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.