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Journal of Micro/Nanolithography, MEMS, and MOEMS

Speckle in optical lithography and its influence on linewidth roughness
Author(s): Oscar Noordman; Andrey Tychkov; Jan Baselmans; James G. Tsacoyeanes; Gary Politi; Michael Patra; Vladan Blahnik; Manfred Maul
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Paper Abstract

In recent years speckle in optical projection microlithography received increasing interest because of its potential contribution to linewidth roughness (LWR). Speckle is a light interference effect that causes the dose delivered to the reticle to be nonuniform, causing a linewidth variation of the patterns imaged in the resist. The contrast of the speckle pattern is shown to be caused by a combination of temporal and spatial coherence effects of the light. The temporal part, determined by the bandwidth of the laser light and the duration of the laser pulse, is found to be the dominant contributor to speckle in today's ArF optical lithography. The spatial distribution of the speckle pattern depends on the intensity distribution of the light in the pupil. Consequently, the spatial frequencies of the LWR induced by speckle depend on the illumination condition, which is confirmed experimentally by exposing wafers with different amounts of speckle contrast. The experiments demonstrate that the amplitude of the LWR induced by speckle is consistent with theory and simulations. Its amplitude is small compared to other sources of LWR, but it is clearly present and should not be ignored when extending ArF optical lithography into future technology nodes.

Paper Details

Date Published: 1 October 2009
PDF: 10 pages
J. Micro/Nanolith. 8(4) 043002 doi: 10.1117/1.3256131
Published in: Journal of Micro/Nanolithography, MEMS, and MOEMS Volume 8, Issue 4
Show Author Affiliations
Oscar Noordman, ASML Netherlands B.V. (Netherlands)
Andrey Tychkov, ASML Netherlands B.V. (Netherlands)
Jan Baselmans, ASML Netherlands B.V. (Netherlands)
James G. Tsacoyeanes, ASML Wilton (United States)
Gary Politi, ASML Wilton (United States)
Michael Patra, Carl Zeiss SMT AG (Germany)
Vladan Blahnik, Carl Zeiss SMT AG (Germany)
Manfred Maul, Carl Zeiss SMT AG (Germany)

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