A coating thickness uniformity model for physical vapour deposition systems—further validity tests

Abstract

A model has been developed which considers the ratio between the coating thicknesses on sample faces towards and away from the vapour source. The model demonstrates that this ratio is an explicit hyperbolic cotangent function of ( s 2l ), where s is the source-to-substrate distance and l is a mean free path related to the distance which a vapour particle will travel before becoming thermalized. Previous work has shown the model to be valid under gas evaporation and simple diode ion-plating conditions, though investigations were generally restricted to deposition by electron beam (EB) evaporation. In this work we demonstrate the validity of the model for TiN coatings produced by reactive ion plating with discharge enhancement and for metallic coatings deposited by resistive evaporation, magnetron sputtering and cathodic arc evaporation. The results indicate how thickness uniformity can be influenced by the type of source used and we suggest that this is primarily due to the initial energy of the vapour flux and the effects of source geometry. In particular, changes in the vapour emission characteristics of EB bun sources are shown to have a significant effect.