REACTIVE SPUTTERING USING 2 REACTIVE GASES, EXPERIMENTS AND COMPUTER MODELING

The reactive sputtering process is very simple to use as long as one wants to deposit fully formed compounds. If, however, an intermediate composition is required it is necessary to use quite advanced process control. Reactive sputtering from an elemental target in argon with the addition of one reactive gas have been extensively studied. Also studies of reactive cosputtering have been reported. The interest for such studies increased dramatically when the high-temperature superconductive thin films were introduced. In this article we will treat the process of reactive sputtering from an elemental target in argon with the addition of two reactive gases. In such a process, e.g., oxy-nitride films can be formed. The fundamental reactive sputtering model has been modified to handle two reactive gases. By this new model it is possible to simulate two gases having different reactivity and sticking coefficients to the elemental metal involved. It is possible to predict complex effects in the processing region where the two gases compete to form different compounds. The ''hysteresis effect'' for this two-gas reactive sputtering process differs significantly from the hysteresis effect observed in a single gas reactive sputtering process. Poisoning the target by one gas prevents formation on the target of the compound based on the other gas. It should, however, be possible to ''tune'' the process to deposit any desired composition. A large fraction of these composition intervals occur inside the ''hysteresis'' region. The simple one-gas reactive sputtering process operates on a single curve. The two-gas process will operate on a complex processing surface. Results from computer simulations as well as experiments will be reported in order to explain the physical background to the observed complex behavior.