High energy ion irradiation effects on thin oxide p-channel MOSFETs

P-channel MOSFETs of a commercial 0.25 μm CMOS technology have been irradiated by high linear energy transfer (LET) iodine (I) and low LET silicon (Si) ions up to 300 Mrad(Si) and 500 Mrad(Si), respectively. Threshold voltage variations (ΔV_TH) up to -0.46 V and -0.44 V have been measured at the highest I and Si doses. Both oxide positive trapped charge (ΔV_OX) and interface states (ΔV_IT) contribute to ΔV_TH with a ratio ΔV_IT/ΔV_OX=1 (<1) for high (low) LET ions. After 40 days at room temperature most of the positive charge is recombined by electron tunneling from the oxide interfaces, while only a small amount (6%-16%) of interface states is annealed. A huge 1/f noise increase (higher for I ions) is observed after irradiation. Finally radiation induced soft breakdown (radiation induced leakage current) conduction through the gate oxide is generated by high (low) LET ions for |V_g|>1.6 V (>3.4 V).