Electron transport coefficients in mixtures of CF₄and CF₂radicals

Abstract

Electron kinetics determines the rate of production of chemically active species in processing plasmas. Precise transport coefficients are needed to describe conditions such as those found in plasma assisted technologies for semiconductor production, but these are affected by the density of free radicals, which in themselves depend on the chemical kinetics. We present transport coefficients for electrons in mixtures of CF 4 with CF 2 (and we also show similar results for other radicals) for ratios of the electric field to the gas number density E/N from 1 to 1000 Td (1 Td = 10 −21 V m 2 ). Our analysis of non-conservative collisions revealed a range of E/N where electron attachment to radicals significantly changes the electron kinetics compared with pure CF 4 gas. The results are obtained using simple solutions for Boltzmann's equation and exact Monte Carlo simulations.

Modelling of anomalous Doppler broadened lines, thermalization of electrons and the role of radicals in discharges at high E/N

“…Our calculations [16,17] indicate that the addition of radicals even at the level of 10% does not affect very much the mean energy and the EEDF (see figure 1). On the other hand the effect on the drift velocity is significant and one example is shown for the mixture that includes argon in figure 2.…”

“…On the other hand the effect on the drift velocity is significant and one example is shown for the mixture that includes argon in figure 2. The comparison between the two figures means that while mean energy is not perturbed much by the presence of radical and the shape of EEDF is not affected the elastic cross section for radicals which does not have a minimum fills the cross section in the region of the Ramsauer Townsend minimum in CF 4 and it changes the optimum conditions for the negative differential conductivity [16,18]. This is a proof that by selecting a mixture one may control independently the momentum and the energy balance and in particular the number balance.…”

“…In this work we have calculated the electron transport coefficients for mixtures consisting of CF 4 /CF 2 [16] and of CF 4 /Ar/CF 2 [17]. Argon was present at 10% while the abundance of the radical was varied from 0.01% to 10% thus covering realistic abundances found in plasma applications.…”

Modeling of the effect of radicals on plasmas used for etching in microelectronics

“…The most abundant radical in plasmas containing CF 4 is CF [15,16] and it can be found even at abundances of the order of several %. As CF have attachment at low energies with thresholds considerably smaller than that of the dissociative electron attachment for electrons in CF 4 the overall attachment rate is enhanced and extended to lower energies.…”

Transport Coefficients in Mixtures Ar/H2

“…Transport coecients are obtained by using a two term approximation (TTA) to the electron Boltzmann equation [3] and by Monte Carlo simulations [4,5] (MCS). The TTA technique is very frequently used in plasma modeling in spite of its limited accuracy [6].…”