Patent ID: 7061601

Claim:
A method for measuring defects on a first surface and a second surface of a double-sided object comprising: directing a first light beam in a first plane of incidence toward a first position on the first surface of the object; directing a second light beam in a second plane of incidence toward a second position on the first surface of the object, wherein the angle between the first plane of incidence and the second plane of incidence is not equal to zero; directing a third light beam in a third plane of incidence toward a third position on the second surface of the object; directing a fourth light beam in a fourth plane of incidence toward a fourth position on the second surface of the object, wherein the angle between the third plane of incidence and the fourth plane of incidence is not equal to zero; separating a first surface scattered light intensity into a first scattered light beam and a second scattered light beam, wherein the first surface scattered light intensity comprises light intensity scattered from the first position and the second position; separating a second surface scattered light intensity into a third scattered light beam and a fourth scattered light beam, wherein the second surface scattered light intensity comprises light intensity scattered from the third position and the fourth position; detecting the first scattered light beam; detecting the second scattered light beam; detecting the third scattered light beam; and detecting the fourth scattered light beam.