Defects in irradiated MOS structures

• Main Author: Vranch, Richard Leslie
• Published: University of Cambridge 1985
• Subjects: 530.41; Metal oxide semiconductor
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.354693

The MOS device is the basic switching element in modern integrated circuits, and its reliability is vital to the successful operation of electronic equipment. Exposure to ionising radiation seriously affects MOS devices because of charge trapping and the formation of defects at the silicon-silicon dioxide interface. After an introductory chapter on MOS devices and radiation effects, experiments are described which give information about the nature of the interface defects and how they interact with each other. A particular device current Irec is measured whose magnitude depends on the recombination of charge carriers at the defects. The device is so minute, and the interface so thin, that the paramagnetic defects are too few in number to be detected and identified by conventional electron spin resonance methods. However, the static and microwave magnetic fields corresponding to spin resonance affect the recombination of carriers on the defects, and this causes a detectable change in Irec. This phenomenon is called Spin-Dependent Recombination (SOR), and a survey of SOR studies in semiconductors is given in Chapter 2 . The experimental results confirm a model which suggests that SOR occurs between adjacent trapped pairs. The results of the experiments are compared with ESR data on similar (but much larger) MOS structures. Spin-Dependent Generation of carriers is also investigated. The recombination is also found to be strongly dependent on a static magnetic field of zero to 5 milliTesla, even with no microwaves. Results of experiments on these "non-resonant" spin-dependent effects are presented with a model, relating them to the resonance experiments, which involves the recombination of singlet and triplet electron-hole pairs in a magnetic field. Electrical charge injection can affect MOS devices in similar ways to ionising radiation, and this is discussed in Chapter 6. Experimental results are presented which show that there are spin-dependent effects associated with defects produced by electrical charge injection. There are two Appendices, on slow radiation-induced instabilities in MOS structures, and on the size of the recombination current Irec�