Investigation The Mechanism Of Ni Based Ohmic Contacts To SiC

SiC is proposed to be the best materials to fabricate high temperature, high voltage, high frequency devices due to its wide bandgap (3.2～3.4eV), high thermal conductivity and high-saturation drift velocity.Ohmic contact as a basic process is very important to determine the properties of SiC devices. The elements Al, Co, Ti, Pt and Ni was used as ohmic contact metals to SiC for years, however, Ni is recently proposed to be the best one. To form a good Ni/SiC ohmic contacts, high temperature treatment over 950℃is always needed although Ni-Si alloy could form at 500℃. Some researchers believed that the mechanism of Ni/SiC ohmic contact was due to the silicate, that is, nickel-silicate/SiC Contact, but others thought that the graphite layer between the silicate and the substrate might play a very important role. In fact, the reported specific contact resistances were quite different even the concentration of the substrates was the same. This might be related to the differences of the processes and the interface. Thus, it is very important to study the mechanism of ohmic contact process.Ni/SiC ohmic contacts were fabricated in this experiment. The I-V characteristics of the samples annealed at 500℃and 950℃was measured, which presented a rectifier I-V and an ohmic I-V, respectively. The specific contact resistance calculated by the method of TLM was about 3.2×10—3Ω·cm2. The depth profile of elements and their electric configurations were measured by using XPS, which showed that Ni2Si was a dominant phase in the contact layer and graphite C networks, but the graphite layer or nanocrystalline graphite was not observed by XRD, when the samples were annealed after 950°.