Topography effects on high-NA EUV

While optical EUV lithography with 0.33NA can now routinely print 30nm pitch patterns and EUV lithography with 0.55NA can print 20nm pitch patterns, variations in the Critical Dimensions (CDs) caused by photon and resist stochastics require innovations in the design of the entire photoresist stack for all resist types. Additionally, the reduction in Depth-of-Focus (DoF) from 0.33NA to 0.55NA EUV lithography is stated in the 2nd Rayleigh equation as proportional to the imaging wavelength and the numerical aperture squared of the projection lens. It is important to note that such quantification should also include the role incoming topography has on further reducing the DoF for high NA layers. In this presentation, we created variable programmed topography at both micron and millimeter size length scale. These wafers with known variable topography were then used to develop the methodology for quantifying the change in the DoF of an overlaid patterned pitch 28 Line/Space layer. These wafers offer a first look at the change in the DoF both after development, as well as, after the pattern was etched into the stack.