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29 October 2014 Impact of reticle writing errors on the on-product overlay performance
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The on-product overlay specification and Advanced Process Control (APC) are getting extremely challenging particularly after the introduction of multi-patterning applications like Litho-Etch-Litho-Etch (LELE). While the Reticle Writing Error (RWE) contribution could be marginalized for quite some time in the layer-to-layer overlay budget, it will become one of the dominating overlay contributors when the intra-layer overlay budget is considered. While most of the overlay contributors like wafer processing, scanner status, reticle transmission, dose, illumination conditions drop out of the intra-layer overlay budget, this is certainly not the case for reticle to reticle writing differences. In this work, we have studied the impact of the RWE on the on-product overlay performance. We show that the RWE can be characterized by an off-line mask registration tool and the modelled results can be sent as feed-forward corrections to the ASML TWINSCANTM. By doing so, the overlay control complexity (e.g. send-ahead wafers, APC settling time) can be reduced significantly. Off-line characterization enables that all reticles virtually become equal after correction (at least to the level of correction capability of the scanner). This means that all higher order RWE contributions (currently up to a third order polynomial) can be removed from the fingerprint. We show that out of 50 production reticles (FEOL, 28-nm technology), 30% can be improved on residual level when non-linear feed-forward corrections are considered as well. The additional benefit of feeding forward linear corrections to the scanner is even higher: it is anticipated that a large portion of the APC variation might find its origin in the RWE contribution. In order to send feed-forward corrections to the scanner, we obviously rely on the quality of the off-line RWE measurements. These measurements are usually provided by a registration tool at the mask shop. To secure the quality, an independent experimental verification test was developed to check if off-line RWE measurements can be used as feed-forward corrections to the scanner. The test has been executed on an ASML NXT: 1950i scanner and was designed such to isolate the reticle writing error contribution. The match between the off-line measurements and the experiment is striking.
© (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Richard van Haren, Hakki Ergun Cekli, Xing Lan Liu, Jan Beltman, Anne Pastol, Jean Massin, Emilie Dupre La Tour, Maxime Gatefait, and Frank Sundermann "Impact of reticle writing errors on the on-product overlay performance", Proc. SPIE 9235, Photomask Technology 2014, 923522 (29 October 2014);

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