Abstract

Nanostructures have been etched into silicon by laser direct writing with a minimum linewidth of 50 nm (Fig. a).¹ The technique is based on the efficient etch reaction of molten silicon with molecular chlorine forming volatile silicon chlorides, which are removed through the gas phase. The spatial confinement is achieved by using a continuous-wave focused laser beam to generate a molten zone of only a few tens of nanometers, although the laser spot diameter is about 600 nm and the temperature profile spreads over several microns in bulk substrates. Solid silicon is not etched noticeably. For producing structures with a high resolution, the substrate is translated by direct-current XY motor stages with internal encoders and a repeatability of 25 nm. The optical system is designed with a stationary beam to achieve minimal diffraction-limited spot sizes. The resulting linewidth is determined by the incident laser power. The trench depth is a function of chlorine pressure and scan speed. The native oxide, which is not removed before the direct etching process, protects the solid surface against etching by dissociated chlorine.

© 1996 IEEE