Transport Coefficients For Electrons in Mixtures CF4/Ar/O2 and CF, CF2 or CF3 Radicals
Ž. Nikitović, V. Stojanović, M. Radmilović-Radjenović,
Institute of Physics, University of Belgrade, Pregrevica 118, 11080 Belgrade, Serbia
Full Text PDF
Transport coefficients for electrons in mixtures of CF4 with Ar and O2 for ratios of the electric field to the gas number density E/N from 1 Td to 1000 Td (1Td=10-21 V m2) are presented. The analysis of non-conservative collisions revealed a range of the reduced electric field E/N where electron attachment introduced by radicals significantly changes electron kinetics obtained for mixtures without dissociation of CF4 gas. The results obtained by using a simple, Two Term solutions for Boltzmann's equation are verified by Monte Carlo simulations. It was found that three body attachments for oxygen is not significant for pressures that are standard in plasma etching equipment i.e. below 1 Torr. Furthermore, the attachment to CF, CF2 and CF3 at low mean energies is significant, several orders of magnitude. At the same time the mean energy and energy distribution functions for the given E/N are the same as in unperturbed gas mixture. The large changes of the attachment rate are sufficient to change the nature of plasmas and turn them into ion-ion plasmas with very few electrons for realistic abundances.
DOI: 10.12693/APhysPolA.120.289
PACS numbers: 51.10.+y, 52.20.-j, 52.65.Pp, 52.65.Rr, 52.77.-j