High ion density dry etching of compound semiconductors

The use of plasma sources that generate high ion densities (> 1011 cm−3) enables dry etching of compound semiconductors at high rates with anisotropic sidewalls. In this paper we review the use of several types of electron cyclotron resonance (ECR) plasma sources and contrast the result with those obtained under reactive ion etching conditions. Various problems occurring in dry etching will be discussed, including aspect ratio dependent etch rates, mask erosion, sidewall roughening and damage introduction into the semiconductor. This damage may consist of point and line defect creation, non-stoichiometric surfaces, resputtering of mask materials or deposition of contaminating films. The use of low or high substrate temperatures to control the desorption kinetics of etch products is also discussed; at low temperatures problems can occur with condensation of the etch gases onto the substrate, while at elevated temperatures it is necessary to thermally bond the sample to the r.f. powered electrode to obtain reproducibility. Etch selectivity between the components of heterostructure systems such as GaAs/AlGaAs, GaAs/InGaP, InGaAs/AlInAs and GaN/AlN is usually much worse under high ion density conditions because of the high rates and large physical component.