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Characterization of the Photoacid Diffusion Length



Shuhui Kang, Vivek Prabhu, Wen-Li Wu, Eric K. Lin, Kwang-Woo Choi, Manish Chandhok, Todd Younkin, Wang Yueh


The photoacid diffusion length is a critical issue for EUV photoresists and photolithography because it governs critical dimension (CD), line-edge-roughness (LER) and line-width-roughness (LWR). This paper provides an approach to characterize the photoacid diffusion length in a laboratory setting by applying a bilayer stack technique. This approach leverages the nm change in film thickness that occurs in the one-dimensional photoacid gradient of the bilayer stack. Further, the bilayer stack maximizes the initial acid gradient such that it mimics an ideal step exposure. In addition, using a previously derived kinetics modeling approach (S. Kang et al. Proceedings of SPIE, 6923, 692317(2008)), the measured diffusion length was predicted providing a rapid materials screening process conditions towards improved CD and LER optimization. This paper extends the experimental work to provide photoresist metrics, based upon the measured kinetics parameters and the diffusion length, that next-generation resist must meet for sub-22 nm CD. These metrics are discussed in terms of general correlations and contributions from the photoacid and resist materials properties that provide insight on resist design. In particular, the trapping kinetics of the photoacid are crucial to leverage to achieve better LER and CD control at low dose, rather than adding more quencher. A few resist deign concepts are discussed based upon these findings.
Proceedings Title
Proceedings of SPIE
Conference Dates
February 23-March 27, 2009
Conference Location
San Jose, CA, US
Conference Title
SPIE Advanced Lithography


Diffusion length, photoacid, photoresist, kinetics, FTIR, PDMS


Kang, S. , Prabhu, V. , Wu, W. , Lin, E. , Choi, K. , Chandhok, M. , Younkin, T. and Yueh, W. (2009), Characterization of the Photoacid Diffusion Length, Proceedings of SPIE, San Jose, CA, US, [online], (Accessed April 18, 2024)
Created February 26, 2009, Updated October 12, 2021