|
Silicon Carbide (SiC) combines unique material properties (wide band gap, high breakdown electric field, high electron drift velocity, high thermal conductivity, chemical inertnes), which makes it a very promising material for development of high -power, -temperature and -frequency semiconductor devices. For realization of such application potential, developing of low resistive and thermally stable ohmic contact is still required. In this paper, we report on fabrication and characterisation of nickel silicides ohmic contacts to n-type 4H-SiC. The contacts on Si-faced 4H-SiC (0001) substrates with the specific resistance of 0.074 Ùcm were fabricated by DC magnetron sputtering of Ni and Si thin films. One set of structures has the Ni/Si/SiC scheme, the second one has the Si/Ni/SiC scheme. Standard Ni/SiC contact was prepared to compare features of the ohmic contacts on this substrate. The different Ni/Si thickness ratios of 66/60, of 45/83 and of 27/101 (nm) were designed to produce the stoichiometric Ni2Si, NiSi and NiSi2 compound, respectively. The contact structures were annealed at 600°C for 15 min, and subsequently from 800 to 1100°C for 3-5 min in N2 flow. The structure, composition, morphology and electrical properties of the contacts were examined using XRD, RBS, AFM and I-V measurements respectively. Ohmic properties were characterized by extracting specific contact resistivity using c-TLM method. The results indicate that the stoichiometric nickel silicides are formed after first step annealing (600°C). The Ni(66 nm)/Si(60 nm) contact annealead at 1050°C show a low contact resistivity of r ~ 5×10-5 Ùcm2 with excelent surface morphology. Results of the specific contact resistivity measurements show that the resistivity of the Si/Ni/SiC contact was one order lower than that of the Ni/Si/SiC contact (r ~ 3×10-4 Ùcm2). The optimal metallization scheme was selected to use in semiconductor device technology. The work was supported by INTAS (Grant Ref. Nr 06-1000014-5957) and by the Ministry of Science and Higher Education, Poland, under the grant 3T11B 042 30. |