Minimization of dry etch damage in III-V semiconductors

Dry etch damage is a potential worry when etching III-V semiconductors. Eve n though very low levels of damage are possible in modern dry etch processe s, it is nevertheless of interest to be able to detect any residual damage and understand its origins. We have used measurements of photoluminescence intensity from GaAs and InGaAs quantum well heterostructures to probe the d amage in a non-invasive way. At low damage levels, two factors influencing possible damage penetration have been found: the ratio of atomic to molecul ar ions in the discharge and the effect of ambient light. Samples were etch ed using SiCl4 reactive ion etching and also a more complex multi-component discharge. Comparative studies were made on samples bombarded by the separ ate constituent ions of a SiCl4 discharge using a mass-resolving ion implan ter fitted with a deceleration lens. The experiments show that molecular io ns contribute less to deep damage than do atomic ions. This is relevant, fo r example, if using high pump powers to sustain the discharge, such as in I CP or ECR. Further studies of laser illumination on the sample during etchi ng show that a form of radiation enhanced diffusion can modify the damage d istribution. This is relevant, for example, if laser interferometry is used for end-point detection. Thus for low damage in low damage etch processes, etch parameters that minimize atomic ion content in the discharge should b e used and ambient illumination should be avoided if possible.