It is crucial for Cu TSV to be reliable at the back-end-of-line (BEOL) procedure particularly at high temperature process step. Any unreliable Cu TSV may cause residual from thermal stress due to the mismatch of the coefficient of thermal expansion. Therefore, it is important to investigate on the behavior of Cu pumping whether it will affect the electrical performance in BEOL integration. Two sets of Cu pumping with pitch 30 μm and 40 μm were annealed to measure their resistance at the temperature lower than 250°C. Based on the results, the narrow pitch of 30μm can be applied in post via last process below 250°C for BEOL procedure in 3D integration.