Simultaneous Formation of Ohmic Contacts for Both N- and P-Type 4H-Sic Using Nial-Based Contact Materials

Abstract

In order to simplify a fabrication process of silicon carbide power MOSFETs (metal oxide semiconductor field effect transistors), development of a simultaneous formation process of ohmic contacts to both the p-well and n-source regions of the SiC devices using same contact materials and one step annealing was challenged. We succeeded to develop NiAl-based contact materials which provided ohmic behaviors for both n-and p-type 4H-SiC after one step annealing. The Ni/Al and Ni/Ti/Al ohmic contacts were prepared by depositing sequentially Ni, (Ti) and Al layers with various layer thicknesses onto the n-and p-type SiC substrates which were doped with N at 1×10 19 cm -3 and with Al at 8×10 18 cm -3 , respectively. The Ni(50 nm)/Al(5 ~ 6 nm) contacts showed ohmic behaviors for both the n-and p-type SiC substrates after annealing at 1000 ˚C. The Ni(20 nm)/Ti(50 nm)/Al(50 ~ 70 nm) contacts showed ohmic behaviors for both the n-and p-type SiC substrates after annealing at a lower temperature of 800 ˚C. The specific contact resistances of these contacts were measured to be in the order of 10 -3 Ω-cm 2 for both p-and n-type SiC, and were found to have strong dependence of the Al layer thicknesses of materials. The interfacial microstructures of the NiAl-based contacts were also observed by transmission electron microscopy (TEM) to understand the current transport mechanism through the metal/SiC interfaces.

Codeposition of Cu/Ni thin films from mixed precursors in supercritical carbon dioxide solutions

“…A metalmetal bond tends to form in the film-substrate interface, combining like an all-proportion miscible alloy system, resulting in favorable adhesion and in an increase in the film strength. 1) Among the most promising alloying elements (Mg, Ag, Mn, Al, Cr, Sn, Ti) [2][3][4][5][6][7][8] for Cu metallization investigated to date, the Cu-Ni alloy 9) is one of the most attractive materials because Cu and Ni are miscible at all proportions above about 350 °C. 10,11) Therefore, we do believe that the Cu-Ni system can be used as a suitable prototype system for alloy wiring applications.…”