Patent ID: 6956644

Claim:
A method for detecting an anomaly on a top surface of a substrate, or within the substrate, comprising: directing a first radiation beam having a first ultraviolet or deep ultraviolet wavelength to illuminate a first spot on the top surface of the substrate at a first non-zero angle measured from a normal direction to the top surface; directing a second radiation beam having a second wavelength to illuminate a second spot on the top surface of the substrate at a second angle measured from a normal direction to the top surface, wherein the second wavelength is greater than the first wavelength, so that radiation from the second beam penetrates the surface of the substrate by a distance greater than that by radiation from the first beam; causing relative motion between the first and second radiation beams and the top surface of the substrate so that the spots scan paths on the top surface; detecting radiation from the first radiation beam scattered by the top surface in the first spot to provide a single output corresponding to a position of the first spot on the top surface; detecting radiation from the second radiation beam scattered by the top surface in the second spot to provide a single output corresponding to a position of the second spot on the top surface; and generating from the outputs first data set(s) containing only data on anomalies at or substantially at the surface of the substrate and second data set(s) containing data on anomalies away from the surface of the substrate, so that anomalies at or substantially at the surface of the substrate are detectable independently from anomalies away from the surface of the substrate from the data sets.