Electron Transport, Ionization, and Attachment Coefficients in C2F4 and C2F4 /AR Mixtures
In the use of perfluorocyclobutane (c-C4F8) as a plasma processing gas for silicon dioxide etching, perfluoroethylene (C2F4) is produced as a by-product of electron and photon impact on c-C4F8, and also as a product of thermal decomposition of c-C4F8. Consequently, dissociative processes can make C2F4 a significant gas constituent. Therefore, in order to model c-C4F8 plasmas, it is important to know the electron transport, ionization, and attachment coefficients of C2F4 in order to understand fully the chemical and physical processes occurring in the discharge. This knowledge may also be of relevance to gaseous dielectrics since C2F4 may be produced in SF6 circuit breakers by vaporization of polytetrafluoroethylene insulators.1 Measurements of electron transport, ionization, and attachment coefficients are reported in this paper for pure C2F4 gas. In addition, measurements of the electron drift velocity and the effective ionization coefficient as functions of the density-reduced electric field E/N are reported for mixtures of C2F4 with Ar, which may be useful in efforts to obtain electron collision cross sections for C2F4 using Boltzmann codes. The effect of Penning ionization on the measured effective ionization coefficients in C2F4/Ar mixtures is also investigated.
KeywordsCircuit Breaker Electron Energy Distribution Function Electron Drift Velocity Attachment Coefficient Gaseous Dielectric
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