Stagnation Flow Reactor Investigation of Tin Oxide CVD from Monobutyltin Trichloride

Abstract

Tin oxide chemical vapor deposition from monobutyltin trichloride (MBTC) was performed in a stagnation flow reactor at reduced pressures (15-100 Torr) and temperatures of 573-923 K. Growth from mixtures exhibits multiple activation energies, decreasing from kcal mol−1 at temperatures ⩽673 K to kcal mol−1 at temperatures >673 K, indicating a change from one growth mechanism to another. Heterogeneous chemistry governs growth from these precursors at ⩽673 K and most likely at higher temperatures as well, although previous work suggests that gas-phase MBTC pyrolysis/oxidation may begin to contribute at the highest temperatures examined here. The pressure dependence of the growth rate indicates an approach to the mass-transport limit at 923 K. In growth from mixtures, deposition rates are dramatically higher than those produced by (by a factor of over 20 at the lowest substrate temperatures). Potential mechanisms responsible for this increase in rate include both fully heterogeneous processes and rapid formation of a reactive complex. We conclude that multiple reaction pathways, including both gas-phase and surface processes, must be considered to develop a robust model of tin oxide growth from typical MBTC precursor mixtures. © 2004 The Electrochemical Society. All rights reserved.