| 摘要 |
PURPOSE:To detect the existence and non-existence of a foreign material on inspection surface by detecting a beam for optical scan with a detection means, and modulating the optical intensity of a beam from a light source in synchronization with the optical beam scan at the time of inspecting surface state, using a signal from the detection means. CONSTITUTION:In a beam scan system (scan system) for scanning the surface of a substrate such as a reticule or the like with a beam (laser beam), a beat signal is obtained from sideward scattered light from a foreign substance, using heterodyne interference. In this case, the light intensity of a beam from a light source means is modulated, synchronized with a scanning process, for detecting the existence or non-existence of the prescribed size of a foreign substance with high accuracy. Thereafter, frequency shifters 41 to 43 modulate the light intensity of an incident beam during the scan thereof, and thereby act to correct the positional unevenness of detection sensitivity. This modulation is implemented through the adjustment of voltage applied from drivers 40 to 42, to the frequency shifter 41 or 43. |
