Charge collection in SOI capacitors and circuits and its effect on SEU hardness

Abstract

Focused ion microbeam and broadbeam heavy-ion experiments on capacitors and SRAMs are used to investigate increased saturation upset cross sections recently observed in some silicon-on-insulator (SOI) integrated circuits (ICs). Experiments performed on capacitors show a very strong bias and oxide thickness dependence for charge collection. In combination with three-dimensional (3-D) simulations, these data suggest that the mechanism for charge collection in capacitors is due to perturbation of the substrate electric fields by charge deposition in the substrate. For substrates biased in depletion, these perturbations induce displacement currents through the oxide. Charge collection by displacement currents can be substantially reduced or mitigated by using heavily doped substrates. Experiments performed on SRAMs also show enhanced charge collection from displacement currents. However, experimental data and 3-D simulations show that for SRAMs, a second mechanism also contributes to charge collection. The 3-D simulations suggest that the charge collection results from drain and body-tie heavy-ion strikes within a few tenths of a micron of the body-to-drain junctions. These charge collection mechanisms can substantially reduce the SEU hardness and soft-error reliability of commercial SOI ICs.

Charge Collection Measurements on SOI Capacitors using Heavy Ion Microprobe at GSI

“…The charge collection efficiency is 32% and 30% respectively. These values are in good agreement with the 37% efficiency obtained in [11] for a 0.176gm thick buried oxide SOI P-type substrate capacitor from the same technology and biased at VG=+20V [12] bombarded with 50 MeV Cu projectiles.…”

A review of ion beam induced charge microscopy

“…IBIC measurements showed that the induced charge is significantly larger than that expected from the region above the BOX. This observation lead to a more detailed investigation of the phenomenon [103][104][105][106] and to the theory of charge induction in MOS structures based on the Gunn theorem [23].…”

LET dependence of the charge collection efficiency of silicon microdosimeters

“…An amplification effect was observed for device bias of 20 V, a possible mechanism for this effect is high field avalanche multiplication at corners of the depletion region. Recent studies into charge collection in SOI structures have shown that significant charge collection can be induced by displacement currents across the oxide [15]. Simulation of the charge collection processes for these devices are planned to gain insight into the physical origins of the multiplication effect and to study the importance of induced displacement currents.…”