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

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 (O-3), O-2, 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 O-3 yielded viable and sustained 111203 growth with TMIn. These measurements also provided details about the In2O3 growth mechanism and enabled us to verify that both the TMIn and O-3 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 degrees C, the In2O3 growth per cycle was nearly constant at 0.46 angstrom/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 x 10(-3) Omega cm, and carrier concentrations as large as 7.0 x 10(19) cm(-3). This TMIn/O-3 process for In2O3 ALD should be suitable for eventual scale-up in photovoltaics.