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. ► The surface roughness in fs-laser processing depends on Si substrate temperature. ► The roughness is proportional to the substrate temperature at low fluences. ► The roughness, however, decreases with increasing fluences from 0.5 to 1.0 J/cm 2. ► Further increment of the fluence does not affect the roughness. ► Si substrate temperature should alter its fs-laser ablation process.