Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
2000-01-14
2002-05-28
McPherson, John A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S319000, C430S396000
Reexamination Certificate
active
06395457
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for manufacturing active matrix liquid crystal displays (AMLCDs), and more particularly to a method for manufacturing AMLCDs which can prevent disconnection of signal lines and short circuit by improving the step coverage of the liquid crystal displays (LCDs) having a layered structure.
2. Description of the Related Art
In conventional AMLCDs, switching devices having integrated active elements such as thin film transistors (TFTs) are used to drive and control pixels in the LCDs. As shown in
FIG. 1
, a conventional LCD with TFT arrays has rectangular pixel electrodes
12
arrayed in rows and columns on a transparent substrate
11
. Each of gate lines (address lines)
13
is formed between the rows of the pixel electrodes
12
, and each of source lines (data lines)
14
is formed between the columns of the pixel electrodes
12
. The TFTs
15
are electrically connected with the gate lines
13
and source lines
14
, in the vicinity of an intersection between the gate lines
13
and the source lines
14
.
FIG. 2A
shows a plan view of a part of liquid crystal display elements of the conventional LCD, and
FIG. 2B
shows a sectional view taken along line
2
B—
2
B in FIG.
2
A.
Referring to
FIGS. 2A and 2B
, the conventional LCD includes a TFT array, a gate line
13
and a gate electrode
13
a
formed on a transparent glass substrate
11
. An insulating layer
21
is formed to cover the gate electrode
13
a
and a gate bus line
13
b
formed on the transparent substrate
11
. A source line
14
is formed across the gate line
13
on the insulating layer
21
. Near each crossing point where the gate and source lines
13
and
14
cross each other, an intrinsic semiconductor layer
16
is formed on the gate electrode
13
a
branched out of the gate line
13
. The insulating layer
21
is formed between the semiconductor layer
16
and the gate electrode
13
a
. A source electrode
14
a
which is branched out from the source bus line
14
is formed on a portion of the intrinsic semiconductor layer
16
over one side of the gate electrode
13
a
. A drain electrode
17
is formed over another side of the gate electrode
13
a
, opposite the source electrode
14
a
. In this manner, the TFTs having non-linear active elements are formed, in which the source and drain electrodes respond in accordance with the charges applied to the corresponding gate electrode.
An n
+
semiconductor layer
22
is formed on the intrinsic semiconductor layer
16
, and the source electrode
14
a
and the drain electrode
17
, both made of metal, are formed thereon. The source and drain electrodes
14
a
and
17
, respectively, are ohmic-contacted with the impure semiconductor layer
22
.
In the TFT, as shown in
FIG. 2B
, the drain electrode
17
having an ohmic contact with the n+ semiconductor layer
22
is electrically connected with a pixel electrode
12
through a contact hole
19
formed in an insulating passivation layer
25
. Basically, such a TFT includes the gate electrode
13
a
, the insulating layer
21
, the intrinsic semiconductor layer
16
, the impure semiconductor layer
22
, the drain electrode
17
and the source electrode
14
a
. All of them are formed by repeating the steps of thin film-depositing, exposing and developing photo-resist by using masks and etching.
The aforementioned conventional AMLCD has a layered structure, in which each element thereof is formed of a thin layer. As the thin layers are piled up, overlapping portions are formed at each crossing area where the gate and source lines cross, and at areas where the drain electrodes are connected with the pixel electrodes on the TFTs arranged in rows and columns on the substrate.
Generally, a shape of one layer affects the shape of any other layer formed thereon. For example, if the shape of a first formed layer has a reversed taper and/or a shoulder, a second thin layer formed thereon will replicate the formed layer. That is, when a first metal layer has a reversed taper portion and/or a shoulder, an insulating layer formed thereon will replicate the formed layer in manufacturing an LCD. Consequently, any metal layer formed on such insulating layer has disconnected lines or short circuit problems.
These problems frequently occur when a thin film is formed with metals (e.g., Cr) which are hard to etch into a predetermined pattern, e.g., a tapering shape, or when a dry-etching method is used in the patterning process. In other words, the shape of a taper in a metal layer from which a drain electrode is formed determines the shape of an insulating passivation layer formed on the drain electrode, and affects the shape of a pixel electrode formed on the insulating passivation layer. The insulating passivation layer can have a desired shape only when the taper of the metal layer has a desired shape. Further, disconnection in the pixel electrode, resulting from a level difference (steps) within the drain electrode, can be prevented if the insulating passivation layer has a desired shape.
In the case where a metal layer for the drain electrode
17
is etched in a reverse-tapered shape (FIG.
3
B), the insulating passivation layer
25
is formed with a shoulder
27
or possibly with a crack. Then the thin pixel electrode
12
is either disconnected or cannot be formed in a desired shape on the shoulder
27
or the crack. Moreover, when the insulating passivation layer
25
has cracks, etchant flows into the drain electrode
17
through the cracks and easily disconnects the drain electrode
17
during the etching step for forming the pixel electrode.
FIG. 3A
shows an example of a disconnected line resulting from the above-mentioned shoulders or cracks and
FIG. 3B
shows a cross-sectional view taken along line
3
B—
3
B of FIG.
3
A.
As shown in
FIGS. 3A and 3B
, the drain electrode
17
has a reverse-tapered end. The insulating passivation layer
25
formed on the drain electrode
17
has a shoulder
27
, and the pixel electrode
12
on the passivation layer
25
is disconnected where the step is formed in the passivation layer
25
. This results in malfunctions and unreliable signal processing.
Therefore, in a layered structure, a good step-coverage is required for stable processing and for obtaining good manufacturing yield. However, it is very difficult to develop and manage a process for shaping a metal layer in a desired manner, after the metal layer is etched. It is also difficult to etch a thin layer made of a metal, such as Cr, to have a fine taper. Similarly, thin layers formed using a dry-etching method cause the layers to be disconnected or cause the layers to form cracks in other thin layers formed thereon. These and other problems arising from the conventional methods decrease yield in manufacturing semiconductor devices such as TFTs.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for manufacturing a liquid crystal display in which a step-coverage in a thin-film layered structure is modified to prevent disconnection of signal lines.
Another object of the present invention is to provide a method of manufacturing a liquid crystal display which overcomes problems and disadvantages of related art.
In order to achieve this and other objects, a manufacturing method according to the present invention includes the steps of forming a first metal layer on a layer, coating photo-resist on the first metal layer, exposing and developing the photo-resist by using a mask with a lin-and-space pattern having a space width smaller than a resolution of an exposure system, etching the first metal layer into a desired pattern, forming an insulating layer on the patterned first metal layer, and forming a second metal layer on the insulating layer.
When the photo-resist formed on the first metal layer is exposed by using the mask with a comb-shaped line-and-space pattern, a first portion (P
1
) of the photo-resist corresponding to a space between the lines in the mask is exposed to less degree than a s
Park Yong-Seok
Son Jong-Woo
Birch & Stewart Kolasch & Birch, LLP
LG Electronics Inc.
McPherson John A.
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