Critical Dimension Bimodality Both Within Wafer and Within Die

With reduction in the die sizes it is very critical to control the Critical Dimension (CD) within a very precise window. In this work we present a root cause analysis and solution to a bimodal CD distribution seen from the center of the wafer. The CD bimodality displays a sharp cliff at the center of the wafer, wherein one side of the wafer has the higher CD and the other side has lower CD with respect to the target value. The bimodality was also seen in the center column of the wafer.