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Etch Stops for Multiple Phase Shift Masks

IP.com Disclosure Number: IPCOM000104965D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 4 page(s) / 111K

Publishing Venue

IBM

Related People

Brunner, TA: AUTHOR [+6]

Abstract

Disclosed are designs and materials for use in multiple phase-shift masks. Phase-shift masks must have layers of dielectric patterned so that the height of different layers is accurate to a percent or so. It is very difficult to etch a large area (5") with features of this accuracy, so etch-stop layers must be used. We propose several schemes using various materials as etch-stop layers for multiple phase-shift masks. Fig. 1 depicts a phase-shift mask where materials 1, 2 and 3 are used on top of a substrate 4 (usually fused silica). For example, material 1 can be SiO&sub2., material 2 can be Al&sub2.O&sub3., and material 3 can be Sc&sub2.O&sub3. which have etch rate ratios of 1000, 20, and 1, respectively, when etched with reactive ion etch (RIE). In addition, Al&sub2.O&sub3.

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Etch Stops for Multiple Phase Shift Masks

      Disclosed are designs and materials for use in multiple
phase-shift masks.  Phase-shift masks must have layers of dielectric
patterned so that the height of different layers is accurate to a
percent or so.  It is very difficult to etch a large area (5") with
features of this accuracy, so etch-stop layers must be used.  We
propose several schemes using various materials as etch-stop layers
for multiple phase-shift masks.  Fig. 1 depicts a phase-shift mask
where materials 1, 2 and 3 are used on top of a substrate 4 (usually
fused silica).  For example, material 1 can be SiO&sub2., material 2
can be Al&sub2.O&sub3., and material 3 can be Sc&sub2.O&sub3.  which
have etch rate ratios of 1000, 20, and 1, respectively, when etched
with reactive ion etch (RIE).  In addition, Al&sub2.O&sub3.  can be
etched in phosphoric acid, which will not etch SiO&sub2.

      Another scheme to use Sc&sub2.O&sub3.  as an etch-stop layer is
depicted in Fig 2.  A thin (10 nm) layer 5 of Sc&sub2.O&sub3.  is
interposed between the SiO&sub2.  layers 1 .  The thin
Sc&sub2.O&sub3.  layer can be etched away by turning up the voltage
in the RIE machine and relying on the physical sputtering to chew
through the thin Sc&sub2.O&sub3.  layer, without the danger of
sputtering all the way through the relatively thick SiO&sub2.  layer
and into the  Sc&sub2.O&sub3.  layer 3.

      Other materials, such as Y&sub2.O&sub3.  and SiN can also be
etched preferentially with respect to SiO&sub2.  These materials are
used in high-power laser mirrors for 248 nm lasers, with total
absorption and scatter of less than 1 percent.

      Fig 3a shows a cross section of the mask structure consisting
of a quartz substrate 4, a first layer 2,for example, of
Al&sub2.O&sub3., that serves both as an etch stop layer and as a
second phase layer, and a further dielectric layer 1, for example, of

SiO&sub2.  that is the primary phase-shift layer The mask has a top
layer of metal 6, typically chrome in the normal way.  In order to
create a phase shift of half wavelength, the chrome layer is removed
by etching, so exposing the phase layer.  The phase layer may then be
etched by a process that terminates on the second phase layer.  This
is...