Extended coupled-wave method for the light absorption of an EUV grid mask

The simulation optimization of EUV masks is one of the key technologies in lithography imaging simulation. The internal and external electromagnetic field distribution of a grating mask can be analyzed by using the rigorous coupled-wave analysis method. However, the result obtained by the coupled-wave method alone is a complex amplitude of light, which cannot directly provide the EUV light absorption distribution. Moreover, during the calculation, an energy non-conservation problem at the boundary of the absorption material should be generated by the standard algorithm. To overcome this problem, an extended potential transmittance method to analyze the mask absorption characteristics is introduced in this paper. The potential transmittance method can describe not only the absorptivity of the film system but also the absorptivity and power change of the diffraction lights with different orders of the grating. Assuming the potential transmittance of each diffraction light can be calculated independently, the total absorption of the grating layer can be determined by the sum of the power distribution of all the diffracted light.