Ultrasonic Wire Saw Cutting Technology And Experimental Research On SiC Single Crystal

Having excellent electrical and physical and chemical properties such as a large band gap,high breakdown field strength,high saturated electron drift velocity,high thermal conductivity,high radiation resistance and low dielectric constant,SiC single crystal is becoming a ideal semiconductor material which applied in high-density integration of electronic devices and short-wavelength optoelectronic devices in high temperature,high frequency,radiation,power and other fields.Compared to other semiconductor materials such as silicon,however,SiC single crystal is more harder and fragile,which make the cutting process being a major bottleneck,especially in the wafer cutting process the SiC wafer is prone to crack and the surface roughness and flatness is inferior and all the defects are difficult to eliminate in the subsequent operation,thus leading to limit the SiC single crystal wide application.In this dissertation,combination theoretical analysis and experimental research method is used to investigate cutting mechanism and process of SiC single crystal wafer and process parameters for the practical application are obtained,which has important theoretical significance and practical value.This dissertation presents a composite processing method that the diamond wire saw ultrasound-assisted cutting SiC single crystal wafer,which is in the conventional wire saw,an ultrasonic vibration is applied transversely to the wire saw,and which formed composite cutting motion of the wire saw in transverse vibration and longitudinal motion.The physical model of the composite cutting process for SiC single crystal is developed and the kinematics and dynamics analysis are conducted.Based on the abrasive kinematic equation,the mathematical modeling for cutting chip formation process is proposed,through microstructure observation and analysis and ultrasound-assisted cutting mechanism is studied,the experimental and simulation results show that the ultrasound-assisted wire saw cutting SiC single crystal can effectively improve the surface quality and reduce the cutting force.A single abrasive cutting process model is developed to study the chip generation and the influence of process parameters on the depth of cut for the abrasive distributing on the wire saw which contact the different cutting surface of SiC single crystal,and the theoretical model for material removal rate is obtained.A single point diamond tool scratches experiment study the cutting mechanism of SiC single crystal,which verify the truth that the cutting process of brittle material has two material removal methods,brittle fracture and plastic plowing,and the transformation conditions from the brittle to plastic are discussed,which provides an important basis for eliminating cutting defects and improving the wafer surface quality.The mathematical model of cutting force for SiC single crystal is established to study the impact of process parameters and vibration parameters on the cutting force.The single factor and multiple factors orthogonal experiments are conducted to test cutting force,and the empirical equation of cutting force and the main factors affecting cutting force are obtained.Compare to the theoretical analysis,the experiments results have good consistency with the theoretical analysis which verify the validity of the theoretical model.The surface formation of SiC single crystal wafer and improvement mechanism of the wafer surface under ultrasonic condition is investigated,the single factor and multivariate experiments for the surface roughness and morphology are conducted and the Response Surface Methodology(RSM)is used to analyze the surface roughness of wafer and the optimal combination of process parameters,while the failure of wire saw and broken of abrasive are studied.The simulation model of single abrasive cutting SiC single crystal wafer is established based on ABAQUS,and the different parameters for abrasive angle,wire saw velocity,workpiece feed rate are simulated in different combination.In different aspects,the simulation validates the experimental results and the correctness of proposed theoretical model.