Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2002-04-19
2003-04-22
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S138000, C349S122000
Reexamination Certificate
active
06552759
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a substrate of a liquid crystal display device (LCD), and a method for manufacturing the same. In particular, the present invention relates to a method for manufacturing a substrate of a liquid crystal display wherein an organic layer and a pixel electrode thereon are firmly cohering to each other.
2. Description of Related Art
A conventional substrate of a liquid crystal display device having a switching element and a pixel electrode is formed, mentioned as follows, referring to
FIGS. 1
a
and
1
b.
FIGS. 1
a
and
1
b
show the inverse staggered structure of the thin film transistor (TFT).
Referring to
FIG. 1
a,
a gate electrode
60
a
is formed on a transparent substrate
10
. A gate insulation layer
50
is deposited thereon to cover the gate electrode
60
. A semiconductor layer
90
with an island shape is formed on the gate insulation layer
50
on the gate electrode
60
. On the surface of the semiconductor layer
90
, ohmic contact layers
92
a
and
92
b
are formed in separate regions. On one ohmic contact layer
92
a,
a source electrode
70
a
is formed and a data line
70
connecting to the source electrode
70
a
is formed on the gate insulation layer
50
. On the other ohmic contact layer
92
b,
a drain electrode
70
b
is formed. As the gate electrode, source electrode and the drain electrode are formed, a TFT acting as a switching element is completed.
On the substrate having the TFT, an organic layer
55
, including a benzocyclobutene (or BCB) generally containing combinations of C, H and O elements, is formed. A contact hole
30
is formed to expose some surface of the drain electrode
70
b
by patterning the organic layer
55
. The reason for using the organic layer of the substrate of the LCD is that after being coated on the substrate of which surface has stepped profile, the surface of the organic layer does not project the stepped profile. That is substantially flat surface of the organic layer is formed. Also, the organic layer has a lower coefficient constant similar to the inorganic layer, such as silicon oxide (SiO
x
) or silicon nitride (SiN
x
) . Therefore, after the organic layer is formed on the substrate, a pixel electrode can be formed over the area on which the data line is formed in order to maximize the aperture ratio. In that regard, an ITO (Indium Tin Oxide) layer is deposited on the organic layer having the contact hole
30
and is patterned to form a pixel electrode
40
by etching the ITO layer with the photo-resist
88
pattern using a wet etching method. It is possible to overlap the pixel electrode and some portion of the data line because problems such as cross talk do not occur between them due to the characteristics of the organic material mentioned above.
However, during the etching process, the ITO layer can be easily peeled off from the organic layer or a vacancy can occur between the ITO layer and the organic layer because the coherency between them is very weak. As a result, the etchant can penetrate into the vacancy so that the pixel electrode can be over etched, as shown in
FIG. 1
b.
FIG. 1
b
shows the undesirable patterned results which (A) is the peeled off portion of the pixel electrode (B) and (C) are the over etched portion of the pixel electrode.
If the edge portions of the ITO layer, which constitutes the pixel electrode, are over etched by the etchant, then the size of the pixel electrode is reduced and becomes irregular. This is referred to as a CD loss. As a result, the aperture ratio becomes smaller than the expected value.
SUMMARY OF THE INVENTION
In order to overcome the above-mentioned problem, an object of the present invention is to suggest a method for manufacturing a substrate of the LCD in which the coherence between the pixel electrode and the organic layer is enhanced as well as the structure of the LCD by the same method. Another object is to protect the pixel electrode from being over etched by enhancing the coherence of the pixel electrode with the organic layer.
Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
The present invention suggests a method in which an intermediate thin layer
156
is formed by treating the surface of the organic layer
155
with plasma of H
2
, as shown in
FIG. 2
a.
The organic layer typically comprises C, H, and O radicals. As a result, the surface of the organic layer has an unstable state. The present invention suggests an enhanced method for making the surface of the organic passivation layer more stable by treating it with plasma containing H element. Consequently, the pixel electrode fabricated on the treated region has stronger adherence and maintains its shape and size. When the surface of the organic layer is treated with the H
2
plasma, the surface has an O—H bonding structure. Therefore, as an ITO layer or a metal layer is deposited thereon, the coherence of it on the organic layer is enhanced. As a result, it is possible to protect the inorganic layer, such as an ITO layer or an metal layer deposited on the organic layer, from being peeling off and being undesirably patterned.
According to this scope, the present invention suggests an LCD comprising a substrate, a TFT on the substrate, an organic layer covering the TFT, an intermediate layer
180
, as shown in
FIG. 2
b
is formed by treating the surface of the organic layer with H
2
plasma, a contact hole exposing a surface of a drain electrode of the TFT by removing some portion of the organic layer and the intermediate layer, a pixel electrode connecting to the drain electrode through the contact hole. The present invention also suggests an LCD according to the above-mentioned structure wherein the intermediate layer is further formed on the side wall of the contact hole.
Additionally, the present invention suggests a method for manufacturing an LCD comprising steps of forming a TFT on a substrate, forming an organic layer covering the TFT, treating the surface of the organic layer with H
2
plasma, forming a contact hole exposing some surface of the drain electrode by removing some of the organic layer and intermediate layer, forming a pixel electrode connecting to the drain electrode through the contact hole. The present invention also suggests a method for manufacturing an LCD according to the above-mentioned method wherein the step of forming a contact hole is performed after forming the organic layer, and then the step of treating the surface of the organic layer is performed so that the side wall of the contact hole also has the intermediate layer on the surface.
These and other aspects, features and advantages of the present invention will be better understood by studying the detailed description in conjunction with the drawings and the accompanying claims.
REFERENCES:
patent: 5523865 (1996-06-01), Furuta et al.
patent: 5622814 (1997-04-01), Miyata et al.
patent: 5721601 (1998-02-01), Yamaji et al.
patent: 5821138 (1998-10-01), Yamazaki et al.
patent: 02-074901 (1990-03-01), None
patent: 03-209435 (1991-09-01), None
patent: 08-017798 (1996-01-01), None
Bae Sung-Sik
Choi Jae-Beom
Hwang Kwang-Jo
Kim Woong-Kwon
LG Electronics Inc.
Ton Toan
LandOfFree
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