Method of fabricating color filter substrate for liquid...

Details Method of fabricating color filter substrate for liquid... Method of fabricating color filter substrate for liquid...

2003-04-21

2004-01-27

McPherson, John A. (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Radiation modifying product or process of making

Screen other than for cathode-ray tube

C430S200000

Reexamination Certificate

active

06682862

ABSTRACT:

The present invention claims the benefit of Korean Patent Application No. P2002-083198 filed in Korea on Dec. 24, 2002, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a method of fabricating a color filter substrate for a liquid crystal display device.
2. Discussion of the Related Art
Due to rapid development in information technology, display devices have evolved to process and display increasingly large amounts of information. Flat panel display technologies have been recently conceived and developed for display devices having small thickness, light weight, and low power consumption. Among these technologies, the liquid crystal display (LCD) device is already widely used for notebook computers, desktop monitors, and other application because of its superior resolution, color image display, and image quality.
In general, an LCD device includes an upper substrate, a lower substrate, and a liquid crystal layer disposed between the upper and lower substrates. The LCD device uses an optical anisotropy of a liquid crystal material and produces an image by varying the transmittance of light according to the arrangement of liquid crystal molecules by an electric field.
The lower substrate, which is usually referred to as an array substrate, includes thin film transistors and pixel electrodes. The lower substrate is fabricated through repeated photolithography processes to pattern a previously formed thin film. The upper substrate, which is usually referred to as a color filter substrate, includes a color filter layer for displaying color images. The color filter layer commonly includes sub-color filters of red (R), green (G), and blue (B). The color filter layer is formed by various methods including, for example, a dyeing method, an electro-deposition method, a pigment dispersion method, and a printing method. In general, the pigment dispersion method is more commonly used because it forms a fine pattern with good reproducibility.
FIGS. 1A
to
1
D are cross-sectional views showing a method of fabricating a color filter substrate for a liquid crystal display (LCD) device according to the related art. Here, the pigment dispersion method is used.
In
FIG. 1A
, a black matrix
15
is formed on an insulating substrate
10
by depositing a metal material or coating a resin and patterning the metal material or the resin through a photolithography process. The black matrix
15
blocks light leakage, which is caused by irregular operation of liquid crystal molecules, in regions except pixel electrodes of an array substrate (not shown). The black matrix
15
also prevents light from going into a channel of a thin film transistor of the array substrate.
As shown in
FIG. 1B
, a color resist
17
, which may be one of red, green and blue resists, for example a red one, is coated on the substrate
10
including the black matrix thereon by spin coating. A mask
20
having a light transmitting portion and a light blocking portion is disposed over the red resist
17
, and the red resist
17
is exposed to light using the mask
20
. Here, the red resist
17
is shown to have a negative property. That is, a portion of the red resist
17
that is not exposed to light is removed.
As shown in
FIG. 1C
, the red resist
17
of
FIG. 1B
is developed, and a red color filter pattern
17
a
is formed. Then, the red color filter pattern
17
a
is cured and hardened.
As shown in
FIG. 1D
, green and blue color filter patterns
17
b
and
17
c
are formed on the black matrix
15
through similar processes as shown in
FIGS. 1B and 1C
. Next, an overcoat layer
23
and a common electrode
25
are subsequently formed on the substrate
10
including the color filter patterns
17
a
,
17
b
and
17
c
. The overcoat layer
23
protects the color filter patterns
17
a
,
17
b
and
17
c
, and flattens the surface of the substrate
10
having the color filter patterns
17
a
,
17
b
and
17
c
. The common electrode
25
is made of a transparent conductive material, such as indium-tin-oxide and indium-zinc-oxide. The overcoat layer
23
may be omitted.
In the fabrication method of the color filter substrate using the pigment dispersion, since the color filter substrate is fabricated by repeated processes of coating, exposing, developing, and curing of a color resist, the fabrication method is complicated, thereby requiring much time and equipment. To solve the above problem, a fabrication method of a color filter substrate using thermal imaging has been proposed, as disclosed for example in U.S. Pat. No. 6,242,140.
FIGS. 2A
to
2
D show a method of fabricating a color filter substrate using thermal imaging according to the related art.
As shown in
FIG. 2A
, a black matrix
35
is formed on an insulating substrate
30
by depositing a metal material or coating a resin, and patterning the metal material or the resin by photolithography.
Then, as shown in
FIG. 2B
, a first color transcription film
40
is disposed over the substrate
30
including the black matrix
35
. The first color transcription film
40
includes a supporting film
40
a
, a light-to-heat conversion (LTHC) layer
40
b
, and a color filter layer
40
c.
Next, as shown in
FIG. 2C
, the first color transcription film
40
is adhered to the substrate
30
without bubbles. A laser head
50
, from which a laser beam is generated, is disposed over the first color transcription film
40
. The laser beam is applied to the first color transcription film
40
in a portion where a first color filter pattern will be formed later while the laser head
50
is reciprocated in a straight line. In the first color transcription film
40
exposed to the laser beam, the LTHC layer
40
b
transforms light absorbed from the laser beam into thermal energy, thereby emitting thermal energy. Then, the color filter layer
40
c
is transferred on the substrate
30
due to the emitted thermal energy. Here, the color filter substrate may be a stripe type where color filter patterns in a line have the same color. In that case, a first line is exposed to the laser beam by moving the laser head in a straight line, but second and third lines are skipped. Similarly, a fourth line is exposed to the laser beam. In this manner, all the lines of the first color filter pattern are exposed by the above method, and the first color transcription film
40
is removed.
As shown in
FIG. 2D
, the first color filter pattern
45
a
is formed between the adjacent black matrixes
35
on the substrate
30
. The first color filter pattern
45
a
may be a red color filter. A second color filter pattern
45
b
and a third color filter pattern
45
c
are formed through the same process shown in
FIGS. 2B and 2C
. The second and third color filer patterns
45
b
and
45
c
may be green and blue color filters, respectively. The substrate
30
having the color filter patterns
45
a
,
45
b
and
45
c
is placed in a hardening furnace, and the color filter patterns
45
a
,
45
b
and
45
c
are hardened. An overcoat layer
47
is formed on the color filter patterns
45
a
,
45
b
and
45
c
. The overcoat layer
47
protects the color filter patterns
45
a
,
45
b
and
45
c
and flattens the surface of the substrate
30
otherwise having steps. A common electrode
49
is formed on the overcoat layer
47
by depositing a transparent conductive material, such as indium-tin-oxide and/or indium-zinc-oxide.
In the thermal imaging method, manufacturing throughput of the color filter substrate is influenced by an application direction of the laser beam, wherein the laser beam is applied to the transcription film in a direction parallel to a pixel length of the LCD device. For example, in a color filter substrate of a video graphic array (VGA) LCD device, which has a resolution of 640 by 480, the VGA LCD device has sub-pixels of 640 by 3 lines (i.e., 1920 lines). Thus, the laser head
50
must scan 640 times for each color filter pattern. Therefore, total number of scans

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