Apparatus for measuring position of an X-Y stage
US5552888A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Dec 2, 1994 |
| Grant date | Sep 3, 1996 |
| Priority date | — |
| Expiry date | Dec 2, 2014 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG03F9/70
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
An interferometer used to measure distance to an object is provided with a laser sheath. The sheath encloses a substantial part of the measurement beam's path to provide a controlled environment which reduces environmental influences on the measured distance. The sheath is of variable length and responsive to a follower so as to maintain a sheath end nearest the object at a small distance from the object. An environmental controller controls the environment within the sheath. The environment within the sheath can be a vacuum or a suitable gas or gas mixture. A corrector can be used to compensate the interferometer's measured-distance signal for detected environmental characteristics to produce a corrected signal which indicates distance between the interferometer and the reflective surface. The apparatus and methods can be used to measure and control stage position in a projection-type wafer exposure system which is affected by variations in its atmospheric environment.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.