Раздел 2 Перпое занятие

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solid-state devices having three layers of alternately²⁵ negative or pos­itive ty e semiconductor material.

The early history of modern semiconductor technology can be traced²⁶ to December 1947 when J. Bardeen and W. Brattain observed transistor action through point contacts applied to polycrystalline ger­manium. Germanium has become the material in common use. It was realized that transistor action occurred within the single grains²⁷ of polycrystalline material.

G. Teal originally recognized²⁸ the immense²⁹ importance of single-crystal semiconductor materials as well as for providing the physical realization of the junction transistor. G. Teal reasoned³⁰ in 1949, that polycrystalline germanium’s uncontrolled resistances and electronic traps³¹ would affect³² transistor operations in uncon­trolled ways. Additionally³³, he reasoned that polycrystalline mate­rial would provide inconsistent product yields and thus be costly. He was the first to define chemical purity³⁴, high degree of crystal perfection³⁵ and uniformity of structure as well as controlled chem­ical composition (i. e. donor or acceptor³⁶ concentration) of the single-crystal material as an essential foundation for semiconduc­tor products.

The next decade witnessed³⁷ the “universal” semiconductor ma­terial, silicon. Silicon gradually gained³⁸ favour over germanium as the “universal” semiconductor material.

Silicon is to the electronics revolution what steel was to the in­dustrial revolution.

2. Silicon has been the backbone (основа) of the semicon­ductor industry since the inception of commercial³⁹ transistors and other solid-state devices.

The dominant role of silicon as a material for microelectronic circuits is attributable⁴⁰ in large part to the properties of its oxide.

Silicon dioxide is a clear glass with a softening⁴¹ point higher than 1,400 degrees C. If a wafer⁴² of silicon is heated in an atmo­sphere of oxygen or water vapour⁴³, a film of silicon oxide forms on rts surface. The film considered is hard and durable⁴⁴ and adheres^{45 We}ll. It makes an excellent insulator. The silicon dioxide is particu- ^Ia*ly important in the fabrication of integrated circuits because it can act as a mask⁴⁶ for selective introduction of dopants⁴⁷.

Микроэлектроника настоящее и будущее

Silicon’s larger band⁴* gap⁴⁹ permitted⁵⁰ device operation at higher temperatures (important for power devices) and thermal oxidation of silicon produced a non-water-soluble stable oxide (as compared to germanium’s oxide) suitable for passing p-n junctions, serving as an “impermeable⁵¹ diffusion mask” for common dopants, and as insula­tor coating⁵² for conductor overlayers⁵³.

Oxygen concentration present influences many silicon wafer prop­erties, such as wafer strength, resistance to thermal warping (скачок), minority carrier lifetime and instability in resistivity.

The presence of oxygen contributes to both beneficial and detri­mental⁵⁴ effects. The determental effects can be reduced if the oxygen is maintained³⁵ at less than 38 ppms. Thus, the oxygen range⁵⁶ of the wafer present should be controlled. The results achieved with silicon are great.

However, although the silicon wafer clearly is a fundamental in­gradient in the fabrication of an integrated circuit, the silicon materi­als specification⁵⁷ may not be critical element in developing a success­ful new 1C product strategy.

Large-scale integration (LSI) of devices has put great demands on electronic-grade single-crystal material. The semiconductor indus­try now requires high purity and minimum point-defects concentra­tion in silicon in order to improve the component yield per silicon wafer. These requirements have become increasingly stringent⁵⁸ as the tech­nology changes from large-scale integration (LSI) to very large-scale integration (VLSI) and very large-scale integration (VLSI) to very high speed integrated circuits (VHSIC).

The yield (or circuit performance) of a device and the intrinsic and extrinsic materials properties of silicon are interdependent. The silicon wafer substrate must be practically defect-free when the active device density may be as high as 10 to 10 per chip.

To increase further the speed of semiconductor devices requires not only refinements⁵⁹ in present designs and fabrication techniques, but also new materials that are inherently⁶⁰ superior to materials pres­ently being used, like germanium and silicon. New material under con­sideration is gallium arsenide.

Gallium arsenide has a much higher electron mobility than ger­manium and silicon. The opportunities⁶¹ present are as follows: it is