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Illumination System for Excimer Laser and Annular Pupil

IP.com Disclosure Number: IPCOM000104532D
Original Publication Date: 1993-Apr-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 1 page(s) / 49K

Publishing Venue

IBM

Related People

Goodman, DS: AUTHOR

Abstract

Schwarzschild objectives are commonly used in excimer laser repair tools since they are simple and achromatic, which simplifies the problem of viewing at a wavelength different from that at which the process is done. However, these objectives have annular pupils, which complicate the problem of illumination. For the best imaging in many repair applications, the angular distribution should be uniform over an annulus. In addition, the illumination should be uniform over the object plane. Excimer beams are rectangular and their divergences are not isotropic, so there is a problem in efficiently using the excimer light. Geometrically, the problem is that of converting a rectangular beam into an annular one. An efficient means of so doing is described.

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Illumination System for Excimer Laser and Annular Pupil

      Schwarzschild objectives are commonly used in excimer laser
repair tools since they are simple and achromatic, which simplifies
the problem of viewing at a wavelength different from that at which
the process is done.  However, these objectives have annular pupils,
which complicate the problem of illumination.  For the best imaging
in many repair applications, the angular distribution should be
uniform over an annulus.  In addition, the illumination should be
uniform over the object plane.  Excimer beams are rectangular and
their divergences are not isotropic, so there is a problem in
efficiently using the excimer light.  Geometrically, the problem is
that of converting a rectangular beam into an annular one.  An
efficient means of so doing is described.

      The beam is first elongated by an anamorphic telescope.  Since
excimers have a greater divergence in the direction of the greatest
beam width, this elongation also tends to equalize the divergences.
The beam is next reflected from a curved mirror, resulting in a beam
shape that is roughly half of an annulus.  To obtain a complete
annulus, this beam is directed toward a beamsplitter, where half of
the light passes through, while the other half is reflected,
producing a second half annulus that is inverted relative to the
other.  Next, the two beams are made parallel by two prisms, which
also bring the two half annuli together.  Following th...