Micron-scale modifications of Si surface morphology by pulsed-laser texturing - art. no. 155323

The morphologies of Si surfaces are modified with single, tightly focused n anosecond laser pulses and characterized by atomic force microscopy (AFM). Dimple-shaped features with diameters 1-4 mum and depths 1-300 nm are produ ced by varying the laser-spot diameter and the peak energy densities F-0 in the range 0.4<F-0<1.3 J cm(-2). Greater control of the depth of shallow di mples and quantitative comparison of theory and experiment is enabled by fi rst removing the native oxide of Si with dilute HF acid. We develop approxi mate analytical solutions for two-dimensional fluid-flow driven by gradient s in the surface tension; these solutions provide fundamental insight on ho w the morphology depends on laser parameters and the thermophysical propert ies of the melt and its surface. Quantitative comparisons between theory an d experiment are enabled by using numerical simulations of heat flow in one -dimension as inputs to the analytical fluid-flow equations; we find good a greement with AFM data for the dimple shape and depth.