Accelerated Lifetesting and Failure Modes of Thin Film W Contacts on Si-Ge Thermoelectric Alloys

The stability of sputtered thin film W contacts on heavily doped Si-Ge alloy has been determnined from measurements of contact resistance versus time for aging temperatures in the range 550-725°C. Contact failure time has been found to obey an Arrhenius type relation with an activation energy of 76 ± 5 kcal/mole and a projected lifetime of over ten years at temperatures be low 450°C. Contact resistance remains approximately constant for the first 80% of contact lifetime and then increases rapidly through several orders of magnitude, These large contact increases are accompanied by loss of contact adhesion and buckling. Comparison of this data with that from diffusion experiments indicates that the activation energy for contact failure is comparable with that for the initial stages of WSi2 layer growth iu W-Si systems.