12 April 2007 Identifying materials limits of chemically amplified photoresists
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Chemically amplified photoresists are likely to remain the primary imaging materials for the semiconductor industry. As feature sizes decrease to dimensions comparable to the characteristic size of the molecules in the photoresist, a significant challenge lies in identifying the ultimate resolution limit of these materials. To address this challenge, we investigated model photoresist materials with high resolution measurements to examine the effect of individual factors among interdependent process steps on line-edge roughness (LER). Using a bilayer film sample geometry, we measured the internal deprotection interface with nanometer resolution as a function of photoacid size, initial resist copolymer composition, and amine base quencher by neutron reflectivity and infrared spectroscopy. After development, we found that the resist chemistry and additives can play an important role in LER through its influence on acid diffusion. However, these model experiments suggest that there is a limit in LER even with an idealized exposure image contrast and decreases in the width of the reaction-diffusion front. However, there may be opportunities to further decrease LER during development by tuning the response of the photoresist to the developer solution.
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Wen-li Wu, Vivek M. Prabhu, and Eric K. Lin "Identifying materials limits of chemically amplified photoresists", Proc. SPIE 6519, Advances in Resist Materials and Processing Technology XXIV, 651902 (12 April 2007); doi: 10.1117/12.720424; https://doi.org/10.1117/12.720424

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