Interfacial oxide growth and filling-up behaviour of the micro-gap in silicon fusion bonding processes

In the silicon fusion bonding (SFB) process, the influence of post-annealing atmospheres on the micro-gap existing at the Si-Si bonding interface was investigated with the observation of ultrasonic images, angle lap-stained junctions and cross section SEM morphologies. Additionally, the bonding strength and the electrical properties of diodes were compared after annealing processes at 100/dg fo 10 s to 10 h in wet O₂, dry O₂ and N₂ atmospheres. Our results show that a significant saving of annealing time necessary to eliminate the non-contact micro-gap region having a width of ≤ 0.1 μm can be obtained if the hydrogenbonded wafer pair is pre-stabilized and post-annealed in wet O₂ (95°C water bubbling) rather than in a dry O₂ or N₂ atmosphere. Based on the above result, we propose that the stabilizing and annealing step in highlt oxidizing atmosphere has an important role in the oxide filling-up phenomenon between wafer and wafer gap, in addition to the well-known mechanism of wafer plastic deformation at high temperature followed by solid-state diffusion of Si and O atoms.