Si(substrate) / Ta(10nm) / Cu(25nm) / W(10nm) and Si(substrate) / Co(150nm) / Ta(10nm) samples, prepared by DC magnetron sputtering, were investigated. The samples were annealed at several temperatures ranging from 423 to 823K for various times. The composition distributions were detected by means of secondary neutral mass spectrometry. Microstructural characterization of samples was carried out by means of transmission electron microscopy. It was shown that the changes in the composition profiles were mainly caused by grain boundary diffusion and the effective grain boundary diffusion coefficients of Ta in Cu were determined both by the “first appearance” and “centre-gradient” methods. The activation energy was 100kJ/mol. The importance of the Ta penetration into the Cu and its accumulation at the Cu/W interface could lead to an increase of the Ta content in the copper film. This could be an important factor in the change/degradation of the physical parameters (e.g. the electrical resistance) of interconnects. Furthermore a Ta segregation factor in Cu was evaluated. Preliminary results in the Si(substrate)/Co(150nm)/Ta(10nm) indicate fast grain-boundary diffusion of the Si into the Co layer, formation of a cobalt silicide layer at the Co/Si interface and Si accumulation first at the Ta/Co interface and later a retarded accumulation at the free Ta surface.

Investigations of Diffusion Kinetics in Si/Ta/Cu/W and Si/Co/Ta Systems by Secondary Neutral Mass Spectrometry. A.Lakatos, G.Erdelyi, G.A.Langer, L.Daroczi, K.Vad, A.Csik, A.Dudas, D.L.Beke: Vacuum, 2010, 84[7], 953-7