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15 March 2006 What determines the ultimate resolution? The critical relationship between exposure tools and photoresists
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Abstract
As the resolution of optical lithography is being pushed for 45-nm half-pitch node, there is a growing concern about the printing capability of chemically amplified resists. The chemical amplification involves photoacid diffusion that causes contrast degradation of latent image or, in other words, resist blur. In this paper, we study the influence of the resist blur in high-NA ArF immersion lithography by using an interferometric exposure tool. Contrast ratio between the resist latent image and the original aerial image was measured for half pitch from 50 nm to 80 nm. Acid diffusion length for a high-resolution ArF resist was determined as 11 nm in sigma (26 nm in full width at half maximum) assuming Gaussian blur kernel. The results revealed that the influence of resist blur is in fact a significant issue for the 45-nm half pitch node. We consider that reduction of acid diffusion length is highly desirable. Given the tradeoff between the resist resolution and sensitivity, increasing illumination intensity in the exposure tools can be an effective means to overcome the challenge of the resist blur. We also demonstrate resist imaging of 30-nm line-and-space pattern with high-index immersion fluid. The reduction of acid diffusion will be even more important if the ArF immersion is to be extended beyond 45-nm half-pitch node with high-index fluids. While the focus of the paper is on high-NA ArF immersion lithography, our findings are also relevant to EUV lithography.
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Tokuyuki Honda, Yasuhiro Kishikawa, Yuichi Iwasaki, Akinori Ohkubo, Miyoko Kawashima, and Minoru Yoshii "What determines the ultimate resolution? The critical relationship between exposure tools and photoresists", Proc. SPIE 6154, Optical Microlithography XIX, 615422 (15 March 2006); https://doi.org/10.1117/12.656123
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