TSV-annealing: A thermo-mechanical assessment

Reported here is an experimental study and mechanical characterization of the annealing process of TSV structures. A major focus of this study is the extent of thermo-mechanical stresses, which form during this processing step. Results of bowing as well as copper protrusion measurements before and after the annealing process are presented as indicators for the stress development during the heating treatment. EBSD measurements show that this behavior is linked to a transformation of the copper grain structure. By these means, it is possible to reconstruct the development of stresses during the annealing process. From this hypothesis, the main boundary conditions for calculations can be derived. Using this approach, an FE model is presented, which calculates the thermo-mechanical stresses in the silicon substrate after annealing. Results from this simulation are validated using experimental results from μ-Raman spectroscopy (μRS). The present study therefore provides not only interesting insights into the mechanical phenomena within the TSV annealing. As a potentially valuable tool for the optimization of this process it also provides a method for calculating emerging stresses.