CHEMISTRY OF TITANIUM DRY ETCHING IN FLUORINATED AND CHLORINATED GASES

The chemistry of the dry etching of titanium thin films has been investigated in fluorinated and chlorinated environments. In CF4/O2 plasma the hard native stoichiometric oxide, TiO2, always present on the titanium surface, results in a non-reproducible induction time. During etching the surface of titanium is covered by a highly fluorinated layer which protects the metal by the reaction with oxygen. Chlorine is not able to remove the native oxide unless drastic conditions are realized. Once this layer is removed with fluorine, the reaction with molecular chlorine proceeds also without plasma. Fluorine atoms act by making the titanium surface more reactive towards chlorine.