Optical Metrology Tool Equipped with Modulated Illumination Sources

An optical metrology tool, comprising:

• a first illumination source configured to generate illumination of a first wavelength;
• at least one additional illumination source configured to generate illumination of an additional wavelength, the additional wavelength different from the first wavelength, the first illumination source and the at least one additional illumination source configured to illuminate a surface of a sample disposed on a sample stage;
• a set of illumination optics configured to direct illumination of the first wavelength and illumination of the at least one additional wavelength from the first illumination source and the at least one additional illumination source to the surface of the sample;
• a set of collection optics;
• a detector configured to detect at least a portion of illumination emanating from a surface of the sample, wherein the set of collection optics is configured to direct illumination emanating from the surface of the sample to the detector;
• a first illumination switching device optically coupled to the first illumination source, wherein the first illumination switching device is configured to control transmitted intensity of the illumination of the first wavelength;
• at least one additional illumination switching device optically coupled to the at least one additional illumination source, wherein the at least one additional illumination switching device is configured to control transmitted intensity of the illumination of the additional wavelength;
• and
• an illumination control system communicatively coupled to the first illumination switching device and the at least one additional switching device, wherein the illumination control system is configured to modulate transmitted intensity of the illumination of the first wavelength and transmitted intensity of the illumination of the additional wavelength by controlling one or more characteristics of the illumination switching device.