Method and apparatus for aligning mask and wafer
US3990798A · kind A · utility
16Cited by
5References
10Claims
0Family size
Assignee
Inventor
Key dates
| Filing date | Mar 7, 1975 |
| Grant date | Nov 9, 1976 |
| Priority date | — |
| Expiry date | Mar 7, 1995 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG02B27/40
- WIPO fieldOptics
- WIPO sectorInstruments
Abstract
In a semiconductor photolithographic mask alignment system, a unique bifocus element is included in the microscope for permitting simultaneous focusing on the mask and semiconductor wafer surface, even though the mask and wafer separation is greater than the microscope depth of field. The bifocus element is preferably located at the rear focal plane of the microscope objective and is designed to image, at the same location, light from the mask polarized in a first direction and light from the wafer polarized at right angles to the first direction.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.