Mechanism of 157 nm Photodegradation of Poly[4,5-difluoro-2,2- bis(trifluoromethyl)-1,3-dioxole-co-tetrafluoroethylene] (Teflon AF)

Abstract

The photodegradation at 157 nm of thin films of a series of Teflon AF copolymers has been comprehensively examined using electron spin resonance, NMR, FTIR, and Raman spectroscopies, mass spectrometry and X-ray photoelectron spectroscopy. The mechanism of degradation involves reaction at the dioxole units, and as a consequence the sensitivity to degradation increases across the series Teflon AF 1200, 1600, and 2400. A major volatile product is hexafluoroacetone formed by degradation at the dioxole unit. NMR and volatile product analysis confirm that degradation occurs largely at the dioxole unit leading to an array of new chain-end species. Main-chain and chain-end carbon-centered radicals were identified as arising from abstraction reactions and main-chain cleavage, respectively. In addition to loss of the dioxole units, XPS analysis indicates extensive char formation at the film surface, providing evidence of loss of fluorine atoms which in turn may react with free radical intermediates to form stable products identified by NMR. The implications for design of materials for 157 nm photolithography are discussed.

Nanoparticle chemisorption printing technique for conductive silver patterning with submicron resolution

“…Regarding the origin of carboxylate group, VUV irradiation on perfluorinated polymers has been reported to cause photodegradation into several products, including carboxylic acid pendants on the polymer chain 34 35 36 37 . We obtained both X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) spectra of the Cytop films before and after VUV irradiation, as presented in Fig.…”

Development of partially fluorinated EUV-resist polymers for LER and sensitivity improvement

“…In the case of FITMAd and FITAdOM, small amount of Hydrogen fluoride (HF) were detected. Previous studies indicated that HF was generated by a decomposition of fluoropolymers under 157 nm irradiation [10,11]. We infer that FITMAd and FITAdOM are decomposed then HF is generated under EUV exposure.…”

Photoimaging and Lithographic Processes in Polymers

“…Although polymers included in resist formulations are supposed to be transparent at the exposure wavelength, they still absorb at short wavelengths such as 254, 248, 193, and 157 nm, and especially at 13.4 nm, and undergo photolysis reactions [35,[77][78][79][80][81][82][83][84]. The photolysis reactions cause main-chain scission, pendant groups scission, accompanied by outgassing when small molecules are released to the environment, and photo cross-linking.…”

“…The double bonds --CF¼CF--and >CF¼CF 2 were detected with FTIR as well, monitoring the characteristic peaks at 1720 and 1735 cm À1 , respectively [78]. ESR analysis of Teflon AF irradiated at 157 nm reveals formation of radicals by main-chain scission, as well as cleavage of C--O bonds in the perfluorodioxole ring, yielding a variety of volatile and non-volatile photochemical products [80].…”