Plasma-induced damage of GaAs during etching of refractory metal contacts

Abstract

The effect of plasma-induced damage on the majority carrier transport properties of p-type GaAs has been studied by monitoring changes in sheet resistance (Rs) of thin conducting layers under various plasma conditions including etch conditions for refractory metal contacts. Rs determined from transmission line measurements are used to evaluate plasma-induced damage for electron cyclotron resonance (ECR) and reactive ion etch (RIE) conditions by varying the thickness and doping of epitaxial layers. Damage depths calculated from Rs data show a strong dependence on doping levels. This can be explained by a plasma-damage-induced trap density profile which tails off into the sample. Consistent trends have been observed where Rs increases with increasing dc bias, increasing microwave power, and decreasing pressure, thus showing Rs increases as either the ion energy or ion flux increases. The lowest plasma-induced damage observed in this study occurs with ECR at low microwave power and no rf biasing. Under rf-bias conditions, samples exposed to the ECR (1 mTorr total pressure) show more damage than those exposed to the RIE (8 mTorr total pressure) at comparable dc bias. We have also observed Rs dependence on ECR plasma chemistry where Rs is lower in SF6/Ar plasmas than Ar and N2 plasmas possibly related to interactions of F or S atoms with the GaAs surface. Moderate anneal temperatures (200–500 °C) have shown significant Rs recovery.