An Experimental Study On A Typical Silicon Nitride Chemical Mechanical Polishing Process

Silicon nitride ceramic material is widely used for its high strength, highthermostability, chemical resistance and other excellent performance in the industrialand defense. Currently, the ultra-precision machining of silicon nitride material ismainly through fine grinding with superhard abrasive and mechanical polishing toachieve. Both precision machining methods are based on the form of brittle crack torealize silicon nitride material removal. Since its hard and brittle characteristics, therewill be some surface defects like scratches and residual stress on the surface of thesilicon nitride ceramic with the general grinding and grinding process, which can notget high-quality surface and affect the performance of parts. Chemo-mechanicalpolishing (CMP) is a combination technique of mechanical grinding and chemicaletching. It is with the grinding of abrasive particles and chemical corrosion ofpolishing slurry in the grinding media to form a smooth, almost no damage surface.CMP is mainly used for polishing flat or sphere part, but polishing process andequipment on complex surface parts are ralely reported. This paper focused on atypical complex part of silicon nitride ceramic in aerospace, defense weapons area, aCMP platform was established on high precision CNC jig grinding MK2945C, and theexperimental study on ultra-precision CMP process was accomplished; based onmaterial properties of silicon nitride, Cerium Oxide (CeO2) was chosen as a polishingmedium and polishing slurry was deployed. In order to obtain high quality surface,reveal the CMP process parameters influence on surface roughness and efficiency,experimental study was carried out on slurry concentration, slurry flow rate, polishingwheel speed and polishing time using single factor test method, respectively. Bymeasuring the polished surface roughness, a detailed analysis of each processparameters in the coarse and fine polishing to the quality was developed, and specificmeasures were suggested to improve surface roughness of surface quality, to provideexperimental reference for the follow-up process optimization.According to the influence about each parameter of rough polishing and finepolishing on the process surface,Orthogonal experiment was designed, and the CMPprocessing parameters of rough polishing and fine chemical mechanical polishing wereoptimized separately, to obtain a more reasonable process parameters. Experimentswere carried out to verify the process optimization, and clean and no damage surface of silicon nitride ceramic was achieved, the surface roughness value of10nm.Experiments show that the process is stable and reliable, and has some practical value.According to the experiments, the chemical and mechanical action of CMP areinextricably linked, a single factor can not make a comprehensive judgment of thesurface quality, only when the chemical corrosion and mechanical action achieved acertain balance can get low roughness and no damage surface. Therefore it is need tooptimize the combination processing, so that the mechanical action and chemicalaction can achieve a certain balance, and get high quality process surface.