Impact of mask topography and flare on process window of EUV lithography

Mask three-dimensional effect (M3D) and flare are the critical issues for lithography in advanced technology nodes, especially for the extreme ultraviolet lithography (EUVL). The M3D effect leads to a shrinkage of critical dimension (CD) and the flare causes the unwanted background exposure. To evaluate impact of these two effects on EUVL performances, the process windows (PWs) of various test patterns under nominal condition are firstly simulated. And then an optimal source is selected by comparing PW values. At last, M3D is introduced by considering absorber thickness, and the flare is introduced by adding a constant distribution across the exposure field. All simulations are implemented by employing SLitho, a commercial software from Synopsys. The test patterns in simulations include line space, tip2tip and tip2line patterns, and the gaps of tip2tip and tip2line are 40, 45 and 50nm. The results of simulation show that mask topography will reduce the DOFs of test patterns, and constant flare has almost no effect on the DOFs of many test patterns.