Silicon carbide(SiC)single crystal,as one of the most common third-generation semiconductors at present,is widely used in the manufacturing of electrical components and high-power devices because of its excellent physical properties such as high temperature resistance,wear resistance and good thermal conductivity.However,SiC is a typical difficultto-machine material with strong chemical inertness,ultra-high hardness and brittleness.As a core component,the substrate material usually requires extremely high surface quality of silicon carbide.At present,the commonly used methods in industry include chemical mechanical polishing,electrochemical mechanical polishing and catalyst etching,but they all have some defects.Therefore,it is particularly important to study the surface polishing method of SiC single crystal.Based on gas discharge theory and ultrasonic effect,combining ultrasonic vibration-assisted method with conventional electrolyte plasma oxidation method,this paper puts forward an ultrasonic-assisted electrolyte plasma polishing method,aiming at optimizing and improving the existing polishing technology and improving the material removal rate on the basis of realizing nano-scale non-damage smooth surface of SiC single crystal.In this thesis,the mechanism of plasma oxidation of electrolyte and mechanical removal of oxide layer are analyzed,and the cavitation effect,thermal effect,chemical effect and mechanical effect produced by ultrasonic wave during propagation are analyzed,which verifies the synergistic effect of ultrasonic vibration assistance in the oxidation process of SiC single crystal.COMSOL Multiphysics software was used to simulate the ultrasonic-assisted electrolytic plasma oxidation process of SiC single crystal.The corresponding two-dimensional system model was established and the relevant boundary conditions were set.The simulation data of current density,oxidation efficiency,material removal rate and surface roughness after oxidation were obtained.The simulation results were analyzed,and the effects of oxidation time and voltage on the oxidation process were studied.The mechanical removal process of oxide layer was simulated by using molecular dynamics software LAMMPS,and the action mechanism of abrasive particles in the polishing process was expounded from the microscopic level.When CeO2 soft abrasive particles were ground,the Si-O bond in the oxide layer of silicon dioxide(SiO2)broke and was taken away by the flowing abrasive particles and polishing solution,and finally the oxide layer was removed to achieve nano-smooth polishing effect.The experimental scheme of ultrasonic-assisted electrolytic plasma oxidation and mechanical removal of oxide layer for SiC single crystal was designed,and the corresponding experimental platform was built.Experiments are divided into two categories:non-ultrasonic experiments and ultrasonic-assisted experiments.During the experiment,plasma gas layer observation and current collection in the circuit were carried out.The surface composition and morphology of SiC single crystal samples after material oxidation and mechanical removal of oxide layer were detected respectively,and the surface roughness was obtained and the corresponding material removal rate was calculated.The experimental results show that compared with the experimental results without ultrasound,the results with ultrasound assistance are better.Comparing the simulation analysis with the experimental results,the overall trend is basically the same,and the fitting effect of the simulation results is good.By calculating their error rates,we can get that the relative error of current density is 13.44%,the relative error of oxidation rate is 9.03%,and the relative error of surface roughness is 5.84%,which verifies the accuracy of the simulation,and also shows that the simulation method can be used as an auxiliary means for mechanism research and experimental analysis in ultrasonicassisted electrolyte plasma polishing. |