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.
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