Conventional electrodeposition process is widely used for various kinds of functional parts such as electronics, anti-corrosion, decoration and so on. However, this process has serious problem due to a large quantity of waste fluid including toxic substance. Recently, environmental regulation has been strengthened, so that the production line may be needed to be closed system for recycling the waste fluids. Moreover, the additionl processes such as masking and etching is indispensable in producing the patterned circuit board, leading to high cost for final products. We have developed the novel electrodeposition process to solve the environmental and cost problems of a conventional electrodeposition. As shown in Fig. 1, the novel deposition system is simply composed of electrodes, metal solution and polyelectrolyte. By applying potential between two electrodes, metal films are deposited at solid-solid interface, i.e., cathode electrode and polyelectrolyte; electrolyte solution is separated from cathode electrode by polyelectrolyte in which metallic ions can be diffused through ion-exchange reaction. Therefore, when this system is accumulated into small probe system, this process enables electrodeposition of metals only by attaching polyelectrolyte surface into cathode surface in a serial patterning manner, whereas conventional electrodeposition process is based on immersing the substrate of interest into electrolyte solution. We call this novel system, “solid electrodeposition (SED)”. The characteristics of the process are as follows.
1) The system needs only small amount of electrolyte solution, and washing of the cathode substrate after metal deposition is not necessary because of growth of the films at solid-solid interface, leading to much small amount of waste solution.
2) Site-selective deposition can be achieved only by controlling the contact area of the polyelectrolyte used for deposition (Fig. 2a).
3) Since the deposition can proceed through diffusion of metal ions through fine, large amount of ion channels in polyelectrolytes, metal films constructing of tiny crystallites are deposited (Fig. 2b).
Electrical resistivity of the copper films deposited by SED process is comparable with that of bulk copper, indicating high purity, well-defined copper films are deposited on the substrates. From these results, this process offers an effective, environmentally friendly methodology for fabricating metal films in atmospheric conditions and can be, therefore, applied for various microelectronic applications.
