CCD based confocal filtering for improved accuracy in x-ray proximity alignment
US5452090A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Apr 22, 1994 |
| Grant date | Sep 19, 1995 |
| Priority date | — |
| Expiry date | Apr 22, 2014 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG03F9/7088
- WIPO fieldOptics
- WIPO sectorInstruments
Abstract
In a reverse darkfield (RDF) microlithography alignment system a confocal spatial filtering system discriminates against topographical features other than the alignment mark. A CCD detector array provides flexible confocal filtering via a pixel weighting matched to the optical system. The confocal filtering system employs empirical filter optimization accomplished by correlating stored images with resulting overlays. The empirical optimization of the filter reweights the CCD array and correlates back to measured overlay results. This not only enhances the proven process insensitivity of RDF systems, but combines it with the improved resolution and noise rejection of confocal imaging. Alternatively the means for confocal spatial filtering is comprised of a filter matched to the instantaneous image of an alignment target; for example, a double slit filter matched to the image of a single alignment mark edge.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.