Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1999-02-10
2002-01-08
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S187000, C349S138000, C438S149000
Reexamination Certificate
active
06337723
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a liquid crystal display device (LCD) and more particularly, the present invention relates to a method of manufacturing an LCD in which a pixel electrode is formed on a photosensitive passivation layer.
2. Description of the Background Art
Generally, a conventional liquid crystal display device in which a pixel electrode is formed on a photosensitive passivation layer includes a gate bus line
60
and a data bus line
70
which are arranged in a matrix array, as shown in FIG.
1
. At the end portions of the gate bus line
60
and the data bus line
70
, a gate pad
60
c
and a data pad
70
c
connected to an output of a driving IC are formed, respectively. The LCD further includes a TFT which functions as a switching element and is driven by an electrical signal from the gate bus line
60
and the data bus line
70
. The TFT is disposed at the intersection portion of the gate bus line and data bus line. The LCD also includes a pixel electrode
40
connected to the TFT.
The TFT includes a gate electrode
60
a
derived from the gate bus line
60
, a source electrode
70
a
derived from the data bus line
70
and a drain electrode
70
b
arranged to face the source electrode
70
a
. The gate electrode
60
a
is covered by a gate insulating layer (not shown). A semiconductor layer
90
is disposed over the gate electrode
60
a
on the gate insulating layer. The source electrode
70
a
and the drain electrode
70
b
are disposed at each side of the semiconductor layer
90
. The drain electrode
70
b
is connected to the pixel electrode
40
through a contact hole
30
a
formed at a passivation layer (not shown). At the overlapped portion of the adjacent gate bus line
70
, a storage capacitance electrode
35
is connected to the pixel electrode
40
through a storage contact hole
30
b.
Referring to
FIG. 2
which is a cross-sectional view of
FIG. 1
cut along line A—A in
FIG. 1
, the structure and method of manufacturing of the LCD in which a pixel electrode is formed on the photosensitive passivation layer will be explained in detail.
On a transparent substrate
10
, a gate bus line
60
, a gate electrode
60
a
derived from the gate bus line
60
and a gate pad
60
b
disposed at the end of the gate bus line
60
are formed. A gate insulating layer
50
including SiN
x
or SiO
x
is formed so as to cover the entire surface of the substrate including the gate bus line
60
, the gate electrode
60
a
and the gate pad
60
b
. An island-shaped semiconductor layer
90
including a-Si (amorphous silicon) is formed on the gate insulating layer
50
over the gate electrode
60
a
. Ohmic contact layers
90
a
and
90
b
including n
+
type a-Si are formed separately on the semiconductor layer
90
. A source electrode
70
a
and a drain electrode
70
b
are connected to the ohmic contact layers
90
a
and
90
b
, respectively. A data bus line
70
connected to the source electrode
70
a
is formed on the gate insulating layer
50
. A TFT is completed by forming the gate electrode
60
a
, the semiconductor layer
90
, the ohmic contact layers
90
a
and
90
b
, the source electrode
70
a
and the drain electrode
70
b.
A passivation layer
80
including a photosensitive acrylic resin is formed on the entire surface of the substrate having the TFT. A drain contact hole
30
a
, a storage contact hole
30
b
(
FIG. 1
) and a gate pad contact hole
30
c
are formed by patterning the passivation layer
80
. The method of forming the contact holes includes the steps of exposing the photosensitive passivation layer with a mask, developing the passivation layer with a developer and removing the remaining passivation layer material at the contact holes with an etchant which is CF
4
+O
2
or SF
6
+O
2
gas. At the same time, some portions of the gate insulating layer
50
covering the gate pad
60
b
are removed to form a gate pad contact hole
30
c
exposing the gate pad
60
b
by using the CF
4
+O
2
or SF
6
+O
2
gas.
After the contact holes are formed, a pixel electrode
40
and a gate pad terminal
40
a
are formed by depositing an ITO (Indium Tin Oxide) on the entire surface of the substrate and then patterning the ITO layer.
The reason for using the photosensitive material for the passivation layer is that the manufacturing process is simplified because a photo resist is not used and the contact hole can be formed by etching the passivation layer directly.
In above mentioned conventional method, the surface of the passivation layer is not smooth and uniform because it is attacked by the CF
4
+O
2
or SF
6
+O
2
etching gas. As a result of the etching gas attacking the passivation layer surface, the pixel electrode formed on the uneven surface of the passivation layer has an undesired, uneven shape. Furthermore, when the remaining passivation layer and the gate insulating layer are removed to form a gate contact hole with the CF
4
+O
2
or SF
6
+O
2
etching gas, the drain electrode can be cut off as shown in region F of
FIG. 2
, or the gate pad and the gate insulating layer can be over-etched as shown in region G of FIG.
2
.
According to the conventional method, the metal layer disposed under the passivation layer can be cut off or over-etched by the CF
4
+O
2
or SF
6
+O
2
etching gas, when the passivation layer is patterned so that the quality of the LCD becomes inferior.
SUMMARY OF THE INVENTION
In order to overcome the problems in the conventional methods described above, preferred embodiments of the present invention provide a method of manufacturing an LCD in which a passivation layer including a photosensitive acrylic resin has a smooth, even surface after the passivation layer is patterned and a metal layer under a passivation layer including a photosensitive acrylic resin is not cut off. In addition, preferred embodiments of the present invention provide a method of manufacturing an LCD in which a gate pad and a gate insulating layer are not over-etched when the gate insulating layer is patterned to form a gate contact hole.
To solve the above-described problems with the conventional methods and to achieve the results described in the preceding paragraph, preferred embodiments of the present invention provide a method of manufacturing an LCD using an etching gas including one of CF
4
+H
2
, C
x
F
y
+H
2
, C
x
F
y
+C
x
F
y
H
z
, C
x
F
y
+C
x
F
y
H
z
+H
2
and C
x
F
y
H
z
. The method according to preferred embodiments of the present invention includes the steps of forming on a substrate, a switching element, bus lines connected to the switching element and pads at the end of each of the bus lines, coating a photosensitive passivation layer on an entire surface of the substrate, forming contact holes exposing an electrode and a pad by exposing and developing the passivation layer such that a portion of the passivation remains, removing a remaining portion of the passivation layer at the contact hole using an etching gas including at least one of CF
4
+H
2
, C
x
F
y
+H
2
, C
x
F
y
+C
x
F
y
H
z
, C
x
F
y
+C
x
F
y
H
z
+H
2
and C
x
F
y
H
z
and forming a pixel electrode connected to the exposed electrode through the contact hole.
Other advantages, features and novel elements of preferred embodiments of the present invention will become apparent from the following description of preferred embodiments of the present invention with reference to the drawing figures attached hereto.
REFERENCES:
patent: 5229645 (1993-07-01), Nakashima
patent: 5668380 (1997-09-01), Wuu et al.
patent: 5978058 (1999-11-01), Sung
patent: 6037195 (2000-03-01), Toriyama et al.
Birch & Stewart Kolasch & Birch, LLP
LG. Philips LCD Co. Ltd.
Ton Toan
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