Investigation of film thickness uniformity on substrates located close to the source axis.

The thickness uniformity that can be obtained near the source axis in evaporation systems having long source-to-substrate distances (~50 cm) and small area sources has been investigated using multiplebeam interferometry. Silver films were evaporated from resistance-heated dimple boats in standard vacuum and ultrahigh vacuum onto stationary and rotating substrates 3.86 cm in diameter symmetrically placed about the source axis. Thickness variations in the films were measured across substrate diameters, and the average film thicknesses were compared. Similar data were also obtained for aluminum, aluminum oxide, and germanium films. Random thickness variations have been found on all the films, which are much larger than the uniform thickness gradations predicted by the geometric theory. These variations can be minimized but not eliminated by planetary rotation of the substrates.