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

Abstract

In this study, we investigated the effects of C4F8/O2 and Ar/O2 component ratios in C4F8 + O2 + 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/O2 and Ar/O2 mixing ratios result in nonmonotonic (with maximums at ∼10% to 15% O2) 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/O2 mixing ratios at constant fraction of C4F8) through the polymer film thickness or by the O atom flux (in the case of C4F8/O2 mixing ratios at constant fraction of Ar) through the balance of adsorption sites.

On Relationships between Plasma Chemistry and Surface Reaction Kinetics Providing the Etching of Silicon in CF4, CHF3, and C4F8 Gases Mixed with Oxygen

“…The set of chemical reaction with corresponding rate coefficients for each gas mixture was taken from our previous model-based works dealt with CF 4 + Ar/O 2 , refs. [ 13 , 17 , 23 ] CHF 3 + Ar/O 2 [ 31 ] and C 4 F 8 + Ar/O 2 [ 13 , 32 ] plasmas. Earlier, these kinetic schemes have been used by several authors and demonstrated the decent similarity between model-predicted and measured F atom densities [ 11 ].…”

“…The similar rule can also be applied to other ion-driven effects on the etched surface, such as the removal of the fluorocarbon polymer film, the destruction of chemical bonds between surface atoms, and the ion-stimulated desorption of low volatile reaction products. The rate of heterogeneous chemical reaction [ 22 , 23 , 32 , 40 ], where is the fluorine atom flux, is the effective reaction probability [ 9 , 10 , 11 ], is the fraction of adsorption sites occupied by chemically inert species, is the fraction of vacant adsorption sites, and is the sticking coefficient of etchant species to the vacant adsorption site. That is why the parameter is not only the exponential function of surface temperature (as it typically takes place for the spontaneous reaction mechanism) but also depends on many plasma-related factors that retard or accelerate the chemical reaction through the change in .…”