Optimization of the Vaporization of Liquid and Solid CVD Precursors: Experimental and Modeling Approaches



Two representative examples of the vapor phase transport of liquid and solid molecular precursors from a bubbler and a saturator, respectively, are presented. The influence of the vaporization conditions on the amount of vaporized precursor makes it possible to propose a model suitable for delivering high flow rates for, for instance, large-scale reactors or continuous deposition in conveyor-belt reactors. For the liquid compound Ti(OiPr)4 (TTIP) used in atmospheric pressure CVD of TiO2 thin films, the vapor flow rate increases linearly with the carrier gas flow rate up to a critical value, and also exponentially with the bubbler temperature. A numerical model is developed to simulate the experimental data. To illustrate the case of solid precursor, the sublimation of Fe(C5H5)2, used in the MOCVD of iron thin films, is studied. In this case, the amount of vaporized ferrocene is not proportional to the carrier gas flow rate. A model is developed for a powdery precursor, taking into account the gas/solid exchange surface and therefore the initial amount of precursor in the saturator. It can be used to predict the best vaporization conditions required to maximize and keep constant the precursor flow rate delivered to the CVD reactor.