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.

Characterization and mitigation of 3D mask effects in extreme ultraviolet lithography

“…However, the resulting image cross section exhibits a pronounced shift of the horizontal line to the left. Image shifts, which depend only on the feature orientation, can be easily compensated by a shift of the mask in the z-direction, the so-called mask focus position, and/ or by simple rule-based OPC corrections of the mask layout [25]. The different shadowing of vertical and horizontal features causes a shift of the process windows along the threshold axis (see right of Figure 5).…”

Fast 3D thick mask model for full-chip EUVL simulations

“…Pattern shift is another such effect caused by mask-side non-telecentricity due to the oblique chief ray angle. It is important to note that the large global pattern shift observed in early EUV simulations using 3D mask models is largely a modeling artifact and can be corrected by transforming the mask diffraction coefficient to the optimum object plane before passing it to the subsequent simulation steps [4][5] . This process mimics the EUV scanner setup stage that moves the mask to the optimum mask focal plane.…”

“…One of such effects is asymmetric shadowing effect that presents itself as HV print bias between horizontal (H) and vertical (V) features. Although it can be modeled to a certain degree using the rule-based HV mask bias in the thin mask model 4 , the accuracy becomes inadequate as the feature size reduces 5 . Pattern shift is another such effect caused by mask-side non-telecentricity due to the oblique chief ray angle.…”

Stochastic resist patterning simulation using attenuated PSM for EUV lithography

“…However, a thick absorber structure is not desirable because it induces many practical problems in the mask manufacturing as well as many lithographic performances [7].…”