Mr. Steven A. Bassett Profile

Steven A. Bassett

at SUNY Poly SEMATECH

SPIE Involvement:

Author

Publications (2)

Proceedings Article | 14 September 2001 Paper

Study of obscuration in catadioptric lenses

Martin McCallum, Bruce Smith, Steve Bassett, Julian Cashmore, James Webb

Proceedings Volume 4346, (2001) https://doi.org/10.1117/12.435646

KEYWORDS: Nanoimprint lithography, Binary data, Combined lens-mirror systems, Lenses, Diffraction, Monochromatic aberrations, Phase shifts, Coherence (optics), Photomasks, Lens design

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Proceedings Article | 24 August 2001 Paper

Photoresist outgassing at 157 nm exposure

Stefan Hien, Steve Angood, Dominic Ashworth, Steve Basset, Theodore Bloomstein, Kim Dean, Roderick Kunz, Daniel Miller, Shashikant Patel, Georgia Rich

Proceedings Volume 4345, (2001) https://doi.org/10.1117/12.436834

KEYWORDS: Fluorine, Polymers, Contamination, Oxygen, Photoresist materials, Plasma, Absorption, Silicon, Vacuum ultraviolet, Molecules

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Contamination of optical elements during photoresist exposure is a serious issue in optical lithography. The outgassing of photoresist has been identified as a problem at 248nm and 193nm in production because the organic films that can be formed on an exposure lens can cause transmission loss and sever image distortion. At these exposure energies, the excitation of the photo acid generator, formation of acid, and cleavage of the protecting group are highly selective processes. At 157nm, the exposure energy is much higher (7.9 eV compared to 6.4 eV at 193nm) and it is known from laser ablation experiments that direct laser cleavage of sigma bonds occurs. The fragments formed during this irradiation can be considered as effective laser deposition precursors even in the mid ppb level. In this study, methods to quantify photoresist outgassing at 157 nm are discussed. Three criteria have been set up at International SEMATECH to protect lens contamination and to determine the severity of photoresist outgassing. First, we measured film thickness loss as a function of exposure dose for a variety of materials. In a second test we studied the molecular composition of the outgassing fragments with an exposure chamber coupled to a gas chromatograph and a mass spectrometer detector. Our third method was a deposition test of outgassing vapors on a CaF₂ proof plate followed by analysis using VUV and X-ray photoelectron spectroscopies (XPS). With this technique we found deposits for many different resists. Our main focus is on F- and Si- containing resists. Both material classes form deposits especially if these atoms are bound to the polymer side chains. Whereas the F-containing films can be cleaned off under 157nm irradiation, cleaning of Si-containing films mainly produces SiO₂. Our cleaning studies of plasma deposited F-containing organic films on SiO₂ did not indicate damage of this surface by the possible formation of HF. Despite that we strongly recommend engineering measures to overcome contamination by resist, such as optimizing the purge flow between the final lens element and wafer surface or utilization of a lens pellicle.

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