First project period 04/2006 - 09/2010

Description

Motivation

In addition to electronic, magnetic and optical properties, modern microelectronic technologies necessitate also the consideration of mechanical material parameters. This is first due to the fact that thermal misfit during processes at elevated temperatures as well as ion impact during ion implantation or thin film deposition can cause stresses in the electronic structures. Second, stresses or even mechanical damage can occur in mechanical technologies such as chemical mechanical polishing (CMP). This situation becomes even more complicated since complex materials (stacks of thin films having different properties, piezoelectric or other mechanically active materials, porous substances) get increasingly involved in microelectronic technologies. Therefore, we observe an increasing need for methods which enable one to determine mechanical parameters of those materials, in particular in form of thin films.

Our approach

During the past years, we have developed a novel approach for the determination of mechanical properties of solid materials and thin films which is based on mathematical modelling and high-accuracy nanoindentation. The theoretical method called "image load method" [G6-1] delivers the complete (three-dimensional) stress and strain which are formed in one or more thin film(s) and the underlying substrate under the influence of a spherical indenter. The results of the modelling are then compared with experimental data received by our high-performance nanoindenter UMIS 2000 [G6-2].

In this manner, different problems can be addressed:

• Measurement of the mechanical properties of thin films (Young´s modulus, yield strength, …),
• Identification of failure modes during the mechanical impact,
• Prediction of the behaviour of a given material or thin film/substrate compound under mechanical load,
• Design of optimum structures (e.g. stacks of thin films having different mechanical properties) which have best resistance against mechanical damage.

The approach is further developed both in its theoretical and experimental parts. For instance, inhomogeneous materials shall be included in the modelling. On the experimental side, a lateral force unit (LFU) was recently constructed which makes it possible to apply forces and to measure displacements in lateral direction with the same accuracy as in the usual (normal direction) nanoindentation.

Research in the graduate program

Within the graduate school we will concentrate on subjects which are important for microlectronics, for instance the characterisation of nanoporous materials with respect to their behaviour during CMP or basic investigations of mechanical properties of important microelec-tronic materials. The project is related to several other projects, such as project SJ3 of Prof. Yang Chunsheng and Prof. Zhu Jun (Shanghai Jiao Tong Univ.), and offers interesting possibilities for co-operation.

References