Electron-impact-ionization dynamics of SF6

Abstract

A detailed understanding of the dissociative electron ionization dynamics of $\mathrm{S}{\mathrm{F}}_{6}$ is important in the modeling and tuning of dry-etching plasmas used in the semiconductor manufacture industry. This paper reports a crossed-beam electron ionization velocity-map imaging study on the dissociative ionization of cold $\mathrm{S}{\mathrm{F}}_{6}$ molecules, providing complete, unbiased kinetic energy distributions for all significant product ions. Analysis of these distributions suggests that fragmentation following single ionization proceeds via formation of $\mathrm{S}{{\mathrm{F}}_{5}}^{+}$ or $\mathrm{S}{{\mathrm{F}}_{3}}^{+}$ ions that then dissociate in a statistical manner through loss of F atoms or ${\mathrm{F}}_{2}$, until most internal energy has been liberated. Similarly, formation of stable dications is consistent with initial formation of $\mathrm{S}{{\mathrm{F}}_{4}}^{2+}$ ions, which then dissociate on a longer time scale. These data allow a comparison between electron ionization and photoionization dynamics, revealing similar dynamical behavior. In parallel with the ion kinetic energy distributions, the velocity-map imaging approach provides a set of partial ionization cross sections for all detected ionic fragments over an electron energy range of 50--100 eV, providing partial cross sections for ${\mathrm{S}}^{2+}$, and enables the cross sections for $\mathrm{S}{{\mathrm{F}}_{4}}^{2+}$ from $\mathrm{S}{\mathrm{F}}^{+}$ to be resolved.