Nucleation and Conformality of Iridium and Iridium Oxide Thin Films Grown by Atomic Layer Deposition
2016
Mattinen, Miika | Hämäläinen, Jani | Gao, Feng | Jalkanen, Pasi | Mizohata, Kenichiro | Räisänen, Jyrki | Puurunen, Riikka L. | Ritala, Mikko | Leskelä, Markku
Nucleation and conformality are important issues, when depositing thin films for demanding applications. In this study, iridium and iridium dioxide (IrO₂) films were deposited by atomic layer deposition (ALD), using five different processes. Different reactants, namely, O₂, air, consecutive O₂ and H₂ (O₂ + H₂), and consecutive O₃ and H₂ (O₃ + H₂) pulses were used with iridium acetylacetonate [Ir(acac)₃] to deposit Ir, while IrO₂ was deposited using Ir(acac)₃ and O₃. Nucleation was studied using a combination of methods for film thickness and morphology evaluation. In conformality studies, microscopic lateral high-aspect-ratio (LHAR) test structures, specifically designed for accurate and versatile conformality testing of ALD films, were used. The order of nucleation, from the fastest to the slowest, was O₂ + H₂ > air ≈ O₂ > O₃ > O₃ + H₂, whereas the order of conformality, from the best to the worst, was O₃ + H₂ > O₂ + H₂ > O₂ > O₃. In the O₃ process, a change in film composition from IrO₂ to metallic Ir was seen inside the LHAR structures. Compared to the previous reports on ALD of platinum-group metals, most of the studied processes showed good to excellent results.
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