Imaging contrast improvement for 160nm line features using sub resolution assist features with binary, 6% ternary attenuated phase shift mask with process tuned resist

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 improvement 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 resist. A low contrast resist process tuned for isolated lines patterned on an ASML/300 stepper (0.57NA with 0.6/0.8 annular and 0.75 sigma conventional illumination). And a high contrast resist tuned for dense lines patterned on a SVGL Micrascan 3 (0.6 NA with 0.8 sigma conventional, and 0.6/0.8 annular). Reported results are process improvements across pitch, developing process with scattering bars and not printing of side lobes. Simulation results with low and high contrast resist, Binary vs. 6% 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 features 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% larger (under exposed) region. Thus far, at sizing, the experimental results matched prediction; the low contrast resist 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 for the two cases (high vs, low contrast resist with binary mask) examined and make it possible to explore better solutions. For instance, under a fixed set of develop and FEB conditions, analysis of infinite contrast resists did not move the danger of sub resolution features printing much above the +10% CD sizing. However using a 6% ternary attPSM moved the printing limit to +20% of target CD size. The results of process window improvements with an attenuated PSM (6%) 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.