Simulation And Experimental Study On Subsurface Damage Of Single Crystal Silicon In High-speed Grinding Progress

With the increasing integration of integrated circuits,the conversion efficiency of monocrystalline silicon solar cells has increased and the micro-nano electromechanical systems have become smaller,smarter,and more versatile.Monocrystalline silicon is widely used in various fields and its surface quality is also required higher and higher.The traditional processing technology has the disadvantages of low processing efficiency and difficult control,and the lapping process has serious defects on the surface of the workpiece.High-speed grinding with good grinding performance for hard and brittle materials such as single crystal silicon is gradually becoming the mainstream processing technology of silicon wafers.However,the grinding process inevitably causes processing damage to the silicon wafer,which affects the subsequent polishing process time and efficiency.At present,the study on the mechanism of high-speed grinding of subsurface damage of silicon wafers is not perfect.It is important to thoroughly study the mechanism of high-speed grinding of subsurface damage of silicon wafers for the ultimate high-efficiency machining of silicon wafers with high gloss,high flatness,and no damage.In theory,molecular dynamics simulation is an effective and reliable method for high-speed grinding processes.It provides a quick way to explore macroscopic features from the microscopic details of the system.This paper analyzes the molecular dynamics cutting and grinding simulation at home and abroad,and understands the ductile domain processing characteristics of single-crystal silicon under high-speed grinding,thereby deepening the mechanism of single-crystal silicon removal and subsurface damage under highspeed grinding by simulation and experimental studies.The main research content and conclusions are as follows:(1)A molecular dynamics model for high-speed grinding of monocrystalline silicon single-grained abrasive particles was established.The monocrystalline silicon workpiece atoms were divided into Newtonian layers,constanttemperature layers,and fixed boundary layers.The calculation of the atom's equation of motion,the ensemble selection and the energy minimization process in the simulation calculation are briefly introduced,and suitable simulation parameters are selected to improve the calculation efficiency.(2)Using molecular dynamics theory,based on the established threedimensional molecular dynamics simulation model for single-crystal silicon highspeed grinding,the coordination number and equivalent stress of the system in high-speed grinding were studied,from grinding force,friction coefficient,potential energy and average temperature.Perspective analysis of the chip formation process,the formation of grinding surface mechanism.During the high-speed grinding process,the energy generated by the abrasive grain extrusion and shearing is stored in the lattice of single-crystal silicon in the form of lattice strain energy.When the strain energy exceeds a certain value,the atomic bond of silicon will be In the fracture,silicon atoms in the front end of the abrasive grain are accumulated to form chips,which completes the material removal process.(3)Based on the established high-speed grinding molecular dynamics simulation model of single crystal silicon,this chapter carries out a quantitative analysis of the subsurface damage thickness during high-speed grinding of single crystal silicon.Firstly,the crystal defects and the advantages and disadvantages of the crystal structure identification method were studied and analyzed.The advantages of co-neighbor analysis method for detecting the damage of the single crystal silicon subsurface layer were discussed.The depth of subsurface damage of single crystal silicon decreases first and then increases with the increase of grinding speed.When the grinding speed is lower than 150 m/s,as the grinding speed increases,the time for rearrangement of the atomic lattice beneath the abrasive particles is shortened,the generation of amorphous structures such as dislocations decreases,and the depth of subsurface damage decreases..When the grinding speed exceeds 150 m/s,the high temperature in the processing area becomes the dominant factor to promote the nucleation of dislocation,and the movement causes the subsurface damage to increase.The above analysis shows that the depth of damage of the single crystal silicon sublayer depends on the competition mechanism between grinding temperature and deformation time,and this mechanism depends on the grinding speed.(4)Based on the experimental platform set up,single diamond abrasive grains were used to scratch single crystal silicon wafers at different speeds.Finally,the combined results of molecular dynamics simulations and experimental results are compared and analyzed from the material stack height and surface topography on both sides of the scratch.The results show that as the scratch rate increases,the height of the material on both sides of the scratches gradually decreases.Within a certain range,the grinding speed increases and the grinding thickness decreases,and the single-crystal silicon brittle materials will mainly produce chips in the form of plastic deformation,and the form of brittle fracture will be reduced,thereby improving the surface quality.(5)There are some differences between the results of molecular dynamics simulation and the experimental results.For example,there are no microcracks and brittle peeling during the simulation.The main reason is that there is a gap between simulation and experimental scale,but there are no theoretical or theoretical errors.The simulation results and experimental results are close to each other on the scratch surface topography and material accumulation,which proves that the results of molecular dynamics simulation in this paper are effective and reliable,and are applicable to the research of high-speed grinding machining mechanism.