Effects of Substrate Preparation on the Stress of Nb Thin Films

It is well known that intrinsic stress plays an important role in the superconducting material properties of niobium (Nb) thin films and in the resulting electrical characteristics of superconducting-insulating-superconducting (SIS) junctions made from these films. The role of sputtering pressure, gun operating parameters and substrate fixturing on Nb film stress has been investigated by a number of researchers. In this paper we discuss the role of wafer preparation on the stress of Nb thin films. We have found that ex-situ substrate cleaning and baking as well as in-situ cleaning and deposition sequencing have a significant effect on the resulting measured film stress. Index Terms —Ionmill, Nb, sputter, stress.