Investigation of the effects of different annealing ambients on Ag/Al bilayers: Electrical properties and morphology

Abstract

Ag (200 nm)/Al (8 nm) bilayer structures on SiO2 substrates were annealed at temperatures ranging from 300 °C–700 °C and for 30 min in He–H, Ar, or NH3 ambient. Upon annealing, Al segregates to the surface where it reacts with residual oxygen to form an Al-oxide passivation layer. Rutherford backscattering spectrometry and Auger spectroscopy showed the formation of an AlxOy diffusion barrier at the Ag/SiO2 interface. Apart from the surface passivation that resulted from annealing, the Ag/Al/SiO2 in different ambients, the adhesion of Ag to SiO2 was also improved. A strong correlation between the resistivity and the residual Al in the Ag film was observed. Resistivity values equivalent to that of the as-deposited sample were obtained only for temperatures at 700 °C or above. Scanning electron microscopy (SEM) combined with energy dispersive spectroscopy was used to study the effect of the different ambients on the observed surface morphology. The SEM studies showed that the passivated surfaces were not uniform but have hillocks and holes randomly distributed. In contrast to Ag on SiO2, no agglomeration was observed in the Ag/Al/SiO2 system.