Structure and properties of TiN coatings

Abstract

During the last few years there has been increasing interest in TiN thin films deposited by various physical vapour deposition methods. Since the films are grown by various techniques and using different process parameters the variation in the actual growth conditions is considerable. This gives rise to a large scatter in the microstructures and hence also in the properties of the films. In this paper reported microstructures of thin films of TiN are reviewed and are also correlated to physical properties such as the electrical resistivity and the hardness of the films. For example, one important microstructural feature is voids located in the grain boundaries. Such voids result in low hardness values and high resistivities. The origin of the various microstructures that are obtained is also discussed in terms of the growth conditions used. The voids mentioned above can, for example, occur because of deviation from stoichiometry, too low a substrate temperature or impurities in the films, but also because of substrate-induced growth effects specially if multiphase substrates such as high speed steels are used. In addition to single-phase TiN films, two-phase or multiphase films containing the phase Ti2N are also discussed. In many cases such films show extremely high film hardnesses. However, it is shown that the high hardnesses are mainly caused by the specific microstructures that can develop rather than by the Ti2N phase itself.