SiGe Channel Technology: Superior Reliability Toward Ultra-Thin EOT Devices—Part II: Time-Dependent Variability in Nanoscaled Devices and Other Reliability Issues

The time-dependent variability of nanoscaled Si_0.45 Ge_0.55 pFETs with varying thicknesses of the Si passivation layer is studied. Single charge/discharge events of gate oxide defects are detected by measuring negative bias-temperature instability (NBTI)-like threshold voltage (V_th) shift relaxation transients. The impact of such individually charged defect on device V_th is observed to be exponentially distributed. SiGe channel devices with a reduced thickness of their Si passivation layer show a reduced average number of active defects and a reduced average impact per charged defect on device V_th. Our model for the superior reliability of the SiGe channel technology previously proposed in Part I, which is based on the energy decoupling between channel holes and dielectric defects, is shown to also explain these experimental observations. Other reliability mechanisms, such as 1/f noise, body biasing during NBTI, channel hot carriers, and time-dependent dielectric breakdown, are also investigated. None of these mechanisms are observed to constitute a showstopper for the reliability of this promising novel technology.