Impact of Ionizing Radiation on the SiO2/SiC Interface in 4H-SiC BJTs

Degradation of SiO2 surface passivation for 4H-SiC power bipolar junction transistors (BJTs) as a result of ion irradiation has been studied to assess the radiation hardness of these devices. Fully functional BJTs with 2700 V breakdown voltage are implanted with 600 keV helium ions at fluences ranging from 1 x 10(12) to 1 x 10(16) cm(-2) at room temperature. These ions are estimated to reach the SiO2/SiC interface. The current-voltage characteristics before and after irradiation show that the current gain of the devices starts degrading after a helium fluence of 1 x 10(14) cm(-2) and decreases up to 20% for the highest fluence of ions. Simulations show that the helium ions induce ionization inside the SiO2, which increases the interface charge and leads to a degradation of the BJT performance. Thermal annealing of the irradiated devices at 300 degrees C, 420 degrees C, and 500 degrees C further increases the amount of charge at the interface, resulting in increased base current in the low-voltage range.