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 degrees 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 mu m at 400 degrees C. The dark spots that exist in the in-situ SEM annealing stage at 310 degrees 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 degrees 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. (C) 2017 The Electrochemical Society. All rights reserved.