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Self-Scanning Differential Interferometer for Surface Measurement Applications

IP.com Disclosure Number: IPCOM000111418D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 41K

Publishing Venue

IBM

Related People

Makosch, G: AUTHOR

Abstract

In a scanning differential interferometer like (LASSI), usually the object of measurement is moved on a translation stage under the two sensing laser beams focused simultaneously on the object surface. The phase difference of the two beams reflected from the surface, varying in accordance with the surface profile, is measured by an appropriate phase monitor.

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Self-Scanning Differential Interferometer for Surface Measurement
Applications

      In a scanning differential interferometer like (LASSI), usually
the object of measurement is moved on a translation stage under the
two sensing laser beams focused simultaneously on the object surface.
The phase difference of the two beams reflected from the surface,
varying in accordance with the surface profile, is measured by an
appropriate phase monitor.

      A novel differential interferometer is proposed which is
equipped with an internal scanning mechanism by which the surface
profile can be measured without moving the object but by scanning the
two laser beams internally across the object surface.  This is
accomplished by a tiltable glass plate controlled by a galvanometric
scanner, which is implemented in a telecentric interferometer
assembly according to the Figure.  In this arrangement, the two beams
reflected on the object, which are then recombined by a Wollaston
prism, remain stationary in front of the phase detector independent
of the amount of beam deflection by the glass plate.  Besides
improvements of the measurement precision and speed, the advantages
of this technique are generally seen for applications demanding short
scanning lengths, e.g., roughness measurement and step measurement of
phase-shifting masks.  The proposed technique represents a very
compact and cheap solution that can be easily implemented in other
existing differential interferometers.