Master of Science (MS)
The microlithographic process, essential in the fabrication of silicon chip integrated circuits, uses high-energy radiation to transfer a pattern onto a thin film of polymer resist. Pattern transfer occurs by modifying the properties (solubility or volatility) of the polymer film exposed to radiation. Poly(olefin sulfones) exhibit a high sensitivity to x-rays, which is a desirable property for polymer resists, but typically undergo a glass transition around room temperature and a thermal degradation at moderate temperatures. The thermal properties of the poly(olefin sulfones) reduce the processing latitude for industrial microelectronics applications. Poly(unsaturated olefin sulfones) containing a carbon-carbon double bond in the polymer backbone exhibit good thermal stability and film forming properties comparable to those observed with poly(methyl methacrylate), PMMA. The potential utility of these new resins prompted a study of the mechanism of degradation promoted by x-ray radiation. In this study, the effect of x-ray radiation on polysulfones with varied chemical structures was analyzed using x-ray absorption near-edge structure (XANES) spectroscopy. The volatile by-products formed upon irradiation of each polysulfone were characterized by in-situ mass spectroscopy. Distinct differences between the mode of degradation of poly(olefin sulfones) such as poly(butane-1 sulfone), PBS,and that of poly(hexadiene sulfone), PHS, were observed. The energy positions of the sulfur K-edge in irradiated PBS are approximately 2473 eV, (sulfide) and 2479 eV (sulfone). Decomposition is accompanied by sulfide formation and the evolution of butene-1 in the gaseous by-products. In contrast, the sulfur K edge spectra of PHS exhibits the following energy positions, 2473 eV (sulfide), 2475 eV (sulfoxide), 2478 eV (sulfone) and 2482 eV (sulfonate). Only sulfur oxide by-products were observed in the mass spectra indicating that the predominant mode of degradation is oxidative. Further studies will be required to elucidate the mechanism of this new mode of degradation.
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Calderon, Gina Marie, "The radiation-induced degradation of poly(diene sulfones) as x-ray resists" (2002). LSU Master's Theses. 2202.