White spots reduction by ultimate proximity metal gettering at carbon complexes formed underneath contact area in CMOS image sensors

White spots reduction by the ultimate proximity metal-gettering technology for CMOS image sensors is demonstrated. Metal contaminants in photodiodes (PDs) causing white spots can be captured by carbon complexes, as metal gettering sites, formed underneath contact areas in CMOS image sensors without any layout area penalty. High density carbon complexes take advantage of the ultimate proximity to PDs to trap not only Fe and Ni as fast diffusion metal but also W as slow diffusion metal. The optimization of the gettering site layout resulted in neither the increase of mean dark current nor the degradation of transistor performances in the pixel area. Furthermore, the optimization of the C implantation and post treatment (PT) effectively reduced white spots by about one order. This ultimate proximity metal gettering is a promising technology for high image-quality CMOS image-sensors.