Multilayer structures of cobalt and silicon have been deposited as an ohmic contact on n-type 4H-SiC substrates in order to obtain lower contact resistance and higher thermal stability. The metal structures were prepared by using electron beam evaporation on top of the silicon face of the 4H-SiC substrates, and were annealed in an atmosphere of argon with 10% hydrogen. The metal film thickness was monitored during the film deposition, and the ratio of the cobalt and silicon was fixed at 0.5 for the formation of the silicon-rich silicide structure (CoSi2). The electrical property of the ohmic contact has been significantly improved by the reduction of the oxide content in the metal contact layer. A two-step annealing process was employed to reduce oxidation problems that may occur in the heat treatment at high temperatures. The specific contact resistance of the contact structure prepared by the two-step annealing process was measured to decrease by more than one order of magnitude compared to that prepared by one-step annealing. The best result has been obtained as 1.8 × 10−6 Ω cm2 for Co/Si/Co/Si/Co metal structures after two-step annealing, at 500 °C for 600 s and 800 °C for 120 s. In the field emission scanning electron microscopy, the interface of the contact structure and SiC substrate was observed to have smooth surface morphology with CoSi2 grains.
Source:IOPscience
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