Thinning processing method of large-size SiC wafer

Abstract

The invention discloses a thinning processing method of a large-size SiC wafer. According to the method, during thinning processing, solid wax is evenly smeared on a ceramic plate, a product needing to be thinned is fixed to the ceramic plate through the wax to complete attaching work, in this way, the attaching mode of a traditional thinning process is changed, the Bow value and the Warp value of the product are not changed during attaching, and therefore the product can be attached to the ceramic plate. According to the method, the Bow value and the Warp value, generated by processing stress, of a product are effectively eliminated by removing the thickness of the wax, the Bow value and the Warp value of the product are effectively controlled, the yield of the product is improved, meanwhile, the performance of the product can be effectively improved in batch processing, and the wavelength yield and the STD after the substrate is processed can be better represented in the epitaxial process.

Description

Technical Field

[0001] The invention relates to the field of semiconductor technology, and in particular to a method for thinning a silicon carbide wafer. Background Art

[0002] Silicon carbide (SiC) material 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 is a group IV-IV compound semiconductor material composed of carbon and silicon. It has a variety of allotropic types and is the second hardest material in the world. It is very stable in terms of heat, chemistry and mechanics. In terms of physical properties, SiC has the characteristics of high hardness, high wear resistance, high thermal conductivity, high thermal stability and good heat dissipation. In terms of chemical properties, a silicon oxide film is easily formed on the surface of SiC to prevent further oxidation, but the oxide film will rapidly undergo oxidation reaction at high temperatures. The typical structure of silicon carbide can be divided into two categories. One is a cubic silicon carbide crystal form with a zinc blende structure, called 3C-SiC or B-SiC, where 3 refers to the number of faces in the periodic table sequence. The other is a large periodic structure of a hexagonal or rhombus structure, among which typical ones are 6H-SiC, 4H-SiC, 15R-SiC, etc., collectively referred to as a-SiC. Among them, 4H-SiC and 6H-SiC are materials required for two semiconductors. Silicon carbide has similar properties to other semiconductor materials. The saturated electron velocity of 4H-SiC is twice that of Si, which provides SiC components with higher current density and higher voltage. It is often used as silicon carbide power devices. 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. In the process of silicon carbide body growth, it is necessary to precisely control parameters such as silicon-carbon ratio, growth temperature gradient, crystal growth rate, and airflow pressure, otherwise polymorphic inclusions are likely to occur, resulting in unqualified crystals.

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

[0005] Silicon carbide has a high hardness, which is second only to diamond in the world. This hardness not only has the characteristics of high thermal conductivity, high breakdown electric field, and high radiation resistance, but also brings considerable difficulty to processing. Some traditional processing methods cannot process this material at all, making it difficult to maintain high-precision processing of this material;

[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 hardness of the two poles is different. Therefore, the Bow / Warp value of silicon carbide wafers is very easy to change during processing.

[0007] The traditional grinding wheel thinning process uses microporous ceramic vacuum adsorption processing or other methods to completely fit on the ceramic disc. This processing method generally has no repair effect on the Bow value and Warp value, because when fitting, we use external force to flatten the product and fit it on the ceramic disc, so that the original Bow value and Warp value of the product are flattened by the external force. After the processing is completed and the external force is released, the Bow value and Warp value of the product will rebound. Therefore, the traditional thinning process has poor repair ability for Bow and Warp. At present, the market has put forward higher and higher requirements for the growth yield, BOW (bend), and WARP (warpage) of silicon carbide wafers, and is particularly looking forward to developing a processing method for large-size, high-performance siliconized silicon wafers.

[0008] In actual production, due to inconsistent stress of silicon carbide crystals, wire cutting processing occasionally results in large BOW and WARP values, which leads to the scrapping of silicon carbide substrate wafers. BOW and WARP values ​​are important parameters of silicon carbide wafers, so we have developed this thinning processing method to 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 grinding products" was developed. The patent authorization announcement number is CN110722692A. This invention patent is mainly aimed at the processing method of controlling the BOW value of products in the double-sided grinding of LED sapphire substrates. After a full understanding, it was found that:

[0010] 1. In the processing of LED sapphire substrate, 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 the silicon carbide substrate wafer is double-sided polished. Therefore, this method is not suitable for the processing of silicon carbide substrate wafers;

[0011] 2. The double-sided grinding thinning method has inconsistent upper and lower disc speeds. Usually, the upper disc speed is 1 / 3 of the lower disc speed. The thickness reduction on both sides is uneven, and it is impossible to accurately calculate and process. Therefore, the BOW value can only be roughly processed without strong pertinence, so the effectiveness is not high.

[0012] 3. Sapphire has no polarity and can grow on both sides of the epitaxial layer. Silicon carbide wafers have carbon surfaces and silicon surfaces (bipolarity, similar to the north and south poles of a magnet). Silicon surfaces are generally used for growth during epitaxial growth. Therefore, this patented method cannot control the BOW value of silicon carbide substrate processing by faceting. Silicon carbide substrates need to specifically remove the BOW value of the silicon surface to better match the growth requirements of the epitaxial layer. Summary of the invention

[0013] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a thinning method for large-size SiC wafers. The present invention develops a single-sided thinning method specifically for the BOW value control of bipolar products such as silicon carbide wafers, which can more effectively reduce the BOW value of the silicon carbide substrate and better control the surface shape of the silicon carbide wafer, thereby achieving surface shape consistency, which can better match the consistency of epitaxial batch growth.

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

[0015] A method for thinning a large-size silicon carbide wafer comprises the following steps:

[0016] S1, faceting the silicon carbide wafer, aligning the carbon surface of the silicon carbide wafer toward the U surface of the plug, and aligning the silicon surface toward the H surface of the plug, and measuring the surface parameters of the silicon carbide wafer to determine the surface parameters of the silicon carbide wafer before processing;

[0017] S2, placing the measured silicon carbide wafers in the planetary wheel of the grinding machine in order for thinning processing;

[0018] S3, chamfering the ground silicon carbide wafer;

[0019] S4. Use wax to bond the chamfered silicon carbide wafer to the ceramic plate: Place the ceramic plate on a heating table, use solid wax to evenly apply the wax to the ceramic plate, place the silicon carbide wafer on the ceramic plate with the carbon surface facing up, and fill the gap between the silicon carbide wafer and the ceramic plate with wax. Since the silicon carbide wafer is uneven due to bending and warping, the large curved areas are filled with wax, so that the warping and bending will not be deformed by pressure during processing, making it impossible to remove; Then use a cooling plate with cooling water inside to cool the ceramic plate for a set time, so that the temperature of the ceramic plate is reduced to the set temperature, and the silicon carbide wafer is fixed on the ceramic plate with wax to complete the bonding work;

[0020] S5, installing the ceramic plate with the silicon carbide wafer bonded thereto on a thinning machine, and performing thinning processing on the carbon surface of the silicon carbide wafer;

[0021] S6. Dewaxing the thinned silicon carbide wafer from the ceramic plate: removing the thinned ceramic plate from the thinning machine, placing it on a heating table, heating it for a set time, waiting for the wax to melt, and removing the wafer from the ceramic plate;

[0022] S7, turning over the silicon carbide wafer, with the silicon surface of the silicon carbide wafer facing upward, repeating steps S4 to S6 again to thin the silicon surface of the silicon carbide wafer to obtain the desired silicon carbide wafer product.

[0023] Furthermore, in step S1, the parameters measured include BOW (bow), WARP (warpage) and TTV (thickness uniformity) of the product.

[0024] Furthermore, in step S1, a surface profile detection device FRT or similar sorting equipment is used to measure the surface profile parameters of the silicon carbide wafer.

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

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

[0027] Furthermore, in step S4, the temperature of the heating table is 100-180°C; the temperature of the cooling plate is 10-18°C; the cooling plate is used to cool the ceramic plate for 5-15 minutes to reduce the temperature of the ceramic plate to within 20°C.

[0028] Furthermore, in step S5, a 800#-15000# diamond grinding wheel is used, with a feed speed of 0.1-0.8um / s, a rotation speed of 2000-7000rpm, a rotation speed of 100-800rpm of the workbench, and a processing temperature of 20±2°C 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 stage is 120-200°C.

[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:

[0033] (1) The present invention changes the bonding method of the traditional thinning process without changing the Bow value and Warp value of the product during bonding. In this way, the Bow value and Warp value of the product caused by processing stress are effectively eliminated by thickening, and the Bow value and Warp value of the product are effectively controlled, which 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. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0036] Figure 3 The present invention is a flowchart of a method for obtaining a large-size silicon carbide wafer in an embodiment of the present invention. DETAILED DESCRIPTION

[0037] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the present invention, but the protection scope of the present invention is not limited to the following specific embodiments.

[0038] Unless otherwise defined, all the professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0039] Example:

[0040] A method for thinning a large-size silicon carbide wafer comprises the following steps:

[0041] S1, faceting the silicon carbide wafer, aligning the carbon surface of the silicon carbide wafer toward the U surface of the plug, and aligning the silicon surface toward the H surface of the plug, and measuring the surface parameters of the silicon carbide wafer to determine the surface parameters of the silicon carbide wafer before processing;

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

[0043] Use surface detection equipment FRT or similar sorting equipment to measure the surface parameters of silicon carbide wafers.

[0044] S2, placing the measured silicon carbide wafers in the planetary wheel of the grinding machine in order for thinning processing;

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

[0046] S3, chamfering the ground silicon carbide wafer;

[0047] Use 600#-2000# diamond chamfering grinding wheel, process diameter 150~200±0.2mm, process speed 3-8mm / s, process temperature 20±2℃.

[0048] S4. Use wax to bond the chamfered silicon carbide wafer to the ceramic plate: Place the ceramic plate on a heating table, use solid wax to evenly apply the wax to the ceramic plate, place the silicon carbide wafer on the ceramic plate with the carbon surface facing up, and fill the gap between the silicon carbide wafer and the ceramic plate with wax. Since the silicon carbide wafer is uneven due to bending and warping, the large curved areas are filled with wax, so that the warping and bending will not be deformed by pressure during processing, making it impossible to remove; Then use a cooling plate with cooling water inside to cool the ceramic plate for a set time, so that the temperature of the ceramic plate is reduced to the set temperature, and the silicon carbide wafer is fixed on the ceramic plate with wax to complete the bonding work;

[0049] The temperature of the heating table is 100-180°C; the temperature of the cooling plate is 10-18°C; the cooling plate is used to cool the ceramic plate for 5-15 minutes to reduce the temperature of the ceramic plate to within 20°C.

[0050] S5, installing the ceramic plate with the silicon carbide wafer bonded thereto on a thinning machine, and performing thinning processing on the carbon surface of the silicon carbide wafer;

[0051] The carbon surface of the silicon carbide wafer is thinned using a 800#-15000# diamond grinding wheel at a feed speed of 0.1-0.8um / s, a grinding wheel rotation speed of 2000-7000rpm, a worktable rotation speed of 100-800rpm, and a processing temperature of 20±2°C.

[0052] The processing time of thinning process is 7-15min.

[0053] S6. Dewaxing the thinned silicon carbide wafer from the ceramic plate: removing the thinned ceramic plate from the thinning machine, placing it on a heating table, heating it for a set time, waiting for the wax to melt, and removing the wafer from the ceramic plate;

[0054] The temperature of the heating stage is 120-200°C, and the heating time is 5-15 minutes.

[0055] S7, turning over the silicon carbide wafer, with the silicon surface of the silicon carbide wafer facing upward, repeating steps S4 to S6 again to thin the silicon surface 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 the thinning process, it can be seen that the thinning process method can effectively improve the Bow / Warp value after the grinding process. After statistics, it can be seen that the BOW of the silicon carbide product can be reduced by 13 to 16 microns. This process can effectively reduce the BOW value of the product.

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

[0058]

[0059]

[0060] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is 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 in the protection scope of the present invention.

Claims

1. A method for thinning a large-size silicon carbide wafer, characterized in that: The following steps are involved: S1, faceting the silicon carbide wafer, aligning the carbon surface of the silicon carbide wafer toward the U surface of the plug, and aligning the silicon surface toward the H surface of the plug, and measuring the surface parameters of the silicon carbide wafer to determine the surface parameters of the silicon carbide wafer before processing; S2, placing the measured silicon carbide wafers in the planetary wheel of the grinding machine in order for thinning processing; S3, chamfering the ground silicon carbide wafer; S4. Use wax to bond the chamfered silicon carbide wafer to the ceramic plate: Place the ceramic plate on a heating table, use solid wax to evenly apply wax to the ceramic plate, place the silicon carbide wafer on the ceramic plate with the carbon surface facing upward, and fill the gap between the silicon carbide wafer and the ceramic plate with wax; then use a cooling plate with cooling water inside 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 on the ceramic plate by wax to complete the bonding work; S5, installing the ceramic plate with the silicon carbide wafer bonded thereto on a thinning machine, and performing thinning processing on the carbon surface of the silicon carbide wafer; S6. Dewaxing the thinned silicon carbide wafer from the ceramic plate: removing the thinned ceramic plate from the thinning machine, placing it on a heating table, heating it for a set time, waiting for the wax to melt, and removing the wafer from the ceramic plate; S7, turning over the silicon carbide wafer, with the silicon surface of the silicon carbide wafer facing upward, repeating steps S4 to S6 again to thin the silicon surface of the silicon carbide wafer to obtain the desired silicon carbide wafer product.

2. A method for thinning a large-size silicon carbide wafer according to claim 1, characterized in that: In step S1, the measured parameters include BOW, WARP and TTV of the product.

3. A method for thinning a large-size silicon carbide wafer according to claim 1, characterized in that: In step S1, a surface profile detection device FRT or similar sorting equipment is used to measure the surface profile parameters of the silicon carbide wafer.

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

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

6. A method for thinning a large-size silicon carbide wafer according to claim 1, characterized in that: In step S4, the temperature of the heating stage is 100-180°C; the temperature of the cooling plate is 10-18°C; the cooling plate is used to cool the ceramic plate for 5-15 minutes to reduce the temperature of the ceramic plate to within 20°C.

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

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

9. The method for thinning a large-size silicon carbide wafer according to claim 1, characterized in that: In step S6, the temperature of the heating stage is 120-200°C.

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

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