Impact of Tungsten Contamination on the Sensing Margin of a CMOS-image-sensor Cell

Abstract

We investigated the impact of tungsten contamination on minority-carrier recombination lifetime, the photodiode dark/photo current and sensitivity of a pinned photodiode, and the sensing margin of a CMOS image sensor (CIS) cell. After an intentional tungsten contamination and followed by driving at 800 °C for 30 min, tungsten contaminant were located from the surface to p- and n-type regions of a photodiode. The tungsten contamination degraded minority-carrier recombination life-time and the dark current and sensitivity of a pinned photodiode; i.e., there was a good correlation between the minority recombination lifetime and the sensitivity of a photodiode. As a result, tungsten contamination directly degraded the sensing margin of a CIS cell photodiode; i.e., it decreased with increasing tungsten contaminant concentration.