Chemically dependent traps and polytypes at Pt/Ti contacts to 4H and 6H-SiC

We have used low energy etectron-excited nanoluminescence (LEEN) spectroscopy and x-ray photoemission spectroscopy (XPS) to probe deep level defect states Lit interfaces of 4H and 6H-Sic with Ti/Pt metallization. These studies aim to identify process conditions under which thermally stable ohmic and Schottky contacts can be obtained on SiC while minimizing the formation of deep level electrorde states. Depth-dependent LEEN measurements establish the presence of localized states and their spatial distribution on a nanometer scale. Spectra from the near interface region of 6H-SiC indicate the existence of a SiC polytype with a higher build gap of similar to3.4 eV. Excitation of the intimate metal-SiC interface reveals a process-dependent discrete state deep within the SiC band gap. XPS measurements reveal consistent differences in the C Is chemical bonding changes with specific process steps. Analogous chemical treatments of 4H-SiC also produce a lower band gap SiC polytype with similar to2.5 eV energy extending tens of nanometers beyond the interface-confirmed by transmission electron microscopy. This work is the first to show the effect of metal-semiconductor interactions not only on localized states but also on the lattice,structure of the semiconductor near the interface. (C) 2002 American Vacuum Society.