Formation and thermal stability of Ni/WSi/Ti/Pt composite ohmic contacts to n-SiC for high power device applications

Ni/WSi/Ti/Pt Ohmic contacts to n-SiC were investigated as a function of annealing temperatures up to 1000 degrees C. Annealing at temperatures between 950 degrees and 1000 degrees 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 atomically smooth surface morphologies and exhibited minimal contact expansion. The residual carbon, resultant from the decomposition of SiC and reaction with Ni to form Ni2Si, was constrained by reaction with the WSi and Ti layers forming carbide phases of W and Ti spatially distant from the metal semiconductor interface. Our results demonstrate that the Ni/WSi/Ti/Pt composite Ohmic contact maintains the desirable electrical properties associated with Ni contacts and possess excellent interfacial, compositional and surface properties which are required for reliable high power and temperature device operation.