Atomic layer deposition of noble metals: Exploration of the low limit of the deposition temperature
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Yung-Liang Tung and Yun Chi Department of Chemistry, National Tsing Huang University, Hsinchu 30013, Taiwan
Kai Arstila and Kristoffer Meinander Department of Physical Sciences, University of Helsinki, FIN-00014 Helsinki, Finland
Markku Leskelä Department of Chemistry, University of Helsinki, FIN-00014 Helsinki, Finland (Received 17 June 2004; accepted 4 August 2004)
The low limit of the deposition temperature for atomic layer deposition (ALD) of noble metals has been studied. Two approaches were taken; using pure oxygen instead of air and using a noble metal starting surface instead of Al2O3. Platinum thin films were obtained by ALD from MeCpPtMe3 and pure oxygen at deposition temperature as low as 200 °C, which is significantly lower than the low-temperature limit of 300 °C previously reported for the platinum ALD process in which air was used as the oxygen source. The platinum films grown in this study had smooth surfaces, adhered well to the substrate, and had low impurity contents. ALD of ruthenium, on the other hand, took place at lower deposition temperatures on an iridium seed layer than on an Al2O3 layer. On iridium surface, ruthenium films were obtained from RuCp2 and oxygen at 225 °C and from Ru(thd)3 and oxygen at 250 °C, whereas no films were obtained on Al2O3 at temperatures lower than 275 and 325 °C, respectively. The crystal orientation of the ruthenium films was found to depend on the precursor. ALD of palladium from a palladium -ketoiminate precursor and oxygen at 250 and 275 °C was also studied. However, the film-growth rate did not saturate to a constant level when the precursor pulse times were increased.
I. INTRODUCTION
Noble metals have many potential applications in integrated circuits. Platinum, ruthenium, and iridium are potential electrode materials in dynamic random access memories (DRAMs) and in ferroelectric random access memories (FRAMs).1–4 They are also potential gate electrode materials in metal-oxide-semiconductor field effect transistors (MOSFETs).5–7 Furthermore, ruthenium and palladium have been studied as barrier or seed materials for copper interconnects in the integrated circuits.8–10 Deposition of noble metals by chemical vapor deposition (CVD) has extensively been studied.11 Atomic layer deposition (ALD)12 is another promising method for noble metal deposition for these applications because of the excellent conformality and good large-area uniformity13,14 of the deposited films.
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0426 J. Mater. Res., Vol. 19, No. 11, Nov 2004
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Low deposition temperatures have many benefits in the above mentioned applications of noble metals. Smoother films are obtained at lower deposition temperatures because of less pronounced crystal growth.15,16 Smooth bottom electrodes have been shown to provide lower leakage currents in the memory capacitors.1,17 In addition, less aggressive process conditions (e.g., lower deposition temp
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