Post-annealing processes to improve inhomogeneity of Schottky barrier height in Ti/Al 4H-SiC Schottky barrier diode

To improve the high resistance and low breakdown voltage (BV) of a 4H-SiC Schottky barrier diode (SBD), the metal annealing process is conventionally used; this process stabilizes the Schottky barrier height (SBH). In this paper, we apply a post-metal annealing process to 4H-SiC Ti-SBD chips and verify the effect of the changes on electrical characteristics based on the post-annealing process. The results of experiments show that the condition of 873 K/30 min annealing created a stable SBH and a low value of on-resistance (R_on), which improved inhomogeneity. Based on the results of EDX and TEM analysis, the cause of improved SBH at the condition of 30 min was attributed to the generation of TiSi_x (which has a higher SBH than Ti). On the other hand, the improved value of R_on at the condition of 30 min was attributed to the change to γ-phase Ti₃Al (which has a low resistance because diffused Al is present) caused by proper annealing. However, when more heat is applied in the cases of 773 K/60 min and 873 K/60 min, R_on increased and the SBH decreased. The results of EDX and TEM analysis showed that the low SBH was caused by Al spiking, which created an Al Schottky junction with a lower SBH than that of the Ti Schottky junction. Higher R_on resulted from the change to α-TiAl phase at the Al-Ti interface layer because of excessive diffusion of Ti and Al, which is due to the overly applied heat. From the results produced by this work, we can enhance the Al-Ti 4H-SiC SBD electrical characteristics by applying a suitable post-annealing process.