Electron-impact total ionization cross sections of silicon and germanium hydrides

Abstract

Electron-impact total ionization cross sections of some silicon and germanium compounds have been calculated by applying a new theoretical model that has been found to be reliable for a wide range of molecules. The new theory, the binary-encounter-Bethe (BEB) model, combines the binary-encounter theory and the Bethe theory for electron-impact ionization, and uses simple theoretical molecular orbital data-binding energies, average kinetic energies, and occupation numbers-which are readily available from molecular structure codes. Total ionization cross sections of SiH, SiH 2 , SiH 3 , SiH 4 , Si 2 H 6 , Si(CH 3 ) 4 , GeH, GeH 2 , GeH 3 , GeH 4 , and Ge 2 H 6 are presented for incident electron energies T from threshold to 1 keV, and compared to available experimental data. Theory and experiment agree well for SiH x , x=1-4, from thresholds to T<80 eV, while theoretical peaks occur at lower T than experimental peaks for SiH x , x=1-3. No experimental data are available for germanium hydrides for comparison. The theoretical cross sections are given by a compact analytic form suitable for applications in plasma processing. ©1997 American Institute of Physics. History:Received 27 January 1997; accepted 4 March 1997 Electron-impact total ionization cross sections of some silicon and germanium compounds have been calculated by applying a new theoretical model that has been found to be reliable for a wide range of molecules. The new theory, the binary-encounter-Bethe ͑BEB͒ model, combines the binary-encounter theory and the Bethe theory for electron-impact ionization, and uses simple theoretical molecular orbital data-binding energies, average kinetic energies, and occupation numbers-which are readily available from molecular structure codes. Total ionization cross sections of SiH, SiH 2 , SiH 3 , SiH 4 , Si 2 H 6 , Si͑CH 3 ͒ 4 , GeH, GeH 2 , GeH 3 , GeH 4 , and Ge 2 H 6 are presented for incident electron energies T from threshold to 1 keV, and compared to available experimental data. Theory and experiment agree well for SiH x , xϭ1 -4, from thresholds to T Ͻ80 eV, while theoretical peaks occur at lower T than experimental peaks for SiH x , xϭ1 -3. No experimental data are available for germanium hydrides for comparison. The theoretical cross sections are given by a compact analytic form suitable for applications in plasma processing.

Rf discharge dissociative mode in NF3and SiH4

“…As is known [67], for depositing the a-Si : H film the presence of SiH 2 and SiH 3 is required. For the production of these molecules as a result of dissociation reactions (17) and (18), as we said above, the electrons with the threshold energy of 8.4 eV have to be present in the discharge [64]. The neutral and negatively charged SiH − 3 radicals take part in the formation of dust particles [36].…”

Collision processes of Hydride species in Hydrogen plasmas: III. The Silane family

“…Theoretical calculations of total ionization cross sections for these systems have been performed within the binary-encounter-Bethe (BEB) model [23]. For the SiH 4 molecule, they agree well (∼ 10%) with the experimental data of Refs.…”

“…(1a)) and dissociative (Eqs. (1b),(1c)) ionization of SiH y molecules by electron impact have been subject of several experimental [19,20,21,22] and theoretical [23,24] studies. Most extensively has been studied the e + SiH 4 collision system, for which the partial cross sections for six dissociative ionization channels have been measured in the energy range from threshold to 400 eV [19] and to 100 eV [22].…”

Gas Source Techniques for Molecular Beam Epitaxy of Highly Mismatched Ge Alloys

“…However, when comparing relative sensitivity factors (Rg) for different atoms and molecules, assuming it can be approximated by the ratio of ionization cross sections at 150 eV [61], a Ge2H6 molecule is expected to have an Rg approximately double that of GeH. The Rg for Si(CH3)4 is nearly four times that of GeH [62]. We attribute the difference between (H3Ge)4C:Ge fluxes and C:Ge atomic mole fractions to the difference in Rg between our Ge source and (H3Ge)4C.…”