Impact on OPC treatment accuracy due to illumination pupil shape deviation for 110-nm target CD

We have investigated the impact due to subtle deviation form the actual illumination pupil shape to the intended setting. We show that the impact on resist CD prediction is a function of feature pitch and the predicted CD error can be significant. Consequently, the calculated MEEF through pitch can also be notably different for the non-uniform illumination aperture plane. In this study, we have investigated CD error and MEEF through pitch for 6 percent attenuated PSM and CPL mask using LithoCruiser. The annular non-ideal illumination aperture plane used in this investigation is generated externally and then imported into LithoCruiser. Here a small percentage of pixel deviation is introduced into the shape of the annular aperture to emulate the possible error that could occur in a scanner. Gaussian and SuperGaussian intensity distributions are used to compare with the ideal rectangular intensity profile. We found that the shape deviation of the distributions are used to compare with the ideal rectangular intensity profile. We found that the shape deviation of the aperture can cause a larger CD error compared to intensity variation at the aperture can cause a larger CD error compared to intensity variation at the aperture plane. It appears that the CD error and the MEEF are both larger for 6 percent attPSM than CPL mask. We have shown that by applying OPC, it is possible to reduce the predicted CD error caused by 'non-ideal' illumination aperture. The presented simulations are performed at NA equals 0.8 using KrF.