Electrochemical and Electroless Ni deposition and Applications

Abstract

Electrochemical and Electroless Ni deposition and Applications

Kyounghoon Moon Department of Materials science and Chemical engineering Graduate school of Hanyang University

Metal deposition is an important technology which can control surface luster and improve physical characteristics such as corrosion resistivity, hardness, thermal stability. So, metal deposition is used in a variety of industries such as semiconductor device, photocatalyst, cutting tools, etc.

There are various methods for thin film deposition such as physical vapor deposition(vacuum evaporation, sputtering), chemical vapor deposition, electrochemical deposition and electroless deposition etc. However, PVD and CVD processes have problems that require high temperature and high vacuum processes. Electrochemical and electroless deposition is a wet process which is very easy and cheap for the film deposition.

First, electroless deposition is a chemical reaction deposition in an aqueous solution without the use of external electrical power. Electroless deposition has the advantage of being able to deposit on the surface of non-conductive materials. Reduction of metal ion occurs on the surface by oxidation of reducing agent.

In this research, properties of electroless Ni-W-P thin film on the diamond powder with different parameters (temperature, pH etc.) were studied. The concentration of sodium tungstate was increased from 0 to 0.2M to obtain Ni-W-P films containing various W and P contents which were characterized using field effect scanning electron microscope(FE-SEM) and energy dispersive spectrometer (EDS) and X-Ray Diffraction(XRD). Corrosion resistivity and hardness were observed to determine the effect of W content.

The growth rate of Ni-W-P film was increased with increase of bath temperature and showed smooth surface regardless of the pH value. By increasing W content, hardness and corrosion resistivity was increased compare to Ni-P binary film. Also, the structure was changed from amorphous to crystalline structure.

Next, electrochemical deposition uses an electrical current to reduce the metal ion in an aqueous solution. Usually, electrochemical deposition is done for a purpose of uniform coating to enhance properties on the conductive surface. However, in this research, high stress Ni layer which can occur crack or defect was deposited on the Si surface.

We have described a kerf-free method called Electrodeposit Assisted Stripping (EAS) process with membrane Si to reduce the cost of the silicon material used as Emitter-Wrap-Through(EWT) solar cell. A highly stressed Ni film was electrodeposited from two types of process at a room temperature. By EAS process, a thin membrane Si film can be repetitively detached from a macro-porous Si substrate without kerf-loss, which dramatically reduces the manufacturing cost of a solar cell. Internal stress was measured by the deflection method with a deposit stress analyzer. The surface morphology and vertical view of Ni stress layer and spalled Si layer were observed by optical microscope and field effect scanning electron microscope (FE-SEM)

Moreover, via hole which is the path for the carrier at EWT solar cell can filled by Ni electrodeposition after EAS process. Via hole Ni filling was controlled by the time, surfactant concentration and the current density. The surface morphology and vertical view of via hole Ni filling were observed by optical microscope and field effect scanning electron microscope (FE-SEM)