Patent ID: 7839506

Claim:
An inspection apparatus configured to measure a property of a substrate, the inspection apparatus comprising: a light source configured to supply a radiation beam; an optical element configured to focus the radiation beam onto a surface of the substrate; a beamsplitter configured to separate the radiation beam once reflected from the surface of the substrate into first and second orthogonally polarized sub-beams; a first polarizing beamsplitter configured to split the first sub-beam into two sub-sub-beams with about 0 and 90 degree polarization respectively; a second polarizing beamsplitter rotated by about 45 degrees with respect to the first polarizing beamsplitter and configured to split the second sub-beam into two sub-sub-beams with about 45 and 135 degree polarization respectively; and a detector system configured to detect simultaneously an angle-resolved spectrum of all four sub-sub-beams reflected from the surface of the substrate.