Morphological study of the Al-Ti ohmic contact to p-type SiC

The composition 70 wt.% Al was recently reported to provide low resistance Al-Ti ohmic contacts with excellent electrical uniformity on p-type SiC. Using scanning electron microscopy and atomic force microscopy, an investigation of the surface morphology and edge definition of the annealed contacts was conducted, and the morphology of the buried metal/semiconductor interface was examined by etching away the contact metallization and imaging the freshly exposed SiC surface. This information provides guidance on the suitability of the contact for devices with small feature sizes and shallow p-type epilayers. Patterned contacts exhibited good edge definition, a root-mean-square surface roughness of 11 nm, and a root-mean-square interfacial roughness of 12 nm. The deepest observed penetration of the metallization into the SiC was 65 nm, and the lateral length scale of the morphological features at the buried metal/semiconductor interface was sufficiently small compared to the active area of the contact to allow good contact-to-contact reproducibility. The interfacial reactions and ohmic contact formation mechanism are considered from the point of view of the materials characterization study presented here and the binary Al-Ti and quaternary Al-C-Si-Ti phase diagrams.