Silane-Free Adhesive Electroless Deposition of a Nickel/Phosphorous Layer on Si Wafer

Electroless deposition (ELD) of nickel/phosphorous (Ni/P) layers has been a valuable method for creating diffusion barriers in the silicon (Si) industry, particularly in the formation of metal contact or interconnection structure in integrated circuits or microelectromechanical systems ^[1,2]. The ELD of Ni/P layers is a catalytic reaction that requires either a trace amount of seed Ni ^[3] or noble metals such as palladium ^[4] to lower the activation energy for nucleation and growth. Because the ELD process occurs on the catalyst-attached Si surface, the adhesion of Ni/P films is related to the interfacial properties of the catalyst and Si surface. In the first part of this presentation, we develop a post-annealing-free, adhesive Ni/P layer on an aminosilane-modified (ETAS-modified) Si surface through an ELD catalyzed by a novel, home-made polyvinylpyrrolidone-capped palladium nanocluster (PVP-Pd). X-ray photoelectron spectroscopy analysis reveals that ETAS was covalently bonded on the Si surface, whereas the amino groups on ETAS bridged with the palladium core in the PVP-Pd. Because of above two effects, the ELD Ni/P layer showed superior adhesion on the Si wafer without the need of conventional post-annealing treatment. Compared with the Ni/P films deposited on bare Si surfaces by using commercial Sn/Pd colloids, the adhesion of the Ni/P film catalyzed by either PVP-Pd on the ETAS-modified Si wafer improved more than 4-fold.

Later on, we report our new finding regarding to prepare adhesive ELD Ni/P film on Si wafer without the requirement of silane-modification and post annealing by innovating catalyst system. Switching from PVP-Pd to polyvinyl alcohol-capped palladium nanocluster (PVA-Pd), it is found the surface modification by aminosilane-compound can be omitted, while the resulting ELD Ni/P film still exhibits adequate adhesion.

Reference:

[1] S. Furukawa, M. Mehergany, Sensors Actuators 56 (1996) 261.

[2] K.Y. Lee, J.T. Huang, P.S. Chao, J.M. Lin, H.J. Hsu, Microelectron. Eng. 113 (2014) 147.

[3] S.J. Cherng, C.M. Chen, W.P. Dow, C.H. Lin, S.W. Chen, Electrochem. Solid-State Lett.

14 (2011) P13.

[4] C. R. Shipley Jr., U.S. Pat. 3,011,920 (1961).