High-speed, high-resolution, large area inspection using multiple optical fourier transform cells
US5966212A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jul 18, 1996 |
| Grant date | Oct 12, 1999 |
| Priority date | — |
| Expiry date | Jul 18, 2016 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01N21/95623
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
A system includes multiple optical Fourier transform cells which simultaneously scan a device under test. The illuminated area for each Fourier transform cell is small to provide high resolution, while the number of cells is large to cover a relatively wide area and keep inspection speed high. The advantages of optical computing performed by Fourier transform optics also keeps the inspection speed high because illuminated areas are large when compared to the resolution and Fourier transforms are linear shift invariant so that optical measurements can be performed during scanning. In one embodiment, Fourier transform cells are offset from each other perpendicular to the scan direction by less that the width of an illuminated area. This provides complete coverage during scanning of a device under test. Because the illumination for the Fourier transform is collimated, the system is insensitive to focusing errors due to fluctuations in working distance.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.