Etching of thin metal films using a ballistic model

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Abstract
A two-dimensional model for plasma etching has been developed based on simulation by ballistic deposition (SIMBAD), a two-dimensional model for film growth over topography. By incorporating the effects of shadowing, adatom mobility, and incident flux distributions, SIMBAD is able to predict microstructure and density of films deposited by physical vapor deposition methods such as evaporation and sputtering. The plasma etch has been similarly modeled using an appropriate incident angular distribution for reactive species and a fixed probability of reaction. Simulation predictions are shown to agree well with experimental results for etching of tungsten films sputtered over trenches. For a 0.9-μm-thick tungsten film on a 1.8-μm-wide 0.6 aspect ratio trench with 80° sidewalls, the etch rate on the sidewalls was found to be about twice the rate on the horizontal sections of film for a CF4/O2 plasma etch. This is in agreement with the computed results.

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