Distortion-free stacked CMOS image sensor with 8.6-μm pitch micro-bump interconnections

A distortion-free stacked CMOS image sensor with high density micro-bump interconnections was developed. This sensor consists of a photodiode substrate and storage node substrate and was fabricated with a wafer-on-wafer stacking technology. More than 90,000 micro-bump interconnections at a pitch of 8.6 μm per chip convey the signals. A distortion-free image was successfully obtained with the developed sensor. A parasitic light sensitivity of -160 dB was achieved by means of a light shield that uses the three-dimensional structure. It was confirmed that the stacking process caused no harm to the CMOS image sensor characteristics. A connection yield of over 99.9 % and reliable connections for practical applications were achieved.