Binary mask designs with single- and double-layer absorber stacks for extreme ultraviolet lithography and actinic inspection.

In this study, we propose binary mask (BIM) designs with single- and double-layer absorber stacks with high optical contrast at a wavelength of 13.5 nm for use in extreme ultraviolet lithography (EUVL) and actinic defect inspection. The optimum thickness of the absorber stack was estimated using a method based on the transfer matrix. In the double-layer designs, [Ag/SnTe] has a minimum thickness of ∼32  nm with almost 100% optical contrast compared to the TaN layer. In addition, a SnTe absorber layer was deposited using radio frequency magnetron sputtering. The optical constant of the SnTe layer at 13.5 nm wavelength was determined using the density of the layer, which was obtained from x-ray reflectivity measurements. The reflectance of the SnTe single-layer absorber stack was measured in the EUV region and compared with the simulated reflectance by using the calculated optical constants. The results show that the new BIM designs for EUVL and actinic inspection can be helpful in reducing the geometric shadow effect compared to the TaN absorber layer with a thickness of ∼70  nm.