Low temperature metal oxide film deposition and reaction kinetics in supercritical carbon dioxide

Abstract

An effective method is developed for low temperature metal oxide deposition through thermal decomposition of metal diketonates in supercritical carbon dioxide (scCO 2) solvent. The rates of Al(acac) 3 (Aluminum acetyl acetonate) and Ga(acac) 3 (Gallium acetyl acetonate) thermal decomposition in scCO 2 to form conformal Al 2O 3 and Ga 2O 3 thin films on planar surfaces were investigated. The thermal decomposition reaction of Al(acac) 3 and Ga(acac) 3 was found to be initialized at ∼ 150 °C and 160 °C respectively in scCO 2 solvent, compared to ∼ 250 °C and 360 °C in analogous vacuum-based processes. By measuring the temperature dependence of the growth rates of metal oxide thin films, the apparent activation energy for the thermal decomposition of Al(acac) 3 in scCO 2 is found to be 68 ± 6 kJ/mol, in comparison with 80–100 kJ/mol observed for the corresponding vacuum-based thermal decomposition reaction. The enhanced thermal decomposition rate in scCO 2 is ascribed to the high density solvent which effectively reduces the energy of the polar transition states in the reaction pathway. Preliminary results of thin film deposition of other metal oxides including ZrO x , FeO x , Co 2O 3, Cr 2O 3, HfO x from thermal decomposition of metal diketonates or fluorinated diketonates in scCO 2 are also presented.