Extrapolation of high-voltage stress measurements to low-voltage operation for thin silicon-oxide films

Breakdown and wearout in MOS capacitors fabricated with 10 nm-thick silicon oxide films on p-type silicon are discussed. They have been stressed at high voltages. The high-voltage-stress-induced changes in the oxide properties are extrapolated to low operating voltages. The stress voltages ranged from -7.5 V to -14.5 V. The fluence during the stress was systematically varied front 2*10/sup -5/ C/cm/sup 2/ to 6 C/cm/sup 2/ by varying the stress time at each voltage. The number of interface traps generated by the stress increased as the stress voltage and fluence increased. However, the interface trap generation rate decreased as the fluence increased. The trap generation rate at low operating voltages was very high, but because the current through the oxide was small, the total number of traps generated was low. The trap generation rate was proportional to the inverse square root of the fluence with a voltage dependence that decreased as the fluence increased. Extrapolation of the high-voltage-stress measurements to 5 V shows that easily detectable changes in the oxide properties would only occur after several years of 5 V operation. Extrapolation of charge-to-breakdown and time-to-breakdown data to 5 V operation indicates that breakdown would occur after hundreds of years of device operation.<
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