Target compound layer formation during reactive sputtering

It is well known that a compound layer may form at the target surface durin g reactive sputtering. However, the significance of this layer for the resp onse to a change in target conditions has so far not been carefully investi gated. The standard model for the reactive sputtering process [S. Berg et a l., J. Vac. Sci. Technol. A 5, 202 (1987)] does not allow for calculations of the compound thickness at the target surface. For simplicity it has been assumed that a single monolayer is responsible for the poisoning of the ta rget. However, experiments clearly indicate that the compound layer thickne ss may be significantly thicker than one monolayer. For several reasons it is important to be able to quantify the thickness of this layer. The format ion of the compound layer introduces memory effects into the system when th e processing conditions are changed. The sputter erosion time for the compo und layer depends on its thickness. We will present an extension of the bas ic reactive sputtering model that allows for the formation of an arbitrary thickness of the compound layer at the target surface. From this model it i s possible to examine the layer thickness dependence on the major processin g parameters (reactive gas supply, target current, etc.). Experimental stud ies of the transient target voltage and process pressure support the validi ty of the new model. (C) 1999 American Vacuum Society.