Accuracy in CD-SEM metrology

Accuracy in CD-SEM metrology is divided into two discrete categories. The first category is the certification of the measuring tools' (CD-SEMs) magnification behavior. This involves magnification stability, magnification linearity and magnification calibration to a certified reference The second category is the interpretation of physical feature dimensions from their representation in the CD-SEM's digital image. To date, the algorithms used to interpret physical dimensions from CD-SEM images trace their history to image analysis algorithms developed decades ago. This paper evaluates the currently used feature analysis algorithm available in commercial CD-SEMs and compares their behavior to a newer approach developed by Nanometrology. Measurement algorithms must be stable and not contain arbitrary free parameters. In addition, the basis for the construct of the algorithm should be founded on an understanding of e-beam sample interactions and the resulting video signal profiles resulting from this interaction.