A comparative study of refractory metal nitridation in an NH3 ambient

Thin passivation layers for Ag films have been formed by annealing Ag/Ti and Ag/Cr bilayer films evaporated on oxidized substrates in an ammonia ambient. Rutherford backscattering spectrometry (RES) and Auger depth profiles have shown the segregation of the refractory metal (Ti or Cr) at the surface and interface. Ti or Cr diffused out through the silver layer and reacted with ammonia to form a TiN or CrN layer that self-encapsulated the silver film. At the interface, Ti reduced SiO2 and formed a Ti-oxide/Ti-silicide structure to promote the adhesion of Ag to the underlying oxide, whereas there was no interfacial reaction detected in the Ag/Cr systems. Silver films in Ag/Ti bilayer structures exhibited a strong <111> texture component, with the fiber axis parallel to the film normal. in contrast, nearly random oriented grains were observed in Ag films on Cr underlayers. RES analysis confirmed that the encapsulated silver layers had minimal Ti accumulations. X-Ray diffraction analysis indicated the absence of intermetallic phase transformation. As a result, resistivity values of about 2 mu Omega-cm were measured in the encapsulated Ag bilayer films, which are comparable to that of the bulk values. (C) 1997 Elsevier Science S.A.