Investigation Of TiC Ohmic Contacts To N-type 4H-SiC Semiconductor

New generation semiconductor material silicon carbide(SiC) is the ideal material for fabricating high-temperature, high-frequency, high-power devices. The technique of ohmic contacts is difficulty and key technology of new semiconductor material research, especially wide band gap semiconductor devices. Ohmic contact is not only related to the variety of electrode materials, but also effected by semiconductor surface states. This paper selects new electrode material TiC combined with ECR(electron cyclotron resonance) hydrogen plasma surface treatment technology, which is developed independently by our team, and investigates TiC/SiC ohmic contacts, how to decrease the specific contact resistivity of ohmic contacts in detail concerned SiC surface treatment technique.Metallic carbide material TiC is a kind of low resistivity and stable compound metal with a low work function which is lower than that of n-type 4H-SiC. Besides, its adhesion to SiC is very good. These characteristics make TiC an ideal material of fabricating n-type 4H-SiC ohmic contacts. In this paper, the surface of n-type 4H-SiC was treated by ECR hydrogen plasma, TiC electrodes were fabricated by the method of sputtering and lift-off process, and the annealing was performed at low temperature(<800℃). Standard method linear transmission model(TLM) was used to measure the I-V curves and calculate specific contact resistivityρ_c. The results indicated that TiC electrodes formed ohmic contacts without annealing and the treatment of ECR hydrogen plasma decreased specific contact resistivity obviously. Lowest value of specific contact resistivity 2.45×10^-6Ω·cm² was obtained after annealing at 600℃; After annealing above 600℃the property of ohmic contacts started to degenerate, but the specific contact resistivity was still much lower than that of samples which weren't treated by hydrogen plasma. This phenomenon showed that ECR hydrogen plasma treatments had a significant effect to avoid deterioration of ohmic contacts under high temperature.Improvements of ohmic contacts treated by ECR hydrogen plasma are ascribed to the effect on SiC surface cleaning and surfaces states passivation. X-ray diffraction(XRD) measurement was used to identify the phases and the variety of phase structure formed at the interfaces of electrode material at various annealing temperarues. The results indicated that the increase of specific contact resistivity after annealing at 800℃was due to C stacking at contact interface. On the whole, as to the fabrication of TiC n-type 4H-SiC ohmic contacts and the SiC surfaces were treaded ECR hydrogen plasma, it has shown excellent superiority. The process avoided high temperature annealing at 800-1200℃and made great sense in avoiding high-temperature deterioration and improving the long-term thermal stability of devices.