U.S. patent application number 13/087384 was filed with the patent office on 2011-08-04 for integrated circuit having line end created through use of mask that controls line end shortening and corner rounding arising from proximity effects.
This patent application is currently assigned to MACRONIX INTERNATIONAL CO., LTD.. Invention is credited to Chih-Hao Huang, Chin-Cheng Yang, Chiao-Wen Yeh.
Application Number | 20110191728 13/087384 |
Document ID | / |
Family ID | 40844815 |
Filed Date | 2011-08-04 |
United States Patent
Application |
20110191728 |
Kind Code |
A1 |
Yang; Chin-Cheng ; et
al. |
August 4, 2011 |
INTEGRATED CIRCUIT HAVING LINE END CREATED THROUGH USE OF MASK THAT
CONTROLS LINE END SHORTENING AND CORNER ROUNDING ARISING FROM
PROXIMITY EFFECTS
Abstract
An integrated circuit that includes a line end created through
use of a mask that controls line end shortening and corner rounding
arising from proximity effects is provided. The mask includes a
main feature having opaque and transmissive areas arranged to
reflect a patterned feature of the line end, at least one of an
opaque edge or a transmissive edge located at each end of the main
feature, wherein the opaque edge has a set of transmissive assist
features arranged therein such that the set of transmissive assist
features align alternately with the transmissive areas of the main
feature, and the transmissive edge has a set of opaque assist
features arranged therein such that the set of opaque assist
features align alternately with the opaque areas of the main
feature.
Inventors: |
Yang; Chin-Cheng; (Hsinchu,
TW) ; Yeh; Chiao-Wen; (Hsinchu, TW) ; Huang;
Chih-Hao; (Hsinchu, TW) |
Assignee: |
MACRONIX INTERNATIONAL CO.,
LTD.
Hsinchu
TW
|
Family ID: |
40844815 |
Appl. No.: |
13/087384 |
Filed: |
April 15, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11971900 |
Jan 9, 2008 |
7939225 |
|
|
13087384 |
|
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Current U.S.
Class: |
716/53 |
Current CPC
Class: |
G03F 1/36 20130101; Y10T
428/24802 20150115 |
Class at
Publication: |
716/53 |
International
Class: |
G06F 17/50 20060101
G06F017/50 |
Claims
1. An integrated circuit having a line end created through use of a
mask that controls line end shortening and corner rounding arising
from proximity effects, the mask comprising: a main feature having
opaque and transmissive areas arranged to reflect a patterned
feature of the line end, wherein each end of the main feature
includes at least one of an opaque edge and a transmissive edge;
the opaque edge includes a set of transmissive assist features
arranged therein such that the set of transmissive assist features
align alternately with the transmissive areas of the main feature,
and the transmissive edge includes a set of opaque assist features
arranged therein such that the set of opaque assist features align
alternately with the opaque areas of the main feature.
2. The integrated circuit according to claim 1, wherein the set of
opaque assist features comprises first opaque portions aligning
with the transmissive areas, and the set of transmissive assist
features comprises first transmissive portions aligning with the
opaque areas.
3. The integrated circuit according to claim 2, wherein the set of
opaque assist features further comprises second opaque portions
aligning with the opaque areas and separating from the first opaque
portions by a distance of less than 0.6 .lamda./NA and greater or
equal to 0.3 .lamda./NA.
4. The integrated circuit according to claim 2, wherein the set of
transmissive assist features further comprises second transmissive
portions aligning with the transmissive areas and separating from
the first transmissive portions by a distance of less than 0.6
.lamda./NA and greater or equal to 0.3 .lamda./NA.
5. The integrated circuit according to claim 4, wherein the
distance ranges from 0.4 .lamda./NA to 0.6 .lamda./NA.
6. The integrated circuit according to claim 3, wherein the
distance ranges from 0.4 .lamda./NA to 0.6 .lamda./NA.
7. The integrated circuit according to claim 1, wherein each
transmissive assist feature and opaque assist feature has a
dimension ranging from 0.4 .lamda./NA to 0.6 .lamda./NA.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of and claims the priority
benefit of an application Ser. No. 11/971,900, filed on Jan. 9,
2008. The above-mentioned patent application is hereby incorporated
by reference herein and made a part of this specification.
BACKGROUND
[0002] This application relates to the process of fabricating a
semiconductor device. More particularly, the invention relates to a
mask that effectively corrects optical proximity effects when an
image feature is formed on an image surface during semiconductor
fabrication.
[0003] In the manufacture of semiconductor devices, many
photolithographic process steps are involved to define and create
the image feature of circuit elements or layouts onto a substrate
layer. Conventional photolithography process is performed using a
mask having opaque and transparent regions that causes light to
fall on photosensitive material in a desired pattern. After light
is shone through the mask onto the photosensitive material, the
photosensitive material is then developed leaving the printed image
of the circuit and/or component of the substrate layer. The image
substrate is subsequently processed with techniques such as
etching, deposition and doping to alter the substrate layer with
the transferred pattern. As the feature size continues to decrease
to approach the resolution of the fabrication process, circuit
designers are forced to deal with proximity effect problems that
arise as a consequence of the optical lithographic process.
[0004] One problem that arises from the optical photolithography
process includes "line end shortening" that results in the
shortening or "pull-back" of the line ends in the printed image. In
order to compensate for line end shortening, the circuit designers
often add additional features, such as hammer heads 10 shown in
FIG. 1 onto the line ends 1 before carrying out the
photolithographic process. These hammer heads 10 can effectively
compensate by optical proximity correction (OPC) for the problem of
line end shortening in some situations. However, if these hammer
heads 10 are arranged too close to each other, a pattern bridging
problem can potentially be created in the printed image as
illustrated in FIG. 1. The prior art describes a system to control
line-end shortening arising from optical effects by using double
exposure. The system includes defining an unexposed line on the
photoresist layer using a first mask and exposing the photoresist
layer through the first mask. The system also requires a second
mask for defining an exposure region and a second exposure that cut
through the unexposed line on the photoresist layer, so as to
resolve the pattern bridging problem and create two opposing line
ends on opposite sides of the exposure region. Other additional
features, such as scattering bars may also be placed adjacent to
the line ends to control line end shortening problem.
[0005] "Line corner rounding" is the degree to which feature
corners that should be at sharp angles are instead rounded by the
lithography process. In some cases, the line corner rounding may
lead to pattern bridging problem. The line corner rounding may also
result in a decreased tolerance for overlay shift in the double
patterning methods. The line corner rounding may be corrected by
adding serifs to outside corners, which are called positive serifs,
and subtracting serifs from the inside corners, which are called
negative serifs, to the feature in the photomask. This is shown in
FIG. 2, in which the positive serif 193 has been added to the
outside corner of the feature 171, and the negative serif 197 has
been removed from the inside corner of the feature 171.
[0006] In the semiconductor fabrication which involves double
patterning technique (DPT), a patterned feature may be produced by
two consecutive exposures via either one mask or two different
masks. It is also important to maintain the accuracy of pattern
shape produced by double exposure in order to avoid short form
pattern overlay. Therefore, there is a need to provide a mask
design which effectively control line end shortening and corner
rounding arising from proximity effects to achieve desired pattern
accuracy and gain more process window.
BRIEF SUMMARY
[0007] In one embodiment of the invention a mask is provided to
produce an image feature on an image surface during a semiconductor
fabrication process. The mask includes a main feature that has
opaque and transmissive areas arranged in the form of the image
feature. Each end of the main feature may include at least one of
an opaque edge and a transmissive edge. The opaque edge has a set
of transmissive assist features arranged therein such that the set
of transmissive assist features align alternately with the
transmissive areas of the main feature, and the transmissive edge
has a set of opaque assist features arranged therein such that the
set of opaque assist features align alternately with the opaque
areas of the main feature.
[0008] Another embodiment of the invention provides a system for
exposing a photoresist layer during semiconductor fabrication. The
system includes a mask, a positioning means for positioning the
mask over the photoresist layer, and an exposure means for exposing
the photoresist layer through the mask. The mask includes a main
feature having opaque and transmissive areas arranged to reflect an
image feature of the photoresist layer. Each end of the main
feature may include at least one of an opaque edge and a
transmissive edge. The opaque edge has a set of transmissive assist
features arranged therein such that the set of transmissive assist
features align alternately with the transmissive areas of the main
feature. The transmissive edge has a set of opaque assist features
arranged therein such that the set of opaque assist features align
alternately with the opaque areas of the main feature.
[0009] Another embodiment of the invention provides an integrated
circuit that includes a line end created through use of a mask that
controls line end shortening and corner rounding arising from
proximity effects. The mask includes a main feature having opaque
and transmissive areas arranged to reflect a patterned feature of
the line end, at least one of an opaque edge or a transmissive edge
located at each end of the main feature, wherein the opaque edge
has a set of transmissive assist features arranged therein such
that the set of transmissive assist features align alternately with
the transmissive areas of the main feature, and the transmissive
edge has a set of opaque assist features arranged therein such that
the set of opaque assist features align alternately with the opaque
areas of the main feature.
[0010] Additional embodiments, including their respective
advantages, will be set forth in the description which follows. It
is to be understood that both the foregoing general description and
the following detailed description are exemplary and explanatory
only and are not restrictive of the invention, as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The embodiments illustrated in the figures of the
accompanying drawings herein are by way of example and not by way
of limitation. In the drawings:
[0012] FIG. 1 is a prior art plan view of a mask design and a
printed image resulted from the mask design;
[0013] FIG. 2 is a prior art plan view of a conventional mask
design with OPC assist features added to corners and edges of the
main mask feature;
[0014] FIG. 3a is a partial plan view of a mask according to one
example of the present invention;
[0015] FIG. 3b shows a printed image feature resulted from exposure
using the mask illustrated in FIG. 3a; and
[0016] FIG. 4 is a plan view of a mask according to another example
of the present invention.
DETAILED DESCRIPTION
[0017] Although the present invention has been described herein
with reference to specific example embodiments, it will be evident
that various modifications and changes may be made to these
embodiments without departing from the broader spirit and scope of
the invention. Accordingly, the specification and drawings are to
be regarded in an illustrative rather than a restrictive sense.
Wherever possible, the same reference numbers will be used
throughout the drawings to refer to the same or like parts.
[0018] Examples of the present invention provide a mask for
producing an image feature on an image surface during a
semiconductor fabrication process. The mask is designed to
effectively control line end shortening and line corner rounding
problems without altering the semiconductor fabrication process.
The mask may include a main feature that has both opaque and
transmissive areas arranged in the form of the image feature. Each
end of the main feature may include at least one of an opaque edge
and a transmissive edge. The opaque edge includes a set of
transmissive assist features arranged therein such that the set of
transmissive assist features align alternately with the
transmissive areas of the main feature, and the transmissive edge
includes a set of opaque assist features arranged therein such that
the set of opaque assist features align alternately with the opaque
areas of the main feature. Specifically, the set of transmissive
assist features may be aligned between two adjacent transmissive
areas of the main feature. And the set of opaque assist features
may be similarly aligned between two adjacent opaque areas of the
main feature.
[0019] The opaque and transmissive areas of the main feature may be
arranged as arrays of parallel lines or other configurations
depending on the circuit design desired. In some examples of the
invention, the opaque areas of the main feature may reflect the
regions of the photoresist layer to be exposed during
photolithographic process. For other examples, the transmissive
areas of the main feature may reflect the unexposed regions of the
photoresist layer. In accordance with one example of the present
invention, the set of opaque assist features includes first opaque
portions aligning with the transmissive areas. The set of opaque
assist features may further include second opaque portions aligning
with the opaque areas. The opaque assist features may be applied or
disposed in the transmissive edge of the main feature in such a way
that the first opaque portions are separated from the second opaque
portions by the transmissive edge. The first opaque portions may be
disposed adjacent to the transmissive areas, with each of the first
opaque portions separated from its neighboring first opaque
portions by the transmissive edge. Also, each of the second opaque
portions may be separated from its neighboring second opaque
portions by the transmissive edge.
[0020] The first opaque portions may be separated from the second
opaque portions by a first distance, and the second opaque portions
may be separated from the opaque areas of the main feature by at
least the first distance and the height of the first opaque
portion. As examples of the invention, the first distance may be
less than 0.6 .lamda./NA, wherein .lamda. is the wavelength of the
light source used during photolithography, and NA is the numerical
aperture of the optical system. In accordance with some examples,
the first distance may be greater or equal to 0.3 .lamda./NA. For
example, the first distance may range from 0.4 .lamda./NA to 0.6
.lamda./NA. In addition, the first opaque portions may be separated
from the main feature by a second distance. Therefore, the second
opaque portions may be separated from the opaque areas of the main
feature by the first distance, height of the first opaque portion,
and the second distance. As a specific example, the second distance
may be zero.
[0021] In terms of the dimension, each of the opaque assist
features may have a dimension of less than 0.6 .lamda./NA. For
example, the width (w) or height (h) of the opaque assist feature
may be 0.3 .lamda./NA or less. And when the width of the opaque
assist feature is less than 0.3 .lamda./NA, the corresponding
height may be any value less than or equal to 0.6 .lamda./NA, and
vice versa. As a specific example of the invention, the opaque
assist features have their dimensions that are less than 0.6
.lamda./NA and greater than 0.4 .lamda./NA. In accordance with
certain examples of the invention, the opaque assist features may
include opaque squares or opaque rectangles.
[0022] Within the opaque edge of the main feature, the set of
transmissive assist features which includes the first and second
transmissive portions is also applied. The transmissive assist
features may similarly share the same dimension constrains as the
opaque assist features of the mask. The first transmissive portions
may be disposed adjacent to the opaque areas, with each of the
first transmissive portions separated from its neighboring first
transmissive portions by the opaque edge. The first transmissive
portions may be separated from the second transmissive portions by
the first distance, and the second transmissive portions may be
separated from the transmissive areas of the main feature by at
least the first distance and height of the first opaque portion.
And each of the second transmissive portions may be separated from
its neighboring second transmissive portions by the opaque edge. In
addition, the first transmissive portions may be separated from the
opaque areas by the second distance. Therefore, the second
transmissive portions may similarly be separated from the
transmissive areas of the main feature by the first distance,
height of the first transmissive portion, and the second distance.
In accordance with other examples of the invention, the
transmissive assist features may also include transmissive squares
or transmissive rectangles. Accordingly, the assist features of the
invention may be provided to create different tones from the edges
of the main feature. Besides the improvement from the line end
shortening problem, the angles of incidence are also kept uniform
using the mask of the invention to prevent the corner rounding
problem. Such arrangement of the assist features also ensure that
the assist features are not erroneously printed out.
[0023] One specific example of mask is partially illustrated in
FIG. 3a. Referring to FIG. 3a, the mask 200 has a main feature 201
which includes opaque areas 211 and intervening transmissive areas
212 arranged as an array to reflect the printed feature. Each of
the opaque areas 211 has a hollow portion or transmissive portion
211 a to allow incident light to pass through. At the top end of
the main feature 201, a transmissive edge 221 is provided. A set of
opaque assist features including first opaque rectangles 223 are
arranged within the transmissive edge 221 in such a way that the
first opaque rectangles 223 are located to align with the
transmissive areas 212 and substantially adjacent to corners 213 of
the opaque areas 211 as shown in FIG. 3a. In other words, the first
opaque rectangles 223 align alternately with the opaque areas 211
of the main feature 201. Each of the first opaque rectangles 223
has a dimension that is less than or equal to 0.6 .lamda./NA. For
example, the first opaque rectangle 223 has a width (w) or height
(h) of less than or equal to 0.6 .lamda./NA. FIG. 3b depicts a
printed image feature 230 with improved profile resulted from
exposure using the mask 200 illustrated in FIG. 3a.
[0024] Another example of the mask 300 is also provided as
illustrated in FIG. 4. Referring to FIG. 4, the mask 300 has a main
feature 301 which includes opaque areas 311 and intervening
transmissive areas 312 arranged as an array to reflect the printed
image feature. At the top end of the main feature 301, a
transmissive edge 321 may be provided. The mask 300 also has a set
of opaque assist features which include first and second opaque
squares 322 and 323 arranged within the transmissive edge 321 such
that the set of opaque assist features 322 and 323 align
alternately with the opaque areas 311 of the main feature 301. The
first opaque squares 322 align with the transmissive areas 312 and
are substantially adjacent to corners 313 of the opaque areas 311
as shown in FIG. 4. The second opaque squares 323 align with the
opaque areas 311 of the main feature 301 and are separated from the
first opaque squares 322 by a distance d1 that ranges from about
0.4 .lamda./NA to about 0.6 .lamda./NA. In one example of the
invention, each of the first and second opaque squares 322 and 323
has a dimension, such as width or height of less than or equal to
0.6 .lamda./NA. In one specific example, each of the first and
second opaque squares 322 and 323 may have a width or height that
ranges from 0.4%/NA to 0.6 .lamda./NA.
[0025] The main feature 301 may also have an opaque edge 331 at an
opposite end of the main feature 301. A set of transmissive assist
features that include the first and second transmissive squares 332
and 333 are arranged within the opaque edge 331 such that the set
of transmissive assist features 332 and 333 align alternately with
the transmissive areas 312 of the main feature 301. As shown in
FIG. 4, the first transmissive squares 332 align with the opaque
areas 311 and are substantially adjacent to corners 314 of the
transmissive areas 312. The second transmissive squares 333 align
with the transmissive areas 312 and are separated from the first
transmissive squares 332 by the distance d1 that ranges from about
0.4 .lamda./NA to about 0.6 .lamda./NA. In another example of the
invention, each of the first and second transmissive squares 332
and 333 has a dimension, such as width or height of less than or
equal to 0.6 .lamda./NA. According to one specific example, each of
the first and second transmissive squares 332 and 333 may have a
width or height that ranges from 0.4 .lamda./NA to 0.6
.lamda./NA.
[0026] It is noted that the assist features of the invention are
not limited to specific geometrical shapes as described above.
Other shapes of the assist features, including but not limited to
circular, oval, triangular and polygonal shapes may also be
encompassed within the scope of the invention as long as their
dimensions meet the constrains set forth above.
[0027] Examples of the present invention also provide a system for
exposing a photoresist layer during semiconductor fabrication. The
system provides a mask having a main feature with opaque and
transmissive areas arranged to reflect an image feature of the
photoresist layer, an opaque edge or a transmissive edge located at
one end of the main feature, wherein the opaque edge includes a set
of transmissive assist features arranged therein such that the set
of transmissive assist features align alternately with the
transmissive areas of the main feature and the transmissive edge
includes a set of opaque assist features arranged therein such that
the set of opaque assist features align alternately with the opaque
areas of the main feature. The system also includes a positioning
means for positioning the mask over the photoresist layer and an
exposure means for exposing the photoresist layer through the
mask.
[0028] In accordance with examples of the invention, the mask is
positioned over the photoresist layer on a surface of a
semiconductor wafer by the positioning means. The exposure means
then exposes the photoresist layer through the mask. The mask may
be subjected to either a single patterning process or double
patterning process depending on the image feature required for the
photoresist layer. And the patterning process may include those
that involve single exposure or double exposure to the mask. The
exposure means includes but is not limited to commercially
available photolithography exposure tool, equipment, machine. The
exposed photoresist layer is then developed using a photoresist
developer. Depending on whether photoresist is a positive or
negative type, the exposed or unexposed portions may be dissolved
by the developer. The semiconductor fabrication may further include
chemical etching, deposition, ion implantation or other necessary
processes to the remaining portions or material layers. For
example, the wafer may be etched through the photoresist layer by
wet etching or dry etching to yield the desired feature.
[0029] In addition, the present invention also provides an
integrated circuit having a line end created through use of a mask
that controls line end shortening and corner rounding arising from
proximity effects. The mask includes a main feature having opaque
and transmissive areas arranged to reflect a patterned feature of
the line end, an opaque edge or a transmissive edge located at one
end of the main feature, wherein the opaque edge includes a set of
transmissive assist features arranged therein such that the set of
transmissive assist features align alternately with the
transmissive areas of the main feature, and the transmissive edge
includes a set of opaque assist features arranged therein such that
the set of opaque assist features align alternately with the opaque
areas of the main feature.
[0030] In accordance with examples of the invention, the process
for fabricating a semiconductor chip with polysilicon lines created
through use of the mask may also be provided. The invention is not
limited to creating line ends in polysilicon lines. It can also
used to create line ends in metal lines or any other type of signal
line. Note that the above process can be carried out automatically
under software control. Alternatively, the above process can be
carried out manually by a human being. In addition, the mask design
of the invention may be implemented in either a single patterning
or double patterning process while still maintaining a high
tolerance of overlay shift.
[0031] Other examples of the invention will be apparent to those
skilled in the art from consideration of the specification and
practice of the invention disclosed herein. It is intended that the
specification and examples be considered as exemplary only, with a
true scope and spirit of the invention being indicated by the
following claims.
[0032] It will be appreciated by those skilled in the art that
changes could be made to the embodiments described above without
departing from the broad inventive concept thereof. It is
understood, therefore, that this invention is not limited to the
particular embodiments disclosed, but it is intended to cover
modifications within the spirit and scope of the present invention
as defined by the appended claims.
* * * * *