Ionization dynamics of CF 4–H 2O complexes: a full dimensional ab initio trajectory study

Abstract

The ionization dynamics of the complexes composed of CF 4 and H 2O, which plays an important role in plasma dry-etching processes on semi-conductor surface, have been investigated by means of full dimensional direct ab initio trajectory calculations in order to shed light on mechanism of plasma dry etching of silicon surface by CF 4. Effect of a water molecule existing near CF 4 on the ionization dynamics of CF 4 was examined. The trajectory calculations showed that the water molecule affects strongly the reaction mechanism: namely, H 2O molecule reacts with CF 4 + to form [CF 3OH 2] + complex after the ionization of CF 4. The reaction is expressed by [ CF 4– H 2 O] → − e − hν [ CF 4– H 2 O] + ver →[ CF 3 OH 2] ++ F where [CF 4–H 2O] + ver means a vertical ionized point of the complex. The fraction of the kinetic energy of F atom is 40% of the total available energy, 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 [CF 3OH 2] + complex. Also, we found the other reaction channel expressed by [ CF 4– H 2 O] → − e − hν [ CF 4– H 2 O] + ver → CF 3 ++ F+ H 2 O This channel is three-body dissociation channel. The reaction mechanism was discussed on the basis of the present calculations.