Surface nanostructuring by femtosecond laser irradiation through near-field scanning optical microscopy

A near-field scanning optical microscopy (NSOM) and a double-frequency femtosecond laser (400 nm, 100 fs) were applied to push the optical resolution further down to sub-50 nm on thin UV photoresist. A 20-nm feature size can be obtained. It is at a resolution of lambda/20 (lambda: laser wavelength) and a/2 (a: NSOM probe aperture diameter), respectively. It is proved that laser power and exposure time can affect feature size of lithography patterns. In this paper, the effect of probe-to-sample distance on dot-pattern features is studied, and different dot-pattern shapes are generated: dumbbell-dot, ellipsoid-dot and circle-dot. The simulated light field spatial distributions across the nano-aperture based on Bethe-Bouwkamp model is found to agree with experimental results very well. (c) 2006 Elsevier B.V. All rights reserved.