Optical detection system for detecting defects and/or particles on a

Abstract

An optical detection system capable of detecting even small particles or defects on a specimen such as a mask with high sensitivity and being unaffected by diffracted light from the edges of the pattern even when inspecting a thick specimen. The optical detection system includes a light emission means for illuminating a pattern surface on the specimen with light, a first light reception optical system placed on the pattern surface side of the specimen for receiving scattered light emanating from the pattern surface, a second light reception optical system placed on the glass side of the specimen in symmetry with the first light reception optical system relative to the pattern surface for receiving scattered light emanating from the pattern surface through the specimen and a corrective optical element for correcting for differences in the aberration states of the first and second light reception optical systems.