Preparation of iridium metal films by spray chemical vapor deposition
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.99
Preparation of iridium metal films by spray chemical vapor deposition Yoshiyuki Seki1, Yutaka Sawada1, Hiroshi Funakubo2*, Kazuhisa Kawano3, and Noriaki Oshima3
1 Center for Hyper Media Research, Graduate School of Engineering, Tokyo Polytechnic University, 1583 Iiyama, Atsugi, Kanagawa 243-0297, Japan
2 Department of Materials Science and Engineering, Tokyo Institute of Technology, J2-43, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa, 226-850 Japan
3 Advanced Materials Research Laboratory, TOSOH Corporation, 2743-1, Hayakawa, Ayase-shi, Kanagawa, 252-1123, Japan
ABSTRACT
Metal Ir films were prepared by spray chemical vapor deposition (CVD) in air from an Ir precursor, (1,3-cyclohexadiene)(ethylcyclopentadienyl)iridium, Ir(EtCp)(CHD). Film deposition was ascertained at 270–430ºC on a SiO2/Si substrate and the deposition rate increased with the deposition temperature but was saturated above 330ºC. The obtained films consisted of Ir metal without any iridium oxide impurity irrespective of the deposition temperature. Films tended to orient to (111) with increasing deposition temperature. Resistivity of these Ir films decreased with increasing film thickness and reached to values on the order of 10-6 Ω・cm, which was the same order of the values for bulk Ir metal. Good step coverage was observed for the Ir metal films deposited at 270ºC and 330ºC. This shows that the simple spray CVD process in air is a good candidate for depositing Ir metal films with good conductivity and step coverage.
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INTRODUCTION Metal Ir films have been widely used as electrodes, especially for the oxide capacitors used in ferroelectric random access memory (FeRAM) cells.. For these applications, chemical vapor deposition (CVD) is one of the promising deposition processes due to the good step coverage. This is because a three-dimensional capacitor structure is essential for the capacitor-type FeRAMs to increase the capacitance by increasing the capacitor area on the limited footprint of the substrate. The Ir-based electrodes, such as Ir, IrO2, and Ir/IrO2, have been considered promising candidates for FeRAMs constructed using most-widely used ferroelectric Pb(Zr,Ti)O3 (PZT) thin films, since the Ir-based electrodes improve the reliability of PZT ferroelectric capacitors, including their endurance, imprint and retention properties. CVD of Ir metal films has been reported, but good step coverage has not been achieved [1, 2]. We developed a spray chemical vapor deposition method in which the CVD source is sprayed onto the heated substrate under atmospheric air [3–8]. This process does not require an expensive set-up, and it supplies a high concentration of source gas to the substrate due to the high process pressure; such high process pressure
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