Target poisoning during reactive magnetron sputtering: Part II: the influence of chemisorption and gettering

As generally accepted gettering of the reactive gas by the sputtered target material plays an important role for most reactive gas/target combinations. The influence of the gettering process and the chemisorption of reactive gas on the target have been modelled by Berg et al. (J. Vac. Sci. Technol. A 5(2) (1987) 202–207). However, in this model the effect of ion implantation was not included. Therefore, a model is proposed which takes ion implantation into account. The model is used to understand the target voltage behaviour during reactive sputtering of aluminium in an argon/oxygen mixture. At high pumping speed or low current, a target voltage increase is noticed before the critical point. This can be attributed to chemisorption of oxygen on the aluminium target. Chemisorption of oxygen reduces the erosion rate of the target, which enhances the poisoning of the aluminium target by reactive ion implantation. At low pumping speed or high current, i.e. when gettering dominates the reactive sputtering process, the effect of chemisorption on the target voltage is less pronounced due to the competition between reactive ion implantation and chemisorption.