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

Abstract

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.

Growth Temperature Influence on Atomic-Layer-Deposited In2O3 Thin Films and Their Application in Inorganic Perovskite Solar Cells

“…Figure 1 c shows that the growth rate was directly dependent on the deposition temperature, increasing with temperature with no separate temperature window within which a constant growth rate was observed, as reported earlier with other conditions [ 23 , 24 ]. Otherwise, our results are inconsistent with the previous reports; ALD-deposited In 2 O 3 thin film with TMIn with ozone and TEIn with ozone was proposed in ALD process windows between 100 and 200 °C [ 29 , 31 ] and others [ 28 ]. Figure 1 c shows that the growth rate of In 2 O 3 increased drastically from 0.009 nm/cycle to 0.035 nm/cycle at a growth temperature of 115 to 150 °C.…”

“…It is also shown that the indium possesses 3 + valency states in the In 2 O 3 lattice structure in all the growth temperatures. Our findings are consistent with the previous reports for ALD-In 2 O 3 using other precursors [ 24 , 25 , 29 , 30 ].…”

“…In 2 O 3 films grown at 200 and 250 °C observed intense peaks at 2θ of 21.7°, 30.9°, 33.1°, 35.6°, 42.1°, 46.0°, 51.4°, and 61.0° assigned to the (211), (222), (123), (400), (332), (431), (440), and (622) planes, respectively. These were in good agreement with the standard JCPDS #44–1087 of the cubic phase of the In 2 O 3 [ 29 , 34 , 35 ], and films showed the polycrystalline nature with a preferred orientation (222) plane. This kind of growth behavior has also been identified by previous ALD growth [ 25 , 26 , 27 , 31 ].…”

“…Therefore, as temperature increases possibly enhanced the reactivity of surface-adsorbed species with ozone due to thermal activation of adsorption of Et 3 In [ 26 ]. Similar growth behavior results were observed in ALD-In 2 O 3 thin films using the Me 3 In precursor with ozone reactant [ 29 ] at a growth temperature of 250 °C. Using these obtained GPC, In 2 O 3 thin films were grown with different cycle numbers at 115, 200, and 250 °C temperatures on Si substrates.…”

Atomic-Layer-Deposition of Indium Oxide Nano-films for Thin-Film Transistors

“…Regarding the C 1 s XPS spectra shown in Fig. 4a, the film deposited at 160 °C displays a peak at 289.8 eV, which should correspond to C-O [21]. When the deposition temperature is increased to 180 °C, the peak becomes much weaker.…”