Investigation of hot-carrier induced interface damages via small-signal characteristics of drain-to-substrate gated-diode

The DC gated-diode current measurement has been used extensively to study hot-carrier induced degradation in MOSFETs. This technique relies on the property of interface states acting as effective recombination centres to detect their presence. According to Shockley-Read-Hall recombination theory (Muller and Kamins, 1986), gated-diode generation/recombination current is mainly contributed by states close to the midgap. This paper presents a study of the small-signal characteristics of the drain-to-substrate junction of an n-channel MOSFET configured as a gated diode to study hot-carrier induced degradation. This small-signal admittance consists of the small-signal drain-to-substrate capacitance and conductance (C_db and G_db). Similar to DC gated diode characterisation, the small signal admittance uses the change in the space charge region of the gated-diode to detect the presence and the spatial distribution of hot-carrier induced interface and trapped charges. G_db is sensitive to change in midgap interface states acting as recombination centres as well as any change in bulk recombination due to change in the volume of the spatial charge region. It corresponds to the slope of the DC diode I-V characteristics of the junction. Change in C_db reflects the width of the diode space charge region. Therefore, the information obtained from the analysis of C_db and G_db before and after electrical stressing are complementary to each other. We compare experimental results for C_db and G_db to show the applicability of this method to characterize hot carrier stress response of submicron MOSFETs