DIRECT WRITING OF SILICON GRATINGS WITH HIGHLY COHERENT ULTRAVIOLET-LASER

Silicon gratings with periods from 180 to 550 nm were fabricated with a laser ablation technique in which the interference fringe from an in tense and coherent ultraviolet laser at 266 nm directly melted silicon surface. The scanning electron microscopy and atomic force microscopy pictures showed that the corrugations were in quite good quality with the depth as large as 70 nm. The measurement of grating period depend ence on temperature showed that rapid thermal annealing could release the thermal strains, which were built during the melting and cooling p rocess in laser ablation, and make the grating period variation more r egular. Also, with an air gap between the sample and prism surfaces, t he fabricated gratings had weaker thermal strains and more re alar tem perature dependencies, All the measurement results of temperature depe ndence were consistent with theoretical predictions. (C) 1997 American Institute of Physics. [S0003-6951(97)03943-0].