Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2000-02-17
2003-03-04
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S043000, C349S046000, C349S047000, C349S122000, C349S138000, C257S059000, C257S072000
Reexamination Certificate
active
06529251
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to liquid crystal display devices with TFTs (Thin Film Transistors) and methods of manufacturing the same.
BACKGROUND OF THE INVENTION
Conventionally, TFT liquid crystal display devices are widely used to display high quality images. The following description will discuss a method of manufacturing a semiconductor substrate in such liquid crystal display devices.
The basic structure of the TFT included in such liquid crystal display devices is of a reverse stagger type; therefore, the gate electrode provided in the bottom layer is preferably made of a metal that can be selective etched. Here, the description will be based on an assumption that a Ta metal film is used as a material for the gate electrode as illustrated in FIG.
6
(
a
) and FIG.
8
(
b
).
First, as shown in FIG.
6
(
a
), a gate electrode
52
composed of a Ta metal film is deposited on a glass substrate
51
using a PVD technique (Physical Vapor Deposition technique, which is a sputtering technique).
Next, as shown in FIG.
6
(
b
), a resist
53
is deposited on the gate electrode
52
and patterned as required for the gate electrode
52
using a photolithography technique.
Then, as shown in FIG.
6
(
c
), the gate electrode
52
is fabricated into a predetermined electrode pattern using a PE (Plasma Etching) technique, a RIE (Reactive Ion Etching) technique, or a wet etching technique, and the resist
53
is removed.
Then, as shown in FIG.
6
(
d
), a GI (Gate Insulator) film
54
(typically composed of SiN
x
), an I—Si film
55
, and a n+ film
56
are successively formed, typically, using a PE-CVD technique (Plasma-Enhanced Chemical Vapor Deposition technique).
After forming these three films, similarly to the patterning of the gate electrode
52
, the I—Si film
55
and the n
+
film
56
that constitute a channel layer are fabricated like an island as shown in FIG.
7
(
a
) using a photolithography technique as well as a PE (plasma etching) technique, an RIE (Reactive Ion Etching) technique, or a wet etching technique so as to form a semiconductor layer.
Thereafter, a resist (not shown) is applied on the gate insulator film
54
according to a pattern, and the gate insulator film
54
is etched above the connecting terminal section of the gate electrode
52
. Typically, the gate electrode
52
serves as the connecting terminal.
Subsequently, as shown in FIG.
7
(
b
), a source electrode
57
(source and drain electrodes in the strict sense of the terms; however since the drain electrode is formed simultaneously with the source electrode, they may be collectively referred to as the source electrode) of Ti, Al, W, Ta, etc. is deposited using a PVD technique, and patterned using the same method as that used to form the gate electrode
52
.
Subsequently, using the same source mask as that used in the patterning of the source electrode
57
, the n
+
film
56
is etched off the channel section to form a TFT (Thin Film Transistor)
58
(see FIG.
7
(
c
)).
Thereafter, a pixel electrode
59
composed of a transmissive conductive film (typically, an ITO film) is deposited using a PVD technique as shown in FIG.
7
(
d
), and fabricated into a predetermined electrode pattern using a wet etching technique as shown in FIG.
8
(
a
).
Lastly, as shown in FIG.
8
(
b
), a TFT protection film
60
is formed using a PE-CVD technique, completing the manufacturing process of a TFT array substrate.
Incidentally, in recent years, a low resistance metal, such as Al, an Al alloy, or Cu, is used to constitute electrodes in a high precision liquid crystal display panel (see Japanese Laid-Open Patent Application No. 6-148683/1994 (Tokukaihei 6-148683: laid-open on May 27, 1994), Japanese Laid-Open Patent Application No. 7-169967/1995 (Tokukaihei 7-169967: laid-open on Jul. 4, 1995), and Japanese Laid-Open Patent Application No. 10-253976/1998 (Tokukaihei 10-253976: laid-open on Sep. 25, 1998) for examples). However, if, for example, the gate electrode
52
is composed of the foregoing Al material instead of Ta, and the source electrode
57
is composed of an Al material, a defect in the gate insulator film
54
causes the gate electrode
52
, which lies beneath the source electrode
57
, to erode during the etching of the source electrode
57
.
A further problem arises during the wet etching of the ITO film, which is the last step, that the gate electrode
52
, as well as the source electrode
57
, erodes because of the use of HCl, HBr, or other strong acids, unless a sufficiently thick insulator film (for example, the gate insulator film
54
) is provided.
Nonetheless, it is difficult to form a thick inorganic insulator film, because its formation and etching steps are time-consuming and an undesirable electrostatic capacity is created between those electrodes provided above and below the thickened insulator film.
Japanese Laid-Open Patent Application No. 4-163528/1992 (Tokukaihei 4-163528: laid-open on Jun. 9, 1992) discloses a technology to protect the pixel electrode from peeling during patterning by depositing the pixel electrode over two interlayer insulator films. The interlayer insulator films in such a configuration have a double-layered structure constituted by an organic insulator film and an inorganic insulator film that is formed on the organic insulator film.
Therefore, in the etching process of the interlayer insulator films, the inorganic film is subjected to dry etching (the total thickness of the film is 3.13 &mgr;m), which is followed by etching of the organic film. Here, the organic film is thick and inevitably needs to be etched using a liquid agent. A problem arises, however, that acid and alkaline solutions and other liquid agents that erode the Al material constituting the Al electrode can not be used in the treatment of the organic film. Another problem is that the organic film is more likely to cause source-to-drain leakage than the inorganic film.
The aforementioned problems of the source electrode
57
and the gate electrode
52
composed of Al materials are summed up as below:
(1) A defect in the gate insulator film
54
causes the gate electrode
52
and the terminal section formed from the gate electrode
52
to be etched during the patterning of the source electrode
57
.
(2) During the patterning of the pixel electrode
59
composed of an ITO film, the source electrode
57
and the gate electrode
52
erode, as the strong acid liquid, such as HCl used for the etching of the pixel electrode
59
seeps through defects in the gate insulator film
54
. A possible solution that would offer protection to the Al electrode from erosion is to modify the foregoing manufacturing process so as to form an ITO film on the TFT protection film; however, a simple change in the process could not give satisfactory results in protecting the Al electrode from erosion.
(3) If the pixel electrode is deposited over an interlayer insulator film having a double-layered structure constituted by an organic insulator film and an inorganic insulator film that are sequentially deposited, available chemical agents are limited by the need to protect the Al material for the Al electrode from erosion during the etching of the thickened organic film.
Further, erosion of the foregoing Al electrodes, i.e., the source electrode
57
and the gate electrode
52
reduces the output of good quality liquid crystal display devices, and accordingly adds to the manufacturing cost.
SUMMARY OF THE INVENTION
The present invention has objects to offer a liquid crystal display device that is capable of preventing erosion of an Al material of which the source or gate electrode of the liquid crystal display device is composed, and to offer a method of manufacturing such a liquid crystal display device.
In order to achieve the objects, a liquid crystal display device in accordance with the present invention includes:
a first electrode having an Al or Al alloy layer;
a pixel electrode provided above the first electrode, and
at least two interlayer insulator layers interposed between the
Hibino Yoshitaka
Hirobe Toshihiko
Tarui Tetsuya
Chowdhury Tarifur R.
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
Sikes William L.
LandOfFree
Liquid crystal display device and method of manufacturing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Liquid crystal display device and method of manufacturing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Liquid crystal display device and method of manufacturing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3055838