Metals on 6H-SiC: contact formation from the materials science point of view

Metal-6H-SiC interface reactions were studied under three different aspects; phase relations, diffusion reaction, and electronic properties. For the first, powder pellets were annealed at different temperatures to achieve thermodynamic equilibrium. The resulting phases were evaluated using XRD. For the second, bulk diffusion couples were prepared and annealed. Cross sections of the reaction layers were investigated in a SEM using secondary and backscattered electrons as well as energy dispersive X-ray analysis. For the third, the electronic properties of thin film metal contacts were evaluated as a function of annealing treatment. The results of the three aspects were combined. ur metals investigated (Ni, Cr, W, Ti) are unstable on 6H-SiC. They react at elevated temperatures in accordance with the phase diagrams but in different morphologies. Ni is the most, W the least reactive metal. All metals form ohmic contacts on n-type 6H-SiC after an appropriate annealing procedure. Ti gives the lowest, Ni the highest contact resistance. Ti forms either ohmic or Schottky contacts depending on the annealing temperature which correlates with a change in the diffusion path.