Electron impact ionization of the TiCl_x (x = 1 - 3) free radicals

Titanium tetrachloride (TiCl₄) is used for the plasma-assisted chemical vapor deposition of titanium nitride films. We studied the electron impact ionization of TiCl_x (x = 1 - 3) free radicals, which are abundant constitutents in TiCl₄-containing processing plasmas, for electron energies from threshold to 100 eV. Absolute partial cross sections for the formation of all singly charged molecular ions were measured using the fast-beam technique. Dissociative ionization was found to be the dominant process for TiCl₃ whereas the formation of the respective parent ions plays a more important role for TiCl₂ and TiCl. Total single ionization cross sections for the three radicals could not be determined with reasonable accuracy because of problems in the determination of the cross sections for the formation of the atomic ions Ti⁺ and Cl⁺ for the three targets and, as a consequence, no comparison of the measured cross sections with calculated total single ionization cross sections is possible.