Gas-phase chemistry and reactive-ion etching kinetics for silicon-based materials in C4F8 + O2 + Ar plasma

In this study, we investigated the effects of C4F8/O-2 and Ar/O-2 component ratios in C4F8 + O-2 + Ar gas system on plasma parameters, gas-phase chemistry, and etching kinetics for Si, SiO2, and Si3N4 under the condition of inductively coupled radiofrequency (13.56 MHz) plasma. The use of plasma diagnostics by Langmuir probes, together with the zero-dimensional plasma modeling, allowed one to compare two different gas mixing regimes in respect to (a) electrons- and ions-related plasma parameters; (b) steady-state densities of plasma active species; and (c) formation and decay kinetics for F atoms and polymerizing radicals. It was shown that variations in both C4F8/O-2 and Ar/O-2 mixing ratios result in nonmonotonic (with maximums at similar to 10% to 15% O-2) Si, SiO2, and Si3N4 etching rates as well as in opposite changes in corresponding effective reaction probabilities. The model-based analysis of etching mechanisms allowed one to suggest that the net effect from all heterogeneous (i.e., appeared on the etched surface) interaction pathways may be controlled either by the fluorocarbon radical flux (in the case of Ar/O-2 mixing ratios at constant fraction of C4F8) through the polymer film thickness or by the O atom flux (in the case of C4F8/O-2 mixing ratios at constant fraction of Ar) through the balance of adsorption sites.

Automated summary

The study investigated the effects of C4F8/O-2 and Ar/O-2 component ratios in a gas system on plasma parameters and etching kinetics for various materials. The results showed that changes in the component ratios led to nonmonotonic etching rates and different reaction probabilities. The analysis suggested that the effects on the etching mechanisms may be controlled by the flux of fluorocarbon radicals or oxygen atoms.