Decomposition Pathways for a Model TiN Chemical Vapor Deposition Precursor

A computational study of small-molecule elimination, modeling chemical vapor deposition (CVD) pathways, from a model single-source precursor of titanium nitride is reported. A comparison of possible multiply bonded intermediates is made. Calculated geometries for all species agree well with experiment. Transition states for energetically favorable 1,2-elimination to form multiply bonded intermediates are four-centered geometries with a “kite-shape” (i.e., one obtuse and three acute angles). Processes involving the transfer of H from an amido (NHR) ligand to the leaving group (X) are predicted to be the most favorable. In cases where a group other than H (in this case, methyl) is transferred from the amido (NMeR) to X, the TS has a square shape and a much higher barrier to 1,2-elimination. Pathways to cyclic intermediates and β-H elimination pathways are also compared with 1,2-elimination. The β-H elimination process to form an organic imine and a Ti-amido is found to be kinetically and thermodynamically disfavored versus the lower energy 1,2-elimination processes. Pathways to the formation of cyclic products (η²-imine complexes), recently suggested by experimentalists as a potential decomposition route for TiN precursors, have slightly higher barriers and may be competitive with 1,2-elimination processes under CVD conditions. Analysis of the data for all decomposition reactions suggests that interaction between the metal and the small molecule being eliminated plays an important role in stabilizing the transition state and making it energetically accessible. It is proposed that enhancing these interactions will result in lower activation barriers and potentially lower processing temepratures in CVD of transition-metal-containing materials in which such reactions are the rate-determining step.