Nanomoulding is simple and economical but moulds with nanoscale features are usually
prohibitively expensive to fabricate because nanolithographic techniques are mostly serial
and time-consuming for large-area patterning. This paper describes a novel, simple and
inexpensive parallel technique for fabricating nanoscale pattern moulds by silicon etching
followed by thermal oxidation. The mask pattern can be made by direct photolithography
or photolithography followed by metal overetching for submicron- and nanoscale features,
respectively. To successfully make nanoscale channels having a post-oxidation
cross-sectional shape similar to that of the original channel, an oxidation mask to promote
unidirectional (specifically horizontal) oxide growth is found to be essential. A silicon
nitride or metal mask layer prevents vertical oxidation of the Si directly beneath it.
Without this mask, rectangular channels become smaller but are V-shaped after
oxidation. By controlling the silicon etch depth and oxidation time, moulds with high
aspect ratio channels having widths ranging from 500 to 50 nm and smaller can
be obtained. The nanomould, when passivated with a Teflon-like layer, can be
used for first-generation replication using ultraviolet (UV) nanoembossing and
second-generation replication in other materials, such as polydimethylsiloxane (PDMS).
The PDMS stamp, which was subsequently coated with Au, was used for transfer
printing of Au electrodes with a 600 nm gap which will find applications in plastics
nanoelectronics.