| Abstract
| - The use of 157 nm as the next lower wavelength for photolithography for the production ofsemiconductors has created a need for transparent and radiation-durable polymers for use in soft pellicles,the polymer films which protect the chip from particle deposition. The most promising materials for pelliclesare fluorinated polymers, but currently available fluorinated polymers undergo photodegradation and/orphotodarkening upon long term exposure to 157 nm irradiation. To understand the mechanism of thephotodegradation and photodarkening of fluorinated polymers, mechanistic studies on the photolysis ofliquid model fluorocarbons, including perfluorobutylethyl ether and perfluoro-2H-3-oxa-heptane, wereperformed employing UV, NMR, FTIR, GC, and GC/MS analyses. All hydrogen-containing compoundsshowed decreased photostability compared to the fully perfluorinated compounds. Irradiation in the presenceof atmospheric oxygen showed reduced photostability compared to deoxygenated samples. Photolysis ofthe samples was performed at 157, 172, 185, and 254 nm and showed only minor wavelength dependence.Mechanisms for photodegradation of the fluorocarbons are proposed, which involve Rydberg excited states.Time-dependent density functional theory has been used to predict the excitation spectra of modelcompounds.
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