Formation mechanism, interface characteristics and the application of metal/SiC thin-film ohmic contact after high-temperature treatment
Chen Wu, Xudong Fang, Qiang Kang, Ziyan Fang, Hao Sun, Dong Zhang, Libo Zhao, Bian Tian, Ryutaro Maeda, Zhuangde Jiang
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/TaSi 2 /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. • Highly stable SiC ohmic contacts (SiC/Ti/TaSi 2 /Pt and SiC/Ni/W) for high temperature working environment up to 600 °C were obtained. • At the contact interface, the alloy phase with lower work function formed by high temperature annealing reduces the Schottky barrier, and the interatomic diffusion promotes the electron tunneling effect, forming the ohmic contacts. • Intrusion of oxygen atoms is the key causing contact failure and Ta-based barrier layer and coating protective layer significantly improves high temperature tolerance of the SiC ohmic contacts. • The Ti/TaSi 2 /Pt ohmic contact was applied to fabricate SiC piezoresistive pressure sensor chips, and the operating temperature of the chips in air is raised to 600 °C.