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Über dieses Buch

Recent years have seen silicon integrated circuits enter into an increasing number of technical and consumer applications, until they now affect everyday life, as well as technical areas. Polycrystalline silicon has been an important component of silicon technology for nearly two decades, being used first in MOS integrated circuits and now becoming pervasive in bipolar circuits, as well. During this time a great deal of informa­ tion has been published about polysilicon. A wide range of deposition conditions has been used to form films exhibiting markedly different properties. Seemingly contradictory results can often be explained by considering the details of the structure formed. This monograph is an attempt to synthesize much of the available knowledge about polysilicon. It represents an effort to interrelate the deposition, properties, and applications of polysilicon so that it can be used most effectively to enhance device and integrated-circuit perfor­ mance. As device performance improves, however, some of the proper­ ties of polysilicon are beginning to restrict the overall performance of integrated circuits, and the basic limitations of the properties of polysili­ con also need to be better understood to minimize potential degradation of circuit behavior.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Deposition

Abstract
Silicon integrated circuits are playing an increasingly important role in the electronics industry. The content of integrated circuits in electronic products has increased continuously over the past decade until today it can dominate the value, as well as the cost, of a computer. One of the critical factors leading to this rapid increase in the use of integrated circuits in electronics has been the development of high-density, metal-oxide-semiconductor (MOS) integrated circuits, which allow complex logic or large, dense memories to be built on a single silicon chip. Key to the fabrication of these dense MOS chips is the use of poly-crystalline silicon as a gate-electrode material. The use of polysilicon allows realization of a self-aligned structure, greatly improving the device characteristics by reducing parasitic capacitance. It also permits more complex structures to be fabricated because of its compatibility with high-temperature silicon integrated-circuit processing.
Ted Kamins

Chapter 2. Structure

Abstract
In our discussion of polysilicon deposition in Chapter 1, we looked at the overall chemical reactions. We focused our attention on the processes occurring in the gas phase and the macroscopic chemical reactions occurring at or near the wafer surface. In this chapter we want to look in more detail at the microscopic processes occurring at the surface of the growing film both during and after nucleation because these processes strongly influence the structure of the material deposited. We will first discuss nucleation of polycrystalline silicon on both amorphous and single-crystal surfaces and then consider the influence on the film structure of surface diffusion of the adsorbed atoms during the continued deposition. We will next look at the techniques used to evaluate polycrystalline films and relate the information they reveal to the detailed structure and other properties of the films. Finally, we will examine changes in the structure which can occur during device processing after the films are deposited.
Ted Kamins

Chapter 3. Dopant Diffusion and Segregation

Abstract
In a defect-free, single-crystal of silicon, dopant impurities diffuse into the perfect lattice structure by interacting with point defects, such as silicon vacancies and interstitials. In addition to the point defects in which exist in equilibrium with the crystal lattice, the point-defect concentration can also be influenced externally (eg, by injecting interstitials into the silicon lattice as the surface of the crystal is oxidized). These additional interstitials can significantly enhance the impurity diffusion rate in perfect crystals of silicon.
Ted Kamins

Chapter 4. Oxidation

Abstract
In most integrated circuits, the polysilicon device features are electrically isolated from overlying conductors (either metal or additional layers of polysilicon) by silicon dioxide, which can be either thermally grown on the polysilicon or deposited. For many applications the oxide must simply be highly insulating. However, specialized devices, such as electrically erasable, programmable, read-only memories (EEPROMs) used with increasing frequency in VLSI circuits require a thin oxide with well-controlled conductivity above the polysilicon. Numerous studies have shown that the oxidation rate of polysilicon can differ substantially from that of single-crystal silicon and also that the electrical properties of the oxide grown on polysilicon can be inferior to those of a similar thickness of oxide grown on single-crystal silicon.
Ted Kamins

Chapter 5. Electrical Properties

Abstract
Polycrystalline-silicon (polysilicon) films formed by chemical vapor deposition are used in a wide variety of VLSI applications requiring very different electrical properties. High-value load resistors for static random-access-memory (RAM) cells utilize the high resistance of lightly doped polysilicon to provide a convenient and stable resistor that limits the current flowing in the cell. The excellent technological compatibility of polysilicon with high-temperature, integrated-circuit processing allows straightforward fabrication of self-aligned gates and convenient interconnections in VLSI circuits. Although a resistivity of less than about 10-3 Ω2-cm, eight orders of magnitude less than for static RAM load resistors, is routinely achieved, the lower bound on the resistivity of polysilicon can limit the performance of silicon-gate integrated circuits which use polysilicon interconnections to conduct signals long distances across a chip [5.1]. As feature sizes become smaller and intrinsic device delays decrease on chips of increasing overall dimensions, the resistance of polysilicon interconnections is becoming a more serious limitation on integrated-circuit performance.
Ted Kamins

Chapter 6. Applications

Abstract
In previous chapters we considered the properties of polysilicon that make it useful in integrated circuits. In this chapter, we want to proceed further and discuss the applications of polysilicon explicitly. Because of the wide range of integrated-circuit devices in which polysilicon is now used, this discussion cannot be all inclusive. A few of the more important applications are considered in detail, and others are briefly mentioned.
Ted Kamins

Backmatter

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