Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Utilizing nonaqueous bath
Reexamination Certificate
2000-05-12
2002-04-09
Wong, Edna (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Utilizing nonaqueous bath
C205S224000, C205S139000, C205S325000
Reexamination Certificate
active
06368485
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a technique for forming an oxide coating film by anodic oxidation of metal, especially aluminum or an aluminum alloy. More specifically, the present invention relates to a forming electrolyte for forming an oxide coating film on metal, a method for forming an oxide coating film that utilizes the forming electrolyte, a metal whose surface has an oxide coating film that is formed by using the forming electrolyte, and a method for manufacturing a metal wiring whose surface has an oxide coating film that is formed by using the forming electrolyte. The present invention can effectively be utilized, in particular, in the forming treatment of gate wiring of thin film transistor (TFT) devices of liquid crystal display panels, or wiring of integrated circuits.
BACKGROUND ART
Metals and alloys are utilized in various industrial applications using their characteristic properties. In particular, aluminum, aluminum alloys and the like are effectively used for wiring of TFT devices, integrated circuits and the like because of their low specific resistance. As for the wiring of these devices, it is necessary to form an insulation film on its surface in order not to cause short-circuit between the wiring and other wiring or electrodes.
As a method of forming an insulation film on the surfaces of aluminum, aluminum alloys and the like, there has been known a forming treatment by anodic oxidation. In this method, an oxide film is formed on a surface of aluminum, aluminum alloys or the like by electrochemically oxidizing the surface in a forming electrolyte. Because this method has a function of recovering defects resulting from uniformity of substrate, it is excellent in that it can easily form a dense and smooth oxide coating film. For this reason, the oxide film forming method by the forming treatment has been effectively utilized in the wiring production process of TFT devices or integrated circuits.
As the forming electrolyte used for the oxide coating film formation for aluminum, aluminum alloys etc., various compositions have been proposed so far. For example, JP-A-58-147069 (the code “JP-A” herein used means a Japanese patent unexamined publication [Kokai]) discloses use of aqueous solution of ammonium tartrate, and JP-A-63-164 discloses use of aqueous solutions of citric acid and sodium tartrate as the forming electrolyte. Further, JP-A-61-133662 discloses use of a forming electrolyte composed of 1:3 mixture of 1% aqueous solution of ammonium borate or 3% aqueous solution of tartaric acid and propylene glycol. JP-A-2-85826 discloses use of a forming electrolyte composed of 3% aqueous solution of tartaric acid, which is diluted with ethylene glycol or propylene glycol, and adjusted to around pH 7 with aqueous ammonia. In JP-A-6-216389, used is a forming electrolyte composed of 3:7 (volume ratio) mixture of aqueous solution of 1% ammonium tartrate, aqueous solution of 1% ammonium adipate, aqueous solution of 1% ammonium oxalate or 1% aqueous solution of ammonium citrate, and ethylene glycol. In JP-A-8-50304, used is a forming electrolyte composed of 9:1:10 mixture of 3% aqueous solution of tartaric acid, 15% acetic acid, and 3% ethylene glycol. In JP-A-8-286209, an aqueous solution of inorganic acid ammonium salt selected from ammonium tetraborate, ammonium pentaborate, and ammonium borate, and aqueous solution of organic acid ammonium salt selected from ammonium tartrate, ammonium citrate, ammonium adipate, ammonium phthalate, ammonium oxalate, ammonium salicylate and ammonium carbonate are used as the forming electrolyte.
While various forming electrolytes have been proposed so far as mentioned above, those forming electrolytes could not afford an oxide coating film of sufficient insulation property when metal, in particular, aluminum or an aluminum alloy, is anodically oxidized by using these forming electrolytes. Therefore, in order to prevent dielectric breakdown, it has been necessary to further form another insulation film on the formed oxide film. Especially in case of manufacturing of TFT devices, a thick SiN film is formed on the oxide film by CVD to compensate insulation. Since CVD is performed at an elevated temperature, there has been arisen a problem that needlelike minute projections called hillocks are produced on the aluminum-containing surface of the metal, grow and penetrate the gate insulation film to generate defects in display panels during that operation.
Moreover, the anodic oxidation using the conventional forming electrolytes also suffers a drawback of slow formation speed. In order to obtain a higher formation speed, the formation current density must be made higher exceeding a required level. Therefore, raising the throughput using the conventional forming electrolytes has suffered a certain bound.
On the other hand, it has been proposed to use alloys composed of aluminum added with silicon or copper as wiring materials in order to suppress hillock generation in integrated circuits. Gate wiring composed of these alloys whose surfaces have anodic oxide coatings can be also used for TFT-LCDs, and using aluminum added with rare earth elements (JP-A-7-45555, JP-A-8-250494, and JP-A-8-306693), or added with valve metals (JP-A-8-286209) has been tried recently.
In order to effectively suppress the hillock generation by using aluminum added with rare earth elements, however, a relatively large amount of rare earth elements needs to be added (T.Onishi, E. Iwamura, and K. Takagi, J.Vac.Sci.Technol. A, 15 (4), 2339 (1997)). When a large amount of rare earth elements is added, however, a specific resistance of the wiring becomes quite high compared with that of pure aluminum, and there is a negative effect that the rare earth element is moved into an oxide coating film during anodic oxidation, causing a harmful influence. As for these methods, it has also been proposed that a part or whole of rare elements in a state of solid solution is deposited as an intermetallic compound by heat treatment at 300° C. or higher to lower a specific resistance, but a wiring having a specific resistance of 4 &mgr;&OHgr;·cm or lower favorably used in a large or high-definition TFT-LCD has not been obtained. Therefore, the hillock generation could not be effectively suppressed while good physical property was maintained.
Therefore, the present invention aimed at solving the problems of these conventional arts.
That is, an object of the present invention is to provide a novel forming electrolyte which can form an oxide coating film having sufficient insulation property for metals including aluminum and aluminum alloys. Another object of the present invention is to provide a forming electrolyte that can afford a high formation rate and raise the throughput of processes including anodic formation. A still further object of the present invention is to provide a forming electrolyte that can suppress the hillock generation on metal surface by using that forming electrolyte for anodic oxidation of metals such as aluminum and aluminum alloys.
The present invention also aimed at providing a method for forming an oxide film of good insulation property at a high throughput, a metal having a highly insulating oxide coating film in which the hillock generation is suppressed, and a method for manufacturing an aluminum containing metal wiring capable of suppressing the hillock generation effectively while maintaining a low specific resistance.
DESCRIPTION OF THE INVENTION
In order to achieve the foregoing objects, the present inventors earnestly conducted studies. As a result, we found that a combination of particular solute and solvent can provide a forming electrolyte for forming metal oxide coating film which can achieve the objects, and thus completed the present invention. That is, the present invention provides a forming electrolyte for forming a metal oxide coating film which comprises one or more kinds of solutes selected from the group consisting a salt of inorganic acid and salt of organic carboxylic acid dissolved in a solvent having a
Mizutani Fumikazu
Takaha Hiroshi
Takeuchi Sachie
Ue Makoto
Mitsubishi Chemical Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Tran Thao
Wong Edna
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