Obtaining a Low and Wide Atomic Layer Deposition Window (150-275 °C) for In2 O3 Films Using an InIII Amidinate and H2 O.

Abstract

Indium oxide is a major component of many technologically important thin films, most notably the transparent conductor indium tin oxide (ITO). Despite being pyrophoric, homoleptic indium(III) alkyls do not allow atomic layer deposition (ALD) of In2 O3 using water as a co-precursor at substrate temperatures below 200 °C. Several alternative indium sources have been developed, but none allows ALD at lower temperatures except in the presence of oxidants such as O2 or O3 , which are not compatible with some substrates or alloying processes. We have synthesized a new indium precursor, tris(N,N'-diisopropylformamidinato)indium(III), compound 1, which allows ALD of pure, carbon-free In2 O3 films using H2 O as the only co-reactant, on substrates in the temperature range 150-275 °C. In contrast, replacing just the H of the anionic iPrNC(H)NiPr ligand with a methyl group (affording the known tris(N,N'-diisopropylacetamidinato)indium(III), compound 2) results in a considerably higher and narrower ALD window in the analogous reaction with H2 O (225-300 °C). Kinetic studies demonstrate that a higher rate of surface reactions in both parts of the ALD cycle gives rise to this difference in the ALD windows.