Three-dimensional (3D) integration in semiconductor technology provides an alternative to keeping the current pace of miniaturization and enhances the capabilities of devices. The advantages can be summarized briefly as increased density, broader functionality, and higher performance per unit area, by making efficient use of the third dimension. However, three- dimensional integration opens up a new myriad of challenges in design and fabrication, which must be overcome in order to achieve large scale production.
There are several ways for implementing 3D integration, however, a great number of ideas involves an interconnection through silicon with a so-called Through Silicon Via (TSV) to bind the different device layers. One issue with TSVs is the mechanical stability regarding temperature changes in the structure, which is the typical scenario during processing with thermal cycles and also in normal device operations. This situation leads to high mechanical stress in the structure in connection with microstructural properties, which weaken the stability of the crystal (dislocations, grain boundaries), and can cause a fracture of the metal layers causing complete failure of a TSV.
Our work addresses this problem in TSV structures with the goal to identify potential failures and to acquire advanced insight towards mechanical reliability. For this purpose we use our tool, titled ViennaFEM, to perform 2D and 3D thermomechanical simulations. Our target structure is a state of the art open TSV technology. It uses wafer bonding and TSVs to directly integrate low output sensors with their associated analog amplification and signal processing circuitry.
With both simulations one can have different, but complementary, perspectives of the thermal-stress development in the structure. In the 2D case it is possible to observe how the stress develops around a sufficiently large structure and this helps to determine regions subjected to fatigue (silicon cracking and crack propagation). However in the 3D case, one can identify stress peaks in the whole structure and can also study the stress development on the surfaces of the structures.