In the lithography process, if particles fall on the reticle, it will cause frame defocus, abnormal CD, bin fail ,and even low yield after exposure. This issue is more and more important in 90nm, 60nm, and 45nm processes.Nikon scanners have a pellicle particle detector (PPD) function that detects particles on the reticle surface before and after exposure. But how do you make sure the PPD function is working? And is the PPD sensitivity what you want? Until now, there has been no method to monitor this issue. Even Nikon and other mask shops could not provide a monitoring method.We offer an easy method that not only makes sure that the PPD function is working, but also monitors the sensitivity you want. The method is to make a monitor reticle by laying a hair on the reticle surface. If the position on the reticle with a hair triggers all alarms with C grade during PPD examination, we say this PPD function is ready because the width of the hair is about 75 um, and this is just the desired size.
Edge defocus can be reduced by several techniques on a Nikon S204 scanner. By using main software MCSV version 3.44 or above, as well as disable range, and scan direction. Edge defocus can be reduced but is not eliminated at 3 o'clock and 4 o'clock. Wafer flatness is studied to investigate the cause of this defocus. The chuck shape is the key to avoid to defocusing at these two positions. Modification of chuck shape can reduce yield loss.