Researching the silicon direct wafer bonding with interfacial SiO₂ layer^*

A silicon wafer direct bonding with a thin SiO₂ layer at the interface was investigated. An atomic force microscope (AFM) was employed to characterize the surface roughness and a shearing test was carried out to evaluate the bonding strength. Experiments were performed to analyze the relations of surface roughness and bonding strength with the thickness of SiO₂ which was grown by thermal oxidation and plasma enhanced chemical vapor deposition (PECVD) respectively. The bonding strength can reach up to 18 MPa for thermal oxidation and 8 MPa for PECVD after a 2-h 400 °C annealing. Results indicate that the bonding strength is negatively correlated to the thickness of SiO₂ at the interface, which is important in designing the MEMS-based devices and other devices built with wafer direct bonding.