Thin films indentation size effects in microhardness measurements

Microhardness measurements of various thin films (e.g., Cu, Ta, Al, Ge), deposited by evaporation and magnetron sputtering techniques or Diamond-Like Carbon (DLC) films produced by plasma enhanced chemical vacuum deposition (PECVD), were carried out. Microhardness measuring equipment consists of a standard tester with flat field optics and a diamond stylus probe. Vickers-indentation measurements were performed with constant loads of: 4, 5, 10, 20, 30, 50, 100, and 200 g, in a continuous pressure. After indentation, the obtained stamps were examined by means of optical and scanning electron microscope techniques. It was found that the microhardness values of the above mentioned thin films, strongly dependent on the methodological principles of the measuring technique. Generally, there is a strong relation between the Indentation Size Effects (ISE), following an indentation, and the obtained microhardness, due to unsuitable mechanical load. As a result, various defects, e.g. stratifications, cracks, flaws, etc. are generated causing erroneous microhardness values. In this paper, a novel method for microhardness measurement of thin films is suggested. This method is based on an iteration approach, used for choosing of the correct load value, in order to avoid ISE. These measurements are of a non-destructive type, and the obtained microhardness values are not influenced by the mechanical load and the thickness of the film, but only by thin film properties. According to this method, every indentation must be accompanied with a structural control of the stamp quality.