Optimization of a Low Damage, High Resolution Etch Process for SiN x in an ECR Reactor

An electron cyclotron resonance (ECR) reactor was used to develop a low damage etch process for patterning submicron features in films on GaAs substrates. Statistically designed experiments were performed to optimize the process with regard to the following response variables (in order of importance): plasma damage to the underlying GaAs substrate, sidewall profile (anisotropy), selectivity to photoresist, uniformity, and etch rate. Damage, as measured by the change in sheet carrier concentration of uniformly doped epilayers, increased with decreasing chamber pressure. Langmuir probe measurements indicated that the ion saturation current increased with decreasing chamber pressure. Further analysis of the data revealed that damage was strongly correlated with ion current density. Dependence of damage on ion energy was found to be a second‐order effect. These findings indicate that in an ECR ion flux, not ion energy, plays the major role in introducing damage to the substrate. The addition of low level RF power was necessary to provide sidewall profile control. The data suggest that a high resolution, low damage plasma etch process can be uniquely achieved using an ECR reactor.