Molecular Orbital Studies of Titanium Nitride Chemical Vapor Deposition:  Gas Phase Complex Formation, Ligand Exchange, and Elimination Reactions

Abstract

The chemical vapor deposition (CVD) of titanium nitride can be carried out with TiCl4 or Ti(NR2)4 and NH3. The present study uses molecular orbital methods to examine complexes of NH3 with TiCl4 and Ti(NH2)4 and the subsequent reaction paths for ligand exchange and elimination reactions which may occur in the gas phase. Geometry optimizations were carried out at the B3LYP/6-311G(d) level of density functional theory, and energies were calculated using a variety of levels of theory, up to G2 for systems with five or fewer heavy atoms. The TiCl4·NH3, TiCl4·(NH3)2, and Ti(NH2)4·NH3 complexes are bound by 14.9, 30.9, and 7.9 kcal/mol, respectively. The barrier for TiCl4 + NH3 → TiCl3NH2 + HCl is 18.4 kcal/mol and is lowered by 23.1 kcal/mol with the introduction of a second NH3. The computed barrier height of 8.4 kcal/mol for the Ti(NH2)4 + NH3 ligand exchange reaction is in very good agreement with the experimental activation energy of 8 kcal/mol for Ti(NMe2)4 + NH3 ligand exchange. The barrier for formation of Ti(NH2)2NH by elimination from Ti(NH2)4 is 33.5 kcal/mol and is reduced by 10 kcal/mol when assisted by an additional NH3. However, examination of the free energies at CVD conditions indicates that the reactions without catalysis by an extra NH3 are favored. Further elimination of NH3 from Ti(NH2)2NH can yield a diimido product, Ti(NH)2, or a nitrido product, Ti(NH2)N, but the barriers and heats of reaction are sufficiently high to make these reactions unlikely in the gas phase during the CVD process.

Computational study on transamination of alkylamides with NH3 during metalorganic chemical vapor deposition of tantalum nitride

“…The calculated energetics for the analogous pathway to generate Ta Supplementary Information (Fig. 3S) for comparison and their activation barriers were similarly as high as $45 kcal/ mol [22][23][24]. The use of NH 3 as a co-reactant, however, decreased the carbon content in the CVD films from 30 to 1 at% [4], consistent with a facile pathway for elimination of carboncontaining ligands.…”

“…Fig. 3a illustrates the calculated energetics of the transamination of a dimethylamido ligand of TBDTMT with NH 3 [24][25][26]. The NH 3 addition to the unsaturated Ta center has a reaction enthalpy (DH1 298 ) of À2.1 kcal/mol.…”

Synthesis of Nanostructured TiN Using a Two‐Step Transition Metal Halide Approach

“…14 However, according to the theoretical ab initio studies conducted on the ammonolysis of TiCl 4 (g)-NH 3 (g) gas phase reaction and the gas-liquid reaction of TiCl 4 (g)-NH 3 (l), substitution of up to three Cl atoms (x 5 3) by NH 2 groups appears to follow an exothermic reaction with excess NH 3 , while the complete ammonolysis of TiCl 4 to form Ti(NH 2 ) 4 is largely endothermic. [18][19][20] The formation of Ti(NH) 2 , however, requires more energy. The room-temperature reaction study by Fowles and Pollard 14 shows that the fully reacted powder contains three chlorine species (x 5 3) replaced by the amide (NH 2 ) groups.…”

“…When the temperature is raised to 10001C in the case of N 2 and Ar, the ends of the tube are at a high enough temperature to sublime NH 4 Cl and the atmosphere is probably similar to that of a TiCl 4 -N 2 -H 2 system where TiN is formed around 9001-10001C with the possibility of dissociation of NH 3 into N 2 and H 2 . 20 Table II show the crystallite size of the TiN determined from XRD line broadening of (200) peak at 42.71 using the Scherrer equation. The crystallite size calculations were performed five times for TiN obtained at each temperature and the mean and standard deviation have been included in Table II.…”

CVD Reactions of TiCl4 with Ammonia: a Quantum Chemical Study

“…5,6 Despite that a great deal of attention has been paid to this system, the mechanism of this CVD reaction is not yet understood. There are several recent calculations 7,8 to explore the CVD reaction in gas phase, using gradient-corrected density functional theory with the Becke three-parameter exchange functional and the Lee-Yang-Parr correction functional (B3LYP). All these calculations have been examined the subsequent reactions paths for ligand exchange and elimination reactions, but were limited to the single molecule reactant.…”