Micron-scale modifications of Si surface morphology by pulsed-laser texturing

The morphologies of Si surfaces are modified with single, tightly focused nanosecond laser pulses and characterized by atomic force microscopy (AFM). Dimple-shaped features with diameters 1 - 4 μm and depths 1 - 300 nm are produced by varying the laser-spot diameter and the peak energy densities F₀ in the range 0.4 < F₀ < 1.3 J cm^-2. Greater control of the depth of shallow dimples and quantitative comparison of theory and experiment is enabled by first removing the native oxide of Si with dilute HF acid. We develop approximate analytical solutions for two-dimensional fluid-flow driven by gradients in the surface tension; these solutions provide fundamental insight on how the morphology depends on laser parameters and the thermophysical properties of the melt and its surface. Quantitative comparisons between theory and experiment are enabled by using numerical simulations of heat flow in one-dimension as inputs to the analytical fluid-flow equations; we find good agreement with AFM data for the dimple shape and depth.