Mechanisms of adsorption and decomposition of metal alkylamide precursors for ultrathin film growth

Atomic layer deposition film growth is usually characterized by the presence of a transient (nonlinear) regime, where surface reactions of precursors take place on the substrate, resembling the first stages of chemical vapor deposition and affecting the composition of the forming interface. Here, the adsorption and decomposition of tetrakis(dimethylamido)titanium, Ti [N (CH3) 2] 4, tetrakis(dimethylamido)zirconium, Zr [N (CH3) 2] 4, tetrakis(dimethylamido)hafnium, Hf [N (CH3) 2] 4, pentakis(dimethylamido) tantalum, Ta [N (CH3) 2] 5, and bis(t -butylimido)-bis(dimethylamido)tungsten, [(CH3) 3 CN] 2 W [N (CH3) 2] 2, on a silicon substrate are investigated using density functional methods. These alkylamides are widely used for deposition of both diffusion barriers and high-permittivity (high- κ) materials. Adsorption is found to be dissociative, with scission of metal-ligand bonds being more feasible than scission of N-C bonds, suggesting that decomposition of ligands is not favored at low temperatures. However, decomposition through C-H bond scission may ultimately lead to the formation of Si-C bonds, without significant kinetic requirements and producing highly stable structures. The overall feasibility of the adsorption/decomposition pathway outlined here explains the presence of carbon at the interface in alkylamide-based deposition schemes.