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1 April 2009 Main chain decomposable star shaped polymer for EUV resist
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The Extreme Ultra Violet lithography (EUVL) is expected to be the most promising semiconductor fabrication technology for 22 nm node and beyond. Kozawa and his colleagues have documented that non-constant acid diffusion coefficient have a significant impact on the latent image quality of 22 nm patterns. We prepared a novel main chain decomposable star shaped polymer (STAR polymer) to examine the concept. STAR polymer consists of a core unit and several arm units which connect to the core unit as shown in Fig.1. The arm units are partially protected poly (p-hydroxystyrene) (PHS) base linear polymer. The core unit that attached on the arm units employs easily acid cleavable group. The adoption of living anion polymerization for the arm units of the STAR polymer makes the controlled polymerization of one monomer unit possible. Based on this material design concept, the protecting group on the arm unit is de-protected by the acid generated during exposure and continues its reaction at the Post Exposure Bake (PEB) step and the acid will also cleave the bonding of the core unit which would then result in a lower molecular weight polymer of lower Tg. The concept of the novel polymer, which is the decomposition of the core and protecting group of arm units of the STAR polymer, was confirmed with a gel-permeation-chromatography (GPC) study. The thermal property of the exposed and unexposed area was also investigated through a thermal flow method. The Tg decrease of the exposed area was observed with the STAR polymer, regardless of increase in Tg of the linear polymer. General lithographic performance on EUV exposure for STAR polymer was also discussed.
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Jun Iwashita, Takeyoshi Mimura, Taku Hirayama, and Takeshi Iwai "Main chain decomposable star shaped polymer for EUV resist", Proc. SPIE 7273, Advances in Resist Materials and Processing Technology XXVI, 72733O (1 April 2009);

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