Freeform and SMO

The effect of the source pixel intensity and polarization on imaging is analyzed. The pixilated source is an artifact of the discrete overlapping diffraction orders from the pupil stop of the illumination and from the pupil stop of the projection lens. The intensity of the discrete source pixels is sensitive to the image log slope (ILS) and the mask error enhancement factor (MEEF). There are trade-offs between minimizing the MEEF and maximizing the process window (PW). The pixilated source intensity allows one to better balance these trade-offs. Although the source intensity has a large effect on MEEF and PW, mixed polarization states of XY and transverse magnetic (TM) or of transverse electric (TE) and TM have limited value because of low k1 sampling of the projection lens and because effects of the wafer stack of thin-films dominate.