Effect of microstructure on hardness of submicrometre thin films and nanostructured devices

Abstract

The manufacture of mechanical devices such as microelectromechanical systems from thin films can lead to circumstances where the scale of the mechanical deformation induced by device operation is comparable with the scale of the microstructure of the materials from which they are made. A similar observation occurs when using indentation tests to assess the hardness of thin films, where the plastic zone dimensions may be comparable with the grain size. The present paper highlights the effect of grain size, shape and orientation on the indentation response of copper thin films used for semiconductor metallisation. The conditions under which continuum behaviour is observed are discussed, and the effect of crystallographic anisotropy on the choice of appropriate design data will be highlighted for copper coatings. The choice of test conditions such as control method and loading protocol required to generate reliable data is also discussed.