High-accuracy high-stability method and apparatus for measuring distance from surface to reference plane

US6124934A · kind A · utility

Inventors

• Arie Shahar · Afula, IL
• Richard W. Woods · Catonsville, US
• Nira Schwartz · Yehud Monosson, IL

Key dates

• Filing date: Jan 8, 1999
• Grant date: Sep 26, 2000
• Expiry date: Jan 8, 2019

Classification

• Technology area (CPC G): Physics
• CPC primary: G01S17/08
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

A system for measuring the distance of an examined surface from a reference plane includes two detectors and a radiation source for directing a beam along a path which includes a first focussing lens for focussing the beam as a spot on the surface and reflecting it. A collecting lens converts the reflected radiation to a reflected beam. A splitter directs part of the reflected beam through a second path which includes a second focussing lens for focussing part of the reflected beam onto a surface of the first detector. Its position on the first detector corresponds to the distance of the examined surface under the spot from the reference plane, according to by a first equation with two terms: a first drawback error and a first surface displacement. The other part of the reflected beam propagates through a splitter and along a third path which includes a third focussing lens for focussing the other part of the reflected beam onto a second spot on a surface of the second detector. Its position on the second detector corresponds to the distance of the examined surface from the reference plane according to a second equation with two terms: a second drawback error and a second surface d…