Through-silicon via (TSV) filling by copper electrodeposition is the key technology used in 3D packaging. The thermal expansion coefficient (TEC) mismatch between the copper and silicon causes TSV pumping. Electrodeposited copper with a low TEC additive starts to contract at 120°C. The difference in expansion length between conventional copper and electrodeposited copper with the low TEC additive increases with annealing. This difference is about 47 μm at 400°C. The dark spots that exist in the in-situ SEM annealing stage at 310°C and their number increase with the increasing annealing temperature. Based on an FE-AES analysis, several 100-nm dark spots are carbon precipitates. From the X-ray diffraction, the lattice constant contracts by annealing at 420°C for 1 hour. The as-deposited copper has carbon inclusions in its lattice. This carbon diffuses out at high temperature, hence the lattice contract. This non-equilibrium to equilibrium transformation by annealing causes copper contraction during the annealing.

Electrodeposited copper is widely used in TSV filling due to its low resistivity. Unfortunately, its TEC of 17 × 10 −6 / • C causes thermal stress during annealing due to the mismatch with silicon TEC of 2 × 10 −6 / • C. In the upper region of the TSV, stress is released by the extrusion of copper when annealing. The results showed the extrusion height of copper TSV increases with the increase of temperature and the extrusion height is about 1.2 μm at 500 • C for conventional copper TSV. Also, at via the bottom corner, this stress due to the mismatch in TEC between copper and silicon is accumulated. That stress is the reason for the cracks at the bottom corner of the conventional copper TSV. With our low TEC copper, the extrusion height of copper decreases to only 0.3 μm and no cracks occur at the via bottom corner. In addition, the resistivity values of low TEC copper are always lower than that of conventional copper in as electrodeposited copper and after annealing at different temperatures. The results suggest that the low TEC copper is not only good at reducing thermal stress in TSV due to annealing but also decreasing the resistivity of copper TSV.

Previously, we have reported the low thermal expansion copper electrodeposited in solution containing 2-Mercapto-5benzimidazolesulfonic acid sodium salt dihydrate (2M5S). In this research, we investigated the electrochemical behavior 2M5S additive by CVS and LSV measurements. The 2M5S additive showed an inhibition effect during electrodeposition of copper, both in the absence and presence of Cl − . Using a combination of the 2M5S leveler with another SDDACC leveler and SPS accelerator, the thermal expansion of copper was reduced and the TSV was filled without defects. The SEM results showed that the copper pumping height of low TEC copper in PECVD SiO 2 TSV was only 0.5 μm. Meanwhile, the copper pumping height of reference conventional copper in PECVD SiO 2 TSV was about 2 μm. Furthermore, compared with thermal stress curve in Si around the conventional copper TSV, thermal stress curve in Si around the low TEC copper TSV was much lower and the KOZ also was reduced to about 1 μm.

A new leveler, sulfonated diallyl dimethyl ammonium bromide copolymer, exhibits the void-free through silicon via (TSV) bottomup filling with 5 minutes. The leveler has been characterized by CVS measurements with different concentrations at different RDE rotation speeds. The results show that SDDABC assisted the formation of a strong inhibition layer on copper surface when 16 ppm concentration has been added. Furthermore, bottom-up TSV filling with nearly no deposit on TSV sidewall is achieved with 16 ppm of SDDABC. Also, the filling time of 20 × 45 μm TSV is only 5 minutes.

Copper through-silicon via (TSV) is the key technology used in 3D packaging. During the fabrication process, copper TSV is exposed to a high temperature between 400°C and 600°C. For conventional copper TSV, we observed the cracks at the bottom of TSV after annealing at 500°C and a very high copper extrusion height, which destroys the overlying layers above the TSV. We also succeeded to prevent cracks at the bottom of the TSV and reduce the copper extrusion height by using the low thermal expansion coefficient (TEC) copper.