Fabrication of two-dimensional periodic structures in an amorphous silicon film by four-beam interference lithography

Abstract

Two dimensional (2D) periodic structures were produced in an amorphous silicon (a-Si) film by means of femtosecond-laser interference lithography. In order to fabricate 2D periodic structures in the a-Si film, we used four-beam interference lithography. The four beams were generated by using two crossed gratings, and the four beams were,superposed onto the a-Si film by using a focusing lens so that 2D periodic patterns were realized in the sample through four-beam interference lithography. In order to prepare two crossed gratings, titanium dioxide gratings were fabricated by a lift-off technique. The surface relief profiles of the gratings were designed so that the +1(st)- and -1(st)-order diffracted light intensities were maximized. When the He-Ne laser beam was incident on the prepared 2D periodic structures, the 2D diffraction pattern was observed. The scanning-electronmicroscopy images of the laser-patterned samples showed that the formation of the 2D periodic structure in the a-Si film was ascribed to the combined effect of spatially selective crystallization and laser ablation, which were induced by a laser-interference pattern.