Metallization of Titanium Nitride via Electrografted Nitrophenyl–Vinylpyridine Copolymer Seed Layer for Micro/Nano-Fabrication

Abstract

Ongoing advancements in the design and fabrication of semiconductor devices have prompted the exploration of chemical approaches for the metallization of titanium nitride (TiN), a uniquely conductive ceramic material, as alternatives to conventional, high-cost, physical-based deposition techniques. Although direct electrolytic deposition of thin metallic films onto TiN surfaces remains industrially impractical, electroless metallization using an amine-terminated seed layer presents a promising solution. In this study, a copolymer of 4-nitrophenyl and 4-vinylpyridine (a PVP-like film) is successfully electrografted onto the TiN surface via diazonium chemistry. The interaction between the resulting amine-terminated PVP-like seed layer and a PdCl₂/HCl activator is throughout investigated to provide insight into the autocatalytic mechanism underlying the electroless nickel plating process. This process facilitates the formation of a compact, continuous nickel–boron (Ni–B) thin film. The electrolessly deposited Ni–B layer serves as a robust base for subsequent electrolytic copper deposition, enabling the effective filling of serpentine structures in silicon microdevices. Thus, this work introduces a fully aqueous metallization approach suitable for microelectromechanical systems (MEMS). More importantly, covalent bonding of the electrografted polymer, as confirmed by X-ray photoelectron spectroscopy (XPS), is discussed to elucidate the strong adhesion properties of the PVP-like/Ni–B/Cu multilayer stack on the TiN surface.