Apparatus with four light detectors for checking surface of mask with pellicle
US4889998A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jan 26, 1988 |
| Grant date | Dec 26, 1989 |
| Priority date | — |
| Expiry date | Jan 26, 2008 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01N2021/4721
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
An apparatus for detecting foreign particles on a transparent pellicle comprises a first illuminating device having a first optical axis crossing a surface of the pellicle at a predetermined angle for supplying a light beam onto said transparent pellicle along said first optical axis and a second illuminating device having a second optical axis crossing the surface of said pellicle at an angle different from said predetermined angle for supplying a light beam to said transparent pellicle along said second optical axis. The apparatus further includes a detector for comparing quantity of light of a light beam scattered by a foreign particle and directed to a predetermined direction from said first illuminating device with quantity of light of a light beam scattered by the foreign particle and directed to a predetermined direction from said second illuminating device and for determining a surface of the transparent pellicle on which said foreign particle exists.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.