New possibilities of mechanical surface characterization with spherical indenters by comparison of experimental and theoretical results

The topic of this work is a novel approach for the determination of mechani cal properties of thin films on a substrate based on the theoretical modeli ng of spherical indentation into a film substrate system together with its adequate experimental realization. First, some results of a novel analytica l solution were compared to results of finite element (FE) calculations and to flat punch models. Then, SiO2 layers on silicon were investigated as an example. The measured load-displacement curves for spherical indentations were compared to curves simulated by means of the theoretical model. When u sing appropriate elastic parameters of the film and substrate a complete ag reement can be achieved. Finally, the onset of plastic deformation within S iO2 was determined by a multiple partial unloading procedure with a 4 mu m sphere. It was found that the load necessary to start plastic deformation i n a 538 nm SiO2/Si system is only 60% of the value that was obtained for a 2007 nm SiO2 layer, although the plastic hardness is the same. Using the th eoretical model it can be shown that the plastic deformation starts within the him and that - despite the different critical loads measured - the crit ical von Mises stress is the same. (C) 1999 Elsevier Science S.A. All right s reserved.