Extensions of Boundary Layer Modeling of Photomask Topography Effects to Fast-CAD using Pattern Matching

摘要

In lithography for the 45nrn node and beyond, phase errors introduced through electromagnetic field (EMF) effects at photomask openings are significant sources of error in calculating on-wafer images. These edge effects create distortion in both real and imaginary field transmission, which leads to a tilt in the process window, and must be addressed in mask design to avoid loss of process latitude. This study presents a new formulation for pattern matching, which allows EMF effects to be included via boundary layer modeling to facilitate extremely fast assessment of EMF impact on imaging. Boundary layers are first used to model these edge effects, by adding additional transmission features to a layout to represent the error transmissions caused by edges. Pattern matching is then used to determine susceptibly to various pre-existing perturbations, in the presence of defocus. This process can be extremely fast and hotspot detection can be run on an entire chip in hours, compared to days for aerial imaging. Correlation between pattern matching and full aerial imaging can be as high as 0.97 for coherent imaging, and ≈ 0.75 for off-axis dipole illumination. This pattern matching framework is extremely flexible and can be used for fast assessment of any series of effects which can be described as a path difference in the pupil or as a transmission on the mask.