The Deposition of Niobium Thin Films by dc Diode and Substrate Bias Sputtering

Abstract

The room-temperature properties of sputtered niobium films can be made to approach those of the bulk metal either by deposition after extensive presputtering on substrates heated to ∼700°C, or by the application of a small negative bias to unheated substrates. The effectiveness of the former method is associated with the crystallization of the films in the bcc form of bulk niobium and the absence of the high-resistivity tetragonal form found in sputtered tantalum films (β-Ta). High substrate temperature is a critical factor in both the purity and degree of orientation of the film. Bias sputtering reduces the impurity content of the films both as a result of low-energy ion bombardment and considerable enhancement of the deposition rate with increasing negative bias.