Ir Thin Films for PZT Capacitors Prepared by MOCVD Using a New Ir Precursor
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C11.37.1
Ir Thin Films for PZT Capacitors Prepared by MOCVD Using a New Ir Precursor H.Fujisawa, S.Watari, M.Shimizu, H.Niu and N.Oshima1 Department of Electrical Engineering and Computer Sciences, Graduate School of Engineering, Himeji Institute of Technology, 2167 Shosha, Himeji, Hyogo 671-2201, Japan 1 Tokyo Research Center, TOSOH Corporation, 2743-1, Hyakawa, Ayase, Kanagawa 252-1123, Japan ABSTRACT Preparation of Ir thin films for PZT capacitors by MOCVD using a new liquid Ir precursor, Ir(EtCp)(CHD) was investigated. Ir thin films with a highly reflecting surface and (111)-orientation were successfully obtained at 230-400oC. When Ir(EtCp)(CHD) was used, shorter incubation time (20min at 230oC and not observed above 240oC) and higher nucleation density (300-400mm-2 at 250-300oC) were observed because of its lower decomposition temperature (300oC) than that of previously reported liquid precursor, Ir(EtCp)(COD). Resistivity of 100nm-thick Ir films grown at 250-350oC were less than 20µΩ⋅cm. PZT capacitors with top and bottom electrodes prepared using Ir(EtCp)(CHD) showed D-E hysteresis loop with Pr of 15µC/cm2 and Ec of 60kV/cm. No degradation of switching up to 1010 switching cycles by bipolar pulses of ±231kV/cm (±3V) and 500kHz. INTRODUCTION Ir and IrO2 electrodes have been extensively investigated for Pb(Zr,Ti)O3 (PZT) capacitors in non-volatile ferroelectric random access memory (NV-FeRAM) since it was reported that fatigue and imprint properties of PZT capacitors with Ir-based electrodes were significantly improved [1,2]. For the future realization of high-integrated NV-FeRAM with three-dimensional ferroelectric capacitors, MOCVD (metalorganic chemical vapor deposition) technique of ferroelectric thin films and electrode materials will be indispensable because of its highly conformal growth, high growth rate and compatibility with LSI process. Thus there have been several reports on MOCVD of Ir-based electrodes using various solid precursors, such as IrCp(COD) (Cp:cyclopentadienyl, COD:1,5-cyclooctadiene) [3], Ir(MeCp)(COD) (Me:CH3) [3-5], Ir(acac)3 (acac:acetyacetonate) [6-9], Ir(thd)(cod) (thd:2,2,6,6-tetramethyl-3,5-heptanedionate) [9,10]. On the other hand, we have developed the MOCVD technique of Ir and IrO2 electrodes using a liquid precursor, Ir(EtCp)(COD) (Et:C2H5), with higher vapor pressure than that of solid precursors [11,12]. Three-dimensional Ir/PZT/Ir capacitors were successfully fabricated solely by MOCVD [13]. However, film growth using Ir(EtCp)(COD) had several drawbacks, such as a long incubation time at the initial growth stage and low nucleation density at high growth temperature (>350oC). In this study, we report preparation of Ir electrode using a newly developed liquid Ir precursor, Ir(EtCp)(CHD) ((1,3-cyclohexadiene)(ethylcyclopentadienyl)iridium) and its applications to Ir/PZT/Ir capacitors.
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EXPERIMENTAL PROCEDURE Chemical properties of Ir(EtCp)(CHD) are summarized in Table I. This precursor has a higher vapor pressure (0.1Torr at 75oC) and lower decomposition temperat
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