Thermal stability of amorphous Ni-Nb on semiconductor substrates

Abstract

The thermal stability of amorphous metal films is of prime importance in high temperature semiconductor device applications. Suitable thin film deposits of amorphous Ni-Nb, 58 at % Ni have been prepared by sputter deposition onto Si, GaAs, and GaP substrates. The amorphous character and crystallization behavior of the films have been monitored by x-ray diffraction (XRD). Polycrystalline Au and Ni overlayers were found to lower the NiNb crystallization temperature by about 100 and 150°C, respectively. In addition, Auger depth profiles were used to monitor the various interdiffusion reactions between the amorphous metal, polycrystalline metal overlayers and semiconductor substrates. For example, the feasibility of NiNb as a diffusion barrier between Au and a semiconductor substrate was found to depend on the substrate. Following a one hour 500°C anneal, very little interdiffusion was observed in the Au/NiNb/Si system. However on a GaAs or GaP substrate the Au and NiNb interdiffused extensively. These studies have demonstrated the viability of amorphous metal films as effective diffusion barriers in semiconductor contact applications, but emphasize the need for careful selection of compatible material combinations.