- 1Key Laboratory of Materials Physics, Institute of Solid State Physics, HFIPS, Chinese Academy of Sciences, Hefei, China
- 2University of Science and Technology of China, Hefei, China
The total ionizing dose (TID) effect is one of the main causes of the performance degradation/failure of semiconductor devices under high-energy γ-ray irradiation. In special, the concentration of doubly-hydrogenated oxygen vacancy (a case study of
Introduction
More and more new semiconductor materials are widely used as the core electronic components of sensors, detectors, radar and so on. In extreme service environments, semiconductor devices are inevitably affected by harsh radiation effects. All kinds of high-energy particles will cause serious ionization or displacement damage to semiconductors, then lead to the degradation/failure of the electrical performance of semiconductor devices, and pose adverse effects on the safety and lifetime of the entire electronic systems (Benton and Benton, 2001).
As early as 1964, Hughes and Giroux conducted a preliminary study (Hughes and Giroux, 1964) on the performance degradation of semiconductor devices (MOS) under the total ionizing dose (TID). They found that TID-induced performance degradation is due to the additional charge generated in the oxide layer (SiO2) rather than on the surface. In subsequent decades, a large number of experimental studies of ionizing irradiation showed that the key mechanism of the performance degradation induced by the TID is the formation of oxide charged defects (Not) in the gate oxide region (Hughes, 1965a; Hughes, 1965b; Kooi, 1965; Zaininger, 1966). Therefore, identification of neutral defects in SiO2 before irradiation and exploration of the evolution of charged defects after irradiation are the basis for studying the TID effect of MOS devices.
In 1956, Robert used electron paramagnetic resonance (EPR) for the first time to measure radiation-induced defects in crystalline or amorphous SiO2 (Weeks, 1963) and found two basic types of oxygen vacancies in SiO2, including deep (
The pre-existing concentration of defects in SiO2 is still known little. Density functional theory (DFT) calculations suggest that relative concentrations of different pre-existing trap species, and order of magnitude estimates of the actual concentration of defects have been suggested by etch-back experiments of irradiated oxides (Devine et al., 1993). It is found that the initial concentration of doubly-hydrogenated oxygen vacancy before irradiation is relatively high, while its charged concentration after irradiation is the lowest among the oxide charged defects (Rowsey et al., 2011a). In the process of ionizing irradiation, the evolution process of doubly-hydrogenated oxygen vacancy and its specific contribution to the TID effect are still unclear. It is thus urgent to establish a dynamic model of the TID effect that includes the dynamic of doubly-hydrogenated oxygen vacancy to reveal their influence mechanism.
In this paper, a one-dimensional (1-D) dynamics model of mobile particles and fixed defects in the oxide layer (SiO2) of typical silicon MOS devices is developed to systematically study the influence of doubly-hydrogenated oxygen vacancy on the TID effect. This work provides theoretical guidance by controlling the concentration of doubly-hydrogenated oxygen vacancy for the radiation-hardening-by-design (RHBD) techniques of semiconductor devices.
Simulation methods
Dynamics model
The model framework is shown in Figure 1. First, the initial distribution of defects can be determined by EPR measurements (Lenahan and Conley, 1998; Lu et al., 2002). The reaction events and rate coefficients between mobile particles and defects are mainly given by the DFT calculations (Rowsey et al., 2011a; Rowsey et al., 2011b). Then, with this information, the continuity equations of mobile particles and fixed defects can be described based on the rate theory. In addition, the Poisson equation is established to determine the spatial electric field distribution. Finally, the finite difference method is employed to solve the ordinary differential equations (ODEs). The evolution and distribution of oxide charged defects and electric fields can thus be obtained by this model.
Continuity equation
The continuity Eq. 1 in Figure 1, where
The generation rate of e-h pairs induced by ionizing irradiation is given as follows (Oldham, 2000),
where G0 represents the density of e-h pairs per unit ionizing dose, Y is the survival rate of the e-h pairs after initial recombination, which is set to be 0.01 for SiO2 under γ-ray irradiation (Shaneyfelt et al., 1991), and R is the dose rate (rad/s).
The reaction rates of mobile particles with fixed defects are determined by the rate theory, which is proportional to the reactant concentrations. Comprehensively considering all reaction events, the total reaction rate of the particle i is given by (Xu et al., 2018),
where the j, m and n are termed as the other reactants, and the α and β represent the forward and reverse reaction rate coefficients, respectively.
Since the fixed defect is immobile and has no additional generation, the continuity equation includes only the reaction term (
Reaction events and coefficients
Since deep- and shallow-level defects cannot be transformed into each other, we only consider the dynamics of deep-level defects (
For oxygen vacancy (
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TABLE 1. Chemical reaction and rate coefficients (Bunson et al., 2000; Rowsey et al., 2012; Patrick et al., 2015; Sharov et al., 2022).
The accumulation of the charged defects results in the formation of a built-in electric field in the oxide layer. The electric field can be solved by Poisson’s equation as below (Esqueda et al., 2012; Jafari et al., 2015),
where,
An important parameter is the density of Not, with units of cm−2, which can be integrated from the distribution of each oxide charged defect as (Esqueda et al., 2011),
where Lox is the thickness of the oxide layer, and x refers to the distance from the Gate.
Numerical method
The finite difference method with a uniform spatial grid is adopted for solving the partial differential equations (PDEs). Here the lsoda solver of the C version (Whitbeck, 1991) is employed to solve the corresponding ODEs. The key to using the finite difference method to solve the above time and space related problems is the setting of appropriate initial values and boundary conditions. The initial concentration of charged defects and charged particles is set to 0. In the 1-D model, there are two boundaries of Gate/SiO2 and Si/SiO2 in contact with the SiO2 layer. The mobile particles can flow freely at both boundaries, so the first kind of boundary conditions are adopted. In addition, we specify that the electrostatic potential is continuous at all boundaries (Xu et al., 2018).
Results and discussions
This section presents the evolution and distribution of defects in the SiO2 layer of an NPN-type MOS capacitor (Lox = 200 nm) irradiated by γ-rays of
Validation and verification
The simulated density of oxide charged defects (Not) is compared with the experimental ones (Tuttle et al., 2010) to verify our model. Figure 2 shows the time evolution of the density of Not, under the time of
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FIGURE 2. Comparison of the evolution of Not with the experiment for the MOS capacitor with a 200 nm SiO2 layer under 5 V bias.
The influence of on and
In the following, we studied the key factors of the oxide charged defects for the TID effect, such as their composition, distribution and evolution. Figure 3A shows the distributions of different oxide charged defects under the TID of 10 krad with the dose rate of 10 rad/s at 300 K.
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FIGURE 3. Distributions of (A) different oxide charged defects under the TID of 10 krad, and (B) evolution of
Also as shown in Figure 3A, with increasing the distance from the Gate, the densities of
As given above,
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FIGURE 4. Evolution of
We also simulated the densities of
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FIGURE 5. Evolution of
It has been known that the TID effect of devices is closely related to the electric field near the Si/SiO2 interface (
According to Eq. 8, when the gate voltage (
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FIGURE 6. Electric fields at the Si/SiO2 interface with increasing the density of
Conclusion
In summary,
Data availability statement
The original contributions presented in the study are included in the article/Supplementary Material; further inquiries can be directed to the corresponding author.
Author contributions
GL: Methodology, Software, Data Curation, Formal analysis, Writing—Original Draft. JL: Methodology, Formal analysis, Software, Writing—Review and; Editing. QZ: Writing—Review and; Editing. YL: Formal analysis, Writing—Review and; Editing, Funding acquisition.
Funding
This work was supported by the National Natural Science Foundation of China (Grant No. 11975018), the National MCF Energy R&D Program (Grant No. 2018YEF0308100), and the Outstanding member of Youth Innovation Promotion Association CAS (Grant No. Y202087). Some of the calculations were performed at the Center for Computational Science of CASHIPS, the ScGrid of Supercomputing Center, and the Computer Network Information Center of the Chinese Academy of Sciences. This research work was also supported by the Tianhe-2JK computing time award of the Beijing Computational Science Research Center (CSRC).
Conflict of interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Publisher’s note
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.
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Keywords: total ionizing dose effect, dynamic modeling, doubly-hydrogenated oxygen vacancy, microscopic mechanism, MOS devices
Citation: Lu G, Liu J, Zheng Q and Li Y (2022) Influence of doubly-hydrogenated oxygen vacancy on the TID effect of MOS devices. Front. Mater. 9:1010049. doi: 10.3389/fmats.2022.1010049
Received: 02 August 2022; Accepted: 07 September 2022;
Published: 28 September 2022.
Edited by:
Weiliang Wang, Sun Yat-sen University, ChinaReviewed by:
Zexiang Deng, Guilin University of Aerospace Technology, ChinaHaiming Huang, Guangzhou University, China
Copyright © 2022 Lu, Liu, Zheng and Li. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Yonggang Li, ygli@theory.issp.ac.cn