Metallo-organics

A. J. Pearson, Metallo-Organic Chemisty,]ohn Wiley Sons, Inc., New York, 1985. 

Solution Deposition of Thin Films. Chemical methods of preparation may also be used for the fabrication of ceramic thin films (qv). MetaHo-organic precursors, notably metal alkoxides (see Alkoxides, metal) and metal carboxylates, are most frequently used for film preparation by sol-gel or metallo-organic decomposition (MOD) solution deposition processes (see Sol-GEL technology). These methods involve dissolution of the precursors in a mutual solvent control of solution characteristics such as viscosity and concentration, film deposition by spin-casting or dip-coating, and heat treatment to remove volatile organic species and induce crystaHhation of the as-deposited amorphous film into the desired stmcture. 

Ilic, M. R., Jovanic, P. B., Radosevic, P. B. and Rajakovic, L. V., Sorption of hydrogen cyanide onto activated carbon cloth impregnated with metallo-organic compounds, Sep. Sci. Technol., 1995, 30(13), 2707 2729. 

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials May attack some forms of plastics Stability During Transport Stable Neutralizing Agents for Acids and Caustics Not pertinent,- Polymerization Hazardous polymerization unlikely to occur except when in contact with alkali metals or metallo-organic compounds Inhibitor of Polymerization 10 -20 ppm tert-butylcatechol. 

The alkoxides and aryloxides, particularly of yttrium have excited recent interest. This is because of their potential use in the production of electronic and ceramic materials,in particular high temperature superconductors, by the deposition of pure oxides (metallo-organic chemical vapour deposition, MOCVD). They are moisture sensitive but mostly polymeric and involatile and so attempts have been made to inhibit polymerization and produce the required volatility by using bulky alkoxide ligands. M(OR)3, R = 2,6-di-terr-butyl-4-methylphenoxide, are indeed 3-coordinate (pyramidal) monomers but still not sufficiently volatile. More success has been achieved with fluorinated alkoxides, prepared by reacting the parent alcohols with the metal tris-(bis-trimethylsilylamides) ... 

Platinum Platinum-coated titanium is the most important anode material for impressed-current cathodic protection in seawater. In electrolysis cells, platinum is attacked if the current waveform varies, if oxygen and chlorine are evolved simultaneously, or if some organic substances are present Nevertheless, platinised titanium is employed in tinplate production in Japan s. Although ruthenium dioxide is the most usual coating for dimensionally stable anodes, platinum/iridium, also deposited by thermal decomposition of a metallo-organic paint, is used in sodium chlorate manufacture. Platinum/ruthenium, applied by an immersion process, is recommended for the cathodes of membrane electrolysis cells. ... 

These ideas might be used to explain the interesting results obtained recently by Williams et al.53 These workers observed formation of crystalline polystyrene when the reaction was initiated by triphenyl methyl potassium (or some other potassium metallo-organic compounds) in a hexane solution, but an amorphous polymer was formed in benzene. They point out that the catalyst is soluble in benzene but insoluble in hexane, and suggest that the heterogeneity of the catalyst is responsible for the results. Although this might be the case, an alternative explanation could be advanced.42 1... 

Chirkov IM, Matkovsky PE, Dyachkovsky FS (1976) Polymerization with Complex Metallo-organic Catalysts, M Chemistry, p414 (in Russian)... 

Vollmar, Petterson, and Petruzzelli27 in 1949 disclosed that the following commercial applications of comparative absorptiometry were being made in the petroleum industry sulfur in hydrocarbon mixtures, tetraethyllead fluid in gasoline, additives (such as metal soaps) in lubricating oils, and the metal content of metallo-organic derivatives. Complete documentation of subsequent developments in the petroleum industry is out of place here but it is easy to cite proof that comparative absorptiometry has been successful in that industry.27 32... 

Only fragmented data are available on polymerization of other methacrylates. Propagation constants and the respective Arrhenius parameters for the homopolymerization of various methacrylates initiated by sodium metallo-organics were reported recently +3,56) and are given in Table 2. 

Several books have recently been published on the subject of CVD, each dealing with a specific aspect of the technology, such as CVD for microelectronics or metallo-organic CVD. With many of his colleagues, the author has felt the need for a general, systematic, objective, and balanced review solely devoted to CVD, which would cover all its scientific, engineering, and applications aspects, coordinate the divergent trends found today in the CVD business, promote interaction and sharpen the focus of research and development. 

Two maj or contributors to this rapid growth are plasma CVD and metallo-organic CVD (MOCVD). Both are extensively reviewed in this new edition. Likewise, the growing importance of CVD in the production of semiconductor and related applications is emphasized with a systematic and detailed analysis of the role of CVD in this field. 

Diffijsionbarrierlayersforadvancedsemiconductorinte-grated circuits of titanium nitride deposited by metallo-organic CVD (MOC VD)... 

Metallo-organic CVD (MOCVD) and plasma CVD are developing rapidly, not only in the semiconductor-microelectronic area but also in hard coatingsfor erosion andwearapplicationssincethelower deposition temperature now permits the use of a broader spectrum of substrates. Special emphasis hasbeen given to these two areas in this second edition of the CVD Handbook (see Ch. 4 and 5). 

Thermal activation which typically takes place at high temperatures, i.e., >900°C, although the temperature can also be lowered considerably if metallo-organic precursors are used (MOCVD). 

Metallo-organic CVD (MOCVD) is major area of CVD which is rapidly growing, particularly in semiconductor and optoelectronic applications. It is treated separately in Ch. 4. 

Metal carbonyls form a large and important group of compounds which are used widely in the chemical industry, particularly in the preparation of heterogeneous catalysts and as precursors in CVD and metallo-organic CVD (MOCVD). 

Hydrides are an important group of precursors that are used to deposit single elements such as boron or silicon. As described in Ch. 4, they are also used in conjunction with metallo-organics to form III-V and II-VI semiconductor compounds as shown in the following examples ]... 

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... 

Metallo-organics are compounds in which the atom of an element is bound to one or more carbon atoms of an organic hydrocarbon group. Many of the elements used in MOCVD are the metals of groups Ila, Ilb, Illb, IVb, Vb, and VIb, which are non-transitional. The metallo-organics thus complement the halides and carbonyls, which are the precursors for the deposition of transition metals (Groups IVa, Va, and Via) and their compounds. 

The term metallo-organic is used somewhat loosely in CVD parlance, since it includes compounds of elements, such as silicon, phosphorus, arsenic, selenium, and tellurium, that are not considered metallic. To conform to what appears to be a well-established tradition, such nonmetal compounds will be included here as metallo-organics. 

In the following sections, the major categories of metallo-organic compounds used in CVD are reviewed. Others are described in the review of materials produced by CVD in Chs. 6-12. These metallo-organics form only a small proportion of the total number of compounds available and there are many that could be profitably investigated. 

These alkyls are nonpolar volatile liquids. The methyl metallo-organics start to decompose at 200°C and the ethyl metallo-organics at approximately 110°C. 

Common metallo-organic alkyls, alicyclic, and aryl compounds and their relevant properties are listed in Table 4.1 l l Many additional organometallic compounds are available commercially as listed in Ref 7. 

Most metallo-organic compounds are monomers with some important exceptions, such as trimethyl aluminum which is a dimer. Their vapor pressures are usually directly related to the molecular weight, with the lower molecular weight compounds having the higher volatility. 

To be useful as CVD precursors, a metallo-organic compound should be stable at room temperature so that its storage and transfer are not a problem. It should also decompose readily at low temperature, i.e., below 500°C. The compounds listed in Table 4.1 meet these conditions with the exception of the alkyls of arsenic and phosphorus, which decompose at higher temperatures. For that reason, the hydrides of arsenic and phosphorus are often preferred as CVD precursors (see Ch. 3). These hydrides however are extremely toxic and environmental considerations may restrict their use. 

Alkyls, Alicyclic, and Aryl Metallo-Organic Componnds... 

Most metals can be deposited by MOCVD and in some cases the process is an important industrial operation. The metals most readily deposited by MOCVD are the non-transition metals. The following is a summary of the metallo-organic precursors and deposition condition presently used in development or production. 

Zilko, J. L., Metallo-Organic CVD Technology and Equipment, in Handbook of Thin-Film Deposition Processes and Techniques, (K. K. Shuegraf, ed.), Noyes Publications, Park Ridge, NJ (1988)... 

Hoffman, D. M., et al., Plasma-Enhanced CVD of Silicon Nitride Films from a Metallo-Organic Precursor, J. Mater. Res., 9(12) 3019-3021 (1994)... 

---