Patent ID: 6850333

Claim:
A metrology instrument for samples containing grating-like microstructures comprised of a plurality of linear elements thereon, the instrument comprising: an illumination source directing light along an illumination path from the illumination source to the sample, the sample having at least one grating-like microstructure formed thereon, the sample producing a characteristic optical signature when illuminated, an elongated pupil aperture located in the illumination path, an objective focusing the light received from the aperture to the sample, the elongated pupil aperture and objective defining an elongated illumination spot on the sample, the elongated pupil aperture and elongated illumination spot having respective long directions which are perpendicular to each other, the measurement relation of the sample to the instrument being such that the long direction of the illumination spot is oriented generally transverse to linear elements of the microstructure, an optical detector located along a reflection path for detecting the optical signature produced from the illuminated sample.