INFLUENCE OF REACTANT TRANSPORT ON FLUORINE REACTIVE ION ETCHING OF DEEP TRENCHES IN SILICON

The reactive ion etching of silicon by fluorine in high-aspect ratio f eatures was modeled to assess the relative importance of reactant tran sport on etching rate at the bottom of rectangular trenches. The flux of ions to the feature bottom was found by summing two components: ion s arriving directly from the plasma and ions reflected from the sidewa lls before reaching the bottom. The transport of neutral reactants wit hin the feature was modeled with diffuse scattering and reaction rates following the kinetics reported by Gray et al. [J. Vac. Sci. Technol. B 11, 1243 ( 1993)] at all surfaces. The etching rate was found to de pend most strongly upon the ion flux under typical process conditions, because of relatively low fluorine reaction probability and low react ant depletion within the feature. Reactant transport limitations are e xpected to be more important under conditions of low fluorine to ion f lux ratio, high-substrate temperature, and high-ion energy.