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The MOS Structure

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Silicon Devices and Process Integration

The MOS structure consists of a semiconductor covered by an insulator upon which a conductive electrode is deposited (Fig. 4.1). The term MOS stands for Metal-Oxide-Silicon and stems from earlier technologies that utilized aluminum, silicon dioxide (or simply oxide), and silicon to form the capacitor between source and drain of an MOS Field-Effect Transistor, MOSFET (Chap. 5). The need for a gate conductor that can withstand high-temperature annealing and allow self-alignment of gate to source-drain led to the development of heavily doped n-type or p-type polysilicon gate-conductors to replace aluminum. While doped polysilicon is the gate-conductor of choice for oxide thickness above ˜3nm, its low conductivity compared to metals begins to seriously impact MOSFET performance as device dimensions are reduced to the nanoscale range. Metal-gates, such as tungsten, molybdenum, and fully-silicided polysilicon have therefore become necessary to overcome this limitation. Also, as the silicon-dioxide thickness is reduced below ˜2nm, the level of power-consumption caused by tunneling current through the oxide becomes prohibitive. For such dimensions, it is necessary to replace silicon-dioxide with alternate dielectrics of higher dielectric constant

As will be discussed in Chap. 5, there are several advantages of replacing silicon with semiconductor variants such as silicon-germanium (SiGe) and silicon-carbon (Si : C) alloys, or germanium. In this chapter, however, the term MOS will be used to describe all of the above combinations of gate-conductor, insulator, and semicon ductor.

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(2009). The MOS Structure. In: Silicon Devices and Process Integration. Springer, Boston, MA. https://doi.org/10.1007/978-0-387-69010-0_4

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  • DOI: https://doi.org/10.1007/978-0-387-69010-0_4

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