TELLURIUM ALKYLGERMYLS

TGA of Tellurium alkylgermyls Te(GeR3)2 (R = Me, Et, nBu)

    Three tellurium alkylgermyls: Te(GeMe3)2, Te(GeEt3)2, and Te(GenBu3)2 were synthesized and characterized by several methods, including thermogravimetric analysis (TGA) in an inert atmosphere (to avoid reaction of the molecules with air and moisture - same atmosphere encountered in the deposition process), at atmospheric pressure.[Fig.1]

    All 3 tellurium alkylgermyls (Te(GeMe3)2, Te(GeEt3)2, and Te(GenBu3)2) could be volatized without leaving significant residues, proving that molecule decomposition did not occur under these conditions, despite quite high temperatures (up to 325°C.). The volatility of the complexes, according to TGA, follows following order: highest for Te(GeMe3)2 (full evaporation at 170° C), intermediate for Te(GeEt3)2 (fully evaporated at ~265° C), lowest for Te(GenBu3)2) (complete evaporation at ~325°C). All these molecules fulfil the criteria of CVD/ALD molecules in terms of their volatility and evaporation patterns.[[i]]

[i] H. Ishii, J. Gatineau, Julien, Application Number 13/168535, US Patent Application 20120021590, «  Tellurium Precursors for Film Deposition », http://www.freepatentsonline.com/20120021590.pdf

Bis(trimethylgermyl)tellurium Te(GeMe3)2

Te(GeMe3)2 (+SbCl3) for Sb2Te3 films by CVD

     Bis(trimethylgermyl)tellurium Te(Me3Ge)2  was applied as Te precursor for the CVD growth of Sb2Te3 films on Si wafers (using SbCl3 as Sb precursor, precursor ratio Te:Sb=1:10 (Sb rich conditions). Deposition temperatures were 60° C to 250° C; process pressure 10 Torr. Stoichiometric (stable composition) Sb2Te3 layers were obtained at 80-200° C, according to EDX measurements: the percent atomic ratio of Sb:Te was approximately 40:60. Film deposited at 150° C, contained ~55 to 60 atomic % Te and ~25-35 atomic % Sb, as per Auger spectroscopy measurements. Film deposited at 60° C was crystalline rhombohedral phase Sb2Te3, according to XRD. The grain size increased from ~0.2 μm at 80° C and 0.4-0.6 μm at 100-150° C., to ~1-2 μm at 200° C, as per SEM measurements.

Te(GeMe3)2 (+GeCl2:dioxane) for GeTe films by CVD

    Te(Me3Ge)2 as Te precursor (combined with  GeCl2:dioxane (Ge source) in precursors ratio Te:Ge=1:2 (Ge rich conditions)) was applied for the CVD growth of  GeTe films on Si substrates at 60-200° C temperatures and 10 Torr pressure. Polycrystalline GeTe films were obtained at 90°C temperature and higher;  the grain size increased with increasing deposition temperature (by SEM). EDX and Auger spectroscopy gave conflicting atomic ratio data. Crystalline rhombohedral phase GeTe films were deposited at 90°C, according to XRD.

Te(GeMe3)2 (+GeCl2:dioxane, SbCl3) for GST by CVD

      Te(GeMe3)2 as Te precursor, combined with GeCl2:dioxane and SbCl3 as Ge and Sb sources (precursors ratio Ge:Sb:Te=2.3:10:1), was applied for the growth of GST by CVD on Si (uncleaned or cleaned with HF), on Si/SiO2 and Si/TiN substrates, at 60-150°C wafer temperature and 10 Torr pressure. The Ge:Sb:Te ratio in the grown layers was ~2:2:5, both by EDX and Auger spectroscopy. Amorphous GST layers were obtained at 80-100°C growth temperature. and crystalline films at 110-150° C, according to SEM.

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