Metalorganic chemical vapor deposition of very thin Pb(Zr,Ti)O 3 thin films at low temperatures for high-density ferroel
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Young Ki Han, Doo Young Yang, and Ki Young Oh Jusung Engineering LTD., #49, Neungpyeong-Ri, Opo-Myeun, Kwangju-Gun, Kyunggi-Do, 464-890, Korea (Received 2 July 2001; accepted 30 September 2001)
The metalorganic chemical vapor deposition of very thin (32 mega bit) ferroelectric memory devices. The growth temperatures were set between 450 and 530 °C to obtain a smooth surface morphology and prevent damage to the underlying reaction barrier layer. The average grain size of a 50-nm-thick film on a Pt electrode was about 34 nm with a size distribution (2) of 11 nm. These values are much smaller than the sol-gel-derived PZT films (55 and 25 nm, respectively). Very thin films with a thickness of approximately 30 nm were prepared at wafer temperatures ranging from 500 to 525 °C. Even with the very small thickness, the films showed good ferroelectric properties with a typical remanent polarization from 10 to 15 C/cm2 and an extremely low coercive voltage of 0.3 V. However, the leakage current density was rather high resulting in nonsaturating polarization versus voltage curves. Even though good ferroelectric properties were obtained, the formation of PtxPby alloys on top of the Pt electrode was consistently observed. This precludes the reliable control of film composition and electrical performance. The adoption of an Ir electrode successfully eliminated intermetallic alloy formation and resulted in better and reproducible process control. A 50-nm-thick PZT film on an Ir/IrO2/SiO2/Si substrate also showed a reasonable ferroelectric performance.
I. INTRODUCTION
Ferroelectric random access memory device (FeRAM) have been attracting great interest as a potential candidate to replace nonvolatile flash memory devices or as a memory element in merged memory logic devices. In both cases, a higher integration level (>32 mega bit) is required for cost effectiveness. High-density FeRAM requires a ferroelectric capacitor technology based on techniques other than the current sol-gel process. This is due to the requirements for a more uniform grain size distribution and uniform thickness distribution over three dimensional topology as well as more cost-effective production. The metalorganic chemical vapor deposition (MOCVD) technique appears to be the appropriate process for depositing a ferroelectric Pb(Zr,Ti)O3 (PZT) layer. There have been numerous reports on MOCVD of PZT thin films.1 The Philips2 and Argon groups3 reported that PZT thin films with excellent ferroelectric a)
e-mail: [email protected] J. Mater. Res., Vol. 16, No. 12, Dec 2001
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properties were obtained by MOCVD at wafer temperatures >650 °C. High-temperature deposition offers a great advantage in controlling the Pb concentration in a film, which is one of the most important process variables, through a self-regulation mechanism.4 High-density FeRAM should have a capacitor over bit-line (COB) structure, similar to the current dynamic random access memories (DRAM), for effective utilization of the chip ar
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