Gate leakage current: A sensitive characterization parameter for plasma-induced damage detection in ultrathin oxide submicron transistors

Abstract

We report the results of experiments performed to study plasma-induced damage in ultrathin gate oxide of metal-oxide-semiconductor field-effect transistors (MOSFETs). The transistors used were 0.35 μm n-channel MOSFETs with ⩽65-Å-thick gate oxides fabricated on 200 mm p/p+ boron-doped silicon substrates using a full complementary metal-oxide-semiconductor flow up to and including metal 2 processes. Our results show that threshold voltage, maximum transconductance, and subthreshold swing as well as charge pumping current became ineffective in discerning charging damage in these thin oxide MOSFETs. In contrast, gate leakage current Ig, measured at a gate-to-substrate voltage of 2 V, is shown to emerge as the more sensitive damage indicator in this case. The sensitivity of Ig is attributed to trap-assisted direct tunneling which is enhanced by decreasing oxide thickness. The sensitivity of Ig in probing charging damage is demonstrated using special MOSFET structures that utilize charge antennas at the polycrystalline silicon gate definition etch, contact etch, and metal etch steps.