Porous metal bond diamond grinding wheel for SiC thinning and SiC thinning method

Abstract

This invention discloses a porous metal-bonded diamond grinding wheel for SiC thinning and a method for SiC thinning. The porous metal-bonded diamond grinding wheel for SiC thinning includes an outer body and a filling cavity disposed inside the outer body, the filling cavity being filled with microspheres. In this application, the outer body of the porous metal-bonded diamond grinding wheel for SiC thinning is filled with microspheres. During the grinding process, as the temperature rises, the microspheres also expand due to heat, and the microspheres squeeze and slide against each other, dynamically filling the filling cavity to buffer and disperse local stress, which helps to reduce contact pressure fluctuations.

Description

Technical Field

[0001] This invention relates to the field of SiC thinning technology, and more specifically, to a porous metal-bonded diamond grinding wheel for SiC thinning and a SiC thinning method. Background Technology

[0002] Silicon carbide (SiC), a wide-bandgap semiconductor material, is widely used in power electronics and radio frequency devices due to its excellent properties such as high hardness, high thermal conductivity, and high breakdown electric field. Thinning is a critical step in SiC device manufacturing, aiming to reduce the SiC wafer to the required thickness to meet device performance requirements. Traditional SiC thinning primarily employs mechanical grinding, removing material through the relative movement of a grinding wheel and the SiC wafer. However, during grinding, the contact stress between the grinding wheel and the SiC wafer concentrates, easily inducing periodic microcracks. These microcracks, under the influence of localized thermal stress gradients caused by uneven coolant penetration, can further propagate, forming so-called "sunburst" defects. Furthermore, due to the high hardness and brittleness of SiC, the surface roughness (Ra) after thinning typically reaches 40 nm, and a subsurface damage layer with a depth of approximately 4 μm exists. These morphological defects severely affect device performance and reliability.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a porous metal-bonded diamond grinding wheel for SiC thinning and a method for SiC thinning, thereby solving the problem of periodic microcrack formation and propagation caused by contact stress concentration between the grinding wheel and the SiC wafer during the grinding process.

[0005] This invention is implemented as follows:

[0006] In a first aspect, the present invention provides a porous metal-bonded diamond grinding wheel for SiC thinning, the porous metal-bonded diamond grinding wheel for SiC thinning includes an outer body and a filling cavity disposed inside the outer body, the filling cavity being filled with microspheres, the coefficient of thermal expansion of the microspheres being 2-3 times that of the coefficient of thermal expansion of the outer body.

[0007] In an optional embodiment, the microspheres have a particle size of 10 μm-50 μm;

[0008] And / or, the microspheres are at least one of shape memory alloy microspheres, silicon microspheres, graphite microspheres, and quartz glass microspheres.

[0009] In an optional embodiment, the microspheres are Ni-Ti alloy microspheres.

[0010] In an optional embodiment, the mass ratio of the outer body to the filled microspheres is 7:(2.5-3.5);

[0011] And / or, the diamond grain size in the outer body is #1500-#2500.

[0012] Secondly, the present invention provides a SiC thinning method, comprising: grinding the SiC element to be thinned using a porous metal-bonded diamond grinding wheel for SiC thinning as described in any of the foregoing embodiments until the thinning thickness meets the requirements.

[0013] In an optional embodiment, the grinding is performed in the presence of a coolant comprising nanosheets and a lubricant, the coolant satisfying at least one of the following characteristics:

[0014] a. The mass fraction of nanosheets in the coolant is 5%-10%;

[0015] b. The thickness of the nanosheet is < 5 nm;

[0016] c. The nanosheets are boron nitride nanosheets.

[0017] In an optional embodiment, the grinding area is further chemically treated with a treatment solution comprising potassium hydroxide and H2O2, wherein the mass ratio of potassium hydroxide to H2O2 in the treatment solution is (2-3):1, and the concentration of H2O2 in the treatment solution is 0.4mol / L-0.6mol / L.

[0018] In an optional embodiment, the temperature of the chemical treatment is 45°C-55°C;

[0019] And / or, the flow rate of the treatment solution is 0.1 mL / min to 1 mL / min;

[0020] And / or, the treatment liquid is sprayed onto the area to be chemically treated using a spray device.

[0021] In an optional embodiment, during the grinding step, the rotating speed of the porous metal-bonded diamond grinding wheel for SiC thinning is 200rpm-500rpm, and the feed rate is 1μm / s-5μm / s.

[0022] The present invention has the following beneficial effects:

[0023] This application fills the outer body of a porous metal-bonded diamond grinding wheel for SiC thinning with microspheres. During the grinding process, as the temperature rises, the microspheres will also expand due to heat, and the microspheres will squeeze and slide against each other, which can dynamically fill the filling cavity to buffer and disperse local stress, which is beneficial to reduce contact pressure fluctuations. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a photograph of the thinned SiC element obtained in Embodiment 1 of this application;

[0026] Figure 2 This is a photograph of the thinned SiC element obtained in Embodiment 5 of this application;

[0027] Figure 3 A photograph of the thinned SiC device obtained in Comparative Example 1 of this application;

[0028] Figure 4 This is a surface view of the thinned SiC element obtained in Embodiment 1 of this application;

[0029] Figure 5 This is a surface view of the thinned SiC device obtained in Comparative Example 1 of this application. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0031] This invention provides a porous metal-bonded diamond grinding wheel for SiC thinning. The porous metal-bonded diamond grinding wheel for SiC thinning includes an outer body and a filling cavity disposed inside the outer body. The filling cavity is filled with microspheres, and the coefficient of thermal expansion of the microspheres is 2-3 times that of the coefficient of thermal expansion of the outer body.

[0032] This application fills the outer body of a porous metal-bonded diamond grinding wheel for SiC thinning with microspheres. During the grinding process, as the temperature rises, the microspheres will also expand due to heat, and the microspheres will squeeze and slide against each other, which can dynamically fill the filling cavity to buffer and disperse local stress, which is beneficial to reduce contact pressure fluctuations.

[0033] The thermal expansion coefficient of the microspheres is higher than that of the outer layer, which helps the microspheres to detect temperature changes in a timely manner and dynamically fill the filling cavity, and is also more conducive to timely buffering and dispersing local stress. However, if the thermal expansion coefficient of the microspheres is too high, it will lead to a decrease in the strength of the porous metal-bonded diamond grinding wheel and a decrease in grinding efficiency.

[0034] In an optional embodiment, the particle size of the microspheres is 10μm-50μm. The particle size of the microspheres affects their ability to dynamically fill the filling cavity. If the particle size is too small, the porosity in the filling cavity is low, and the movement of the microspheres becomes more difficult. If the particle size is too large, it is not conducive to the uniform distribution of stress between the microspheres and the outer layer body, which in turn is not conducive to the dispersion of local stress between the grinding wheel and the SiC element to be thinned.

[0035] In an optional embodiment, the microspheres are at least one selected from shape memory alloy microspheres, silicon microspheres, graphite microspheres, and quartz glass microspheres. The coefficients of thermal expansion of silicon microspheres, graphite microspheres, and quartz glass microspheres meet the aforementioned requirements.

[0036] In an optional embodiment, the microspheres are Ni-Ti alloy microspheres.

[0037] In an optional embodiment, the diamond grain size in the outer body is #1500-#2500;

[0038] The outer layer body includes the contact surface directly with the SiC element to be thinned. Reasonable selection of diamond particle size in the outer layer body is beneficial to balancing grinding efficiency and SiC element surface quality.

[0039] In an optional embodiment, the mass ratio of the outer body to the filled microspheres is 7:(2.5-3.5). If the proportion of microspheres is too small, it will not be conducive to improving the ability to buffer and disperse local stress. However, if the proportion of microspheres is too large, the mass of the outer body will be reduced, the wall thickness corresponding to the filling cavity will be reduced, the friction force and strength provided will be reduced, which will not be conducive to improving efficiency and grinding wheel life.

[0040] In an optional embodiment, the microspheres are Ni-Ti alloy microspheres.

[0041] Ni-Ti alloy is a shape memory alloy with a reversible shape memory effect. It can recover to its initial shape through physical stimulation, and its size and morphology are controllable. It also has high strength, low hardness, and a recovery strain of up to 10%, as well as high environmental stability. Compared with graphite, which is brittle and prone to flaking, and quartz glass, which is hard and easily affected by microcracks, Ni-Ti alloy microspheres have superior advantages.

[0042] The present invention also provides a SiC thinning method, comprising: grinding the SiC element to be thinned using a porous metal-bonded diamond grinding wheel for SiC thinning as described in any one of the foregoing embodiments until the thinning thickness meets the requirements.

[0043] Generally, the thickness reduction is related to the grinding rate, and the required thickness reduction can be met by controlling the processing time.

[0044] In some implementations, a laser confocal sensor can be used to monitor the surface roughness of the SiC element in real time (resolution 0.1 nm) and generate a 3D topography image at regular intervals. When the topography image shows that the surface roughness of the SiC element reaches a preset value and the thinning thickness meets the requirements, the thinning of the SiC element is completed.

[0045] In an optional embodiment, the grinding is performed in the presence of a coolant comprising nanosheets and a lubricant, the coolant satisfying at least one of the following characteristics:

[0046] a. The mass fraction of nanosheets in the coolant is 5%-10%;

[0047] b. The thickness of the nanosheet is < 5 nm;

[0048] c. The nanosheets are boron nitride nanosheets.

[0049] In this application, nanosheets in the coolant can form a solid-like lubricating film at the grinding interface, reducing the coefficient of friction while simultaneously enhancing heat conduction. Selecting thinner nanosheets is beneficial for obtaining smoother SiC components with more balanced thinning effects at various locations. The nanosheets need to be selected to not react with the base fluid and have a lower hardness than silicon carbide to avoid wear on the silicon carbide. For example, boron nitride nanosheets can be selected, which have the following advantages: low hardness; high thermal conductivity (~2000 W / m·K), which can significantly improve heat dissipation efficiency; strong chemical inertness and resistance to acid and alkali corrosion; low coefficient of friction and low flow resistance.

[0050] The coolant also includes a base fluid, the purpose of which is to disperse the nanosheets. This base fluid can be a polyalphaolefin with a high viscosity index, low-temperature performance, and thermal oxidation stability. Additionally, to improve the dispersion effect, a surfactant may be added in some embodiments. Dipotassium amine, for example, can be used, as it possesses both lubricating and antistatic properties. The mass fraction of the surfactant in the coolant can be 0.4%-0.1%.

[0051] It should be noted that, because the grinding wheel in this application is filled with heat-sensitive microspheres, the overall thermal expansion coefficient of the grinding wheel increases, making it more sensitive to temperature changes. If the processing temperature is too high, the improved grinding wheel is prone to deformation or stress and is not stable enough. Therefore, using water in conventional sand mills as a coolant cannot meet the requirements for rapid cooling of the sand milling area, which will lead to excessively high disc temperature. The grinding wheel in this application, when used with the coolant in this application, is more conducive to ensuring timely heat dissipation and temperature stability during the processing.

[0052] In an optional embodiment, the grinding area is further chemically treated with a treatment solution comprising potassium hydroxide and H2O2, wherein the mass ratio of potassium hydroxide to H2O2 in the treatment solution is (2-3):1, and the concentration of H2O2 in the treatment solution is 0.4 mol / L-0.6 mol / L. The potassium hydroxide in the treatment solution can corrode the SiC surface, which helps eliminate stress concentration at the microcrack tips; the H2O2 can form a SiO2 passivation layer on the inner wall of the oxide crack, which helps inhibit crack propagation.

[0053] In an optional embodiment, the temperature of the chemical treatment is 45°C-55°C;

[0054] And / or, the flow rate of the treatment solution is 0.1 mL / min to 1 mL / min;

[0055] And / or, the treatment liquid is sprayed onto the area to be chemically treated using a spray device, which helps to uniformly disperse the treatment liquid on the surface of the SiC element.

[0056] In some implementations, the chemical treatment zone is carried out simultaneously with the grinding process, and the treatment fluid and coolant can be sprayed onto the grinding zone at the same time for chemical treatment and cooling.

[0057] In an optional embodiment, during the grinding step, the rotating speed of the porous metal-bonded diamond grinding wheel for SiC thinning is 200 rpm-500 rpm, and the feed rate is 1 μm / s-5 μm / s. This helps to ensure grinding efficiency while ensuring that the surface smoothness and microcrack condition of the SiC component meet the requirements.

[0058] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0059] Example 1

[0060] This embodiment provides a SiC thinning method, which specifically includes the following steps:

[0061] In the presence of coolant and processing fluid, a porous metal-bonded diamond grinding wheel for SiC thinning is used to grind the area of ​​SiC element to be thinned.

[0062] The porous metal-bonded diamond grinding wheel for SiC thinning rotates at 300 rpm and has a feed rate of 3 μm / s. The porous metal-bonded diamond grinding wheel includes an outer body and a filling cavity disposed inside the outer body. The filling cavity is filled with Ni-Ti alloy microspheres with an average particle size of 30 μm. The diamond particle size in the outer body is #2000, and the mass ratio of the outer body to the filled Ni-Ti alloy microspheres is 7:3.

[0063] The coolant comprises boron nitride nanosheets and polyα-olefin, wherein the mass fraction of the nanosheets in the coolant is 7.5% and the thickness is <5nm;

[0064] The treatment solution is a mixed aqueous solution of 1 mol / L potassium hydroxide and 0.5 mol / L H2O2, the chemical treatment temperature is 50℃, and the flow rate of the treatment solution is 0.5 mL / min.

[0065] Example 2

[0066] This embodiment provides a SiC thinning method, which specifically includes the following steps:

[0067] In the presence of coolant and processing fluid, a porous metal-bonded diamond grinding wheel for SiC thinning is used to grind the area of ​​SiC element to be thinned.

[0068] The porous metal-bonded diamond grinding wheel for SiC thinning rotates at 200 rpm and has a feed rate of 1 μm / s. The porous metal-bonded diamond grinding wheel includes an outer body and a filling cavity disposed inside the outer body. The filling cavity is filled with Ni-Ti alloy microspheres with an average particle size of 10 μm. The diamond particle size in the outer body is #2500, and the mass ratio of the outer body to the filled Ni-Ti alloy microspheres is 7:3.5.

[0069] The coolant comprises boron nitride nanosheets and polyα-olefin, wherein the mass fraction of the nanosheets in the coolant is 5% and the thickness is <5nm;

[0070] The treatment solution is a mixed aqueous solution of 1.2 mol / L potassium hydroxide and 0.4 mol / L H2O2, the chemical treatment temperature is 55℃, and the flow rate of the treatment solution is 1 mL / min.

[0071] Example 3

[0072] This embodiment provides a SiC thinning method, which specifically includes the following steps:

[0073] In the presence of coolant and processing fluid, a porous metal-bonded diamond grinding wheel for SiC thinning is used to grind the area of ​​SiC element to be thinned.

[0074] The porous metal-bonded diamond grinding wheel for SiC thinning operates at a rotation speed of 500 rpm and a feed rate of 5 μm / s. The porous metal-bonded diamond grinding wheel includes an outer body and a filling cavity disposed within the outer body. The filling cavity is filled with Ni-Ti alloy microspheres with an average particle size of 50 μm. The diamond particle size in the outer body is #1500, and the mass ratio of the outer body to the filled Ni-Ti alloy microspheres is 7:2.5.

[0075] The coolant comprises boron nitride nanosheets and polyα-olefin, wherein the mass fraction of the nanosheets in the coolant is 10% and the thickness is <5nm;

[0076] The treatment solution is a mixed aqueous solution of 1.2 mol / L potassium hydroxide and 0.6 mol / L H2O2, the chemical treatment temperature is 45℃, and the flow rate of the treatment solution is 0.1 mL / min.

[0077] Comparative Example 1

[0078] This comparative example provides a SiC thinning method, which specifically includes the following steps:

[0079] Under the condition of using water as coolant, grinding wheels are used to grind the area of ​​SiC element to be thinned;

[0080] The grinding wheel rotation speed and feed rate are the same as in Example 1. The grinding wheel is a solid structure without a filling cavity and is not filled with Ni-Ti alloy microspheres.

[0081] Example 4

[0082] This embodiment provides a SiC thinning method, which differs from Embodiment 1 mainly in that the grinding wheel is different, the coolant is water, and no chemical treatment is performed using a processing solution.

[0083] Example 5

[0084] This comparative example provides a SiC thinning method, which differs from Example 1 mainly in that: no chemical treatment with a processing solution is used.

[0085] Example 6

[0086] This comparative example provides a SiC thinning method, which differs from Example 1 mainly in that the microspheres are made of quartz glass.

[0087] Example 7

[0088] This comparative example provides a SiC thinning method, which differs from Example 1 mainly in that the average particle size of the microspheres is 100 μm.

[0089] Example 8

[0090] This comparative example provides a SiC thinning method, which differs from Example 1 mainly in that the mass ratio of the outer layer to the filled Ni-Ti alloy microspheres is 9:1.

[0091] The surface roughness and subsurface damage layer depth of the thinned SiC devices obtained in the above embodiments and comparative examples were tested using the following methods:

[0092] For surface roughness testing, five points were selected on the surface of the thinned SiC element, and the surface roughness of each point was tested using an atomic force microscope (AFM) and the average value was calculated.

[0093] The method for testing the depth of the subsurface damage layer is as follows: the thinned SiC element is polished until the sunburst pattern is removed.

[0094] The test results are shown in Table 1.

[0095] Table 1

[0096] Surface roughness (nm) Subsurface damage layer depth μm Example 1 10 2.0 Example 2 12 2.5 Example 3 14 2.6 Example 5 24 3.2 Example 6 37 3.8 Example 7 30 3.3 Example 8 28 3.5 Comparative Example 1 40 4.0

[0097] According to Table 1, compared with Comparative Example 1, Examples 1 and 5 show that using the grinding wheel of this application is beneficial for reducing surface roughness and subsurface damage layer depth. Increasing the processing fluid can further reduce surface roughness and subsurface damage layer depth. Comparing Examples 1 and 8 shows that Ni-Ti alloy is more beneficial for reducing surface roughness and subsurface damage layer depth because Ni-Ti alloy has high strength, low hardness, and a strain recovery rate of 10%, while quartz glass has high hardness and is easily affected by microcracks, which may cause new scratches, increasing surface roughness and subsurface damage layer depth. Comparing Examples 1 and 9 shows that excessively large microsphere particle size leads to increased surface roughness and subsurface damage layer depth. This may be because large-diameter microspheres expand significantly when heated, reducing the contact area between diamond and silicon carbide, resulting in less wafer removal within the same processing time, thus leaving residual damage layer from the previous stage. Comparing Examples 1 and 10 shows that if the diamond content is too high, the effect of the microspheres is too small, resulting in higher surface roughness and deeper subsurface damage layer depth.

[0098] It should be noted that for Examples 1-3 and Examples 5-8, the surface temperature of the grinding disc can be maintained between 35-40°C during the grinding process. However, in Example 4, due to the unsuitable selection of coolant, the surface temperature of the grinding disc exceeds 45°C, which causes greater damage to the equipment.

[0099] In addition, the surface images of the thinned SiC devices obtained in Examples 1, 5 and Comparative Example 1 are as follows: Figure 1-3As shown, it can be seen that no "sunburst pattern" is observed on the surface of the thinned SiC element obtained in Example 1, the "sunburst pattern" is only present in the area outlined in red in Example 5 and is not obvious, while the sunburst pattern is obvious on the surface of the thinned SiC element obtained in Comparative Example 1. Further, as... Figure 4-5 The images show the surface profiles of the thinned SiC elements obtained in Example 1 and Comparative Example 1, obtained using the Tropel measurement method. It can be seen that the "sun pattern" in Example 1 almost disappears compared to Comparative Example 1.

[0100] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A porous metal-bonded diamond grinding wheel for SiC thinning, characterized in that, The porous metal-bonded diamond grinding wheel for SiC thinning includes an outer body and a filling cavity disposed inside the outer body. The filling cavity is filled with microspheres, and the coefficient of thermal expansion of the microspheres is 2-3 times that of the outer body. During the grinding process, as the temperature rises, the microspheres expand due to heat. The microspheres will squeeze and slide against each other, dynamically filling the filling cavity to buffer and disperse local stress.

2. The porous metal-bonded diamond grinding wheel for SiC thinning according to claim 1, characterized in that, The microspheres have a particle size of 10μm-50μm.

3. The porous metal-bonded diamond grinding wheel for SiC thinning according to claim 1, characterized in that, The microspheres are at least one of shape memory alloy microspheres, silicon microspheres, graphite microspheres, and quartz glass microspheres.

4. The porous metal-bonded diamond grinding wheel for SiC thinning according to claim 1, characterized in that, The microspheres are Ni-Ti alloy microspheres.

5. The porous metal-bonded diamond grinding wheel for SiC thinning according to claim 1, characterized in that, The mass ratio of the outer body to the filled microspheres is 7:(2.5-3.5). And / or, the diamond grain size in the outer body is #1500-#2500.

6. A method for thinning SiC, characterized in that, include: The SiC element to be thinned is ground using a porous metal-bonded diamond grinding wheel as described in any one of claims 1-5 until the required thinning thickness is achieved.

7. The SiC thinning method according to claim 6, characterized in that, The grinding is performed in the presence of a coolant comprising nanosheets and a lubricant, wherein the coolant satisfies at least one of the following characteristics: a. The mass fraction of nanosheets in the coolant is 5%-10%; b. The thickness of the nanosheet is < 5 nm; c. The nanosheets are boron nitride nanosheets.

8. The SiC thinning method according to claim 6, characterized in that, It also includes chemically treating the grinding area with a treatment solution, wherein the treatment solution includes potassium hydroxide and H2O2, the mass ratio of potassium hydroxide to H2O2 in the treatment solution is (2-3):1, and the concentration of H2O2 in the treatment solution is 0.4 mol / L - 0.6 mol / L.

9. The SiC thinning method according to claim 8, characterized in that, The temperature of the chemical treatment is 45℃-55℃; And / or, the flow rate of the treatment liquid is 0.1 mL / min - 1 mL / min; And / or, the treatment liquid is sprayed onto the area to be chemically treated using a spray device.

10. The SiC thinning method according to claim 6, characterized in that, In the grinding step, the rotating speed of the porous metal-bonded diamond grinding wheel for SiC thinning is 200 rpm - 500 rpm, and the feed rate is 1 μm / s - 5 μm / s.

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