Design Rules for TSV Membranes

The thermo-mechanical robustness of the bottom edge of an open through silicon via (TSV) is investigated by simulating the most critical step during the TSV process flow. In this step, stress arises due to the different thermal expansion coefficients of the materials forming the TSV. By employing the finite element method, the potential energy release rate of a crack at the TSV edge is calculated. The potential energy release rate, which quantifies the crack driving force, reaches its maximum when the diameter of the metal layers is ~1.25× and ~1.5× of the TSV diameter. Furthermore, when the metal diameter is three times the TSV, the crack driving force is reduced by ~50% for both aluminum and copper layers forming the TSV membrane. It was found that the crack tends to propagate perpendicularly to the TSV conductive layer, consistently with experimental observations. Meanwhile, the influence of the TSV membrane on the TSV conductive layer is negligible at distances further than 10% of the TSV height. Results show also that the reduction of 25% of the metal amount of the thickest layer lowers the crack driving force by 40% in comparison to the continuous layer.