Thermal properties of volatile Sc(III) complexes with beta-diketonates - viable precursors for MOCVD processes

K. Zherikova1, L. Zelenina1 and N. Morozova1

1Nikolaev Institute of inorganic Chemistry, SB RAS, Russia

Keywords: scandium(III) beta-diketonates
property: vapor pressure; sublimation, evaporation and melting processes
material: scandium oxide films

Volatile Sc(III) complexes with organic ligands are widely used as precursors in MOCVD processes for preparing of thin oxide films with given functional assignment. In order to obtain successfully new materials with given functional assignment the knowledge about thermal properties of these compounds is necessary first of all.

During present work, we synthesized complexes with acetylacetone Sc(acac)3, dipivaloylmethane Sc(thd)3, trifluoroacetylacetone Sc(tfac)3, pivaloyltrifluoroacetone Sc(ptac)3, and hexafluoroacetylacetone Sc(hfac)3. Compounds obtained were identified by melting point and by means of elemental analysis, IR spectroscopy and mass spectrometry. By XRD analysis the structures of Sc(III) beta-diketonates were defined.

The thermal behavior of the synthesized compounds in the solid state was investigated by the method of difference-scanning calorimetry in vacuum, thermodynamic characteristics of the melting processes (m.p., ΔmeltHm.p., ΔmeltS°m.p.) was determined.

Obtained by static method with a membrane zero-manometer vapor pressure measurement of compounds in regime saturated-unsaturated vapor allowed to calculate mean molar mass of gas phase corresponding to the monomer molecular mass.

The data on melting processes were used for measurement of the temperature dependences of saturated vapor pressure of complexes. After statistical treatment the experimental data obtained were represented as the equation: lnp/p0 = B - A/T. The standard thermodynamic parameters ΔHТ and ΔSºТ of sublimation and evaporation processes were calculated from the p-Т functions and the row of volatility was determined. 

This information about thermal behavior of complexes were used as a guide for MOCVD experiments aimed at achieving metal oxide films to tantalum diffusion barriers with high optical properties. The films obtained were investigated by using different methods: ellipsometry, SEM, XAFs etc. By this approach it was demonstrated that Sc(thd)3 have a perspective application as precursor for MOCVD of films.

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