Patent ID: 7602482

Claim:
An optical inspection method comprising the steps of: providing a movable stage for an object to be inspected, capable of rotational movement for main scanning and translational movement for auxiliary scanning, and adapted to be substantially continuously displaced in both main scanning direction and auxiliary direction, a laser light source, an illumination means for irradiating a laser beam emitted from the laser light source, onto the outer surface of an object to be inspected in the form of an illumination spot having a predetermined size, a scattered/diffracted/reflected light detecting means for detecting light scattered, diffracted and reflected in the illumination spot of the irradiated beam, and converting the detected light into electric signals, an A/D converting means for converting the electric signals into digital data, an inspection coordinate detecting means for detecting a position on the outer surface of the object to be inspected at a time corresponding to the converted digital data, as inspection coordinate data, during inspection, an object/defect determination means for determining the presence of a foreign matter or a defect which is present on the outer surface of the object to be inspected or in the vicinity of the outer surface thereof, from the electric signal or the digital data, a particle size determining means for calculating the size of the thus determined foreign matter or defect, from the digital data, a foreign matter/defect coordinate calculating means for calculating a position coordinate value of the foreign matter or the defect on the outer surface of the object to be detected, from information delivered from the inspection coordinate detecting means; and detecting a foreign matter or a defect which is present on or in the vicinity of the outer surface of the object to be inspected by moving and scanning the object to be inspected at a linear speed which is different between the inner peripheral part and the outer peripheral part of the object to be inspected; wherein said detecting step includes a step of controlling the light quantity of the laser light source so as to change the intensity of the light spot between the inner peripheral part and the outer peripheral part of the object to be inspected.