Homogeneous Decomposition of Aryl- and Alkylimido Precursors for the Chemical Vapor Deposition of Tungsten Nitride: A Combined Density Functional Theory and Experimental Study

Abstract

MOCVD growth of tungsten nitride (WN(x)()) and tungsten carbonitride (WN(x)()C(y)()) thin films has been reported from the complexes Cl(4)(CH(3)CN)W(NR) (1: R = Ph; 2: R = (i)Pr; 3: R = C(3)H(5)). To evaluate the role of the imido substituent in film growth, gas-phase homogeneous decomposition of precursor molecules was investigated using density functional theory (DFT) calculations. Computational results and NMR kinetics of acetonitrile exchange by 2 in solution verified that dissociation of the acetonitrile ligand should be facile for 1-3 in the temperature range used for film growth (>450 degrees C). A computational search for transition states for cleavage of W-Cl bonds in the presence of H(2) carrier gas was consistent with a sigma-bond metathesis pathway. Natural bonding orbital (NBO) analysis and bond energy calculations indicated that 1 has a stronger N-C(imido) bond and a slightly weaker W-N bond than 2 and 3, suggesting a greater role for W-N bond cleavage in depositions from 1. These results are consistent with mass spectrometric fragmentation patterns from 1-3 and low nitrogen content in films deposited from 1 as compared to those from 2 and 3.