Surface Chemistry of Pentakis(dimethylamido)tantalum on Ta Surfaces

Abstract

The surface chemistry of pentakis(dimethylamido)tantalum (PDMAT), a precursor commonly used for atomic layer deposition (ALD), has been investigated on a Ta surface under ultrahigh vacuum (UHV) conditions. Results from both temperature-programmed desorption (TPD) and isothermal kinetic data obtained using an effusive molecular beam arrangement identified H2, CH4, C2H4, HCN, HN(CH3)2, and H2C═NCH3 as the main desorption species. Several reactions involving the amido ligands were observed on the Ta surface starting at about 450 K. Those include not only the expected hydrogenation to dimethylamine and β-hydride elimination to N-methyl methyleneimine but also decomposition to methane and hydrogen cyanide and a carbon−carbon forming step to yield ethylene. Addition of ammonia to the reaction mixture leads to an enhancement in hydrogenation to the amine at the expense of methane formation, but only at temperatures above approximately 550 K. Isotope labeling was used to establish that hydrogenation of the amido groups involves hydrogen atoms from the ammonia but methane formation occurs via intramolecular hydrogen transfer instead.