Simulation And Experimental Research On Anisotropic Ultra-Precision Cutting Of Single Crystal Silicon

Monocrystalline silicon is widely used in very large scale integrated circuit,flexible electronics,infrared optics,micro-nano electromechanical systems and other high-tech fields.The traditional mechanical polishing method is mainly used to make the surface of silicon wafer meet the specific requirements,which is not only inefficient but also has serious pitting and subsurface damage.However,as a new high efficiency and low surface damage machining method,pure mechanical ultra-precision cutting technology has realized the removal of the plastic domain of monocrystalline silicon at the nanometer scale.Due to the regular crystal structure of monocrystalline silicon,the anisotropic effect has a significant effect on the micro-nano removal of the material in the cutting process.In this paper,a molecular dynamics simulation model of monocrystalline silicon on three typical crystal surfaces was established,and the elastoplastic deformation mechanism of different crystal surfaces was summarized by combining nano-indentation and flying cut experiment of single particle diamond.The removal mechanism of monocrystalline silicon anisotropic ultra-precision cutting material was deeply analyzed.The main research conclusions are as follows:1.The characteristic elastic modulus,micro-nano hardness,phase change mechanism and mechanical deformation behavior of amorphous region of the sample were analyzed based on MD nano-indentation simulation and test.It was found that the wider elastic area on the(100)surface was 3.7nm,and a long-range ordered structure appeared directly below the pressure head.(110)surface has a high hardness value of 14.3 GPa and is not prone to mechanical deformation under external load.At the beginning of loading(110),dislocations will occur early.In the process of loading,dislocations in the amorphous regions of the three crystal planes are constantly generated and disappeared.At the depth of 5nm,brittle cracks and slip dislocations will not occur in the three crystal planes,and permanent dislocations will occur in the high-pressure region after unloading.(111)the bottom of the surface amorphous region has better plane retention;In the morphological evolution of amorphous regions,the growth steering mechanism appears with the increase of load.The type of phase transition depends on the distribution of pressure.Si-ii phase and si-iii phase start to grow almost at the same time in the loading process.After unloading,si-iii phase basically disappears,leaving most of the si-ii phase.The anisotropic effect of monocrystalline silicon mainly depends on the arrangement of atoms on its surface and between layers.2.The formation process of micro-topography of precision cutting surface was quantitatively explained from the perspective of atom,and the surface damage thickness and mechanical deformation behavior in the cutting process were studied.Monocrystalline silicon shows obvious anisotropic effect in the ultra-precision cutting process.The removal of the plastic domain of the material under the micro-cutting thickness of 3 nm is mainly completed by the phase transformation and plastic flow generated under the extrusion and shear action of the cutter.As the cutting progresses,the atoms in front of the cutter accumulate to a certain amount,which is removed by the shear action of the cutter.At the same depth,the(110)crystal surface requires a large cutting force,and the friction coefficient of the(100)surface remains basically stable during the cutting process.(100)the surface will have a relatively flat surface topography on the machined surface,but will have a thick subsurface damage;(111)lower subsurface damage thickness will be generated after surface cutting.3.In the flying cutting experiment,the material removal methods of each crystal plane include plastic removal and brittle crack removal,in which(100)the cutting groove of the plane has more chips on both sides and is mostly block-shaped quadrilateral,and the cutting groove area has a wavy cutting morphology perpendicular to the cutting direction;The chip(110)surface has a parallelogram,and chip is thinner,appearance ripple distribution narrower at the bottom of the slot cutting and cutting direction is about 5 ° Angle;The surface(111)is mainly composed of spalling of adhesive wear materials with good cutting surface flatness.The above experimental results are in good consistency with the results of molecular dynamics simulation analysis.In addition,for acoustic emission signal analysis of different crystal surfaces in the process of flying shear test,(110)crystal surface needs larger cutting energy;However,(111)removal methods of crystal surface materials are mainly caused by sliding friction and adhesive wear,with less removal of material volume.