Experimental And Simulation Study On Damage Mechanism Of Silicon Carbide Wafer During Grinding

With the further development of the third generation semiconductor research,SiC wafers have overcome the limitations of silicon wafers by virtue of their unique performance and have been widely used in the market,which makes SiC wafers have made breakthrough progress in many fields,including aerospace,automotive and other industries.SiC is characterized by wide band gap,high thermal conductivity and high bond energy.Because its hardness is close to diamond and it is difficult to cut in semiconductor processing.SiC semiconductor devices are still mainly in the research and development stage,but the process is basically similar to the production process of Si semiconductor.The cutting process is the first stage of semiconductor fabrication,in which an ingot is cut into a wafer,a process that produces a large number of surface defects.If the defect is not removed,the defect is copied to the epitaxial layer.Therefore,it is necessary to remove surface damage and defects before epitaxial machining in order to improve surface quality.Based on molecular dynamics and nano-scratch experiments,the defects generated in grinding process were systematically studied in this thesis,and the ductile transformation process and damage mechanism were obtained through experiments.The microscopic phase transition process was obtained by molecular dynamics.The results of molecular dynamics simulation show that the grinding process of SiC is a process of material plastic removal,and more SiC atomic crystal structures change into amorphous structures after grinding.Higher cutting speeds make the material more ductile and easier to remove.The results show that the best tool parameters are small negative rake angle（-30°）and large clearance angle（15°）.After confirming the optimal tool parameters,the grinding process of series parallel tool was analyzed.The results show that deep longitudinal damage will occur in both serial grinding and parallel grinding,and deep buried defects will appear in parallel grinding.At the same time,a large space between two diamond tool can effectively avoid the lateral force generated by the intermediate chips on the tool.When the first diamond is grinding,the second diamond is grinding the amorphous part.The diamond is not subjected to a large force,but the amorphous part can be effectively removed.But the chip in front of the tool result in a certain atomic attachment,reduce the life of the tool.Single and repeated nano-scratch processes are performed in this study.The surface morphology,friction coefficient and defects of the scratches were studied.The ductile transformation process and the brittle removal and peeling process are found.The results show that with the increase of the number of scratches,the surface quality decreases and the ductile and brittle transition advances.The results of Raman spectroscopy show that serious dislocation and phase transition occur during the scratching process,and the subsurface damage caused by the previous scratch can be eliminated by repeated scratching.The surface of SiC was pretreated by laser modification process.The results show that the friction coefficient of SiC surface is reduced after laser modification,but the surface roughness is low.After the scratch process,the surface roughness is improved.