Patent ID: 7586623

Claim:
A system for illuminating a single feature formed on a wafer, the system comprising: a source configured to generate a beam of light, the source having a first pupil stop with a first pupil hole that is de-centered with respect to the first pupil stop, wherein the first pupil stop has an effective numerical aperture greater than the wavelength of the light used divided by twice the distance between the single feature and an adjacent feature; a detector having a second pupil stop with a second pupil hole that is de-centered with respect to the second pupil stop, wherein the second pupil stop has an effective numerical aperture greater than the wavelength of the light used divided by twice the distance between the single feature and an adjacent feature; a focusing lens; and a beam splitter disposed adjacent to the focusing lens, wherein the beam of light generated by the source is focused on the single feature through the beam splitter and the focusing lens, and diffracted beams of light from the single feature are received in the detector through the focusing lens and the beam splitter.