11 May 2009 Evaluation of an e-beam correction strategy for compensation of EUVL mask non-flatness
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Proceedings Volume 7379, Photomask and Next-Generation Lithography Mask Technology XVI; 73790Q (2009); doi: 10.1117/12.824267
Event: Photomask and NGL Mask Technology XVI, 2009, Yokohama, Japan
Abstract
In extreme ultraviolet lithography (EUVL), mask non-flatness contributes to overlay errors in EUVL scanners. Tight non-flatness targets are required to meet future overlay; for example, the International Technology Roadmap for Semiconductors (ITRS) requires that substrate non-flatness will need to decrease to 36 nm peak-to-valley in 2013. To meet these tight non-flatness values, suppliers must use aggressive polishing steps, adversely impacting substrate yield and mask blank cost of ownership. An alternative option is to use image placement corrections at the writing step of the reticle to compensate for the predicted impact of the non-flatness pattern placement errors, which would allow the specifications to be relaxed. In this paper, we will present the results of using e-beam image placement corrections during mask writing to compensate for mask non-flatness. A low thermal expansion material (LTEM) substrate with about 500 nm of nonflatness was employed. Three different compensation methods were used to calculate the predicted image placement errors based upon the mask non-flatness, including the expected errors from scanner chucking. The mask was designed to use a repeating set of four ASML alignment marks (XPA marks) across the mask. During e-beam writin, one mark was left uncompensated, and the three different compensation methods were applied to the remaining marks. The masks were exposed using the ASML alpha demo tool (ADT). An overview of the viability of e-beam correction methodologies to compensate for mask non-flatness is presented based upon the wafer overlay results.
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Kevin Orvek, Jaewoong Sohn, Jin Choi, Roxann Engelstad, Sudharshanan Raghunathan, John Zimmerman, Thomas Laursen, Yoshitake Shusuke, Tsutomu Shoki, "Evaluation of an e-beam correction strategy for compensation of EUVL mask non-flatness", Proc. SPIE 7379, Photomask and Next-Generation Lithography Mask Technology XVI, 73790Q (11 May 2009); doi: 10.1117/12.824267; https://doi.org/10.1117/12.824267
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KEYWORDS
Photomasks

Scanners

Semiconducting wafers

Extreme ultraviolet lithography

Finite element methods

Extreme ultraviolet

Polishing

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