Control of Plasma Etch Rates, Selectivity and Anisotropy with Plasma Parameters

We discuss the experimental verification of relations derived earlier (1) between observable plasma etch rate, selectivity and anisotropy and reactor parameters for a variety of etch gases. Since the hetergeneous etch reaction is a superposition of neutral and ionic components, it can be shown that such etch chemistry exhibits enhancement and is made anisotropic by the energy transport of ions to the etch surface only when the process is ion dominated. The ion energy transport is controlled by the plasma sheath electric field-electrode area/gas pressure-collision cross section ratio, E.A./pQ, similarly controlling chemical anisotropy for ion dominated etch reactions. Under such circumstances, we show that many etch gases can yield identical ion transport, etch rate and anisotropy for a given rf current, gas pressure, ion-neutral collision cross section & electrode area, Irf/pQA.