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 SiCl4 etch phase and an O2 passivation phase. Care is taken not to intermix O2 with SiCl4. The investigated structures consist of pillars, trenches, stripes, and holes, all with lateral structure size of 1 μm 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 O2 passivation step investigated by optical emission spectroscopy and energy dispersive x-ray analysis that reveals a Si-rich SiOX sidewall.