Role of Ti and W in the Ni-based ohmic contacts to n-type 4H-SiC

Abstract

The paper investigated the influence mechanism of Ti and W on the electrical and structural properties of the Ni-based ohmic contacts to n-type 4H-SiC. The variation of specific contact resistances (SCRs) with different contact structures was found to be correlated to the relative proportion of the total contact area occupied by the (220) plane than that of the (301) plane at the contact interface for the polycrystalline and textured δ-Ni2Si films characterized by the X-ray diffraction (XRD). Due to the formation of metal carbides, the W layer was found to be beneficial for a higher relative proportion contributing to a reduction of SCR. In contrast, the Ti layer was detrimental owing to the incorporation of metal oxides and carbides. Therefore, W is considered a better candidate to improve the thermal stability of Ni-based ohmic contacts to n-type 4H-SiC while maintaining a low specific contact resistance. Moreover, it was found that the free carbon atoms were immobilized or blocked by the W or Ti layer, and a greater distance of free carbon away from the contact surface led to a smoother and more uniform surface morphology. We believe that this discovery provides a valuable insight into the tuning of surface morphology for the wire bonding challenge.