Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2002-12-30
2004-10-19
Gurley, Lynne A. (Department: 2812)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S686000, C438S608000
Reexamination Certificate
active
06806189
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 2002-12277, filed on Mar. 7, 2002 in Korea, which is hereby incorporated by reference for all purposes as if fully set forth herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of silver (Ag) electroless plating on indium tin oxide (ITO) electrode or metal electro lines for a liquid crystal display (LCD) device or a semiconductor element and more particularly, to a method for plating silver (Ag) on indium tin oxide (ITO) electrode or other metal electro lines for the liquid crystal display (LCD) device or the semiconductor element to lower electric resistance of the indium tin oxide (ITO) electrode or the metal lines.
2. Discussion of the Related Art
Generally, a transparent indium tin oxide (ITO) electrode is used as an electrode of flat panel display devices such as a liquid crystal display (LCD) device or a plasma display panel (PDPs). However, as a size of the flat panel display device becomes bigger, the indium tin oxide (ITO) has a disadvantage in that it has a high specific resistance, and thus is not suitable for the large sized flat panel display devices. To overcome this disadvantage, metal having a low resistance is usually plated on the indium tin oxide (ITO) electrode. A representative low resistance metal is silver (silver) and the silver (Ag) may be formed on the indium tin oxide (ITO) electrode in many ways. For example, the silver (Ag) may be formed on the indium tin oxide (ITO) electrode by a sputtering method, a heat-deposition method or a chemical vapor deposition method. However, in case of above mentioned methods, because a sputtering or a deposition of silver (Ag) is not selectively carried out only on the indium tin oxide (ITO) electrode, but on a whole area of a substrate, an additional etching process is needed to remove the unwanted silver, and thus an array substrate manufacturing process becomes complex. A silver (Ag) plating method is suggested to overcome this problem. In case of the silver (Ag) plating method, a manufacturing cost is low and silver (Ag) having a high purity can be obtained compared to other Ag forming methods that are mentioned above. Besides, the silver (Ag) plating method does little damage onto the substrate because it is carried out at a low temperature condition. An electroless plating method, in which an electric current is not applied to plating solution to reduce metal ions in the plating solution, but the metal ions are reduced and then plated on a metal film by a reducing agent in the solution, has been frequently selected among many plating methods. A plating method of silver (Ag) on the indium tin oxide (ITO) electrode using the electroless plating method will be described hereinafter.
To begin with, organic material that exists on the indium tin oxide (ITO) electrode should be removed. A catalytic metal is then deposited on the indium tin oxide (ITO) electrode to oxidize a reducing agent in the electroless plating solution. Because the catalytic metal is not easily deposited on the pure indium tin oxide (ITO) electrode, tin (Sn) is deposited on the indium tin oxide (ITO) electrode first and then the catalytic metal is deposited on the indium tin oxide (ITO) electrode. The catalytic metal may be selected from a group consisting of palladium (Pd), silver (Ag), copper (Cu) and platinum (Pt), etc., and it is efficient to use silver (Ag) as the catalytic metal for electroless plating of silver (Ag) on the indium tin oxide (ITO) electrode. Next, silver (Ag) is plated on the indium tin oxide (ITO) electrode on which the tin (Sn) and the catalytic metal are already formed using the electroless plating solution. The electroless plating solution includes silver nitrate (AgNO
3
), cobalt sulfate (CoSO
4
) and ammonia (NH
3
), etc.
FIG. 1
is a diagram illustrating a reaction mechanism of Ag (silver) electroless plating in which cobalt ion is used as a reducing agent. As shown in the figure, if an electrode that is formed one of copper (Cu), palladium (Pd), platinum (Pt) and nickel (Ni), etc. is dipped into the electroless plating solution, the cobalt sulfate (CoSO
4
) is used as a reducing agent to reduce silver ions (Ag
2+
) and the ammonia (NH
3
) serves to form a complex compound with the silver ions (Ag
2+
) and thus stabilize the silver ions (Ag
2+
) in the electroless plating solution. With the above-mentioned reaction mechanism, silver (Ag) can be plated on the indium tin oxide (ITO) electrode.
However, according to a related art electroless plating method of silver (Ag), the silver agglomerates as reaction time passes by. Because a plated silver (Ag) film does not grow two-dimensionally but grows three-dimensionally and thus forms agglomerations of silver (Ag), an electric resistance becomes increased, and accordingly, the indium tin oxide (ITO) electrode on which the silver (Ag) is plated according to the related art is not suitable for an electrode of a liquid crystal display (LCD) device.
FIGS. 2A
to
2
E are scanning electron microscopic (SEM) photographs taken according to an elapse of time and illustrating surface states of plated silver (Ag) using an related art electroless plating solution.
FIG. 2A
is taken after five seconds from a commencement of the silver (Ag) electroless plating reaction,
FIG. 2B
ten seconds,
FIG. 2C
twenty seconds,
FIG. 2D
thirty seconds and
FIG. 2E
sixty seconds. As shown in the figures, agglomerations “A” becomes bigger as time elapses. It is experimentally found out that values of resistance and roughness of the grown agglomeration are very high. Therefore, the present invention is designed to prevent the agglomeration of the silver (Ag) by mixing magnesium (Mg) compound with the electroless plating solution. According to the present invention, the agglomeration of silver (Ag) can be prevented by a reaction of magnesium ions, and consequently a specific resistance of the silver (Ag) can be lowered.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a method of silver (Ag) electroless plating on indium tin oxide (ITO) electrode and other metal electro lines for a liquid crystal display (LCD) device or a semiconductor element that obviates one or more of problems due to limitations and disadvantages of the related art.
An advantage of the present invention is to provide an electroless plating method for plating silver (Ag) on an indium tin oxide (ITO) electrode in which magnesium (Mg) is added to an electroless plating solution to prevent agglomeration of the silver (Ag) and thus obtain a low specific resistance of the plated silver (Ag) on indium tin oxide (ITO) electrode.
Another advantage of the present invention is to provide an electroless plating method for plating silver (Ag) on a metal electro line in which magnesium (Mg) is added to an electroless plating solution to prevent agglomeration of the silver (Ag) and thus obtain a low specific resistance of the plated silver (Ag) on the metal electro line.
Another advantage of the present invention is to provide an electroless plating method for plating silver (Ag) on an indium tin oxide (ITO) electrode for a liquid crystal display (LCD) device in which magnesium (Mg) is added to an electroless plating solution to prevent agglomeration of the silver (Ag) and thus obtain a low specific resistance of the plated silver (Ag) on indium tin oxide (ITO) electrode.
Another advantage of the present invention is to provide an electroless plating method for plating silver (Ag) on a metal electro line for a liquid crystal display (LCD) device in which magnesium (Mg) is added to an electroless plating solution to prevent agglomeration of the silver (Ag) and thus obtain a low specific resistance of the plated silver (Ag) on the metal electro line.
Another advantage of the present invention is to provide an electroless plating method for plating silver (Ag) on a metal electro line for a semiconductor element in which magnesium (Mg) is added to an electroless plating solution to pr
Cha Seung-Hwan
Kim Jae-Jeong
Gurley Lynne A.
LG.Philips LCD Co. , Ltd.
McKenna Long & Aldridge LLP
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