Silicon substrate temperature effects on surface roughness induced by ultrafast laser processing

We report the effect of substrate temperature (T(sub)) in the range 300-900 K on the surface roughness of silicon wafer resulted from femtosecond laser ablation. The surface roughness observed at the laser fluences less then 0.3 J/cm(2) increases with increasing T(sub). However, the surface roughness decreases with increasing T(sub) for the laser fluences between 0.5 and 1.0 J/cm(2). If the laser fluence is higher than 2.0 J/cm(2), the surface roughness is independent of T(sub). The effect of T(sub) on the surface roughness can be understood in terms of the temperature dependence of optical absorption coefficient of silicon substrate, which eventually alters a mechanism underlying the fs-laser-material ablation process between optical penetration and thermal diffusion processes. (C) 2011 Elsevier Ltd. All rights reserved.