SEM AutoAnalysis for reduced turnaround time and to ensure repair quality of EUV photomasks

Authors

Kokila Egodage*a, Fan Tub, Horst Schneiderb, Christian F. Hermannsb, Grizelda Kersteenc, Bartholomaeus Szafranekb, Kristian Schulza
aCarl Zeiss SMT GmbH, Carl-Zeiss-Promenade 10, 07745 Jena, Germany
bCarl Zeiss SMT GmbH,Industriestrasse 1, 64380 Rossdorf, Germany
cCarl Zeiss SMT GmbH, Rudolf-Eber-Strasse 2,73447, Oberkochen, Germany

Abstract

With the semiconductor industry tending towards adding multiple layers consisting of EUV technology in high-end manufacturing and the production of many EUV scanners to meet customer demands, novel approaches for EUV defect review are being readily investigated. The successor of the quasi industry standard AIMS™ and sole actinic defect review tool available currently is AIMS™ EUV. As the industry already introduced this newcomer in the manufacturing
environment, other steps in the workflow were forced to adapt to the new technology. One example is the automated aerial image analysis process where the DUV aerial image analysis software, AIMS™ AutoAnalysis (AAA), was enhanced for the EUV solution in order to handle high resolution EUV images. This was a necessary step for full automation similar to the process achieved with AIMS™ and AAA.

Another important domain in the back end of line is defect repair where the e-beam based repair tool MeRiT® is also the quasi standard in the mask manufacturing industry especially for high-end photomasks. After undergoing changes to keep up with shrinking feature sizes and complex repairs MeRiT® tools were able to overcome these challenges and fulfill the current industry demands and expectations. For mask makers timely supply of error free high-quality masks is of the essence which can be further ensured by introducing a higher level of automation to the repair workflow. Following a similar approach to the optical counterpart, a digital solution known as SEM AutoAnalysis (SAA) has been developed. With SAA, a quick and fully automated SEM image-based quality assessment after a repair of a photomask is readily achievable. Moreover, the repair technicians benefit vastly by having the complete repair history of a defect for their decision-making process which would lead to a reduction of the turnaround time. As a consequence, unnecessary time wastes during mask un/loading cycles can be avoided.

The myriad data produced in the BEOL, originating from different modalities, can be converted to meaningful information with the help of automation enabling technicians to make better decisions, reducing the risk of mishaps, improve repair quality and reliability of processes in general. Since mask defects that go through each tool are the same, data produced by different tools should retain that common denominator for an efficient assessment. This assessment
needs to be applied to the areas of different modalities where a comparison is possible that led to the investigations to test the feasibility of combining SEM and EUV data. A comparison of SAA results with AIMS™ EUV measurements
analyzed with AAA on the same photomask and defects are presented along with this proceeding. The results show that SAA can provide a valuable preliminary assessment of photomask repairs. Nevertheless, due to the nature of SEM based analysis, AIMS™ EUV technology remains mandatory for a final mask repair qualification and a complete specification check, i.e. mask repair verification. The outcome of this investigation paves the way towards a fully automated BEOL where different workflows and data originating from several tools in the mask shop can be interconnected and controlled. 

Keywords: SEM AutoAnalysis, AIMS™ AutoAnalysis, EUV, SEM, aerial image, MeRiT®, AIMS™

Proceedings Volume 11147, International Conference on Extreme Ultraviolet Lithography 2019; 111471G (2019)
https://doi.org/10.1117/12.2538474
Event: SPIE Photomask Technology + EUV Lithography, 2019, Monterey, California, United States