Improvement of scanning proe microscopy local oxidation nanolithography

"In order to investigate the factors that control the growth of Si local oxide, the authors have a comparative study between tapping and contact mode scanning probe microscopy (SPM) local oxidation experiments using the same SPM tip. The authors fabricated Si oxide wires with an average full width at half maximum (FWHM) of 11.0 nm in tapping mode and 54.8 nm in contact mode under the same oxidation conditions. The standard deviations of the FWHM were 2.1 and 12.2 nm in tapping and contact mode experiments, respectively. Furthermore, the authors quantitatively explained the size of the oxide controlled with tapping mode local oxidation using a model based on the oxidation ratio and the rate constant of the oxidation reaction. The oxidation ratio was estimated to be approximately 10% in tapping mode oxidation, which contributes to the 10 nm scale resolution of the oxide. Moreover, the rate constants in the tapping mode local oxidation reaction were larger than those of the contact mode oxidation. This indicates that local oxidation reaction controlled with tapping mode operation is enhanced and results in the stable oxidation, since space charges accumulated in the oxide are easily neutralized by the modulation of the electric field strength. The results imply the use of tapping mode operation for performing controllable local oxidation nanolithography.