Effect of Operating Pressure on ZnO LPCVD from Zinc Acetate

Abstract

ZnO thin films were prepared from zinc acetate using a horizontal tube hot-wall CVD reactor under various pressure and the dependency of film characteristics on operating conditions was studied. The profile of the thin film grown on microscale trenches and the macroscopic growth rate distribution along the reactor were studied by micro/macro numerical simulations. The experimental results indicate that the CVD reaction mechanism changes with operating pressure. A model was proposed to explain the experimental results. The model reveals that, at higher pressures, ZnO film is formed directly from zinc acetate through the slow surface reaction, as was pointed out in our previous paper APCVD. At low pressure, an active species is formed in the gas phase via a gas-phase reaction, diffuses to the reactor wall and deposits ZnO film via a fast surface reaction. At intermediate pressure (10-300 Torr), these two reaction paths coexist but the active intermediate is deactivated through molecular collisions with nitrogen. The experimental results are best, but not perfectly, explained by assuming the rate of the reverse reaction is proportional to CN23, where CN2 is concentration of nitrogen. © 1995, The Society of Chemical Engineers, Japan. All rights reserved.