Atomic Layer Deposition of Iridium Thin Films by Consecutive Oxidation and Reduction Steps

Abstract

Iridium thin films have been grown by atomic layer deposition (ALD) using Ir(acac)3 (acac = acetylacetonato), ozone, and molecular hydrogen as precursors at low temperatures between 165 and 200 °C. At this temperature range, iridium oxide film results in a process without H2. Therefore H2 had a reducing effect on the film after the oxidizing ozone pulse. On the other hand, methanol was not effective in reducing the oxide film. Ir(acac)3 was sublimed at 155 °C, which sets the lowest deposition temperature limit of 165 °C for the process. Iridium films were successfully deposited on Al2O3 nucleation layers but also directly on bare soda lime glasses and native oxide covered silicon substrates. About 60 nm thick films had resistivities and roughnesses less than 12 μΩ cm and 1.4 nm, respectively. The films contained ≤ 2 atom % hydrogen, ≤ 1 atom % carbon, and 4−7 atom % oxygen as impurities. The Ir films passed the common tape test indicating good adhesion to all tested surfaces. A full Ir coverage over the substrate was obtained with 7 nm thick film.