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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.

An inductively coupled plasma reactive ion etching process was developed for transferring patterns from a thin intermediate mask consisting of Ni or SiNx into GaAs. Smoothed out etch floors and sidewalls can be achieved under an approximately 200V bias by switching between an anisotropic etch phase and a deposition phase by gas chopping. The deposition of Si–O based film that protects the sidewall from chlorine attack is promoted by the addition of O2 to an SiCl4∕N2 gas mixture. The total achieved etch depth was approximately 20μm in this work, but the process can in principle be adopted for a larger depth and other chlorine-etchable III-V semiconductors. SiCl4 is shown to act as a suitable deposition gas as well as an etch gas.

Using Si samples with 400-nm-wide alternately high and low doped p-type layers on p-type substrate, we investigate the dependence of the scanning capacitance microscope (SCM) signal amplitude as a function of oxide thickness and dopant concentration. The oxide layers were created by a standard industrial high temperature oxidation process. Together with the implementation of the newly developed conductive diamond tips, good and quantitatively reproducible contrast for differently doped domains is obtained on all samples. A comparison with conventional metal-oxide-semiconductor theory shows good correlation for the decrease of the capacitance signal with increasing insulator thickness and increasing dopant concentration. Furthermore, geometry effects, such as the influence of the domain width on the SCM signal, are discussed.