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Proceedings Paper

Real-time focus and overlay measurement by the use of fluorescent markers
Author(s): Diederik Maas; Erwin van Zwet
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Paper Abstract

In lithography, overlay control is getting increasingly complex. Advanced Process Control (APC) is introduced to minimize excursions from the process window for the present exposure. APC uses metrology data of previously exposed wafers, hence, there is always a delay of tens of minutes before the required information is available. This paper proposes the combination of a patterned expose beam and a patterned fluorescent marker on a wafer to generate a fluorescent signal that carries real-time information of the focus and/or position error of the expose pattern with the pattern on the wafer. A practical realization requires some changes to the exposure process, stepper design and reticle lay-out. Firstly, a matched pair of markers on the wafer and reticle is required. Secondly, the generated fluorescent signal must be measured, for example with a (spectrally filtered) photon counter close to the expose area of the wafer. At last, the markers from the previous lithography step shall, after development, be filled with fluorescent material. This deposition requires an additional process step. Photon budget calculations suggest an overlay measurement accuracy of less than a tenth of a nm (real-time).

Paper Details

Date Published: 14 April 2014
PDF: 8 pages
Proc. SPIE 9050, Metrology, Inspection, and Process Control for Microlithography XXVIII, 90502W (14 April 2014); doi: 10.1117/12.2047105
Show Author Affiliations
Diederik Maas, TNO (Netherlands)
Erwin van Zwet, TNO (Netherlands)

Published in SPIE Proceedings Vol. 9050:
Metrology, Inspection, and Process Control for Microlithography XXVIII
Jason P. Cain; Martha I. Sanchez, Editor(s)

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