Nano-oxidation of Si using ac modulation in atomic force microscope lithography

In atomic force microscope (AFM) anodization lithography, voltage modulation is an important factor leading to enhanced oxide growth rate, increased aspect ratio of oxide patterns and greater control of oxide features. Through the reduction of space charge buildup in the oxide, ac modulation overcomes the self-limiting character of the oxide. When ac modulation was applied to substrates, the aspect ratio of protruded oxide patterns increased five-fold compared to dc pulse. Controlling electron exposure time between the positive and negative voltages is an important factor for controlling the aspect ratio of oxide patterns. This showed the dependence of applied voltage types and various electron exposure times in ac modulation. By adjusting electron exposure time and reducing space charge in the oxide, this study revealed that ac modulation is superior for obtaining high aspect ratios compared to dc pulse.