Tsuneyuki Sato

Reaction analysis for ZrO2 and Y2O3 thin film growth by low-pressure metalorganic chemical vapor deposition using β-diketonate complexes

A mathematical model was developed for low-pressure metalorganic chemical vapor deposition (LPMOCVD) of ZrO 2 and Y203 film growth. Zr(DPM)a(tetrakis-2,2,6,6-tetramethyl-3,5-heptandionate zirconium (/3-diketonate complex)) and Y(DPM) 3 were used as source materials. The surface reaction rate constant (or the reactive sticking coefficient) was determined by comparing the experimentally observed step coverages on micro-scale trenches with those predicted by a simplified Monte Carlo simulation. A gas-phase reaction rate constant was taken as a disposable parameter to fit the growth rate distributions along the reactor tube by a diffusion reaction transport model. Arrhenius-type equations were proposed for both surface and gas phase reactions. For the surface reactions, the activation energies were 188 kJ/mol (T 909 K) for ZrO 2 and 133 kJ/mol (T < 870 K) for YzO3. For the gas phase reactions, they were 140 and 123 kJ/mol for ZrO 2 and Y203, respectively. The scanning electron microscopy (SEM) micrographs and X-ray diffraction (XRD) patterns revealed that the crystallographic orientation and morphology of the grown films depend on the growth temperature.

Three-dimensional numerical simulation of rotating spoke pattern in an oxide melt under a magnetic field

Abstract On the surface of various oxide melts under a vertical magnetic field, the rotating spoke pattern appears. In order to provide a first basic view of this phenomenon, a series of three-dimensional numerical simulations of LiNbO3 melt flow in a crucible (47 mmφ × 46 mmH) under a uniform vertical magnetic field were performed. In this model, the oxide melt was assumed to be a dielectric fluid with a uniform electric charge density ce0. The Marangoni effect was also taken into account. The simulations indicated that the spoke pattern is caused by the Marangoni instability and the rotating motion is driven by the Lorentz force caused by the interaction between the vertical magnetic field and the radial motion of charged fluid which is driven by the Rayleigh–Marangoni convection in the crucible. A charge density of 0.1 C/m3 is sufficient to express the experimentally observed rotating spoke patterns on the LiNbO3 melt which were reported by Miyazawa et al. (1996).

Micro/macro modeling of CVD synthesis

We propose a CVD reaction scheme in which a source material undergoes a gas-phase reaction to produce an intermediate, and then the intermediate diffuses to the solid surface and changes into a solid film through a surface reaction. A series of simple Monte Carlo (SMC) codes has been developed to simulate the observed film shape on micro-trenches and holes. By using these codes, surface reaction rate constants were determined so as to reproduce the experimentally observed film shape. By means of a macro-scale reactive transport analysis of a hot wall tubular reactor, gas-phase reaction rate constants for single component systems were determined to simulate the experimental growth rate distributions. The composition and growth rate of Yttria stabilized Zirconia (YSZ) film, a solid solution of Yttria and Zirconia, were qualitatively explained by a sum of single components growth rates. As an application of these reaction models, we simulated a rotating-disk CVD reactor under low pressure. The simulations based on a quasi three-dimensional model revealed that the susceptor rotation suppresses the buoyancy convection and forms steeper gradients in temperature and concentration near the susceptor uniformly over wide area. At higher temperatures, the growth rate increased with rotation speed, but at lower temperatures the growth rate decreased with increasing rotation speed because the reduced retention time in the high-temperature region suppressed the gas-phase reaction.

Three-dimensional numerical simulation of oscillatory Marangoni flow in half-zone of low-Pr fluids

3D unsteady numerical simulations were conducted, by means of the finite difference method, to understand the characteristics of stationary and oscillatory 3D Marangoni flows in half-zone liquid bridges of low Prandtl number fluids (Pr=0.01 and 0.02) with different aspect ratios (As=1.0, 1.2 and 1.8). The results clearly explain the transition processes; first from an axisymmetric to a 3D steady flow and the second from a 3D steady to 3D oscillatory flow. Critical Marangoni numbers for each transition as well as the frequency were determined for various conditions. These results were compared with available results of both linear stability analysis and non- linear numerical simulations. The present results agreed well with previously reported values within 6%. In a short liquid bridge, the 3D flows indicate two-fold symmetry in azimuthal direction (m=2). In a longer liquid bridge, however, there appeared a 3D flow with m=1. These basic flows become unstable against time dependent disturbances at Mac2.