Low-temperature wafer bonding using gold layers

The bonding possibility of gold layers was investigated at 25~200degC in wafer scale using a surface activated bonding (SAB) method. The interconnections of Si-to-Si and Si-to-PZT substrates were confirmed using different thickness of gold layers. The influence of surface roughness, vacuum condition, wafer temperature and rolling was studied. The bonded samples were observed using a scan acoustic microscope (SAM). The bonding energy was measured using razor blade test and the bonding strength was evaluated using tensile test. The microstructures on interfaces and the fractured surfaces after tensile test were observed using a scanning electron microscope (SEM) and an optical microscope. The interface of the bonded wafers was nearly void free. The gold layers were effective on metal diffusion and plastic deformation and therefore enlarge the bonded areas.