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

We report the effect of substrate temperature (Tsub) 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/cm2 increases with increasing Tsub. However, the surface roughness decreases with increasing Tsub for the laser fluences between 0.5 and 1.0 J/cm2. If the laser fluence is higher than 2.0 J/cm2, the surface roughness is independent of Tsub. The effect of Tsub 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/cm2.
► Further increment of the fluence does not affect the roughness.
► Si substrate temperature should alter its fs-laser ablation process.