Formation of silicon surface gratings with high-pulse-energy ultraviolet laser

We report the morphology, composition, and interaction mechanisms of silicon surface gratings fabricated with the fourth harmonic (266 nm) of a Q-switched Nd:YAG laser. We paid particular attention to the laser fluence dependence of silicon grating formation. It was found that at low fluence levels, grating formation was mainly caused by silicon oxidation. However, at high fluence levels gratings were formed with thermal ablation. In the former case, it was found that water vapor, instead of oxygen molecules, in the air was the key species providing oxygen for silicon oxidation. In the latter case, grating morphology was controlled by laser fluence level. These conclusions were supported by the measurement results of atomic force microscopy, energy-dispersive x-ray spectroscopy, Fourier-transform infrared spectroscopy, and chemical etching. The results of real-time monitoring of grating growth are also reported. (C) 2000 American Institute of Physics. [S0021-8979(00)07820-8].