Nitrides applications

Mikijelj, B., Mangels.)., Belfield, E., and MacQueen, A. (2004) Silicon nitride applications in modem diesel engines. Report Ceradyne 2004-01-1448. 

Aluminum alkoxides, polymerizations of poly[bis(methoxyethoxyethoxy)phos-phazene] molecular composites, 258-266 Aluminum nitride applications, 427... 

Figure C2.16.2 shows tire gap-lattice constant plots for tire III-V nitrides. These compounds can have eitlier tire WTirtzite or zincblende stmctures, witli tire wurtzite polytype having tire most interesting device applications. The large gaps of tliese materials make tliem particularly useful in tire preparation of LEDs and diode lasers emitting in tire blue part of tire visible spectmm. Unlike tire smaller-gap III-V compounds illustrated in figure C2.16.3 single crystals of tire nitride binaries of AIN, GaN and InN can be prepared only in very small sizes, too small for epitaxial growtli of device stmctures. Substrate materials such as sapphire and SiC are used instead.

The complexity of the apparatus needed for ion implantation makes this method of case hardening of limited application. Further, the case depth is considerably lower than that produced by carburizing or nitriding. The depth of implantation of nitrogen in a steel is about 0.00006 cm (19), ie, so thin that it is difficult to measure the hardness profile by conventional microhardness measurements. 

Nuclear Applications. Use of the nitrides of uranium-235 and thorium as fuels and breeders in high temperature reactors has been proposed (see Nuclearreactors). However, the compounds most frequently used for this purpose are the oxides and carbides. Nitrides could be useful in high... 

J. J. Burke, ed.. Powder Metal Migh-Peformance Applications, Proceedings of the 18th S agamore Army Material Kesearch Conference, Syracuse University Press, Syracuse, N.Y., 1972. Review on siUcon carbide—siUcon nitride ceramics. 

For a large number of applications involving ceramic materials, electrical conduction behavior is dorninant. In certain oxides, borides (see Boron compounds), nitrides (qv), and carbides (qv), metallic or fast ionic conduction may occur, making these materials useful in thick-film pastes, in fuel cell apphcations (see Fuel cells), or as electrodes for use over a wide temperature range. Superconductivity is also found in special ceramic oxides, and these materials are undergoing intensive research. Other classes of ceramic materials may behave as semiconductors (qv). These materials are used in many specialized apphcations including resistance heating elements and in devices such as rectifiers, photocells, varistors, and thermistors. 

The technical problem in die high teiiiperamre application of Si3N4 is that unlike the pure material, which can be prepared in small quantities by CVD for example, die commercial material is made by sintering the nitride with additives, such as MgO. The presence of the additive increases the rate of oxidation, when compared with the pure material, by an order of magnitude, probably due to the formation of liquid magnesia-silica solutions, which provide short-circuits for oxygen diffusion. These solutions are also known to reduce the mechanical strength at these temperatures. 

Early work in ellipsometry focused on improving the technique, whereas attention now emphasizes applications to materials analysis. New uses continue to be found however, ellipsometry traditionally has been used to determine film thicknesses (in the rang 1-1000 nm), as well as optical constants. " Common systems are oxide and nitride films on silicon v ers, dielectric films deposited on optical sur ces, and multilayer semiconductor strucmres. 

The binary compounds of the Group 13 metals with the elements of Group 15 (N, P, As, Sb, Bi) are stmcturally less diverse than the chalcogenides just considered but they have achieved considerable technological application as III-V semiconductors isoelectronic with Si and Ge (cf. BN isoelectronic with C, p. 207). Their stmctures are summarized in Table 7.10 all adopt the cubic ZnS stmcture except the nitrides of Al, Ga and In which are probably more ionic (less covalent or metallic) than the others. Thallium does not form simple compounds... 

Hardness on the Mohs scale is often above 8 and sometimes approaches 10 (diamond). These properties commend nitrides for use as crucibles, high-temperature reaction vessels, thermocouple sheaths and related applications. Several metal nitrides are also used as heterogeneous catalysts, notably the iron nitrides in the Fischer-Tropsch hydriding of carbonyls. Few chemical reactions of metal nitrides have been studied the most characteristic (often extremely slow but occasionally rapid) is hydrolysis to give ammonia or nitrogen ... 

Chemical vapor deposition (C VD) is a versatile process suitable for the manufacturing of coatings, powders, fibers, and monolithic components. With CVD, it is possible to produce most metals, many nonmetallic elements such as carbon and silicon as well as a large number of compounds including carbides, nitrides, oxides, intermetallics, and many others. This technology is now an essential factor in the manufacture of semiconductors and other electronic components, in the coating of tools, bearings, and other wear-resistant parts and in many optical, optoelectronic and corrosion applications. The market for CVD products in the U.S. and abroad is expected to reach several billions dollars by the end of the century. 

Many CVD reactions are being investigated for the deposition of carbides and nitrides, particularly for titanium nitride for semiconductor applications, such as diffusion barrier. The following is a summary of the metallo-organic precursors and deposition condition presently used in development or production of these materials. 

Plasma CVD was first developed in the 1960s for semiconductor applications, notably for the deposition of silicon nitride. The number and variety of applications have expanded greatly ever since and it is now a major process on par with thermal CVD. 

An RF plasma is generated at a frequency of 13.56 MHz. A typical equipment consists ofparallel electrodes as shown inFig. 5.20. It is a cold-wall design which is used extensively forthe deposition of silicon nitride and silicon dioxide for semiconductor applications. 

DLC coatings are already in production in several areas (optical and IR windows) and appear particularly well-suited for abrasion and wear applications due to their high hardness and low coefficient of friction. They have an extremely smooth surface and can be deposited with little restriction of geometry and size (as opposed to CVD diamond). These are important advantages and DLC coatings will compete actively with existing hard coatings, such as titanium carbide, titanium nitride, and other thin film... 

The nitrides reviewed here are those which are commonly produced by CVD. They are similar in many respects to the carbides reviewed in Ch. 9. They are hard and wear-resistant and have high melting points and good chemical resistance. They include several of the refractory-metal (interstitial) nitrides and three covalent nitrides those of aluminum, boron, and silicon. Most are important industrial materials and have a number of major applications in cutting and grinding tools, wear surfaces, semiconductors, and others. Their development is proceeding at a rapid pace and CVD is a major factor in their growth. 

In this chapter, each nitride is listed alphabetically with its basic properties, its major CVD reactions and processes, and its present and potential applications. 

The major application of CVD aluminum nitride is for electronic components. At this time, most of the AIN powder is produced by CVD and originates in Japan and is used by the Japanese industry.b l... 

Boron nitride has two crystalline forms, hexagonal (h-BN) and cubic (c-BN), with much different properties. Hexagonal BN is the more important and has many industrial applications. Its structure is similar to that of graphite which it resembles in many ways. It has a very large anisotropy in the crystal with resulting anisotropic properties. 

The applications of hexagonal boron nitride form an important market, mostly as powder for lubricants and additives. Many of these applications are produced by CVD. 

Cubic boron nitride (c-BN) is a different material altogether from h-BN, with a structure similar to that of diamond, which is characterized by extremely high hardness (second to diamond) and high thermal conductivity.As such, it is a material of great interest and a potential competitor to diamond, particularly for cutting and grinding applications. Its characteristics and properties are shown in Table 10.3... 

Silicon nitride (Si3N4) is a major industrial material which is produced extensively by CVD for electronic and stmctural applications. It is an excellent electrical insulator and diffusion barrier (to sodium and water vapor) and has replaced CVD oxides in many semiconductor... 

The market for silicon nitride is fast growing, particularly in structural and chemical resistance applications and as a thin film in semiconductor devices.P 1... 

CVD titanium nitride (TiN) is the most important interstitial-nitride coating from an application standpoint. It is used extensively to provide wear resistance and as a diffusion barrier and antireflection coating in semiconductor devices. 1 °]... 

The number of oxides is large since most metallic elements form stable compounds with oxygen, either as single or mixed oxides. However, the CVD of many of these materials has yet to be investigated and generally this area of CVD has lagged behind the CVD of other ceramic materials, such as metals, carbides, or nitrides. The CVD of oxides has been slower to develop than other thin-film processes, particularly in optical applications where evaporation. 

Smith, P. M., et al., Chemical Vapor Deposition of Ternary Refractory Nitrides for Difiusion Barrier Applications, Proc. 13th. Int. Conf. on VLSI Multilevel Interconnections, Sandia National Labs., Albuquerque, NM (1996)... 

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