Production of Smooth Deposit Thickness Profiles and Homogeneous Alloys from Parallel Strip Sources

Abstract

Deposit thickness profiles obtained from a set of parallel strip sources were investigated to determine the optimum conditions of strip spacing relative to source‐substrate distance needed for the production of smooth thickness profiles. The study was motivated by a desire to produce homogeneous alloy deposits by sputtering from a target consisting of sets of interspersed parallel strips of the alloying elements. Calculated and experimental profiles revealed a rapid decrease in deposit thickness variation with decreased distance between the strips in the source and with increased distance from strip source to substrate. The percentage composition variation (V_A′) of a binary alloy deposit produced from interspersed strips was found to depend on the composition for a given thickness variation according to the equation V_A′≃(1−C_A)2t′. C_A is the average concentration of A in the deposit, and t′ is the percentage variation in the thickness of a deposit from a single set of parallel strip sources. Thus the variation in concentration is always less than twice the thickness variation because 1−C_A <1 for all alloys. It was found that a strip spacing to source‐substrate distance ratio of 0.5 or less would give sufficient uniformity of thickness for homogeneous alloys to be made from an easily constructed target‐substrate arrangement. The maximum composition variation for a source‐substrate distance ratio of 0.5 was calculated to be 0.012%.