Mechanisms and Models for the Suppressed Defect Dynamics in SiO₂–Si Structures under High‐To‐Low Switched Dose Rate Irradiations

Abstract

Ground tests of total ionizing dose (TID) irradiation of silicon (Si) electronic devices are usually carried out under an equivalent constant dose rate, and most theoretical investigations also focused on this ideal situation. However, the practical TID irradiation occurs with variable dose rates. [1] In space missions such as artificial satellites and Mars exploration, the irradiation dose rate changes dramatically as the mission goes on. [2] Especially, for anomalous areas in the South Atlantic (such as the International Space Station) or deep space exploration missions, the dose rate varies within several orders of magnitude, from 10 À5 to 10 rad(Si) s À1 . The time dependence of the concentrations of induced E 0 γ centers and P b centers (also denoted as N ot and N it in the literature) in the dielectric SiO 2 layer and at the SiO 2 /Si interface [3,4] are found to be different for high dose rate (HDR) and low dose rate (LDR) irradiations, especially for bipolar transistors, called as an enhanced low-dose-rate sensitivity (ELDRS) effect. [5] However, at present, it is widely accepted that these different HDR and LDR defect dynamics are relatively independent when they occur in succession. [6] The physical foundation is that HDR and LDR defect dynamics in SiO 2 -Si structures are dominated by different mechanisms, i.e., hole trapping mechanism for LDR and recombination mechanism for HDR, respectively. [7,8] According to this assumption, it has been suggested that the LDR irradiation following HDR irradiation can reproduce the defect dynamics as induced by LDR-only irradiation. [9] In applications, a switched dose rate (SDR) technique [6,10] has been proposed to be equivalent to the LDR-only damage of bipolar devices.However, our recent work [11] demonstrated that HDR and LDR defect dynamics in SiO 2 -Si structures are governed by the same physics: decelerated generation of E 0 γ centers in disordered SiO 2 and reversible conversion between E 0 γ

Observation and Origin of Anomalous Early Recovery of Base Currents in Low-Dose-Rate γ-Ray-Irradiated PNP Transistors

“…As proved by the data in Figure c,d, the ionizing irradiation also induces E γ ′ in SiO 2 , which converts to P b at the SiO 2 /Si interface. In previous studies, we have derived analytical kinetic models of these defects normalΔ [ E γ ′ ] ( t ) = ( 1 − p ) ( k normalh t ) β + p ( k normalh t ) β Γ ′ [ β , − k normalc t ] normalΔ [ P normalb ] ( t ) = p ( k normalh t ) β − p ( k normalh t ) β Γ ′ [ β , − k normalc t ] Here, k h represents the effective rate constant of E γ ′ buildup due to hole capture; − 0 < β < 1 accounts for the sublinearity of the buildup of E γ ′, which arises from the hierarchically constrained dynamics in glassy materials . Hierarchical constraint means that the energy levels of neutral oxygen vacancies in amorphous SiO 2 are continuously distributed, and the holes are first captured by shallower energy levels and then by deeper energy levels.…”

“…In general, ionizing irradiation will cause significant damage to semiconductor devices because electrically active defects are induced in the materials and interfaces. For example, under total ionizing dose (TID) irradiation, the performance of Si electronic devices decays because positively charged oxygen vacancies of puckered configuration, E γ ′ centers, and amphoteric Si dangling bond, P b centers, are induced in SiO 2 and at the SiO 2 /Si interface, respectively. − The E γ ′ centers are generated because ionizing-irradiation-induced holes are captured by pre-existing neutral oxygen vacancies in SiO 2 . − The P b centers are produced because E γ ′ centers can crack nearby hydrogen molecular (H 2 ) residual from the passivation process and release protons, − which under positive bias can drift to the SiO 2 /Si interface , to depassivate pre-existing P b H and finally produce P b centers. − As illustrated by the orange quadruple angle stars in Figure , the accumulated P b centers (interface traps) act as recombination centers, , resulting in the growth of base current ( I B ) and the degradation of current gain of bipolar devices . As P b centers are continuously produced under ionizing irradiation, excess I B is expected to grow monotonously with the total dose.…”