Investigation of TiW Contacts to 4H-SiC Bipolar Junction Devices

Abstract

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 oC and 950 oC. The contacts were characterized using linear transmission line method (LTLM) structures. To see the formation of compound phases, X-ray Diffraction (XRD) θ-2θ scans were performed before and after annealing. The results indicate that 5 minutes annealing at 950 oC 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 oC and 950 oC was 1.08 × 10-3 5cm2 and 4.08 × 10-4 5cm2, 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.