Thermal stability and performance reliability of Pt/Ti/WSi/Ni ohmic contacts to n-SiC for high temperature and pulsed power device applications

Pt/Ti/WSi/Ni ohmic contacts to n-SiC, initially annealed at 950 and 1000 degreesC for 30 s, were evaluated for thermal stability via pulsed/cyclic thermal fatigue and aging experiments at 650 degreesC. Modifications of material properties in response to cyclic thermal fatigue and aging tests were quantitatively assessed via current-voltage measurements, field emission scanning microscopy, atomic force microscopy, and Rutherford backscattering spectrometry. Negligible changes in the electrical properties, microstructure, and surface morphology/roughness were observed for both annealed ohmic contacts in response to 100 cycles of acute cyclic thermal fatigue. Aging of the 950 degreesC annealed contact for 75 h at 650 degreesC resulted in electrical failure and chemical interdiffusion/reaction between the contact and SiC substrate. The 1000 degreesC annealed contact retained ohmicity after 100 h of aging and was found to be chemically and microstructurally stable. These findings indicate that the 1000 degreesC annealed Pt/Ti/WSi/Ni ohmic contact to n-SiC is thermally stable and merits strong potential for utilization in high temperature and pulsed power devices. (C) 2002 American Institute of Physics.