A thermodynamic study of voiding phenomena in Cu–Cu thermo-compression wafer bonding

The influence of wafer bonding and post-bond annealing conditions on the (cavity) void size and distribution was investigated theoretically and verified experimentally. Based on Cu–Cu thermo-compression bonding at 175 °C for 30 min and subsequent annealing at 200 °C for 1, 6 and 24 h, respectively, in both cases the total void surface reduces with the duration of the heat treatment, showing good correlation between theory and experiment. However, the experimental results revealed that the average void size increases while voids number decreases, which is a deviation from the prediction of the physical model.