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Total Ionizing Dose

and DisplacementDamage Effects in Microelectronics Charles C. Foster

Abstract When exposed to radiation, the function of microelectronic devices is not only degraded by single-event phenomena but by cumulative effects. Most of the energy lost by radiation passing through semiconductors is through ionization. Buildup of charge in gate oxide layers and of interface and border traps due to ionization result in semipermanent damage to the device. These effects are known as total ionizing dose effects. A fraction of the energy of the radiation passing through semiconductors is lost to displacement of atoms from their sites in the crystal lattice structure. The buildup of displacement damage with radiation exposure causes gradual but permanent changes in device performance and limits device lifetime in a radiation environment. Displacement damage will be discussed in the context of non-ionizing energy loss. Keywords: displacement damage, electrical properties, microelectronics, non-ionizing energy loss (NIEL), radiation effects, semiconductors, soft errors, total ionizing dose (TID) effects.

Introduction As radiation (like photons, mesons, protons, neutrons, and heavy ions) passes through material, it loses energy by interaction with the electrons and nuclei of the atoms of the material. While these processes depend on the nature of the radiation, they are the same for all materials. They are independent of the gaseous, liquid, or solid state of the matter, of its chemical and molecular structure, or of its degree of order, from amorphous to crystalline. The effects produced in the material are critically dependent both on the energy-loss processes and the details of the material structures in which the energy is lost. Semiconductor devices are used pervasively on earth and in space and have been developed in many forms to accomplish a wide range of analog and digital functions. They are cheap, small, fast, and lightweight, and have high functionality. But they exhibit a variety of effects when exposed to radiation. These effects have been studied extensively as a result of the use of micro-

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electronics in space, military, and highenergy-physics applications. Because of the value of semiconductor devices in the consumer market, there is great commercial pressure to increase their speed and functionality at low cost. This is usually done by decreasing feature sizes, packing more features on a single chip, and lowering operating voltages. This trend will lead to new radiation sensitivities and effects, including sensitivity to neutrons, protons, muons, and pions at and near the Earth’s surface. As this occurs, the device studies and models developed for space, military, and physics users must be extended to serve the needs of the broader consumer market. Radiation effects in microelectronics are generally classified into single-event upsets (SEUs), total ionizing dose (TID) effects, and displacement damage. This issue of MRS Bulletin focuses on SEUs, and this article discusses TID and displacem