CD error sensitivity to "sub-killer" defects at k1 near 0.4

Recent observations indicate that CD control for the 0.18 mu m process generation using KrF exposure (k(1) = 0.41) could be sensitive to borderline detectable defect sizes (200 to 300nm) on a 4X reticle. IL is of interest to determine if these "subkiller" defect sizes can become process window limiting. It is also important to determine if CD error is sensitive to the interaction between defects and scattering bar (SB) OPC features. The experiment was based on a typical 0.18 mu m process using the: Defect Sensitivity Monitor (DSM) Reticle - designed by MicroUnity and manufactured by Photronics. Only isolated features were investigated in this work. Greater than 10% printed CD error was found for defects occurring on the main feature such as a 200nm bump or a 250nm divot on a 4X reticle. Greater than 6% of the exposure latitude can be lost due to +/-50nm (4X) mask feature width deviations. A 200nm-chrome spot 4X-reticle defect located between, a main feature and an SE can cause more than a 10% printed CD error. Defects occurring on scattering bars such as bump and break types have less influence on the printed CD. The CD error is negligible for +/-100nm SE width variation on a 4X reticle.