Absorber height effects on SWA restrictions and shadow LER

In this study, we look at the 3D effects of absorber height on mask patterns for extreme-ultraviolet lithography (EUVL). Our first consideration is the extent to which sidewall angle (SWA) constrains the process window. Taking 10% of the total CD error budget as an acceptable tolerance, this amounted to 0.2nm of tolerable SWA-induced CD error. Results for the three nominal SWA cases show that the angle needs to be constrained to within about 0.5 degrees. Overall, the results above indicate that not only is there not much change in sensitivity on changing angle as a function of nominal angle, but also that the nominal angle has no large effect on process window size. Secondly, we consider how off-axis illumination shadowing of the mask absorber pattern effects line-edge-roughness (LER). Data suggests shadowing causes minimal differences between the left- and right-side LER for the 22nm half-pitch node under disk sigma = 0.5 illumination and 70nm absorber height. For 16nm half-pitch with crosspole sigma = 0.2, significant differences were seen.