Cu/Si/Cu multilayer structures for Ohmic contact on n-type 4H-SiC substrates

Low temperature processes for Ohmic contacts to n-type 4H-SiC substrates were studied using Cu/Si/Cu multilayer structures as a function of post-annealing and metal deposition conditions. The contact structures were prepared by RF sputtering and electron-beam evaporation on top of the Si face of n-type SiC substrates with doping level of 1.1 x 10(19) cm(-3). The deposited metal thickness was monitored during the deposition, and the ratio of the Cu and Si was varied in the experiment. A two-step annealing technology was performed for decreasing of oxidation problems occurred during high temperature processes. The first step of the annealing was long time process at low temperatures for the intermixing of Si and Cu, while the formation of Cu-silicide phases was achieved at elevated temperatures as the second step. The contact formed after the two-step annealing at 500 degreesC for 600 s and 850 degreesC for 60 s demonstrated the lowest specific contact resistivity of 1.2 x 10(-6) Omega cm(2). The interface between the metal contact and the SiC substrate was observed by transmission electron microscopy, and the interface turned out to have regular distribution of silicide grains with smooth morphology. (C) 2004 Elsevier B.V. All rights reserved.