Molecular orbital studies of titanium nitride chemical vapor deposition: Imido dimer formation and elimination reactions

The dimerization of Ti(NH2)(2)NH has been used as a model for the generaliz ed oligomerization of Ti(NR2)(2)NH in the chemical vapor deposition (CVD) o f titanium nitride films. This study uses molecular orbital methods (specif ically the B3LYP/6-311G(d) level of theory) to examine the dimerization pro cess and the subsequent elimination of N2H4 from this model compound by two different reaction paths. There is no transition structure for the formati on of the dimer from two Ti(NH2)(2)NH molecules, and this reaction is barri erless. The binding energies of the singlet and triplet dimer complexes are 99.1 and 49.0 kcal/mol, respectively. Both N2H4 elimination pathways are e ndothermic, and enthalpies of reaction are 26.2 and 17.7 kcal/mol for the s inglet and triplet pathways, respectively. In both pathways, there is a cro ssing from the singlet to triplet surface prior to the N2H4 elimination tra nsition state. Structures on a reaction path for the exchange of amido and imido ligands in the ring of the dimer complex were also found. This pathwa y could lead to the formation of higher oligomers.