PURPOSE: To distinctly detect only the defects of masks and enabling inspecton to be automatically performed by projecting parallel rays toward the inside of the photo mask and detecting the rays irregularly reflecting on the inside surface of a tansparent plate from the angles differing from main optical axis.
CONSTITUTION: Laser rays are radiated from the side face toward the inside of the photo mask 20 on a mask stage. If there are no defects, the parallel rays radiated like Fig. (a) pass the inside of the glass plate 21 without any hindrance, go out from the other end face and no light is detected even when observed from above, thus the entire part of the field of view appears black. On the other hand, if there are any defects 23, the parallel rays radiated toward the glass plate 21 like Fig. (b) irregularly reflect at the portions of the defects 23 and part thereof go upward and therefor when viewed from above only the defect portions emit light in the black background. The presence or not of defects may be judged from the presence or not light, thus automatic inspection becomes easy. Only the defect portions may be lighted, whereby automatic inspection is made possible and the saving of manpower and the improvement of inspection efficiency may be achieved.
AKIBA MASAKUNI
MICHIZAWA SOUICHI
