EUV simulation extension study for mask shadowing effect and its correction

Abstract

It is well known from 193nm simulation studies that accounting for the electromagnetic (EM) interaction between the incident light and the mask become more important as the mask geometry shrinks. In particular this transition occurs when the size of the mask pattern becomes comparable to the wavelength of light. Early simulation work in EUV lithography indicated rigorous EM calculations are required to predict the subtle effects associated with the mask absorber shadowing effect. These calculations generally show that non-normal mask incidence creates several problems, including HV-bias, slit position dependent bias, and slit position dependent pattern shift. These results are surprising because the mask sizes studied are much larger than the 13.5nm wavelength. If approximate methods could be used rather than the rigorous EM calculations then EUV simulations would be much faster and more accessible. In this study, rigorous EM simulation results are compared with a Kirchoff approximation. The results show that Kirchoff simulations can mimic the shadowing effect with a simple mask bias. It is also found that the pattern shift effect is an artifact caused by a misinterpretation of the rigorous simulation results. With proper biasing depending on the pattern orientation and field position, simple Kirchoff simulation can be used. Thus Any MBOPC tool currently available can handle EUV proximity correction with minor modifications.