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 degreesC 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 degreesC 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 muOmega-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 degreesC. 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.