Transport Coefficients For Electrons in Mixtures CF₄/Ar/O₂and CF, CF₂or CF₃Radicals

Abstract

Transport coefficients for electrons in mixtures of CF 4 with Ar and O 2 for ratios of the electric field to the gas number density E/N from 1 Td to 1000 Td (1Td = 10 -21 V m 2 ) 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 CF 4 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, CF 2 and CF 3 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.