Yield Impact of Backside Metal-Ion Contamination

Abstract

Small amounts (~1010 atms of Fe) of metal-ion contamination remains on local spots on the backside of the wafer. During a thermal process step, 30% of this contamination is transferred to the front side of the wafer where it causes in some specific cases substrate degradation. The source of the contamination is stainless-steel wafer pins that are used in wafer handling on for example litho tracks. This contamination is printed onto the backside wafer surface where two cleaning steps were not able to remove it. Figure 1. Wafer test: 3 clusters of devices failing due to the tripod signal.