Alcohol-Assisted Deposition of Copper Films from Supercritical Carbon Dioxide

Device quality Cu films were deposited from solutions of bis(2,2,6,6-tetramethyl-3,5-heptanedionate) copper(II) [Cu(tmhd) 2 ] in supercritical CO 2 (scCO 2 ) using alcohols as reducing agents in a cold wall, high-pressure reactor. At 270 °C and pressures between 200 and 230 bar, deposition of copper by the reduction of Cu(tmhd) 2 with ethanol was selective for catalytic surfaces such as Co and Ni over the native oxide of Si wafers or TiN. At 300 °C and above, depositions proceeded readily on all surfaces studied. Secondary ion mass spectroscopy indicated that Cu films are remarkably pure; carbon and oxygen contamination were on the order of 0.1% or less. Resistivities of the films were approximately 2 μΩ-cm. Reduction of Cu(thmd) 2 with primary alcohols including methanol, 1-propanol, and 1-butanol proceeded readily to yield copper films on Co substrates at 270 °C. Sterically hindered alcohols were less effective at the same conditions. Deposition with 2-butanol required higher alcohol concentrations while attempted depositions with 2-propanol were not successful. Reaction mechanisms consistent with these observations are discussed.