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Proceedings Paper

Laser cleaning of optical elements in 157-nm lithography
Author(s): Theodore M. Bloomstein; Mordechai Rothschild; Vladimir Liberman; D. E. Hardy; N. N. Efremow Jr.; Stephen T. Palmacci
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Paper Abstract

In-situ laser cleaning is shown to be an effective tool for removal of organic contaminants on CaF2 windows. To study laser cleaning in a controlled fashion, CaF2 substrates were pre-contaminated with 5 to 10 nm of poly(methyl methacrylate), poly(4-hydroxy styrene), poly(norbornene), and poly((beta) -pinene) thin films. Irradiation of all the polymer films showed similar trends. Initially, a high rate of material removal occurs, which depends on the chemistry of the polymer. During this period, the material also undergoes significant bond rearrangement, forming a more tightly bound highly conjugated network. Removal of this residual 'graphitized' film is significantly more difficult, but can be accelerated by the presence of modest levels of oxygen. For oxygen concentrations between 10-1000 ppm, the measured removal rate is approximately 3 nm/(kJ/cm2) ppm oxygen. No effect on removal rate was observed as pulse energy or purge gas flow rate was varied over ranges expected to be used in practical systems.

Paper Details

Date Published: 5 July 2000
PDF: 9 pages
Proc. SPIE 4000, Optical Microlithography XIII, (5 July 2000); doi: 10.1117/12.388993
Show Author Affiliations
Theodore M. Bloomstein, MIT Lincoln Lab. (United States)
Mordechai Rothschild, MIT Lincoln Lab. (United States)
Vladimir Liberman, MIT Lincoln Lab. (United States)
D. E. Hardy, MIT Lincoln Lab. (United States)
N. N. Efremow Jr., MIT Lincoln Lab. (United States)
Stephen T. Palmacci, MIT Lincoln Lab. (United States)

Published in SPIE Proceedings Vol. 4000:
Optical Microlithography XIII
Christopher J. Progler, Editor(s)

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