Comparison of tantalum precursors for use in liquid injection CVD of thin film oxides, dielectrics and ferroelectrics

Thin films of Ta2O5 have been deposited by liquid injection MOCVD using tetrahydrofuran solutions of the mixed ligand precursors Ta(OR)4(thd), (where R = methyl (Me), ethyl (Et), isopropyl (Pri) ; thd = 2,2,6,6-tetramethyl-3,5-heptanedionate), and for comparison tantalum ethoxide (Ta(OEt)5). Thin films were deposited on to (100) orientated silicon wafers. It was found that the temperature for tantalum oxide film deposition was around 250°C for the tantalum ethoxide and around 300°C for the alkoxide / β diketonate precursors. For the alkoxide / β diketonate the temperature for the onset of mass transport controlled growth depended on the precursor structure increasing in the order Ta(OPri)4(thd) < Ta(OEt)4(thd) < Ta(OMe)4(thd). The tantalum oxide films were smooth and specular in appearance but amorphous as grown in the temperature range 250-600°C. They crystallised to the expected δ phase of Ta2O5 on annealing in air at 1000°C. Analysis of the films by Auger electron spectroscopy showed that carbon levels ranged from below the detection limit of 1 atomic up to 3 atomic %. The tailoring of precursors properties for their use in the growth of multi-component oxides is discussed