Low-temperature metallization of silicon carbide

A new processing scheme producing ohmic contacts on alpha SiC devices has been demonstrated. This low temperature (300°C) metallization scheme is competitive with Ni-based contacts processed at much higher temperatures (>900°C), and results in thermodynamically stable metal/SiC contact.; Electrical interconnects were formed on both 4H- and 6H-SiC, metallization being effected through the reaction of a Ni layer with a fugitive Si layer at low temperature. To study the solid state reaction of Ni and Si, Ni was reacted with polycrystalline Si at 850°C and at 300–400°C with single crystal Si, with low pressure chemical vapor deposited (LPCVD) amorphous Si (a-Si), and with sputter-deposited a-Si. The resulting microstructures were examined using X-ray diffraction (XRD), conventional transmission electron microscopy (TEM), energy filtering TEM (EFTEM), and x-ray energy dispersive spectroscopy (XEDS).; NiSi was formed when single crystal Si was used, whereas NiSi₂ was formed when LPCVD a-Si was used. Curiously, sputter-deposited a-Si did not react as quickly as LPCVD a-Si. An amorphous interlayer was found in the as-deposited cases for Ni/crystalline Si and Ni/sputter-deposited a-Si. In both cases, the composition of the amorphous layer mimicked the composition of the phase which would form on annealing.; Devices were processed using Ni and LPCVD a-Si, NiSi forming when the couple was reacted at 300°C for 9 hours (excess Ni was used). Specific contact resistance was measure using the circular transmission line model (TLM). The average specific contact resistance of the NiSi on 6H-SiC was 6.9 × 10−4 Ωcm2. On the other hand, the contacts to 4H-SiC were rectifying.; Reliability of the metallization was tested by annealing at 600°C in air for 300 hours. The specific contact resistance of NiSi on n-type 6H-SiC was reduced during the anneal into the 10−6 Ωcm 2 range. During the anneal, a surface SiO₂ layer formed over the NiSi. This consumption of Si during oxidation of the NiSi led to the NiSi reverting to the more Ni-rich Ni₂Si. As the reaction proceeded, metallic Ni precipitated from the Ni₂Si. The oxidized SiC showed a region under the oxide which was rich in Si. The Ni-rich silicide reacted with the Si-rich layer on the SiC to form Ni₂Si, causing deformation of the edges of the device features...