Abstract

Techniques for fabrication of large, uniform arrays of semiconductor structures with nanometer-scale dimensions are of great interest for investigating quantum size effects. We report on a simple technique for fabricating arrays of Si wires with transverse dimensions ≤ 10 nm. This technique takes advantage of the capabilities of optical interferometric lithography to produce very high spatial frequency gratings and the strongly directional KOH etching of Si. A <110> Si wafer is prepared with thin (50-nm) Si₃N₄ and standard photoresist (0.15 mm) layers. A submicrometer period grating is interferometrically exposed in the photoresist (0.2-1 mm pitch) by using a cw Ar-ion laser source (361 or 488 nm). Following resist development, the grating pattern is transferred into the Si₃N₄ by CF₄ plasma etching. Large area patterns with ~500-1000 nm lines are readily produced. For lines aligned in the <110> direction, a 40% KOH solution provides a highly selective (500:1) wet etch that produces very high aspect ratio Si lines. The etch selectivity also serves to reduce any nonuniformities or edge roughness induced in the lithography and etching steps. At this stage, Si structures with widths of 30-100 nm and depths of 0.5- 1 mm are obtained. Finally, a controlled dry oxidation (~800°C) is used to further reduce the Si dimensions. Large areas of uniform nanometer scale structures, including Si wires isolated by SiO₂ from the substrate, are produced. Photoluminescence and Raman scattering studies will be presented.

© 1992 Optical Society of America