Enhancement of the stability of Ti and Ni ohmic contacts to 4H-SiC with a stable protective coating for harsh environment applications

We report on wafer-level measurements of the long-term stability of Ti and Ni ohmic contacts to n-4H-SiC during thermal treatments in air or air/moisture environments up to 500°C. Contact metallizations with and without a sputtered Ti (20 nm)/TaSi x (200 nm)/Pt (150 nm) diffusion barrier stack and Ti (20 nm)/TiN (10 nm)/Pt (150 nm)/Ti (20 nm) interconnects were compared. A protective coating consisting of a SiO x (250 nm)/SiN y (250 nm) stack deposited by plasma-enhanced chemical vapor deposition (PECVD) was used. The stability of the contact metallizations during long-term thermal treatments in air and air/moisture was studied. The best performance was achieved with Ti ohmic contacts without the Ti/TaSi x /Pt stack. This system successfully withstood 1000 h thermal treatment at 500°C in air followed by 1000 h at 500°C in air/10% moisture. After the aging, the contact failure ratio was below 1% and the specific contact resistivity amounted to (2.5 ± 1.1) × 10-4 cm2. Sc anning electron microscopy (SEM) cross-sectional analysis indicated no degradation in the contact metallization, demonstrating the effectiveness of the SiO x /SiN y protective coating in preventing oxidation of the contacts. These results are very promising for applications in harsh environments, where the stability of ohmic contacts is crucial.