Modeling of Radiation Effects in the MIS Devices

Galina Zayats

doi:10.11648/j.nano.20170501.12

Abstract

We describe space-time evolution of electric charge induced in dielectric layer of simulated metal-insulator-semiconductor structures produced by irradiation with X-rays. The purpose of this article is to develop a model which most fully describes the phenomena occurring under the ionizing irradiation of MOS structures. For this, in addition to known processes, such as a generation of the electron-hole pairs in the dielectric volume, diffusion and drift in the electric field of mobile charge carriers (electrons and holes), capture holes at the traps and recombination of electrons with the trapped holes, we also took into account the formation of surface states. The mathematical model considered includes the continuity equations for free electrons and holes, the Poisson equation, the equation describing the kinetics of hole-charge accumulation at trap levels, and the equation describing the tunneling mechanism of discharge of the charge accumulated in the dielectric. The model developed makes it possible to simulate the processes of charge degradation of silicon structures by the effect of ionizing radiation, and to determine the change in the threshold voltage of the MIS structure under irradiation, the distribution of free and trapped charges in the dielectric, and the distribution of the electric field strength. The type of dose dependence of the change in the threshold voltage of the MIS structure is determined by a number of parameters: the concentration of the traps in the oxide, their distribution over the oxide thickness, the mobility and capture cross sections for electrons and holes, the nature of dependence of these parameters on the electric field in the oxide. The system of equations is solved iteratively by efficient numerical method. The obtained simulation results are in good agreement with the corresponding data presented in other scientific publications.

Highlights

The problem of forecasting and control of bipolar and CMOS integrated circuits (IC) radiation resistance is of great importance today
We considered the SiO2/Si part of a simulated metal-oxidesemiconductor (MOS) structure with two types of trap levels that takes into account both defects within the oxide layer and radiation-induced interface states
In this way we developed both physical and mathematical models of radiation-induced charge accumulation within the oxide layer and surface states due to irradiation with X-rays and the subsequent charge relaxation by means of tunnel discharge

Summary

Introduction

The problem of forecasting and control of bipolar and CMOS ICs radiation resistance is of great importance today. Integrated circuits (IC) are essential part of military and space equipment. As being used in space, such equipment is inevitably exposed to low-level ionizing radiation, causing its degradation and malfunction. One of the urgent tasks of the microelectronics is to design and manufacture ICs with much higher radiation resistance. In this context, mathematical modeling has paramount importance, by providing solid ground for both understanding and prediction of radiation effects of X-rays in semiconductor devices. Mathematical modeling has paramount importance, by providing solid ground for both understanding and prediction of radiation effects of X-rays in semiconductor devices Such a simulation necessarily includes development of efficient diffusion-kinetic models and computational algorithms

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Conclusion