| 摘要 |
PURPOSE:To provide an inspecting device which can detect a very small foreign matter, a defect which has been heretofore difficult to be detected at a high S/N ratio. CONSTITUTION:A laser beam 34 which includes two light components in which frequencies are different by DELTAomega and polarizing directions are coincide is generated. It is branched by a half mirror 13, and one is detected by a photoelectric detector 24, and input as a reference light to a sync detector 25. The other is scanned as a laser beam 35 on an inspecting surface 18 by a scanning optical system having a polygonal mirror 15 and an ftheta lens 16. The beam 35 is intensity- modulated by a beat frequency DELTAomega at a scanning spot position on the surface 18 by a light heterodyne interference. Scattered lights 35 scattered by the matter, a defect existing on the surface 18 are detected by a photoelectric detector 22, and input to the detector 25. The detector 25 detects a scattered light signal in synchronization with the frequency DELTAomega of the previous reference light. |
