Browse Prior Art Database

Repair System for Phase Shift Masks

IP.com Disclosure Number: IPCOM000104640D
Original Publication Date: 1993-May-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 109K

Publishing Venue

IBM

Related People

Dove, DB: AUTHOR [+2]

Abstract

In order to repair the phase layer of a phase shift mask, it has to be added by either a deposition process, or removed by an etch process, until a desired correction has been made to an optical phase shift within the mask. The problem of determining when a sufficient amount of material has been added or removed, is solved by the disclosed repair system which combines the material deposition or removal method with in situ phase measurement.

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This is the abbreviated version, containing approximately 51% of the total text.

Repair System for Phase Shift Masks

      In order to repair the phase layer of a phase shift mask, it
has to be added by either a deposition process, or removed by an etch
process, until a desired correction has been made to an optical phase
shift within the mask.  The problem of determining when a sufficient
amount of material has been added or removed, is solved by the
disclosed repair system which combines the material deposition or
removal method with in situ phase measurement.

      Lithographic masks are commonly repaired by use of highly
focussed beams of either ions or photons to remove excess material
such as spots of contamination or unwanted metallization, or to fill
in pin holes in the opaque layer.  Typically, removal is carried out
by evaporation, ablation or sputtering, while deposition is achieved
by beam stimulated deposition of material supplied as an organic
compound vapor introduced into the vicinity of the beam.  In the case
of masks containing a phase shift layer, it is necessary to be able
to repair the transparent dielectric phase layer as well as the
opaque mask layer.  Since the phase layer is employed to introduce a
desired optical path length, repair of defective regions of the phase
layer must be carried out to a particular optical thickness value so
as to restore the correct phase shift.  Repair of the phase layer
therefore requires the addition or removal of a critical amount of
material.  The material must also have known refractive index and be
optically transparent at the UV wavelength.  It can also be noted
that restoration of a particular phase shift may be carried out by
either addition or removal since the phase shift is arbitrary to the
extent of the wavelength of the light employed.  Since high accuracy
of phase is required, it is highly desirable to combine the repair
and phase measurement capabilities in one system.

      The phase mask repair system consists of an interferometer
designed for the measurement of mask phase shift at UV wavelengths, a
gas handling arrangement that introduces a desired vapor to the mask
surface at the location of the measurement beam and a second finely
focussed beam coincident on the substrate at the location of one of
the interferometer beams.  The second beam may be of ions, electrons
or photons and is employed for material deposition or removal for
phase repair.  A suitable dual beam interferometer designed for phase
shift mask application is described in [1].  This device is a
modification of an optical profilometer [2].  It is convenient that
the focussed beams form spots on the surface with sub-micron
dimensions and be spaced apart by a distance of several micrometers
or more.

      In one form of the repair system, a dual beam interferometer is
adjusted so that one beam is also used as the material modification
beam.  The intensity of this beam may be much larger than that of the
second beam of the interferometer without affecting...