Investigations of barium beta -diketonate complexes used in chemical vapour deposition of high-Tcoxide films

Abstract

This paper discusses barium complexes containing the 2,2,6,6-tetramethyl-3,5-heptanedionate (thd) ligand, describing properties relevant to their use as precursors in MOCVD. We describe the chemical characterization of commercial 'Ba(thd)2', similar oligomeric material we prepared from aqueous Ba(OH)2solution, and the novel complex Ba(thd)2(tetraglyme). Of these three materials, only Ba(thd)2(tetraglyme) has a reproducible chemical composition. We compared the volatility and thermal stability of the barium complexes by means of MOCVD experiments involving film deposition under oxidizing conditions onto sapphire substrates at 500 degrees C. The resulting BaCO3films were characterized by stylus profilometry, SEM, XRD and XPS. Both types of 'Ba(thd)2' initially showed a useful degree of volatility at 250 degrees C, although material we prepared from aqueous Ba(OH)2solution decomposed on a timescale of hours at this temperature. We observed no systematic reduction in the volatility of 'Ba(thd)2' samples stored at room temperature for periods of up to 26 months. We also investigated the effect of triethylamine vapour on the volatilization of 'Ba(thd)2'. In contrast to an earlier report of dramatic volatility enhancement, highly sensitive XPS measurements indicated complete inhibition of barium transport under some conditions. Finally, our experiments with Ba(thd)2(tetraglyme) demonstrated the possibility of using this complex as a precursor in certain types of MOCVD process. © 1994 IOP Publishing Ltd.