Patent ID: 8559008

Claim:
An ellipsometer comprising: a source that emits radiation; a polarization state generator for polarizing the radiation to produce a sample beam that is incident on and reflected by a sample; a polarization state analyzer positioned to receive reflected radiation from the sample; a detector positioned to receive the reflected radiation after the reflected radiation passes through the polarization state analyzer; and a focusing system positioned to receive a portion of the reflected radiation, the focusing system comprising: a beam splitter in a beam path between the sample and the detector, the beam splitter positioned to receive the reflected radiation and to provide the portion of the reflected radiation to the focusing system; a compensator positioned in the beam path between the beam splitter and the detector, the compensator correcting optical aberrations in the reflected radiation caused by the beam splitter; a lens system that receives the portion of the reflected radiation, the lens system magnifies by at least 2× any deviation from a best focus position of the ellipsometer; and a camera positioned to receive the portion of the reflected radiation from the lens system.