Optimization of the absorbance of novolak resin films at 248 nm

Leonard E. Bogan Jr.; Karen A. Graziano

doi:10.1117/12.20112

1 June 1990 Optimization of the absorbance of novolak resin films at 248 nm

Leonard E. Bogan Jr., Karen A. Graziano

Proceedings Volume 1262, Advances in Resist Technology and Processing VII; (1990) https://doi.org/10.1117/12.20112
Event: Microlithography '90, 1990, San Jose, CA, United States

Abstract

It is generally accepted that a 1 jim thick resist film should have an absorbance of no more than 0.25 absorbance unit at the exposure wavelength to enable formation of high-resolution images with vertical wall profiles. Conventional materials are ill-suited for use with KrF excimer laser exposure as the primary component (ca. 80% w/w) of conventional photoresist formulations is novolak resin with absorbance □ 0.6 a.u.flim at 248 nm. This paper describes the optimization of novolak resin composition to give films with minimal absorbance at 248 nm. The deep-UV (248 nm) absorbance of dilute solutions of substituted phenols has been measured and found to follow a welldefmed and predictable pattern. Use of this information to model the absorbance of novolak resin solutions is complicated by the effects of polymer secondary structure on UV absorbance. The absorbance of novolak homopolymer solutions has been studied in four solvents and found to be dependent on polymer composition, secondary structure, molecular weight, and solvent. In order to observe the effects of composition independent of secondary structure, highly branched novolak oligomers were prepared by condensation of commercially available phenols with 2,4,6-tris(dimethylaminomethyl)phenol (Rohm and Haas DMP3O). The optical densities of films of these structurally uniform oligomers were compared. The most transparent copolymers had optical densities which were essentially the same as that of a m -cresol novolak homopolymer, ca. 0.35 absorbance units/Rm.

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Leonard E. Bogan Jr. and Karen A. Graziano "Optimization of the absorbance of novolak resin films at 248 nm", Proc. SPIE 1262, Advances in Resist Technology and Processing VII, (1 June 1990); https://doi.org/10.1117/12.20112

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