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Proceedings Paper

157-nm pellicles: polymer design for transparency and lifetime
Author(s): Roger H. French; Robert C. Wheland; Weiming Qiu; M. F. Lemon; Gregory S. Blackman; Xun Zhang; Joe Gordon; Vladimir Liberman; A. Grenville; Roderick R. Kunz; Mordechai Rothschild
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Paper Abstract

The introduction of 157 nm as the next optical lithography wavelength has created a need for new soft (polymeric) or hard (quartz) pellicle materials. Pellicles should be > 98% transparent to incident 157 nm light and, ideally, sufficiently resistant to photochemical damage to remain useful for an exposure lifetime of 7.5 kJ/cm2. The transparency specification has been met. We have developed families of experimental Teflon™AF (TAFx) polymers with > 98% transparency which can be spin coated and lifted as micron-scale, unsupported membranes. Still higher transparencies should be possible once optimization of intrinsic (composition, end groups, impurities, molecular weight) and extrinsic (oxygen, absorbed hydrocarbons, contaminants) factors are completed. The measured transparencies of actual pellicle films, however, are affected by many factors other than absorption. Film thickness must be precisely controlled so as to allow operation at the fringe maxima for the lithographic wavelength. Roughness and thickness uniformity are also critical. An important part of our program has thus been learning how to spin membranes from the solvents that dissolve our pellicle candidates. Meeting the durability specification at 157 nm remains a major concern. The 157 nm radiation durability lifetime of a polymer is determined by two fundamental properties: the fraction of 157 nm radiation absorbed and the fraction (quantum efficiency) of this absorbed radiation that results in photochemical darkening. Originally it was assumed that lifetime increases uniformly with increasing transparency. We now have cases where materials with very different absorbances (TAFx4P and 46P) have similar lifetimes and materials with similar absorptions (TAFx46P and 2P) have very different lifetimes. These findings demonstrate the importance of the relative quantum efficiencies as the 157 nm light energy distributes itself along degradative versus non-degradative pathways. In an effort to identify chemical and structural features that control lifetime, we have been studying model molecular materials, some quite similar to the monomer units used to make our pellicle candidates. Several of these models have shown transparencies much higher and lifetimes far longer than our best pellicle candidates to date.

Paper Details

Date Published: 30 July 2002
PDF: 8 pages
Proc. SPIE 4691, Optical Microlithography XV, (30 July 2002); doi: 10.1117/12.474605
Show Author Affiliations
Roger H. French, DuPont Co. (United States)
Robert C. Wheland, DuPont Co. (United States)
Weiming Qiu, DuPont Co. (United States)
M. F. Lemon, DuPont Co. (United States)
Gregory S. Blackman, DuPont Co. (United States)
Xun Zhang, DuPont Photomasks, Inc. (United States)
Joe Gordon, DuPont Photomasks, Inc. (United States)
Vladimir Liberman, MIT Lincoln Lab. (United States)
A. Grenville, Intel Corp. (United States)
International SEMATECH (United States)
Roderick R. Kunz, MIT Lincoln Lab. (United States)
Mordechai Rothschild, MIT Lincoln Lab. (United States)

Published in SPIE Proceedings Vol. 4691:
Optical Microlithography XV
Anthony Yen, Editor(s)

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