CVD Precursors Containing Hydropyridine Ligands
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ABSTRACT Hydropyridine is introduced as a new ligand for use in constructing Detachment of hydropyridine precursors for chemical vapor deposition. occurs by a low-temperature reaction leaving hydrogen in place of the pyridine vapor. and a very stable byproduct, hydropyridine, Hydropyridine ligands can be attached to a variety of elements, including main group metals, such as aluminum and antimony, transition metals, such as titanium and tantalum, semiconductors such as silicon, and nonmetals such as phosphorus and arsenic.
PROPERTIES OF IDEAL CVD PRECURSORS An ideal CVD precursor should have a number of properties: 1) Its vapor pressure should be sufficiently high (e.g. relatively low temperature (e. g. less than 200 C). 2)
1 Torr) at a
It should be thermally stable at its vaporization temperature.
3) Its vaporization kinetics should be rapid and reproducible, which is usually the case if it is a non-associated liquid (not a solid) at its vaporization temperature. 4) It should react at temperatures above its vaporization temperature according to a single, well-defined reaction mechanism, to produce a pure product material. 5) The byproducts of its CVD reaction should be stable and nonreactive.
183 Mat. Res. Soc. Symp. Proc. Vol. 363 C 1 995 Materials Research Society
6) The reactants and byproducts should be non-flammable, and non-corrosive.
non-toxic
7)
The precursor should be inexpensive to manufacture and to purify.
8)
It should remain stable during storage.
PROPERTIES OF CVD REAL PRECURSORS Few, if any, CVD precursors satisfy all of these criteria. For example, silicon, a widely used semiconductor, is deposited from a variety of CVD sources, particularly silane, disilane and dichlorosilane, which are hazardous spontaneously flammable gases. It would be advantageous to have CVD sources for silicon which are not as hazardous as these gases. Boron and phosphorus are added to silicon as impurities (dopants) to increase its electrical conductivity. Diborane and phosphine are extremely poisonous gases which are used to provide dopants during CVD of silicon or silicon dioxide. It would be advantageous to have less toxic boron and phosphorus sources which also have lower vapor pressures, so that they could not be spread as easily by gas leaks. Gallium arsenide is another useful semiconductor, which is often made by a CVD process starting from arsine, an extremely toxic gas, and trimethylgallium, which is spontaneously flammable. It would be desirable to have less toxic arsenic sources with lower vapor pressures, and gallium sources which are not spontaneously flammable. Aluminum is a metal that is useful in making interconnections in microcircuits. Currently known CVD aluminum sources include aluminum alkyls, which are spontaneously flammable and also leave carbon impurities in the aluminum, and aluminum hydride complexes, which are unstable when stored at room temperature. Because of these disadvantages, aluminum is not usually made by CVD. It would be desirable to have aluminum CVD sources which make pur
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