Analysis of Electroless Plating Reaction in Deep Recessed Trench

Electroless plating has been extensively applied to electronic devices, since it provides superior throwing power and uniform film formation for complicated geometries. In this study, the formation of a conductive layer in the deep-recessed trenches by using electroless Ni-B plating was investigated. The selection of the complexing agent is important to obtain high uniformity of Ni films in the deep-recessed trenches. Superior uniformity of Ni films in the deep-recessed trenches was obtained by using DL-malic acid as a complexing agent. On the other hand, Ni films from a bath containing glycine were not uniformly deposited, and no deposition was observed at the bottom of the deep-recessed trenches. The influence of the complexing agent on the initial plating reaction was investigated by electrochemical analysis. The deposition reaction obtained from the glycine bath is based on diffusion control. Therefore, nickel ions are mainly reduced at the aperture area of the trenches, and little or no reaction occurred at the bottom area of the trenches in the glycine bath. That is because almost all the Ni ions are consumed at the surface and aperture area. On the other hand, the Ni deposition is not dominated by diffusion control in the DL-malic acid bath. Accordingly, uniform deposition in the trenches can be achieved since the nickel ions reached the bottom of the trenches. In conclusion, it is important to plate uniformly in deep-recessed trenches so that the deposition reaction will not be dominated by the diffusion control state.