157 nm was once touted as a next generation lithography platform. However, the poor performance of critical components has resulted in this technology being passed over for 193 nm immersion lithography or extreme UV lithography. One such component was the pellicle. Pellicles are thin, polymeric, free standing films that protect the photomask from dust contamination. Due to the position of the pellicles above and below the focal plane of the photomask, any dust particles that land on the pellicle will be out of focus when the image is projected onto the silicon wafer. Pellicles for 193 nm lithography have been manufactured from perfluorinated polymers, such as Teflon® AF (TAF) and Cytop®. However, these polymers do not have the transparency or photostability for 157 nm photolithography to become a commercially viable process. During 2003-2004 the UQ group studied the photodegradation of TAF with 157 nm light. A range of sensitive techniques such as X-ray Photoelectron Spectroscopy (XPS), 19F solution-state Nuclear Magnetic Resonance (NMR) spectroscopy, Raman Spectroscopy and Fourier Transform Infrared (FTIR) spectroscopy were used to study the photodegradation of the polymer. The data from these analyses were used to formulate a photodegradation mechanism for TAF polymers.

This project was carried out in collaboration with Sematech and was also supported by the Queensland State Government through a Smart State Fellowship.

Figure 1 XPS spectra of Teflon AF films irradiated at a variety of doses.


Dr Paul Zimmerman – Sematech

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  1. Blakey, I.; George, G. A.; Hill, D. J. T.; Liu, H.; Rasoul, F.; Whittaker, A. K.; Zimmerman, P. XPS and 19F NMR Study of the Photodegradation at 157 nm of Photolithographic-Grade Teflon AF Thin Films. Macromolecules 2005, 38, 4050-4053.

  2. Blakey, I.; George, G. A.; Hill, D. J. T.; Liu, H.; Rasoul, F.; Rintoul, L.; Zimmerman, P.; Whittaker, A. K. Mechanism of 157 nm Photodegradation of Poly[4,5-Difluoro-2,2- Bis(Trifluoromethyl)-1,3-Dioxole-Co-Tetrafluoroethylene] (Teflon AF). Macromolecules (Washington, DC, United States) 2007, 40, 8954-8961.