193-nm immersion lithography is the only choice for the 45-nm logical node at 120-nm half pitch and extendable to 32-
and 22-nm nodes. The defect problem is one of the critical issues in immersion technology. In this paper, we provided a
methodology to trace the defect source from optical microscope images to its SEM counterparts after exposure. An
optimized exposure routing was also proposed to reduce printing defects. The average defect count was reduced from
19.7 to 4.8 ea/wafer.
We introduce a novel in-scanner aerial image sampling technique using a sensor wafer that can be loaded into a production scanner to acquire data at the wafer plane, and under exact production conditions in terms of all optical settings and parameters of the actual scanner and an actual reticle. We demonstrate the applicability of this system to CD uniformity characterization of a production scanner in combination with a test reticle. CD estimates can be directly obtained from the image data by applying a fixed threshold, by employing a calibrated resist model to the sensor data, or by using the sensor data to accurately calibrate a complete lithography model. The linear response of the sensor provides complete information on the imaging process, and CD data can be immediately correlated to other image parameters, such as contrast, ILS, peak signal values, etc. We demonstrate the ability of the system to characterize CD variations and through-pitch curves, and to generate CD uniformity maps across the exposure field. We have extensively studied the repeatability and reproducibility of the system, and show its ability to detect changes in imaging performance over time in a production environment, differences between exposure tools, or different mask manufacturing processes.