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16 May 1994 Lithographic performance of isomeric hydroxystyrene polymers
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The synthesis and lithographic characterization of the three positional isomers of polyhydroxystyrene is described. Large differences in dissolution rates are found as a function of the position of the hydroxy group, which are explained in terms of intra- versus intermolecular hydrogen bonding and steric shielding of the hydroxy group by the polymer backbone. In plots of log(dissolution rate) versus developer strength, linear plots are observed for the 2- and 4-isomers, whereas for poly(3- hydroxystyrene), a break occurs in the plot, leading to two linear regions. While the 2-hydroxy isomer is too slow and the 4- hydroxy isomer too fast for use in conventional dissolution inhibition systems, the copolymerization of both allows one to choose any dissolution rate between these extremes ('dial a dissolution rate'-copolymers). Determination of the copolymerization parameters of the corresponding 4- and 2- acetoxystyrene precursors by the method of Kelen and Tudos shows the polymerization to be nearly ideal and azeotropic (r1 equals 0.76, r2 equals 0.94). Analysis of the dissolution rates as a function of developer strength according to the Huang-Reiser-Kwei equation shows that the critical concentrations c are a linear function of copolymer composition, whereas the penetration exponents n show a minimum near unity in the region of the 1:1 copolymer, down from the values of 3.2-3.3 observed for all three homopolymers. The 1:1 copolymer shows a dissolution rate comparable to novolak resins, and when formulated into a photoresist together with a diazonaphthoquinone sensitizer resolved 0.4 micrometers features at a dose of 340 mJ/cm2. The thermal flow resistance of the resist was found to be improved over that of novolak resists although not to the degree expected from the increased Tg of the 1:1 copolymer.
© (1994) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Ralph R. Dammel, M. Dalil Rahman, Ping-Hung Lu, Anthony Canize, and Varadaraj Elango "Lithographic performance of isomeric hydroxystyrene polymers", Proc. SPIE 2195, Advances in Resist Technology and Processing XI, (16 May 1994);

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