Effects of poly depletion on the estimate of thin dielectric lifetime

Poly-gate depletion during the accelerated time-dependent breakdown (TDDB) test of single-doping-type capacitors (both electrodes of the doping type) results in an overestimate of dielectric lifetime at operation voltage. Simple high-field data extrapolation fails to take into account the voltage-dependent poly band bending. A three-orders-of-magnitude overestimate of lifetime at 5 V for 68-AA oxide equivalent poly/poly capacitors was found. After correcting for the poly depletion effects, the slope of the TDDB projection line decreases by 18%. The effects can be minimized by performing TDDB testing below the top poly inversion voltage. Fermi-Dirac statistics quantitatively explained the phenomenon. Calculated maximum allowable TDDB voltages for different gate doping and oxide thickness are presented as guidelines for test design.<
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