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Phase Grating Laser Ablation Masks Providing Control of Light Transmission for Different Features within the Mask

IP.com Disclosure Number: IPCOM000117755D
Original Publication Date: 1996-May-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 4 page(s) / 163K

Publishing Venue

IBM

Related People

Dove, D: AUTHOR [+3]

Abstract

Laser ablation is a powerful tool for the formation of penetrations through thin layers of polymers and is of considerable interest as a manufacturing tool in the electronic packaging industry. Typically, a high power excimer laser is allowed to be incident upon a mask that contains a pattern consisting of transparent regions that are imaged upon the surface of a polymer, or other material including metals, and regions that are highly reflective so as to exclude or mask the laser beam. In this way, the pattern of transparent regions of the mask can be transferred to the polymer. If the radiation is of sufficient intensity and duration, the incident radiation ablates away the polymer, or other chosen material, so forming a pattern of cuts or depressions in the form of vias, lines or other shapes.

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This is the abbreviated version, containing approximately 43% of the total text.

Phase Grating Laser Ablation Masks Providing Control of Light Transmission
for Different Features within the Mask

      Laser ablation is a powerful tool for the formation of
penetrations through thin layers of polymers and is of considerable
interest as a manufacturing tool in the electronic packaging
industry.  Typically, a high power excimer laser is allowed to be
incident upon a mask that contains a pattern consisting of
transparent regions that are imaged upon the surface of a polymer, or
other material  including metals, and regions that are highly
reflective so as to exclude  or mask the laser beam.  In this way,
the pattern of transparent regions  of the mask can be transferred to
the polymer.  If the radiation is of  sufficient intensity and
duration, the incident radiation ablates away  the polymer, or other
chosen material, so forming a pattern of cuts or  depressions in the
form of vias, lines or other shapes.  Due to the high  power levels
required, simple metal masks are degraded by the laser and  are not
satisfactory.  Instead, multilayer stack interference filter masks
are employed containing 10 or more layers of alternating high and
low refractive index.  These layers must be highly transparent and
resistant to the uv radiation of the excimer laser.  In addition,
film thickness must be closely controlled to achieve high
reflectivity at the laser wavelength.  The layers are subsequently
etched to provide the  desired transparent regions.

      Recently, a phase grating approach offering great simplicity in
mask fabrication has been disclosed, (1,2).  These masks offer only a
single intensity in the transparent regions so that all features are
ablated to the same level.  The present disclosure describes an
improved grating mask that allows for control of intensity from
feature to feature.

      At the present time, multilayer interconnections are carried
out by a combination of ablation and conventional photoactive polymer
technology.  By use of the single ablation mask with feature related
intensity control it is anticipated that considerable process
simplification may be achieved, leading to the use of ablation as a
replacement for the photoactive polymer process.  By the use of a
single mask, registration is automatically established between
through via and other features.

      In the phase grating mask, exclusion of the laser radiation is
achieved by patterning the mask with an array of closely spaced
features that scatter the beam through an angle large enough that it
escapes capture by the imaging lens.  These features are typically
chosen so that the optical path length through adjacent features
differs by 1/2 wavelength so as to provide efficient scattering and
strong attenuation of the zero order beam.  The thickness difference
required is of the order of only several hundred nanometers and is
easily achieved by deposited film or etching techniques.  The
periodic structure i...