Shinichi Okita

Wafer edge-shot algorithm for wafer scanners

The requirement for the higher resolution is pushing up the NA of the projection lens, so the DOF becomes shallower and the focus budget becomes tight. On the other hand, the requirement for the higher through-put is still demanding. To achieve the best throughput, the alternate scanning exposure sequence is inevitable to current wafer scanners. To realize the alternative scanning exposure, it is necessary to perform precise focusing control even at the partial shot on the wafer edge region. A wafer edge stepwise focusing algorithm is developed. This algorithm utilizes multi-points focusing sensors and dynamically switches the focusing sensors during alternating scan exposure of the partial site on the wafer edge region. Thus the amount of the defocus on the wafer edge region is minimized. The actual performance of the wafer edge stepwise focusing algorithm is discussed. This algorithm can be used with or without pitching motion control of the wafer leveling stage. The influence of the pitching motion control to the focusing performance is also discussed.

Method to predict CD variation caused by dynamic scanning focus errors

From 1970s IC industry has made dramatic progress due to the advancement of photo- lithography technology. At the beginning of the 21st century, photo- lithography technologies are still acting the major role of manufacturing the leading edge devices. The requirement for the higher resolution is pushing up the NA of the projection lens. As the result, DOF becomes shallower and the focus budget becomes tight. Close study for the focus error impact to CD variation becomes more and more important. A method to predict focus error induced CD variations resulting from dynamic wafer scanning has been developed. CD variations across an exposure image field are calculated from a CD lookup table that relates a CD value to the monitored focus error components.