How curvilinear mask patterning will enhance the EUV process window: a study using rigorous wafer+mask dual simulation

It has been known for quite a long time that the best possible process window obtainable for 193i layers is by using ILT correction. These are typically converted (at a high runtime cost) to Manhattan masks both for reasons of mask manufacturability as well as computational efficiency; OPC M3D and rigorous simulators have, until very recently, been optimized for speed to run primarily with Manhattan shapes. We have recently shown that the insertion into production of multibeam mask writers makes writing curvilinear masks possible and that it is preferable to move toward a completely curvilinear paradigm, not only because the ILT is better, but because the mask manufactured will have reduced variability. Recent studies have shown a similar need for ILT-style corrections for EUV, mainly due to more complex thick mask effects. We extend the work using Monte-Carlo methods for mask variability to show that EUV layers more strongly require curvilinear approaches to mask writing in order to minimize the wafer PV bands due to both the tighter overall tolerances combined with the smaller wavelength (13.5 vs, 193) which transfers mask defects to wafer over smaller lengthscales.