Evaluating the Process Performances of Binary, PSM and OMOG Masks in Advanced Technology Node

As the critical dimension of mask shrinks, revolutionary mask making methods have been invented to improve the performance of existing wafer steppers, like attenuated phase shifting mask (PSM) and thin Opaque MoSi on Glass (OMOG) mask. Those masks have their own pros and cons. We have done a pseudo finite difference time domain (pFDTD)_simulation study the lithography process performances of three types of masks in the advanced technology node. Both symmetric and asymmetric patterns are simulated. We found that all three masks exhibit similar process window in symmetric test patterns while dramatically differ in the asymmetric pattern. For this specific asymmetric pattern, PSM and OMOG masks show larger depth of focus (DOF) than Binary mask. However, the Mask Error Enhancement Factor (MEEF) and Normalized image log-slope (NILS) are terribly not lithography-friendly using PSM.