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.