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Amorphous carbon films for use as both variable-transmission apertures and attenuated phase shift masks for deep ultraviolet lithography

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2 Author(s)
Windt, David L. ; Bell Laboratories, Lucent Technologies, Murray Hill, New Jersey 07974 ; Cirelli, Raymond A.

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We describe the development of amorphous carbon (a-C) films grown by magnetron sputtering for use in optical elements for sub-0.25-μm deep ultraviolet (DUV) lithography. We have measured the transmittance of a-C films deposited onto quartz substrates as a function of film thickness, and find that the films are ideally suited for use in variable-transmission apertures that can be used to improve DUV process latitude: we can achieve essentially any transmittance (T) desired in the range 0≪T≪100% by controlling the film thickness (t) in the range 200≫t≫0 nm with subnanometer precision. We also find that the transmittance remains stable after prolonged exposure to high intensity DUV radiation. We describe a masked deposition technique to produce variable-transmission apertures using a-C films of various thicknesses, and also discuss the use of these films in attenuated phase shift masks, given that we can simultaneously achieve ∼6%–8% transmittance and a phase shift of 180° at either λ=248 nm or 193 nm. © 1999 American Vacuum Society.

Published in:

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures  (Volume:17 ,  Issue: 3 )