Contact formation in SiC devices

Abstract

In SiC devices designed for high temperature and high power applications, both ohmic and Schottky contacts are required which are stable at high temperature. The microstructure of contacts is very important to learn. Transmission electron microscopy (TEM) is a powerful method to reveal the microstructure of the contacts. Various contacts to SiC were investigated by TEM in cross-section and are discussed. TiN, Ni and Ni 2Si are ohmic contacts to n-type SiC, while multilayers and WN x contacts are used for Schottky purposes. Magnetron sputtered TiN layers were deposited at 700 °C onto cubic and hexagonal SiC as well. The contacts are ohmic, single crystalline, epitaxial, non-reactive and stable at high temperature. Ni contacts evaporated onto hexagonal SiC and subsequently annealed at 950 °C showed ohmic behavior, but Ni reacted with SiC. The reaction resulted in the formation of nickel silicide together with the formation of high number of voids. Deposition and annealing of Si/Ni multilayer contacts resulted in a void-free Ni 2Si contact layer preserving low contact resistivity. For Schottky purposes, multilayered contacts of Ti/Pt/Au/Ti can be used up to 575 °C, while WN x contacts are rectifying at least up to 800 °C.