The residual pattern of double thin-film over-etching for the fabrication of continuous patterns with dimensions varying from 50 nm to millimeters over a large area.

Attempts at heavy edge over-etching of a single thin film under a photoresist to leave behind a residual smaller patterned line as a mask for nanostructure fabrication frequently fail due to detachment of the photoresist above it. We have accordingly developed a technique named 'residual pattern of double thin-film over-etching' (RDTO) to obtain a nanoscale residual pattern of the bottom thin film after extensive edge over-etching. When Au and Cr were used as the top and bottom thin films, respectively, heavy over-etching of Cr for use as a mask for nanopatterning of the underlying silicon substrate was feasible. Three patterns were fabricated for demonstration of the RDTO technique, and nanopatterns with linewidths as small as 50 nm were obtained. More importantly, our technique allows the fabrication of a single pattern with feature dimensions that vary continuously from a few tens of nanometers to a few millimeters at different positions. In addition, we have developed simple models to analyze the hydrodynamic and surface tension effects during the over-etching procedure to show the feasibility of RDTO. This technique will find diverse applications in micro- and nano-fluidics, lab-on-a-chip nano-arrays and biomedical engineering.