Near-field optical nanopatterning of crystalline silicon

Nanoscale photochemical and photophysical etching of Si in $Cl2$ atmosphere is demonstrated by means of an optical near-field setup. With 351 nm $Ar+$-laser radiation and low intensities, the etching mechanism is purely photochemical. In this regime, the width of patterns—which is about 115 nm at full width at half maximum (FWHM)—corresponds, approximately, to the diameter of the fiber tip. The vertical etch rate is of the order of 1 nm/s. With 514.5 nm $Ar+$-laser light etching is observed only at significantly higher laser-light intensities. Patterns with width down to about 30 nm at FWHM have been achieved. Here, the lateral resolution corresponds to about 1/18 of the laser wavelength employed.