Submicrometer lithography by near-field optical microscopy

Optimization of (i) intensity of illumination and (ii) thickness of resist was made looking for the conditions when high spatial resolution could be achieved by optical near-field lithography. Standard set-up of near-field illumination through a tapered Al-coated fiber tip was employed for the exposure of positive resist OFPR-5000(EG), which is photo-sensitive for wavelength lambda < 450 nm. Tip was scanned along the line at near-field conditions of constant sample-to-tip separation to produce adjustable exposure dose of the spin-coated resist film. Femtosecond, 120 fs, pulses of the power P < 1 mW (at 82 MHz repetition rate) at 400 nm were coupled into a fiber (< 1 m length) and delivered to the surface of the resist for illumination. The issues of NSOM fabrication using tapered Al-coated tips are addressed. To achieve a reproducible and high aspect ratio (approaching 1 : 1) NSOM-based lithography there should be found resists allowing to produce thin films (< 100 nm) with low surface roughness (< 10 nm).