Micropatterning of the SiO₂ coated Si surface using femtosecond laser diffraction

Dot-array patterns with a-few-µm period were formed on oxidized-Si substrates by Fresnel diffraction of Ti:sapphire femtosecond laser radiation. Si wafers were coated with thin SiO₂ films in order to prevent the surface degradation during laser processing. SiO₂ layers with various thicknesses from 0 to 1.2 µm were grown by thermal oxidation, and exposed to several laser conditions. The modified surface morphology and the depth of the dots were characterized, revealing periodic fine patterns of 3-µm depth for 0.2-µm SiO₂/Si samples irradiated for 30 s at 130-mJ/cm² laser fluence.