Nickel and Nickel Oxide Thin Films as Absorber Layer Materials of Extreme Ultraviolet Masks

Abstract

We propose nickel and nickel oxide as absorber materials in extreme ultraviolet (EUV) masks in order to mitigate the shadowing effect caused by a combination of absorber pattern height and oblique incidence angle (theta = 6 degrees) of the EUV light. Since Ni-based materials have high extinction coefficients (k = 0.0549-0.07359), they exhibit lower EUV reflectivity than tantalum compounds that are widely studied as absorber materials for EUV mask. Therefore, EUV mask with a thinner Ni based absorber shows image contrast and normalized image log slope (NILS) comparable to those of a mask with a thicker Ta-based absorber. Further, the Ni-based absorber reduces horizontalvertical critical dimension (H-V CD) bias and show improved focus margin because of smaller CD variation with focus shift. Therefore, the lithographic process window can be enlarged by adopting Ni-based absorber.