| Summary: | 碩士 === 國立清華大學 === 化學工程學系 === 104 === Electroless deposition of nickel-phosphorus (Ni-P) film is a promising skill for the preparation of diffusing barrier layer in silicon and circuit board industry. Typically, Sn/Pd colloid is the most common catalyst for electroless deposition. However, lacking of distinct adsorbing mechanism, the mechanical adhesion of Ni-P film catalyzed by Sn/Pd colloids on bare silicon surface is usually not satisfactory, particularly in the smooth surface such as silicon wafer and glass. Therefore, we devote to develop alternative to replace Sn/Pd colloids. In this study, the development of above-mentioned new catalyst is systematically discussed, including catalyst synthesis, interaction with silanized substrate and the improvement of mechanical adhesion of subsequent electroless Ni-P film.
Using polyvinyl alcohol (PVA, molecular weight 9000-10000) as the protective agent, palladium nitrate as the precursor and formaldehyde as the reductant, we successfully synthesized PVA-capped palladium colloids (PVA-Pd) aqueous dispersion. Transmission electron microscopy (TEM) analysis reveals the well-defined nano-particle of PVA-Pd is a face centered cubic nano-crystal with the size of 2-5 nm.
This novel PVA-Pd is then applied as the catalyst for electroless plating of nickel-phosphorous (Ni-P) layer on a 3- 2-(2-aminoethylamino) ethylamino propyl trimethoxysilane (ETAS)-modified silicon surface. The ETAS modification of substrate is evaluated by X-ray photoelectron spectroscopy (XPS) and water contact angle. In addition, evidenced by XPS, the binding energy of both Pd center of PVA-Pd and nitrogen of ETAS are both chemically shifted due to the interaction between Pd center and long pair electrons of the amino group on ETAS. Unlike commercial Sn/Pd colloids which are physically adsorbed on the substrate, our PVA-Pd is found to chemically adsorb on the substrate so that the adhesion of subsequent Ni-P film is enhanced.
A 200 nm-thick Ni-P layer is then electroless deposited on the PVA-Pd adsorbed silicon surface by using a commercial Ni-P bath at 80oC for 1 minute. Compared with the mechanical adhesion of Ni/P layer made by commercial Sn/Pd colloids on bare silicon surface, the mechanical adhesion of Ni/P layer made by our PVA-Pd and ETAS surface modification is significantly improved from 4.63MPa to 10.83MPa without the need of post annealing.
However, in our previous study or even in searching all relevant literatures, the control of ETAS modification and its relation to the adhesion of ELP film has never been explored. Most studies either directly utilize silane-compound to improve adhesion of deposited film or aim to control, explain or tune the morphology of ETAS modification but without conducting ELP. Very few reports went into details of how different levels of silane-compound modification influence the interfacial properties and most importantly, how these different interfacial properties connect to the adhesion of subsequent ELP layer. In this report, we aim to elaborate how microscopic ETAS modification affects macroscopic ELP film adhesion. In particular, several levels of ETAS modification on Si wafer were created by controlling the immersion time of ETAS stock solution; then these samples were carefully characterized by means of atomic force microscopy (AFM), water contact angle (WCA) and X-ray photoelectron spectroscopy (XPS) to verify the configurations of ETAS layer. Finally a scenario of ETAS modification on Si wafer versus immersion time is proposed accordingly and the relation between ELP Ni-P film adhesion and ETAS configuration with or without a post rapid thermal annealing (RTA) treatment is discussed. To the best of our knowledge, this is the first report trying to connect the effect of molecular silane-compound modification with macroscopic film adhesion in the field of surface modification.
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