Patent ID: 7218392

Claim:
A method for detecting an anomaly only on a top surface of a substrate, comprising: directing a first ultraviolet radiation beam at the top surface of the substrate at a first angle measured from the normal direction to the top surface to illuminate a first spot on the top surface; directing a second ultraviolet radiation beam at the top surface of the substrate at a second angle measured from the normal direction to the top surface to illuminate a second spot on the top surface, wherein said first and second ultraviolet radiation beams contain radiation components of different ultraviolet wavelengths; detecting ultraviolet radiation from the first ultraviolet radiation beam scattered by the top surface of the substrate; detecting ultraviolet radiation from the second ultraviolet radiation beam scattered by the top surface of the substrate; and causing relative motion between the first and second radiation beams and the surface of the substrate so that the beams scan paths on the surface to detect said anomaly on different parts of the top surface.