Silicon carbide wafer processing method for reducing thinning stress

Abstract

The invention provides a silicon carbide wafer processing method for reducing thinning stress, and relates to the technical field of semiconductor processing. The method comprises the following steps: processing the front surface of a silicon carbide wafer; brushing a UV glue layer on the front surface of the silicon carbide wafer; flatly curing the surface of the UV adhesive layer; pasting a protective film on the cured UV adhesive layer; and after the silicon carbide wafer is fixed, grinding and thinning the back surface of the silicon carbide wafer. The front surface is brushed with a UV glue layer, the high step difference generated by processing of the front surface is eliminated, the surface of the UV glue layer is kept flat, the SiC wafer cannot deform due to vacuum adsorption, and the SiC wafer almost has no internal stress; in the grinding process, all parts of the SiC wafer are evenly stressed, the back face of the machined wafer is uniform, after the SiC wafer is separated from adsorption, no redundant stress is released, it is guaranteed that the thinned wafer cannot be broken, and the yield and the percent of pass are improved.

Description

Technical Field

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

[0002] Silicon carbide (SiC) chips have been widely used in high-power electronic devices due to their excellent electrical properties and high thermal conductivity. However, with the continuous increase in power density, the front graphic layers of SiC chips, including the hard passivation layer, PI passivation layer and metal layer, need to be thickened to meet higher performance requirements. Although this thickening design improves the performance of the chip, it also leads to a higher step difference on the chip surface.

[0003] At present, the thinning of SiC wafers mainly adopts the back grinding technology. This technology adheres the wafer to a UV film, uses vacuum to adsorb the SiC wafer, and then grinds it. This method can achieve the thinning of general wafers.

[0004] Existing thinning technology has obvious shortcomings when processing SiC wafers with high step differences. This is because when using vacuum adsorption of SiC wafers, due to the step differences on the surface of the SiC wafer, the continuous vacuum adsorption force during the thinning process will cause deformation stress on the wafer. After thinning, the stress is released, increasing the risk of wafer fragments and may also have an adverse effect on the electrical properties of the manufactured SiC chip. Summary of the invention

[0005] The problem to be solved by the present invention is that the existing SiC wafer thinning method will generate wafer deformation stress when processing SiC wafers with step differences, thereby increasing the risk of wafer fragments.

[0006] To solve the above problems, in a first aspect, the present invention provides a method for processing a silicon carbide wafer with reduced thinning stress, comprising:

[0007] The front side of the silicon carbide wafer is processed;

[0008] Apply UV adhesive layer on the front side of silicon carbide wafer;

[0009] Solidify the UV adhesive layer surface flatly;

[0010] Paste a protective film on the cured UV adhesive layer;

[0011] After the silicon carbide wafer is fixed, the back side of the silicon carbide wafer is ground and thinned.

[0012] Optionally, applying a UV adhesive layer on the front side of the silicon carbide wafer and curing the surface of the UV adhesive layer to make it flat includes:

[0013] UV glue is applied layer by layer on the front side of the silicon carbide wafer, and after being flattened layer by layer, a UV glue layer is formed.

[0014] Optionally, the UV glue is a UV photosensitivity viscosity reducing glue.

[0015] Optionally, the thickness of the UV adhesive layer is n times the step height of the front side of the silicon carbide wafer, where n is greater than 1 and less than 3.

[0016] Optionally, the protective film is a film made of non-UV material.

[0017] Optionally, the protective film includes a base layer and an adhesive layer, the adhesive layer is bonded to the base layer, the adhesive layer does not contain UV photosensitizing components, the adhesive layer has a viscosity greater than the adhesive interface viscosity after UV glue exposure, and the base layer is made of acid-resistant material.

[0018] Optionally, after grinding and thinning the back side of the silicon carbide wafer, the silicon carbide wafer processing method for reducing thinning stress further includes:

[0019] The back side of the ground silicon carbide wafer is subjected to acid etching treatment.

[0020] Optionally, after the back side of the ground silicon carbide wafer is subjected to acid etching treatment, the silicon carbide wafer processing method for reducing thinning stress further comprises:

[0021] Clean the grinding and acid etching residues, then clean the processed silicon carbide wafers and dehydrate them.

[0022] Optionally, after cleaning the grinding and acid etching residues, cleaning the processed silicon carbide wafer, and dehydrating, the silicon carbide wafer processing method for reducing thinning stress further includes:

[0023] UV light is applied to the front side of the silicon carbide wafer.

[0024] Optionally, after the UV light is irradiated on the front side of the silicon carbide wafer, the silicon carbide wafer processing method for reducing thinning stress further includes:

[0025] The protective film is removed to obtain a thinned silicon carbide wafer.

[0026] The present invention provides a method for processing silicon carbide wafers with reduced thinning stress. Compared with the prior art, the method has the following beneficial effects:

[0027] After the processing, a UV adhesive layer is applied to the front side of the SiC wafer to fill and eliminate the high step difference caused by the processing on the front side. The UV adhesive layer covers the structure formed by the processing on the front side to keep the surface of the UV adhesive layer flat. A protective film is attached to the surface of the UV adhesive layer. Vacuum adsorption will not cause the SiC wafer to deform, and there is almost no internal stress in the SiC wafer. During the grinding process, the SiC wafer is subjected to uniform force at all locations, and the wafer will not deform or deflect, so that the back side of the processed wafer is symmetrical, further reducing or eliminating the thinning stress of the SiC wafer. After the SiC wafer is released from adsorption, there is almost no excess stress release, ensuring that the SiC wafer finally removed will not be broken, thereby improving the yield and qualified rate of SiC wafer processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 A schematic flow chart of a method for processing a silicon carbide wafer to reduce thinning stress provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application are clearly and completely described. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0031] The embodiment of the present application provides a silicon carbide wafer processing method for reducing thinning stress, thereby solving the problem that the existing SiC wafer thinning method will generate wafer deformation stress and increase the risk of wafer fragmentation when processing SiC wafers with step differences, thereby achieving the purpose of reducing or eliminating SiC wafer thinning stress.

[0032] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0033] like Figure 1 As shown, a method for processing a silicon carbide wafer to reduce thinning stress provided in an embodiment of the present application includes:

[0034] Step 1: Finish processing the front side of the silicon carbide wafer.

[0035] Step 2: Apply a UV adhesive layer on the front side of the silicon carbide wafer, wherein the UV adhesive layer covers the structure formed by the front side processing to eliminate the step difference.

[0036] Step 3: Flatten and solidify the surface of the UV adhesive layer.

[0037] Step 4: Apply protective film to the cured UV adhesive layer.

[0038] Step 5: After the silicon carbide wafer is fixed, the back side of the silicon carbide wafer is ground and thinned.

[0039] In this embodiment, a UV adhesive layer is applied to the front side of the SiC wafer after processing to fill and eliminate the high step difference on the front side caused by processing. The UV adhesive layer covers the structure formed by the processing on the front side to keep the surface of the UV adhesive layer flat. The UV adhesive layer is cured, and a protective film is attached to the surface of the UV adhesive layer. The protective film protects the front UV adhesive layer and the structure on the front side from being damaged during the subsequent grinding and thinning process. Then, the protective film on the front side of the SiC wafer can be vacuum-adsorbed to adsorb and fix the SiC wafer. At this time, the front side of the SiC wafer is flat without high step difference, and the vacuum adsorption will not cause the SiC wafer to deform. At this time, the adsorbed S The front side of the SiC wafer is subjected to external adsorption force as a whole, and there is almost no internal stress. The back side of the fixed SiC wafer is ground and thinned. During the processing when the grinding wheel is close to the back side of the wafer, since the front side of the SiC wafer is flat, the SiC wafer is subjected to uniform force at all locations, and the wafer will not deform or deflect during the grinding process. This makes the back side of the processed wafer symmetrical, further reducing or eliminating the thinning stress of the SiC wafer. After the SiC wafer is released from adsorption, there is almost no excess stress release, ensuring that the SiC wafer finally removed will not be broken, thereby improving the yield and qualified rate of SiC wafer processing.

[0040] Each step is described in detail below.

[0041] Step 1: Finish processing the front side of the silicon carbide wafer.

[0042] Specifically, other semiconductor manufacturing processes such as epitaxial growth, ion implantation, photolithography, and etching are performed on the front side of the wafer. These processes need to be completed in sequence according to the process requirements so that the front side of the wafer meets the required circuit structure and performance requirements and a SiC wafer chip is constructed. At this time, the front side of the SiC wafer has high and low step differences due to the circuit structure, etc. These high and low step differences may cause the SiC wafer to be deformed due to uneven force during subsequent adsorption and fixation, thereby causing deformation internal stress in the SiC wafer. In the subsequent processing, the deformed SiC wafer is processed, which can easily cause uneven processing. After processing, the SiC wafer is not restrained and the deformation stress is released. However, at this time, the thickness of the SiC wafer itself becomes thinner, and the released stress may cause fragments of the thinned SiC wafer.

[0043] Step 2: Apply UV adhesive layer on the front side of the silicon carbide wafer.

[0044] Step 3: Flatten and solidify the surface of the UV adhesive layer.

[0045] Step 2 and step 3 have a sequence, but they need to be performed alternately. Specifically, UV glue is applied layer by layer on the front of the SiC wafer, and after being flattened and cured layer by layer, a UV glue layer is formed, that is, the UV glue is evenly applied layer by layer on the entire surface of the front of the wafer to avoid defects such as bubbles, sagging, and uneven thickness in the UV glue layer, and the steps on the front of the SiC wafer are filled. During the UV glue application process, the layers can be overlapped before they are fully cured, and when they are fully cured, there will be no obvious boundaries between the layers. The thickness of the UV glue layer is n times the step height on the front of the silicon carbide wafer, where n is greater than 1 and less than 3, that is, the UV glue layer needs to completely cover the structure formed by the wafer front processing to ensure that it can provide sufficient support and protection during grinding and thinning; however, the thickness of the UV glue layer should not be too large, because the UV glue layer has a certain compression elasticity, and the thicker the UV glue layer, the greater the deformation when it is subjected to force, so the thickness of the UV glue layer is controlled to be less than 3 times the step height, and no obvious deformation will occur when subjected to force, thereby ensuring that the wafer will not generate internal stress when adsorbed.

[0046] UV glue should have good adhesion and be able to adhere firmly to the surface of the wafer during the grinding process. At the same time, after UV light exposure, it can be easily removed after thinning is completed. According to the size, material and subsequent thinning process requirements of the wafer, select UV glue with appropriate viscosity, curing speed, peel strength and transparency. In this application, the UV glue is a UV photosensitive viscosity reduction glue. The surface viscosity of the glue after photosensitive is lower than the internal interconnection strength of the UV glue, that is, the surface viscosity of the UV glue after photosensitive is lower than the viscosity inside the UV glue. The UV glue can be selected from acrylic UV viscosity-reducing glue, silicone-based UV viscosity-reducing glue, two-component high-temperature resistant UV viscosity-reducing glue and other mixed glues. The selection of UV glue is not limited to the above-mentioned ones, and other UV photosensitive viscosity-reducing glues can also be selected. When the entire UV glue layer is subjected to UV light, the viscosity of the UV glue layer surface is reduced after photosensitive, but the viscosity of the UV glue layer is still strong, and it is easy to peel off from the wafer as a whole.

[0047] Common UV glue curing methods include ultraviolet irradiation curing and thermal curing. For UV glue, ultraviolet irradiation curing is generally used. The UV light of a specific wavelength and intensity is used to irradiate the glue layer, causing the UV glue to undergo a photochemical reaction, thereby achieving curing. During the curing process, the wafer should be placed stably to avoid deformation or cracking of the glue layer due to vibration or movement. Ensure that the glue layer is completely cured and tightly bonded to the front of the wafer to form a flat and solid protective layer, providing a stable base for subsequent film lamination and grinding.

[0048] Step 4: Apply protective film to the cured UV adhesive layer.

[0049] Specifically, the protective film is made of non-UV material. The protective film should have good transparency, flexibility and acid corrosion resistance, and can effectively protect the front of the wafer from damage during the grinding and corrosion process. The protective film includes a base layer and a glue layer, the glue layer is bonded to the base layer, the glue layer and the base layer do not contain UV photosensitive denaturing materials or components, especially the glue layer cannot contain UV photosensitive denaturing materials or components, the glue layer viscosity is greater than the glue interface viscosity after UV glue exposure, that is, the glue layer viscosity of the protective film is greater than the UV glue interface viscosity after UV glue exposure, so as to facilitate the removal of the protective film and peel off the UV glue layer on the wafer surface. The base material of the protective film is an acid-resistant material. The glue layer of the protective film can be acrylic glue or rubber-type glue, etc., and the base layer of the protective film can be a polyester (PET) film, a polyvinyl chloride (PVC) film or a polyurethane (PU) film, etc.

[0050] You can use professional film laminating equipment, such as an automatic film laminating machine, to evenly stick the protective film on the surface of the cured UV adhesive layer. During the film laminating process, avoid bubbles, wrinkles, and edge lift on the protective film, and ensure that the protective film and UV adhesive layer fit tightly without gaps.

[0051] Step 5: After the silicon carbide wafer is fixed, the back side of the silicon carbide wafer is ground and thinned.

[0052] Specifically, place the silicon carbide wafer with a protective film on a special fixture of the grinding equipment, adjust the position of the wafer so that its back faces the grinding wheel, and firmly fix the wafer by vacuum adsorption to ensure that the wafer will not move or loosen during the grinding process.

[0053] You can first use a coarser diamond grinding wheel, such as a grinding wheel with a grit of about #2000, to rough grind the back of the wafer at a faster speed and a larger feed rate to quickly remove most of the excess material and make the wafer thickness close to the target thickness. During the rough grinding process, the grinding parameters, such as the grinding wheel speed, feed speed, grinding pressure, etc., should be continuously adjusted to ensure grinding efficiency and surface quality. When the wafer thickness is close to the target thickness, replace it with a finer diamond grinding wheel, such as a grinding wheel with a grit of about #30000, and perform fine grinding at a slower speed and a smaller feed rate to further refine the surface roughness of the back of the wafer, improve the surface flatness, remove the damaged layer generated during the rough grinding process, and make the back of the wafer reach the required final thickness and surface quality requirements. The speed in the rough grinding stage can be set at 50rpm to 100rpm, and the grinding is carried out for a certain period of time according to the set pressure, usually 5 to 10 minutes. During this period, the grinding fluid is replenished in time to efficiently remove the material; the speed in the intermediate stage is adjusted to 50rpm to 70rpm, and the grinding time is 5 to 10 minutes, taking into account both grinding efficiency and surface quality; the speed in the fine grinding and polishing stages is controlled at 60rpm to 70rpm, and the grinding time is 5 to 10 minutes to prevent surface scratches caused by high speed and ensure improved smoothness.

[0054] Optionally, after grinding and thinning the back side of the silicon carbide wafer in step 5, the silicon carbide wafer processing method for reducing thinning stress further includes:

[0055] Step 6: Perform acid etching on the back side of the ground silicon carbide wafer.

[0056] Specifically, a suitable wet acid etching equipment, such as an etching tank, is selected. The wafer is placed in the acid etching solution, the temperature is controlled at 20°C, and the wafer is immersed for 300 seconds. The wafer rotation speed is stabilized at 3rpm to ensure the uniformity of etching. At the same time, the concentration of the acid etching solution is monitored. When the concentration is low, the existing acid etching solution is automatically discharged and replenished to etch away the damaged layer. The acid etching solution can be mixed with the following components: 49% hydrofluoric acid solution, 70% nitric acid solution, 85% phosphoric acid solution, 98% sulfuric acid solution and 10% citric acid solution. The volume ratio of these mixed components can be 1:4.63:1.48:0.65:1.11.

[0057] Step 7: Clean the grinding and acid etching residues, then clean the processed silicon carbide wafer and dehydrate it.

[0058] Specifically, the silicon carbide wafer is removed from the grinder, placed in a dedicated cleaning tank, and ultrasonically cleaned with deionized water or alcohol or other cleaning agents for 10 to 15 minutes. The cleaning can be performed multiple times to completely remove the polishing liquid, acid etching liquid and possible adsorbed impurities remaining on the surface. The silicon carbide wafer is then dehydrated. The dehydration method may be spin drying, baking, organic alcohol dehydration, high-purity nitrogen drying, or natural drying in a clean environment, etc. The dehydration method is not limited to the above-mentioned dehydration methods, and other dehydration methods that do not damage the silicon carbide wafer are also acceptable.

[0059] Step 8: UV light is applied to the front side of the silicon carbide wafer.

[0060] Specifically, the UV light energy must meet the requirements for UV glue denaturation. The front side of the SiC wafer with a non-UV film is treated with UV light to reduce the viscosity of the UV glue layer and effectively soften the UV glue layer, making it easier to remove the protective film later.

[0061] Step 9: Remove the protective film to obtain a thinned silicon carbide wafer.

[0062] After UV irradiation, the viscosity of the UV adhesive layer surface is reduced, and the UV adhesive layer is also softened. When UV irradiation is performed, the illumination can be performed from the back of the wafer. The thinned wafer has a certain light transmittance. When the illumination is performed from the back of the wafer, the interface where the UV adhesive layer and the wafer are bonded is mainly irradiated to reduce the viscosity of the UV adhesive layer at the bonding interface. The viscosity of the non-UV film will not be affected. At this time, the viscosity of the non-UV film is used to peel off the protective film and the UV adhesive layer together. This step can remove the UV adhesive layer at the same time, avoiding the complicated operation of removing the UV adhesive alone. Specifically, tweezers or similar tools can be used to gently grasp a corner of the protective film and slowly peel it off from the surface of the wafer. If the protective film is difficult to peel off, an appropriate amount of solvents such as acetone or isopropyl alcohol can be used to gently wipe the edge of the protective film to warp the edge of the protective film and soften the UV adhesive layer before peeling it off.

[0063] In summary, compared with the prior art, the present invention has the following beneficial effects:

[0064] 1. Apply UV adhesive layer to the front of SiC wafer after processing, fill and eliminate the high step difference caused by processing on the front, cover the structure formed by processing on the front with UV adhesive layer, keep the surface of UV adhesive layer flat, and paste protective film on the surface of UV adhesive layer. The protective film protects the front UV adhesive layer and the structure of the front from being damaged during the subsequent grinding and thinning process, adsorb and fix the SiC wafer, and vacuum adsorption will not cause deformation of SiC wafer, and there is almost no internal stress in SiC wafer; because the front of SiC wafer is flat, during the grinding process, the force on SiC wafer is uniform, and the wafer will not be deformed or skewed during the grinding process, so that the back of the processed wafer is symmetrical, further reducing or eliminating the thinning stress of SiC wafer, and there is almost no excess stress release after the SiC wafer is separated from adsorption, so as to ensure that the SiC wafer finally removed will not be broken, and improve the yield and qualified rate of SiC wafer processing.

[0065] 2. The thickness of the UV adhesive layer is greater than the step height on the front side of the silicon carbide wafer but less than 3 times the step height. At this time, the UV adhesive layer completely covers the structure formed by the front side of the wafer to ensure that it can provide sufficient support and protection during grinding and thinning. The UV adhesive layer of this thickness will not produce obvious deformation under force, thereby ensuring that the wafer will not generate internal stress when being adsorbed.

[0066] 3. After UV light exposure, the viscosity of the UV adhesive layer decreases and the UV adhesive layer is softened, but the viscosity of the non-UV film will not be affected. At this time, the protective film and the UV adhesive layer are peeled off together by utilizing the viscosity of the non-UV film. The UV adhesive layer is removed at the same time, avoiding the complicated operation of removing the UV adhesive alone.

[0067] 4. The processing method of the present application is not only applicable to SiC chip wafers with step differences, but also applicable to thinning processing of chips with step differences made of other materials. The processing method can be integrated into existing processing technology, with low equipment investment and low process flow adjustment cost.

[0068] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0069] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for processing a silicon carbide wafer to reduce thinning stress, characterized in that: include: The front side of the silicon carbide wafer is processed; Apply UV adhesive layer on the front side of silicon carbide wafer; Solidify the UV adhesive layer surface flatly; Paste a protective film on the cured UV adhesive layer; After the silicon carbide wafer is fixed, the back side of the silicon carbide wafer is ground and thinned.

2. The method for processing a silicon carbide wafer with reduced thinning stress as claimed in claim 1, characterized in that: The UV adhesive layer is applied on the front side of the silicon carbide wafer; The UV adhesive layer surface is flat and cured including: UV glue is applied layer by layer on the front side of the silicon carbide wafer, and after being flattened layer by layer, a UV glue layer is formed.

3. The method for processing a silicon carbide wafer with reduced thinning stress as claimed in claim 1, characterized in that: The UV glue is a UV-sensitive adhesive with reduced viscosity.

4. The method for processing a silicon carbide wafer with reduced thinning stress as claimed in claim 1, characterized in that: The thickness of the UV adhesive layer is n times the step height of the front side of the silicon carbide wafer, where n is greater than 1 and less than 3.

5. The method for processing a silicon carbide wafer with reduced thinning stress as claimed in claim 1, characterized in that: The protective film is a film made of non-UV material.

6. The method for processing a silicon carbide wafer with reduced thinning stress as claimed in claim 5, characterized in that: The protective film includes a base layer and an adhesive layer, the adhesive layer is bonded to the base layer, the adhesive layer does not contain UV photosensitizing components, the adhesive layer has a viscosity greater than the adhesive interface viscosity after UV glue exposure, and the base layer is made of acid-resistant material.

7. The method for processing a silicon carbide wafer with reduced thinning stress according to any one of claims 1 to 6, characterized in that: After grinding and thinning the back side of the silicon carbide wafer, the method further comprises: The back side of the ground silicon carbide wafer is subjected to acid etching treatment.

8. The method for processing a silicon carbide wafer with reduced thinning stress as claimed in claim 7, characterized in that: After the back side of the ground silicon carbide wafer is subjected to acid etching treatment, the method further comprises: Clean the grinding and acid etching residues, then clean the processed silicon carbide wafers and dehydrate them.

9. The method for processing a silicon carbide wafer with reduced thinning stress as claimed in claim 8, characterized in that: After cleaning the grinding and acid etching residues, cleaning the processed silicon carbide wafer, and dehydrating, the method further comprises: UV light is applied to the front side of the silicon carbide wafer.

10. The method for processing a silicon carbide wafer with reduced thinning stress according to claim 9, wherein: After the UV light is irradiated on the front side of the silicon carbide wafer, the method further comprises: The protective film is removed to obtain a thinned silicon carbide wafer.

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