Validation of a fast and accurate 3D mask model for SRAF printability analysis at 32nm node

The accuracy of a fast 3D thick mask model is evaluated for 6% AttPSM having sub-resolution assist features (SRAF). The main features and SRAFs are designed to print 40nm lines or spaces on wafer (k1~0.28) through pitch from 100nm to 500nm. The resulting optimum SRAF sizes vary from 10nm to 48nm depending on the main feature pitch, mask tone and illuminator shape. The model accuracy is evaluated on both main feature CDs and SRAF side lobe intensities by comparing with a rigorous model. The fast 3D model shows improvements in both areas over thin mask model, particularly in SRAF printability prediction.