| 摘要 |
PURPOSE:To detect the defects of repetitive patterns at a constant speed with high reliability by delaying the signal of the quantity of transmitted light through the repetitive patterns by the time corresponding to the repetitive pitches of the patterns and determining the difference between this and the signal of the quantity of light of this time. CONSTITUTION:An object 24 of repetitive patterns like, for example, checkered patterns, disposed on a stage 23 is irradiated with the scanning light 22 from a light source 1, and the signal TL of the quantity of transmitted light is obtained. The signal TLA past an amplifier 27 is delayed by the preset prescribed time (as much as integer times the repetitive pitches of the patterns of the object 24) in a delay circuit 29 to the signal TLB. The difference DS between the two signals TLA and TLB is obtained with a differential amplifier 28, and this is inputted together with a stage position signal ST into an arithmetic circuit by which the defect parts of the patterns are specified. |
