Eun-Suck Choi

Improvements in tunability of (Ba0.5Sr0.5)TiO3 thin films by use of metalorganic chemical vapor deposited (Ba,Sr)RuO3 interfacial layers

The conducting oxide (Ba,Sr)RuO3 (BSR), which offers an appropriate match in structure with (Ba,Sr)TiO3 (BST), was investigated as an interfacial layer to obtain a high tunability and high dielectric constant in BST films. The (100)-textured BST films deposited onto BSR interfacial layers showed smoother smaller grain size than those without BSR layers. The tunability and dielectric constant of the BST films increased with increasing BSR seed layer thickness and showed ∼70% tunability and a dielectric constant of 1300 at interfacial layer of 150 A. The tunability and dielectric constant of BST films increased nearly two times and two and a half times, respectively, as much as that of BST films without BSR interfacial layers. The higher tunability and dielectric constant have been attributed to the suppression of low-dielectric layer formation and the reduced thermal stress by lattice mismatch.

Bottom Electrode Structures of Pt/RuO2/Ru on Polycrystalline Silicon for Low Temperature (Ba,Sr)TiO3 Thin Film Deposition

Electrode structures of Pt/RuO2/Ru on polysilicon and (Ba,Sr)TiO3(BST) thin films on Pt/RuO2/Ru/poly-Si structures were prepared by metal-organic chemical vapor deposition (MOCVD). The barrier layers of RuO2/Ru deposited by MOCVD showed a stable interface and did not affect the surface morphology of the platinum bottom electrode even at a high annealing temperature of 800°C in oxygen ambient. Contacts in the annealed state up to 800°C exhibited linear current-voltage characteristics with a constant specific contact resistance of 5.0 ×10-5 Ωcm2. The excellent leakage current characteristics and dielectric properties of 50-nm-thick BST films were due to the stable and smooth morphologies of the bottom electrodes at BST deposition temperature.

Liquid-delivery metal-organic CVD of strontium bismuth tantalate thin films using Sr[Ta(OC2H5)5(OC2H4OCH3)]2 and Bi(C6H5)3 precursors

SrBi 2 Ta 2 O 9 (SBT) thin films were deposited onto Pt/Ti/SiO 2 /Si substrates by liquid-delivery metal-organic (MO) CVD using Sr[Ta(OC 2 H 5 ) 5 (OC 2 H 4 OCH 3 )] 2 and Bi(C 6 H 5 ) 3 precursors. The film composition was primarily controlled by varying the deposition temperature and the concentration of the single-mixture solution. The stoichiometric SBT thin films deposited at 540°C were well crystallized, and showed a relatively high intensity of α-axis orientation of (200), as well as the main peaks of (115) and (008). The SBT films, annealed at 750°C in ambient oxygen showed a good ferroelectric property, a saturated hysteresis loop even at an applied voltage of 2 V. The remanent polarization (2P r ) and coercive field (E c ) of SBT films annealed at 750°C were 12 μC cm -2 and 60 kV cm -1 , respectively, at an applied voltage of 5 V.

Bottom Electrode Structures of Pt / RuO2 / Ru for Integration of ( Ba , Sr ) TiO3 Thin Films on Polysilicon

The new electrode structures of Pt/RuO 2 /Ru on polysilicon were prepared by metallorganic chemical vapor deposition (MOCVD). The barrier layers of RuO 2 /Ru deposited by MOCVD showed a stable interface and did not affect the surface morphology of the platinum bottom electrode even at a high annealing temperature of 800°C. The barrier layers effectively alleviated the interdiffusion of Pt, O, and Si at annealing temperatures above 700°C in an O 2 ambient. Contacts in the as-deposited state exhibited linear current-voltage characteristics with a specific contact resistance of 5.0 × 10 -5 Ω cm 2 . Contacts subjected to thermal annealing up to 800°C for 1 h in an oxygen ambient showed almost constant contact resistance. The (Ba, Sr) TiO 3 films deposited by MOCVD at low temperature on Pt/RuO 2 /Ru/polysilicon showed attractive electrical properties in high-density memory devices applications.

Effect of NH4OH Concentration on Surface Qualities of a Silicon Wafer after Final-Touch Polishing

The effect of NH 4 OH concentration on surface qualities, namely, haze level, roughness, and number of remaining particles after final-touch polishing, of silicon wafers was investigated. This investigation found that the surface qualities of the final touch polished silicon wafers were degraded by the agglomeration of colloidal silica abrasives and a weakly formed passivation layer on the silicon-wafer surface at lower NH 4 OH concentration and enhanced with increasing NH 4 OH concentration in alkaline slurry. These results were confirmed by measuring the secondary-abrasive size, zeta potential of the colloidal silica abrasive in the slurry, and X-ray photoelectron spectroscopy on the silicon-wafer surface.

Contact Properties of Pt / RuO2 / Ru Electrode Structure Integrated on Polycrystalline Silicon

The buffer layers of RuO 2 /Ru in Pt/RuO 2 /Ru/poly-Si (polycrystalline silicon) structure were prepared by metallorganic chemical vapor deposition (MOCVD) and dc magnetron sputtering. The harrier layers of RuO 2 /Ru deposited by MOCVD showed a stable interface, and did not affect the surface morphology of the platinum bottom electrode even at a high annealing temperature of 800°C. The barrier layers effectively prevented the interdiffusion of Pt, O, and Si at annealing temperatures above 700°C in O 2 ambient. On the other hand, the barrier layers of RuO 2 /Ru formed by dc sputtering showed severe intermixing and strongly influenced the platinum morphology at high temperature annealing. Contacts in Pt/MOCVD(RuO 2 /Ru)/poly-Si and Pt/dc sputtered (RuO 2 /Ru)/poly-Si structures showed the specific contact resistance of 5.0 x 10 - 5 and 2.0 x 10 -3 Ω cm 2 , respectively. The barrier layers of RuO 2 /Ru formed by MOCVD in Pt/RuO 2 /Ru/poly-Si structure were attractive for integration of high dielectric constant (Ba,Sr)TiO 3 .

Ferroelectric SrBi2Ta2O9 thin film deposition at 550 °C by plasma-enhanced metalorganic chemical vapor deposition onto a metalorganic chemical vapor deposition platinum bottom electrode

Ferroelectric bismuth-layer SrBi2Ta2O9 (SBT) thin films were prepared on Pt/SiO2/Si substrates by plasma-enhanced metalorganic chemical vapor deposition. The platinum bottom electrode deposited by metalorganic chemical vapor deposition shows a dense smooth state after deposition of SBT films and prevents bismuth diffusion into the platinum layer. The c-axis oriented SBT films were crystallized at a deposition temperature of 550 °C. The dielectric constant and dissipation factor of SBT films are 310 and 0.08, respectively, at 100 kHz. The remanent polarization and the coercive field obtained for 180 nm thick Sr0.9Bi2Ta2O9 films deposited at 550 °C were 15 μ/cm2 and 50 kV/cm, respectively, at an applied voltage of 5 V. The leakage current density was about 5.0×10−7 A/cm2 at 250 kV/cm. The films showed fatigue-free characteristics up to 7.0×109 switching bipolar pulses under 5 V.

Integration of platinum bottom electrode on poly-Si for ferroelectric thin films

Platinum bottom electrodes are integrated directly on poly-Si by metalorganic chemical vapor deposition (MOCVD) and dc sputtering. Platinum films deposited directly on poly-Si by MOCVD at 400°C do not form platinum-silicide after annealing at 700°C in oxygen ambient. On the other hand, Pt films deposited on poly-Si at 350°C by dc sputtering were changed to form platinum-silicide at 700°C. Pt films deposited on poly-Si by MOCVD effectively prevent the diffusion of oxygen and silicon at high temperatures in oxygen ambient. MOCVD-Pt films for integration directly on poly-Si are potentially attractive for the ferroelectric random access memory (FRAM) application.

Ferroelectric SrBi2Ta2O9 thin films deposited by liquid injection MOCVD using novel bimetallic alkoxide precursor

Abstract The ferroelectric SBT films were deposited on Pt/Ti/SiO2/Si substrates by liquid injection metalorganic chemical vapor deposition (MOCVD) with single-mixture solution of Sr[Ta(OEt)5(dmae)]2 and Bi(C6H5)3. The Sr/Ta and Bi/Ta ratio in SBT films depended on deposition temperature and mol ratio of precursor in the single-mixture solution. At the substrate temperature of 400°C, Sr/Ta and Bi/Ta ratio were close to 0.4 and 1 at precursor mol ratio of 0.5∼1.0. As-deposited film was amorphous. However, after annealing at 750°C for 30 min in oxygen atmosphere, the diffraction patterns indicated polycrystalline SBT phase. The remanent polarization (Pr) and coercive field (Ec) of SBT film annealed at 750°C were 4.7 μC/cm2and 115.7 kV/cm at an applied voltage of 5 V, respectively. The SBT films annealed at 750°C showed practically no polarization fatigue up to 1010 switching cycles.

The Tunable Characteristics of Ni-Doped (Ba 0.5 Sr 0.5 )TiO 3 Thin Films Deposited onto MOCVD-(Ba 0.5 Sr 0.5 )RuO 3 Conductive Interfacial Layers

The conductive oxide (Ba,Sr)RuO 3 (BSR), which offers an appropriate match in structure with (Ba,Sr)TiO 3 (BST), was investigated as an interfacial layer to obtain a high tunability and high dielectric constant in Ni-doped BST films. The BSR conductive interfacial layers improved the tunability of Ni-doped BST films. Ni-dopant concentration in BST films has a strong influence on the material properties including dielectric and tunable properties. The dielectric constant and tunability of Ni-doped BST films slightly decreased with increasing Ni-dopant concentration. Tunability and dielectric loss of undoped BST films were approximately 42 % and 1.7 % at E = 198 kV/cm, respectively. The dielectric and tunable properties can be improved by insertion of BSR interfacial layers in Ni-doped BST films.