Browse Prior Art Database

Extremely Precise Characterization of Lenses

IP.com Disclosure Number: IPCOM000116713D
Original Publication Date: 1995-Oct-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 4 page(s) / 93K

Publishing Venue

IBM

Related People

Wagner, D: AUTHOR

Abstract

Disclosed is an interferometric testing method for lenses which allows the economic production of lenses used in steppers for the 256 Mbit chip lithography. The testing method provides a sensitivity of about 10(-7) of the zonal focal length, that is 1 pm along 1 cm of zonal length of a lens with 1 m focal length, and is substantially insensitive to environmental influences or systematic defects.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Extremely Precise Characterization of Lenses

      Disclosed is an interferometric testing method for lenses which
allows the economic production of lenses used in steppers for the 256
Mbit chip lithography.  The testing method provides a sensitivity of
about 10(-7)  of the zonal focal length, that is 1 pm along 1 cm of
zonal length of a lens with 1 m focal length, and is substantially
insensitive to environmental influences or systematic defects.

      A parallel light beam is focussed in the focal plane of a lens.
When using an aperture and positioning a mirror rotated by an angle
&alpha.  in the focal plane then the reflected beam leaves the lens
under the same angle as the incident beam.  The rotation of the
mirror by an angle &beta.  at point M as shown in Fig.1 may be split
into a translation T and a rotation.  After the lens the reflected
beam has the same direction as the incident beam.  The translation T
however caused a phase shift P which shall be measured.  The phase
shift P depends on the zonal focal length and the angle &beta.  and
by measuring &beta.  and the phase shift P the zonal focal length may
be calculated.  To measure the phase shift P, a reference beam is
provided by a beamsplitter in the beam's way to the lens and after
passing the beamsplitter both the measuring beam and the reference
beam are combined for interference.

      Fig. 2 shows an arrangement with two identical interferometers.
Measuring beam and reference beam of both the interferometers are on
the same mirror and reference beam, middle of the lens, middle of the
reference lens and point M are all situated along a straight line.

      To investigate the accurateness of the proposed arrangement the
following influences and defects have to be considered:  wave-length
stability of the laser, environmental influences and systematic
defects.  As to the wave-length stability of the laser, a HeNe laser
with a frequence stability of about 10(-8)  seems suitable.

      The environment mechanically influences the proposed
arrangement by vibrations...