U.S. patent application number 09/767304 was filed with the patent office on 2002-07-25 for contact hole model-based optical proximity correction method.
Invention is credited to Chen, Ming-Jui, Lin, Chin-Lung.
Application Number | 20020098427 09/767304 |
Document ID | / |
Family ID | 25079078 |
Filed Date | 2002-07-25 |
United States Patent
Application |
20020098427 |
Kind Code |
A1 |
Chen, Ming-Jui ; et
al. |
July 25, 2002 |
CONTACT HOLE MODEL-BASED OPTICAL PROXIMITY CORRECTION METHOD
Abstract
A contact hole model-based optical proximity correction method.
The method includes building a contact hole model from the database
obtained through a series of test patterns each having a plurality
of contact holes of different line widths but identical distance of
separation. Line width offsets due to proximity effect are
eliminated by referring to the contact hole model.
Inventors: |
Chen, Ming-Jui; (Hsinchu,
TW) ; Lin, Chin-Lung; (Hsinchu Hsien, TW) |
Correspondence
Address: |
CHARLES C.H. WU & ASSOCIATES
Suite 710
7700 IRVINE CENTER DRIVE
Irvine
CA
92618-3043
US
|
Family ID: |
25079078 |
Appl. No.: |
09/767304 |
Filed: |
January 23, 2001 |
Current U.S.
Class: |
430/30 |
Current CPC
Class: |
G03F 1/36 20130101; G03F
7/70483 20130101 |
Class at
Publication: |
430/30 |
International
Class: |
G03C 005/00 |
Claims
What is claimed is:
1. A contact hole model-based optical proximity correction method,
comprising the steps of: providing a photomask; forming a plurality
of rectangular test patterns on a photomask with each test pattern
having a plurality of contact holes having different line widths
but identical distance of separation on a photomask, wherein line
width is the side of each contact hole and the distance of
separation is the distance from a point along the side of the
contact hole to the same position of a neighboring contact hole;
performing a photo-exposure of a photoresist layer on a silicon
chip using a photomask with the test patterns thereon and
developing the photoresist layer to obtain a plurality of test
patterns having different line widths but identical distance of
separation on the silicon chip; measuring the line widths of the
test patterns on the silicon chip; comparing the line widths of the
test patterns on the silicon chip with the line widths of the test
patterns on the photomask; and establishing a contact hole model
for selecting suitable line widths from the panel of test patterns
so that contact holes can be precisely reproduced in an actual
photolithographic pattern transfer operation.
2. A contact hole model-based optical proximity correction method,
comprising the steps of: providing a photomask; forming a first
group of test patterns on a photomask with each test pattern
containing a plurality of contact holes having different line
widths but identical distance of separation on a photomask, wherein
the line width is the side of each contact hole and the distance of
separation is the distance from a point along the side of the
contact hole to the same position of a neighboring contact hole;
forming a second group of test patterns on a photomask with each
test pattern containing a plurality of contact holes having
different line widths but identical distance of separation on a
photomask, wherein the second group of test patterns differ from
the first group of test patterns in their distance of separation
between neighboring contact holes; forming a plurality of groups of
test patterns on the photomask such that each group of test
patterns has a different distance of separation between neighboring
contact holes; performing a photo-exposure of a photoresist layer
on a silicon chip using a photomask with the test patterns thereon
and developing the photoresist layer to obtain a plurality of test
patterns having different line widths and distance of separation on
the silicon chip; measuring the line widths of the test patterns on
the silicon chip; comparing the line widths of the test patterns on
the silicon chip with the line widths of the test patterns on the
photomask; and establishing a contact hole model for selecting
suitable line widths from the panel of test patterns so that
contact holes can be precisely reproduced in an actual
photolithographic pattern transfer operation.
3. A contact hole model-based optical proximity correction method,
comprising the steps of: providing a photomask; forming a plurality
of rectangular test patterns on a photomask with each test pattern
having a plurality of contact holes having different line widths
but identical distance of separation on a photomask, wherein line
width is the side of each contact hole and the distance of
separation is the shortest distance from a contact hole to its
neighboring contact hole; performing a photo-exposure of a
photoresist layer on a silicon chip using a photomask with the test
patterns thereon and developing the photoresist layer to obtain a
plurality of test patterns having different line widths on the
silicon chip; measuring the line widths of the test patterns on the
silicon chip; comparing the line widths of the test patterns on the
silicon chip with the line widths of the test patterns on the
photomask; and establishing a contact hole model for selecting
suitable line widths from the panel of test patterns so that
contact holes can be precisely reproduced in an actual
photolithographic pattern transfer operation.
4. The method of claim 3, wherein the ratios formed by dividing the
distance of separation between neighboring contact holes by line
width of the contact holes are referred to as the pitch ratios.
5. The method of claim 4, wherein pitch ratios used by the test
patterns on the photomask includes 1:0.8, 1:1, 1:1.2, 1:1.4, 1:1.6,
1:1.8, 1:2, 1:2.4, 1:2.8, 1:3.4, 1:4, 1:5 and 1:6.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] The present invention relates to an optical proximity
correction method. More particularly, the present invention relates
to a contact hole model-based optical proximity correction
method.
[0003] 2. Description of Related Art
[0004] As the level of integration in an integrated circuit
continues to increase, dimensions of each circuit device must
reduce correspondingly. Photolithography is an important step in
the fabrication of semiconductors. Photolithography is involved in
processes related to the fabrication of metal-oxide-semiconductor
(MOST) devices such as the patterning thin films and the marking
out areas for implanting dopants. In addition, whether the
semiconductor industry is able to produce devices with smaller
critical dimensions depends very much on the future development of
photolithography. To attain higher level of integration, a few
methods capable of increasing mask resolution has been suggested.
One such method is optical proximity correction (OPC).
[0005] The idea behind optical proximity correction is the
eliminate line offset due to proximity effect. Proximity effect
refers to the phenomenon that occurs when a beam of light shines
through an optical mask and projects onto a wafer. Due to
diffraction of light beam on passing a material medium, the light
beam will expand out somewhat. Furthermore, some of the light may
pass through the photoresist layer into the wafer and then reflect
back from the semiconductor substrate leading to interference.
Hence, some portion of the photoresist may be double-exposed. The
seriousness of such occurrences is intensified when the feature
line width of an integrated circuit is small, especially when the
wavelength of the light source approaches the width of a line
pattern.
[0006] At present, contact hole model-based optical proximity
correction method relies on test patterns established by the
differences in distances and line widths as a database for actual
correction.
[0007] FIG. 1A is a sketch showing the test patterns used by a
conventional contact hole model-based optical proximity correction
method.
[0008] As shown in FIG. 1A, the square contact hole 102 in test
pattern 100 has a line width 104. Distance of separation or pitch
from one contact hole 102 to its neighboring contact hole is
labeled 106. For example, line width 104 of the square contact hole
102 in test pattern 100 is 0.8 .mu.m and distance of separation
between neighboring contact holes is 1.6 .mu.m. Similarly, line
width of contact hole 112 in test pattern 110 is 0.84 .mu.m and
distance of separation between neighboring contact holes 112 is
1.68 .mu.m. Finally, line width of contact hole 116 in test pattern
114 is 0.88 .mu.m and distance of separation between neighboring
contact holes 116 is 1.76 .mu.m. Using a photomask having the test
patterns 100, 110 and 114 thereon, a layer of photoresist is
exposed and then developed. Thereafter, line widths of various
patterns on the developed photoresist layer are measured. Because
of proximity effect, contact hole patterns on the wafer are
slightly different from the original test patterns on the
photomask. Most probably, the corners of the square holes may be
rounded and line width may be smaller. After measuring the actual
line widths, a line width versus distance of separation graph may
be plotted for both the predicted and the actual values.
[0009] FIG. 1B is a graph showing the line width versus distance of
separation relationship in a conventional contact hole model-based
proximity correction method.
[0010] As shown in FIG. 1B, when the distance of separation between
contact holes is getting smaller, actual line width measured on the
photoresist layer is getting longer than the intended line width on
the photomask. Conversely, when the distance of separation between
contact holes is getting larger, actual line width measured on the
photoresist layer is getting closer to the intended line width on
the photomask.
[0011] Using the established optical proximity correction model
shown in FIG. 1B, proper optical mask line widths can supposedly be
selected to form the desired line width on the photoresist layer
during a contact hole forming process. In practice, the established
model can hardly produce the kind of accuracy demanded. This is
because proximity effect may vary according to distance of
separation, thereby changing the effect on line width. In other
words, when the distance of separation is greater than a few times
the line width, proximity effect has little influence on line width
dimensions. However, as distance of separation is not much
different from the line width, proximity effect can affect the
ultimate line width dimensions of the contact holes considerably.
Hence, a simple distance of separation versus line width
relationship can hardly produce the kind of prediction needed for
forming contact holes having correct dimensions and position.
[0012] Accurate reproduction of contact holes and conductive lines
in an integrated circuit is getting more important especially when
the semiconductor devices are getting smaller. There is very little
tolerance for a misaligned contact hole or a conductive line having
a line width too width or too narrow in an integrated circuit.
Hence, optical proximity correction is increasingly important in
photolithographic processes.
SUMMARY OF THE INVENTION
[0013] Accordingly, one object of the present invention is to
provide a contact hole model that can simulates the actual
photolithographic conditions more accurately than a conventional
model so that up to standard silicon chip is produced after a
photolithographic process. Consequently, productivity is increased
and quality is improved.
[0014] To achieve these and other advantages and in accordance with
the purpose of the invention, as embodied and broadly described
herein, the invention provides a contact hole model-based optical
proximity correction method. The method utilizes a series of test
patterns each having a plurality of contact holes separated by
identical distance but a different contact hole line width to serve
as a database for establishing a contact hole model. Using the
contact hole model, proximity effect that may lead to line width
offset can be eliminated. Ultimately, desired dimensions of a
device are more accurately reproduced and production errors are
minimized.
[0015] It is to be understood that both the foregoing general
description and the following detailed description are exemplary,
and are intended to provide further explanation of the invention as
claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and
constitute a part of this specification. The drawings illustrate
embodiments of the invention and, together with the description,
serve to explain the principles of the invention. In the
drawings,
[0017] FIG. 1A is a sketch showing the test patterns used by a
conventional contact hole model-based optical proximity correction
method;
[0018] FIG. 1B is a graph showing the line width versus distance of
separation relationship in a conventional contact hole model-based
proximity correction method;
[0019] FIG. 2A is a sketch showing the test patterns used by a
contact hole model-based optical proximity correction method
according to a first embodiment of this invention;
[0020] FIG. 2B is a graph showing the line width versus distance of
separation relationship according to the test patterns shown in
FIG. 2A;
[0021] FIG. 2C is a sketch showing the test patterns used by a
contact hole model-based optical proximity correction method
according to an extension of the test patterns shown in FIG.
2A;
[0022] FIG. 2D is a graph showing the line width versus distance of
separation relationship according to the extension test patterns
shown in FIG. 2C; and
[0023] FIG. 3 is a sketch showing the test patterns used by a
contact hole model-based optical proximity correction method
according to a second embodiment of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] Reference will now be made in detail to the present
preferred embodiments of the invention, examples of which are
illustrated in the accompanying drawings. Wherever possible, the
same reference numbers are used in the drawings and the description
to refer to the same or like parts.
[0025] FIG. 2A is a sketch showing the test patterns used by a
contact hole model-based optical proximity correction method
according to a first embodiment of this invention.
[0026] Optical proximity correction (OPC) is a method of increasing
the resolution of an optical mask. Resolution of an optical mask
can be increased by eliminating line width offset due to proximity
effect. In this invention, a series of test patterns each having a
plurality of contact holes separated by identical distance but a
different contact hole line width is used to form a database for
establishing a contact hole model. Using the contact hole model,
proximity effect that may lead to line width offset can be
eliminated.
[0027] As shown in FIG. 2A, the square contact hole 202 in test
pattern 200 has a line width 204. Distance of separation or pitch
from one contact hole 202 to its neighboring contact hole is
labeled 206. For example, line width 204 of the square contact hole
202 in test pattern 200 is 0.8 .mu.m and distance of separation
between neighboring contact holes is 1.6 .mu.m. Similarly, line
width of contact hole 212 in test pattern 210 is 0.84 .mu.m and
distance of separation between neighboring contact holes 212 is 1.6
.mu.m. Finally, line width of contact hole 216 in test pattern 214
is 0.88 .mu.m and distance of separation between neighboring
contact holes 216 is 1.6 .mu.m. Using a photomask having the test
patterns 200, 210 and 214 thereon, a layer of photoresist is
exposed and then developed. Thereafter, line widths of various
patterns on the developed photoresist layer are measured. Because
of proximity effect, contact hole patterns on the wafer are
slightly different from the original test patterns on the
photomask. Most probably, the corners of the square holes may be
rounded and line width may be smaller. After measuring the actual
line widths, a line width versus distance of separation graph may
be plotted for both the predicted and the actual values.
[0028] FIG. 2B is a graph showing the line width versus distance of
separation relationship according to the test patterns shown in
FIG. 2A.
[0029] As shown in FIG. 2B, when line width of contact holes is
getting smaller, actual line width measured on the photoresist
layer is getting longer than the intended line width on the
photomask. Conversely, when line width of the contact holes is
getting larger, actual line width measured on the photoresist layer
is getting closer to the intended line width on the photomask. This
is because proximity effect occurs when a beam of light shines
through an optical mask and projects onto a wafer. Due to
diffraction of light beam on passing a material medium, the light
beam will expand out somewhat. Furthermore, some of the light may
pass through the photoresist layer into the wafer and then reflect
back from the semiconductor substrate leading to interference.
Hence, some portion of the photoresist may be double-exposed. The
seriousness of such occurrences is intensified when the feature
line width of an integrated circuit is small.
[0030] FIG. 2C is a sketch showing the test patterns used by a
contact hole model-based optical proximity correction method
according to an extension of the test patterns shown in FIG.
2A.
[0031] As shown in FIG. 2C, test patterns using the rule of having
different line width but identical distance of separation are
expanded to form groups. In other words, test patterns 218, 220 and
222 together form a group with contact holes having different line
widths but a first identical distance of separation between
neighboring contact holes. Similarly, test patterns 224, 226 and
228 together form a group with contact holes having different line
widths but a second identical distance of separation between
neighboring contact holes; test patterns 230, 232 and 234 together
form a group with contact holes having different line widths but a
third identical distance of separation between neighboring contact
holes; and, test patterns 236, 238 and 240 together form a group
with contact holes having different line widths but a fourth
identical distance of separation between neighboring contact holes.
For example, test patterns 218, 220 and 222 as a group has a
distance of separation between neighboring contact holes of 1.64
.mu.m while the line widths 204 are 0.8 .mu.m, 0.84 .mu.m and 0.88
.mu.m respectively. Similarly, test patterns 224, 226 and 228 as a
group has a distance of separation between neighboring contact
holes of 1.68 .mu.m while the line widths 204 are 0.8 .mu.m, 0.84
.mu.m and 0.88 .mu.m; test patterns 230, 232 and 234 as a group has
a distance of separation between neighboring contact holes of 1.72
.mu.m while the line widths 204 are 0.8 .mu.m, 0.84 .mu.m and 0.88
.mu.m; and, test patterns 236, 238 and 240 as a group has a
distance of separation between neighboring contact holes of 1.76
.mu.m while the line widths 204 are 0.8 .mu.m, 0.84 .mu.m and 0.88
.mu.m. Using the aforementioned groups of patterns as shown in FIG.
2C, a series of contact hole models can be established.
[0032] FIG. 2D is a graph showing the line width versus distance of
separation relationship according to the extension test patterns
shown in FIG. 2C. As shown in FIG. 2D, test patterns having
different line widths but identical distance of separation between
neighboring contact hole are grouped together as a group model.
Utilizing grouping according to the distance of separation, several
models are obtained and a graph for correcting optical proximity
effect is plotted.
[0033] FIG. 3 is a sketch showing the test patterns used by a
contact hole model-based optical proximity correction method
according to a second embodiment of this invention.
[0034] As shown in FIG. 3A, the square contact hole 302 in test
pattern 300 has a line width 204. Distance of separation or pitch
from one contact hole 302 to its neighboring contact hole is
labeled 306. For example, line width 204 of the square contact hole
302 in test pattern 300 is 0.8 .mu.m and distance of separation
between neighboring contact holes is 0.8 .mu.m. Similarly, line
width of contact hole 312 in test pattern 310 is 0.4 .mu.m and
distance of separation between neighboring contact holes 312 is 0.8
.mu.m. Finally, line width of contact hole 316 in test pattern 314
is 0.2 .mu.m and distance of separation between neighboring contact
holes 316 is 0.8 .mu.m. The test patterns 300, 310 and 314 have
contact holes of different line widths but identical distance of
separation between neighboring holes. The ratio between line width
and distance of separation between neighboring lines called pitch
ratio is an important design parameter. For example in FIG. 3, the
test pattern 300 has a pitch ratio of 0.8:0.8, that is, 1:1. On the
other hand, the test pattern 310 has a pitch ratio of 0.4:0.8, that
is, 1:2. Similarly, the test pattern 314 has a pitch ratio of
0.2:0.8, that is, 1:4. In other words, each test pattern in FIG. 3
is established using a different pitch ratio of the contact holes.
The pitch ratios used in this invention include also 1:0.8, 1:1,
1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2, 1:2.4, 1:2.8, 1:3.4, 1:4, 1:5, 1:6
and so on. Using a photomask having the aforementioned test
patterns thereon, the test patterns are transferred to a
photoresist layer and then developed. Line widths on the developed
photoresist layer is measured. Due to proximity effect, the contact
hole patterns on the silicon chip will differ slightly from the
original patterns on the photomask. The corners may be rounded and
line width may be reduced. By comparing the measured line widths
with the original line widths on the photomask, a contact hole
model for optical proximity correction is obtained.
[0035] In summary, the invention is capable of more accurately
determining the deviation of contact hole from the desired
dimensions after a photolithographic pattern transfer so that more
standardized and reliable semiconductor product is obtained.
[0036] It will be apparent to those skilled in the art that various
modifications and variations can be made to the structure of the
present invention without departing from the scope or spirit of the
invention. In view of the foregoing, it is intended that the
present invention cover modifications and variations of this
invention provided they fall within the scope of the following
claims and their equivalents.
* * * * *