The growth behavior and step coverage of TiO 2 thin films deposited by liquid-delivery metallorganic chemical vapor deposition ͑MOCVD͒ at temperatures ranging from 410 to 490°C were investigated. The film growth rates were controlled by the gas phase thermal decomposition reaction of the precursors, and the reaction shows an apparent activation energy of ϳ90 kJ/mol. The gas phase thermal decomposition produced several intermediate precursor molecules with different sticking coefficients. The intermediate precursors played a crucial role in the film growth and step coverage change. As the growth rate decreases, the step coverage degrades, which can be explained by Langmuir's isothermal adsorption model of the precursors with the assumption of the various intermediate molecular structures of the precursors. The bulkier intermediate molecular structure of the precursor increases the steric hindrance between the previously adsorbed molecules and the impinging molecules so that the step coverage improves. The unusual step coverage of an MOCVD SrTiO 3 film previously observed for a low precursor injection rate was successfully explained using the results derived from the TiO 2 MOCVD and nonsticking property of the Ti-precursor molecules on the SrO surface.The ceramic thin films ͑Ba,Sr͒TiO 3 ͑BST͒, 1-4 SrTiO 3 ͑STO͒, 5 and Pb͑Zr,Ti͒O 3 6-8 deposited by metallorganic chemical vapor deposition ͑MOCVD͒ have been investigated by many researchers as capacitor materials of dynamic random access memories or ferroelectric random access memories. Considering the shrinking cell area of memory devices, these materials should be deposited on three-dimensional ͑3D͒ structures as contact holes. 9,10 The MOCVD method can produce these films with satisfactory growth rate, electrical properties, and conformal deposition over the severe 3D structures applicable to mass production. However, a nonuniform cation composition of the deposited film over a 3D contact hole has been reported even with the MOCVD technique when the contact hole diameter is below 150 nm. 11 In some cases, the films grew predominantly at the bottom corner of the contact hole, which is unusual. 11 To improve the thickness and composition uniformity of the multication oxide films, an understanding of the deposition behavior of the films on contact holes is necessary. However, it is not easy to understand the details of MOCVD of multicomponent oxide thin films because the deposition is affected by many complex factors. The above-mentioned materials commonly have a Ti component. Therefore, the MOCVD behavior and step coverage of the TiO 2 films are investigated first in this study. From these experimental results, the experimental results on the compositionally nonconformal STO thin film deposition that were previously reported by the authors are analyzed again in this paper. Figure 1 shows the schematic diagram of the system for the deposition of TiO 2 thin films. It is composed of an inverted vertical MOCVD reactor, where the sample surface faces downward, and a liquid...
The metalorganic chemical vapor deposition of very thin (<50 nm) Pb(Zr,Ti)O 3 (PZT) thin films was performed for high density (>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/cm 2 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 Pt x Pb y 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/IrO 2 /SiO 2 /Si substrate also showed a reasonable ferroelectric performance.
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