Improvement in contact resistance of 4H-SiC by excimer laser doping using silicon nitride films

We have proposed a novel method of low-temperature nitrogen doping into 4H-SiC(0001) induced by KrF excimer laser irradiation to a SiN_x film. The SiN_x film with a thickness of 100 nm was deposited on an n-type 4H-SiC(0001) substrate by chemical vapor deposition. Laser beam size on the sample surface was 300 μm×300 μm. Irradiation fluence was 1.0 J/cm²-4.0 J/cm², and the number of shots was from 1 shot to 30 shots. Laser irradiation was performed in a vacuum chamber to avoid oxidation of the SiC surface. High concentration nitrogen doping (∼1×10²¹ /cm³ at the surface) and very low contact resistance with ohmic I-V characteristics can be achieved by laser ablation of the SiN_x film. In the case of laser irradiation at the fluence of 2.0 J/cm², the SiN_x film was almost ablated without laser ablation of the SiC substrate. Then, excellent ohmic contact characteristics was obtained at the irradiation number of 5 shots, and it was hardly deteriorated up to 30 shots. In the case of irradiation fluence above 3.0 J/cm², ablation of the SiC substrates was induced and ohmic contact characteristics were deteriorated with increasing the number of shots. From these results, we conclude that excellent ohmic contact characteristics without irradiation damage to SiC substrates can be obtained in a stable.