Experimental and Theoretical Studies of Radical Production in RF CCP Discharge at 81-MHz Frequency in $\hbox{Ar/CF}_{4}$ and $\hbox{Ar/CHF}_{3}$ Mixtures

Abstract

In this paper, the experimental and theoretical studies of RF capacitive-coupled-plasma (CCP) discharge at frequency of 81 MHz in Ar/CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> and Ar/CHF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> mixtures were carried out. The density distributions of CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , F, and H radicals in the interelectrode gap were measured by the spatially resolved emission and absorption spectroscopies. In the CHF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /Ar discharge, the measurements of plasma density and electron temperature were also carried out by using the probe technique. The experimental data were analyzed on the base of the self-consistent simulation of RF CCP discharge. The multipurpose hybrid approach was used in which the self-consistent particle-in-cell MC method is applied to describe the behavior of electrons and ions, whereas the behavior of neutral species is treated by the fluid model, taking into account the complicated plasma chemistry in the Ar/CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> and Ar/CHF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> mixtures. The comparative analysis of the experimental and simulation results has shown that, in the Ar/CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> plasma, the main source of CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> radicals is the electron-impact dissociation of CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> , whereas the chain reactions with H and F atoms play a crucial role in CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> radical production in Ar/CHF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> with the chain branching being caused by electron-impact dissociation of HF. The good agreement between the calculated and experimental densities of CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , H, and F radicals shows that the present model correctly describes the chain mechanism. The results of probe measurements in the CHF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /Ar discharge also agree well with the calculated plasma density and mean electron energy in the bulk. At the same time, the simulation revealed the rather lower electronegativity as compared with the known literature data. The simulation has shown that the electron attachment to CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> radicals may strongly increase the negative-ion density. The direct measurements of negative ions together with CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> densities are necessary to make clear the question. The results of this paper directly indicate that the kinetics of electron attachment and detachment to polymeric neutral products and radicals is of great importance for the correct description of fluorocarbon-plasma electronegativity.