Improved near-infrared sensitivity of a back-side illuminated image sensor with a metal reflector

Abstract

To improve the near-infrared sensitivity of an image sensor that has a conventional pixel structure, we made use of the metal wiring layer as a reflector in addition to the method of back-side illumination from the etched back surface of the sensor. We fabricated an image sensor that has a remaining silicon substrate thickness of 32 ± 4μm and evaluated the spectral sensitivity. For 830nm light, the sensitivity is about the same as for front-side illumination. For a wavelength of 970 nm, the sensitivity was 2.2 times as high as for front-side illumination. The image sensor with reflector has about 30% higher sensitivity than without the reflector. © IEICE 2009.