Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1997-05-05
2001-05-29
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S139000
Reexamination Certificate
active
06239850
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a liquid crystal electro-optical (display) device, and particularly, to an active matrix liquid crystal electro-optical (display) device (referred to simply hereinafter as “LCD”) using a thin film transistor (referred to simply hereinafter as “TFT”) and to a process for fabricating the same.
2. Description of the Related Art
Active matrix LCDs are widely used in color LCDs having a large number of pixels, because they not only can suppress cross talk among the pixels, but also enable high speed driving.
In active matrix LCDs, the pixels are each driven individually by the corresponding TFTs. The TFTs, in turn, are driven by a plurality of wiring patterns formed in rows and columns on a glass substrate constituting the display panel of the LCD. Generally, the wiring patterns are formed by depositing a low-resistance aluminum (Al) layer on the substrate, and then patterning the Al layer by means of wet etching. A higher aperture ratio can be achieved by decreasing the wiring pattern width. Recent studies have focused on performing patterning by a better and more controlled dry etching process.
Attempts to carry out dry etching using a high frequency electric field on an insulator, i.e., the glass substrate, however, sometimes generate charge up on the substrate resulting in induced discharge among the wiring patterns. Such a discharge could damage the fine wiring patterns. Alternate approaches that prevent charge up from occurring are sought.
FIG. 6
shows a wiring pattern formed on a glass substrate
10
in a conventional active matrix LCD.
FIG. 6
shows a gate driver
11
formed on a glass substrate
10
. A plurality of gate bus patterns
11
1
,
11
2
,
11
3
, . . .
11
n
, made of Al or an Al alloy, extend from the gate driver
11
along the row direction. A data driver
12
is formed on the glass substrate
10
, and a plurality of data bus patterns
12
1
,
12
2
,
12
3
, . . .
12
n
, also made of Al or an Al alloy, extend from the data driver
12
along the column direction. Gate bus patterns
11
1
,
11
2
,
11
3
, . . .
11
n
constitute the patterns of a first layer, while the data bus patterns
12
1
,
12
2
,
12
3
. . .
12
n
constitute the patterns of a second layer. TFTs are formed so as to correspond to respective crossing points of gate bus patterns
11
1
,
11
2
,
11
3
, . . .
11
n
with data bus patterns
12
1
,
12
2
,
12
3
. . .
12
n
. The crossing points define a TFT matrix. Furthermore, a connection pad
13
is formed in the substrate
10
in order to electrically connect the substrate
10
with another substrate (not shown in the figure) disposed opposed thereto.
Discharge attributable to the charge up occurs in the hatched region shown in
FIG. 6
when dry etching gate bus patterns
11
1
,
11
2
,
11
3
, . . .
11
n
or data bus patterns
12
1
,
12
2
,
12
3
. . .
12
n
. This charge up could, due to plasma discharge, damage the gate bus patterns
11
1
,
11
2
,
11
3
, . . .
11
n
or the data bus patterns
12
1
,
12
2
,
12
3
. . .
12
n
. Dielectric breakdown of the gate insulating film is generated which can cause element failure when a high electric field is locally applied to the gate bus patterns
11
1
,
11
2
,
11
3
, . . .
11
n
. Dry etching is widely employed in the fabrication of Si LSIs as well as for so-called SOI structures. However, in the case of LCDs, the size of the substrate
10
is too large and dry etching generally proceeds from the periphery. Accordingly, the peripheral region represented by hatched lines in
FIG. 6
is exposed to plasma for a particularly long duration of time.
As a solution, it has been proposed circumventing the discharge. This may be done by forming, during LCD fabrication, a short ring
14
, by using a short circuit in the gate bus patterns
11
1
,
11
2
,
11
3
, . . .
11
n
and in the data bus patterns
12
1
,
12
2
,
12
3
. . .
12
n
. The short ring
14
is removed upon the completion of the LCDs, i.e., at the point during the fabrication each of the panels are cut apart. Each of the data bus patterns
12
1
,
12
2
,
12
3
. . .
12
n
are connected to the short ring
14
at contact holes
14
a.
However, in order to achieve yet higher performance, definition and resolution, it is important to further reduce the resistance of the wiring layers and to further narrow wire width. The short ring
14
of
FIG. 6
has been insufficient for lowering discharge.
It has been found that damage attributed to a discharge occurs frequently when a metal having a low resistivity, such as Al, is employed in the wiring layer, as well as in fine wires having a width as narrow as about 3 &mgr;m. This may be explained as follows. When a metal having low resistivity is exposed to a plasma, the metal is more apt to suffer local concentration of electric field because the electric field applied to the metal is hard to attenuate. Moreover, an electric field tends to concentrate at the portion having a finer dimension.
The problem of damaged wiring patterns from plasma discharge is particularly serious when fabricating a high resolution LCD using a large area substrate, a low resistivity metal such as Al as the wiring material, and when employing dry etching to form the wiring pattern. Furthermore, plasma discharge not always occurs only when performing dry etching. For instance, the source and drain of a TFT are formed by a process of ion implantation using a resist mask. Sometimes the substrate is treated in an oxygen plasma to strip off the resist which was hardened by the ion implantation. Discharge may also occur in the course of such an oxygen plasma treatment.
SUMMARY OF THE INVENTION
In the light of the aforementioned circumstances, an object of the present invention is to overcome the aforementioned problems, and to provide a novel and useful liquid crystal electro-optical (display) device and a process for fabricating the same.
More specifically, an object of the present invention is to provide a liquid crystal electro-optical (display) device which realizes minimization of the damage attributed to plasma discharge, and to provide a process for fabricating the same.
Thus, according to a first aspect of the present invention, there is provided a process for fabricating a liquid crystal electro-optical (display) device having a wiring pattern provided on a substrate constituting a liquid crystal display panel, comprising: a step of forming a discharge accelerating pattern structure in the wiring pattern exclusive of the display region of the liquid crystal display panel, so that a distance between neighboring wire pattern is set at a length twice or less as long as that of a minimum wire width of the individual wiring pattern.
According to a second aspect of the present invention, there is provided a process for fabricating a liquid crystal electro-optical (display) device as described in the first aspect above, wherein the wiring pattern is formed by dry etching.
According to a third aspect of the present invention, there is provided a process for fabricating a liquid crystal electro-optical (display) device as described in the first aspect above, wherein the distance between the neighboring wiring patterns is set at such a length that discharge occurs easily among the wiring patterns.
According to a fourth aspect of the present invention, there is provided a process for fabricating a liquid crystal electro-optical (display) device as described in any one of the first to third aspects, wherein the discharge accelerating pattern structure is provided as a branched structure from the wiring pattern and comprises a branch having an end, so that the distance between the end and the wiring pattern disposed opposed thereto is set at a length twice or less as long as that of the minimum wire width of the wiring pattern.
According to a fifth aspect of the present invention, there is provided a liquid crystal electro-optical (display) panel comprising a substrate having a wiring pattern provided thereon, wherein the wi
Koyama Jun
Ohori Tatsuya
Takei Michiko
Zhang Hongyong
Fish & Richardson P.C.
Semiconductor Energy Laboratory Co,. Ltd.
Sikes William L.
Ton Toan
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