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17 October 2014 On the benefit of high resolution and low aberrations for in-die mask registration metrology
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With the introduction of complex lithography schemes like double and multi – patterning and new design principles like gridded designs with cut masks the requirements for mask to mask overlay have increased dramatically. Still, there are some good news too for the mask industry since more mask are needed and qualified. Although always confronted with throughput demands, latest writing tool developments are able to keep pace with ever increasing pattern placement specs not only for global signatures but for in-die features within the active area. Placement specs less than 3nm (max. 3 Sigma) are expected and needed in all cases in order to keep the mask contribution to the overall overlay budget at an accepted level. The qualification of these masks relies on high precision metrology tools which have to fulfill stringent metrology as well as resolution constrains at the same time. Furthermore, multi-patterning and gridded designs with pinhole type cut masks are drivers for a paradigm shift in registration metrology from classical registration crosses to in-die registration metrology on production features. These requirements result in several challenges for registration metrology tools. The resolution of the system must be sufficiently high to resolve small production features. At the same time tighter repeatability is required. Furthermore, tool induced shift (TIS) limit the accuracy of in-die measurements. This paper discusses and demonstrates the importance of low illumination wavelength together with low aberrations for best contrast imaging for in-die registration metrology. Typical effects like tool induced shift are analyzed and evaluated using the ZEISS PROVE® registration metrology tool. Additionally, we will address performance gains when going to higher resolution. The direct impact on repeatability for small features by registration measurements will be discussed as well.
© (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Dirk Beyer, Dirk Seidel, Sven Heisig, Steffen Steinert, Susanne Töpfer, Thomas Scherübl, and Jochen Hetzler "On the benefit of high resolution and low aberrations for in-die mask registration metrology", Proc. SPIE 9235, Photomask Technology 2014, 92351S (17 October 2014);

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