Investigations on Ni-Ti-Al ohmic contacts obtained on p-type 4H-SiC

Transfer Length Method (TLM) based-structures were fabricated on 0.8 pm-thick epitaxial p-type Silicon Carbide (4H-SiC) layers. TLM mesas were defined by a 2 mu m height using an SF6/O-2 reactive ion etching. TLM metal patterns were obtained by a lift-off procedure and electron beam deposition of Ni, Ti, Al and Pt. The patterned samples were annealed in Argon ambient at temperature ranging from 700 degrees C up to 1000 degrees C in a RTA furnace with a rapid heating ramp (up to 50 degrees C/s) to complete the ohmic contact with the p-type SiC layer. Specific contact resistances were extracted from current/voltage measurements. To identify and follow the profile evolution of constituting element in the contacts and at the SiC/contact interface, the ohmic contacts were characterized using Secondary Ion Mass Spectrometry and Energy-Dispersive X-Ray spectroscopy before and after annealing. Ohmic contacts are obtained only for the Ni/Ti/Al and Ni/Ti/Al/Ni stacking layers and not for the Ti/Al/Ti/Ni and Ti/Al/Ti/Pt/Ni compositions. The specific contact resistance of Ni/Ti/Al/Ni stacking layers was observed to decrease from 2.7x10(-4) Omega.cm(2) at 700 degrees C and 6.3x10(-5) Omega.cm(2) at 750 degrees C to a minimal value of 1.5x10(-5) Omega.cm(2) at 800 degrees C. Ohmic contacts are obtained with a reproducibility of 80 %.