Coating thickness fall-off with source to substrate distance in PVD processes

The way in which coating thickness varies as a function of source to substrate distance in physical vapour deposition (PVD) is obviously an important factor when designing or optimising PVD plant. Studies made with electron beam evaporation-based PVD systems are reported, where coatings can be deposited in the presence of a low pressure inert gas (i.e. gas evaporation) or with plasma assistance (ion plating). We demonstrate that the coating thickness on substrate surfaces positioned directly above facing the vapour source follows an inverse power function of source to substrate distance; the work expands on preliminary findings previously reported. The influence of inert gas pressure, substrate biasing, evaporation rate, evaporant material and condition of the source are discussed, with reference to vapour emission-transportation phenomena and ionisation conditions.