Dark Current Spectroscopy of Transition Metals in CMOS Image Sensors

We have investigated the effects of deliberate heavy metals contamination on dark current and image defects in CMOS Image Sensors (CIS). Analysis of dark current in these imager dice has revealed different behaviors among most important 3d metals present in the process line. We have implanted directly in 3 Mega array pixels the following metals: Cr, V, Cu, Ni, Fe, Ti, Mo, W, Al and Zn. Analyzing the dark current "spectrum" as obtained for fixed integration periods of time by means of standard image-testing equipment, these impurities can be identified and detected with a sensitivity of ∼ 109 traps/cm3 or higher.