Etching a substrate: processes – Forming or treating material useful in a capacitor
Reexamination Certificate
2000-12-28
2004-01-27
Norton, Nadine G. (Department: 1765)
Etching a substrate: processes
Forming or treating material useful in a capacitor
C438S030000, C438S745000
Reexamination Certificate
active
06682658
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transparent electrode capable of improving etching characteristics. The present invention is also directed to an etchant suitable for etching a transparent electrode.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) of an active matrix driving system uses thin film transistors (TFT's) as switching devices to display a natural moving picture. Since such a LCD can be made into a smaller device in size than the existent Brown tube, it has been widely used for a monitor for a personal computer or a notebook computer as well as for office automation equipment such as a copy machine, etc. and portable equipment such as a cellular phone, a pager, etc.
Recently, the active matrix LCD trends toward overlapping a pixel electrode
108
of a transparent electrode with a signal wire
106
such as a gate line or a data line as shown in
FIG. 1
so as to enhance the aperture ratio. In this case, an organic insulating film
104
having a low dielectric constant is entirely coated on a substrate
102
provided with the signal wire
106
in order to minimize insulation between the signal wire
106
and the pixel electrode and a parasitic capacitance. The LCD having the pixel electrode
108
overlapped with the signal wire
106
has an aperture ratio which is improved by the overlapping area between the signal wire
106
and the pixel electrode
108
in comparison to a LCD in which the pixel electrode
108
does not overlap with the signal wire
106
, but rather is spaced, by a desired distance (i.e., about 5 to 10 &mgr;m) from the signal
106
.
The pixel electrode
108
is usually made from a transparent conductive material such as indium-tin-oxide (ITO). This ITO film is entirely deposited on the organic insulating film
104
and thereafter patterned in such a manner to overlap with the signal wire
106
. Upon patterning of the ITO film, however, the edge portion of the ITO film may be often twisted or damaged after being etched with an etchant. If the edge portion of the ITO film formed on the organic insulating film
104
is twisted or damaged, then the width of the overlapping portion between the pixel electrode
108
and the signal wire
106
is narrowed which generates light leakage from the overlapping portion. Pattern badness of the ITO film is caused by a poor interface-bonding characteristic of the ITO film to the organic insulating film
104
. Particularly, pattern badness is caused by a fact that the ITO film is etched with an etchant which has a high concentration of strong acid and also the etching of the ITO film is made at a low speed.
In order to reduce the bad pattern of the ITO film, a surface treatment process of the organic insulating film
104
for strengthening the adhesive force between the organic insulating film
104
and the ITO film is performed. An example of such a surface treatment includes a method of forming an acid film on the organic insulating film
104
using an acid such as HNO
3
or H
2
SO
4
, etc. Other examples include a method of forming a hydrogen film on the surface of the organic insulating film
104
or ion-doping the surface of the organic insulating film
104
with oxygen. Even when a surface treatment of the organic insulating film
104
is made, if the ITO film is etched by a doping system in which the substrate
102
is precipitated within a chamber filled with an etchant, then the etchant permeates into the interface between the organic insulating film
104
and the ITO film to generate the pattern badness of the ITO film as mentioned above. In this case, the etchant for etching the ITO film includes a high concentration of strong acid, and the etching thereof is conducted for a long time. For instance, the etchant for etching the ITO film has a very high acid concentration such that the ratio of oxalic acid (C
2
H
2
O
4
) to de-ionized water is less than 1 to 10. The time required for etching the ITO film using such a high-concentration of etchant is more than 1000 seconds.
The ITO film has applications for a display device and an ink-jet head besides a LCD. Also, the ITO film is applicable to a pixel electrode for an X-ray detecting device having a structure similar to the active matrix LCD. However, in the device or equipment employing the ITO film, a transparent electrode or a pixel electrode, etc. applied with ITO is liable to generate a bad pattern because the etching characteristics of the ITO is poor.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a transparent electrode that has improved etching characteristics.
A further object of the present invention is to provide an etchant suitable for etching said transparent electrode.
In order to achieve these and other objects of the invention, a transparent electrode applied to a liquid crystal display device according to the present invention is made from indium-zinc-oxide (IZO) having an amorphous structure so that it can be etched in a short period of time with a low concentration of etchant.
A transparent electrode applied to an X-ray detecting device according to the present invention and electrodes consisting of a capacitor are made from indium-zinc-oxide (IZO) so is to have a fast etching speed.
An etchant for etching the transparent electrode, according to the present invention, is a mixture to which a desired compositional ratio of oxalic acid is added.
REFERENCES:
patent: 4699470 (1987-10-01), McLaughlin et al.
patent: RE33921 (1992-05-01), McLaughlin et al.
patent: 5319206 (1994-06-01), Lee et al.
patent: 5952779 (1999-09-01), Arai et al.
patent: 5969474 (1999-10-01), Arai
patent: 7333656 (1995-12-01), None
patent: 11264995 (1999-09-01), None
Inoue, Manufacture of Liquid Crystal Display Device, Sep. 28, 1999, English Abstract of JP 11264995 A, 3pp.
Ahn You Shin
Lee Hu Kag
Birch & Stewart Kolasch & Birch, LLP
LG. Philips LCD Co. Ltd.
Norton Nadine G.
Umez-Eronini Lynette T.
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