Electron Collision Cross Sections and Transport Parameters in CHF₃

Abstract

The modeling of gas discharges requires the accurate experimental or theoretical determinations of a large amount of atomic and molecular collision data. Among these are the interactions of electrons with CHF₃ due to its applications to replace CF₄ in low pressure plasma processing employed in the semi-conductor industry for etching and deposition. However only a modest amount has been published on low energy electron scattering cross sections of CHF₃ and nothing on its electron transport parameters. This study looks at electron drift velocities in the low E/N regime to determine vibrational excitation and total scattering cross sections in CHF₃. the total scattering cross section was estimated by Christophorou¹ using the Born approximation and as expected, it is quite large due to the polar character of CHF₃. Recently, Sanabia etal² have measured the total cross section for 0-20eV electrons. It is approximately constant above 2 eV at 15 x 10^-16 cm² and then below 2eV increases rapidly as the electron energy tends to zero— characteristic of s-wave scattering. Other electron collision cross sections have not been reported in the literature for low electron energies, however the similarity of CHF₃ to CH₄and CF₄ would suggest that it has large low-energy vibrational excitation cross sections.