Focusing technique suitable for use with an unpatterned specular substrate
US5266790A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Dec 21, 1992 |
| Grant date | Nov 30, 1993 |
| Priority date | — |
| Expiry date | Dec 21, 2012 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG03F9/7049
- WIPO fieldOptics
- WIPO sectorInstruments
Abstract
A microlithographic stepper, employing a Half-Field Dyson projection optical system, achieves focusing of an image of a first-layer reticle pattern on a completely unpatterned reflective wafer surface by including a repetitive diffraction pattern on the reticle which has a configuration in which a particular ordinal diffraction order is normally missing. In response to being simultaneously illuminated with each of two incident monochromatic beams of light, diffraction orders generated by the repetitive diffraction pattern are imaged on the reflective wafer surface and then reflected back to and reimaged on the repetitive diffraction pattern on the reticle. Diffraction orders generated on the first encounter with the repetitive diffraction pattern generate light in the originally missing ordinal diffraction order on the second encounter. If more than one diffraction order from the first encounter contribute toward generating this missing-order light, then the light intensity of the originally missing order will depend on focus position of the wafer. Best focus will generate either maximum or minimum light intensity of the originally missing order. Using a single wavelength, a single…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.