Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Including integrally formed optical element
Reexamination Certificate
2002-05-10
2003-11-25
Le, Dung A. (Department: 2818)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Including integrally formed optical element
Reexamination Certificate
active
06653159
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to a method of fabricating a thin film transistor liquid crystal display(TFT-LCD), and more particularly, to a method of fabricating a thin film transistor liquid crystal display to prevent the Mentsuki Effect.
2. Description of the Prior Art
Due to continued development and advancement in electrical technology, the range of application as well as the demand for flat panel displays is ever increasing. A liquid crystal display (LCD) is one type of flat panel display and is employed extensively in small-scale products, such as sphygmomanometer, to various portable electronic devices such as PDAs and notebooks, to such an extent as the commercial big panel display.
At present, the LCD device is primarily composed of a thin film transistor (TFT) with a matrix structure to drive liquid-crystal-pixels so as to generate color-rich graphics. The conventional TFT-LCD includes a transparent substrate having a matrix of thin film transistors, pixel electrodes, scan lines, signal lines, a color filter and liquid-crystal materials between the transparent substrate and the color filter. Since TFT-LCD has the advantages of lightweight, low energy consumption, and free of radiation emission, the TFT-LCD is extensively applied to informational products and has a great potential for the future.
Please refer to
FIG. 1
of cross-sectional diagrams of fabricating a single TFT-LCD devicedevice
10
according to the prior art. The prior art technology utilizes the photo-etching-processes(PEP) seven times to form the TFT-LCD device
10
on a transparent glass substrate
11
of a twist-nematic(TN) TFT-LCD
10
system. Only the thin film transistor, the pixel electrode, the scan line, the signal line, the pad and a portion of crossing over of the scan line and the signal line are shown in FIG.
1
.
As shown in
FIG. 1A
, the glass substrate
11
comprises at least one transistor area
210
for forming a thin film transistor(TFT), at least one pad area
220
for forming a pad electrode, and at least one cross over region
230
of scan lines and signal lines. In the prior art method, a first metal layer (not shown) is deposited on the surface of the glass substrate
11
, then a first photo-etching-process(PEP-
1
) is performed to form a gate electrode
12
in the transistor area
210
, a pad electrode
14
in the pad area
220
, and a scan line
16
passing through the cross over region
230
. The gate electrode
12
is connected to another scan line (not shown) on the surface of the glass substrate
11
.
As shown in
FIG. 1B
, after the PEP-
1
, a first isolation layer
18
, a second isolation layer
22
, a semiconductor layer
24
and an etching stop layer (not shown) are deposited on the glass substrate
11
. Then, a second photo-etching-process (PEP-
2
) is performed to form an etching stop layer
26
above the gate electrode
12
, and other portions of the etching stop layer are totally removed. The semiconductor layer
24
is composed of polysilicon or amorphous silicon; the etching stop layer
26
is made of silicon nitride to prevent the semiconductor layer
24
from erosion in subsequent etching process.
As shown in
FIG. 1C
, a doped silicon conductive layer
28
is deposited on the semiconductor layer
24
and the etching stop layer
26
. Then, a third photo-etching-process(PEP-
3
) is performed to pattern the doped silicon conductive layer
28
, the semiconductor layer
24
and the second isolation layer
22
and remove the doped silicon conductive layer
28
, the semiconductor layer
24
and the second isolation layer
22
positioned (a) except the transistor area
210
and (b) except the cross over region
230
for forming a signal line pattern to act as a bottom isolation layer of the subsequent signal line (not shown).
As shown in
FIG. 1D
, a transparent conductive layer (not shown) is formed on the doped silicon conductive layer
28
and the first isolation layer
18
. Then, a fourth photo-etching-process(PEP-
4
) is performed for forming a transparent conductive layer
32
on the signal line pattern to act as an auxiliary signal line
32
, and two pixel electrodes
34
are formed each side of the auxiliary signal line
32
on the first isolation layer
18
.
As shown in
FIG. 1E
, a fifth photo-etching-process(PEP-
5
) is performed to form an opening in the first isolation layer
18
so as to expose the pad electrode
14
in the opening. Further, as shown in
FIG. 1F
, a second metal layer (not shown) is deposited over the glass substrate
11
. Then, a sixth photo-etching-process(PEP-
6
) is performed to form a main signal line above the auxiliary signal line
32
, and a pad signal line
39
in the pad area
220
. The second metal layer
38
is electrically connected to the pixel electrode
34
. Another etching process is performed to form an opening in the second metal layer
38
so as to expose the etching stop layer
26
in the opening, therefore, the thin film transistor(TFT)
42
is formed.
Finally, as shown in
FIG. 1G
, a passivation layer
44
is deposited over the glass substrate
11
. Then, a seventh photo-etching-process(PEP-
7
) is performed to remove the passivation layer
44
positioned (a) above the opening of the pad area
220
and (b) on the surface of the pixel electrode
34
, thus portions of the pad signal line
39
and the pixel electrode
34
are exposed.
In summary, the prior art method of fabricating a signal line
36
provides a glass substrate
11
, followed by forming a first isolation layer
18
and a second isolation layer (not shown in
FIG. 2
) on the glass substrate
11
. After some photo etching processes, a patterned semiconductor layer
24
and a patterned doped silicon conductive layer
28
are formed over the glass substrate
11
and a signal line is patterned. Afterwards, a transparent conductive layer
32
is patterned on the signal line pattern to act as an auxiliary signal line. Finally, a second metal layer
38
is formed on the transparent conductive layer
32
to act as a main signal line, and the overlapped main signal line and the auxiliary signal line form a signal line
36
.
However as shown in
FIG. 2
, the semiconductor layer
24
and the doped silicon conductive layer
28
are patterned by a same photo mask, and the transparent conductive layer
32
and the second metal layer
38
are patterned by another photo mask. Therefore, after two photo-etching-processes, misalignments and etching errors will be formed. In one liquid crystal display with millions of pixels, this misalignment or overetching phenomena happened frequently. The distance between the signal line
36
and each side of the pixel electrode
34
is defined as &dgr;0. Actually, after the etching process, the distances between the signal line
36
and each side of the pixel electrode
34
varies between &dgr;1 and &dgr;2 due to the misalignment of the process. When the main signal line
38
is formed in the subsequent process, the distances between the signal line
36
and each side of the pixel electrode
34
become &dgr;3 and &dgr;4 due to the misalignment of the PEP. These misalignment errors are shown in
FIG. 3
of a top view diagram.
When the distances between the signal lines
36
and each side of the pixel electrodes
34
are unequal(&dgr;3≠&dgr;4) or exceed a tolerance, the LCD panel would have a bright lines problem, namely the Mentsuki Effect. Therefore, it is important to avoid the problem mentioned above.
SUMMARY OF INVENTION
It is therefore an object of the present invention to provide a method of fabricating a thin film transistor liquid crystal display(TFT-LCD). The method is used to simplify the process and prevent the Mentsuki Effect of the thin film transistor liquid crystal display.
The present invention provides a method of fabricating a thin film transistor liquid crystal display(TFT-LCD). A TFT-LCD is fabricated on a substrate comprising at least one transistor area for forming a thin film transistor and at least one cross over region of a scan line and a signal line.
AU Optronics Corp.
Hsu Winston
Le Dung A.
LandOfFree
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