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Proceedings Paper

Overlay leaves litho: impact of non-litho processes on overlay and compensation
Author(s): Matthias Ruhm; Bernd Schulz; Eric Cotte; Rolf Seltmann; Tino Hertzsch
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Paper Abstract

According to the ITRS roadmap [1], the overlay requirement for the 28nm node is 8nm. If we compare this number with the performance given by tool vendors for their most advanced immersion systems (which is < 3nm), there seems to remain a large margin. Does that mean that today’s leading edge Fab has an easy life? Unfortunately not, as other contributors affecting overlay are emerging. Mask contributions and so-called non-linear wafer distortions are known effects that can impact overlay quite significantly. Furthermore, it is often forgotten that downstream (post-litho) processes can impact the overlay as well. Thus, it can be required to compensate for the effects of subsequent processes already at the lithography operation. Within our paper, we will briefly touch on the wafer distortion topic and discuss the limitations of lithography compensation techniques such as higher order corrections versus solving the root cause of the distortions. The primary focus will be on the impact of the etch processes on the pattern placement error. We will show how individual layers can get affected differently by showing typical wafer signatures. However, in contrast to the above-mentioned wafer distortion topic, lithographic compensation techniques can be highly effective to reduce the placement error significantly towards acceptable levels (see Figure 1). Finally we will discuss the overall overlay budget for a 28nm contact to gate case by taking the impact of the individual process contributors into account.

Paper Details

Date Published: 17 October 2014
PDF: 10 pages
Proc. SPIE 9231, 30th European Mask and Lithography Conference, 92310O (17 October 2014); doi: 10.1117/12.2068206
Show Author Affiliations
Matthias Ruhm, GLOBALFOUNDRIES Dresden (Germany)
Bernd Schulz, GLOBALFOUNDRIES Dresden (Germany)
Eric Cotte, GLOBALFOUNDRIES Dresden (Germany)
Rolf Seltmann, GLOBALFOUNDRIES Dresden (Germany)
Tino Hertzsch, GLOBALFOUNDRIES Dresden (Germany)

Published in SPIE Proceedings Vol. 9231:
30th European Mask and Lithography Conference
Uwe F. W. Behringer, Editor(s)

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