Characterization of Microbridges Generated on Negative Resist Patterns

We analyze the mechanism of microbridge formation on chemically amplified negative resist patterns through direct observation of progressive development in alkali-developers. The microbridge formation was attributed to contact occurring between adjacent resist patterns due to swelling of the resist. These swollen resist patterns contracted upon immersion in deionized water; however, bridge structures remained as microbridges between these patterns. The swelling of the resist films occurred more easily at defocus positions than at a focus center, and the microbridges localized near the top of the pattern at defocus positions and delocalized at a focus center. An optical simulation suggested that both the crosslinking density and its distribution determine the number and position of the microbridges. A scaling law governing microbridge formation is observed as a function of focus position and exposure dose.