Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-10-27
2002-07-02
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C257S764000, C257S770000, C349S043000
Reexamination Certificate
active
06414738
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to display devices such as liquid crystal display devices which perform display by controlling a state of liquid crystal enclosed between substrates, or current-controlled display devices which perform display by making EL (electroluminescence) devices and LED (light-emitting diode) devices emit light by means of driving current. More particularly, the present invention relates to electrical connect techniques of conductive films constituting the electrodes and wiring in the display devices described above.
2. Description of Related Art
In display devices such as liquid crystal display devices and current-controlled display devices, display is controlled by using switching elements such as thin film transistors. Although transparent substrates are used as supports in such display devices, when general-purpose glass is used as the transparent substrate, the fabrication process of panels must be performed at low temperatures. Accordingly, recently, liquid crystal display devices and the like which use a polycrystalline silicon thin film transistor (hereinafter referred to as TFT) are actively developed.
In a polycrystalline silicon TFT fabricated by the low-temperature process, as shown in
FIG. 8
, island-like polycrystalline silicon films
2
are formed on a substrate
1
, and a channel region
4
, a source region
3
, and a drain region
5
are formed on the island-like polycrystalline silicon films
2
. A gate electrode
7
faces the channel region
4
with a gate oxide film
6
composed of a silicon oxide film therebetween. A TFT
30
configured as described above is covered with a first interlevel insulating film
10
composed of a silicon oxide film. Contact holes
101
and
102
are opened through the first interlevel insulating film
10
at the positions corresponding to the source region
3
and the drain region
5
. A source electrode
8
and a drain electrode
9
composed of aluminum or an aluminum alloy are electrically connected to the source region
3
and the drain region
5
, respectively, through the contact holes
101
and
102
.
Also, a second interlevel insulating film
11
composed of a silicon oxide film is formed on the front surface of the source electrode
8
and the drain electrode
9
, and a contact hole
103
is made through the second interlevel insulating film
11
at the position corresponding to the drain electrode
9
. Thus, a transparent display electrode
12
composed of an ITO film is electrically connected to the drain electrode
9
through the contact hole
103
in the second interlevel insulating film
11
. Since the drain electrode
9
composed of an aluminum film and the transparent display electrode
12
composed of an ITO film are not electrically connected well to each other, by intervening a contact metal
17
composed of a molybdenum film (Mo) or the like between the drain electrode
9
and the transparent display electrode
12
, the drain electrode
9
and the transparent display electrode
12
are in ohmic contact with each other.
However, in the configuration shown in
FIG. 8
, when the anneal process is performed after wiring layers such as the source electrode
8
and the drain electrode
9
are formed on the source region
3
and the drain region
5
composed of polycrystalline silicon, it has been found that contact failure occurs between the source electrode
8
and the source region
3
and between the drain electrode
9
and the drain region
5
. That is, silicon in the polycrystalline silicon film diffuses into the aluminum film at the electrical connection (joining area) between the drain region
5
composed of the polycrystalline silicon film and the drain electrode
9
composed of the aluminum film, and thus, contact resistance increases. The contact resistance increases remarkably when the anneal process is performed at a temperature of 300° C. or more after wiring layers such as the source electrode
8
and the drain electrode
9
are formed on the source region
3
and the drain region
5
composed of polycrystalline silicon. Such contact failure, which prevents a circuit from operating normally, results in display failure of pixels, which is a fatal defect in the case of a liquid crystal display device. However, in the known art, the problem of silicon diffusion into the aluminum alloy could not be solved completely.
Also, with respect to the method for bringing the drain electrode
9
composed of an aluminum film into ohmic contact with the transparent display electrode
12
composed of an ITO film, there has been only one method of intervening a metal film such as molybdenum, and freedom in design and process of liquid crystal display devices was limited.
SUMMARY OF THE INVENTION
In view of the problems described above, it is an object of the present invention to provide a new configuration of display devices such as liquid crystal display devices, in which electrodes and wiring can be connected with a low resistance.
DISCLOSURE OF INVENTION
In order to achieve the object described above, in accordance with the present invention, a display device having a first electrical connection between a polycrystalline silicon film and an aluminum film includes a first titanium nitride film provided between the polycrystalline silicon film and the aluminum film.
In the present description, an aluminum film means a film composed of aluminum alone and also means an aluminum alloy film including aluminum as a major constituent.
In accordance with the present invention, the first titanium nitride film intervenes between the polycrystalline silicon film and the aluminum film, and the first titanium nitride film functions as a diffusion-prevention film. That is, silicon does not diffuse from the polycrystalline silicon film into the aluminum film even if the anneal process is performed at a high temperature of 300° C. or more after a wiring layer composed of the aluminum layer is formed on the polycrystalline silicon. Accordingly, the contact resistance at this portion can be maintained at a low level.
Also, in accordance with the present invention, preferably a second titanium nitride film is provided between the aluminum film and the ITO film at a second electrical connection between the aluminum film and a transparent display electrode composed of an ITO film through a contact hole in an interlevel insulating film. In accordance with the present invention, at the second electrical connection, since the transparent display electrode composed of an ITO film and the aluminum film are electrically connected to each other with the second titanium nitride film therebetween, the transparent display electrode (ITO film) and the aluminum film can be brought into ohmic contact with each other. Also, since the second titanium nitride film is formed on the surface of the aluminum film, even if wet-etching using a hydrofluoric acid-based etchant is employed when making a contact hole into the interlevel insulating film, what is exposed on the bottom of the contact hole upon completion of etching is the second titanium nitride film which is resistant to the hydrofluoric acid-based etchant, not the aluminum film. Thus, when the contact hole is made into the interlevel insulating film, etching does not affect the aluminum film. Also, when patterning is performed onto the ITO film, even if the interlevel insulating film has cracks or the like, what is touched by a bromine-based etchant for etching the ITO film is the second titanium nitride film which is resistant to the bromine-based etchant, not the aluminum film. Thus, disconnection or the like does not occur in the aluminum film. Therefore, in accordance with the present embodiment, reliable liquid crystal display devices can be fabricated.
Also, if the same titanium nitride film is provided between the polycrystalline silicon film and the aluminum film and between the aluminum film and the transparent display electrode (ITO film), deposition can be performed with the same target when the sputtering process is
Oliff & Berridg,e PLC
Parker Kenneth
Seiko Epson Corporation
LandOfFree
Display does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Display, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Display will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2827319