Simulation And Experimental Study On The Planarity Of Silicon Carbide In Chemical Mechanical Polishing

Silicon carbide (SiC) ceramic is an ideal material for manufacturing thelarge-aperture lightweight space mirror, however, due to the characteristics of highhardness, high wear resistance, high brittleness, low fracture toughness, chemicalstability, SiC has a poor machinability. Chemical mechanical polishing (CMP)which combined the effects of chemical etching and mechanical friction to removethe material is an ideal way to realize ultra-precision machining for material difficultto machine, such as SiC. However, the CMP mechanism, such as material removalmechanisms, form mechanism of the material removal non-uniformity, have notbeen understood completely, The control of CMP process has been depending on thesemi-empirical or empirical means in some extend. In this paper, to obtain the planof high material removal rate, high surface quality and high surface planarity of SiC,a theoretical analysis and experimental research was conducted. It is of greatsignificance for the improvement of CMP technology of SiC.Firstly, a model of relative motion was established to investigate the effects ofparameters such as the rotational speed of workpiece and abrasive tool, on therelative velocity and trajectory distribution of the workpiece. On the basis of thetrajectory distribution, the influence factors of wear of workpiece and abrasive tooland the conditions to implement the uniform wear of them in CMP were analyzed.A CMP simulation model was established by using ABAQU software in thecase of direct contact between workpiece and polishing pad, the effects of thepolishing pressure, the thickness, elastic modulus and poisson’s ratio of polishingpad and the friction coefficient of workpiece and polishing pad on the contactpressure distribution and its non-uniformity were analyzed. Based on the technologyof retaining ring, the effects of the width and pressure of the retaining ring, the gapbetween the workpiece and the retaining ring, the structure of the retaining ring onthe contact pressure distribution and its non-uniformity were discussed.The experiments of chemical mechanical polishing of SiC were conducted onthe basis of the above theoretical analysis. The surface planarity was described asthe arithmetic average deviation of surface profile after polishing. In the CMPprocess, the effects of polishing pressure, relative velocity, the slurry concentration,polishing pad, and retaining ring on the material removal rate, surface roughness,surface morphology and surface planarty in chemical mechanical polishing ofsilicon carbide ceramic were studied by using single factor experiment method.