Dong-Yeon Park

HIGHLY (200)-ORIENTED PT FILMS ON SIO2/SI SUBSTRATES BY SEED SELECTION THROUGH AMORPHIZATION AND CONTROLLED GRAIN GROWTH

Highly (200)-oriented Pt films on SiO 2 /Si substrates were successfully prepared by a combination of a dc magnetron sputtering using Ar/O 2 gas mixtures and subsequent controlled annealing. The intensity ratio of (200) to (111) planes ( I 200 / I 111 ) was over 200. The (200)-oriented Pt microcrystallites were less susceptible to amorphization due to their lower strain energy with oxygen incorporation than (111)-oriented ones. The controlled grain growth from the selected (200)-oriented seed microcrystallites during subsequent annealing provided a kinetic pathway where grain growth of the seed microcrystallites was predominant, while suppressing the nucleation of surface energy-driven, (111)-oriented seed microcrystallites and subsequent (111) preferred orientation.

MOCVD of PZT Thin Films with Different Precursor Solutions for Testing Mass-Production Compatibility

Metallorganic chemical vapor deposition (MOCVD) of thin ( 16 megabit) ferroelectric memory devices. The growth temperatures were set between 420 and 530°C to obtain a smooth surface morphology and to prevent damage to the underlying reaction barrier layer. A dome-type CVD chamber with a single- or double-cocktail precursor solution liquid delivery system was used for deposition. Four different precursor solution sets were investigated from the viewpoint of mass-production compatibility. The types of solvents had a great influence on the vaporizer lifetime and the level of oxygen incorporation into the PZT film that critically affected the electrical performance. The deposition behavior, including the within-wafer-thickness uniformity, was also dependent on the type of the precursor solutions. The oxygen injection method had a great influence on the Pb composition, the interfacial reaction between the film and the Ir electrode as well as the electrical properties. When nonpreheated oxygen was injected, the interfacial reaction became a serious problem resulting in the formation of IrO 2-x and Pb x Ir y O z layers without sufficient oxygen incorporation into the PZT film. Preheated oxygen was effective in incorporating Pb into the PZT films without serious interfacial reactions except for thin IrO 2-x layer formation.

Dependence of ferroelectric performance of sol-gel-derived Pb(Zr, Ti)O3 thin films on bottom-Pt-electrode thickness

Pb(Zr,Ti)O3 (PZT) thin films were deposited on Pt/Ti and Pt/IrO2 electrode stacks with various Pt thicknesses (30–200 nm) by a sol–gel process. The sputter-deposited Pt films showed a (111)-preferred texture irrespective of the thickness. However, a high-resolution x-ray diffraction study of the Pt films showed that the films were composed of three kinds of grains with slightly different lattice parameters. The grains with a bulk-like lattice parameter grew with increasing Pt thickness, which was accompanied with an improvement in the crystalline quality. Accordingly, the crystallization and ferroelectric behavior of the 100-nm-thick PZT films improved with increasing Pt film thickness. However, the PZT films on the Pt/IrO2 electrode showed a deteriorated ferroelectric performance due to the outward diffusion of the Ir (O) onto the Pt surface, which increases the depolarizing field and amount of charge injection by the formation of a conducting phase.

Preferred Orientation Controlled Giant Grain Growth of Platinum Thin Films on SiO2/Si Substrates

Platinum thin films were deposited by reactive magnetron sputtering on SiO2/Si substrates. Argon-oxygen sputtering gas mixtures were used to control the microstructure and the preferred orientation of platinum films. As the oxygen fraction in the sputtering gas increased, the preferred orientation of as-deposited film was changed from (111) to random orientation. Post-sputtering anneal was done at 750–1,000°C range in air ambient to study the effects of the incorporated oxygen on the grain growth behaviors of platinum films. After sputtering and anneal at optimum conditions, the 1-µm thick Pt films completely transformed to giant grains with sizes as large as several millimeters. Furthermore, the preferred orientation of the giant grains could be controlled to either (111) or (200).

Effects of IrO2/Pt hybrid electrodes on the crystallization and ferroelectric performances of sol-gel-derived Pb(Zr, Ti)O3 thin film capacitors

The effects of IrO 2 /Pt layered hybrid bottom and/or top electrode structures on the leakage current density versus voltage (J-V), polarization versus voltage (P-V), ferroelectric imprint, and fatigue properties of chemical-solution-derived Pb[Zr x Ti 1 - x )O 3 (PZT, Zr/Ti = 35/65) thin films were investigated. The best P-V and J-V performances were obtained from a capacitor with nonhybrid electrodes (Pt/PZT/Pt capacitor). However, the poor fatigue performance of the capacitor required the adoption of hybrid electrode structures. A thin IrO 2 layer, as thin as 6 nm, which was inserted between top Pt electrode and PZT layer was sufficient for improving the fatigue performance without any degradation of the other ferroelectric properties. However, the same layer adopted on the bottom Pt electrode was not effective in improving the fatigue performance with degradation in P-V and J-V properties. This was ascribed to IrO 2 layer dissolution into the PZT layer during the crystallization annealing of the PZT thin film. A thicker IrO 2 layer resulted in more serious degradation.

Characterization of Platinum films Deposited by a Two-Step Magnetron Sputtering on SiO2/Si Substrates

In this study, defect-free Pt films with good adhesion were deposited on SiO 2 /Si substrates by a two-step magnetron sputtering. This method consists of the first sputtering step using Ar/O 2 gas mixture and the second step using Ar. After two-step deposition, an annealing process was followed at 600-1,000 °C in ambient atmosphere. In the first step, oxygen containing Pt films were deposited. Oxygen incorporated in the Pt films completely diffused out during the high temperature annealing. After the annealing process, the film became dense without catastrophic failures such as hillock, pinhole or buckling. Adhesion strength of films produced by this process was good enough to pass a tape test. It is believed that the good adhesion and the observed microstructural evolution are related to the oxygen in Pt films introduced during the first sputtering step. Adhesion, microstructural evolution and the role of oxygen in Pt films are briefly discussed.

A study of liquid delivery MOCVD of lead oxide thin films on Pt and Ir substrates

Lead oxide thin films were deposited on Pt/SiO 2 /Si and Ir/IrC 2 /SiO 2 /Si substrates by liquid delivery metallorganic chemical vapor deposition (MOCVD) at substrate temperatures ranging from 475 to 525°C using a dome-typeCVD chamber in order to understand the MOCVD behavior of ferroelectric Pb(Zr,Ti)O 3 films. The precursor and oxidant were bis-tetramethylheptanedionato-Pb dissolved in ethylcyclohexane and O 2 , respectively. The lead oxide films were nicely grown on the Pt electrode irrespective of the deposition temperature. However, the film growth on the Ir electrode was hampered by the in situ oxidation of the Ir film when the growth temperature was above 500°C. The film grown at 525°C contained metallic Pb components which may largely degrade the electrical properties of the film. A smaller oxygen flow rate reduced the oxidation of the Ir film and enhanced the lead oxide film growth with a smaller content of metallic Pb. An interesting observation was that the reactively sputtered IrO x electrodes are reduced during the lead oxide CVD process and produced similar film growth behaviors as that on Ir electrodes.

Characterization of Pb x Pt y Alloy Formation on a Pt Substrate during Liquid-Delivery MOCVD of Pb ( Zr , Ti ) O3 Thin Films

Pb x Pt y alloy formation and its influence on Pb(Zr,Ti)O 3 (PZT) film growth during liquid-delivery metallorganic chemical vapor deposition (MOCVD) of ferroelectric PZT thin films on Pt electrodes are investigated. When an excessive amount of Pb precursor and a deficient amount of oxygen are supplied during MOCVD at temperatures near 550°C, Pb diffuses along the grain boundaries into the Pt substrate, causing the formation of an alloy layer. Compared to a thicker Pt electrode (150 nm), a thinner Pt substrate (50 nm) enhances the alloy layer formation due to the higher diffusion of Pb along the more abundant Pt grain boundaries. The alloy layer enhances the Pb incorporation into the PZT film and improves the crystallization of the PZT layer on top due to better structural compatibility between PZT and the alloy. When the deposition temperature is 570°C the alloy formation is initiated in the early stage of the film deposition but undergoes thermal decomposition in the later stage (> ∼ 15 min). Therefore, a constant Pb concentration is obtained after the initial decrease for a deposition period <15 min.

Investigation of the Deposition Behavior of a Lead Oxide Thin Film on Ir Substrates by Liquid Delivery Metallorganic Chemical Vapor Deposition

Lead oxide thin films were deposited on Ir/IrO 2 /SiO 2 /Si substrates by liquid delivery metalorganic chemical vapor deposition at 525 °C in order to understand its influence on Pb-based ferroelectric film growth. The Ir substrates were variously pretreated in situ to control the surface oxidation state. Fully oxidized lead oxide films were grown on a nonoxidized Ir or fully oxidized IrO 2 surface. The lead oxide film growth on partially oxidized IrO x (x < 2) was hampered resulting in metallic Pb incorporation which may largely degrade the electrical properties of the film. IrO x oxidizes quickly consuming the supplied oxygen.

Thickness Effects on the Pyroelectric Properties of Chemical-Solution-Derived Pb(Zr0.3,Ti0.7)O3 Thin Films for the Infra-Red Sensor Devices

The pyroelectric and dielectric properties of Pb(Zr0.3,Ti0.7)O3 (PZT) thin films are systematically investigated as functions of film thickness ranging from 0.3 to 1 µm. For better detectivity of the film, high pyroelectric coefficient, low dielectric coefficient and loss tangent are needed. It can be achieved by highly textured (111) preferred orientation and dense microstructure. To minimize the unwanted preferred orientation with increasing film thickness, a step-by-step annealing process and highly textured (111) Pt bottom electrodes are applied. With increasing film thickness, the squareness of polarization hysteresis loops and remanent polarization values are maximized. Although there is a slight variation of preferred orientation with film thickness, dielectric properties are markedly changed due to microstructural variation. Because of the large improvement of loss tangent, the figure of merit is improved with film thickness. It is maximized at a thickness of 1 µm. The maximum pyroelectric coefficient measured by the Byer-Roundy method is 38 nC/cm2K.