Synthesis and characterization of (β-diketonate) zirconium alkoxides for low temperature chemical vapor deposition of lead zirconium titanium thin films

Abstract

Metal alkoxides have been known for many years. Recently, a renewed interest in these compounds has arisen as they have been found to be viable precursors for metal oxide film synthesis. Lead zirconium titanate(PZT) films have shown promise for many applications in the electronics industry. Chemical vapor deposition(CVD) of PZT thin films has been hampered by the lack of a suitable zirconium precursor for low temperature chemical vapor deposition. Currently, both zircbnium alkoxides and zirconium β-diketonate complexes are employed in the CVD process of PZT films. The alkoxides, although volatile are moisture sensitive and are not easily handled under normal atmospheric conditions. Tetrakis β-diketonate complexes of zirconium are more stable than the alkoxides, but they have a deposition temperature that is too high for commercial use. A mixed (β-diketonate)zirconium alkoxide compound could provide the necessary stability while maintaining the volatility necessary for low temperature CVD.

From the above reasoning, it was decided to prepare a zirconium di-(2,2,6,6 tetramethyl-3,5 heptadione) di-tert-butoxide compound. The compound was characterized and subjected to a variety of volatility studies. Thermogravimetric analysis provided evidence that the compound was volatile enough to be used in thin film synthesis. Initial attempts at film deposition, however, resulted in no film growth. Changing deposition parameters also resulted in no film growth. Visual inspection of the residue left after the deposition trials gave the first indication that the compound had undergone some change. Analysis of the material left in the reactor suggested the formation of a zirconium cluster compound. Further decomposition studies also resulted in the formation of the same zirconium cluster compound.

Attempts to make the compound more stable at deposition temperatures centered on changing the alkoxide. Tri-tert-butyl alcohol(tritox) was prepared, however, the synthesis of the tritox - β-diketonate zirconium complex was unsuccessful. Other changes involved using pivalic acid to replace the alkoxide. Reactions with pivalic acid and zirconium di-(2,2,6,6 tetramethyl-3,5 heptadione) di-tert-butoxide resulted in the decomposition of the starting material.

Other β-diketonate complexes were also investigated. Compounds synthesized from 2.4 pentadione(Acac), 1-benzoyl acetone(Bzac) and dibenzoyl methane(Dbzm) could not be purified in order to subject them to chemical vapor deposition.

A zirconium complex with two different β-diketonate ligands was also synthesized. The complex was not investigated as a precursor for chemical vapor deposition because the isomers of the complex could not be separated.