ABSTRACT

CONTENTS 13.1 Introduction ...................................................................................................................... 381 13.2 Theoretical Approaches .................................................................................................. 382 13.3 Core Boundary of Microelectronics: Si-SiO2 Interface............................................... 383 13.4 Defects at the Si-Dielectric Interface............................................................................. 385 13.5 Defects in the Substrate .................................................................................................. 388 13.6 Defects in Gate Oxides.................................................................................................... 390 13.7 Reliability Phenomena and the Role of Hydrogen and Other Defects.................... 391 13.8 Defects in Pentacene Devices ......................................................................................... 394 13.9 Summary........................................................................................................................... 395 Acknowledgments ..................................................................................................................... 395 References.................................................................................................................................... 395

The control of concentrations and properties of intrinsic defects and impurities has been an integral part of the microelectronics revolution. Overcoordinated and undercoordinated atoms, extrinsic species, and defect complexes have been the subjects of numerous studies, both theoretical and experimental. Deviations from ideal crystallinity in the bulk of electronic materials and their interfaces have been identified as the key culprits of important reliability phenomena. Nevertheless, despite the mass of accumulated information on defect formation in traditional materials, especially in silicon and silicon-based devices, key questions remain under debate. Moreover, with the current drive to replace silicon-based materials in various applications, including designs with nanostructures and organic systems, new challenges emerge for the characterization and control of novel defect configurations. Defects and impurities may appear in electronic materials in all stages, from the initial

growth of materials to aging of fully developed devices. For example, oxygen is a common impurity in silicon, especially Czochralski-grown Si, incorporated into the bulk material during growth from the melt. Oxygen of course can appear in various forms, including defect configurations during the later stage of thermal oxidation of silicon. Finally, oxygen can migrate to various parts of a device and participate in defect formation during the

and defects. One common device impurity that stands out in significance and complexity of behavior is hydrogen. The presence of hydrogen may be either intentional, for example during the postoxidation passivation of dangling bonds of the Si-SiO2 system, or inadvertent when it is provided by extraneous or internal sources. In this chapter, we review results from theoretical studies on several of the most

important effects of device defects and impurities, especially hydrogen. Emphasis is placed on first-principles approaches (also known as ab initio approaches), in particular, quantum mechanical calculations within density functional theory (DFT) [1,2]. In recent years, firstprinciples approaches have become an integral part of studies of electronic devices, because of the availability of increased computational power. The strengths and limitations of these approaches are presented with examples of combinations with other theoretical methods. We discuss defect formation and dynamics in a silicon substrate, in amorphous SiO2, and at the Si-SiO2 interface. We point out the relevance of impurities for notable reliability phenomena, such as bias-temperature instability (BTI) [3] and radiation damage [4], and we discuss the importance of defects in novel materials, namely pentacene [5].