Defect detection system
US4314763A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jan 4, 1979 |
| Grant date | Feb 9, 1982 |
| Priority date | — |
| Expiry date | Jan 4, 1999 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01N21/9501
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
A laser beam projected through a prism in a direction normal to the surface of a circular wafer is focused into a spot area and scanned along a spiral path on this surface. The focusing means comprises a relatively large aperture lens and the prism is on the lens axis. The retroreflected specular light passes through the lens and is prevented from reaching a light detector in the image plane of the lens by the prism. When the beam illuminates a microscopic surface defect on the wafer, the light is diffracted and reflected therefrom, and the lens captures that portion of the reflected light within the solid angle subtended by the lens, and passes that portion thereof not blocked by the prism, to the light detector. The output of the detector may be employed to intensity modulate the beam of a cathode-ray tube display, the beam of which is spirally scanned in synchronism with the scanning of the light beam.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.