Spatial filter for optically based defect inspection system
US5172000A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Nov 2, 1990 |
| Grant date | Dec 15, 1992 |
| Priority date | — |
| Expiry date | Nov 2, 2010 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG02B27/46
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
In an imaging system (10) for detecting defects in a specimen (14) having a repetitive pattern (16), a spatial filter (50) receives a spatial frequency spectrum produced by a Fourier transform lens (34) and blocks preselected spatial frequency components thereof. The spatial filter includes an array of substantially parallel opaque stripes (70a-70c) that are positioned on a substantially transparent substrate (72). In one embodiment, the stripes are spaced apart by equal distances (78) and are of increasing widths (76a-76c) that correspond to the orders of diffraction of the Fourier transform pattern (45) produced by the Fourier transform lens. The spatial filter can be used to filter light spots forming a Fourier transform pattern for specimens having repetitive pattern sizes included within a specified range of sizes.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.