Proceedings Article | 14 October 2011
KEYWORDS: Extreme ultraviolet, Photomasks, Calibration, Scanning electron microscopy, Inspection, Image processing, Defect detection, Computational lithography, Image analysis, Transmission electron microscopy
Many efforts in EUV are currently focused on detecting and reducing defects on blanks and patterned masks. Bumps and
pits found on blank substrates are particularly of concern since these effectively cause phase change and often print
severely under EUV conditions. With the current inspection of EUV blanks and patterned masks being primarily highresolution
DUV or e-beam based, it becomes very challenging to assess the impact of the detected defects. Even with the
realization of EUV AIMSTM, expected in 2014, the nature of the buried multi-layer defect in terms of its location, size,
shape, and profile will always be uncertain.
In this paper, we have demonstrated several techniques that can be used for EUV defect disposition both in short- and
long-term. These techniques include use of SEM images for absorber-defect disposition, and AFM images for
determining the printability of buried defects. In the case of absorber defects, the SEM image of the defect is processed
through a novel contour-extraction algorithm which accurately extracts the contours of the defective and generates the
contour of the reference patterns. The mask contours are then simulated in Luminescent's EUV Defect Printability
Simulator (DPS), a fast and accurate EUV simulator, and the EUV aerial images subsequently analyzed in the Aerial
Image Analyzer (AIA). For buried defects, models characterizing the growth of the multi-layer defect from substrate and
multi-layer to the surface have been developed and can be calibrated in several ways, including using cross-sectional
TEM profiles of buried defects. Using the calibrated buried defect growth model then, and the surface profile of the
buried defect as indicated in the SEM and AFM images, the exact nature of the buried defect is "recovered". Knowing
the profile of the buried pit or bump defect through the multi-layer then allows estimation of its printability impact in
DPS. Furthermore, this also enables computing changes that could be then made to the absorber pattern in order to
compensate for the buried defect printability, i.e., in Luminescent's Multi-layer Defect Compensation (MDC). This
technique of inverting to the shape and height of the buried defect can also be refined later once EUV aerial images are
available.
While defectivity on EUV masks is currently the #1 concern in its high-volume adoption, disposition of the detected
defects to EUV conditions is also very crucial. The proposed disposition techniques using Computation Lithography can
be used in combination with print-tests to make the overall EUV mask defect handling flow manufacturable.
