INTERFACIAL OXIDE-GROWTH AND FILLING-UP BEHAVIOR 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 1100-degrees-C for 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 noncontact micro-gap region having a width of less-than-or-equal-to 0.1 mum can be obtained if the hydrogen-bonded wafer pair is pre-stabilized and post-annealed in wet O2 (95-degrees-C water bubbling) rather than in a dry O2 or N2 atmosphere. Based on the above results, we propose that the stabilizing and annealing step in highly 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.