Impact of mask absorber properties on printability in EUV lithography

The impact of mask absorber properties on printability in EUV lithography was studied from the viewpoint of lithographic requirements which can give high imaging contrast and reduce the shadowing effect. By using the refractive indices of the elements and compounds employed as absorbers, their reflectivity on multilayer blanks, aerial image on wafer plane and printed CDs depending on absorber thicknesses were simulated. This predicted an optimum Ta-based absorber's thickness. Several patterned masks of LR-TaBN absorber with various thicknesses were prepared. Each patterned mask was exposed with the newly developed small-field-exposure-tool (SFET). It was demonstrated that optimized absorber thickness can, without loss of printability performance, reduce CD difference between horizontal and vertical pattern that has been known to be caused by shadowing effect.