Comparison of via-fabrication techniques for through-wafer electrical interconnect applications

Several techniques for fabrication of through-wafer vias in silicon have been compared in terms of achievable via diameter, shape and geometry and their influence on mechanical strength of silicon dies/wafers. The assessed techniques are: powder blasting, laser melt cutting, laser ablation, and deep reactive ion etching. The resolution of each method and influence on geometry was evaluated by fabrication of through-wafer holes and slots in 240 μm-thick silicon wafers. The mechanical strength is measured using ring-on-ring (RoR) and four-point bending methods. Additional stress-relief post-processing was applied to improve mechanical strength. Comparing the performance of bipolar transistors, before and after fabrication of laser ablated vias, indicates that the electrically affected zone does not exceed 10-20 μm around the via edge.