Proximity printing problems include mask areas
up to 200 microns x 200 microns and resist thicknesses up to 100 microns.
Moreover, usually partial coherent and broadband illumination is used. Rigorous
electromagnetic modeling is generally not suitable for the simulation of such
The Fraunhofer IISB in-house package Dr.Fresnel offers fast
and robust approximate methods for the simulation of mask proximity printing.
Comparisons with rigorous electromagnetic simulations have shown that the
approach meets the precision requirements of the modeling of mask proximity
Features of Dr.Fresnel are:
- Different scalar and vector near-field diffraction approximations
- Handling of 2D (lines/spaces) and 3D (polygons, ellipses) mask geometries
- Illumination with partial coherent broadband light
- Simulation of photoresist bleaching
- Mask optimization, process window analysis
The coupling of Dr.Fresnel with existing modules of Dr.LiTHO enables one to simulate the entire lithographic process including imaging, resist development and analysis of resist profiles.