the wafer is less than 70 μm, and the Sori is less than 120 μm; further, the Bow of the wafer is less than 40 μm, and the Sori is less than 90 μm. The maximum surface crack step height is not more than 70% of the damage layer depth. The surface crack step height refers to the micro-cracks on the surface of the wafer after the laser-induced cleavage. In this process, due to the angle deviation of each micro-crack and the cleavage plane, a crack step is formed repeatedly in the laser-induced cleavage direction.

[0031] In addition, the surface roughness of the thinned wafer obtained by thinning is not higher than 10 nm, and further, the surface roughness of the thinned wafer is not higher than 7 nm. The surface roughness of the polished wafer obtained by polishing is not higher than 0.2 nm; further, the surface roughness of the polished wafer obtained by polishing is not higher than 0.1 nm,

[0032] In the laser single wafer cleavage for the silicon carbide substrate with a size of more than 8 inches, the wavelength is 800-1200 nm, the scanning pitch is 0.5-5 mm, the ultrasonic cleavage frequency is 50-500 KHZ, and the scanning time is 10-40 min.

[0033] The laser-induced cleavage wafer of the present application can be obtained by laser-induced cleavage and vibration cleavage, for example, by the steps S01-S04, wherein,

[0034] S01, detecting the (0001) crystal plane of the silicon carbide ingot to obtain crystal plane position information;

[0035] S02, calculating the included angle value between the crystal plane position information and a first plane, and determining whether the included angle value meets the preset included angle value requirement, wherein the first plane is always perpendicular to a first direction in which a first laser beam is located;

[0036] S03a, if yes, the first laser beam is started to scan the silicon carbide ingot to form a to-be-cleaved surface containing a plurality of cracks and extending along the first plane; S03b, if no, the angle of the silicon carbide ingot and / or the angle of the first direction are adjusted, and the step S02 is returned until the included angle value meets the preset included angle value requirement;

[0037] S04, applying vibration to the to-be-cleaved surface to obtain a silicon carbide wafer.

[0038] The steps S01 to S04 can also be described in detail as follows:

[0039] S01, detecting a (0001) crystal face of the silicon carbide crystal ingot to obtain crystal face position information.

[0040] Specifically, the crystal face detection can be performed by using the principle of Bragg diffraction. That is, the silicon carbide surface crystal is composed of crystal face families A, B and C, and the interplanar spacing is d. When laser rays are projected to the silicon carbide crystal at a grazing angle α, the scattering of the lattices on the crystal face A and the scattering of the lattices on the crystal faces B and C interfere with each other. For the same layer of laser scattering rays, when the included angle between the scattering rays and the crystal face is equal to the grazing angle, the rays produce constructive interference in this direction. For the same layer of scattering rays, when the included angle between the scattering rays and the crystal face is equal to the grazing angle, the rays produce constructive interference in this direction. For different layers of scattering rays, when the optical path difference is an integer multiple of the wavelength, the scattering rays of each face strengthen each other to form a very large light intensity. By using this principle, the crystal face detection is completed, and the crystal face information is obtained.

[0041] S02, calculating an included angle value between the crystal face position information and a first plane, and judging whether the included angle value meets a preset included angle value requirement, wherein the first plane is always perpendicular to a first direction in which the first laser beam is located.

[0042] Specifically, the first plane is a plane in which the silicon carbide crystal ingot is located and which is substantially perpendicular to the first laser beam. The first direction is the direction in which the first laser beam is irradiated. The included angle value is the included angle between the (0001) crystal face of the silicon carbide crystal ingot and the first plane of the silicon carbide crystal ingot. The preset included angle value can be a certain value selected in the range of 0-10°. Further, the preset included angle value can be a certain value selected in the range of 0.5-3.5° or 4.5-7°. For example, it can also be 0° or 4°. The requirement of the preset included angle value can be equal to the preset included angle value, or can be within 10% of the preset included angle value, for example, 4±0.1°.

[0043] S03a, if yes, starting the first laser beam to scan the silicon carbide crystal ingot to form a to-be-peeled surface containing a plurality of cracks and extending along the first plane.

[0044] Specifically, if the included angle between the (0001) crystal face of the silicon carbide crystal ingot and the first plane of the silicon carbide crystal ingot is within the preset included angle value range, the first laser beam is started to perform laser scanning on the silicon carbide crystal ingot to form a to-be-peeled surface containing a plurality of cracks and extending along the first plane. The average output power of the first laser beam can be 0.8-3.5 W, the wavelength can be 780-1100 nm, the scanning speed can be 300-700 mm / s, the scanning pitch can be 0.1-0.5 mm, the scanning time can be 10-40 min, and the scanning times can be 2-6 times.

[0045] S03b, if not, adjust the angle of the silicon carbide crystal ingot and / or the angle of the first direction, and return to S02, until the included angle value meets the requirement of the preset included angle value, then proceed to S03a.

[0046] Specifically, if the angle between the (0001) plane of the silicon carbide crystal ingot and the first plane of the silicon carbide crystal ingot is not within the preset included angle value range, the angle of the silicon carbide crystal ingot can be adjusted, i.e. the (0001) plane of the silicon carbide crystal ingot is adjusted, or the first direction in which the first laser beam is located can be adjusted. After adjustment, return to S02 to calculate the included angle value and determine whether it meets the preset included angle value. If it does, proceed to S03a; if it does not, continue to adjust the included angle value until it meets the preset included angle value.

[0047] S04, apply vibration to the to-be-peeled surface to obtain a silicon carbide peeled sheet.

[0048] Vibration is applied to the to-be-peeled surface in S03a to make the to-be-peeled surface extend along the crack or break, obtaining a peeled sheet. The vibration can be achieved by mechanical vibration, ultrasonic method, etc. For example, for the ultrasonic method, the frequency of the ultrasonic wave can be 100-150 KHZ, the ultrasonic time can be 10-60 s, and the emission mode can be continuous wave or pulse wave.

[0049] The thickness of the silicon carbide peeled sheet obtained by the above processing method can be 100-1000 μm. The size is not less than 8 inches, Bow≤60 μm, Sori≤100 μm, the damage layer depth is ≤100 μm, and the maximum value of the surface crack step height is not more than 70% of the damage layer depth.

[0050] In addition, in order to solve the problem of edge collapse, the step S03 is further provided with the following step based on the steps S01 to S04: in the case that the included angle value meets the requirement of the preset included angle value, the second laser beam is used to scan the silicon carbide ingot in the circumferential direction of the silicon carbide ingot, and the second direction where the second laser beam is located is ensured to be always parallel to the first plane. The cracking direction of the first laser beam is perpendicular to the laser incidence direction, and the cracking direction of the second laser beam is along the laser incidence direction, which is adjusted by spot shaping. The peeling of the circumferential edge of the silicon carbide ingot is facilitated, and the damage layer depth and the surface step crack depth can be further optimized. The second laser head is arranged to be capable of linkage control with the first laser head, and the two laser heads are used to successively peel the silicon carbide ingot. The first laser head generates the first laser beam to peel the area of the silicon carbide ingot except the circumferential edge, and the second laser head generates the 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 are controlled to ensure that the two are in the same plane to generate cracks. Compared with the peeling result of only the first laser beam, the second laser beam can optimize the damage layer depth and the surface step crack depth by at least 10%. The average output power of the second laser beam is 0.3-0.5 times the average output power parameter of the first laser beam, the wavelength is 780-1100 nm, the scanning speed is 0.3-0.5 times the scanning speed parameter of the first laser beam, the scanning interval is 0.1-0.5 mm, the scanning time is 10-40 min, and the scanning times are 2-6.

[0051] Then at least a part of one single face of the single peeled sheet is thinned and / or at least a part of the other single face of the single peeled sheet is thinned, thereby obtaining a thinned sheet. The thinning includes coarse grinding and fine grinding, and the roughness of the fine grinding is smaller than that of the coarse grinding. The thinned sheet is sequentially subjected to single sheet single face coarse polishing, middle polishing and fine polishing to obtain a required polished sheet.

[0052] In addition, the 8-inch or more silicon carbide substrate of the present application is subjected to single sheet single face chemical mechanical polishing. The coarse polishing uses polyurethane and acidic alumina polishing liquid; the middle polishing uses non-woven fabric and manganese oxide polishing liquid or non-woven fabric and alumina polishing liquid; and the fine polishing uses damping cloth and alkaline silicon oxide polishing liquid.

[0053] Example 1

[0054] The present application is an 8-inch silicon carbide substrate, the relative stress of which is 16.8, the SFQR is 1.064 μm, the Bow is 2.346 μm, the Sori is 6.953 μm, the Bow change before and after epitaxy is 1.269 μm, the Sori change before and after epitaxy is 4.789 μm, the hydrophilic contact angle is 6°, and the surface metal ion concentration is less than 1.9 x 1010 cm-2 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.

[0055] Example 2

[0056] The present application is an 8-inch silicon carbide substrate with a relative stress of 32.8, SFQR of 1.211 μm, Bow of 6.762 μm, Sori of 14.865 μm, Bow change before and after epitaxy of 3.281 μm, Sori change before and after epitaxy of 7.691 μm. The hydrophilic contact angle is 9°, and the surface metal ion concentration is less than 3.7 x 10 10 cm-2 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.

[0057] Example 3

[0058] The present application is an 8-inch silicon carbide substrate with a relative stress of 33.8, SFQR of 1.395 μm, Bow of 8.256 μm, Sori of 13.314 μm, Bow change before and after epitaxy of 4.283 μm, Sori change before and after epitaxy of 7.211 μm. The hydrophilic contact angle is 10°, and the surface metal ion concentration is less than 2.7 x 10 10 cm-2 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 diagram of Example 3 is shown in Figure 1 The Bow-Sori diagram of the silicon carbide substrate is shown in Figure 2

[0059] Comparative Example 1

[0060] Comparative Example 1 is a performance test of an existing 8-inch silicon carbide substrate.

[0061] Table 1: Silicon carbide substrate performance table

[0062]

[0063] Referring to Table 1, from Example 1, Example 2, and Example 3, it can be seen that the relative stress of the 8-inch or more silicon carbide substrate of the present application is not higher than 50, indicating that the processing stress of the present application is low. In addition, while the processing stress of the present application is low, the substrate has good flatness, hydrophilicity, and low surface metal ion concentration.

[0064] ​Compared with Comparative Example 1, Example 1 showed an 82% reduction in relative stress, a 0.52 μm reduction in SFQR, a significant reduction in Bow and Sori, a significant reduction in the amount of change before and after epitaxy, a contact angle controlled within 10° to exhibit hydrophilicity, and a two-order-of-magnitude reduction in ionic contamination concentration.

[0065] This invention was supported by the Taishan Industrial Leading Talent Project Special Fund.

[0066] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A silicon carbide substrate of 8 inches or larger, characterized in that, The relative stress of the silicon carbide substrate is not higher than 50. The silicon carbide substrate has an SFQR of no more than 2 μm, a Bow of no more than 25 μm, a Sori of no more than 45 μm, and a profile change of no more than 10 μm before and after epitaxy.

2. The silicon carbide substrate according to claim 1, characterized in that, The relative stress of the silicon carbide substrate is 10 to 40.

3. The silicon carbide substrate according to claim 2, characterized in that, The relative stress of the silicon carbide substrate is 15–30.

4. The silicon carbide substrate according to claim 1, characterized in that, The silicon carbide substrate has an SFQR of 1–1.5 μm, a Bow of <15 μm, a Sori of <25 μm, and a surface profile change of no more than 8 μm before and after epitaxy.

5. The silicon carbide substrate according to claim 4, characterized in that, The silicon carbide substrate SFQR is no higher than 1 μm, the silicon carbide substrate Bow is less than 10 μm, Sori is less than 15 μm, and the surface profile change before and after epitaxy is no higher than 5 μm.

6. The silicon carbide substrate according to claim 1, characterized in that, The silicon carbide substrate is obtained by sequentially thinning, polishing, and cleaning a laser-induced cracking strip.

7. The silicon carbide substrate according to claim 6, characterized in that, The size of the release strip is not less than 8 inches, the curvature is ≤60μm, the warp is ≤100μm, 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.

8. The silicon carbide substrate according to claim 6, characterized in that, The laser-induced cracking release sheet is obtained through the following steps: S01, detecting the (0001) crystal plane of the silicon carbide ingot to obtain the 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 requirements of the preset angle value, wherein the first plane and the first direction where the first laser beam is located are always perpendicular; S03a, if satisfied, starting the first laser beam to scan the silicon carbide ingot to form a surface to be released containing multiple cracks and extending along the first plane; S03b, if not satisfied, adjusting the angle of the silicon carbide ingot and / or the angle of the first direction, and returning to step S02 until the angle value meets the requirements of the preset angle value; S04, applying vibration to the surface to be released to obtain the silicon carbide release sheet.

9. The silicon carbide substrate according to claim 1, characterized in that, The silicon carbide substrate has a hydrophilic surface with a contact angle of no more than 10°.

10. The silicon carbide substrate according to claim 9, characterized in that, The hydrophilic contact angle is no higher than 5°.

11. 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 × 10⁻⁶. 10 pcs / cm 2 .

12. The silicon carbide substrate according to claim 11, characterized in that, The surface metal ion concentration is not higher than 4 × 10⁻⁶. 10 pcs / cm 2 .

13. The silicon carbide substrate according to claim 12, characterized in that, The surface metal ion concentration is not higher than 2×10⁻⁶. 10 pcs / cm 2 .

14. The silicon carbide substrate according to any one of claims 1 to 13, characterized in that, One surface of the silicon carbide substrate has a refractive index of 2.5 to 2.8; the other surface of the silicon carbide substrate has a refractive index of 2.6 to 2.7.

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