Argon Plasma Treatment of 4H-SiC Surface before Nickel Ohmic Contacts Formation by UV Laser Annealing

Laser Thermal Annealing (LTA) is a necessary fabrication step to improve the 4H-SiC devices by reducing their ON-state resistance. Because the LTA annealing is achieved at the end of the front-end fabrication, the classical Radio Corporation of America cleaning (RCA) cannot be used without affecting the material deposited on the frontside. Therefore, in this study, we investigate the argon (Ar) plasma surface treatment, achieved in our sputtering tool, before the ohmic contact fabrication, as an alternative surface preparation to the RCA sequence. As the Ar plasma modifies the SiC surface morphology, it affects its wetting properties. That can play a key role in the ohmic contact formation by LTA since the nickel turns into liquid phase during the laser irradiation. For an Ar plasma treatment of 30 min, a specific contact resistance of 5.0×10 -5 Ω.cm 2 has been obtained for an annealing at 5.0 J.cm 2 , which is in the same range than the contact fabricated by LTA involving a classical RCA cleaning.