VUV/O 3 activated bonder for low-temperature direct bonding of Si-based materials

Direct bonding at low temperature is an attractive technology for joining dissimilar materials without large thermal stress. Vacuum ultraviolet (VUV) activation is an effective way for surface cleaning with less damage. Meanwhile, the obtained hydrophilic surfaces are also beneficial for the direct bonding. In this paper, we developed a VUV/O3 activated bonder for the direct bonding of Si-based materials at low temperature. High bonding strength for Si/glass and glass/glass bonded pairs was achieved after annealing at 200 oC. Atomic force microscopy (AFM) and water contact angle tester were conducted to analyze effects of VUV on surface roughness and wettability. Si-Si, Si-glass and glass-glass bonding interfaces were also observed by transmission electron microscopy (TEM). Defect-free and tight interfaces of Si/Si and Si/glass were obtained. However, the glass/glass bonding interface was full of microvoids which can be attributed to the less deformation of subsurfaces during the annealing process. Moreover, based on the surface and interface studies, bonding mechanisms for Si-based materials direct bonding via VUV activation was discussed.