Three-level charge pumping study of radiation-induced defects at SiSiO 2 interface in submicrometer MOS transistors

Abstract

The charge pumping response of interface traps and near-interfacial oxide traps (border traps) induced by Co 60 gamma rays in submicrometer (0.5 μm channel length) metal-oxide-semiconductor transistors has been studied. Using an improved three-level charge pumping technique, the energy distribution of interface trap parameters (emission times, capture cross-sections and interface state density) has been determined after irradiation in both the upper and lower parts of the silicon band gap on n-channel devices. The influence of border traps on three-level charge pumping measurements is demonstrated for the first time. Good agreement has been found between standard charge pumping and three-level charge pumping characteristics in terms of ‘breakpoint frequency’ at which the charge recombined per cycle deviates from the fast interface state response. The distance of border traps from the interface has been estimated to be ∼ 15–20 Å from a trap-to-trap tunneling model. In addition, a new technique is presented based on three-level charge pumping measurements to determine a border trap distribution in the silicon band gap.