CVD epitaxial

Generally, epitaxial films have superior properties and, whenever possible, epitaxial growth should be promoted. The epitaxial CVD of silicon and III-V and E-VI compounds is now a major process in the semiconductor industry and is expected to play an increasingly important part in improving the performance of semiconductor and optoelectronic designs (see Chs. 13-15). 

Fig. 6 Deposition system used for epitaxial CVD. Heating in this case is accomplished by banks of lamps (e.g., upper right). (Photo courtesy of Applied Materials Inc.) (View this art in color at www.dekker.com.)...

In practical applications, gas-surface etching reactions are carried out in plasma reactors over the approximate pressure range 10 -1 Torr, and deposition reactions are carried out by molecular beam epitaxy (MBE) in ultrahigh vacuum (UHV below 10 Torr) or by chemical vapour deposition (CVD) in the approximate range 10 -10 Torr. These applied processes can be quite complex, and key individual reaction rate constants are needed as input for modelling and simulation studies—and ultimately for optimization—of the overall processes. 

Silicon Epitaxy. A critical step ia IC fabricatioa is the epitaxial depositioa of sdicoa oa an iategrated circuit. Epitaxy is defined as a process whereby a thin crystalline film is grown on a crystalline substrate. Silicon epitaxy is used ia bipolar ICs to create a high resistivity layer oa a low resistivity substrate. Most epitaxial depositioas are doae either by chemical vapor depositioa (CVD) or by molecular beam epitaxy (MBE) (see Thin films). CVD is the mainstream process. 

Molecular beam epitaxy is a non-CVD epitaxial process that deposits silicon through evaporation. MBE is becoming more common as commercial equipment becomes available. In essence, silicon is heated to moderate temperature by an electron beam in a high vacuum... 

Chemical vapor deposition may be defined as the deposition of a solid on a heated surface from a chemical reaction in the vapor phase. It belongs to the class of vapor-transfer processes which is atomistic in nature, that is the deposition species are atoms or molecules or a combination ofthese. Beside CVD, they include various physical-vapor-deposition processes (PVD) such as evaporation, sputtering, molecular-beam epitaxy, and ion plating. 

Metallo-organic CVD (MOCVD) is a specialized area of CVD, which is a relatively newcomer, as its first reported use was in the 1960s for the deposition of indium phosphide and indium anti-monide. These early experiments demonstrated that deposition of critical semiconductor materials could be obtained at lower temperature than conventional thermal CVD and that epitaxial growth could be successfully achieved. The quality and complexity of the equipment and the diversity and purity of the precursor chemicals have steadily improved since then and MOCVD is now used on a large scale, particularly in semiconductor and opto-electronic applications.91P1... 

Several precursors and CVD reactions are available to deposit silicon. The deposit can be either single crystal (epitaxial), polycrystalline, or amorphous. 

Reif, R., Low Temperature Silicon Epitaxy by Plasma Enhanced CVD, Proc. 5th European Conf. on CVD, (J. Carlsson and J. Lindstrom, eds.), pp. 13-19, Univ. ofUppsala, Sweden (1985)... 

Plasma CVD and thermal laser CVD are also used particularly in the deposition of GaAs. The formation of epitaxial GaAs at 500°C and polycrystalline GaAs at 185°C has been reported,... 

Huelsman, A. D., and Reif, R., Plasma Deposition of GaAs Epitaxial Films from Metal-Organic Sources, Proc. 10th Int. Conf. on CVD, (G. Cullen, ed.), pp. 792-802, Electrochem. Soc., Pennington, NJ 08534 (1987)... 

CVD is used in silicon production in two major areas 1) in the production of ultra-pure silicon from which single-crystal ingots are made, and 2) in the preparation of epitaxial and poly cry stalline films. 

The CVD reactions used to produce epitaxial silicon are described in Ch. 8. Originally, atmospheric-pressure CVD was used, but it is gradually being replaced by low-pressure CVD in spite of higher equipment cost and complexity. Low-pressure CVD appears to yield a better film with less autodoping and pattern shift. 

Polysilicon is a contraction of polycrystalline silicon, (in contrast with the single-crystal epitaxial silicon). Like epitaxial silicon, polysilicon is also used extensively in the fabrication of IC s and is deposited by CVD.f l it is doped in the same manner as epitaxial silicon. Some applications of poly silicon films are ... 

Many problems must be solved before practical, reliable, and cost-effective diamond semiconductor devices become available. Yet, the prospects are good, particularly if epitaxial single-crystal or highly oriented poly crystalline diamond can be effectively produced by CVD.P5]... 

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