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A new method for simulating mask topography effects is described. A model comprising a set of functions is generated
based on the results of test patterns simulated using rigorous mask simulation. The functions are combined with the thin
mask diffraction pattern in order to create a modeled thick mask diffraction pattern. The mask diffraction pattern is
subsequently used in the lithosimTM simulation tool to generate the wafer image.
Results are described for 1D and 2D test structures. The 1D test structures is a line and space test pattern where the line
is set at 40nm width and the space is varied from 40nm to 1000nm. The illumination setting chosen was a TE polarized
dipole illumination with a pole distance of 0.9 and a pole radius of 0.01. First the accuracy of the simulator itself was
verified using thin mask calculation and comparing the data to another simulator. The intensity profiles are virtually
identical. The RMS of the difference between the two plots is 8E-05. Next the model is compared to the rigorous
calculation. The RMS of the difference between the two plots is 3E-03. The standard deviation of the CD difference
between the model and the rigorous calculation, calculated for 5 thresholds (0.1, 0.11, 0.12, 0.13, and 0.14) and for all
the structures, is 0.38nm. We also demonstrate that the mask model can be used with different optical settings by
showing an example of two additional defocus values with an identical RMS of 3E-03.
For the 2D test pattern made of a dense contact array, the mask fields are computed using rigorous calculation and
compared to the model. The difference between the fields is within the error of the rigorous calculation. The resulting
wafer images are almost identical. No re-scaling of the data was applied to either the mask fields or the wafer images.
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