U.S. patent application number 11/688663 was filed with the patent office on 2007-07-12 for liquid crystal display substrate fabrication.
Invention is credited to Deok-Won Lee, Soon-Young Park.
Application Number | 20070159612 11/688663 |
Document ID | / |
Family ID | 32653198 |
Filed Date | 2007-07-12 |
United States Patent
Application |
20070159612 |
Kind Code |
A1 |
Park; Soon-Young ; et
al. |
July 12, 2007 |
LIQUID CRYSTAL DISPLAY SUBSTRATE FABRICATION
Abstract
In order to prevent exposure mismatch on a boundary between
exposure regions that causes pattern connection defects (including
stitch defects), exposure is performed twice or more on a whole
exposure region of a glass substrate. The exposure method includes
aligning a reticle in a scanning direction, exposing the reticle
pattern onto the glass substrate, moving the glass substrate
one-half of the width of the reticle, and exposing an exposure area
twice by repeating the exposing and moving steps.
Inventors: |
Park; Soon-Young;
(Hadong-Gun, KR) ; Lee; Deok-Won; (Seongnam,
KR) |
Correspondence
Address: |
BRINKS HOFER GILSON & LIONE
P.O. BOX 10395
CHICAGO
IL
60610
US
|
Family ID: |
32653198 |
Appl. No.: |
11/688663 |
Filed: |
March 20, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10723491 |
Nov 25, 2003 |
7211372 |
|
|
11688663 |
Mar 20, 2007 |
|
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Current U.S.
Class: |
355/53 ;
355/67 |
Current CPC
Class: |
G03F 7/70791 20130101;
G03F 7/70466 20130101; G03F 7/70425 20130101 |
Class at
Publication: |
355/053 ;
355/067 |
International
Class: |
G03B 27/42 20060101
G03B027/42; G03B 27/54 20060101 G03B027/54 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2002 |
KR |
86066/2002 |
Claims
1-10. (canceled)
11. An exposure apparatus for exposing a reticle onto an exposure
area of a substrate, the apparatus comprising: a mask stage for
supporting a reticle comprising a reticle pattern, the reticle
pattern characterized by a reticle width, a reticle length, and a
scanning direction; a substrate stage for supporting an LCD
substrate comprising an exposure area, the substrate stage moving
the LCD substrate perpendicular to the scanning direction no
greater than one-half of the reticle width between exposures of the
reticle; and an illuminative optical system for exposing the
reticle pattern along the scanning direction onto a portion of the
exposure area, the substrate stage and illuminative optical system
repeatedly moving and exposing to expose an entirety of the
exposure area at least twice.
12. The exposure apparatus of claim 11, where the reticle length is
longer than the reticle width and where the scanning direction is
along the reticle length.
13. The exposure apparatus of claim 11, where the reticle pattern
is repetitive.
14. The exposure apparatus of claim 11, where the substrate stage
moves the substrate perpendicular to the scanning direction
approximately one-half of the reticle width so that the entirety of
the exposure area is exposed twice.
15. The exposure apparatus of claim 11, where the substrate stage
moves the substrate perpendicular to the scanning direction less
than one-half of the reticle width so that the entirety of the
exposure area is exposed more than twice.
16. The exposure apparatus of claim 11, where the illuminative
optical system is an equimultiple erect optical system.
17. The exposure apparatus of claim 11, where the reticle length is
at least as wide as the exposure area.
18. The exposure apparatus of claim 11, where the reticle and the
LCD substrate move together.
19. An exposure apparatus for exposing a reticle onto an exposure
area of a substrate, the apparatus comprising: a substrate stage
for moving a substrate along an X-axis and a Y-axis that is
perpendicular to the X-axis; a mask stage for moving a reticle
along the Y-axis; and an illuminative optical system for taking a
plurality of exposures of the reticle along the Y-axis onto an
exposure region on the substrate, the mask stage moving the
substrate along the X-axis in order to expose an entirety of the
exposure region at least twice.
20. The exposure apparatus of claim 19, where the reticle is
characterized by a reticle width and a reticle length, the reticle
length disposed along the Y-axis and greater than the reticle
width.
21. The exposure apparatus of claim 19, where the reticle comprises
a repetitive reticle pattern.
22. The exposure apparatus of claim 19, where the mask stage moves
the substrate along the X-axis in order to expose an entirety of
the substrate twice.
23. The exposure apparatus of claim 22, where the reticle is
characterized by a reticle width, and where the mask stage moves
the substrate along the X-axis by approximately one-half of the
reticle width.
24. The exposure apparatus of claim 19, where the mask stage moves
the substrate along the X-axis in order to expose an entirety of
the substrate more than twice.
25. The exposure apparatus of claim 24, where the reticle is
characterized by a reticle width, and where the mask stage moves
the substrate along the X-axis by less than one-half of the reticle
width.
26. The exposure apparatus of claim 19, where the illuminative
optical system scans the reticle along the Y-axis.
27. The exposure apparatus of claim 19, where the substrate and
reticle move together along the Y-axis.
28. The exposure apparatus of claim 27, where the substrate and
reticle move together along the Y-axis during exposure at the same
speed.
29. The exposure apparatus of claim 19, where the illuminative
optical system generates an illumination region of the reticle
comprising a length direction perpendicular to the Y-axis.
30. The exposure apparatus of claim 19, where the reticle is at
least as long as the exposure region along the Y-axis.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to LCD (Liquid Crystal
Display) panel substrate fabrication, and more particularly to an
exposure method and system for fabricating an LCD panel substrate
without stitch defects.
[0003] 2. Description of the Prior Art
[0004] The exposure apparatus used for fabricating a liquid crystal
display device substrate is generally either a step-and-repeat
apparatus or a step-and-scanning apparatus. The step-and-repeat
apparatus sequentially exposes an exposure region of a unit cell,
while the step-and-scanning apparatus transcribes a reticle or a
mask pattern onto each exposure region of an array substrate by
synchronously moving the reticle or the mask and a substrate in the
same direction.
[0005] FIG. 1 shows a conventional projective exposure
steppe-and-repeat apparatus for fabricating an LCD substrate, As
shown in FIG. 1, an LCD pattern on a reticle or a mask (hereafter,
"reticle") 103 is illuminated by an illuminating optical system
102, and is exposed onto a predetermined exposure area on a plate
106. The plate 106 is typically a rectangular glass substrate
placed on an XY stage 105.
[0006] When a pattern is transferred by the exposure, the plate 106
is moved by a predetermined distance by moving the XY stage 105.
The LCD pattern is then exposed onto a new exposure area. Thus, the
process of exposing the LCD pattern may occur multiple times in
multiple different locations on the plate 106.
[0007] When a new pattern from a new reticle is needed, the reticle
103 is exchanged for another reticle by the reticle exchanging
mechanism 110. Again, the LCD pattern on the new reticle is
sequentially exposed onto a predetermined exposure region a
predetermined number of times. As a result, multiple reticle
patterns are transferred to the plate 106 at multiple
locations.
[0008] In the above-described step-and-repeat exposure apparatus,
the position of the plate 106 on the XY stage 105 is correctly
monitored by a laser interferometer 107 and the coordinates of the
position are determined. The alignment of the reticle 103 is
performed by a reticle alignment system 108, and the alignment of
the plate 106 is performed by a plate alignment system 109.
[0009] FIG. 2 shows an example of four LCD substrate patterns
transferred to the plate 106 by the exposure apparatus of FIG. 1.
As shown in FIG. 2, in transferring the entire LCD substrate
pattern, the overall pattern is divided into, for example, six
pattern regions labeled A, B, C, D, E and F. At each boundary
portion between patterns (as examples, boundary 202 or boundary
204), a small amount of overlap exposure is carried out as the
patterns are exposed onto 6 different positions. In the example
shown in FIG. 2, each pattern region A, B, C, D, E, and F is
exposed through one of six different reticles that holds the
appropriate pattern for the pattern region. The six patterns are
generated by repeatedly exposing and replacing reticles, thereby
forming an entire LCD substrate pattern, four of which are shown in
FIG. 2.
[0010] In exposing a reticle according to the above-described
method, there is often an alignment discrepancy that occurs at
boundary portions between patterns. FIG. 3 shows two examples of
alignment discrepancy that may result from alignment error of the
reticle and the plate, the distortion of the projective optical
system, and other imperfections in the system,
[0011] A examples, when a pattern to be transferred is subject to a
rotation error, or when there is a positional error with respect to
the positions of the patterns A and B to be transferred, then there
is an alignment discrepancy at the boundary of the exposed patterns
as shown in FIG. 3. An additional source of alignment discrepancy
or overlap error is projection lens distortion in the system.
[0012] When any alignment error occurs, there arises the problem
that the LCD substrate generated by the exposure process does not
have the characteristics that it was designed to have. The LCD
substrate is therefore unusable for an LCD display, and represents
a waste of time and materials. Not only the step-and-repeat
apparatus, but also the step-and-scanning apparatus experience the
same problem.
[0013] Recently, LCD panels have significantly increased in size,
but the size of the exposure region covered by any particular mask
has not. Thus, more exposure cycles are necessary to expose the LCD
substrate. Accordingly the problem has worsened, even as commercial
demand for LCD displays is increasing.
[0014] In other words, because an LCD display incorporates a large
LCD substrate, exposure has to be performed many times to fabricate
the LCD substrate. In an attempt to prevent alignment discrepancy,
there have been attempts to carry out exposure using a minute
overlap portion between exposures.
[0015] Nevertheless, in those attempts, pattern alignment
discrepancy occurs between an overlapped region and a
non-overlapped region. In other words, in some instances, exposure
happens twice in the minute overlap region, exposure happens only
once in another region, and pattern discrepancy occurs between the
two regions after etching. After completing the fabrication of the
liquid crystal display device, the pattern discrepancy looks like a
stitch, and accordingly the screen is defective.
[0016] Thus, there is a need to address the problems noted above,
and others previously experienced.
SUMMARY OF THE INVENTION
[0017] Methods and systems consistent with the present invention
help reduce or eliminate stitch defects in LCD substrates. In one
implementation, a step-and-scanning exposure technique is employed
that does not suffer from the relatively slow speed of
step-and-repeat systems. The exposure technique may include
aligning a reticle along a scanning direction; and repeatedly
exposing a reticle pattern onto a substrate and moving the plate by
a half reticle width or less to thereby expose the whole substrate
twice or more.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 illustrates a step-and-repeat exposure apparatus.
[0019] FIG. 2 illustrates LCD substrate pattern arrangement on an
underlying substrate.
[0020] FIG. 3 shows examples of irregular pattern connection.
[0021] FIG. 4 is a perspective view illustrating a scanning
exposure apparatus.
[0022] FIG. 5 is a schematic illustration of a scanning type
exposure apparatus.
[0023] FIG. 6 is a perspective view illustrating a scanning
exposure technique.
[0024] FIG. 7 is a process diagram showing the steps taken to
fabricate an LCD substrate.
DETAILED DESCRIPTION
[0025] FIG. 4 is a perspective view illustrating a schematic
construction of a scanning exposure apparatus 400. The apparatus
400 includes an illuminative optical system 403 for transcribing a
pattern from a mask 401 onto a substrate 402, and a projective
optical system 404 including multiple projective optical system
modules 404a, 404b, 404c, 404de, and 404e. The apparatus 400 also
includes a mask stage (shown in FIG. 5) for supporting the mask
401, a substrate stage 405 for supporting a glass substrate 402,
and alignment detecting systems 406a, 406b.
[0026] FIG. 4 also shows a coordinate system 408, showing that the
optical axis of the projection optical system 404 lies along the
Z-axis. The direction of synchronous movement of the mask 401 and
the glass substrate 402 (i.e., the scanning direction) lies along
the Y-axis, perpendicular to the Z-axis. The movement direction of
the glass substrate 402 may also be made along the X-axis. In other
words, the substrate stage 405 moves in both in the X-direction and
the Y-direction, carrying with it the glass substrate 402. When the
mask 401 is scanned, the glass substrate 402 and the mask 401 may
synchronously move in the Y-direction.
[0027] As shown in FIG. 5, the illumination optical system 403
emits a light beam (i.e., the exposure light) from a light source
506 such as an ultrahigh pressure mercury lamp. The illumination
optical system 403 includes a dichroic mirror 507, a wavelength
selecting filter 508, and a light guide 509. The illumination
optical system 403 also includes illumination system modules
disposed to provide light to each of the projective optical modules
404a-404e.
[0028] The light beam emitted from light source 506 is converged by
the elliptical mirror 505, and is directed to the dichroic mirror
507. The dichroic mirror 507 reflects light having a selected
exposure wavelength, while light of other wavelengths passes
through. The light reflected by the dichroic mirror 507 is incident
on the wavelength selecting filter 508. The filter 508 filters the
incident light to pass a pre-selected wavelength of the incident
light appropriate for conducting exposure by projection optical
system 404. The filtered light is then directed to the light guide
509 that splits the filtered light into five beams. One beam is
directed to each projective optical module 404a-404e via a
reflecting mirror 511.
[0029] An exposure shutter 512 is also present and is freely
movable in or out of the light path. During periods of
non-exposure, the exposure shutter 512 is moved or inserted into
the light path in order to stop light from reaching the mask 401.
On the other hand, during exposure periods, the exposure shutter
512 is moved out of the light path in order to illuminate the mask
401.
[0030] To that end, a shutter operating unit 516 for advancing and
retreating the exposure shutter 512 is installed in the optical
system 403. A control unit 517 controls the shutter operating unit
516.
[0031] As noted above, light is diverged from the light guide 509
and is directed through each illumination system module 403 through
the reflecting mirror 511.
[0032] Each illumination system module 403 includes an input
illuminative system and a condenser optical system. In addition,
the illuminative system modules 403 are arranged in X and Y
directions at regular intervals. Thus, light from each illumination
system module 403 illuminates a different region of the mask
401.
[0033] As shown in FIG. 5, the input illuminative system obtains a
uniform illumination light beam from the light guide 509. In
addition, a light intensity adjustment mechanism is provided in the
input illuminative system to control the intensity of light in the
light beam.
[0034] Light transmitted through the light intensity adjustment
mechanism reaches a fly eye lens 514 through a relay lens 513. The
fly eye lens 514 will equalize illumination intensity on the
condenser 515 (part of the condenser optical system). Thus, light
transmitted through the fly eye lens 514 illuminates a region of
the mask 401 uniformly through the condenser 515.
[0035] In addition, a light intensity monitoring mechanism is also
provided in the condenser optical system. The light intensity
monitoring mechanism monitors illumination intensity by reflecting
part of the light incident on the half mirror 519 incident into a
detector 520. The detected illumination intensity is output to the
control unit 517. In response, the control unit 517 adjusts the
light intensity to a predetermined value by monitoring and
controlling the light intensity monitor and the light intensity
adjusting mechanism.
[0036] Light transmitted through the mask 401 is incident into the
projective optical system modules 404a-404e. As a result, the
pattern in the illumination region of the mask 401 is exposed, as
an equimultiple erect image, onto the glass substrate 402. More
particularly, the pattern on the mask 401 is exposed onto resist
coated on the glass substrate 402.
[0037] Each projective optical system module 404a-404e includes two
groups of catadioptric systems, an image shift mechanism for moving
a pattern image on the mask 401 in an X-direction or a Y-direction,
and an image multiplier, an image rotator, and a field
diaphragm.
[0038] Light transmitted through the mask 401 is incident into the
image shift mechanism. The image shift mechanism shifts the image
pattern on the mask 401 along the X-axis or the Y-axis. Light
transmitted through the image shift mechanism is incident into the
first catadioptric system.
[0039] The first catadioptric system forms an intermediate image of
the mask image at the position occupied by the field diaphragm. The
field diaphragm sets a projection region on the glass substrate
402. Light transmitted through the field diaphragm is incident into
the second catadioptric system and is subsequently incident into
the projection region on the glass substrate defined by the field
diaphragm.
[0040] An exposure method that employs the scanning type projective
exposure apparatus 400 is described next with reference to FIG. 6.
FIG. 6 shows a reticle 601 on which an LCD substrate pattern is
formed that is scanned by the apparatus 400, a projective optical
system 604 that is movable and that includes multiple projective
optical system modules, a glass substrate 602 (supported by a
substrate stage) on which will be formed the LCD substrate, and an
exposure region 603 that outlines the LCD substrate area that
includes the pixel and transistor switching circuitry for the LCD
substrate.
[0041] The Scanning exposure apparatus 400 employs an equimultiple
erect orthoscopic image scanning system. Accordingly the pattern on
the reticle 601 is transcribed onto the glass substrate 602 without
magnification or reduction (i.e., in a 1:1 proportion).
[0042] The projective optical system 604 scans the reticle 601
along the scanning direction (along the Y-axis) using a rectangular
(slit-shaped) illumination region having a length direction 605
perpendicular to the scanning direction. As the reticle 601 is
scanned, it is moved in the Y axis direction at a pre-selected
speed VP. In one implementation, the longer side of the reticle 601
(disposed along the longer axis direction 606) is arranged to lie
along the scanning direction (the Y axis direction). As a result, a
relatively large exposure area is scanned across the glass
substrate 602, and accordingly exposure time may be reduced.
[0043] The scanning projective exposure apparatus 400 is an
equimultiple erect orthoscopic image scanning system, and thus may
synchronize movement of the glass substrate 602 with the reticle
601. In other words, the glass substrate 602 is moved at speed VR,
and VR and VP may be identical.
[0044] As described below, exposure is performed twice or more on
the exposure region 603 of the glass substrate 602. In order to
help illustrate an exposure process in which the exposure region
603 is exposed twice, the reticle 601 is shown to include a leading
pattern section A and a trailing pattern section B. The dashed line
separating the two pattern sections is for reference only and forms
no part of the reticle pattern. The pattern in leading pattern
section A is symmetric to the pattern in trailing pattern section
B.
[0045] Initially, the longer axis direction 606 of the reticle 601
is arranged along the Y axis direction, the glass substrate 602 is
arranged horizontal to the reticle 601 and one-half of the reticle
pattern (the leading section A) is overlapped with an edge portion
603A of the exposure region 603. The apparatus 400 then scans the
reticle pattern onto the exposure region 603 while the reticle 601
and the glass substrate move at speed VP=VR. Accordingly, as shown
in FIG. 6, exposure is performed on the edge portion 603A of the
exposure region 603 on the glass substrate 602. As a result, the
edge portion 603A is exposed by the leading pattern section A,
while the trailing pattern section B exposes an unused or
non-resist coated outer portion beyond the edge portion 603A.
[0046] Next, the exposure apparatus 400 moves the glass substrate
602 along the -X axis one-half width of the reticle 601 (e.g.,
one-half of the length of the shorter side of the reticle 601). The
reticle pattern is again scanned, and the reticle pattern is
transcribed while the reticle 601 and the glass substrate 602 move
at speed VP=VR, As a result, the edge portion 603A is exposed by
the trailing pattern section B, which is symmetric to the leading
pattern section A. Thus, the edge portion 603A has been exposed
twice, while substrate portion 603B is newly exposed with the
leading edge pattern section A.
[0047] Again, the exposure apparatus 400 moves the glass substrate
602 along the -X axis one-half width of the reticle 601. The
exposure apparatus 400 again scans the reticle 601 to transcribe
the reticle pattern onto the exposure region 603 of the glass
substrate 602. As a result, the substrate portion 603B is exposed a
second time, in this instance with the trailing pattern section B,
while substrate portion 603C is newly exposed with the leading
pattern section A.
[0048] By repeating the above-explained process, the whole exposure
region 603 of the plate is exposed twice.
[0049] The exposure apparatus 400 prevents the generation of stitch
defects on the exposure region 603 by exposing the exposure region
603 twice or more in the manner noted above. Thus, there are no
minute overlap regions between distinct pattern sections on the
exposure region 603 that are susceptible to stitch defects. In
other implementations, the movement length along the, -X axis of
the glass substrate 602 may be less than one-half of the reticle
pattern 601 width in order to expose the exposure region 603 more
than twice. For example, the movement length may be one-third of
the reticle pattern 601 width so that the exposure region 603 is
exposed three times.
[0050] FIG. 7 is a process diagram showing the steps taken to
fabricate an LCD substrate. Initially, the exposure apparatus 400
is setup to align a reticle along a scanning direction, the reticle
characterized by a reticle width and a reticle length and
comprising a reticle pattern (Step 702). Subsequently, the exposure
apparatus 400 scans the reticle pattern along the reticle length
onto a portion of an exposure area on a substrate (Step 704). Next,
the exposure apparatus 400 moves the substrate perpendicular to the
scanning direction no greater than one-half of the reticle width
(Step 706). If the entirety of the exposure area has been exposed
at least twice (Step 708), then the process is complete. Otherwise,
the exposure apparatus 400 returns to Step 704 for another
exposure.
[0051] As described above, by exposing the whole exposure region
603 of glass substrate 602 twice or more, stitch defects are
prevented in the exposure region 603. Accordingly, manufacturing
yield and LCD panel picture quality are improved.
* * * * *