Silicon carbide wafer processing method for reducing thinning stress

Abstract

The present invention provides a method for processing a silicon carbide wafer to reduce thinning stress, and relates to the field of semiconductor processing technology. The method comprises: completing the processing of the front side of the silicon carbide wafer; applying a UV adhesive layer on the front side of the silicon carbide wafer; flattening and curing the surface of the UV adhesive layer; applying a protective film to the cured UV adhesive layer; and after fixing the silicon carbide wafer, grinding and thinning the back side of the silicon carbide wafer. Brushing the UV adhesive layer on the front side fills and eliminates the high step difference on the front side caused by processing, keeping the surface of the UV adhesive layer flat, and vacuum adsorption will not cause deformation of the SiC wafer, and the SiC wafer has almost no internal stress; during the grinding process, the SiC wafer is evenly stressed, and the back side of the processed wafer is symmetrical. After the SiC wafer is released from adsorption, no excess stress is released, ensuring that the thinned wafer will not break, thereby improving the yield and qualified rate.

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 are widely used in high-power electronic devices due to their excellent electrical properties and high thermal conductivity. However, as power density continues to increase, the front-side 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. While this thickening design improves chip performance, it also results in a large step difference on the chip surface.

[0003] At present, the thinning of SiC wafers mainly adopts 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 fragmentation and may also have an adverse effect on the electrical performance of the SiC chip produced. 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 fragmentation.

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

[0007] Finish processing the front side of the silicon carbide wafer;

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

[0009] Flatten and solidify the surface of the UV adhesive layer;

[0010] Apply protective film to 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 surface of the silicon carbide wafer and solidifying 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-sensitive adhesive with reduced viscosity.

[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 photosensitive denaturing 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-corrosion-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 performing acid etching on the back side of the ground silicon carbide wafer, the silicon carbide wafer processing method for reducing thinning stress further includes:

[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 irradiated on the front side of the silicon carbide wafer.

[0024] Optionally, after the UV light is applied to the front surface 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 to reduce thinning stress. Compared with the prior art, it has the following advantages:

[0027] After 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 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 the SiC wafer has almost no internal stress. During the grinding process, the SiC wafer is subjected to uniform force at all parts, and the wafer will not produce problems such as deformation or position deviation, making 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 qualification 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 following briefly introduces the drawings required for use in the embodiments or the description of the prior art. 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 any creative work.

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

[0030] To make the objectives, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application are clearly and completely described. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0031] The embodiments of the present application provide a method for processing silicon carbide wafers that reduces thinning stress, thereby solving the problem that existing SiC wafer thinning methods generate wafer deformation stress when processing SiC wafers with step differences, thereby increasing the risk of wafer fragmentation, 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 with reference to the accompanying drawings and specific implementation methods.

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

[0034] Step 1: Process 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 caused by processing on the front side. The UV adhesive layer covers the structure formed by 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 and has no high step difference. The vacuum adsorption will not cause the SiC wafer to deform. At this time, the adsorbed S The front of the SiC wafer is subjected to external adsorption force as a whole, and there is almost no internal stress. The back of the fixed SiC wafer is ground and thinned. During the processing, the grinding wheel is close to the back of the wafer. Since the front of the SiC wafer is flat, the SiC wafer is evenly stressed. The wafer will not deform or deflect during the grinding process, making the back of the processed wafer symmetrical, further reducing or eliminating the SiC wafer thinning stress. After the SiC wafer is released from adsorption, there is almost no excess stress release, ensuring that the SiC wafer will not be broken when it is finally removed, thereby improving the yield and qualification rate of SiC wafer processing.

[0040] Each step is described in detail below.

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

[0042] Specifically, other semiconductor manufacturing processes such as epitaxial growth, ion implantation, photolithography, and etching are carried out 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 constructs a SiC wafer chip. 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 is likely to cause uneven processing. After processing, the SiC wafer is not constrained 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] Steps 2 and 3 follow a sequential order, but they need to be performed alternately. Specifically, UV adhesive is applied layer by layer to the front of the SiC wafer. After each layer is flattened and cured, a UV adhesive layer is formed. This means that the UV adhesive is evenly applied layer by layer to the entire front surface of the wafer, preventing defects such as bubbles, sagging, and uneven thickness in the UV adhesive layer. Any steps on the front of the SiC wafer are filled. During the UV adhesive application process, layers can be overlapped before they are fully cured. Once fully cured, no distinct boundaries are formed between the layers. The thickness of the UV adhesive layer is n times the step height on the front of the SiC wafer, where n is greater than 1 and less than 3. This means that the UV adhesive layer must completely cover the structure formed on the front of the wafer to ensure adequate support and protection during grinding and thinning. However, the UV adhesive layer should not be too thick, as the UV adhesive layer has a certain degree of compressive elasticity. A thicker UV adhesive layer will deform more when subjected to stress. Therefore, the UV adhesive layer thickness is controlled to be less than 3 times the step height to prevent significant deformation when subjected to stress, thereby ensuring that no internal stress is generated on the wafer during adsorption.

[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 and material of the wafer and the requirements of the subsequent thinning process, select a UV glue with appropriate viscosity, curing speed, peel strength and transparency. In this application, the UV glue is a UV photosensitive viscosity-reducing glue. The surface viscosity of the glue after exposure is lower than the internal interconnection strength of the UV glue, that is, the surface viscosity of the UV glue after exposure is lower than the internal viscosity of the UV glue. The UV glue can be selected from mixed glues such as acrylic UV viscosity-reducing glue, silicone-based UV viscosity-reducing glue, and two-component high-temperature resistant UV viscosity-reducing glue. The choice of UV glue is not limited to the several types listed above, and other UV photosensitive viscosity-reducing glues can also be selected. When the entire UV glue layer is subjected to UV light exposure, the viscosity of the surface of the UV glue layer is reduced after exposure, but the viscosity of the internal UV glue layer is still strong, and it is easy to peel off from the wafer as a whole.

[0047] Common UV adhesive curing methods include ultraviolet (UV) curing and thermal curing. UV curing is typically achieved by UV light, which illuminates the adhesive layer with a specific wavelength and intensity, causing a photochemical reaction and curing. During the curing process, the wafer must be kept stable to avoid deformation or cracking of the adhesive layer due to vibration or movement. This ensures that the adhesive layer is fully cured and tightly bonded to the front of the wafer, forming a flat, solid protective layer that provides a stable base for subsequent lamination and polishing.

[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 treatment process. The protective film includes a base layer and an adhesive layer, the adhesive layer is bonded to the base layer, the adhesive layer and the base layer do not contain UV photosensitive denaturing materials or components, especially the adhesive layer cannot contain UV photosensitive denaturing materials or components, the adhesive layer viscosity is greater than the adhesive interface viscosity of the UV adhesive after exposure, that is, the adhesive layer viscosity of the protective film is greater than the UV adhesive interface viscosity of the UV adhesive layer after exposure, so as to facilitate the removal of the protective film and peeling off the UV adhesive layer on the wafer surface. The base material of the protective film is an acid corrosion-resistant material. The adhesive layer of the protective film can be acrylic glue or rubber-type glue, etc., and the base 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 apply the protective film evenly to the surface of the cured UV adhesive layer. During the laminating process, avoid bubbles, wrinkles, and edge warping of the protective film, and ensure that the protective film and UV adhesive layer are tightly attached 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, the silicon carbide wafer with a protective film is placed on a special fixture of the grinding equipment, the position of the wafer is adjusted so that its back faces the grinding wheel, and the wafer is firmly fixed 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 size 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 size 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 damage 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 coarse grinding stage can be set at 50rpm to 100rpm, and the grinding is carried out for a certain 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, select suitable wet acid etching equipment, such as an etching tank. Place the wafer in the acid etching solution, control the temperature at 20°C, soak for 300 seconds, and stabilize the wafer rotation speed at 3rpm to ensure etching uniformity. At the same time, monitor the concentration of the acid etching solution. 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 a mixture of 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 time can be 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 can be spin drying, baking, organic alcohol dehydration, high-purity nitrogen blowing or natural drying in a clean environment, etc., not limited to the above dehydration methods, and other dehydration methods that do not damage the silicon carbide wafer can be used.

[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 adhesive 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 adhesive layer and effectively soften the UV adhesive 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 irradiating from the back of the wafer, the interface where the UV adhesive layer and the wafer are bonded is mainly irradiated, reducing 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 separately. Specifically, you can use tweezers or similar tools to gently grab 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, use an appropriate amount of solvents such as acetone or isopropyl alcohol 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 existing technology, the present invention has the following beneficial effects:

[0064] 1. After 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 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 applied to the surface of the UV adhesive layer to protect the UV adhesive layer and the structure on the front side from being damaged during the subsequent grinding and thinning process. The SiC wafer is adsorbed and fixed. Vacuum adsorption does not cause deformation of the SiC wafer, and the SiC wafer has almost no internal stress. Since the front side of the SiC wafer is flat, the force is evenly distributed on the SiC wafer during the grinding process, and the wafer will not be deformed or skewed during the grinding process. The back side of the processed wafer is symmetrical, further reducing or eliminating the stress of the SiC wafer thinning. 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 qualification 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 wafer front processing 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 is not affected. At this time, the adhesiveness of the non-UV film is used to peel off the protective film and the UV adhesive layer together. The UV adhesive layer is removed at the same time, avoiding the complicated operation of removing the UV adhesive separately.

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

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

[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: Finish processing the front side of the silicon carbide wafer; Applying UV glue layer by layer on the front surface of the silicon carbide wafer and flattening the layers to form a UV glue layer, wherein the UV glue is a UV photosensitive adhesive with reduced viscosity, and the thickness of the UV glue layer is n times the step height of the front surface of the silicon carbide wafer, where n is greater than 1 and less than 3; A protective film is applied to the cured UV adhesive layer, wherein the protective film comprises a base layer and an adhesive layer, the adhesive layer is bonded to the base layer, the adhesive layer does not contain UV light-sensitive denaturing 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; After the silicon carbide wafer is fixed, the back side of the silicon carbide wafer is ground and thinned; The back side of the ground silicon carbide wafer is subjected to acid etching treatment.

2. The method for processing a silicon carbide wafer to reduce thinning stress according to claim 1, wherein: The protective film is a film made of non-UV material.

3. The method for processing a silicon carbide wafer with reduced thinning stress according to claim 1, wherein: After performing acid etching on the back side of the ground silicon carbide wafer, the method further comprises: Clean the grinding and acid etching residues, then clean the processed silicon carbide wafers and dehydrate them.

4. The method for processing a silicon carbide wafer with reduced thinning stress according to claim 3, wherein: After cleaning the grinding and acid etching residues, cleaning the processed silicon carbide wafer, and dehydrating, the method further comprises: UV light is irradiated on the front side of the silicon carbide wafer.

5. The method for processing a silicon carbide wafer with reduced thinning stress according to claim 4, wherein: After irradiating the front surface of the silicon carbide wafer with UV light, the method further includes: The protective film is removed to obtain a thinned silicon carbide wafer.

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