Analysis of 193-nm immersion specific defects

A great deal of research effort is focused on accelerating the development of 193-nm immersion lithography because it appears to be the most suitable lithographic solution available for 65-nm-and-below semiconductor devices. To realize a 193-nm immersion process, we must find ways to detect and analyze immersion specific defects, and then establish processes that let us avoid such defects. In this paper, we examine immersion specific defects and ways to detect and eliminate them in production processes. Through comparison of dry exposure and immersion exposure processes, we have found that "bridges" and "water-marks" are the most significant immersion specific defects using current developable top-coats. Although we confirmed that the current solvent-removable top-coat process is better for avoiding immersion specific defects, we also found that the defect density with a developable top-coat was still low enough for volume production. We also investigated the causes of immersion specific defects and hypothesized that DI water permeation and the local topology of the top-coat play an important role in the generation of immersion specific defects. To test whether this was so, we evaluated the change in the top-coat film thickness by the quartz crystal microbalance technique. We confirmed that top-coat swelling caused by water permeation into the top-coat film is a major cause of immersion specific defects.