Macro- and micro-scale simulation of growth rate and composition in MOCVD of yttria-stabilized zirconia

Yttria-stabilized zirconia (YSZ) thin film was grown by low-pressure metalorganic chemical vapor deposition (LPMOCVD) using beta-diketonate complexes of zirconium and yttrium, tetrakis(2,2,6,6-tetramethyl-3,5-heptadionato) zirconium and tris(2,2,6,6-tetramethyl-3,5-heptadionato) yttrium, respectively. Growth rate distribution and film composition in a hot wall tubular reactor were quantitatively reproduced by a transport model including gas-phase and surface reactions, assuming linear additivity of the individual growth rates of zirconia (ZrO2) and yttria (Y2O3). At low temperatures (773, 823 K) the growth rates are controlled by the gas-phase and surface reactions. Since the rate constants Of Y2O3 are larger than those of ZrO2 at low temperatures, the film is richer in Y than the feed ratio, However, at high temperatures (> 848 K), the growth rates of each oxide system are limited by the mass transfer rates of each intermediate, and the film composition in the reactor tube is nearly equal to the feed ratio. The shapes of YSZ film grown on micro-size trenches can be qualitatively interpreted by a Monte Carlo simulation assuming a linear combination of the growth rates of ZrO2 and Y2O3. The surface reaction Of Y2O3 is faster than that of ZrO2 at low temperatures, thus the film near the mouth of the trench is richer in Y than that at the bottom, However, at high temperature, the film composition becomes constant regardless of its position in the trench, because its growth rate is limited by the mass transfer rates of the intermediates. (C) 2002 Elsevier Science B.V. All rights reserved.