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Photomask Dimensional Metrology in the SEM: Has Anything Really Changed?



Michael T. Postek, Andras Vladar, Marylyn H. Bennett


Photomask dimensional metrology in the scanning electron microscope (SEM) has not evolved as rapidly as the metrology of resists and integrated circuit features on wafers. This has been due partly to the 4x (or 5x) reduction in the optical steppers and scanners used in the lithography process, and partly to the lesser need to account for the real three-dimensionality of the mask structures. So, where photomasks are concerned, many of the issues challenging wafer dimensional metrology at 1x are reduced by a factor of 4 or 5 and thus could be temporarily swept aside. With the introduction of advanced masks with optical proximity correction and phase shifting features used in 100 nm and smaller circuit generations, that is rapidly changing. Fortunately, photomask metrology generally benefits from the advances made for wafer metrology, but there are still unique issues to be solved in this form of dimensional metrology. It is likely that no single metrology method or tool will ever provide all necessary answers. As with other types of metrology, resolution, sensitivity and linearity in the three-dimensional measurments of the shape of the lines and phase shifting features in general (width, Height and wall angles) and the deparatures from the desired shape (surface and edge roughness, etc.) are the key parameters. Different methods and tools differ in their ability to collect averaged and localized signals with an acceptable speed, but in any case, application of thorough knowledge of the physics of the given metrology is essential to extract the needed information. This paper will discuss the topics of precision, accuracy and traceability in the SEM metrology of photomasks. Current and possible new techniques utilized in the measurements of photomasks including charge suppression and highly accurate modeling for electron beam metrology will also be explored to answer the question Has anything really changed?
Proceedings Title
Proceedings of SPIE, 22nd Annual BACUS Symposium on Photomask Technology, Brian J. Grenon, Kurt R. Kimmel, Editors
Pt. 1
Conference Dates
September 30-October 4, 2002
Conference Location
Monterey, CA
Conference Title
Mask Metrology


charging, critical dimension, metrology, photomask, scanning electron microscope, SEM


Postek, M. , Vladar, A. and Bennett, M. (2002), Photomask Dimensional Metrology in the SEM: Has Anything Really Changed?, Proceedings of SPIE, 22nd Annual BACUS Symposium on Photomask Technology, Brian J. Grenon, Kurt R. Kimmel, Editors, Monterey, CA (Accessed June 22, 2024)


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Created December 1, 2002, Updated February 19, 2017