Electron irradiation effects on power MOS transistors

Abstract

Electron irradiation has been used to enhance the switching speed of the internal diode in high-voltage power MOS structures (BV DSS > 500 V). By using 12 MeV electron irradiation at room temperature it has been found that the reverse recovery time and the reverse recovery charge of power MOS internal diode can be reduced in a well controlled manner up to 70% and 90% of their initial value respectively increasing the radiation dose from 0 to 15 Mrads. Anyway an undesirable decrease of about 3V has been observed in the gate threshold voltage. This effect has been ascribed to the damage produced in the gate oxide of the device due to the electron irradiation. By annealing the device at temperature >315 °C it has been possible to restore the threshold voltage without heavily enhance the carrier lifetime. DLTS measurements have been performed on electron-irradiated devices to identify the recombination centres introduced in the forbidden gap of the silicon. A comparison has been made with gold-diffused devices. The results obtained confirm that electron irradiation is feasible for power MOS transistors.