The process window for a particular feature type can be improved by improving the aerial image or tuning the resist process. The aerial image can be improved by means of illumination or by means of mask enhancements. The illumination can be on-axis or off-axis tuned to feature type and mask. Mask enhancements being OPC and phase shifting. We illustrate process window improving by imaging enhancement with binary and attenuated mask, with conventional and annular off-axis illumination, with and without OPC. The OPC is Sub resolution assist features (SRF). The SRF structure modifies the aerial image of the primary feature and allows for reducing dense-iso bias across pitch leading to a larger overlapping DOF across multiple pitches (ODOF). Across pitch studies with a binary mask were carried out for semi-dense and isolated lines. This study was conducted with two types of resists. A low contrast resist process tuned for isolated line as patterned on an ASML/300 stepper. And a high contrast resist tuned for dense lines patterned on a SVGL Micrascan 3. Reported results are process improvements across pitch, developing process with scattering bars and not printing of side lobes. Simulation result with low and high contrast resist, Binary vs. 6 percent transmission masks will also be reported. PROLITH/3 simulation study conducted with a low contrast resist suggested that the isolated line resist would print the 80nm sub resolution feature at sizing. Further, that a high contrast resist would not print them at sizing but would print them when the 160nm lines were sized roughly 10 percent larger region. Thus far, at sizing, the experimental results matched prediction; the low contrast resists process printed the sub resolution features. As for process window matching across the chosen pitches, this process showed an imperfect solution with over exposure to eliminate the sub resolution patterns. Simulations appear to make good predictions of the two cases examined and make it possible to explore better solutions. For instance, under a fixed set of develop and PEB conditions, analysis of infinite contrast resist did not move the danger of sub resolution feature printing much above the +10 percent CD sizing. However, using a 6 percent ternary attPSM moved the printing limit to +20 percent of target Cd size. The result of process window improvements with an attenuated PSM using a high contrast resist will be discussed. In all the cases, sub resolution feature OPC for isolated lines was compared with no OPC feature.