19 July 1989 Linewidth Edge Detection Algorithm for Coherent Image Profiles
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Abstract
Accurate CD linewidth and overlay measurement are dependent upon the ability to correctly find edges of line objects. Software algorithms used to find edges often have difficulty distinguishing the edges of features to be measured from surrounding noise and coherent edge ringing. The problem becomes even more difficult when an optical scanning microscope operates in a highly coherent mode and enhanced edge ringing and interference effects are present. Simple edge detection algorithms such as thresholding and steepest slope become confused and may select erroneous artifacts. As a result, optical measurement systems have leaned toward high NA illumination systems and broad spectral bandwidth, both of which reduce coherent edge ringing but are accompanied by a loss in accuracy. Alternative techniques such as correlation and adaptive signal processing also have difficulties finding true edges due to the variation in image profiles resulting from changes in materials, layer thickness, edge slope, etc. This paper describes an alternative approach based on a combination of mean-square integration (MSI) and adaptive techniques with function parameters determined from the digitized waveform. This approach has been successfully utilized on experimental data and appears to work for a wide variety of signal waveforms. Theoretical and experimental results are given.
© (1989) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Diana Nyyssonen, Bob Monteverde, "Linewidth Edge Detection Algorithm for Coherent Image Profiles", Proc. SPIE 1087, Integrated Circuit Metrology, Inspection, and Process Control III, (19 July 1989); doi: 10.1117/12.953088; https://doi.org/10.1117/12.953088
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