| 摘要 |
PURPOSE:To avoid to judge like presence of a defective pattern though actually not existed by producing two independent electric signals by the displacement of two photoelectric signals from two pattern inspection lens systems and comparing in the duration the one signal with the other. CONSTITUTION:A set of two patterns formed on a photomask are detected by two photoelectric converters 20 and 22, and two detected electric signals from the converters are applied to a signal difference detector 26 of a differential amplifier. The difference signal from the detector 26 is applied, on one hand, to monostable multivibrators 28a, 28b and, on the other hand, through an inverter 30 to monostable multivibrators 32a, 32b. The outputs from the multivibrators 28a, 28b are applied through a flip-flop 34 to an AND gate 40, while the outputs from the multivibrators 32a, 32b are applied through a flip-flop 36 to an AND gate 42. A reference pulse oscillator 38 is provided between the detector 26 and the gates 40 and 42 at the connecting point. Both the gates 40 and 42 compares the outputs from the flip- flops 34 and 36 with the output from the oscillator 38 and apply outputs through counters 44 and 46, respectively to a digital comparator 48. In this manner, the com parator 48 compares the two patterns to judge whether there is a defect or not. |
