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

A coating thickness uniformity model for physical vapour deposition (P VD) in low-pressure gas, is described. The model is derived from consi deration 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), whe re 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 va pour thermalisation. Experimental work, which has been performed to te st the validity of the model under various deposition conditions, is r eviewed and updated. The results demonstrate that the model can be app lied to PVD by thermal evaporation (using resistive or electron beam h eating), and to plasma-based systems which employ magnetron sputtering or cathodic are evaporation sources, or which operate under ion plati ng conditions. Data from the model can be used for predictive purposes or to provide information on phenomena such as vapour particle therma lisation and virtual source effects.