Ionization dynamics of CF4–H2O complexes: a full dimensional ab initio trajectory study Original Research Article

The ionization dynamics of the complexes composed of CF4 and H2O, 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 CF4. Effect of a water molecule existing near CF4 on the ionization dynamics of CF4 was examined. The trajectory calculations showed that the water molecule affects strongly the reaction mechanism: namely, H2O molecule reacts with CF4+ to form [CF3OH2]+ complex after the ionization of CF4. The reaction is expressed by[CF4–H2O] →−e−hν [CF4–H2O]+ver→[CF3OH2]++Fwhere [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 energy, which is significantly smaller than that of the dissociation of free CF4 (65%). The reaction energy is dissipated mostly as the internal energy of the [CF3OH2]+ complex. Also, we found the other reaction channel expressed by[CF4–H2O] →−e−hν [CF4–H2O]+ver→CF3++F+H2OThis channel is three-body dissociation channel. The reaction mechanism was discussed on the basis of the present calculations.