Surface Characterization of Cr/Ni and Ni/Cr Ohmic Contacts on n-Type 3C-SiC

The structure of the interface in metal to n-type 3C-SiC ohmic contacts has been important in determining the specific contact resistance and hence the functionality of devices. Recently, the use of Cr/Ni metallization on n-type 3C-SiC has shown an equivalent specific contact resistance to standard Ni contacts with but with an improved surface morphology and reduced interdiffusion [1]. In this paper, we examine for the first time the interfacial characteristics of metallizations containing layers of Ni and Cr (Au/Ni/Cr/ and Au/Cr/Ni) on n-type 3C-SiC. A study of these layered structures both as-deposited and annealed at 750-1000°C has been performed using depth profiling with X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Elemental mapping by AES in conjunction with SEM imaging have also been used to examine the distribution of elements and the surface morphology after annealing. For the Au/Ni/Cr/n-SiC structure, the analysis has shown a wide-scale interdiffusion of the layers after annealing with the formation of surface globules which were enriched in Ni and Si. In comparison, the Au/Cr/Ni/n-SiC metallizations have shown a limited indiffusion of Ni and outdiffusion of C and Si with the formation of relatively smooth surfaces. These results have indicated that the intermediate layer of Cr has acted as a diffusion barrier for the Ni. The Au/Cr/Ni/n-SiC contacts annealed at 1000 °C have correlated with a minimum in specific contact resistance as measured using circular transmission line model (CTLM) test patterns. [1] P.W. Leech, M.H. Kibel, A. Barlow, G.K. Reeves, A.S. Holland, P. Tanner, Microelectronic Engineering, 215:111016 (2019).