Limitations of resist-based characterization of EUV mask surface roughness

The feasibility of wafer-plane measurements of EUV mask surface roughness has been analyzed through stochastic resist simulations at various defocus conditions, for mask surface roughness values ranging between 50 pm and 500 pm rms. With partial coherence of 0.5, NA of 0.25, defocus of 100 nm and mask surface roughness of 50 pm rms, 1.3% of the total resist LER is contributed by the mask surface roughness induced aerial image phase roughness, while 39.1% of the total LER contribution comes from the absorbed photon image. 31.4% of the LER contribution is from the acid image and 27.9% is attributable to the quencher image at the end of the PEB reaction/diffusion processes. For surface roughness values of interest ranging between 50 pm and 150 pm rms, partial coherence of 0.5 and 100 nm defocus, the sensitivity of wafer plane aerial image LER to mask surface roughness is 9.5 nm/nm-rms, while the resist LER sensitivity is 2.9 nm/nm-rms. With hypothetical scaling of the resist parameters, the resist LER sensitivity to mask surface roughness increases to 6 nm/nm-rms.