Three-dimensional nanostructures enabled by customised voltage waveform-induced local anodic oxidation lithography

Atomic force microscope-based local anodic oxidation nanolithography has been recognised as an effective approach for the fabrication of nanoscale patterns for next-generation electronic devices. Particularly, the use of oscillating tips can reduce the spatial size of the processed patterns and significantly increase the tool lifetime. However, it is still very challenging to achieve three-dimensional nanostructures as oxidation occurs only in a nanoscale water bridge formed between the tip and the sample, where multiple parameters must be precisely and strategically controlled to obtain nanopatterns with different heights. In this paper, a new local anodic oxidation lithographic technique is researched with the application of customised voltage waveforms to generate 3D nanostructures on silicon wafers. The relationship between pulse waveform parameters and oxidation growth was investigated. Through adjusting the tip-scan frequency and modulation of pulses, it was shown that waveform-modulated local anodic oxidation could fabricate 3D nanostructures across a region in a single scan.