Adaptive spatial filter for surface inspection
US5276498A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | May 12, 1992 |
| Grant date | Jan 4, 1994 |
| Priority date | — |
| Expiry date | May 12, 2012 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01N2201/067
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
An inspection apparatus for a light diffracting surface employs a planar array of individually addressable light valves for use as a spatial filter in an imaged Fourier plane of a diffraction pattern, with valves having a stripe geometry corresponding to positions of members of the diffraction pattern, blocking light from those members. The remaining valve stripes, i.e. those not blocking light from diffraction order members, are open for transmission of light. Light directed onto the surface, such as a semiconductor wafer, forms elongated curved diffraction orders from repetitive patterns of circuit features. The curved diffraction orders are transformed to linear orders by a Fourier transform lens. The linear diffraction orders from repetitive patterns of circuit features are blocked, while light from non-repetitive features, such as dirt particles or defects is allowed to pass through the light valves to a detector. Patterns of stripes can be recorded corresponding to the repetitive features of different integrated circuits. Different filters may be rapidly switched electronically in synchronization with a beam scanning a patterned surface inspecting different light diffracting …
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.