Models of etching in plasmas and beams

Plasma-assisted etching processes, although by now commonplace in the IC fabrication facility, continue to be characterized by lack of thorough understanding of processes and the effects of process parameters on performance. Reactive ion beam etching techniques, on the other hand, have been shown to be well controlled, reproducible and understandable in a fundamental manner. Since ion beam techniques are not likely to supplant plasma-assisted processes in the fabrication facility, we are interested in using fundamental information obtained from beam experiments to quantitatively predict and characterize the performance of plasma-assisted processes. In this paper we are interested in modeling plasma-assisted etch processes which rely on ion bombardment to produce anisotropic etching, such as etching Si in Cl2discharges. We apply the detailed chemical sputtering model for this system that we have developed from beam experiments, together with reactive species generation and basic ion and neutral transport processes in discharges. This model yields generalized expressions for etch rates and selectivity as a function of process parameters such as gas pressure, flow rate and electrode bias voltage. Qualitative results of the model are compared to experiments, where possible. Types of measurements needed and further applications of this model will be discussed.