Wafer Bonding for Backside Illuminated Image Sensors

Backside illuminated image sensors combine small pixel area with high signal-to-noise ratio. Wafer bonding is a key enabling process step for manufacturing of backside illuminated image sensors. The fully CMOS processed image sensor wafer is bonded to a blank silicon carrier wafer and then back thinned to reveal the photodiodes. As a result the photodiodes are on top of the metal interconnects thereby eliminating any shading of the photosensitive area. Plasma activated fusion wafer bonding enables a room temperature wafer bonding with highest wafer-to-wafer alignment accuracy.