Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-03-23
2002-06-25
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S187000
Reexamination Certificate
active
06411356
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of patterning a pixel electrode of a liquid crystal display (LCD) device including a switching element for driving and controlling a liquid crystal. More specifically, the present invention relates to a patterning method for manufacturing a liquid crystal display having a TFT (thin film transistors) functioning as a switching element in which a passivation layer covers the TFT and a pixel electrode is connected to an output electrode of the TFT on the passivation layer, and also relates to a structure of a liquid crystal display device manufactured by this method.
2. Description of the Background Art
Conventionally, an LCD has a structure as shown in
FIG. 1
which illustrates a plane view of an enlarged LCD panel. A gate line
17
is arranged to extend in a horizontal direction and a data line
15
is arranged to extend in a vertical direction which crosses the gate line
17
perpendicularly. At the intersection portion of the gate line
17
and the data line
15
, a TFT including a gate electrode
17
a
, a source electrode
15
a
, a drain electrode
15
b
and a semiconductor layer
22
is formed. A passivation layer (not shown) is formed thereon. A pixel electrode
4
connected to the drain electrode
15
b is formed on the passivation layer.
When patterning the pixel electrode
4
according to the conventional method, the actual patterned shape is often different from the originally designed shape or desired shape.
FIG. 2
shows the typically distorted shape of the pixel electrode
4
after being patterned by the conventional method.
The dotted line
55
in
FIG. 2
is the boundary of the originally designed shape of the pixel electrode
4
. As seen in
FIG. 2
, the pixel electrode
4
has a distorted boundary portion having a width W
2
and tearing-off portions
20
in the pixel electrode. Here, W
1
is a width of the data line
15
.
Referring to
FIGS. 3
a
-
3
j
which are cross-sectional views cut along the a—a line of the
FIG. 1
, a conventional method for manufacturing the LCD will be explained in order to illustrate the reason for the pixel electrode having an undesired pattern shown in FIG.
2
.
On a transparent substrate
11
, a metal selected from the group of aluminum (Al), aluminum alloy, chromium (Cr) or molybdenum (Mo) is deposited to form a first metal layer
50
. A photo resist
51
is coated on the first metal layer
50
as shown in
FIG. 3
a.
The photo resist
51
is patterned to have a predetermined shape. Using a wet etching method, the first metal layer
50
is patterned according to the shape of the photo resist
51
to form a gate line (not shown) and to form a gate electrode
17
a
which is derived from the gate line. Then the remaining photo resist on the gate line and the gate electrode
17
a
is removed as shown in
FIG. 3
b
. The gate electrode
17
a
can be anodized to eliminate hillocks thereon. In addition, the cross-sectional shape of the gate electrode
17
a
preferably has a tapered shape.
On the substrate having the gate electrode
17
a
, a gate insulating layer
23
including an inorganic insulating material such as SiN
x
or SiO
x
, an amorphous silicon (or a-Si)
52
and an n
+
type impurity doped a-Si (or N
+
type a-Si)
53
are sequentially deposited. A photo second resist
61
is coated thereon as shown in
FIG. 3
c.
The second photo resist
61
is patterned to have a predetermined shape. According to the patterned second photo resist
61
, the a-Si material
52
and the n
+
type a-Si material
53
are simultaneously etched to form a semiconductor layer
22
and an ohmic contact layer
25
. The remaining second photo resist
61
on the ohmic contact layer
25
is removed as shown in
FIG. 3
d.
A second metal layer
54
including chromium or aluminum is deposited and a third photo resist
63
is coated on the second metal layer
54
as shown in
FIG. 3
e.
The third photo resist
63
is patterned to have a predetermined shape. According to the patterned third photo resist
63
, the second metal layer
54
is patterned via a wet etching method to form a data line
15
. At the same time, a source electrode
15
a
derived from the data line
15
and a drain electrode
15
b
which faces the source electrode
15
a
are formed on the ohmic contact layer
25
whereas the source electrode
15
a
and the drain electrode
15
b
are separated via a distance. The n
+
type a-Si material
53
between the source electrode
15
a
and the drain electrode
15
b
is removed via a dry etching method using the source electrode
15
a
and the drain electrode
15
b
as a mask. The remaining photo resist on the source electrode
15
a
and the drain electrode
15
b
is removed as shown in
FIG. 3
f.
A passivation layer
26
including an organic material such as BCB (or benzocyclobutene) is coated thereon via a spin coating method. A fourth photo resist
65
is coated so as to have a thickness that is less than a thickness of the passivation layer
26
as shown in
FIG. 3
g.
The fourth photo resist
65
is patterned to have a predetermined shape. According to the patterned fourth photo resist
65
, the passivation layer
26
is patterned via a dry etching method to form a contact hole
30
which exposes a portion of the drain electrode
15
b
. The remaining fourth photo resist
65
on the passivation layer
26
is removed as shown in
FIG. 3
h.
On the passivation layer
26
, an ITO(or Indium Tin Oxide)
55
is deposited so as to have a thickness of about 500 Å. On the ITO layer
55
, a fifth photo resist
67
is coated as shown in
FIG. 3
i.
The fifth photo resist
67
is patterned to have a predetermined shape. According to the patterned fifth photo resist
67
, the ITO layer
55
is patterned via a wet etching method to form a pixel electrode
4
as shown in
FIG. 3
j.
In the above mentioned conventional method, because the passivation layer
26
has a lower dielectric constant (lower than 3.0) than the inorganic material and forms an organic insulating layer(BCB) which can even a surface property thereof, the pixel electrode
4
disposed on the passivation layer can be overlapped with the data line
15
so that the aperture ratio can be maximized.
However, after the passivation layer
26
including an organic material such as BCB is patterned by using the fourth photo resist
65
as shown in
FIGS. 3
g
and
3
h
, the surface of the patterned passivation layer
26
can be rough and uneven.
If the pixel electrode
4
is formed on the uneven surface of the passivation layer
26
, the patterned pixel electrode
4
has distorted edge portions and tearing-off portions as shown in FIG.
2
.
The cause of the formation of the distorted pattern is explained hereafter in detail.
When the passivation layer having an Si bond structure such as BCB is patterned, the substrate which has the passivation layer and patterned photo resist is inserted into an etching chamber filled with an etching gas such as O
2
/SF
6
or O
2
/CF
4
. The portions of the passivation layer exposed through the patterned photo resist are removed by changing a volatile material SiF4 according to the chemical reaction of the Si functional group of the passivation layer and the F radical of the SF
6
or CF
4
. At the same time, the photo resist is removed by etching with O
2
gas.
As the etching speed of the passivation layer and the etching speed of the photo resist is similar, the thickness of the photo resist is the same as that of the passivation layer. So, when the patterning of the passivation layer is finished, the photo resist is almost completely removed.
However, it is very difficult to coat the photo resist to have a uniform thickness. Therefore, after the patterning of the passivation layer is finished, the portions where the photo resist is thicker have some remaining photo resist. Otherwise, at the portion where the photo resist is thinner, some surfaces of the passivation layer are over-etched by the etching gas as shown in FIG.
4
.
For example, when
Kim Woong Kwon
Lim Kyoung Nam
Birch & Stewart Kolasch & Birch, LLP
Chowdhury Tarifur R.
LG Philips LCD Co., Ltd.
Sikes William L.
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