1.5 Challenges

Due to the high power loss densities in the interconnect structures, the materials for these structures are required to have a high electrical conductivity to provide a good electrical connection between two or more contacts. The heat transfer of the connected contacts has to be reduced or enhanced according to design requirements of the particular device. This requested feature is only possible by changing the material or the material composition in the case of binary or ternary materials. Since the exchange of materials often requires several additional process steps, such design decisions have to be considered carefully due to additional cost. Hence, the achievable optimum device characteristics are often not realizable in terms of given economical constraints. Therefore, other solutions have to be found to implement them in the fabrication process. The first step for the implementation is the determination of the electrical and thermal behavior for non-optimal device structures. Together with given constraints of fabrication and the design requirements, the best solution can be obtained using adaptive optimization strategies provided from state-of-the-art optimization frameworks [40,41,42,43,44].

For changing electrical or economical requirements, a similar optimization procedure can be applied. Because some of those requirements demand alternative materials, various numbers of new materials have been introduced and are gaining more and more importance for future applications. However, their application is very expensive and can be expressed as the ``Cost of Ownership'' (COO), which includes the costs for fabrication and for additional precautions like the maximum allowed electrical or thermal burden.

Moreover, many new constraints appear if new materials are considered for optimization. For instance the use of Cu interconnect lines demands additional barrier layers to avoid the diffusion of Cu into the surrounding dielectrics [26]. Therefore, the application of alternative materials like Perovskites [28,29,45] or other high-$\kappa$ materials [45,22,27] or low-$\kappa$ materials [46,21] is very limited with respect to the benefits per costs ratio.