Nanooxidation of silicon with an atomic force microscope: A pulsed voltage technique

The use of an atomic force microscope (AFM) as an active tool to realize silicon nanolithography is now well known, using a continuous voltage applied between the AFM tip and the surface. The main drawback of this technique is the poor reliability of the tip due to the strong tip-surface interaction. An original way which both increases the reliability and improves the nanolithography resolution is the use of pulsed voltages instead of continuous polarization. In such a case, the interaction time of the tip with the surface under electric field decreases. The frequency oscillation (in noncontact mode) of the cantilever is taken as a reference, and pulsed voltages with variable phase and duty cycle are used. We show that the variation of the phase allows a 100% modulation of the oxide width. Finally, combining this lithography technique with wet etching, a 17.5 nm wide and 5.5 nm height nanowire has been obtained starting from a silicon-on-insulator substrate.