Indium Oxide Thin Films by Atomic Layer Deposition Using Trimethylindium and Ozone

• Published in: Journal of physical chemistry. C Vol. 120; no. 18; pp. 9874 - 9883
• Main Authors: Mane, Anil U, Allen, Amy J, Kanjolia, Ravindra K, Elam, Jeffrey W
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 12-05-2016
• Subjects: atomic layer deposition; indium oxide; quartz crystal microbalance; transparent conducting oxide; trimethyl indium
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.6b02657

We investigated the atomic layer deposition (ALD) of indium oxide (In2O3) thin films using alternating exposures of trimethylindium (TMIn) and a variety of oxygen sources: ozone (O3), O2, deionized H2O, and hydrogen peroxide (H2O2). We used in situ quartz crystal microbalance measurements to evaluate the effectiveness of the different oxygen sources and found that only O3 yielded viable and sustained In2O3 growth with TMIn. These measurements also provided details about the In2O3 growth mechanism and enabled us to verify that both the TMIn and O3 surface reactions were self-limiting. In2O3 thin films were prepared and characterized using X-ray diffraction, ultraviolet–visible spectrophotometry, spectroscopic ellipsometry, X-ray photoelectron spectroscopy, and scanning electron microscopy. The electrical transport properties of these layers were studied by Hall probe measurements. We found that, at deposition temperatures within the range of 100–200 °C, the In2O3 growth per cycle was nearly constant at 0.46 Å/cycle and the films were dense and pure. The film thickness was highly uniform (<0.3% variation) along the 45 cm length of our tubular ALD reactor. At higher growth temperatures the In2O3 growth per cycle increased due to thermal decomposition of the TMIn. The ALD In2O3 films showed resistivities as low as 3.2 × 10–3 Ω cm, and carrier concentrations as large as 7.0 × 1019 cm–3. This TMIn/O3 process for In2O3 ALD should be suitable for eventual scale-up in photovoltaics.