Preparation And Polishing Characteristics Of Magnetorheological Elastic Polishing Pad For Single-crystal SiC

As a third-generation semiconductor material,SiC features high forbidden band width,high thermal conductivity,high breakdown field strength,high saturation electron mobility and low relative permittivity,and is widely used in 5G communication,smart grid,new energy vehicles and other fields.SiC is used for electronic device fabrication and epitaxial film growth,which requires an ultra-smooth surface without damage or defects.However,due to its high hardness,high brittleness physical properties and stable chemical properties,it is difficult to guarantee a high quality surface while obtaining efficient processing.Chemical Mechanical Polishing（CMP）is considered to be one of the most effective processing technique to obtain global flattening of semiconductor materials.Magnetorheological elastomers（MREs）are smart materials that can control their material mechanical properties by adjusting the applied magnetic field strength.This paper proposes to use MRE as the polishing pad in CMP,and control the hardness of the MRE polishing pad through the applied magnetic field to control the mechanical removal in the polishing process.Meanwhile,the magnetic particles in MRE are used as solid-phase catalyst to oxidize the SiC surface in a heterogeneous Fenton reaction,which reduces the polishing process difficulty,achieves efficient material removal,and obtains a high-quality processed surface.Firstly,the material modulus change of MRE polishing pad under the action of applied magnetic field was investigated according to the principle of magnetic control of MRE,and the mechanism of·OH generation by magnetic particles on the surface of MRE was analyzed according to the principle of heterogeneous Fenton reaction,and the processing principle of MRE polishing pad for SiC was elaborated.Secondly,designed a process for the preparation of MRE polishing pads based on the prepolymerization method.A series of MRE polishing pads were prepared by selecting the preparation parameters that affect the magneto-control performance of MRE.The magneto-control performance and polishing properties of MRE were investigated by magnetron mechanical test,microscopic chain string observation and polishing test.The results show that has better magneto-control properties the magnetic particle CIP than Fe₃O₄.The larger the mass fraction of CIP,the better the magneto-control properties and the better the polishing effect.The larger the particle size of CIP,the more regular the chain strings formed,but the smaller the number of chain strings,the smaller the magnetic energy density,but the effect on the magneto-control properties and polishing effect is not significant.Anisotropic MREs form a more regular chain strings and exhibit better magneto-control properties and polishing performance.As the polishing magnetic field strength increases,the modulus material of MRE increases,the material removal rate increases,and the surface quality becomes better.Thirdly,the heterogeneous Fenton reaction polishing characteristics of MRE polishing pads were studied by polishing tests,grinding chips analysis,and the material removal mechanism was established.The results showed that better polishing effects were obtained in MRE polishing using H₂O₂ polishing solution than deionized water polishing solution.The material removal rate of 1194.27 nm/h and the surface roughness of R_a 4.420 nm were obtained when polishing with H₂O₂ polishing solution for 60 min.From the analysis of the grinding chips after 60 min of polishing,it was found that the H₂O₂ polishing solution polished with laminated loose chips,and the O element accounting for 38.585 wt%.XPS demonstrates that the laminated loose chips is Si O₂ oxide.This proves that MRE polishing pads can undergo a heterogeneous Fenton reaction during polishing.On this basis,the effect pattern of heterogeneous Fenton reaction parameters on polishing was investigated by single-factor experiments.The solid phase catalyst Fe₃O₄ than CIP have better heterogeneous Fenton reaction polishing effect.The smaller the particle size of Fe₃O₄,the larger the specific surface area,and the better polishing effect was obtained at a particle size of 0.3μm.The greater the concentration of H₂O₂ in the polishing solution,the greater the material removal rate,and the surface roughness R_a first decreases and then increases.Greater material removal rates and lower surface roughness in polishing solution with p H=3.Finally,the material removal behavior of MRE magnetron-heterogeneous Fenton reaction composite polishing was investigated.It was found that the mechanical action of abrasive particles in MRE polishing dominates in material removal（63.74%contribution）,the contribution of magneto-controlled polishing to material removal was 10.99%,the contribution of heterogeneous Fenton reaction to material removal was 22.02%,and the contribution of magneto-controlled and heterogeneous Fenton reaction interaction to material removal was small.The SiC-Abrasive Particles-MRE polishing pad contact state analysis of a single abrasive grain reveals.The increase in hardness of the MRE polishing pad under magnetic control and the decrease in hardness of the SiC surface under heterogeneous Fenton reaction can both increase the depth of the abrasive grain pressed into the SiC surface and produce greater material removal.