Flatness & Nanotopography -- Measurement

Nanotopography is measured by two techniques: light scattering and interferometery. Light scattering tools typically employed for particle and surface-defect characterization can be used to measure the local slope change over the entire surface of the wafer. The local slope change may be integrated to yield height or topography information. Since the beam size can be on the order of fractions of a micron, nanotopography can be measured. Optical interference measurement is straightforward: a beam is split into two components; one component is reflected from the wafer surface, while the second is reflected from a reference mirror; the interference of the combination of the two beams is a measure of the topology of the wafer surface. With both techniques signal filtering is used to separate the low-wavelength features (e.g. warp) so that only the high-wavelength/low-frequency information, i.e. the true surface nanotopography is measured.

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