Evolution of high aspect ratio and nano-grass structures using a modified low plasma density reactive ion etching

Nano-Electronic Center of Excellence, Nano-Electronic and Thin Film Lab, School of Electrical and Computer Eng, University of Tehran, Tehran, Iran

^a e-mail: mohajer@ut.ac.ir

Received: 21 September 2010
Revised: 13 January 2011
Accepted: 17 February 2011
Published online: 21 July 2011

Abstract

We report a modified deep reactive ion etching method to realize high aspect ratio features and nano-grasses on silicon substrates. This etching technique uses sequential etching and passivation sub-cycles and it is based on three gases of H₂, O₂ and SF₆ in the presence of rf-plasma. By adjusting the etching parameters such as the flows of various gases, the plasma power and duration of each cycle, the process can be controlled to obtain high aspect ratio vertical structures on silicon substrates. Features with aspect ratios of the order of 30–50 and heights of the order of 25–30 μm are obtained. On the other hand, one can program the etching parameters to achieve grass-full structures in desired places and with pre-designed patterns. The formation of nano-grass on silicon surface, improves its wetability with water and oil spills. This property has been used to entrap carbon nanotubes onto nano-structured surfaces in desired places.