Ionization dynamics of CF4-H2O complexes: a full dimensional ab initio trajectory study

The ionization dynamics of the complexes composed of CF4 and H2O, which pla ys an important role in plasma dry-etching processes on semi-conductor surf ace, have been investigated by means of full dimensional direct ab initio t rajectory calculations in order to shed light on mechanism of plasma dry et ching of silicon surface by CF4. Effect of a water molecule existing near C F4 on the ionization dynamics of CF4 was examined. The trajectory calculati ons showed that the water molecule affects strongly the reaction mechanism: namely, H2O molecule reacts with CF4+ to form [CF3OH2](+) complex after th e ionization of CF4. The reaction is expressed by [CF4-H2O] --> (hv)(-e) [CF4-H2O](ver)(+) --> [CF3OH2](+) + F where [CF4-H2O](ver)(+) means a vertical ionized point of the complex. The fraction of the kinetic energy of F atom is 40% of the total available ener gy, which is significantly smaller than that of the dissociation of free CF 4 (65%). The reaction energy is dissipated mostly as the internal energy of the [CF3OH2](+) complex. Also, we found the other reaction channel express ed by [CF4-H2O] (-e)--> (hv) [CF4-H2O](ver)(+) --> CF3+ + F + H2O This channel is three-body dissociation channel. The reaction mechanism was discussed on the basis of the present calculations. (C) 2001 Elsevier Scie nce B.V. All rights reserved.