AVS 58th Annual International Symposium and Exhibition
    Thin Film Division Tuesday Sessions
       Session TF-TuA

Paper TF-TuA1
Indium Oxide Atomic Layer Deposition Facilitated by the Synergy between Oxygen and Water

Tuesday, November 1, 2011, 2:00 pm, Room 107

Session: ALD: Fundamental Reactions and Film Properties
Presenter: Jeffrey Elam, Argonne National Laboratory
Authors: J.A. Libera, Argonne National Laboratory
J.N. Hryn, Argonne National Laboratory
J.W. Elam, Argonne National Laboratory
Correspondent: Click to Email
This study describes how In2O3 films can be prepared by ALD using alternating exposures to cyclopentadienyl indium (InCp) and combinations of H2O and O2, even though H2O and O2 are ineffective when used individually. Nanostructured photovoltaics would benefit enormously from the capability to deposit conformal indium-tin oxide (ITO) films inside of high aspect ratio structures. For instance, our previous In2O3 ALD method using InCp and O3 enabled ITO growth inside of anodic alumina membranes producing higher photocurrents through radial charge collection in dye-sensitized solar cells. However, this process yielded poor thickness conformality due to the In2O3-catalyzed thermal decomposition of O3, and this shortcoming motivated our search for an O3–free process. We were surprised to discover that when H2O and O2 were used together, either as a simultaneous exposure (SE) or in the sequence H2O-O2 (WO) or O2-H2O (OW), very uniform, highly conducting In2O3 films were deposited at 1.0-1.6 Å/cycle over large areas (12”x18”) at temperatures as low as 100°C. In-situ quartz crystal microbalance, mass spectrometry, and Fourier transform infrared measurements revealed that the H2O and O2 work synergistically to facilitate the In2O3 ALD. Each molecule performs a necessary but distinct role in the growth mechanism. Next, we conducted a thorough study of this process for all three growth modes (SE, WO, OW) over the temperature range 100-250°C using spectroscopic ellipsometry, ultraviolet-visible transmission, X-ray diffraction, scanning electron microscopy, and Hall probe measurements. These measurements identified a remarkable correlation between the film structure and electrical properties around an amorphous-to-crystalline phase transition near the deposition temperature of 140°C.