Laser cleaning of optical elements in 157-nm lithography

Theodore M. Bloomstein; Mordechai Rothschild; Vladimir Liberman; D. E. Hardy; N. N. Efremow Jr.; Stephen T. Palmacci

doi:10.1117/12.388993

5 July 2000 Laser cleaning of optical elements in 157-nm lithography

Theodore M. Bloomstein, Mordechai Rothschild, Vladimir Liberman, D. E. Hardy, N. N. Efremow Jr., Stephen T. Palmacci

Proceedings Volume 4000, Optical Microlithography XIII; (2000) https://doi.org/10.1117/12.388993
Event: Microlithography 2000, 2000, Santa Clara, CA, United States

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.

Citation Download Citation

Theodore M. Bloomstein, Mordechai Rothschild, Vladimir Liberman, D. E. Hardy, N. N. Efremow Jr., and Stephen T. Palmacci "Laser cleaning of optical elements in 157-nm lithography", Proc. SPIE 4000, Optical Microlithography XIII, (5 July 2000); https://doi.org/10.1117/12.388993

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