Atomic Layer Deposition and in Situ Characterization of Ultraclean Lithium Oxide and Lithium Hydroxide

Abstract

We demonstrate the ultraclean atomic layer deposition (ALD) of Li2O and LiOH using lithium tert-butoxide (LiOtBu) precursor with H2O and plasma O2 as oxidants, along with conversion of Li2O and LiOH products to Li2CO3 upon CO2 dosing. Using LiOtBu and H2O results in LiOH below 240 °C and Li2O above 240 °C for otherwise identical process parameters. Substituting plasma O2 as the oxidation precursor results in a combination of Li2CO3 and Li2O products, indicating modification of the ALD reaction preventing volatilization of the C from the Li precursor. The chemistry of the films is definitively characterized for the first time with XPS utilizing an all-UHV transfer procedure from the ALD reactor. We use in situ UHV gas dosing to investigate the reaction mechanisms of ALD Li2O and LiOH with H2O and CO2 to simulate reactions upon air exposure. Lastly, we employ in situ spectroscopic ellipsometry to determine the reaction kinetics of thermal LiOH decomposition, and we report an activation energy of 112.7 ± 0.6 kJ/mol.