PLASMA PARAMETERS AND ACTIVE SPECIES KINETICS IN Cl2 + BCl3 + Ar GAS MIXTURE
Abstract
The investigation of electro-physical plasma parameters, steady-state gas phase composition and reactive-ion etching kinetics of silicon in Cl2 + BCl3 + Ar gas mixture under conditions of RF 13.56 MHz inductive discharge was carried out. The investigation procedure included plasma diagnostics by Langmuir probes as well as the 0-dimensional (global) modeling of plasma chemical kinetics. Fixed processing parameters were represented by the argon fraction in a feed gas (10%), total gas pressure (6 mTorr) and bias power (300 W). It was found that the substitution of Cl2 for BCl3 at constant input power a) does influence electrons- and ions-related plasma parameters; b) lowers plasma electronegativity; and c) causes opposite changes in densities of chlorine atoms and BClx radicals. An increase in input power at any fixed feed gas composition results in increasing both dissociation degrees for original molecules and densities of dissociation products. It was shown that the dependence of SiO2 etching rate on the Cl2/BCl3 mixing ratio exhibits the non-monotonic shape (with a maximum of ~ 120 nm/min for Cl2 + 40% BCl3 + 20% Ar gas mixture), and an increase in both BCl3 fraction and input power caused the same effect for the SiO2 + Cl reaction probability. This contradicts with the change in ion energy flux. It was suggested that BClx radicals also play a role of chemically active species being involved in SiOy + BClx → SiOy-1 + BClxO heterogeneous reactions. Such reactions provide an increase in the amount of adsorption sites for chlorine atoms.
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