Abstract
In extreme ultraviolet lithography (EUVL), the application of off-axis illumination (OAI) leads to degradation in aerial image contrast, resulting in an unacceptably high mask error enhancement factor as the pattern pitch becomes smaller, even if an attenuated phase-shifting mask (AttPSM) of optimized attenuation is employed. We show that this is an intrinsic problem of OAI and cannot be remedied by adopting a thinner absorber, a smaller chief ray angle of incidence at the object side, or a projection optics box with a higher numerical aperture. Based on simulation results using the best conditions for OAI, we may conclude that single-patterning EUVL will probably end at a technology node with the minimum pitch of 22 nm, unless we can come up with other innovative ways for performing EUVL imaging or designing and formulating resists with blurs less than 5 nm at reasonable exposure dose.
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