Dissociative ionization of silane by electron impact

We studied the electron impact ionization of silane (SiH₄) which is widely used in the plasma deposition of different silicon-containing thin films. Absolute partial cross-sections for the formation of all fragment ions were measured in a high resolution double focusing sector field mass spectrometer with a modified ion extraction stage for electron energies from threshold to 100 eV. No evidence for the formation of stable parent SiH₄⁺ ions was found in agreement with previous experimental investigations. The single positive fragment ion formation is the dominant ionization process. We observed the following product ions: SiH₃⁺, SiH₂⁺, SiH⁺, Si⁺, H₂⁺, and H⁺. The agreement between our measured absolute partial ionization cross-sections and two earlier data sets obtained by different techniques is generally good for the silicon-containing fragment ions taking into account quoted uncertainties of ± 10% to ± 20%, but less satisfactory for the formation of atomic and molecular hydrogen ions which were found to be produced with significant excess kinetic energies, particularly in the case of H⁺. A comparison of the total SiH₄ ionization cross-section derived from the measured partial ionization cross-sections and a calculated cross-section based on the Binary-Encounter-Bethe (BEB) model showed excellent agreement in the energy range above 30 eV.