Abstract
Aryl-iodonium salts are utilized as photoacid generators (PAGs) in semiconductor photolithography and other photo-initiated manufacturing processes. Despite their utilization and suspected toxicity, the fate of these compounds within the perimeter of semiconductor fabrication plants is inadequately understood; the identification of photolithography products is still needed for a comprehensive environmental impact assessment. This study investigated the photolytic transformation of a representative iodonium PAG cation, bis-(4-tert-butyl phenyl)-iodonium, under conditions simulating industrial photolithography. Under 254-nm irradiation, bis-(4-tert-butyl phenyl)-iodonium reacted rapidly with a photolytic half-life of 39.2 s; different counter ions or solvents did not impact the degradation kinetics. At a semiconductor photolithography-relevant UV dosage of 25 mJ cm−2, 33% of bis-(4-tert-butyl phenyl)-iodonium was estimated to be transformed. Six aromatic/hydrophobic photoproducts were identified utilizing a combination of HPLC–DAD and GC–MS. Selected photoproducts such as tert-butyl benzene and tert-butyl iodobenzene had remarkably higher acute microbial toxicity toward bacterium Aliivibrio fischeri compared to bis-(4-tert-butyl phenyl)-iodonium. Octanol–water partition coefficients estimated using the Estimation Programs Interface Suite™ indicated that the photoproducts were substantially more hydrophobic than the parent compound. The results fill a critical data gap hindering the environmental impact assessment of iodonium PAGs and provide clues on potential management strategies for both iodonium compounds and their photoproducts.
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Acknowledgements
The authors acknowledge members of the Onium PAG Consortium of the Semiconductor Industry Association for helpful discussions on this article.
Funding
This study was funded by the Semiconductor Industry Association (SIA) and Semiconductor Research Corporation (SRC) (award # 2818.004). UA/NASA Undergraduate Internship Program is acknowledged for providing partial support for RDP.
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XZN performed the experiments; coordinated the investigation processes; analyzed, interpreted, and visualized data; and wrote the manuscript. RDP participated to photolytic experiments and obtained log POW using EPI Suite. RP participated in Microtox experiments and photolytic experiments. JC interpreted data and acquired funding. LA interpreted data and participated in GC–MS analysis. JAF interpreted data and acquired funding. RSA interpreted data; acquired funding; and conceptualized the investigation.
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Niu, XZ., Pepel, R.D., Paniego, R. et al. Fate of bis-(4-tert-butyl phenyl)-iodonium under photolithography relevant irradiation and the environmental risk properties of the formed photoproducts. Environ Sci Pollut Res 29, 25988–25994 (2022). https://doi.org/10.1007/s11356-022-19376-8
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DOI: https://doi.org/10.1007/s11356-022-19376-8