Towards a comprehensive understanding of the chemical vapor deposition of titanium nitride using Ti(NMe2)4: a density functional theory approach

Abstract

A gas phase mechanistic investigation of the chemical vapor deposition (CVD) of titanium nitride (TiN) from the decomposition of Ti(NMe₂)₄, tetrakis(dimethylamido)titanium (TDMAT) as a single source precursor as well as from the reaction of Ti(NMe₂)₄ with NH₃, i.e., the ammonia assisted mechanism is carried out and reported herein within the framework of density functional theory. Contrary to the theoretical result reported previously for a model TDMAT, metallacycle formation and β-H elimination pathways are found to be the major decomposition pathways responsible for the decomposition of TDMAT, and this finding is in accord with the experimental observation. Interestingly, agostic interaction is found to play a key role in promoting β-H elimination in the decomposition of TDMAT. A new additional pathway of decomposition of TDMAT has been identified theoretically in this present study. Exploration of the complex gas phase mechanism and thereby a detailed identification of the reaction intermediates enable us in realizing the origin of incorporation of carbon contamination in TiN films produced from TDMAT alone and then how the contamination is removed in the presence of ammonia. The ammonia assisted mechanism is found to proceed through the formation of a pre-equilibrium complex. The computed barrier height of 7.3 kcal mol⁻¹ for the initial transamination process associated with the Ti(NMe₂)₄ + NH₃ reaction is found to be in very good agreement with the experimental activation energy. The total rate constant k_tot for the ammonia assisted mechanism is calculated to be 1.28 × 10⁻⁵¹ cm³ molecule⁻¹ s⁻¹ at 298.15 K.