Summary

“Nanoreliability” and “Nano Fracture Mechanics” issues have been put on the agenda for two main reasons. Firstly future nanotechnology products, i.e. products including nanoscopic components or nanoscale modified materials, have to withstand thermo-mechanical environmental and functional loading during life time. Secondly, sufficient mechanical reliability of non nanoscale, but microscale components can be reached only by better understanding and modifying of nanoscale driven processes of material deterioration, which finally lead to device failure. Because of the scaling, traditional methods for testing and simulative reliability assessment have to be refined or replaced by new, appropriate tools.

The authors give a brief overview about some new approaches with respect to nanomechanical reliability assessment for electronics, sensors, MEMS/NEMS and their packaging. Performing finite element analysis (FEA) questions arrive on the feasibility to extend continuum mechanics simulation to the submicron and nanoscale structures. Homogenization methods and inclusion of material property gradients in the mechanical modeling are on answer to the problem. Furthermore, the determination of material properties as FEA input data is a crucial issue. Because of scaling effects, material properties have to be measured on the components themselves or on micro/nano structures manufactured in a similar way (e.g. on thin wafer films instead of a micromachined die). In sole cases simulation of mechanical behavior is to be carried out by molecular modeling methods.

A principal new experimental method for nanomechanical testing developed by the authors is referred to in more detail. The method bases on local digital image correlation (DIC) applied to high resolution micrographs captured from stressed objects in SEM, FIB or AFM equipment. As a result deformation fields with nanoscopic resolution are determined. The method can be used to analyze material behavior on a nanoscale and to generate respective input data for further numerical mechanical analysis. One application is the evaluation of cracks or defects by the deformation field at the very near crack tip field. Stress intensity factors and fracture toughness values for very small cracks could be obtained, too.

Residual and mechanically/thermally induced stresses are a severe cause for nano component failures. The mentioned DIC technique allows to measure very locally inherent materials and component stresses by stress release due to ion milling in a FIB equipment. Stress release leads to deformation fields of nanoscopic extension, which can be measured by DIC and inversely allows to compute stresses and related quantities at the place of ion milling. The authors present measurements performed on thin Si3N4 membranes as used in different kinds of MEMS and/or sensors applications. It is shown that local residual stresses can be measured very accurately.

References

1. Michel, B., Keller, J., NanoDAC – a new technique for micro- and nanomechanical reliability analysis of lead-free solder interconnects, Int. Conf. on Lead-free Soldering, Toronto, Canada, 24-26 May 2005.
2. Michel, B., Nanoreliability – Combined Simulation and Experiment, European Conf. on Mechanical and Multiphysics Simulation and Experiments in Microelectronics and Microsystems, inv. plenary lecture, Berlin, 18-20 April 2005.
3. Michel, B., Microreliability, Nanoreliability – Reliability Issues for MEMS, in: H. Knobloch and Y. Kaminorz (eds.), Micro Nano Integration, Springer, Heidelberg, Berlin, New York, 2003, 269-275.