Nucleation and Conformality of Iridium and Iridium Oxide Thin Films Grown by Atomic Layer Deposition

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, O-2, air, consecutive O-2 and H-2 (O-2 + H-2), and consecutive O-3 and H-2 (O-3 + H-2) pulses were used with iridium acetylacetonate [Ir(acac)(3)] to deposit Ir, while IrO2 was deposited using Ir(acac)3 and O-3. 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 O-2 + H-2 > air approximate to O-2 > O-3 > O-3 + H-2, whereas the order of conformality, from the best to the worst, was O-3 + H-2 > O-2 + H-2 > O-2 > O-3. In the O-3 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.