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