On the microscopic origin of the frequency dependence of hole trapping in pMOSFETs

A detailed understanding of the physical mechanisms behind hole capture in pMOSFETs is essential for a number of reliability issues, including the negative bias temperature instability (NBTI), hot carrier degradation, random telegraph and 1/f noise. In order to better understand the controversial frequency dependence of NBTI, we study the frequency dependence of hole capture on individual defects by extending the time-dependent defect spectroscopy (TDDS) to the AC case. Conventionally, hole capture is explained by a first-order process using effective capture and emission time constants, τ_c and τ_β. Our experimental data clearly reveals, however, that this assumption is incorrect under higher frequencies where modern digital applications typically operate. In particular, the frequency dependence visible in these effective capture times clearly confirms that hole capture must occur via an intermediate metastable state. Interestingly, the metastable state we have previously introduced to explain the DC-TDDS data also fully explains the AC-TDDS case.