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Method for the Fabrication of a Micro-Lithography Mask Incorporating Phase Shifting and Light Absorption Regions

IP.com Disclosure Number: IPCOM000104556D
Original Publication Date: 1993-May-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 4 page(s) / 84K

Publishing Venue

IBM

Related People

Dove, DB: AUTHOR [+2]

Abstract

There is great interest in carrying out micro-lithographic patterning to higher and higher resolution, in order to be able to pack electronic circuits to increasingly higher density. However, the resolution attainable using an optical photoresist system is limited by the numerical aperture of the lens imaging system and the wavelength of the exposing radiation, as is well known.

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Method for the Fabrication of a Micro-Lithography Mask Incorporating Phase Shifting and Light Absorption Regions

      There is great interest in carrying out micro-lithographic
patterning to higher and higher resolution, in order to be able to
pack electronic circuits to increasingly higher density.  However,
the resolution attainable using an optical photoresist system is
limited by the numerical aperture of the lens imaging system and the
wavelength of the exposing radiation, as is well known.

      A phase-shift mask approach, first disclosed in [*]  and later
explored by other workers, employs an optical exposure mask having
regions featured to provide a phase shift in the exposing wave in
such a way that destructive interference occurs at edges of regions
to be defined, thus providing increased sharpness of exposed edges of
photoresist.  The phase shift is produced by ensuring an optical path
length difference one half wavelength between closely spaced regions
of the mask.

      In this disclosure we reveal a novel method that provides a
means for the fabrication of a phase mask of the so-called rim type,
utilizing a resist-swelling technique.  This approach has the
advantage of automatic alignment of the phase-shift regions of the
mask.  Also, means is obtained for control of the width of rim to be
provided.   The steps required to prepare a phase mask with a narrow
region of material of modified optical properties adjacent to the
edges of transparent regions of a metal mask are as follows:

1.  A phase-retarding layer is first deposited upon the quartz mask
    substrate using sputtering or other thin film deposition methods.
    This layer may be of aluminum oxide or other material that is
    transparent to the ultraviolet radiation that is to be
    transmitted through  the mask.  The thickness of this layer is
    such that the optical path length through the layer is one-half
    wavelength different from the path length through the air.

2.  The metal mask is deposited upon the phase-shift layer and is
    patterned by...