Effect of the nature of the substrate on the surface chemistry of atomic layer deposition precursors.
The thermal chemistry of Cu(I)-sec-butyl-2-iminopyrrolidinate, a promising copper amidinate complex for atomic layer deposition (ALD) applications, was explored comparatively on several surfaces by using a combination of surface-sensitive techniques, specifically temperature-programmed desorption and x-ray photoelectron spectroscopy (XPS). The substrates explored include single crystals of transition metals (Ni(110) and Cu(110)), thin oxide films (NiO/Ni(110) and SiO2/Ta), and oxygen-treated metals (O/Cu(110)). Decomposition of the pyrrolidinate ligand leads to the desorption of several gas-phase products, including CH3CN, HCN and butene from the metals and CO and CO2from the oxygen-containing surfaces. In all cases dehydrogenation of the organic moieties is accompanied by hydrogen removal from the surface, in the form of H2on metals and mainly as water from the metal oxides, but the threshold for this chemistry varies wildly, from 270 K on Ni(110) to 430 K on O/Cu(110), 470 K on Cu(110), 500 K on NiO/Ni(110), and 570 K on SiO2/Ta. Copper reduction is also observed in both the Cu 2p3/2XPS and the Cu L3VV Auger (AES) spectra, reaching completion by 300 K on Ni(110) but occurring only between 500 and 600 K on Cu(110). On NiO/Ni(110), both Cu(I) and Cu(0) coexist between 200 and 500 K, and on SiO2/Ta a change happens between 500 and 600 K but the reduction is limited, with the copper atoms retaining a significant ionic character. Additional experiments to test adsorption at higher temperatures led to the identification of temperature windows for the self-limiting precursor uptake required for ALD between approximately 300 and 450 K on both Ni(110) and NiO/Ni(110); the range on SiO2had been previously determined to be wider, reaching an upper limit at about 500 K. Finally, deposition of copper metal films via ALD cycles with O2as the co-reactant was successfully accomplished on the Ni(110) substrate.
Department of Chemistry, University of California, Riverside, California 92521, USA.
Yunxi
Y
Yao
Department of Chemistry, Carleton University, Ottawa, Ontario K1S 5B6, Canada.
Jason P
JP
Coyle
Department of Chemistry, Carleton University, Ottawa, Ontario K1S 5B6, Canada.
Seán T
ST
Barry
Department of Chemistry, University of California, Riverside, California 92521, USA.
Francisco
F
Zaera