Time-multiplexed, inductively coupled plasma process with separate SiCl4 and O2 steps for etching of GaAs with high selectivity

The authors present the results and the optimization procedure for a time-multiplexed dry etching process to etch GaAs in an inductively coupled plasma reactive ion etching system. The gas feed chopping sequence employed a SiCl(4) etch phase and an O(2) passivation phase. Care is taken not to intermix O(2) with SiCl(4). The investigated structures consist of pillars, trenches, stripes, and holes, all with lateral structure size of 1 mu m or less. This feature size is interesting for diffractive elements and cavities in integrated mid-IR optoelectronics. They achieve an aspect ratio of 10 for holes, 17 for trenches, and 30 for stripes with a selectivity of 200:1 on open areas. The improvements in the sidewall morphology are related to the O(2) passivation step investigated by optical emission spectroscopy and energy dispersive x-ray analysis that reveals a Si-rich SiO(X) sidewall. (C) 2009 American Vacuum Society. [DOI: 10.1116/1.3225599]