Formation mechanism, interface characteristics and the application of metal/SiC thin-film ohmic contact after high-temperature treatment

Abstract

SiC, as a representative of the third generation semiconductors, is widely investigated in power devices and sensors. However, ohmic contacts, an important component for signal output of various SiC chips, have always faced challenges with unclear formation mechanism and difficulty to withstand high temperature. To solve such problems, two sets of NPN-type SiC ohmic contact were prepared, including Ti/TaSi2/Pt and Ni/W. Experimental results show that whether ohmic contact can be formed mainly depends on the contact metal. The alloy phase with lower work function is formed after high temperature annealing, which reduces the height and width of the Schottky barrier. For the prepared SiC ohmic contacts, It was demonstrated that the invasion of oxygen atoms cause contacts failure, and incorporation of barrier layer (Ta-based layer) and effective protective layer (Pt layer) determine whether high temperatures can be tolerated. Finally, piezoresistive 4H–SiC pressure sensor chips with dimensions of 3000 μm × 3000 μm × 200 μm were fabricated using the obtained ohmic contacts. Sensor chips output resistance were monitored up to 600 °C in air to show stability of the ohmic contact. The highly stable and high temperature ohmic contact can be applied in a variety of SiC devices.

Keywords

• Silicon carbide (SiC)
• Metal
• Ohmic contact
• Interface diffusion
• Anti-oxidation
• Barrier layer