Speckle reduction track filter apparatus for optical inspection of patterned substrates
US5264912A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Feb 7, 1992 |
| Grant date | Nov 23, 1993 |
| Priority date | — |
| Expiry date | Feb 7, 2012 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01N21/9501
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
An apparatus used to inspect patterned wafers and other substrates with periodic features for the presence of particles, defects and other aperiodic features in which a spatial filter placed in the Fourier plane is used in combination with either broadband illumination, angularly diverse illumination or both. In contrast to prior devices that direct light from a single monochromatic source through a pinhole aperture stop, embodiments are describes that illuminate a patterned substrate using (1) a single monochromatic source with a slit-shaped aperture stop for angularly diverse illumination, (2) a single broadband source with a pinhole aperture stop for broadband illumination, (3) a single broadband source with a slit-shaped aperture stop for both broadband and angularly diverse illumination, or (4) multiple sources with an aperture stop for each source for at least angularly diverse illumination. The spatial filters for these illumination systems are characterized by opaque tracks in an otherwise transmissive filter for blocking the elongated bands produced by diffraction from the periodic features on the illuminates substrate. The filter may be made photographically by exposing h…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.