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Ti Ohmic contacts to relatively highly doped (1 × 1018 cm−3) n-type 4H-SiC have been produced, without high temperature annealing, by means of low temperature electronic cyclotron resonance microwave hydrogen plasma pre-treatment (HPT) of the SiC surface. The as-deposited Ti/4H-SiC contacts show Ohmic properties, and the specific contact resistance obtained is as low as 2.07 × 10−4 Ω·cm2 after annealing at low temperatures (400 °C). This is achieved by low barrier height at Ti/SiC interface, which could be attributed to decrease of surface states density by the HPT releasing Fermi level pinning, and to band-gap narrowing, image-force, and thermionic-field emission at high doping.

Bias temperature stresses (BTSs) are critical factors that cause severe threshold voltage (V th ) instability in silicon carbide (SiC) metal-oxide-semiconductor (MOS) devices. In this work, we studied the behavior of flatband voltage (V fb ) instability in 4H-SiC MOS capacitors under various BTSs from low temperature (LT) to high temperature (HT) considering the combined effects of interfacial traps and mobile ions. Results showed that nitrogen and nitrogen-hydrogen plasma passivation improved the V fb instability. The initial sweeping gate voltage determined the direction of V fb shift. BTSs from LT to HT induced different capacitance-voltage hysteresis characteristics. The V fb shift was further separated according to the contribution of the interface trapped, oxide trapped, and mobile ionic charges. At LT, the charge trapping dominated the shift behavior. The interface trap density was also extracted by another high-frequency and quasi-static method, which was the same as the separated interface trap density at 100 K, confirming the separation correctness of V fb shift. At room temperature, charge trapping and mobile ions with very weak mobility contributed to the V fb shift. At HT, mobile ions that counteracted the charge-trapping effect determined the V fb shift, although the additional traps were activated in the interface and oxide. Physical models of V fb instability under different temperature stresses were proposed. Finally, we chose the 100 K, 273 K, and 423 K to analyze gate bias stresses and stress time induced V fb instabilities as well as their mechanisms.

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