1. Field of the Invention
The invention relates to a method of fabricating metal wires, and more particularly, to a method of increasing the uniformity of an electroplating process for fabricating metal wires with independent patterns.
2. Description of the Prior Art
As electronic product technology develops, human-machine interfaces such as displays are demanded for higher quality. Thin film transistor (TFT) liquid crystal displays (LCDs) are characterized by portability, low power consumption and lack of radiation pollution, and thus are popularly used in various portable information products such as notebooks, personal digital assistants (PDAs), digital cameras, mobile phones, et cetera.
Basically, the conventional TFT-LCD includes a thin film transistor (TFT) array substrate, a color filter, and liquid-crystal materials between the TFT array substrate and the color filter, in which the TFT array substrate includes a transparent substrate having a matrix of thin film transistors, pixel electrodes, scan lines, and signal lines orthogonal to the scan lines. With supporting electrical devices such as capacitors and connecting pads, the TFT-LCDs drive liquid-crystal-pixels to generate color-rich graphics. Hence, how to produce metal wires with strong adhesiveness and low resistance on the transparent substrate for forming the TFTs, pixel electrodes, scan lines, and signal lines described previously has become a critical task for the industry.
Please refer to FIG. 1 through FIG. 4. FIG. 1 through FIG. 4 are perspective diagrams showing the means of fabricating a metal wire 14 as described in U.S. Pat. No. 6,319,741. As shown in FIG. 1, a substrate 1 is first provided, in which the substrate 1 is a glass substrate. Next, a sputtering process is performed to form a nickel layer 2 over the surface of the substrate 1 to provide strong adhesion to the substrate 1.
As shown in FIG. 2, a photolithography and etching process (PEP) is performed to form a patterned nickel layer 12 over the surface of the substrate 1. Next, an electroless plating process is performed to form a gold layer 3 over the surface of the patterned nickel layer 12, as shown in FIG. 3. Preferably, the function of the gold layer 3 is to be utilized as a seed layer for the electroplating process performed afterwards and to prevent nickel from infiltrating to a metal layer (not shown) formed afterwards. Next, an electroplating process is performed to dispose a copper layer 4 over the surface of the gold layer 3 for forming a metal wire 14, as shown in FIG. 4.
Nevertheless, in order to fabricate the metal wire 14, the conventional method often utilizes a plurality of plating bars to connect to each metal wire 14 for connecting to a predetermined negative voltage during the electroplating process and forming a positive electrode. After the electroplating process, the plating bars are removed from each metal wire 14 to prevent short circuiting. Consequently, the fabrication of additional plating bars will significantly increase the complexity of the fabrication process and reduce the utilization area of the substrate. Due to the difficulty of using plating bars, numerous patterns are also required to be disposed over the surface of the TFT array substrate, such as drain metal patterns and electrostatic discharge devices, thereby further increasing the complexity of the process. Moreover, the uniformity of the electrical current during the electroplating process will also be greatly influenced due to inconsistent size and shape of each metal wire 14 thereby affecting the uniformity of the electroplating process.