Novel Ni-based ohmic contacts to n-SiC for high temperature and high power device applications

Novel Pt/Ti/WSi/Ni composite ohmic contacts to n-SiC were investigated as a function of annealing temperatures up to 1000°C. The onset of ohmic behavior occurred after annealing at 900°C. Annealing at temperatures between 950 and 1000°C yielded excellent ohmic behavior. At these temperatures the contact-SiC interface was smooth, defect free and characterized by a narrow Ni₂Si reaction region. The annealed contacts possessed smooth surface morphologies and exhibited minimal contact expansion. The residual carbon, resultant from SiC decomposition, was constrained by reaction with the WSi and Ti metallization layers forming carbide phases of W and Ti. The locations of the carbide phases were spatially distant from the metal semiconductor interface. The anneal optimized (annealed at 950 and 1000°C for 30 s) Pt/Ti/WSi/Ni ohmic contacts to n-SiC were evaluated for thermal stability via pulsed/cyclic thermal fatigue and aging experiments at 650°C. 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°C annealed contact for 75 hours at 650°C resulted in electrical failure and chemical interdiffusion/reaction between the contact and SiC substrate. The 1000°C annealed contact retained omicity after 100 h of aging and was found to be chemically and microstructurally stable. These findings indicate that the 1000°C 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.