The oblique incidence of the illumination system in EUV lithography combined with relative thick absorber layer of EUV mask introduces many unique distortions on the image transfer between mask and wafer, most of these distortions are non-linear thus makes the enhancement of resolution more difficult. This paper focus on analysing the impacts of the absorber layer thickness, multilayer thickness and the light source morphology on the image. And improve the EUV lithography and imaging quality by co-optimization of these three parameters. Besides, the intrinsic features and rules of the impacts of absorber thickness on the imaging properties is revealed. And the different behaviour of 1D dense pattern and isolation pattern during the co-optimization is analysed and elucidated. This study provides a potential new direction for resolution enhancement technology.
The oblique illumination in EUVL system combined with relative thick absorber layer of EUV mask introduces many new challenges for mask simulation, like asymmetric phase deformation, shadowing effects , secondary scattering. Besides, these effects result in the ineffectiveness of the Hopkins approach and require new method for mask diffraction computation. A 3D RCWA algorithm is implemented to perform rigorous computation of lights diffracted by the EUV masks. Several examples are designed, analyzed and presented in this paper. Furthermore, a fast version of the rigorous 3D algorithm is implemented by properly decomposing the 3D model into multiple simpler ones, thus the computational time is reduced.