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

Abstract
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.