| 摘要 |
PURPOSE:To enable a single mark to be identified as a true one by a method wherein a sign of signal waveform from a mark is identified subject to at least one or requirements for changing the waveform successively in positive, negative and positive, or in negative, positive and negative. CONSTITUTION:A V type groove made in a wafer 14 is scanned with beams 6 in the perpendicular direction i.e. 7. At this time, the reflected electrons 8 received by a reflected electron detector 4 and amplified by an amplifier 3 are mean addition-processed by a wave form memory 2 under control of CPU. Any asymmetrical signal wave formed comprising + part represented by 9, 10 and - part represented by 11 can be made symmetrical by adjusting the balance of reflected electron detector 4. In such a constitution, threshold levels 12, 13 keeping away from zero level are set up so that a mark may be identified by detecting a wave form firstly in + side threshold, secondly in - side and thirdly in + side threshold. |
