MASS-FLOW CONTROLLED EVAPORATION SYSTEM

In many (CVD-) processes, there is an increasing demand for delivering reactants as near liquid vapours. Controlling vapours, however, is often a delicate matter. The proven method is the well known ''bubbler'' system, with it's inherent problems: poor stability and poor reproducibility, due to the extremely high sensitivity for changes in temperature. The system described in this paper is an evaporation system, based on mass flow controllers. The vapour is controlled in the liquid phase; thus the amount of vapour is controlled, stable and reproducible, independent of temperature or pressure. Special attention is given to the new possibilities that come into reach with this system, e.g. fluids with very low vapour pressures which are unstable at high temperatures and mixtures can be evaporated properly in this system.