Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath. Usually there is an anode (positively charged electrode), which is the source of the material to be deposited; the electrochemistry that is the medium through which metal ions are exchanged and transferred to the substrate to be coated; and a cathode, which is the substrate (the negatively charged electrode) to be coated. Plating is done in a plating bath that is usually a non-metallic tank (usually plastic). The tank is filled with electrolyte that has the metal in ionic form to be plated. The anode is connected to the positive terminal of the power supply. The anode is usually the metal to be plated (assuming that the metal will corrode in the electrolyte). For ease of operation, the metal is in the form of nuggets and placed in an inert metal basket made out non-corroding metal (such as titanium or stainless steel). The cathode is the substrate to be plated which is connected to the negative terminal of the power supply. The power supply is well regulated to minimize ripples as well to deliver a steady predictable current. As the current is applied, positive metal ions from the solution are attracted to the negatively charged cathode and deposit on the cathode. As a replenishment for these deposited ions, the metal from the anode is dissolved and goes into the solution and balances the ionic potential. The electroplating process can increase the surface brightness and the corrosion resistance of the object to be plated. Following the rapid development of integrated circuit (IC), the quality requirement for wafer electroplating is becoming more and more demanding for fulfilling the increasing needs of IC applications. There are several prior arts concerning the techniques of fountain-type electroplating apparatus and the monitoring devices for the same, for example, the U.S. Pat. No. 6,024,856 disclosed an electrolytic plating process having a substantially steady state electrolyte, wherein the plating properties of the deposit remain constant, but having no electrolytic rectifier for increasing the homogenous of the flow field; the U.S. Pat. No. 4,137,867 disclosed an improved apparatus for bump-plating semiconductor wafer, but having no real-time current monitoring device for enhancing the stability of the electroplating process; and the U.S. Pat. No. 4,906,346 disclosed an improved electroplating apparatus having an electroplating cell for producing finely structure, thick metal depositions of semiconductor wafers, but providing no solution for edge effect so as to generate a good current distribution; and further U.S. Pat. No. 6,027,631 disclosed a cathode joint of single-point contact, which is prone to incur the unevenness of charge distribution.
Please refer to FIG. 1, which is an illustration of a fountain-type electroplating apparatus of prior arts. The electroplating apparatus mainly comprises a plating tank 102, an overflow tank 104, and a pipe 106. Wherein, the plating tank 102 is positioned inside the overflow tank 104 and further comprises a cathode electrode 122 having a substrate attached under thereof, a shell 112, and an mesh shaped anodemesh shaped anode 114 which is a metal plate having plural holes 116. Moreover, an input hole 118 which is connected to the pipe 106 and an exit hole 120 are arranged at the bottom of the overflow tank 104. Restricted by the space of plating apparatus, the pipe 106 is usually an L-shaped pipe so as to connect to the plating apparatus. The mesh shaped anode 114 can be made of titanium or titanium plated with platinum. The substrate 110 may be a silicon wafer.
As seen in FIG. 1, when plating solution is being transported through the pipe 106 into the overflow tank 104, the condition that the vertical length of the upward-connecting part of the pipe 106 is insufficient, or the pipe 106 is deformed, or even the pipe 106 is skewed with a certain angle will result in the plating solution 108 entering the plating tank 102 through the plural holes 116 of mesh shaped anode 114 to form an unsymmetrical flow field, such that the concentration and the flow velocity of the plating solution 108 in the plating tank 102 is not evenly distributed and further will influence the homogeneity of the plating layer.
FIG. 2 is a schematic diagram showing a connecting line and the mesh shaped anode according to the prior arts. As seen in FIG. 1 and FIG. 2, the mesh shaped anode 114 is connected to a connecting line 130 in a single-point contact and the connecting line 130 is made of materials of excellent conductivity and superior anti-oxidization capability, such as gold. Since the impedance of the connecting line 130 is lower than that of the mesh shaped anode made of titanium or titanium plated with platinum, excessive charges are prone to accumulate at the neighboring zone of the point connecting the connecting line 130 and the mesh shaped anode 114 such that the metallic ions ionized from the plating solution 108 by the mesh shaped anode 114 are distributed unevenly according to the different location of the mesh shaped anode 114. The aforesaid phenomenon will cause the different position on plating surface of the substrate 110 to be plated with different plating rate, and further will influence the homogeneity of the plating layer of the substrate 110.
In this regard, the fountain-type electroplating apparatus of the prior arts has the following shortcomings:                1. Unstable flow field existing at the interface between the plating solution and the surface of substrate not only influences the plating quality, but also reduce the plating stability and homogeneity.        2. Irregular bubbles generated at the interface between the plating solution and the substrate, and even accumulated on the surface of the substrate will result in that the plating solution can not come into touch with the surface of the substrate, and consequently the outcome is not as expected since the total plating area is changed.        