The Dissolution Behavior of Tetrafluoroethylene-based Fluoropolymers for 157-nm Resist Materials

摘要

Main-chain-fluorinated base-resins, using the copolymer of tetrafluoroethylene and functional (hexafluoroisopropanol (HFA) group) norbornene, were synthesized. Partial protection of its hydroxyl group as ethoxymethyl group was achieved by two methods, by copolymerization (Method A) or by polymer reaction (Method B). The partial protection by copolymerization was conducted by copolymerizing TFE with the mixture of protected and unprotected monomers (Method A, copolymerization). The partial protection was also carried out by reacting hydroxyl group of the polymer, which is composed of TFE and unprotected monomers with ethoxymethyl chloride in the presence of an arnine (Method B). In the polymer reaction, only exo position of the norbornene unit was protected. Their fundamental properties, such as transparency at 157 nm and solubility in a standard alkaline developer, were characterized and studied. A high transparency, i.e., absorbance of less than 0.4 μm~(-1), was achieved in both methods. However, the polymer prepared by the polymer reaction (Method B) was deprotected more quickly. And this polymer had a higher dissolution rate and development contrast than the polymer prepared by copolymerization (Method A). The Positive-working resists based on this fluororesins were developed and 55 nm dense lines could be delineated by the exposure at 157 nm wavelength with alternating phase shift mask on a 0.9 NA 157 nm exposure tool.