Deep-UV lithography using 248 and 193-nm light will be the imaging technology of choice for the manufacturing of advanced memory and logic devices for the next decade. The extension of 248nm technology to 0.150 micrometers and beyond has been accelerated with techniques, such as, Off Axis Illuminaton (OAI), Optical Proximity Correction (OPC) and Phase Shift Masks (PSM). Rapid development of such enhancements could provide a viable solution for the 0.13micrometers node. This continuous reduction of k1 to near 1/2 wavelength has intensified and issues related to Mask Error Factor (MEEF) have become a concern. Mask Error Factor, a phenomenon first discussed by Maurer et al., is defined as the CD Error at wafer level divided by the CD error at the reticle level multiplied by the lens magnification. The authors have been focusing on several key issues related to this high MEEF at various duty cycles. First, is the impact of MEEF across the entire exposure field for sub-0.15 micrometers imaging with KrF imaging. Secondly, the authors will discuss the coorelation between MEEF through pitch vs critical dimension with respect to partial coherence for bright and dark field imaging. Finally, the process window must be 'corrected' to account for across plate CD variation once the Mask Error Factor for a given critical dimension, pitch, reticle type, illumination condition and photoresist are determined. The authors will address the use of this new metric that can also assist in the specification of reticle CD's. Furthermore, we will address the various imaging solutions, briefly discussing how improvements in photoresist technology can assist and their impact on darkfield and lightfield imaging.