RADIATION EFFECTS AND NEGATIVE BIAS-STRESS IN Ge-CHANNEL FinFET & NANOWIRE DEVICES

Abstract

Two broad categories of radiation effects; total ionizing dose (TID) and single event effects (SEE) in Ge channel devices have been investigated. In addition to that, negative bias temperature instabilities (NBTI) in Ge channel devices have also been explored. The development of highly scaled advanced semiconductor devices necessitates an extensive study of radiation effects in Ge-channel FinFET and GAA nanowire devices. Single-Event-Induced Charge Collection mechanism in Ge-Channel pMOS FinFETs reveals that the peak transient currents due to pulsed-laser or heavy-ion irradiation of Ge pMOS FinFETs are nearly independent of gate bias. This is because the prompt photocurrent is due primarily to a transient source-drain shunt. In contrast, longer-term diffusion charge collection is strongly gate-bias dependent. This bias dependence results from hole injection from the source in response to the transient increase in electron concentration in the channel. The transients measured at the source terminal change polarity when the strike location moves from source to drain, but this effect does not occur for the transients measured at the drain terminal. Geant4-based Monte Carlo simulation of the interaction of high energy protons with various target materials used in Ge channel pFinFET demonstrate that the maximum Linear Energy Transfer (LET) values of the order of 23 MeV-cm^2/mg may need to be accounted for in heavy-ion testing of Ge channel devices. The presence of high-Z materials (such as tungsten) in interconnects extends the maximum Linear Energy Transfer (LET) values to approximately 40 MeV-cm^2/mg. The NBTI-induced degradation in Ge GAA device originates primarily from the interface- and border-trap generation. Devices stressed at high gate voltage show rapid initial degradation and quick saturation dominated by interface-trap generation. Radiation-induced off-state leakage current in Ge GAA nanowires increases with dose due to enhanced band-to-band tunneling caused by charge trapping in the shallow trench isolation (STI).