Method and apparatus for measuring surface distances from a reference plane
US5298976A · kind A · utility
Inventors
Key dates
| Filing date | Nov 16, 1992 |
| Grant date | Mar 29, 1994 |
| Priority date | — |
| Expiry date | Nov 16, 2012 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG03F9/70
- WIPO fieldOptics
- WIPO sectorInstruments
Abstract
A method of measuring the distance of an examined surface from a reference plane, by: (a) directing a parallel beam of radiation along a first optical path in which the parallel beam is focussed as a spot on the examined surface and reflected therefrom; (b) converting the reflected beam to a parallel beam; (c) directing a part of the reflected parallel beam through a second optical path in which the spot is focussed on a surface of a first detector located such that the position of the spot on the first detector includes both drawback errors caused by variations in reflectivity, scattering, and/or interference in the examined surface; and a plane displacement error, representing the distance between the plane of the examined surface and the reference plane; (d) directing another part of the reflected parallel beam through a third optical path in which the spot is focussed on a surface of a second detector located such that the position of the spot on the second detector includes only the drawback errors; (e) and utilizing the outputs of the first and second detectors for providing a measurement of the distance of the examined surface from the reference plane.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.