Reactive DC magnetron sputtering of ultrathin superconducting niobium nitride films

Abstract

DC reactive magnetron sputtering was used to deposit few-nanometer-thick films of niobium nitride for fabrication of superconducting devices. Over 1000 samples were deposited on a variety of substrates, under various chamber conditions. Sheet resistance, thickness and superconducting critical temperature were measured for a large number of samples. Film Tc was improved by changing the way the samples were heated during the deposition, by ex situ rapid thermal processing, and in some cases by the addition of an RF bias to the substrate holder during the sputter deposition. These improvements to the deposition of NbN have enabled the production of superconducting nanowire single photon detectors whose quantum efficiency saturates and was the starting point for work on the superconductor-insulator transition.