Statistical experimental design in plasma etch modeling

The objective of this work is to obtain a comprehensive set of empirical models for plasma etch rates, uniformity, selectivity, and anisotropy. These models accurately represent the behavior of a specific piece of equipment under a wide range of etch recipes, thus making them ideal for manufacturing and diagnostic purposes. The response characteristics of a CCl₄-based plasma process used to etch doped polysilicon were examined via a 2^6-1 fractional factorial experiment followed by a Box-Wilson design. The effects of variation in RF power, pressure, electrode spacing, CCl₄ flow, He flow and O₂ flow on several output variables, including etch rate, selectivity, and process uniformity, were investigated. Etch anisotropy was also measured by scanning electron microscopy analysis on a 2^6-2 fraction of the original experiment. The screening factorial experiment was designed to isolate the most significant input parameters. Using this information as a platform from which to proceed, the subsequent phase of the experiment allowed the development of empirical models of etch behavior using response surface methodology (G. E. P. Box and N. D. Draper, 1987). The models were subsequently used to optimize the etch process