Bilayer resist approach for 193-nm lithography

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Abstract
Tremendous efforts to extend optical lithography beyond the quarter micrometer boundary, which is currently achievable with KrF-excimer laser lithography, are ongoing. One-hundred- ninety-three nm lithography, using ArF-excimer lasers, is believed to be the technology of choice to approach the ambitious sub-0.2 micrometer resolution target. Single layer, positive tone resist systems, which can be developed with aqueous base, would be preferred. However, it might well turn out that the targeted requirements can only be fulfilled by resist systems which involve some type of dry etch steps. This paper focuses on a positive tone bilayer resist system, which is based on novel silicon containing methacrylate polymers bearing acid labile side groups. Due to a unique combination of monomeric building blocks, polymers with high silicon concentrations and, at the same time, high thermal flow stability are obtained. Hardbaked novolac is used as the planarizing layer. Resists systems based on the new silicon containing polymers demonstrated 0.175 micrometer resolution capability, a thermal flow stability greater than 120 degrees Celsius, and an etch selectivity ratio greater than 20.

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