Compositions – Electrically conductive or emissive compositions – Metal compound containing
Reexamination Certificate
2000-11-22
2003-03-18
Kopec, Mark (Department: 1751)
Compositions
Electrically conductive or emissive compositions
Metal compound containing
C252S520100, C349S158000, C349S122000, C349S139000
Reexamination Certificate
active
06533965
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transparent electrically conductive oxide film having superior fine workability, which may be easily etched by weak acids and in which the connection resistance is decreased, and to a technique using the same.
2. Description of the Related Art
Indium-tin-oxide (ITO) films are well known as transparent electrically conductive films used for electrode circuits, pixel electrodes, and the like, in liquid crystal display devices. Since the indium-tin-oxide film which is deposited at elevated temperature and which is in the polycrystalline state has a substantially low resistance of about 200×10
−6
&OHgr;·cm, it has superior low resistivity and high transmittance, which are necessary in conductors for liquid crystal display devices. ITO films have low contact resistance which may be used as the contact resistivity without any problems when tape carrier package (TCP) connection is performed. In order to form circuits and pixel electrodes by etching such indium-tin-oxide films, strong acid etchants, such as a mixed acid of HCl and HNO
3
, or a mixed acid of HCl and H
2
SO
4
, are required. However, if indium-tin-oxide films are etched using such strong acid etchants, the amounts of side etching will be high, resulting in difficulties in fine working.
Furthermore, as liquid crystal devices are increasingly miniaturized, as wiring in sections other than electrodes and wiring composed of indium-tin-oxide films, in which the resistance must be further decreased, wiring composed of copper is coming into use instead of wiring composed of chromium or wiring composed of tantalum as has been used.
However, the strong acid etchants used for etching indium-tin-oxide films are highly capable of etching copper wiring. Since there is a large difference in etching rate between the indium-tin-oxide films and copper and the side etching amount is also increased, if the strong acids for etching the indium-tin-oxide films are used, the copper wiring may be disconnected. Conversely, it is not possible to etch the indium-tin-oxide films using diluted hydrochloric acid or organic acids which are not likely to overetch copper wiring.
Additionally, a technique is also known in which an indium-tin-oxide film in the amorphous state is obtained by a special production method. The amorphous indium-tin-oxide can be etched by organic acids. However, the amorphous indium-tin-oxide film h as high contact resistance, which is disadvantageous.
When the indium-tin-oxide film is deposited at room temperature, a microcrystalline structure is easily produced go, and the resistance is increased to about 1,000×10
−6
&OHgr;·cm, and thus, satisfactory connection resistance is not obtained.
Therefore, as transparent electrically conductive films, indium-zinc-oxide (IZO) films are receiving attention instead of indium-tin-oxide films. An indium-zinc-oxide film is known to be a superior transparent electrically conductive film suitable for fine working because an IZO film has a resistance as low as about 400×10
−6
&OHgr;·cm even if deposited at room temperature. IZO films have substantially the same transmittance as that of an indium-tin-oxide film. ITO films may be etched by weak acids, and the side etching amount is small when etched by weak acids. Furthermore, if the indium-zinc-oxide film is used, for example, diluted hydrochloric acid may be selected as an etchant so as not to etch copper wiring. By using the diluted hydrochloric acid etchant, fine working can be performed even if the circuit structure in which the indium-zinc-oxide film and copper wiring are combined is employed.
However, when the indium-zinc-oxide film is used as wiring for liquid crystal devices and the wiring is used for TCP connection, the connection resistance increases, giving rise to a problem in the case when the miniaturization of wiring in liquid crystal devices is further promoted. The present inventors have also found that when the indium-zinc-oxide film is stored in air, contact resistance increases over time.
Other systems, methods, feature, and advantages of the invention will be or will become apparent to one skilled in the art upon examination of the following section figures and detailed description. All such additional systems, methods, features, and advantages are intended to be included within this description, within the scope of the invention, and protected by the accompanying claims.
SUMMARY OF THE INVENTION
In view of the problems described above, it is an object of the present invention to provide a transparent electrically conductive oxide film which may be etched by weak acids in fine working, and which has low connection resistance and superior transmittance, in which resistance may be also decreased when taped carrier package (TCP) connection is performed, and resistance does not vary with time.
It is another object of the present invention to provide a target which is suitable for use in forming a transparent electrically conductive oxide film having such superior characteristics.
It is another object of the present invention to provide a method for fabricating a substrate provided with the transparent electrically conductive oxide film and to provide a liquid crystal display device provided with a substrate obtained by the fabrication method.
The resistance of an indium-zinc-oxide film may increase when TCP connection is performed. When either an indium-tin-oxide (ITO) film or an indium-zinc-oxide (IZO) film is in the amorphous state, a high-resistivity layer is formed in the surface region when left in air due to reaction with moisture, oxygen, or organic substances. The high-resistivity layer may form because a deficiency in oxygen in In
2
O
3
(excess In) which is a source of electron carriers of the indium-zinc-oxide film is combined with moisture, oxygen, or organic substances in air, and thus the oxygen-deficiency type conductive mechanism is inhibited.
In one aspect a transparent electrically conductive oxide film is composed of a compound oxide containing indium oxide, tin oxide, and zinc oxide, and includes at least a connecting section, in which the tin content is higher than the zinc content in the connecting section, and at least the connecting section has crystallinity.
In the transparent electrically conductive oxide film composed of the compound oxide containing indium oxide, tin oxide, and zinc oxide, in which the tin content is higher than the zinc content at least in the connecting section, and at least the connecting section has crystallinity, in addition to the conductive mechanism in which excess indium of the indium oxide produces electron carriers, the conductive mechanism in which tetravalent tin is activated to increase electron carriers by adding tin as an n-type dopant to indium functions effectively, and simultaneously, an inhibition factor of zinc which consumes electron carriers can be reduced because activated tin acts as an acceptor for electron carriers. Thus, reaction with moisture, oxygen, or organic substances in air is inhibited, and satisfactory low resistance connection is anticipated. Since the transparent electrically conductive oxide film described above can also be easily etched by weak acids and the side etching amount thereof is small, finer working of wiring is possible in comparison with an indium-tin-oxide film. Furthermore, since the transparent electrically conductive oxide film can be etched by weak acids, even if the structure provided with copper wiring is employed, it is possible to carry out etching treatment without eroding the copper wiring.
In one aspect, a transparent electrically conductive oxide film is composed of a compound oxide containing indium oxide, tin oxide, and zinc oxide, in which the atomic percentage of zinc to the total of zinc, indium, and tin is in the range of about 1 at % through about 9 at %, the atomic ratio of tin to zinc is about 1 or more, the atomic percentage of tin to the total of zinc, indium, and tin is about 2
Arai Kazuyuki
Sasaki Makoto
Sung Chae Gee
Alps Electric Co. LTD
Brinks Hofer Gilson & Lione
Kopec Mark
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