Patent ID: 7123357

Claim:
A method for measuring a defect on a surface of an object, comprising: directing a first light beam in a first plane of incidence toward a first position on the object; directing a second light beam in a second plane of incidence toward a second position on the object; directing a third light beam in a third plane of incidence toward a third position on the object; directing a fourth light beam in a fourth plane of incidence toward a fourth position on the object, wherein the angle between the planes of incidence of any two beams is not equal to zero; detecting a first scattered light intensity, wherein the first scattered light intensity comprises light intensity scattered from the first position; detecting a second scattered light intensity, wherein the second scattered light intensity comprises light intensity scattered from the second position; detecting a third scattered light intensity, wherein the third scattered light intensity comprises light intensity scattered from the third position; detecting a fourth scattered light intensity, wherein the fourth scattered light intensity comprises light intensity scattered from the fourth position; comparing the first scattered light intensity and the second scattered light intensity to determine a first aspect ratio of a defect on the surface of the object; comparing the third scattered light intensity and the fourth scattered light intensity to determine a second aspect ratio of a defect on the surface of the object; and calculating a combined aspect ratio of a defect on the surface of the object based on the first aspect ratio and the second aspect ratio.