A new method to calculate Mask Error Enhancement Function, or MEEF, from the intensity slope of the unperturbed
geometry and intensity offset of the perturbed mask is derived. In the limit of small perturbations, the intensity slope
technique is predicted to be the same as MEEF values calculated from the ratio of wafer to mask CD differences scaled
by the magnification. Full chip process window simulations were done to compare the accuracy of this new approach
for 45 to 90nm mask designs for line, space and contact features. The standard deviation was less than 0.11 and the
largest deviation was only 12% for over 5200 MEEF calculations. Below MEEF values of 20, the standard deviation
was less 0.065 and all simulations were within ±0.5.
A significant discovery in this work is the inverse relationship between image intensity slope rather than NILS or ILS at
the location of the printed feature edge and MEEF. Since the image slope decreases closer to the intensity extrema, high
MEEF regions are predicted to be those that print closest to the minimum and maximum intensities.