Immersion lithography has drawn tons of interests as a potential solution for sub-65nm patterning. High refractive index liquid, which is filled in the gap between exposure lens and a photoresist, can improve a resolution through increased effective numerical aperture (NA) of the exposure system. Most attractive liquid for this purpose is water. Our works were conducted as a part of the basic study for immersion lithography and aimed for the verification of leached resist components by water. It was observed that leaching relies largely on the free volume of a polymer and anion size of photoacid generator (PAG). The larger free volume and the smaller anion, the larger T-top resist profile was generated. Additionally, effects of solvents, quenchers and polarity of the polymer were investigated. Detailed results will be reported in this paper.
Hydrophilicity of a resist film is a major property to determine the compatibility of resist film and substrates. By incorporation of polar groups in the side chain of polymer, the hydrophilicity of polymer, eventually, the hydrophilicity of a resist film can be modified. Since most developer for photoresist is aqueous alkaline solution, the polar side groups control not only interaction with a substrate but also dissolution rate of the resist film. We have synthesized model polymers having various polar groups, and investigated the effect of the polarity on the 193nm resist photographic behavior. Acid, lactone, ether, and alcohol were selected as polar groups. Among them, various lactone and alcohol functional groups were selected for further study on the effect of the side group bulkiness. Hydrophilicity of each functional group was estimated by Log P, which can be calculated using simulation program. From the calculation, aliphatic alcohol and lactone have the highest polarity and ether has the lowest. However, the bulkiness of alcohol increases, the polarity is getting lower than that of ether. Polarity and bulkiness of the polar monomers (acid, lactone, ether, and alcohol group) affect wettability against developer, collapse in 1:1 L/S patterns and adhesion to substrates. The resist films have different contact angles by polarity, bulkiness and content of these monomers in polymer. The polymer including lactone group shows excellent lithographic performance and minimizes pattern collapse in 1:1 L/S. Furthermore, we investigated contrast, pattern profile and process margin of 193nm resist according to the polymer polarity.