A full dimensional ab initio dynamics study on the ionization processes ofCF4

The ionization dynamics of CF4, which plays an important role in the initia l processes of plasma dry etching on a silicon surface, has been investigat ed by means of both static ab initio molecular orbital (MO) and full dimens ional direct ab initio dynamics calculations. The static nb initio MO calcu lation (MP4SDQ/6-311G(d, p) level) showed that the CF4+ ion has a structure that is strongly distorted from T-d symmetry and which is expressed by CF3 +-F. The complex is 5.8 kcal mol(-1) more stable in energy than its dissoci ation limit (CF3+ + F). From the dynamics calculations (HF/6-311G(d, p) lev el), it was found that CF4+, formed by the vertical ionization of CF4, deco mposes directly into CF3+ and F via the complex region corresponding to CF3 +-F. The lifetime of the CF3+-F complex is extremely short and may be negle cted. The analysis of the product states showed that 65% of the total avail able energy is partitioned into the relative translational mode between CF3 + and F. The C-F stretching mode of CF3+ is still in the ground state after the dissociation, whereas the CF3 umbrella mode is excited to v = 1-2. The mechanism of the ionization of CF4 is discussed on the basis of the calcul ations in this paper.