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Investigation of the performance of state-of-the-art defect inspection tools within EUV lithography Dieter Van den Heuvel a, Rik Jonckheere a, Bart Baudemprez a, Shaunee Cheng a, Gino Marcuccilli b, Andrew Cross b, Gregg Inderhees b, Paolo Parisi b a IMEC, Kapeldreef 75, B-3001 Leuven, Belgium b KLA-Tencor, 1 Technology Drive, CA 95035 Milpitas, US ABSTRACT Optical bright field wafer inspection followed by repeater analysis is used to find a maximum number of programmed and natural defects on a EUV patterned mask. Each aspect of the inspection methodology affecting the sensitivity of the wafer inspection is optimized individually. A special focus is given to the wafer stack. Simulation is used to predict the optimum stack properties and experimental verification is performed through exposures on the IMEC EUV Alpha Demo Tool. The final result is benchmarked against state-of-the-art patterned mask inspection and blank inspection to evaluate the capabilities and limitations of the optical wafer inspection. In addition, the locations obtained by each inspection technique (wafer and mask) were reviewed on wafer by means of a new automated methodology that is based on a tight stage accuracy of both inspection tool and review SEM. Key words: EUV lithography, wafer inspection, wafer review, reticle defect, wafer stack 1.

INTRODUCTION

Realizing small half pitch via EUV lithography challenges optical bright field wafer inspection. The shrinking target dimensions in combination with LER values observed on the current EUV resist processes make it difficult to detect on the wafer all defects of interest (DOI) that originated from the reticle. These DOI are generally defined as defects that cause a CD shift larger than 10%. This work investigates the limit of optical wafer inspection in EUV lithography, while intending to detect as many printing reticle defects as possible on a EUV mask. The focus is put on reticle defects, because this is the best way to verify the performance of the inspection. Programmed defects on the mask make it possible to verify which of these defects can be detected on wafer, but also which of these mask defects are likely to be missed. Not only programmed defects are included in this study, but also natural defects, because the latter are more typical for those that can be expected in a EUV production process. To do a similar verification on natural defects, the wafer inspection (WI) results are compared to the results of a blank inspection (BI) and a patterned mask inspection (PMI), both performed on a Teron600-series system from KLA-Tencor. On wafer, printable reticle defects end up in the same location in each die exposed on wafer 1. Hence each repeating defect can be attributed to the reticle. Therefore the first goal of this work is to optimize each aspect of wafer inspection that can improve the sensitivity for repeating defects. Reticle layout, wafer layout, inspection tool, inspection recipe and especially wafer stack were all fine-tuned to approach the limit of what optical wafer inspection can do. The signal-to-noise ratio for the defects targeted in this work becomes typically so small, that the optical information from the inspection tool often needs to be complemented by SEM images to conclusively disposition between defects of interest (DOI) and nuisance. However, automated SEM review in itself is also challenged to accurately locate these small defects. Therefore the present work evaluates SEM review in parallel, and more specifically covers the important role that stage accuracy (of both inspection tool and review tool) fulfills in this process. The outcome is a new methodology Metrology, Inspection, and Process Control for Microlithography XXVI, edited by Alexander Starikov, Proc. of SPIE Vol. 8324, 83240L 路 漏 2012 SPIE 路 CCC code: 0277-786X/12/$18 路 doi: 10.1117/12.916979

Proc. of SPIE Vol. 8324 83240L-1 Downloaded from SPIE Digital Library on 10 Apr 2012 to 192.146.1.12. Terms of Use: http://spiedl.org/terms


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