We previously reported a novel polyvinyl alcohol-capped palladium colloids (PVA-Pd) as the catalyst for the electroless plating of nickel-phosphorous (ELP-Ni-P) film on 3-2-(2-aminoethylamino) ethylamino propyl trimethoxysilane (ETAS)-modified Si surface [1]. It was found the interaction between PVA-Pd and amino-moiety on ETAS is the root cause of the superior adhesion of ELP-Ni-P film without the need of post annealing. The adhesion of ELP-Ni-P film catalyzed by PVA-Pd on ETAS-modified Si surface is significantly improved from 4.63 MPa to 10.83MPa when compared with it made via traditional Sn/Pd process.

In this study, the effect of process parameters in this method including annealing temperature, annealing time, ETAS dipping time, PVA-Pd concentration and PVA-Pd dipping time are systematically investigated by means of design of experiments (DOE). From the analysis of variance (ANOVA) table, it is found the annealing temperature, annealing time and ETAS-dipping time have main effects on the adhesion of ELP-Ni-P film. Surprisingly, SEM cross-sectional image of the ELP-Ni-P film made by this method reveals that imperfect self-assembly monolayer (SAM) formation of ETAS aids the formation of nickel-silicide intermetallic (IMC) layer, rendering an even better adhesion before annealing. On the contrary, the adhesion of ELP-Ni-P film deposited on perfect ETAS monolayer becomes worse after post annealing. We speculate that silane-compound may play as a barrier layer for the IMC formation, which may jeopardize the original function of Ni-P film as the barrier layer for the subsequent copper layer in semiconductor industry.

Reference:

[1] T.-C. Wei, T.-C. Pan, C.-M. Chen, K.-C. Lai, and C.-H. Wu, "Annealing-free adhesive electroless deposition of a nickel/phosphorous layer on a silane-compound-modified Si wafer," Electrochemistry Communications, vol. 54, pp. 6-9, 2015.