Achromatic unit magnification optical system
US4171871A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jun 30, 1977 |
| Grant date | Oct 23, 1979 |
| Priority date | — |
| Expiry date | Jun 30, 1997 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG03F7/70225
- WIPO fieldOptics
- WIPO sectorInstruments
Abstract
A unit magnification optical system having micron resolution capability over a broad frequency spectrum. A spherical concave mirror is used to provide unit magnification at high numerical aperture with respect to object and image planes which are both located at or in the proximity of the center of curvature of the mirror, or the optical equivalent thereof. A first refractory element optically close to the object and image planes corrects longitudinal chromatic aberration of the principal rays while a second refractory element optically close to the mirror corrects residual longitudinal chromatic aberration of the marginal rays. In the preferred embodiment, a double prism arrangement located between the first refractory element and the center of curvature of the mirror optically reflects the object and image planes to parallel opposed positions having a common axis perpendicular to the axis of the mirror. The system may be used for either step-and-repeat or scanning exposure operations in fabricating microcircuits.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.