Dissolution Fundamentals of Polyelectrolyte Photoresists
Author: Ashwin Rao
Mentor: Vivek Prabhu
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The dissolution of partially deprotected chemically amplified photoresists is the final step in printing lithographic features. Since this process step can be tuned independently from the design of the photoresist chemistry, fundamental measurements of the dissolution behavior of photoresists may provide needed insights towards improving line-edge roughness. We have studied the dissolution behavior of a model 193-nm photoresist, poly (methyladamantyl methacrylate), as a function of deprotection extent and developer strength. The kinetics of the dissolution process is followed using the quartz crystal microbalance technique, while the steady state swelling behavior is studied using light interferometry. These photoresist films exhibit strong swelling without dissolution over a narrow-range of deprotection levels. At larger extents of deprotection, we observe a combination of swelling with dissolution. Additionally, we find a maximum degree of film swelling with tetramethylammonium hydroxide developer concentration. If photoresist swelling and dissolution strongly affect CD control or LER, these studies provide the insight needed to better design developer materials and strategies.