Thin electroless Co(W,P) film growth on titanium-nitride layer modified by self-assembled monolayer

In this work we present a study of the initial nucleation and growth of electroless cobalt-tungsten-phosphorous (Co(W,P)) film on titanium nitride. This cobalt alloy can be applied as barrier or capping layer for copper interconnects in integrated circuits, flexible printed circuit board, micro-mechanical devices and more. The Co(W,P) was deposited from a basic bath on TiN that had been functionalized by silane based self-assembled monolayer (SAM) activated by gold nano-particles (AuNPs). In this paper we report on the results of using two similar silane monomers: aminopropyltrimethoxysilane (APTMS) and N-(3trimethoxysilylpropyl) diethylenetriamine (TPDA); both use amine groups to attract the AuNPs, but differ in molecular conformity. A detailed study of the initial stages of the Co(W,P) layer growth using high-resolution transmission electron microscopy and atomic force microscopy showing the common and different nucleation densities, surface coverages, morphologies and electrical properties of the Co(W,P) layer induced by the two SAM layers is presented. With scaling behavior of the surface roughness evolution we show that Co(W,P) layers grow in 3D, regardless of the SAM type. This effect is probably due to the fact that the dominant mechanism affecting the nucleation and initial growth is the crystallographic misfit between the catalytic layer and the deposited Co(W,P). The 3D growth of Co(W,P) was observed on both SAMs; nevertheless, on APTMS it was controlled by lateral growth, while on TPDA by surface diffusion.