Automatic focus control method and automatic focus control syste

Details Automatic focus control method and automatic focus control syste Automatic focus control method and automatic focus control syste

1998-06-04

2000-09-05

Le, Que T.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

25055944, G02B 704

Patent

active

061146811

ABSTRACT:
An automatic focus control system comprises an electron beam lens column 1, a device control apparatus 2, and a host computer 3. In the host computer 3, an image processing section 32 and so on are provided. In case of measuring the critical dimension of the patterns in the wafer, after performing the global alignment adjustment, the power spectrum is calculated based on the SEM image of each measuring point in the wafer. After that, in case that the high-frequency component is included more than a prescribed standard value, without performing the automatic focus adjustment, the process for the pattern recognition is performed, and in case that the high-frequency component is included less than the standard value, the process for pattern recognition is performed just before the automatic focus adjustment. Therefore, it is possible to decrease the frequency (times) which performs the process for automatic focus adjustment; as a result, the throughput for measuring is improved.

REFERENCES:
patent: 4045772 (1977-08-01), Bouton et al.

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