Thin platinum films and dispersions of platinum particles are widely used in microelectronics, for example for manufacturing ohmic or Schottky diode contacts, diffusion-barrier films, as coatings for materials subjected to high temperatures and for the manufacture of supported solid catalysts. Among all the metal deposition methods, the method of chemical vapor deposition of an organometallic compound (also known as the MOCVD method or more simply CVD for “metallo-organic chemical vapor deposition”) gives very good results in terms of costs, treatment temperatures, durations, covering power and general quality of the deposit.
The possibility of forming a satisfactory metallic deposit via the MOCVD method depends on the volatility of the precursor compound. Specifically, this method requires the possibility of obtaining a high vapor pressure of the precursor compound and high stability of this same compound.
The principle of MOCVD is that of vaporizing a volatile precursor of the metal, namely an organometallic complex, which decomposes thermally on the substrate to form a metallic layer. In practice, the vaporization takes place under pressure and temperature conditions that make it possible to obtain a sufficient precursor vapor pressure for the deposit, while at the same time remaining within its stability range. As regards the substrate, it is heated beyond this stability range, which allows decomposition of the organometallic assembly and the formation of metal particles. The CVD deposition method has various advantages over the other known methods: the thermolysis temperature in CVD of organometallic compounds is 1 to 2 thousand degrees lower than for the other vapor deposition techniques. The films obtained are dense and continuous, which makes it possible to avoid porosity incompatible with good electrical properties. In contrast with the liquid impregnation method, this method is rapid, and impregnation, washing, drying, calcination and activation steps are avoided. Poisoning of the surface and modifications of the activated material during drying are also avoided. It is thus a rapid and economical method for obtaining controlled depositions of good quality.
Various organometallic Pt compounds, which are complexes containing platinum and organic ligands, are currently widely used. Mention may be made especially of: Pt(acac)2, Pt(PF3)4, (cod)PtMe2, MeCpPtMe3 or EtCpPtMe3. These compounds, also referred to herein as precursors, are widely described in the literature.
These known precursors have the following formulae:

Thus, in the present patent application, the following abbreviations denote the following groups:                (acac)2: bis-acetylacetonate,        (cod): 1,5-cyclooctadiene,        (Cp): cyclopentadienyl.        
However, each of these precursors has limits that constitute a drawback for their use in an MOCVD process in an industrial context.
Thus, various studies have shown that decomposition problems are encountered during the use of Pt(acac)2: the ligand may decompose without decoordinating the metal, which generally leads to a deposit containing a large amount of impurities.
Pt(PF3)4 leads to a deposit containing fluorine, which is prohibitive for certain applications (Martin T. P. et al., J. Chem. Vap. Deposition, 2005, 11, 170-174).
(cod)PtMe2 is an advantageous precursor, but it has moderate volatility, which makes it necessary to work at higher temperatures compared with the other platinum complexes. Furthermore, with this precursor used in solution, deposits that have unreproducible properties are observed, which suggests a lack of stability of the solution of this precursor during long-term storage.
CpPtMe3 is sensitive to air and moisture.
As regards MeCpPtMe3, it is sensitive to air and moisture, and is expensive.
Its analog EtCpPtMe3 shows better stability, but, just like MeCpPtMe3, it is expensive.
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