Study On Mechanism Of Surface Creation In Mechanical Machining Of Crystal Semiconductor Materials

Nanomaterials technology is an important part of nanotechnology.An important way to develop nanofabrication technology is to use the non-traditional ultra precision machining technology to approximate the machining dimension and precision to the limit and to reach the level of nanomaterials.Therefore,studying the mechanism of material removal and surface regeneration in nanoscale processing will provide a theoretical basis for process optimization and prediction model establishment.In this paper,the mechanisms of surface generation of two crystal semiconductor materials(monocrystalline silicon and monocrystalline germanium)are studied.The mechanical response behavior in the indentation/scratching machining was investigated experimentally.From the angle of atomic rearrangement and reconstruction,the adhesion and deformation phenomenon in crystal semiconductor materials are studied on the basis of the theory of crystal structure and dislocation.By means of molecular dynamics simulation,the lattice deformation and dislocation in the machining area was analyzed and the dynamic process and rule of surface generation in nanoscratching processing was studied.Based on the mechanism of mechanical machining,the strategy and method of nanostructured array are studied by using(Atomic force microscope)AFM nanomachining system.The mechanical response of crystal semiconductor materials in indentation/scratching machining was studied by indentation/scratching instrument.It is found that the ratios between plastic depth and maximum depth of crystal semiconductor materials remain unchanged during the indentation period.In order to obtain better machining surface quality,the scratching load should be under 40mN and the scratching speed is about 4?m/s.Through the analysis of the "pop-out" phenomenon of Zhang,it is found that there is phase transformation in the characterization process of crystal semiconductor materials.The establishment and extension of theoretical model of dislocation of Zhang for monocrystalline silicon,the critical load value of monocrystalline silicon during scratching is obtained,that is to say,the critical load of monocrystalline silicon and monocrystalline germanium is 2.24mN,2.26mN respectively.Through molecular dynamics simulation,it is found that there occurs the adhesion phenomenon when the probe starts to contact and unload the surface of the material and the crystal lattice distortion?lattice transformation or non crystallization of the single crystal material in the process of indentation.The material begins to appear a small amount of hexagonal diamond lattice structure transformation and dislocation,and the internal atomic structure is found,therefore,the residual stress is formed when the maximum pressure depth is 10A.In the process of scratching,some of the material atoms in the front end of the probe slip to the front of the probe,produce shear flow and eventually form the accumulation materials of the front end of the probe or the scratching chips.Meanwhile,some atoms of sub surface materials are slipping below the probe and these atoms will form the scratching surface of the material(the groove surface of scratching).And these surfaces are permanently deformed,forming grooves,and residual elastic deformation and residual stress in subsurface atoms.Through the study of AFM processing system,it is found that the actual groove depths of the horizontal parallel array and the vertical parallel array are about 40%and 20%of the theoretical depths respectively.The actual groove depths of the horizontal parallel array and the vertical parallel array are about 50%and about 30%of the theoretical depths respectively.The widths of the square array of orthogonal straight slot on monocrystalline silicon and monocrystalline germanium material are in the range of 30-250nm,the fluctuation value is about 5%-20%and the range of 50-300nm,and the fluctuation value is about 5%-15%,respectively.Under the same theoretical depth,the surface quality of monocrystalline germanium is better than that of monocrystalline silicon.