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
Conference Title: SPIE Advanced Lithography
Pub Type: Conferences
Diffusion length, photoacid, photoresist, kinetics, FTIR, PDMS