Influence of MEEF change on the mask shadowing effect in extreme ultraviolet lithography
The influence of mask error enhancement factor (MEEF) on the mask shadowing effect was investigated for extreme ultraviolet lithography. Imaging properties including horizontalvertical (HV) CD (critical dimension) bias and MEEF change through the pitch according to absorber thickness and process condition were studied using aerial image simulation. The mask structure used in this study consisted of tantalum nitride (TaN) absorber and 2nm ruthenium (Ru) capping layer on the 40 pair of MoSi multilayer. As the absorber thickness increased and the pattern pitch decreased, both HV CD bias and MEEF increased. At the illumination condition of 0.32 numerical aperture (NA), the HV CD bias variation through the pitch was negligible and slightly increased at 1:1 pitch, while it steeply increased at 1:1.2 and 1:1 pitch for NA of 0.25. The MEEF value was below 1.5 for all calculated absorber thicknesses when the pitch was from 1:1.2 to 1:5, whereas it was 3 with 64nm thick TaN for 1:1 pitch at vertical pattern. With the increment of absorber thickness, the MEEF difference between the horizontal and vertical pattern increased. We also calculated the HV overlapping process window (PW) according to TaN thickness using 22nm 1:1 line and space (L/S) pattern. As absorber thickness decreased, the overlapping zone in the EL of the focusexposure plots between the horizontal and vertical features increased. Enough image contrast and HV overlapping PW could be achieved by applying 38nm thick TaN.
meef shadowing effect absorber thickness hv overlapping pw euvl