Simulation Study And Experimental Design Of Ultrasonic-photoelectric Catalytic Polishing Of Single Crystal Silicon Carbide

Silicon carbide is the third generation semiconductor material,and it has many excellent properties,such as high thermal conductivity,high critical breakdown electric field,high saturation electron drift rate,high bonding energy and wide forbidden.With the rapid development of optoelectronics,micro-electromechanical systems and information technology,it puts forward the requirements of sub-nanometer manufacturing accuracy and ultra-smooth surface manufacturing without sub-surface defects on the surface processing accuracy and surface quality of Silicon carbide substrates.However,the extremely strong chemical inertness and hard and brittle characteristics of silicon carbide make it difficult for general processing methods to obtain a silicon carbide surface that meets the manufacturing requirements,and most processing methods will produce a large amount of heavy metal waste liquid,which seriously pollutes the environment.This paper is devoted to analyzing the characteristics of the flow field under ultrasonic vibration,and exploring the erosion effect of abrasive particles on the surface of the specimen in the flow field to establish a complete solid-liquid two-phase flow processing mechanism,and finally to obtain the optimal working condition parameters.Ultrasonic vibration is combined with the principle of photoelectric catalytic oxidation to explore the environmentally friendly and efficient polishing method of single crystal silicon carbide.The theoretical analysis of the velocity of the flow field under ultrasonic vibration was carried out,and obtained the lateral and longitudinal velocity equations of the flow field in one period.Using the COMSOL Multiphysics finite element software to establish the flow field model between the test piece and the polishing pad under ultrasonic vibration,and explored the effects of ultrasonic vibration frequency,amplitude,flow field film thickness and polishing pad shape on the flow field characteristics.Studies have shown that the lateral velocity and pressure of the flow field increase with the increase of frequency and amplitude,and decrease with the increase of the thickness of the flow field film.At the same time,under the porous polishing pad,the flow field velocity and pressure decrease slightly,but the movement of the abrasives was more chaotic,which is beneficial to achieve global planarization.A theoretical analysis of the plastic and brittle stages of abrasive particles impacting the surface of the specimen under microscopic condition was carried out,and obtained the relationship between the material removal volume and the abrasive particle kinetic energy under the impact of single abrasive particles in the plastic deformation stage and the brittle deformation stage.Abaqus software was used to establish the explicit dynamic model of abrasive particles impacting silicon carbide and silicon dioxide,and the material removal rate and energy conversion under abrasive particle shape,size,abrasive impact times,impact velocity and impact angle were explored.The research showed that the material removal rate increases with the increase of abrasive particle impact speed,impact angle,number of impacts and abrasive particle size,and the material removal rate under the impact of regular octahedral abrasive particles is higher than that of spherical abrasive particles.Under the impact of regular octahedral shaped abrasive particles,the test piece produces less elastic deformation energy,and the energy conversion rate under the impact of regular octahedral abrasive particles is much higher than that of spherical abrasive particles.Under different impact times,the two shapes of grinding The energy conversion rate of two shape of abrasives remains basically constant.Compared with diamond abrasive impacting silicon carbide specimens,when using silica abrasive impact the silica oxide layer,a higher material removal rate and a higher energy conversion rate can be obtained at a lower impact speed.According to the principles of photocatalytic oxidation and ultrasonic vibration assisted polishing,an ultrasonic-photoelectric catalytic auxiliary polishing test machine was designed and built.The test machine can adjust various operating parameters of the experiment,and recorded the pressure and friction during the polishing process in real time.The mechanical analysis and modal analysis of the testing machine a carried out to ensure that the testing machine meets the requirements of good strength and rigidity,and can effectively avoid resonance.