Investigation of TiW contacts to 4H-SiC bipolar junction devices

One important challenge in SiC Bipolar Junction Transistor (BJT) fabrication is to form good ohmic contacts to both n-type and p-type SiC. In this paper, we have examined contact study in a SiC BJT process with sputter deposition of titanium tungsten contacts to both n-type and p-type regions followed by annealing at different temperatures between 750 T and 950 T. The contacts were characterized using linear transmission line method (LTLM) structures. To see the formation of compound phases, X-ray Diffraction (XRD) theta-2 theta scans were performed before and after annealing. The results indicate that 5 minutes annealing at 950 T of the n(+) contact is sufficient whereas the p(+) contacts remain non-ohmic after 30 minutes annealing. The n(+) emitter structure contact resistivity after 5 min annealing with 750 degrees C and 950 degrees C was 1.08 x 10(-3) Omega cm(2) and 4.08 x 10(-4) Omega cm(2), respectively. Small amorphous regions of silicon and carbon as well as titanium tungsten carbide regions were observed by high-resolution transmission electron microscopy (HRTEM), whereas less carbide formation and no amorphous regions were found in a sample with unsuccessful formation of TiW ohmic contacts.