Metallization of CVD diamond using metal oxide intermediate layers for electronics packaging

Abstract

The high thermal conductivity of chemically vapor deposited CVD diamond (up to 2000 W/m/K) and its low dielectric constant (approx. 5.6) makes it highly desirable for use as an electronics packaging substrate material. To make CVD diamond amenable to thick film metallization via standard industrial processes, a thin gamma-alumina layer (approx. 1500A) was grown on diamond by reactive evaporation of Al in oxygen over a very thin Cr intermediate-layer (approx. 700A). Commercially available silver and gold thick films were applied to CVD diamond both with and without the metal-oxide inter-layer. The interfaces were characterized by scanning electron microscopy, energy dispersive x-ray spectroscopy, Auger electron spectroscopy and transmission electron microscopy. The intermediate oxide layer was found to result in well-adherent, chemically bonded interfaces between the metallization and the CVD diamond substrates for both Ag and Au pastes. Without the oxide layer, the Ag paste was found to have very poor adhesion to the substrate. The Au paste, developed for non-oxide substrates, was found to be nominally adherent to the CVDD substrate, although quantitative adhesion comparisons between the metallization with and without the oxide inter-layer was not obtained. Microstructural and chemical characterization studies of the interface suggest that the alumina layer enhances adhesion by producing chemically-reacted/solid-solution species across all interfaces and is therefore a very versatile approach for thick film metallization of CVDD