Control of Thickness and Composition Uniformity in Sputtered Superconducting Thin Films

Abstract

The control of composition and thickness uniformity over large areas is essential for most applications of high Tc oxide superconducting thin films. Considerable thickness and composition non-uniformities are commonly encountered in vacuum deposition on stationary substrates. The thickness uniformity in thin films, prepared by evaporation from point or small area sources, is achieved by choosing large distances from the source to the substrates and by planetary motion of the substrates. Evaporation from an off-center small area source on a rotating, parallel, planar substrate holder is equivalent to a ring source. Thickness uniformity can be obtained by adjusting the geometry of such a set-upl. In sputtered thin films, thickness uniformity is accomplished by using large area targets and appropriate geometry and sputtering conditions2. In most applications the cost of the large targets can become prohibitively high. Bunshah and Juntz3 have outlined design considerations for achieving thickness and composition uniformity in the production of massive deposits of alloys by evaporation from multiple ebeam sources. At present, existing commercial program can control only the thickness uniformity of deposited thin films4. They employ either calculated or measured thickness profiles4. The actual profiles can be significantly different from the theoretical profiles. Hence programs based on measured profiles give superior results4. This paper presents a new microcomputer program, based on measured composition and thickness profiles. The program has been developed to control the substrate rotation and scanning for achieving thickness as well as composition uniformities. The results can be used in an existing computer controlled, thin-film, sputter-deposition system.