Chemically capping copper with cobalt

Amorphous cobalt-phosphorus alloy is grown on SiO2 and Cu by chemical vapor deposition from dicobaltoctacarbonyl and trimethylphosphine at 250 °C, 300 °C, and 350 °C. Film properties most relevant to adoption into back-end chip fabrication have been studied. Co(P) is poor in P and C near the Cu interface, relative to the free surface, and no evidence of copper phosphide formation during deposition is observed. Approximately 1.4 nm Co(P) is required for continuity on Cu, and the adhesion between the two materials is strong as measured by a scotch tape peel test, despite C incorporation in Co(P). Dissociation of trimethylphosphine into atomic P and C on the surface of Cu combined with the high reactivity of dicobaltoctacarbonyl on SiO2 result in poor selectivity for growth on Cu compared to SiO2.