Low Stress TSV Arrays for High-Density Interconnection

In three-dimensional (3D) stacking, the thermal stress of through-silicon via (TSV) has a significant influence on chip performance and reliability, and this problem is exacerbated in high-density TSV arrays. In this study, a novel hollow tungsten TSV (W–TSV) is presented and developed. The hollow structure provides space for the release of thermal stress. Simulation results showed that the hollow W-TSV structure can release 60.3% of thermal stress within the top 2 μm from the surface, and thermal stress can be decreased to less than 20 MPa in the radial area of 3 μm. The ultra-high-density (1600 TSV∙mm−2) TSV array with a size of 640 × 512, a pitch of 25 μm, and an aspect ratio of 20.3 was fabricated, and the test results demonstrated that the proposed TSV has excellent electrical and reliability performances. The average resistance of the TSV was 1.21 Ω. The leakage current was 643 pA and the breakdown voltage was greater than 100 V. The resistance change is less than 2% after 100 temperature cycles from −40 °C to 125 °C. Raman spectroscopy showed that the maximum stress on the wafer surface caused by the hollow W-TSV was 31.02 MPa, which means that there was no keep-out zone (KOZ) caused by the TSV array. These results indicate that this structure has great potential for applications in large-array photodetectors and 3D integrated circuits.