| As the third generation semiconductor materials, SiC has excellent characteristics such as strong thermal conductivity, low dielectric constant, strong radiation resistance and good chemical stability, as a consequence, it’s promising in LED lighting, electronics, aerospace, automobile and computer chips. For application of SiC wafers, ultra smooth and defects free surface is requisite, but as a result of high hardness, strong chemical stability? the ultra-precision processing of SiC wafers is difficult, inefficient and costly. Therefore, research on ultra-precis ion polishing process of SiC wafer, reducing the processing costs and achieving atomic ultra smooth surface is an urgency and key technical problems need to be solved for application of SiC semiconductor device.Cluster magnetorheological chemical compound polishing (CMRF) was used for polishing single-crystal SiC. Due to the exist of accommodate-sink ing effect produced by cluster magnetorheological flexible polishing pad, the mechanical damage on surface of wafer caused by abrasive can be reduced greatly, and a lower roughness can be obtained. In addition, the oxidation of hydroxyl radical (· OH) in polishing solution can effectively improve the efficiency of polishing, which makes the surface roughness fall faster.The catalytic effect on fenton reaction of several kinds of solid catalyst and liquid catalyst was compared by chemical corrosion experiments, CMP experiments of single-crystal SiC and concentration detection experiments of catalytic ferrous ions (Fe2-). The fenton corrosion fluid composed by Fe3O4 and H2O2 was confirmed evey efficient in corrosion of single-crystal SiC. The acting principle of solid catalyst was analyzed in this paper. The concentration and stability of Fe2+ in chemical polishing solution are crucial factors deciding the rate and stability of Fenton reaction, and the concentration of Fe2+ is directly affected by the ability of ionizing free Fe2+ of solid catalyst. In order to study the coordination between chemical corrosion and mechanical removal, single factor experiment about crucial factors which affect the fenton reaction rate, such as concentration of catalyst, concentration of oxidant, pH and temperature of polishing liquid were carried out.The compound polishing process of single-crystal SiC was studied. Orthogonal experiment about the factors influencing polishing pressure such as concentration of magnetic particle, concentration of Fe3O4 catalysts, size of magnetic particle and machining gap were performed so as to study their effect on material removal rate and surface roughness when polishing single-crystal SiC. Research of variety of abrasive, size of abrasive particle, polishing solution flow and processing time were studied to figure out their effect on material removal rate by single factor experiment and.It was found that the material removal rate of cerium oxide in CMRF of SiC is highest. The efficiency of 50 nm and W0.5 abrasive on in CMRF single-crystal of SiC was very low. Roughness decreased fast within 60 minutes in the processing time, it dropped to the lowest 0.16 nm at 120 min, and then did not continue to decline.The polishing procedure of single-crystal SiC was divided into rough polishing stage and precise polishing stage and the features of CMP, cluster magnetorheological polishing (MRF) and CMRF in the two stages were compared.In rough polishing, the material removal rate of CMP was much more higher than MRF and CMRF. Roughnes of each area were more consistent after rough cast in the CMP than MRF group and CMRF group. Due to the exist of cluster magnetorheo logical flexible polishing pad, the surface quality of CMRF and MRF group after precise polishing are much better than CMP. The atomic surface roughness (Ra0.16 nm) and ultra smooth SiC surface with very shallow scratches even no seratche in partial area were obtained after precise polishing usw CMRF. Ultra smooth planarization of single-crystal SiC was achieved. |
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