THE EFFECT OF HEAVY-METAL CONTAMINATION ON DEFECTS IN CCD IMAGERS - CONTAMINATION MONITORING BY SURFACE PHOTOVOLTAGE

The role of heavy metal contamination on defect formation in CCD imagers and yield has been investigated. Dislocations, stacking faults, and oxygen precipitates form localized dark current generation sites. The current generation rate is a function of decoration of these defects by heavy metals. The SPV method was successfully applied to monitor in real time the heavy metal contamination level in the processing line and to identify sources of heavy metals. A good correlation between CCD imager performance and diffusion length/contamination level in silicon wafers, after completion of the fabrication sequence, was established. A certain threshold contamination level exists beyond which the probability of crystallographic defect decoration and formation of stacking faults increases dramatically. This level is different for the different defects and the different types of silicon wafers (FZ, MCZ, internally gettered CZ, and epi). © 1990, The Electrochemical Society, Inc. All rights reserved.