Recent observations indicate that CD control for the 0.18 micrometers process generation using KrF exposure could be sensitive to borderline detectable defect sizes on a 4X reticle. It is of interest to determine if these 'sub- killer' 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 OPC features. The experiment was based on a typical 0.18 micrometers process using the Defect Sensitivity Monitor reticle - designed by MicroUnity and manufactured by Photronics. Only isolated features were investigated in this work. Greater than 10 percent printed CD error was found for defects occurring on the main feature such as a 200 nm bump or a 250 nm divot on a 4X reticle. Greater than 6 percent of the exposure latitude can be lost due to +/- 50 nm mask feature width deviations. A 200 nm-chrome spot 4X-reticle defect located between a main feature and an SB can cause more than a 10 percent printed CD error. Defects occurring on scattering bars such as bump a d break types have less influence on the printed CD. The CD error is negligible for +/- 100 nm SB width variation on a 4X reticle.