Lithographic performance of isomeric hydroxystyrene polymers

Ralph R. Dammel; M. Dalil Rahman; Ping-Hung Lu; Anthony Canize; Varadaraj Elango

doi:10.1117/12.175368

16 May 1994 Lithographic performance of isomeric hydroxystyrene polymers

Ralph R. Dammel, M. Dalil Rahman, Ping-Hung Lu, Anthony Canize, Varadaraj Elango

Proceedings Volume 2195, Advances in Resist Technology and Processing XI; (1994) https://doi.org/10.1117/12.175368
Event: SPIE's 1994 Symposium on Microlithography, 1994, San Jose, CA, United States

Abstract

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 T_g of the 1:1 copolymer.

Citation Download Citation

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); https://doi.org/10.1117/12.175368

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