Automatic focus detection method, automatic focus detection apparatus, and inspection apparatus
US6091075A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jun 1, 1998 |
| Grant date | Jul 18, 2000 |
| Priority date | — |
| Expiry date | Jun 1, 2018 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01N21/9501
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
An automatic focus detection method comprises the steps of: irradiating onto a single spot of a sample a plurality of beams of illuminating light transmitted and condensed through an objective lens in a symmetrically diagonal manner with respect to an optical axis of the objective lens; branching reflected light from the same spot of the illuminated sample after transmission through the objective lens, in directions of illumination symmetrical with respect to the optical axis so as to obtain a plurality of optical images; and causing a photoelectric conversion device to receive the branched optical images for conversion to an electric signal representing light intensity distribution of the images, whereby a defocus of the sample is detected based on a discrepancy between the optical axis and the center of the light intensity distribution.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.