Patent ID: 7304735

Claim:
An optical metrology tool for evaluating a sample, comprising: a broadband light source for generating a polychromatic probe beam; illuminating optics for directing the probe beam to illuminate a spot on the sample; collection optics for collecting the probe beam light reflected from the sample; a spectrometer for monitoring the intensity of the collected probe beam light as a function of wavelength and generating output signals in response thereto; a processor for evaluating the sample based on the output signals; and a wavelength selective filter arrangement located in one of the illumination and collection paths prior to the spectrometer, said filter arrangement including; a dispersive optical element to angularly disperse the probe beam as a function of wavelength; and a selective optical filter positioned to receive the angularly dispersed probe beam and selectively partially attenuate one or more wavelengths in the beam in order to partially reduce the intensity thereof so that the intensity of the spectrum received by the spectrometer is more uniform.