Thin films of metallic iridium were grown by atomic layer deposition ͑ALD͒ in a wide temperature range of 225-375°C from tris͑2,4-pentanedionato͒iridium ͓Ir͑acac) 3 ] and oxygen. The films had low resistivity and low impurity contents and good adhesion to the substrate. The film growth rate saturated to a constant value as the precursor pulse times were increased, thus verifying the self-limiting growth mechanism. In addition, the film thickness depended linearly on the number of deposition cycles. The development of the surface morphology with increasing film thickness was studied by atomic force microscopy ͑AFM͒. AFM and X-ray reflectivity analysis showed that the films had smooth surfaces. The films showed a preferred ͑111͒ orientation as studied by X-ray diffraction. The results show that high-quality iridium films can be grown by ALD.Iridium, like the other noble metals and their conductive oxides, is a potential electrode material in dynamic random access memories ͑DRAMs͒ 1-3 and in ferroelectric random access memories ͑FRAMs͒. 4-7 Iridium films prepared by physical vapor deposition ͑PVD͒ have poor step coverage, 8 and therefore chemical vapor deposition ͑CVD͒ and atomic layer deposition ͑ALD͒ 9-11 are more suitable methods for preparing iridium films for the threedimensional storage nodes needed to obtain high storage densities. 12 Another potential application for iridium in microelectronics is gate electrode in metal-oxide-semiconductor field effect transistors ͑MOSFETs͒. 13,14 Iridium thin films are also applicable as optical 15 and protective 16,17 coatings, as active layers in gas sensors, 18 as hydrogen separation membranes, 19 and as catalysts. 20,21 Metallic iridium films have been deposited by CVD from several metallorganic iridium precursors. 22 As far as the authors know, no iridium ALD processes have been reported prior to this paper. ALD is considered to be a special modification of CVD in which the substrate is exposed to one precursor at a time, the precursor pulses being separated by inert gas purging. The precursor molecules adsorb on the surface and/or react with the adsorbed surface species left on the surface during the previous precursor pulse. The growth thus proceeds in a layer-by-layer manner in which one monolayer, or usually a fraction of a monolayer, of the film is deposited during one growth cycle. When the precursor dose is high enough to saturate the precursor adsorption and/or the surface reactions, the film growth becomes self-limiting, that is, the growth rate is constant over the whole surface. 11 The excellent conformality and the good large-area uniformity 23 of the films grown by ALD are consequences of the self-limiting growth mechanism.In this paper we report ALD of iridium thin films. The process is based on oxidative decomposition of Ir͑acac) 3 (acac ϭ 2,4-pentanedione), and the reaction mechanism is expected to resemble the previously studied ALD processes based on oxidative decomposition of RuCp 2 (Cp ϭ cyclopentadienyl), 24 Ru͑thd) 3 (thd ϭ 2,2,6,6-tetramethyl-3,...
