Across-wafer nonuniformity of long throw sputter deposition

Abstract

Physical sputter deposition has been used at longer-than-normal cathode-to-sample distances for semi-directional deposition within high aspect ratio features. “Long throw” sputter deposition can be advantageous over other means of directional sputtering, such as collimated sputter deposition, because of the absence of collimators and related problems. However, due to the finite target size and sample geometry, an asymmetry is observed at the wafer edge with a thicker deposit on the inward-facing walls of trench and via structures compared with the outward-facing walls. We have used numerical simulation as well as metal sputter deposition experiments to characterize this asymmetry, which is typically 2–3:1 at the wafer edge. We also discuss how ionized sputter deposition would alter the deposition profile in the edge region.