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Browse Prior Art Database

Laser Output Coupler to Increase Laser Etching Efficiency

IP.com Disclosure Number: IPCOM000112073D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 72K

Publishing Venue

IBM

Related People

Ehrenberg, SG: AUTHOR [+2]

Abstract

Disclosed is a method to increase etching efficiency of excimer lasers when masks are used. Conventional laser etching of polymer or metal uses a contact mask or a projection mask to define a pattern. In each case, the fraction of the light of the nearly uniform laser beam not needed is thrown away by reflection or by absorption in the mask. Conventional masks can not be used for high power lasers since the heating and high power destroy or distort the masks, and multilayer dielectric masks with the dielectric coating etched away must be used.

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Laser Output Coupler to Increase Laser Etching Efficiency

      Disclosed is a method to increase etching efficiency of excimer
lasers when masks are used.  Conventional laser etching of polymer or
metal uses a contact mask or a projection mask to define a pattern.
In each case, the fraction of the light of the nearly uniform laser
beam not needed is thrown away by reflection or by absorption in the
mask.  Conventional masks can not be used for high power lasers since
the heating and high power destroy or distort the masks, and
multilayer dielectric masks with the dielectric coating etched away
must be used.

      Many patterns to be etched are in the form of a uniform array
of spots.  For example, the via holes used in packages have diameters
in the rant 50 to 150 microns, and the via positions are constrained
to lie on a grid with center to center spacing of from 100 to 300
microns.  Not every grid position needs to be etched, however.

      Proposed is the use of output couplers for high gain excimer
lasers which have high reflectivity coatings with a matching array of
holes etched in the coating.  The near field pattern of the laser
will then form an array of spots when the output coupler is imaged on
the workpiece.  For a mirror with holes or diameter D on a grid of
dimension 2D, the average reflectivity of the mirror will be 80.4%
The Figure shows the configuration of the laser and the output
coupler.  The excimer laser amplification medium 1 is lined up with
the long axis perpendicular to the high reflectivity mirror 2 and the
output coupler 3.  The light exiting through the holes in the coupler
3 is focussed by lens 4 on the part 5.  The laser light which escapes
the holes in the output coupler is shown by the sketched lines 6.  As
long as the distance between the two laser mirro...