MODEL FOR ION-INITIATED TRENCH ETCHING

We model the plasma etching of trenches by Langmuir kinetics for neutr al molecules and bombarding ions. The parallel combination of an isotr opic etch rate for the neutrals and an anisotropic etch rate for the i ons gives an effective etch rate, The ion etch rate is proportional to the normal surface component. of the ion energy flux, An approximate analytical expression for the composite etch rate offers a new approac h to the computation of etch profiles for these mixed systems. Etch pr ofiles are displayed for three cases: the nearly ion flux-limited regi me, an intermediate ease, and the nearly neutral-flux limited regime f or the trench bottom. The numerical calculation of the etch profiles f ollows from the integration of three characteristic strip equations wh ich are nonlinear first-order ordinary differential equations (ODE's).