Passivation of Ag on SiO2 by Annealing Ag-Ti Alloys in an Ammonia Ambient

Encapsulated Ag(Ti) films on oxidized silicon were obtained by nitridation of Ag(19 at.% Ti) alloys in a flowing NH3 ambient at temperatures between 400-700°C for various times. Upon annealing at temperatures ¿ 350°C Ti segregates to the surface and alloy/SiO2 interface. At the free surface Ti reacts with the ammonia to form a TiN(O) surface layer. The Ti that diffuses to the interface dissociates the SiO2 and subsequently reacts with the freed Si and O to form a TiO/Ti5Si3 interfacial bilayer structure. RBS data indicated that the dealloying and hence the encapsulation increases with increasing temperature up to 600°C, whereafter it levels off. Residual Ti concentrations of ~1 at.% was measured at temperatures ¿ 600°C. Resistivity values of ~3 ¿¿-cm were measured in the encapsulated Ag alloys. The results suggest that resistivity is controlled by the residual Ti concentration.