A method for thinning a large-size SiC wafer

Abstract

The application discloses a thinning processing method of a large-size SiC wafer. In the method, solid wax is uniformly applied on a ceramic disc, and a product to be thinned is fixed on the ceramic disc by the wax to complete the bonding work. The bonding mode of the traditional thinning process is changed, the Bow value and the Warp value of the product are not changed during the bonding, the Bow value and the Warp value of the product caused by processing stress are effectively eliminated by the wax, and the Bow value and the Warp value of the product are effectively controlled. The yield of the product is improved, the performance of the product is effectively improved in batch processing, and the wavelength yield and STD of the processed substrate can be better characterized in the epitaxial process.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and more particularly to a method for thinning silicon carbide wafers. Background Technology

[0002] Silicon carbide (SiC) is an important third-generation semiconductor material. Compared with traditional semiconductor materials such as Si and GaAs, it has great application prospects in high temperature, high frequency, high power, optoelectronics and radiation resistance due to its wide bandgap, high critical breakdown electric field, high thermal conductivity and high carrier saturation drift velocity.

[0003] Silicon carbide (SiC) is a group IV-IV compound semiconductor material composed of carbon and silicon. It exhibits various allotropic types and is the second hardest substance in the world, demonstrating excellent thermal, chemical, and mechanical stability. Physically, SiC possesses high hardness, high wear resistance, high thermal conductivity, high thermal stability, and good heat dissipation. Chemically, a thin silicon oxide film easily forms on the SiC surface to prevent further oxidation, but this oxide film rapidly oxidizes at high temperatures. Typical structures of silicon carbide can be categorized into two types: one is the cubic silicon carbide crystal form with a zincblende structure, known as 3C-SiC or β-SiC, where 3 refers to the number of days in the periodic table; the other is a large-period structure with hexagonal or rhombic shapes, typically including 6H-SiC, 4H-SiC, and 15R-SiC, collectively referred to as α-SiC. 4H-SiC and 6H-SiC are two materials required for semiconductors. Silicon carbide has similar properties to other semiconductor materials. The saturation electron velocity of 4H-SiC is twice that of Si, thus providing SiC devices with higher current density and higher voltage, and it is often used as a silicon carbide power device. The biggest difference between 6H-SiC and 4H-SiC is that the electron mobility of 4H-SiC is twice that of 6H-SiC, because 4H-SiC has a higher horizontal axis (a-aixs) mobility. During the growth of silicon carbide crystals, it is necessary to precisely control parameters such as the silicon-to-carbon ratio, growth temperature gradient, crystal growth rate, and gas flow pressure; otherwise, polymorphic inclusions are easily generated, resulting in unqualified crystals.

[0004] Silicon carbide is still in the early stages of development, and the yield of crystal growth is still relatively low, usually less than 50%. This makes it difficult to control the crystal stress after crystal growth, which has a significant impact on the actual processing stability.

[0005] Silicon carbide has a high hardness, second only to diamond in the world. This hardness not only gives it characteristics such as high thermal conductivity, high breakdown electric field, and high radiation resistance, but also brings considerable difficulty to its processing. Some traditional processing methods simply cannot process this material, making it difficult to maintain high precision in its processing.

[0006] Silicon carbide is a very special semiconductor material. Like a magnet, it is a bipolar material. In any case, one side of silicon carbide is a C pole and the other side is a Si pole, and the two poles have different hardness. As a result, the Bow / Warp value of silicon carbide wafers is very easy to change during processing.

[0007] Traditional thinning processes using grinding wheels involve vacuum adsorption of microporous ceramics or other methods to completely bond the wafer to a ceramic disc. These methods generally offer little to no repair of bow and warp values. This is because during bonding, external force is used to flatten the product onto the ceramic disc, flattening its original bow and warp values. Once the force is released after processing, the bow and warp values ​​rebound. Therefore, traditional thinning processes have poor bow and warp repair capabilities. Currently, the market demands increasingly higher yields, bow (bend) values, and warp values ​​for silicon carbide wafers, and there is a strong expectation for the development of a processing method for large-size, high-performance silicon carbide wafers.

[0008] In actual production, due to inconsistent stress in silicon carbide crystals, wire cutting may occasionally result in excessively high BOW and WARP values, leading to the scrapping of silicon carbide substrate wafers. BOW and WARP values ​​are important parameters of silicon carbide wafers. Therefore, our development of this thinning process can effectively control the BOW and WARP values ​​of the product.

[0009] During the research and development process, the invention patent "A Method for Controlling the BOW Value of Polished Products" (patent publication number CN110722692A) was explored. This invention patent mainly addresses the processing method for controlling the BOW value of LED sapphire substrates during double-sided polishing. After thorough understanding, it was discovered that:

[0010] 1. In the processing of LED sapphire substrates, the back side of the substrate is required to be roughened, that is, the substrate is a single polished product (only one side is polished and the other side is ground), while silicon carbide substrate wafers require double-sided polishing. Therefore, this method is not suitable for the processing of silicon carbide substrate wafers.

[0011] 2. Due to the inconsistent rotation speeds of the upper and lower grinding discs, the upper disc rotation speed is usually 1 / 3 of the lower disc rotation speed. The thickness reduction on both sides is uneven, and it is impossible to calculate and process accurately. Therefore, the reduction of BOW value can only be roughly handled and is not very targeted, so the effectiveness is not high.

[0012] 3. Sapphire has no polarity, and epitaxial growth can be performed on both sides. Silicon carbide wafers have a carbon side and a silicon side (bipolarity, similar to a magnet with north and south poles). Epitaxial growth is generally performed using the silicon side. Therefore, this patented method cannot control the BOW value of silicon carbide substrate processing by distinguishing between the two sides. The silicon carbide substrate needs to be specifically removed for the BOW value of the silicon side in order to better match the epitaxial growth requirements. Summary of the Invention

[0013] The technical problem this invention aims to solve is to overcome the shortcomings of existing technologies and provide a thinning process for large-size SiC wafers. This invention develops a single-sided thinning process specifically designed for controlling the BOW (Browser Overhead) value of bipolar products like silicon carbide wafers. This method can more effectively reduce the BOW value of the silicon carbide substrate, better control the surface profile of the silicon carbide wafer, and thus achieve surface profile consistency, which can better match the consistency of epitaxial batch growth.

[0014] The objective of this invention is achieved by at least one of the following technical solutions.

[0015] A method for thinning large-size silicon carbide wafers includes the following steps:

[0016] S1. The silicon carbide wafer is faceted, with the carbon facet of the silicon carbide wafer facing the U facet of the cassette and the silicon facet facing the H facet of the cassette. The surface parameters of the silicon carbide wafer are measured to determine the surface parameters of the silicon carbide wafer before processing.

[0017] S2. Place the measured silicon carbide wafers in the planetary wheel of the grinding machine in sequence for thinning.

[0018] S3. Chamfer the polished silicon carbide wafer;

[0019] S4. After beveling, the silicon carbide wafer is bonded to the ceramic disk using wax: Place the ceramic disk on the heating table and apply solid wax evenly to the ceramic disk. Place the silicon carbide wafer on the ceramic disk with the carbon side facing up. Fill the gaps between the silicon carbide wafer and the ceramic disk with wax. Since the silicon carbide wafer is curved and warped, the larger curved areas are filled with wax. During processing, the warped and bent areas will not be deformed by pressure, making them impossible to remove. Then, use a cooling plate with internal cooling water to cool the ceramic disk for a set time until the ceramic disk temperature drops to the set temperature. The silicon carbide wafer is fixed to the ceramic disk by the wax, completing the bonding process.

[0020] S5. Install the ceramic disk with the silicon carbide wafer attached onto the thinning machine to thin the carbon surface of the silicon carbide wafer.

[0021] S6. Remove the thinned silicon carbide wafer from the ceramic plate: Remove the thinned ceramic plate from the thinning machine, place it on the heating table, heat for a set time, wait for the wax to melt, and remove the wafer from the ceramic plate.

[0022] S7. Flip the silicon carbide wafer so that the silicon side of the silicon carbide wafer faces upward, and repeat steps S4 to S6 to thin the silicon side of the silicon carbide wafer to obtain the desired silicon carbide wafer product.

[0023] Furthermore, in step S1, the parameters measured include the product's BOW (bending), WARP (warping), and TTV (thickness uniformity).

[0024] Further, in step S1, the surface parameters of the silicon carbide wafer are measured using a surface profile inspection device (FRT) or a similar sorting device.

[0025] Furthermore, in step S2, the parameters of the grinding mill are set as follows: rotation speed 10-35 rpm, pressure 10-100 g / cm³. 2 The removal amount is 30-80um, and the processing temperature is 18-24℃.

[0026] Furthermore, in step S3, a diamond chamfering grinding wheel of 600#-2000# is used to process a diameter of 150~200±0.2mm, a processing speed of 3-8mm / s, and a processing temperature of 20±2℃.

[0027] Furthermore, in step S4, the temperature of the heating platform is 100-180℃; the temperature of the cooling plate is 10-18℃; the ceramic plate is cooled using the cooling plate for 5-15 minutes, so that the temperature of the ceramic plate is reduced to below 20℃.

[0028] Furthermore, in step S5, an 800#-15000# diamond grinding wheel is used with a feed rate of 0.1-0.8um / s, a wheel speed of 2000-7000rpm, a worktable speed of 100-800rpm, and a processing temperature of 20±2℃ to thin the carbon surface of the silicon carbide wafer.

[0029] Furthermore, in step S5, the thinning process takes 7-15 minutes.

[0030] Furthermore, in step S6, the temperature of the heating platform is 120-200℃.

[0031] Furthermore, in step S6, the heating time is 5-15 minutes.

[0032] Compared with the prior art, the advantages of the present invention are as follows:

[0033] (1) This invention changes the bonding method of the traditional thinning process so that the Bow value and Warp value of the product are not changed during bonding. In this way, the Bow value and Warp value of the product caused by processing stress are effectively eliminated by the thickness reduction, and the Bow value and Warp value of the product are effectively controlled. This not only improves the yield of the product, but also effectively improves the performance of the product in batch processing. In the epitaxial process, the wavelength yield and STD of the substrate after processing can be better characterized. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the process before processing a method for obtaining large-size silicon carbide wafers in an embodiment of the present invention;

[0035] Figure 2 This is a schematic diagram of the process after processing a method for obtaining large-size silicon carbide wafers in an embodiment of the present invention;

[0036] Figure 3 This is a flowchart illustrating the steps of a method for obtaining large-size silicon carbide wafers according to an embodiment of the present invention. Detailed Implementation

[0037] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0038] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0039] Example:

[0040] A method for thinning large-size silicon carbide wafers includes the following steps:

[0041] S1. The silicon carbide wafer is faceted, with the carbon facet of the silicon carbide wafer facing the U facet of the cassette and the silicon facet facing the H facet of the cassette. The surface parameters of the silicon carbide wafer are measured to determine the surface parameters of the silicon carbide wafer before processing.

[0042] The parameters measured include the product's BOW (bending), WARP (warping), and TTV (thickness uniformity).

[0043] The surface parameters of silicon carbide wafers are measured using a surface profile inspection device (FRT) or a similar sorting device.

[0044] S2. Place the measured silicon carbide wafers in the planetary wheel of the grinding machine in sequence for thinning.

[0045] The parameters for the grinding mill are set as follows: rotation speed 10-35 rpm, pressure 10-100 g / cm³. 2 The removal amount is 30-80um, and the processing temperature is 18-24℃.

[0046] S3. Chamfer the polished silicon carbide wafer;

[0047] Use a 600#-2000# diamond chamfering grinding wheel to process diameters of 150~200±0.2mm, at a processing speed of 3-8mm / s and a processing temperature of 20±2℃.

[0048] S4. After beveling, the silicon carbide wafer is bonded to the ceramic disk using wax: Place the ceramic disk on the heating table and apply solid wax evenly to the ceramic disk. Place the silicon carbide wafer on the ceramic disk with the carbon side facing up. Fill the gaps between the silicon carbide wafer and the ceramic disk with wax. Since the silicon carbide wafer is curved and warped, the larger curved areas are filled with wax. During processing, the warped and bent areas will not be deformed by pressure, making them impossible to remove. Then, use a cooling plate with internal cooling water to cool the ceramic disk for a set time until the ceramic disk temperature drops to the set temperature. The silicon carbide wafer is fixed to the ceramic disk by the wax, completing the bonding process.

[0049] The temperature of the heating plate is 100-180℃; the temperature of the cooling plate is 10-18℃; use the cooling plate to cool the ceramic plate for 5-15 minutes, so that the temperature of the ceramic plate is reduced to below 20℃.

[0050] S5. Install the ceramic disk with the silicon carbide wafer attached onto the thinning machine to thin the carbon surface of the silicon carbide wafer.

[0051] Using 800#-15000# diamond grinding wheels, with a feed rate of 0.1-0.8um / s, a wheel speed of 2000-7000rpm, a table speed of 100-800rpm, and a processing temperature of 20±2℃, the carbon surface of silicon carbide wafers is thinned.

[0052] The thinning process takes 7-15 minutes.

[0053] S6. Remove the thinned silicon carbide wafer from the ceramic plate: Remove the thinned ceramic plate from the thinning machine, place it on the heating table, heat for a set time, wait for the wax to melt, and remove the wafer from the ceramic plate.

[0054] The temperature of the heating table is 120-200℃, and the heating time is 5-15 minutes.

[0055] S7. Flip the silicon carbide wafer so that the silicon side of the silicon carbide wafer faces upward, and repeat steps S4 to S6 to thin the silicon side of the silicon carbide wafer to obtain the desired silicon carbide wafer product.

[0056] As shown in Table 1, in the 10 embodiments given, by comparing the measured values ​​in step (1) with the data after thinning, it can be seen that the thinning process can effectively improve the Bow / Warp value after Grinding. According to statistics, the BOW of silicon carbide products can be reduced by 13 to 16 micrometers. This process can effectively reduce the BOW value of the product.

[0057] Table 1 Comparison of values ​​before and after thinning process

[0058]

[0059]

[0060] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for thinning large-size silicon carbide wafers, characterized in that, Includes the following steps: S1. The silicon carbide wafer is faceted, with the carbon facet of the silicon carbide wafer facing the U facet of the cassette and the silicon facet facing the H facet of the cassette. The surface parameters of the silicon carbide wafer are measured to determine the surface parameters of the silicon carbide wafer before processing. S2. Place the measured silicon carbide wafers in the planetary wheel of the grinding machine in sequence for thinning. S3. Chamfer the polished silicon carbide wafer; S4. After the beveling is completed, the silicon carbide wafer is bonded to the ceramic plate using wax: Place the ceramic plate on the heating table, apply solid wax evenly to the ceramic plate, place the silicon carbide wafer on the ceramic plate with the carbon side facing up, and fill the gap between the silicon carbide wafer and the ceramic plate with wax; then use a cooling plate with internal cooling water to cool the ceramic plate for a set time, so that the temperature of the ceramic plate drops to the set temperature, and the silicon carbide wafer is fixed to the ceramic plate by the wax, completing the bonding work; S5. Install the ceramic disk with the silicon carbide wafer attached onto the thinning machine to thin the carbon surface of the silicon carbide wafer. S6. Remove the thinned silicon carbide wafer from the ceramic plate: Remove the thinned ceramic plate from the thinning machine, place it on the heating table, heat for a set time, wait for the wax to melt, and remove the wafer from the ceramic plate. S7. Flip the silicon carbide wafer so that the silicon side of the silicon carbide wafer faces upward, and repeat steps S4 to S6 to thin the silicon side of the silicon carbide wafer to obtain the desired silicon carbide wafer product.

2. The method for thinning large-size silicon carbide wafers according to claim 1, characterized in that, In step S1, the measured parameters include the product's BOW, WARP, and TTV.

3. The method for thinning large-size silicon carbide wafers according to claim 1, characterized in that, In step S1, the surface profile parameters of the silicon carbide wafer are measured using a surface profile inspection device (FRT).

4. The method for thinning large-size silicon carbide wafers according to claim 1, characterized in that, In step S2, the parameters of the grinder are set as follows: rotation speed 10-35 rpm, pressure 10-100 g / cm³. 2 The removal amount is 30-80um, and the processing temperature is 18-24℃.

5. The method for thinning large-size silicon carbide wafers according to claim 1, characterized in that, In step S3, a diamond chamfering grinding wheel of 600#-2000# is used to process a diameter of 150~200±0.2mm, a processing speed of 3-8mm / s, and a processing temperature of 20±2℃.

6. The method for thinning large-size silicon carbide wafers according to claim 1, characterized in that, In step S4, the temperature of the heating platform is 100-180℃; the temperature of the cooling plate is 10-18℃; the ceramic plate is cooled using the cooling plate for 5-15 minutes until the temperature of the ceramic plate is reduced to below 20℃.

7. The method for thinning large-size silicon carbide wafers according to claim 1, characterized in that, In step S5, an 800#-15000# diamond grinding wheel is used with a feed rate of 0.1-0.8um / s, a wheel speed of 2000-7000rpm, a worktable speed of 100-800rpm, and a processing temperature of 20±2℃ to thin the carbon surface of the silicon carbide wafer.

8. The method for thinning large-size silicon carbide wafers according to claim 1, characterized in that, In step S5, the thinning process takes 7-15 minutes.

9. A method for thinning large-size silicon carbide wafers according to claim 1, characterized in that, In step S6, the temperature of the heating platform is 120-200℃.

10. A method for thinning large-size silicon carbide wafers according to claim 1, characterized in that, In step S6, the heating time is 5-15 minutes.

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