A method for processing a tail piece of a silicon carbide crystal cutting head

Abstract

The application discloses a processing method suitable for silicon carbide crystal cutting head and tail pieces. The method can effectively utilize the silicon carbide crystal cutting head and tail pieces, and the cutting head and tail pieces can be processed into standard substrate pieces after the processing method, without additional processing equipment and with low use cost. The processing method is simple in operation, high in control precision, and high in utilization rate of the cutting head and tail pieces, and is suitable for being widely used for effectively processing batch production or experimental silicon carbide cutting head and tail pieces, and has great industrial application.

Description

Technical Field

[0001] This invention relates to a method for processing the head and tail slices after multi-wire dicing of silicon carbide, and more specifically, to a method for processing the head and tail slices of wafers that cannot be processed according to the normal process after multi-wire dicing on a silicon carbide production line. Background Technology

[0002] Silicon carbide (SiC), as a representative of third-generation semiconductors, possesses characteristics such as a large bandgap, high breakdown electric field, high saturated electron drift velocity, and high thermal conductivity, making it suitable for high-voltage environments exceeding 1200 volts, thus offering significant advantages in harsh environments. Simultaneously, SiC crystals, due to their highly matched lattice constants and coefficients of thermal expansion with the epitaxial layer material GaN, as well as their excellent thermal conductivity, are ideal substrate materials for GaN-based devices, such as LEDs and LEDs. Therefore, SiC crystal materials have become an indispensable substrate material in the field of semiconductor lighting technology. Currently, silicon carbide and silicon carbide-based semiconductor materials have become a research hotspot worldwide.

[0003] Applying silicon carbide crystals to devices requires processing them into wafers of a specific size. The basic process includes crystal growth, ingot inspection, ingot shaping, slicing, marking, grinding, chamfering, polishing, CMP, and cleaning. Due to the high hardness of silicon carbide crystals, crystal processing presents significant challenges. Cutting SiC ingots into wafers with low warpage, uniform thickness, and low cutting loss is crucial for subsequent grinding and polishing. Compared to traditional inner and outer circle cutting, multi-wire cutting offers advantages such as high cutting speed, high processing accuracy, high efficiency, and long lifespan, and has been widely used for the efficient cutting of silicon carbide wafers.

[0004] Currently, the silicon carbide crystal industry typically uses chemical vapor deposition (PVT) to grow single silicon carbide crystals. However, the growth characteristics of PVT limit the thickness of the silicon carbide crystals grown using this method; typically, the usable thickness of a single silicon carbide ingot after end-face shaping is between 10 and 25 mm. Furthermore, silicon carbide crystals have extremely high hardness, requiring multi-wire cutting with diamond cutting fluid, which is expensive, and the wire cutting process is also time-consuming. Therefore, to reduce costs and improve cutting efficiency, the industry currently typically uses multi-crystal ingot bonding followed by batch cutting. Due to the different contact positions of the cutting wire at the beginning and end of the ingot during the cutting process, the offset of the cutting wire at the beginning and end of the cut varies, resulting in a dozen or twenty cut pieces with inconsistent thickness and surface shape in each batch. Typically, these cut pieces are only used as samples to characterize the dislocation density of the crystal. However, some of these head and tail wafers that meet certain thickness requirements can be processed and used as production wafers, which can avoid some unnecessary waste, since the price of a single silicon carbide finished wafer is extremely expensive. Summary of the Invention

[0005] In view of the aforementioned problems with the current common silicon carbide cutting head and tail wafer processing, the inventors of this application realized that, for the processing of head and tail wafers after industrial silicon carbide crystal cutting, in order to ensure the full utilization of the cut head and tail wafers and avoid unnecessary material waste, it is a processing method that meets product requirements to achieve special processing of the cut head and tail wafers under certain thickness conditions.

[0006] In view of the above understanding, the present invention provides a method for processing head and tail pieces of silicon carbide cutting, the steps of which are as follows:

[0007] S1, Screening of cut head and tail wafers: Cut head and tail wafers are screened according to their effective thickness. The screening types include thicker and flat wafers, thicker and uneven wafers, thinner and flat wafers and thinner and uneven wafers. For silicon carbide cut head and tail wafers with an effective thickness (thickness at the lowest point) greater than 450um, the thickness difference between the highest and lowest points of their uneven surfaces cannot be greater than 20um.

[0008] S2, the thicker and flat wafers are classified into two subclasses of 20µm each, and wafers of the same thickness are then polished on both sides together.

[0009] Thin, flat wafers are directly thinned to the lower limit of the standard thickness using a grinder before proceeding with subsequent standard processing.

[0010] After the thicker and uneven wafers are glued to the ceramic disk with wax, most of the uneven surface is smoothed with a single-sided grinder. Then, double-sided grinding is used to grind to the upper limit of the standard thickness before subsequent standard processing. In the wafer glued to the disk process, the head and tail wafers with similar maximum and minimum thicknesses are glued to the same ceramic disk.

[0011] The method involves directly performing thinning and segmented processing on thin, uneven wafers using a grinder process, thinning the wafer multiple times until it reaches the lower limit of the standard wafer thickness, and then performing subsequent standard processing.

[0012] Preferably, in step S2, the ceramic disc has a diameter of 360mm or more.

[0013] Compared with existing technologies, the beneficial effects of this invention are: According to the processing method of this invention, most silicon carbide wafers of varying thicknesses can be reprocessed from the cut head and tail pieces, effectively improving the utilization rate of the cut head and tail wafers. This invention is simple to operate, has a low barrier to entry, and achieves a high utilization rate of the cut head and tail pieces. Attached Figure Description

[0014] Figure 1 The diagram schematically illustrates the processing method of the thicker and flat wafer head and tail wafers in Embodiment 1 of the present invention.

[0015] Figure 2 The diagram schematically illustrates the processing method of the thinner, flatter head and tail pieces in Embodiment 2 of the present invention.

[0016] Figure 3 The diagram illustrates the processing method of the thicker, uneven head and tail pieces in Embodiment 3 of the present invention.

[0017] Figure 4 The diagram illustrates the processing method of the thinner, uneven head and tail sheet in Embodiment 4 of the present invention.

[0018] As shown in the figure:

[0019] 1. Planetary wheel carrier; 2. Metal substrate; 3. Resin liner; 4. Cut head and tail wafers; 5. High-speed grinding wheel; 6. Aluminum alloy base; 7. Diamond grinding wheel teeth; 8, 9 Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1:

[0022] Please see Figure 1 The present invention provides a technical solution: Figure 1 The planetary wheel carrier 1, which holds the cut head and tail wafers 4, is schematically shown in the thicker and flat wafer head and tail wafer processing method of this embodiment. The planetary wheel carrier 1 includes a metal substrate 2 and a resin liner 3.

[0023] It should be understood that the metal substrate 2 is typically made of blued steel or high-carbon steel. This ensures the strength and lifespan of the vehicle substrate.

[0024] A flexible resin liner 3 is applied to the inner hole of the metal substrate 2 to prevent chipping or dark damage caused by impact between the wafer and the metal substrate during the wafer grinding process. The planetary wheel carriers 1 are placed on the double-sided grinding machine in the required number. The silicon carbide cut-head and tail wafers 4, which have been thickness-screened, are placed into the inner hole of each planetary wheel carrier in turn for standard double-sided grinding.

[0025] It should be understood that in this invention, a thicker and flat wafer refers to a wafer with at least one smooth cutting surface and the other cutting surface is allowed to have unevenness factors such as lines and steps, but the thickness difference between the highest and lowest points of the uneven surface cannot be greater than 20 μm, and the effective thickness (thickness of the lowest point) of the silicon carbide cutting head and tail wafer is greater than 450 μm.

[0026] The wafers of different thicknesses mentioned above can be processed into wafers of different specifications according to different processing conditions for use. In this invention, it is defined that: cut-end wafers with an effective thickness of 450-500 μm can be processed into standard 350 μm thick substrate wafers; cut-end wafers with an effective thickness greater than 500 μm can be processed into seed wafers of about 500 μm for use by controlling the amount of material removed.

[0027] Example 2:

[0028] The processing method of the thinner and flat wafer in one embodiment of the present invention mainly adopts a high-speed grinding wheel thinning machine to accurately remove the cutting marks and damaged layers on the cut surfaces of the cutting head and tail wafers. Figure 2 The diagram schematically illustrates the cutting of the head and tail wafers 4 and the high-speed thinning grinding wheel 5 in the thinner and flatter wafer processing method of this embodiment.

[0029] The high-speed grinding wheel 5 mainly consists of a cup-shaped aluminum alloy base 6 and diamond grinding wheel teeth 7. It employs a high rotation speed of 2000–2500 rpm to quickly smooth uneven areas and precisely remove damaged layers from the cut head and tail wafers, effectively controlling the surface removal thickness of the cut head and tail wafers. Specifically, the flat surface of the cut head and tail wafers 4 is horizontally adsorbed onto the processing platform of the thinning machine. Based on the maximum and minimum wafer thickness and the typical damaged layer thickness, the thinning removal amount is set, and the first side processing is automatically completed. The processed wafer is then flipped over, and the second side removal amount is set according to the typical damaged layer thickness, completing the processing.

[0030] It should be understood that in this invention, a thinner and flatter wafer refers to a wafer with at least one smooth cutting surface and the other cutting surface is allowed to have unevenness factors such as lines and steps, but the thickness difference between the highest and lowest points of the uneven surface cannot be greater than 20 μm, and the effective thickness (thickness of the lowest point) is less than 450 μm for silicon carbide cutting head and tail wafers.

[0031] The wafers of different thicknesses mentioned above can be processed into wafers of different specifications according to different processing conditions for use. In this invention, it is defined that: cut-end wafers with an effective thickness of 380-450 μm can be processed into standard 350 μm thick substrate wafers; cut-end wafers with an effective thickness of less than 380 μm can be used as test wafers for crystal defect evaluation after thinning, polishing, and etching.

[0032] Example 3:

[0033] The processing method for thick and uneven wafers in one embodiment of the present invention mainly involves using a single-sided grinding machine to correct the uneven surface of the head and tail wafers after cutting, and then using a double-sided grinding machine to grind to the specified thickness for conventional processing. Figure 3 The diagram schematically illustrates the cutting of the head and tail wafer 4, the single-sided polishing machine 8, and the single-sided polishing ceramic disc 9 in the processing of a thicker and uneven wafer in this embodiment.

[0034] After classifying and screening the thicker and uneven cut head and tail pieces 4 according to their effective thickness, the wafers with similar thickness are glued to the ceramic disk 9 and then the uneven surface is smoothed by a single-sided grinder 8. After that, double-sided grinding is used to grind to the upper limit of the standard thickness before subsequent standard processing.

[0035] It should be understood that in this invention, a thicker, uneven wafer refers to a silicon carbide cut-off wafer with at least one smooth cut surface and the other cut surface having unevenness factors such as lines, steps, etc., and the thickness difference between the highest and lowest points of the uneven surface exceeds 20 μm, while the effective thickness (thickness of the lowest point) is greater than 450 μm.

[0036] The wafers of different thicknesses mentioned above can be processed into wafers of different specifications according to different processing conditions for use. In this invention, it is defined that: cut-end wafers with an effective thickness of 450-500 μm can be processed into standard 350 μm thick substrate wafers; cut-end wafers with an effective thickness greater than 500 μm can be processed into seed wafers of about 500 μm for use by controlling the amount of material removed.

[0037] Example 4:

[0038] The processing method for thin, uneven wafers in one embodiment of the present invention mainly employs a high-speed grinding wheel thinning machine to thin the uneven surfaces of the cut wafers in segments based on the difference between the maximum and minimum wafer thicknesses. This effectively avoids excessive removal of wafer surface material. Figure 1 The schematic illustration shows a similar process for the thicker, flatter wafer head and tail of this embodiment.

[0039] The number of coarse polishing and thinning operations is designed based on the difference between the maximum and minimum thickness of the first and last wafers after cutting, with each thinning operation set to 10µm. This effectively avoids the risk of wafer breakage due to excessive local stress during the thinning process.

[0040] It should be understood that in this invention, a thinner, uneven wafer refers to a silicon carbide cut-off wafer with at least one smooth cut surface and another cut surface having unevenness factors such as lines, steps, etc., and the thickness difference between the highest and lowest points of the uneven surface exceeds 20 μm, while the effective thickness (thickness at the lowest point) is less than 450 μm.

[0041] The wafers of different thicknesses mentioned above can be processed into wafers of different specifications according to different processing conditions for use. In this invention, it is defined that: cut-end wafers with an effective thickness of 380-450 μm can be processed into standard 350 μm thick substrate wafers; cut-end wafers with an effective thickness of less than 380 μm can be used as test wafers for crystal defect evaluation after thinning, polishing, and etching.

[0042] A box of 25 incoming cut wafers can be processed in different ways to achieve effective utilization. (1) 12 wafers are 520-540um thick with a maximum thickness and minimum thickness deviation of about 15um. These 12 wafers can be processed into standard substrate wafers or seed wafers by using the method of embodiment one, placing the 12 wafers on 4 planetary wheels for double-sided grinding, and finally obtaining a polished wafer of about 490um. According to actual needs, it can be finally processed into standard substrate wafers or seed wafers. (2) 9 wafers are 450-490um thick with a maximum thickness and minimum thickness deviation of about 50um. These 9 wafers can be processed into standard substrate wafers or seed wafers by using the method of embodiment three, taking three standard 360 ceramic disks, and applying wax to the ceramic disks symmetrically in a three-wafer-per-disc manner, with the highest point of each wafer facing the outer ring of the ceramic disk. Then, place the ceramic disk with the wafers attached on a single-sided grinder to grind the wafers to about 430um with no obvious height difference on the wafer surface, and then process these wafers into standard substrate wafers by standard process. (3) There are also 3 wafers with a thickness of 350-370 μm and a thickness deviation of about 12 μm between the maximum and minimum thickness of a single wafer. These 3 wafers can be processed using the method of Embodiment 2, using a grinder wheel to precisely thin both sides of the wafer to 330-350 μm. One wafer with a thickness of 330 μm does not meet the thickness requirements for subsequent substrate processing and can be used as a performance characterization wafer. The other two wafers with a thickness of 350 μm can be transferred to subsequent processes to be processed into standard substrate wafers. (4) The last wafer has an effective thickness of 350 μm, but the thickness deviation between the maximum and minimum wafers reaches 100 μm. This wafer can be processed using the method of Embodiment 4, using a grinder wheel to precisely smooth the thickness difference in 5-6 thinning processes. The wafer can be thinned to about 340 μm before being transferred to subsequent processes and finally processed into a standard substrate wafer with the lower limit thickness.

[0043] The above-mentioned cutting head and tail wafer processing methods can be used individually or in combination as needed. Depending on the thickness, the cut head and tail wafers processed by the above methods can be used for various purposes such as substrates, seed crystals, and performance characterization. The utilization rate of the cut head and tail wafers can reach about 70%, which can effectively reduce the overall wafer production cost.

[0044] Table 1 lists some comparisons of the effects between conventional silicon carbide head and tail wafer processing and the present invention. It can be seen that the silicon carbide head and tail wafer processing method of the present invention greatly improves the wafer utilization rate.

[0045] Table 1: Comparison of the effects of conventional silicon carbide head and tail sheet treatment with the present invention

[0046]

[0047] Industrial applicability:

[0048] The silicon carbide cutting head and tail wafer processing method of this invention can effectively process silicon carbide cutting head and tail wafers in conjunction with conventional wafer processing double-sided grinding machines, single-sided grinding machines, and grinders, without requiring additional processing equipment and resulting in low operating costs. This processing method is simple to operate, offers high control precision, and achieves high utilization of the cutting head and tail wafers. It is suitable for widespread use in the effective processing of silicon carbide cutting head and tail wafers in mass production or experimental applications, and has significant industrial applicability.

[0049] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for processing the head and tail pieces of a silicon carbide crystal cutting process, characterized in that, Includes the following steps: S1, Sorting of the cutting head and tail pieces: Based on the effective thickness and the thickness difference between the highest and lowest points of the uneven surface, the cutting head and tail pieces are divided into four categories: Thicker and flat wafers: effective thickness greater than or equal to 450 μm, and the thickness difference less than or equal to 20 μm; Thin and flat wafers: effective thickness less than 450 μm, and the thickness difference less than or equal to 20 μm; Thicker uneven wafer: effective thickness greater than or equal to 450 μm, and the thickness difference exceeds 20 μm; Thinner uneven wafer: effective thickness less than 450 μm, and the thickness difference exceeds 20 μm; Wherein, the effective thickness is the thickness at the lowest point of the wafer thickness; S2 is used to process different types of wafers separately. The thicker and flat wafers are then classified into two 20μm intervals, and wafers of the same thickness interval are then polished on both sides together. The thinner and flat wafer is directly thinned to the lower limit of the standard thickness by a grinder before subsequent standard processing. After the thicker, uneven wafer is glued to a ceramic disk, the uneven surface is smoothed with a single-sided grinder, and then double-sided grinding is used to reach the upper limit of the standard thickness. The diameter of the ceramic disk is 360mm or more, and the glued wafer process glues the head and tail wafers with similar maximum and minimum thicknesses onto the same ceramic disk. The thin, uneven wafer is processed in a grinder-style thinning process, and then thinned in multiple stages until the wafer reaches the lower limit of the standard thickness before proceeding with subsequent standard processing. Each thinning step is set to 10 μm.

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