Stress and strain in polycrystalline thin films

Abstract

Polycrystalline thin films on substrates usually are in a “stressed” state. In the present paper, recent results on stress in polycrystalline films will be reviewed. For Cr and CrN films, it has been shown that the stress is not uniform over the thickness of the film. High tensile stresses are observed near the substrate-film interface. Lower tensile stresses are observed further away from the interface. Moreover, it has been shown that the tensile stress is generated at the grain boundaries. In the case for which the deposition of the film is accompanied by an ion bombardment, a compressive stress is generated. The tensile and compressive stresses in these films are independent and additive. This description, however, does not hold for all high melting point films, notably not for TiN. For c-BN films, the challenge is to form these metastable films and at the same time control the compressive stress within an acceptable range. Here some promising results have been obtained. For low melting point films, some new deposition experiments have been performed and new theories have been formulated. Here the situation is still less clear than with the high melting point films.