Chemical Boundary Layers in CVD I. Irreversible Reactions

Because of the coupling of the temperature dependence of gas-phase reaction rate constants with the steep tempera-ture gradient, present in most CVD reactors, a thin chemical reaction boundary layer can be defined in the gas phase just above the susceptor. This boundary layer will be present under all operating conditions, including lower pressures and ir-respective of the kinetic regime ofthe deposition reaction or the existence of flow and temperature boundary layers. Using this chemical boundary layer concept it proves to be possible to derive deposition rate equations not nly for the gas-phase transport limited regime but also for the gas-phase kinetic regime, or for the case where surface reactions are rate limiting. Chemical vapor deposition (CVD) is an important tech-nique nowadays to grow electronically active and insulat-ing layers for all kind of solid-state devices. Studies that have been performed over the last few decades have mainly dealt with growth, doping, or technical aspects. Flow dynamics, reactor design, and depletion ffects also have received some attention to date, and interest is stil