Absolute total and partial cross-sections for the electron impact ionization of TiCl₄

Titanium tetrachloride (TiCl₄) is used for the plasma-assisted chemical vapor deposition (CVD) of titanium nitride films. We studied the electron impact ionization of TiCl₄ for electron energies from threshold to 500 eV. Absolute partial cross-sections for the formation of all singly charged positive ions and for four doubly charged positive ions were measured using a time-of-flight mass spectrometer (TOF-MS), which can be operated either in the linear mode or in the reflection mode. Dissociative ionization was found to be the dominant process. At lower impact energies up to 40 eV, the ion abundance varies drastically with impact energy, whereas at higher energies, two ionization channels dominate, the formation of the TiCl₃⁺ fragment ion with a maximum cross-section of 3.75×10^-16 cm² at 100 eV and the formation of the Cl⁺ fragment ion with a maximum cross-section of 4×10^-16 cm² at 70 eV. All fragment ions with the exception of TiCl₃⁺ are formed with excess kinetic energy with the Cl⁺ ion showing the broadest distribution of kinetic energies. The cross-section values of the doubly charged ions are approximately one order of magnitude smaller than those of the singly charged ions. The experimentally determined total single ionization cross-section of TiCl₄ is compared with results of semi-empirical calculations and good agreement is found.