AFM: a valid reference tool?

Wafer surface reconstruction from top–down scanning electron microscope images

“…The line width measurement can vary by as much as 100 nm depending on what edge detection algorithm is used [8,12]. Note that it only gives the line width.…”

Metrology, Inspection, and Process Control in Micro‐Scales

“…For the SEM, an edge appears as an intensity change in the image [3]. Thus, the location of the edge can vary greatly, depending on the image analysis technique used.…”

“…In STM, a metallic probe is brought into close proximity of a conductive surface so that a small current flows between them. The current is held constant by a feedback control scheme, allowing the probe to track the height of the surface [3]. Subangstrom resolution is attainable in the normal direction of the surface, and angstrom-scale resolution is attainable in the lateral direction.…”

<title>Evaluating neural network reconstruction of wafer profile from electron microscopy</title>

“…Unfortunately, a top down CD-SEM image intensity does not corresponds directly to actual surface height. 7 Critical dimension metrology of integrated circuits has historically constituted only single parameter characterization which was intended to be representative of the overall line width. The line width measurement can vary by as much as 100 nm depending on which edge detection algorithm is used.7'8 The limitation of single parameter characterization is that there is no distinction between the scale and the shape of the waveform; that is, both the abnormal and normal profile may have the same line width,9 As the line widths continue to decrease, smaller variations begin to have a significant impact in the overall morphology of the line width.…”