Rigorous electromagnetic simulation of mask magnification effects on the diffracted light for EUV binary mask

Extreme ultraviolet (EUV) lithography is expected to be the main candidate in the semiconductor manufacturing starting at 32 nm. As the CD is getting smaller, the aspect ratio of the patterns on the EUV mask is becoming larger. The shadowing effect will become much more significant when keeping the same 4× mask magnification. In this work, mask magnification effects on the diffracted light were explored with rigorous coupled-wave analysis (RCWA) for the sub-32 nm node. The simulated binary mask consists of 70-nm TaBN absorber and 2.5-nm Ru capping layer. The dependences of the diffraction efficiencies on mask pitches were calculated. The impacts of the absorber shadowing were observed from the near field distribution on the EUV mask. The aerial images formed by the diffracted light from the 4× and 8× masks were further evaluated.