A full dimensional ab initio direct trajectory study on the ionization dynamics of SiH4

Abstract

Ab initio MO and direct ab initio trajectory calculations have been applied to the ionization processes of SiH₄ in order to shed light on the reaction mechanism of SiH₄⁺ which plays an important role in plasma dry etching processes. The calculations showed that two reaction channels, I and II, were concerned with the decomposition pathways from the vertical ionized state of SiH⁴. The intermediates for channels I and II were expressed schematically by SiH₃⁺–H and H₂–SiH₂⁺, respectively. The lifetime of the intermediate complex in channel I (SiH₃⁺–H) was negligibly short, suggesting that the reaction proceeds via a direct mechanism. On the other hand, the intermediate complex H₂–SiH₂⁺ has a longer lifetime than SiH₃⁺–H. 35% of the total available energy was partitioned into the relative translocation energy in channel I, whereas it was 8% in channel II. Vibrational- and rotational-excitation of H₂ was found in channel II. The mechanism of decomposition of SiH₄⁺ was discussed on the basis of the theoretical results.