Surface quality improvement of atmospheric pressure plasma polishing (APPP) in machining of silicon ultra-smooth surfaces

Abstract

To produce ultra-smooth optical surfaces on hard brittle materials and functional crystal materials without surface damage, atmospheric pressure plasma polishing (APPP) is developed. And improvement of surface quality by APPP process is analyzed by theoretical simulation and experiments. Quantum chemistry simulation proves that convex topography is removed faster than concave topography, thus surface roughness can be reduced further to form ultra-smooth surface. Experiment on single crystal silicon wafer also shows the surface roughness decreases from Ra 1.179nm to Ra 0.483nm. AFM (atomic force microscope) measurement results of specified roughness index taken at different moment in machining process accord well with theoretical simulation. Average reduced-modulus measured by nano-mechanical test system rises from 14.65GPa to 36.10GPa which demonstrates the improvement of surface mechanical properties. Further calculation also indicates the average residual stress is reduced by 7.64 GPa after machining which reflects the elimination of former deformation layer. Element analysis by X-ray photoelectron spectroscopy and X-ray diffraction indicates that chemical composition is also purified without new contamination introduced, and the overall status of machined surface goes closer to ideal silicon surface with better performance. Copyright © 2012 by JSME.