Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
1999-12-16
2002-08-06
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S323000
Reexamination Certificate
active
06428936
ABSTRACT:
FIELD OF INVENTION
The field of invention relates to lithography in general and, more specifically, to the manufacturing of phase shift masks used in semiconductor processing.
BACKGROUND OF THE INVENTION
Phase shift masks have received increased attention over the years as semiconductor device size continues to shrink. Phase shift masks involve the technique of passing light through transparent mask regions where some transparent mask regions shift the phase of the light through the mask as compared to other transparent mask regions. Thus light that passes through a phase shifting mask contains regions of light that are out of phase with respect to one another.
Traditionally, phase shift masks pass 180° shifted light and unshifted (i.e., 0° phase shift) light. This produces regions of light that are out of phase by 180° with respect to each other. Due to deconstructive interference principles, no light intensity exists where these regions of light overlap on a substrate surface. That is, on the substrate surface where light from the two regions overlap, the 180° shifted light region cancels out the 0° shifted region. The overlap occurs due to the natural spreading of light after it passes through a transparent region of the mask. The spreading may also be referred to as fringing.
By strategically patterning the transparent regions on the mask that corresponds to shifted and non-shifted light such that overlap occurs at specific locations on the substrate surface; the resulting deconstructive interference may be used to enhance optical contrast on the substrate surface. Enhanced optical contrast results in the ability to produce smaller features (such as gates, contacts and metal lines) on the substrate surface. Thus phase shift masks may be used to produce smaller features on the surface of a substrate.
A problem with phase shift masks concerns the result of manufacturing defects in the transparent regions associated with the mask. These manufacturing defects are usually caused by imperfect etching of the transparent regions. A transparent region is etched in order to determine its phase shift as compared to other non etched transparent regions. Typically, etched transparent regions have an 180° phase shift while non etched regions have a 0° phase shift. The depth of the etch determines the amount of phase shift that occurs.
FIGS. 1
a
and
1
b
show an example of the type of defects described above. If an unwanted portion
102
of resist layer
101
or opaque layer
111
or other material remains on the transparent layer
103
during the etching of the transparent layer
103
an imperfection
104
in the transparent region
105
is formed. Since the depth
106
of the transparent region
105
controls the phase shift through the transparent region
105
, imperfection
104
results in an incorrect phase shift for light that passes through imperfection
104
. The defect
102
and
104
can extend completely over the transparent region
105
.
U.S. Pat. No. 5,308,722 entitled “Voting Technique For The Manufacture of Defect-Free Printing Phase Shift Lithography” issued on May 3, 1994 describes a voting technique that addresses the defect problem. A voting technique involves multiple etch steps in order to reduce the effects of a defect mechanism. For example, as shown in
FIGS. 2
a
-
2
e
, the “one step” etch of
FIGS. 1
a
and
1
b
is expanded to a “two-step” etch (also referred to as a “twice voted” etch).
After a first resist layer
201
patterning (
FIG. 2
a
), transparent layer
203
etch (
FIG. 2
b
) and resist layer
201
removal (
FIG. 2
c
), a second resist layer
207
is patterned (
FIG. 2
d
) prior to a second transparent region
205
etch (
FIG. 2
e
). The consequence of the “two step” etch is seen in the height
210
of the imperfection
204
.
Whereas the height
110
of the “one step” etch imperfection
104
is approximately equal to the final etch depth
106
of the transparent region
105
; the height
210
of the two step imperfection
204
is approximately half of this depth
206
. Voting techniques therefore take advantage of the random location of imperfections per resist patterning, transparent region etch and resist removal sequence. The result is lower imperfection height
210
.
Prior art voting techniques are traditionally limited to a final etch depth
106
,
206
that corresponds to a 180° phase shift. As described ahead, however, the overall effects of imperfections
104
,
204
on the devices (such as semiconductor devices) manufactured with phase shift masks may be further reduced by other final etch depth approaches.
SUMMARY OF THE INVENTION
An apparatus comprising a phase shift mask having a transparent region. The transparent region comprises an etched region of a transparent layer. The etched region has a final etch depth that corresponds to a designed for phase shift that is greater than 180°.
REFERENCES:
patent: 5302477 (1994-04-01), Dao et al.
patent: 5308722 (1994-05-01), Nistler
patent: 5376483 (1994-12-01), Rolfson
patent: 5549995 (1996-08-01), Tanaka et al.
Blakely , Sokoloff, Taylor & Zafman LLP
Intel Corporation
Rosasco S.
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