An investigation on the bonding surface energy versus time in low temperature wafer bonding

The procedure of low temperature silicon direct bonding (LTSDB) was investigated by bonding surface energy evolving over annealing time. Two kinds of pretreated approaches, O₂-plasma exposure and warm HN0₃ cleaning, were employed. The dynamic analysis of the bonding surface energy exhibits that the bonding procedure is divided into two phases: (1) rapid reaction between OH groups which leads to a quick enhancement of the bonding strength and (2) slowly further increase of bonding strength and improvement of the bonding uniformity thanks to the out-diffusion of interface voids. As a result of our analysis, we demonstrate that the plasma exposure cannot speed up the diffusion of the bonding byproducts but it increases OH groups on the bonded surfaces