Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1999-12-15
2003-04-15
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S122000, C349S113000
Reexamination Certificate
active
06549252
ABSTRACT:
CROSS REFERENCE TO RELATED ART
This application claims the benefit of Korean Patent Application No. 1998-55053, filed on Dec. 15, 1998, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a liquid crystal display device, in particular to a liquid crystal display device having a TFT (thin film transistor) as a switching element and manufacturing method thereof.
2. Description of Conventional Art
A liquid crystal display (LCD) device employing a thin film transistor (TFT) as a switching element is typically called a thin film transistor-liquid crystal display (a TFT-LCD) device.
The semiconductor layer of the TFT is usually made of an amorphous silicon. But an amorphous silicon thin film transistor (a-Si:H TFT) has some disadvantages such as high cost and low reliability when compared with a cathode-ray tube (CRT). This is because the price of a drive circuit to operate the TFT is expensive and the amorphous silicon thin film transistor requires excessive amounts of lead lines to connect the outer drive circuit.
To solve these problems, employing polycrystalline silicon (hereinafter referred to simply as “Poly-Si”) as a semiconductor layer of the switching element of TFT-LCD device has been suggested. Using Poly-Si, a thin film transistor and the drive circuit can be arranged on a same substrate, which enables the production of a TFT-LCD device without any additional processes to connect the pixel array substrate with the drive circuit as required in the reproduction of the amorphous silicon TFT-LCD device.
Below is a description about a conventional TFT-LCD device using Poly-Si as a semiconductor layer with reference to the drawings.
In general, a TFT-LCD is comprised of a lower back light, a TFT array substrate called a lower substrate and a color filter substrate called an upper substrate.
FIGS. 1
a
to
1
h
illustrate the manufacturing process of the TFT array substrate according to a conventional art.
First, as shown in
FIG. 1
a,
a source line
6
is formed on a substrate
1
using a first mask. A first metal layer is deposited using a sputter and patterned to form the source line
6
. A metal such as chromium, molybdenum, aluminum, titanium, tin, tungsten or copper may be used for the first metal layer. An aluminum alloy is preferred due to its low resistance.
To prevent a hillock that may occur while the first metal layer is deposited as well as to prevent an open line that may occur while the first metal layer is patterned to form the source line
6
, and then a second metal layer
8
is deposited and patterned using a second mask. Molybdenum (Mo) or moly-tungsten (MoW) is usually used for the second metal layer
8
. (See
FIG. 1
b
).
As shown in
FIG. 1
c,
a first insulation film
10
is deposited as an interlayer insulator, which is formed for the insulation between the source line
6
and an active layer that will be formed later. Then, an amorphous silicon layer (a-Si:H)
12
is deposited to form the active layer.
The first insulation film
10
is formed by the atmospheric pressure chemical vapor deposition (APCVD), and the amorphous silicon layer
12
is formed by plasma enhanced chemical vapor deposition (PECVD).
After the deposition, the amorphous silicon layer
12
is subject to a dehydrogenation process to remove the hydrogen bound in it, then to a crystallization process to produce Poly-Si. The dehydrogenation is to inhibit the production of voids during the crystallization and also to improve the electric properties of the crystallized Poly-Si.
As shown in
FIG. 1
d,
islands of active layer
14
are formed by patterning the Poly-Si using a third mask.
As shown in
FIG. 1
e,
a second insulation film
16
and a third metal layer are deposited, respectively by PECVD and sputtering, on the entire surface. Then, gate electrodes
20
and
22
are formed by patterning the third metal layer using a fourth mask. Also, thereafter, the second insulation film
16
is dry-etched to half of its original thickness. The insulation film
16
is not fully etched to protect the polycrystalline silicon layer
14
later in the process.
Next, as shown in
FIG. 1
f,
ion doping is performed to form source/drain regions
28
and
30
of the Poly-Si active layer
14
, excluding the portions underlying the gate electrodes
20
and
22
. Then, first and second protection layers
24
and
26
are deposited on the entire surface.
Thereafter, contact holes
28
′,
32
and
30
′ are formed by a fifth masking process, as shown in
FIG. 1
g.
As shown in
FIG. 1
h,
transparent conductive material is deposited using a sixth mask to form a source electrode
38
and a drain/pixel electrode
40
. The source electrode
38
connects the source line
6
and the source region
28
through the contact holes
32
and
28
′, and the drain/pixel electrode
40
contacts the drain region
30
through the contact hole
30
′.
The conventional art described has the following disadvantages. First, the number of masks required is high leading to misalignment and low yield.
Second, because the source electrode
38
contacts the source line
6
through the contact hole
32
, the contact resistance may increase due to residual matter of the insulation film
10
such as SiO
2
, as a result of incomplete removal of the insulation film.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a TFT-LCD and a method for manufacturing the same that substantially obviates some or all of the problems due to the limitations and limitation related to the conventional art.
An object of this invention is to provide a TFT-LCD fabricated by four-mask process.
Another object of this invention is to provide a TFT-LCD in which the contact resistance by the contact between the source line and the source region of the active layer can be reduced.
A further object of this invention is to provide a TFT-LCD of low price by a simplified manufacture.
In order to achieve the objects, this invention provides, in one aspect, a reflective liquid crystal display device panel includes: a substrate; an insulation layer on the substrate; a semiconductor island on the insulation layer, having source and drain regions and a channel region disposed between the source and drain regions; a gate electrode over the channel region of the semiconductor island; a gate insulation layer between the gate electrode and the channel region of the semiconductor island; a protection layer covering the gate electrode and portions of the source and drain regions, the portions being adjacent to the channel region of the semiconductor island; an ohmic contact layer spaced from the protection layer and formed on the source and drain regions of the semiconductor island; source and drain electrodes formed on the ohmic contact layer, respectively, electrically contacting the source and drain regions of the semiconductor island; and a reflective electrode integrally formed with the drain electrode.
In another aspect, the present invention also provides a reflective liquid crystal display device panel includes: a substrate; an insulation layer on the substrate; a semiconductor island on the insulation layer, having a channel region, first regions adjacent to the channel region, and second regions adjacent to the first regions and positioned at either ends portion thereof; a gate electrode over the channel region of the semiconductor island; a gate insulation layer between the gate electrode and the channel region of the semiconductor island; a protection layer covering the gate electrode and the first regions of the semiconductor island; source and drain electrodes overlapping the second regions of the semiconductor island; and a reflective electrode integrally formed with the drain electrode, wherein the second regions has a lower doped density than the first regions of the semiconductor layer.
The present invention further contemplates a method for fabricating a reflective liquid crystal display device panel, includes the steps of: providing a substr
Lee Sang Gul
Yi Jong Hoon
Birch & Stewart Kolasch & Birch, LLP
LG Philips LCD Co., Ltd.
Parker Kenneth
LandOfFree
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