Dissociative ionization of silane by electron impact

Abstract

We studied the electron impact ionization of silane (SiH 4) which is widely used in the plasma deposition of different siliconcontaining 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 SiH 4 + 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: SiH 3 +, SiH 2 +, SiH +, Si +, H 2 +, and H +. The agreement between our measured absolute partial ionization crosssections 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 SiH 4 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.