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International audience; In this paper, the electrical properties of Ti3SiC2-based ohmic contacts formed on p-type 4H-SiC were studied. The growth of Ti3SiC2 thin films were studied onto 4H-SiC substrates by thermal annealing of Ti-Al layers deposited by magnetron sputtering. In this study, we varied the concentrations of Ti and Al (Ti20Al80, Ti30Al70, Ti50Al50, and Ti), and the annealing temperature from 900 °C to 1200 °C for each concentration. X-ray diffraction and transmission electron microscopy analyzes were performed on the samples to determine the microstructure of the annealed layers and to further investigate the compounds formed after annealing. Using the transfer length method structures, the specific contact resistance (SCR) at room temperature of all contacts was measured. The temperature dependence up to 600 °C of the SCR of the best contacts was studied to understand the current mechanisms at the Ti3SiC2/SiC interface. The experimental results are in agreement with the thermionic field emission theory. With this model, the barrier height of the contact varies between 0.71 and 0.85 eV. Finally, ageing tests showed that Ti3SiC2-based contacts were stable and reliable up to 400 h at 600 °C under Ar.

Metal/semiconductor contacts have a great impact on device performances. Contact properties to wide band gap semiconductors, in particular, are more difficult to control due to the large potential barrier which arises when the metal is deposited on the semiconductor’s surface. Moreover, intrinsic interface states also lead to deviation of the Schottky-Mott limit and the barrier height is no more dependent of the work function of the metal. The contact property has also become very important with the race for miniaturisation toward the nanoscale. Contacts must also be adherent, able to resist to the temperatures for which SiC based-devices are intended, and also they should be compatible with conventional device processing techniques (die attachment). Ohmic contacts to SiC have thus been investigated for decades. The difficulties of controlling the interface properties between the metal and SiC to obtain low resistive ohmic contact have not been overcome yet; the specific contact resistance being proportional to the exponential of the barrier height for a given doping concentration. For example, nickel has been studied for the ohmic contacts on n and p-type, however the presence of voids at the interface has been reported leading to the degradation of the contact properties [1]. More recently low ohmic contact resistance has been reported of Au/Ti/Al/n-type-4H-SiC contact [2]. The formation of TiSi, TiSi2and Ti3SiC2has been reported according to x-ray diffraction experiments after annealing. The formation of Ti3SiC2(or MAX phase) has also been reported in TiAl-based contacts to both n-and p-type [3-6]. This ternary carbide layer is supposed to reduce the barrier height at the contact and thus leads to low contact resistances. The addition of Ge also leads to the formation of Ti3SiC2at lower temperature of annealing [7]. However, other compounds are frequently observed at the interface showing that the control of the interfacial structure must be optimized. The objective of our work is to obtain uniform epitaxial Ti3SiC2thin film on n-type 4H-SiC to form ohmic contact with low resistance by studying the influence of different parameters such as the role of Aluminium on the formation mechanisms, the polarity and doping dependence. The temperature and the annealing time are also parameters to be optimized for the improvement of the ohmic contact.