The trade-offs between thin and thick absorbers for EUV photomasks

Through a series of experiments and simulation studies, this paper will explore the lithographic impact of absorber thickness choice on an EUV photomask and highlight the trade-offs that exist between thick and thin absorbers. Fundamentally, thinning the absorber modifies the intensity and phase of light reflected from the absorber while simultaneously decreasing in the influence of feature edge topography. The decision to deploy a thinner absorber depends on which imaging effect has a smaller impact after practical mitigation and correction strategies are employed. These effects and the ability to correct for them are investigated by evaluating the absorber thickness impact on lithographic imaging performance, stray light effects, topography effects, and CD variability. Although various tradeoffs are described, it is generally concluded that thinning the absorber thickness below around 68 nm is not recommended for a TaBN/TaBO absorber stack.