Reaction Kinetics Investigation of Ni Ohmic Contacts on N-Type 4H-SiC

Investigation of the reaction kinetics between Ni film and 4H-SiC substrate at temperatures which are usually used for ohmic contacts formation provides valuable insights into the studies on fundamental properties of ohmic contacts to 4H-SiC, which are limiting the switching speed, energy efficiency and high-temperature thermal stability of SiC MOSFETs. High Resolution Scanning Electron Microscope (HRSEM) and Raman spectroscopy were used to elaborately characterize the interfacial reaction products under various annealing conditions and to assess the thicknesses of reaction diffusion layers. The square of reaction layer thicknesses versus time followed parabolic law and the apparent active energy of interfacial reaction was derived as 1.5 eV (145 kJ/mol). For Raman spectra, the intensity ratio of two Raman peaks for each nickel silicide detected varied monotonically with temperature in the same trend, indicating that crystal quality of nickel silicide film was improved with annealing temperature rising at micron scale. The red-shift of Ni2Si peak locations at about 140 cm-1 with temperature was suggestive of the polycrystalline Ni2Si film with weaker stress/strain status. Moreover, the in-plane size of graphite cluster aggregating at top surface increased with annealing temperature rising until about 1000°C, which is detrimental to the ohmic contacts from the perspective of device applications.