Atomic layer deposition of stoichiometric In2O3 films using liquid ethylcyclopentadienyl indium and combinations of H2O and O2 plasma

Abstract

Liquid ethylcyclopentadienyl indium (InEtCp) was synthesized, and this compound exhibited superior characteristics, including a relatively high vapor pressure and thermal stability up to 250 °C. In2O3 thin films were subsequently deposited by atomic layer deposition (ALD) using the InEtCp as a precursor together with combinations of oxidants: H2O followed by O2 plasma (WpO), H2O followed by O2 (WO), O2 plasma alone (pO), and O2 plasma followed by H2O (pOW). The growth rates for In2O3 thin films using the pO and pOW processes were much smaller than those using the WO and WpO processes. A self-limiting surface reaction during the WpO process was observed with no delay in nucleation when the pulse times for InEtCp, H2O, and O2 plasma were 0.1, 2.0, and 14 s, respectively, at a growth temperature of 200 °C. For the WO and WpO processes, the In2O3 films are considered to be formed by quite different mechanisms, due to oxidation or lack thereof in the presence or absence of the -O-In-OH* intermediate product. This is due to the difference in the oxidation strength of O2 gas and O2 plasma during the oxidation step in the ALD process. As a result, In2O3 thin films deposited by WpO were obtained with a stoichiometric O/In ratio of 1.5 and a negligibly low residual carbon concentration of around TOF-SIMS detection limit, below 1 ppm. Therefore, InEtCp is one of the promising candidate precursors to form a high quality In2O3 film.