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

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 delta-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.

Automated summary

This paper investigates the influence of Ti and W on the electrical and structural properties of Ni-based ohmic contacts to n-type 4H-SiC. It is found that the specific contact resistances (SCRs) vary with different contact structures due to the proportion of contact area occupied by different crystal planes at the interface. The incorporation of the W layer reduces SCR by contributing to a higher relative proportion, while the Ti layer increases SCR due to the incorporation of metal oxides and carbides. The discovery provides valuable insights into tuning surface morphology for wire bonding.