APCVD of ZnO:Al, insight and control by modeling

Atmospheric pressure chemical vapor deposition (APCVD) of ZnO from diethyl zinc (DEZn) and t-butanol was performed using an industrial reactor design. Deposition profiles were recorded to gain insight in the position dependent variations in layer thickness in such a reactor. We observed that for a deposition temperature below 400 °C most of the deposition took place close to the exit of the gasses, while for increasing temperatures the deposition shifts towards the gas inlet. This trend can be explained by the reaction mechanism through an intermediate alkoxide species from DEZn and t-butanol, which in turn leads to ZnO deposition through a surface reaction. The deposition profile is dependent on the local alkoxide concentration. With increasing temperature, the formation rate increases. This translates in an earlier formation, i.e. in a shift upstream towards gas inlet because this alkoxide formation takes place during the transport through the reactor. Chemical vapor deposition (CVD) is a highly complex system with many interacting physical and chemical processes. Modeling was used to gain insight on the local variations of the concentration of reactive species inside a reactor and was shown to predict the deposition profiles. Moreover, the impact of changes in reactor design on the deposition is discussed.