The effect of the base pressure on the incorporation of oxygen into reactively magnetron-sputtered metal-nitride films has been investigated. A UHV sputtering system with a base pressure of less than 10(-6) Pa was used to examine the relationship between a deliberately introduced background pressure of oxygen and a measured oxygen content in the sputter-deposited TiN films. The results showed that with an oxygen partial pressure of 10(-4) Pa, the deposited TiN was found to include 10-20 at.% of oxygen when measured by the technique of X-ray photoelectron spectroscopy (XPS). When no oxygen was admitted into the system, no trace of oxygen could be detected in the deposited TiN films. The incorporation mechanism is discussed in terms of the coverage-dependent sticking probabilities of O(2) and N(2) on a Ti metal surface. (C) 2008 Published by Elsevier Ltd.