High aspect ratio micro- and nano-machining of silicon using time-multiplexed reactive ion etching

Abstract

A low-density plasma reactive ion etching is reported to realize high aspect ratio silicon nanorods on silicon substrates. Aspect ratios with values more than 100 are obtained for features below 200 nm. The process uses a mixture of three gases of hexaflourosulfide, hydrogen and oxygen in a reactive ion etching system with a programmed passivation and etching sub-cycles. Using these three gases in both etching and passivation sub-cycles allows deep silicon etching with high rates, with no need of an inductive coupling plasma source and a special cooling system. The mask undercut can be around 30 nm, despite a high etch rate of 0.8–1.1 µm min−1. X-ray photoelectron spectroscopy and scanning electron microscopy have been used to investigate the prepared samples. Also, the Knudsen transport model has been applied to the etching process which results in a value of 0.23 for the ‘S’ value as the probability for the reaction at the bottom of the craters.