Tantalum (Ta) and tantalum nitride thin films are highly important as diffusion barriers and adhesion layers in microelectronics and hard coatings for cutting tools. In this study, the effect of the underlying substrate on the phase formation of Ta and the influence of a changing N-2/Ar flow ratio on hardness, phase and composition of reactively formed tantalum nitride have been investigated. Ta is DC sputter deposited and forms beta-Ta on amorphous diamond-like carbon and on the amorphous natural oxide layers of Ti and Si(100) while a 15 nm TaN seed layer results in the formation of alpha-Ta. The chemical composition of the topmost layers of a substrate influences the formation of a-and alpha-Ta. With increasing N-2/Ar flow ratios a transition from amorphous Ta-rich tantalum nitride over face-centered cubic tantalum nitride (fcc-TaN) to (100) textured fcc-TaN at flow ratios above 45% is observed. The hardness of the tantalum nitride thin film reaches a maximum at a flow ratio of 45%, followed by a decrease in hardness for higher N-2/Ar flow ratios. The increase in hardness is associated with a decrease in grain size and shows a stronger correlation for a Meyers and Ashworth relationship than for a Hall-Petch relationship. (C) 2013 Elsevier B.V. All rights reserved.