High-Aspect-Ratio TSV Process With Thermomigration Refilling of Au–Si Eutectic Alloy

Abstract

In this study, a novel high-aspect-ratio through-silicon-via (TSV) with thermomigration refilling of Au-Si eutectic alloy is presented, wherein a via-first polysilicon TSV is first fabricated to obtain small via size and high-aspect-ratio structures with high-quality insulating layers. Following the post-complementary metal-oxide-semiconductor thermomigration of Au, the polysilicon TSV is replaced by Au-Si eutectic alloy to significantly decrease the serial resistivity. The high-quality and highly conformal insulating layer is formed by the thermal oxidation to improve the electrical properties of the TSV. Because the temperature of thermomigration process is 400 °C, which is higher than the Au-Si eutectic point (>363 ± 3 °C), it takes approximately 1 h to replace the polysilicon TSV of diameter 3.31 μm and aspect ratio larger than 18:1 by Au-Si eutectic alloy. Using this method, the serial resistivity of a single via-first polysilicon TSV is decreased drastically from approximately 4 × 10 ^-3 to 5.91 × 10 ^-6 Q·cm and the leakage current is much less than 2.36 pA. The resistivity of TSVs, distributed from 5.91 × 10 ^-6 to 7.34×10 ^-6 Q·cm, did not change after high-temperature storage test (HTST) and temperature cycling test (HCT). The leakage current between two adjacent TSVs is considerably lesser than 3.30 pA after HTST and HCT. The electromigration result shows that TSVs can be used up to 175 mA at 150 °C for 26 h safely.