FORMATION OF ALUMINUM-OXIDE FILMS FROM ALUMINUM HEXAFLUOROACETYLACETONATE AT 350-450-DEGREES C

A study of the thermally activated decomposition of Al(hfa)3 (aluminum hexafluoroacetylacetonate) from the gas phase to form Al2O3 on silicon substrates is reported. The decomposition process was carried out in an open tube atmospheric pressure reactor in either argon or oxygen/argon mixtures in the temperature range, 350-450° C. The chemical vapor deposition process resulted in the formation of aluminum oxide films in all instances. The dielectric strength of Al/Al2O3/Si capacitors which received a post-metal anneal, but did not receive a high temperature annealing treatment, with aluminum oxide films prepared from Al(hfa)3 in argon, was found to be in the range 2-6 MV/cm. The difference between the flatband voltage of the MOS structures and the metal-silicon work function difference was positive, indicative of a net negative oxide charge with a density of approximately 3 × 1011 - 3 × 1012 cm-2, assuming the charge is located at the oxide-silicon interface. Decomposition of Al(hfa)3 was also carried out in oxygen/argon mixtures with the oxygen concentration in the range 10-60 vol %. This process led to the deposition of aluminum oxide films with breakdown fields in the range 8-9 MV/cm. However, the flatband voltages of the Al/Al2O3/Si capacitors were even more positive than those obtained with Al2O3 formed in pure argon. High temperature (800-1000° C) oxygen or nitrogen annealing treatments of alumina films deposited in either argon or oxygen/argon mixtures were evaluated from the point of view of their influence on the oxide film properties. In particular, an annealing process in oxygen at 1000° C for 15 min was found to result in a reduction of the net negative oxide charge, and an improvement of the dielectric strength of films deposited in argon. Films formed in oxygen/argon mixtures did not change appreciably following oxygen annealing, as far as breakdown fields are concerned, but the oxide net negative charge was reduced. As in an earlier study by the authors, of copper film deposition from Cu(hfa)2, it was found that essentially carbon free films could be obtained under appropriate conditions. © 1990 AIME.