Uptake of Copper Acetamidinate ALD Precursors on Nickel Surfaces

Abstract

The adsorption and thermal activation of copper(I)-N,N′-di-sec-butylacetamidinate on a Ni(110) single-crystal surface were characterized in connection with the use of that compound as a precursor for the growth of copper films via atomic layer deposition (ALD) processes. Studies were carried out under ultrahigh vacuum (UHV) conditions by using a combination of X-ray photoelectron spectroscopy (XPS), low-energy ion scattering (LEIS), and temperature-programmed desorption (TPD). A temperature window between approximately 350 and 450 K was identified for the clean deposition of the precursor on the surface: lower temperatures are insufficient for activation of the dissociative adsorption, and higher temperatures lead to continuous decomposition beyond Cu monolayer saturation. Approximately three ALD-like cycles are required to reach full Cu monolayer saturation, the equivalent of a film growth rate of approximately 0.75 Å/cycle. Preadsorption of hydrogen on the surface does not modify any of this behavior because of its rapid desorption at temperatures above 350 K once the gas-phase H2 is removed. A discussion is provided on how hydrogen pressures above the mbar range are required to maintain significant steady-state coverages of hydrogen on the surface. Copper precursors leading to relatively stable organic surface intermediates are required in ALD because their clean removal can only happen in the second half-cycle of processes that rely on hydrogenation reactions.