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Advanced multi-metallic alloy coatings: investigation of thermal decomposition mechanism of metalorganic precursors upon chemical vapour deposition

Final Activity and Management Report Summary - ADALCO3 (Advanced multi-metallic alloy coatings: investigation of thermal decomposition mechanism of metalorganic precursors ...)

The project was devoted to the experimental investigation of thermal conversions of metal complexes with organic ligands on the surface. To perform such an investigation experimental setup with time-of-flight mass spectrometer (TOF MS) as a gas phase recording device was developed and constructed. The advantage of this setup is the possibility to study both adsorption and decomposition of organometallic compounds on different surfaces (substrates) and then to analyse deposited films.

Methodological approach was to use the combination of (i) kinetics of isothermal desorption and (ii) study of temperature programmed desorption (TPD) to study adsorption (estimate two characteristics of adsorption/desorption - activation energy and pre-exponential factor) of large organometallic molecules which are non-conventional objects for these techniques.

Three model compounds being previously identified as precursors of metallic film deposition were studied: copper(I) N,N'-diisopropylacetamidinate [CuAMD]2 and 1,1,1-trifluoro-2,4-pentanedionate (trifluoroacetylacetonate) of copper(II) Cu(tfac)2 and of palladium(II) Pd(tfac)2. Saturated vapor pressure measurements were performed for a quantitative characterisation of [CuAMD]2 volatility. The Clausius-Clapeyron law for the vapor pressure dependence on temperature was found to be: ln(P(atm))= 24 895 -13 520.8/T(K) the thermodynamic parameters enthalpy and entropy of sublimation were found to be 112.42±2.18 kJ/mol and 206.98±5.47 J/(mol*K), respectively. Under the assumption of the first order reaction, desorption rate constant and activation energy Ea were estimated from the obtained isotherms: Ea (kJ/mol) is 67±21 for [CuAMD]2, 18.8±2.0 for Cu(tfac)2, 29.2±4.5 for Pd(tfac)2. Based on data on temperature of desorption peak and activation energy, pre-exponential factor in the desorption equation was calculated: 1.7*10-6 s for Cu(tfac)2 and 2.6*10-6 s for Pd(tfac)2. Obtained values are related to adsorption on the polycrystalline stainless steel surface. High value of activation energy of desorption for [CuAMD]2 indicates that molecules of the compound are chemically adsorbed on surface. It may be concluded that copper complex Cu(tfac)2 is adsorbed worse than palladium complex with the same ligand, in other words sticking probability for Cu(tfac)2 considerably lower than for the Pd(tfac)2 under equal conditions. In addition to above-mentioned results development of a methodological approach to investigation of such complicated objects as organometallic compounds by electron impact mass spectrometry was continued. Conversions of [CuAMD]2 and dimethylgold diethyldithiocarbamate (CH3)2AuS2CN(C2H5)2 vapors which is a promising precursor to produce gold films by MOCVD were studied on the heated surface prior to adsorption study. Thermal decomposition onset (135 and 210 degrees Celsius, respectively) and the main gaseous products were established.

The project was research-oriented one and results contribute mainly into basic science: proposed mechanisms of thermal decomposition of organometallic compounds are of great importance for coordination chemistry. The results of the study performed indicate that copper acetamidinates are quite promising compounds for the low-temperature deposition of copper films, although their thermal stability is poor. For a more stable bis-triluoroacetylacetonato copper and palladium the metallisation rate will be higher for palladium complex, other things being equal. The data obtained may be used for reasonable selection of feeding pulse duration upon pulse CVD for the technological implementation of coatings preparation and for ALD technique.