A COATING THICKNESS UNIFORMITY MODEL FOR PHYSICAL VAPOR-DEPOSITION SYSTEMS - OVERVIEW

A coating thickness uniformity model for physical vapour deposition (PVD) in low-pressure gas, is described. The model is derived from consideration of the proportions of non-thermalised and thermalised vapour fluxes arriving at the front and back surfaces of thin flat substrates. Here, front and back refer to surfaces facing towards and away from the vapour source respectively, and it is shown that R=coth(s/21), where R is the front-to-back coating thickness ratio, s is the source-to-substrate distance, and I is associated with the mean free path for vapour thermalisation. Experimental work, which has been performed to test the validity of the model under various deposition conditions, is reviewed and updated. The results demonstrate that the model can be applied to PVD by thermal evaporation (using resistive or electron beam heating), and to plasma-based systems which employ magnetron sputtering or cathodic are evaporation sources, or which operate under ion plating conditions. Data from the model can be used for predictive purposes or to provide information on phenomena such as vapour particle thermalisation and virtual source effects.