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

Abstract

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 873K/30min annealing created a stable SBH and a low value of on-resistance (Ron), which improved inhomogeneity. Based on the results of EDX and TEM analysis, the cause of improved SBH at the condition of 30min was attributed to the generation of TiSix (which has a higher SBH than Ti). On the other hand, the improved value of Ron at the condition of 30min 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 773K/60min and 873K/60min, Ron 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 Ron 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.