A binary-encounter-Bethe approach to compute electron-impact partial ionization cross sections of plasma relevant molecules such as hexamethyldisiloxane and silane

Electron-impact partial ionization cross sections (PICS) of fragments are reported from threshold to 5 keV energy using a modified form of the binary-encounter-Bethe model. Scaling using mass spectrometry data ensures that the cross sections are of the correct order of magnitude. The total ionization cross sections (TICS) were obtained by summing the PICS of fragments. The PICS and TICS obtained from the modified-binary-encounter-Bethe model are in excellent agreement with the experimental and theoretical results. The molecules investigated are hexamethyldisiloxane and silane. Both these species are highly relevant in plasma processing where the PICS are required to be over an extended energy range. The study of the ionization process in conjunction with mass spectrometry provides correct estimates of the contribution that each charged ion makes to the TICS. The present approach can be easily extended to any species provided that ion energetics and relative cation abundances data are available.