Theoretical Analysis of Placement Error due to Absorber Pattern on Extreme Ultraviolet Lithography Mask

The pattern placement accuracy of an extreme ultraviolet lithography (EUVL) mask strongly depends on the stresses present in the multilayer and absorber films, since film stress causes both out-of-plane and in-plane distortions. To analyze this elastic deformation, we have developed simulation models that handle the interaction between the multilayer and absorber patterns. The models are based on two-dimensional theories of bending plates and plane stress. The numerical calculations employ the finite difference method and the successive over-relaxation method. To examine the validity and accuracy of the models, the deformation of EUVL masks using simple absorber patterns was calculated. For the calculations, we assumed a standard 6 inch quartz substrate with a reflective coating. The influence of the absorber pattern on placement error was investigated by simulations. and it was found that the absorber pattern is the main factor determining the pattern placement accuracy of an EUVL mask.