Actual performance data analysis of overlay, focus, and dose control of an immersion scanner for double patterning

Double patterning requires extremely high accuracy in overlay and high uniformity in CD control. For the 32 nm half pitch, the CDU budget requires less than 2 nm overlay and less than 2 nm CD uniformity for the exposure tool. To meet these requirements, Nikon has developed the NSR-S620D. It includes a new encoder metrology system for precise stage position measurement. The encoder system provides better repeatability by using a short range optical path. For CD uniformity control, various factors such as focus control, stage control, and dose control affect the results. Focus uniformity is evaluated using the phase shift focus monitoring method. The function of "CDU Master" provides dose and focus correction across the exposure slit, along the scan direction, and across the wafer. Stage synchronization variability will also influence CD control. In this paper, we will show the actual results and analysis of the overall performance of S620D, including the exposed result of pitch splitting double patterning. S620D has sufficient performance for the 32 nm half pitch double patterning generation and shows potential for double patterning at the 22 nm half pitch node.