Method and apparatus for automatically and simultaneously determining best focus and orientation of objects to be measured by broad-band interferometric means

US5784164A · kind A · utility

Assignee

• Zygo Corporation · US

Inventors

• Leslie L. Deck · Middletown, US
• Stephen H. Chakmakjian · Fort Collins, US

Key dates

• Filing date: Mar 20, 1997
• Grant date: Jul 21, 1998
• Expiry date: Mar 20, 2017

Classification

• Technology area (CPC G): Physics
• CPC primary: G01B11/2441
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

A method and improved system for automatically and substantially simultaneously focusing and orienting an interferometric optical system, such as an interferometric microscope (25) illuminated by broad-band light, with regard to a surface under test (66), for providing a best focus and orientation of objects to be measured. The optical system (20, 25, 30, 35, 37, 60, 40) includes a pixel array, such as a sparse array (30) onto which an interferogram is imaged. The pixel array (30) is scanned (20, 25) for detecting a peak fringe contrast for the pixels in the array (30) and the scan position at the detected peak fringe contrast for each pixel int he array (30) is saved (40). At least a portion, if not all, of the saved scan positions are fitted to a surface shape for providing a plane of best focus for the surface under test (66), and the surface under test (66) is automatically positioned (40, 35, 60) relative to the optical system for automatically focusing the object under test (66) across the plane of best focus.