Effect of nanoscale surface topography on low temperature direct wafer bonding process with UV activation

Low temperature direct wafer bonding is a promising technology for microelectromechanical systems (MEMS), sensors as well as silicon-on-insulator (SOI) materials. The bond quality is closely related to the wafer-bow, surface adhere energy and nanoscale surface topography. Effective surface activation and nanoscale surface topography evaluation is critical for the bonding process. For the low temperature silicon wafer direct bonding process with ultra violet (UV) light activation, surface nanoscale topography is modified and characterized before and after UV irradiation by the control of irradiation duration. The measured data of nanoscale topography by atomic force microscope (AFM) is evaluated by both bearing ratio and root-mean-square (RMS) approaches, from which the results are then correlated with the bond strength to understand the bonding process. It is shown that the bear ratio approach is more suitable for characterizing the surface roughness and optimizing the bonding process through the control of UV irradiation duration. The approach is also applicable to a wide variety of low temperature wafer bonding process where surface roughness is modified.