Nanostructuring of silicon by laser direct writing

High-resolution laser direct writing is used to structure silicon on the nanometer scale. A continuous-wave laser heats the silicon substrate above the melting point in a chlorine atmosphere. Upon melting silicon reacts rapidly to form volatile silicon chlorides which are removed through the gas phase. Translating the sample during exposure results in narrow trenches which have the width of the generated melt. Reducing the incident laser power to a minimum, trenches with a width of less than 50 nm have been produced. Calculating the melt size as a function of laser power reveals no apparent minimum melt size, leaving the resolution determined by technical restrictions such as optical and mechanical stability as well as surface homogeneity. Applications include direct etching of nanostructures into bulk silicon and into layered structures. In addition, using a resist-type process, structures can be written into thin amorphous silicon layers and transferred by reactive ion etching to other materials.