Mechanisms of Ohmic Contact Formation of Ti/Al-Based Metal Stacks on p-Doped 4H‑SiC

Ohmic contacts on p-doped 4H-SiC are essential for the fabrication of a wide range of power electron devices. Despite the fact that Ti/Al based ohmic contacts are routinely used for ohmic contacts on p-doped 4H-SiC, the underlying contact formation mechanisms are still not fully understood. TLM structures were fabricated, measured and analyzed to get a better understanding of the formation mechanism. SIMS analyses at the Ti3SiC2-SiC interface have shown a significant increase of the surface near Al concentration. By using numerical simulation it is shown that this additional surface near Al concentration is essential for the ohmic contact formation.

Low-Resistance Ohmic Contact Formation by Laser Annealing of N-Implanted 4H-SiC

In this work, pulsed-laser-based tempering was applied for post-implant annealing of n-type N-doped 4H-SiC in order to electrically activate the dopants and to rebuild the crystal structure. The annealing was performed by a frequency-tripled Nd:YVO4 laser with a pulse duration of 60 ns. To evaluate the effects of post-implant annealing, JBS diodes were electrically characterized. The results were compared with implanted, not post-annealed JBS diodes. The electrical measurements showed a significant on-state voltage drop of 40 mV at 6 A for post-implant laser annealed diodes compared to not post-implant annealed diodes.

Reducing On-Resistance for SiC Diodes by Thin Wafer and Laser Anneal Technology

This work presents the influence of Thin Wafer und Laser Anneal Technology on the electrical performance of 4HSiC devices. Substrate thinning and backside ohmic contact formation via laser annealing were successfully applied to in-house designed and manufactured 6 A 650 V SiC diodes at IISB, improving its forward characteristics. The given devices exhibit an on-state voltage drop (VF) reduction from 1.78 V to 1.62 V at 6 A rated current while maintaining blocking capabilities of more than 1.1 kV with leakage currents less than 1 μA at 650 V nominal voltage. On-resistance (RON) was lowered by approx. 30 % to 90 mΩ and 60 % to 12 mΩ in Schottky and conductivity modulation state, respectively. Wafer thinning also allows reducing the influence of non-homogeneous distributed substrate doping concentrations, leading to a more narrow distribution of the forward characteristics of the devices across the wafer.

Influence of gettering on aluminum ohmic contact formation

The study considers the reasons and mechanisms of degradation of reverse characteristics of varicaps with aluminum-based ohmic contacts. The authors present and analyze the experimental results on how gettering affects the reverse current of varicaps, as well as possible mechanisms of such effect. Gettering was performed with a getter site created on the back side of the substrate before the epitaxial layer is deposited on the working side of the substrate. The article demonstrates that the proposed technology using gettering is rather effective in reducing the level of reverse currents and in increasing the yield of devices.