Processing and characterization of alumina thin films on chemically vapor deposited diamond substrates for producing adherent metallizations

In order to make the surface of chemically vapor deposited diamond (CVDD) substrates amenable to metallization by both thin and thick film approaches currently utilized in electronic packaging, a thin, adherent, insulating aluminum oxide film was grown on diamond at low temperatures (<675 K). The film was produced by reactive thermal evaporation of Al and O in an oxygen atmosphere, followed by low-temperature annealing in oxygen. A Cr intermediate layer was deposited on diamond prior to the deposition of aluminum oxide in order to enhance adhesion between the oxide and diamond. The chemistry, crystal structure, and microstructure of the film were characterized in detail via scanning and transmission electron microscopy, as well as Auger electron spectroscopy. Particular attention was given to the mechanisms of bonding across the CVDD-Cr and Cr-alumina interfaces, as well as the stability of the surface treatment following metallization by fritted pastes requiring firing at elevated temperatures. The Cr was found to be bonded with CVDD by Cr23C6 formation, while the bonding between the Cr and alumina layers was provided by the formation of a compositionally modulated solid solution with Al2O3-rich and Cr2O3-rich regions.