Metrology device normalization channel

Abstract

Optical metrology is performed using a light source and a normalization channel. A portion of the light is directed to the normalization channel, which detects the intensity of the light while measurements are acquired from the light reflected from a sample. The measurements are normalized based on the detected intensity of the light in the normalization channel. The light detected in the normalization channel may be synchronized with the measurements. Moreover, the acquisition of the intensity of the light in the normalization channel may be aligned with the measurements. The normalization channel measurements may be a single total intensity value that is applied to all wavelengths in the measurements, or may be a function of wavelength that is applied to the corresponding wavelengths in the spectral measurements.

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