Micro/nano-scratch Damage Mechanism And Simulation Study Of SiC Single Crystal Wafers

With the development of semiconductor industry,the development potential and industrial added value of SiC single crystal are getting higher and higher,and it is used in epitaxial wafers,power devices and substrate materials due to its excellent characteristics,etc.However,SiC single crystal wafers are extremely hard,difficult to process and easy to introduce damage,so it is significant to study the precision ultra-precision processing and damage mechanism of SiC single crystal wafers.The micro-nano scratching technique can reveal the damage deformation mechanism of SiC single crystal wafers from the microscopic point of view,therefore,different scratching parameters and methods are used to explore the damage of SiC single crystal wafers and provide theoretical support for the study of the damage mechanism of SiC single crystal wafers for precision ultra-precision machining.The micron test module of the micro-nano mechanics test system was used to conduct micron scratch tests on the crystal surface of 6H-SiC single crystal wafer(0001)at different velocities and different crystal orientations to analyze the friction coefficient of the scratch,the depth of cut of the scratch and the three-dimensional morphology of the surface.Nano-scratch tests with different spacing and sequence were conducted on the surface of 6H-SiC single crystal wafer(0001)using the nano-testing module of the micro-nano-mechanical test system to analyze the friction force,surface morphology,scratch residual depth,scratch cross-sectional profile and scratch residual stress of the scratches,and then to investigate the influence of different scratch parameters on the scratch mechanism of 6H-SiC single crystal wafer.A multi-scratch simulation model was used to investigate the difference between single-scratch and double-scratch processing at different pitches,and the effect of different scratching sequences on material deformation was investigated and compared with the experimental results.The results are as follows.(1)When the static load is 4 N and 6 N and the scratching speed is from 0.2mm/min to 1.6 mm/min,the scratching friction coefficient,scratching cutting depth,scratching width,scratching accumulation height and surface roughness increase as the load and scratching speed increase,lower speed scratching can reduce the wear of the scratching head to some extent,and increasing the scratching speed appropriately will increase the plastic deformation area.The degree of scratch material accumulation and cratering differs in different crystal directions,and the friction coefficient,scratch peak height and valley depth are smaller when scratching along[1120] and [1120] crystal directions,and larger when scratching along [2110] and[ 1210 ] crystal directions,and the former is easier to achieve plastic domain processing than the latter.(2)Different scratch spacing mainly affects the scratch cross-section profile curve and the average friction between two scratches,and the smaller the scratch spacing,the greater the degree of influence.When the static load is 100 m N,the smaller residual tensile stress between two scratches is transformed into smaller residual compressive stress as the scratch spacing increases.When the static load is90 m N,the surface material accumulation of non-sequential scratches is less,the surface roughness value is lower,and the residual stresses are more uniformly distributed;while the residual tensile stresses at the grooves of the three scratches in sequential scratches gradually increase.When loaded with a dynamic load of 0-180 m N,the residual tensile and compressive stresses around the scratches are small when the load is about 10 m N;as the load increases,the Raman peak intensity changes significantly;Most of the residual tensile stresses are around the sequential scratches at a load of about 180 m N,and residual compressive stresses exist locally,and the surface material fragmentation at the end of the scratches is serious for SiC single crystal wafers,while the residual compressive stresses around the non-sequential scratches are distributed more than those around the sequential scratches,and the end cracks are relatively less and the surface quality is higher.(3)The simulation results show that when the scratch spacing is small,the second scratch processed by a single scratch head has a significant effect on the first scratch,and the groove depth and friction force of the second scratch are larger than those of the first scratch.When two scratch heads are processed simultaneously,it is easier to obtain two scratches with the cross-sectional profile symmetrical about the middle position of the scratch.The different scratching order has a significant effect on the deformation of SiC single crystal sheet material,and the plastic deformation of the cross-sectional profile is relatively severe for sequential scratches,while the cross-sectional profile has better symmetry for non-sequential scratches,and the simulation results are more consistent with the experimental results.