Carbon dioxide is an environmentally benign solvent with high surface wetting properties, tunability, recyclability and low viscosity. With these potential advantages, condensed and/or supercritical (sc) CO2 has the potential to replace the aqueous chemical mechanical planarization processes used in the microelectronics industry to form multi-layer interconnects from porous low ê inorganic and organic interlayer dielectrics. We have studied the use of organic peroxides and various ligand families as oxidants and chelants for copper in sc CO2. Copper chelation kinetics and surface composition analyses will be discussed along with results from electrochemical measurements made in aqueous and low dielectric strength media.

Specifically, the oxidation and removal kinetics of copper(0) foil and cuprous oxide (Cu2O) powder were studied in both hexanes (at 1 bar) and supercritical carbon dioxide (at a constant density of 0.8 g/cm3) using excess t-butylperacetate (t-BuPA) as the oxidant and excess 1,1,1-trifluoro-2,4-pentanedione (tfacH) as the chelating agent. Temperatures examined were 19 to 68 oC for hexanes and 35 to 60 oC for carbon dioxide. A heterogeneous kinetic model was developed and verified to capture the temperature, copper surface area, and concentration effects on the kinetics. We were able to determine the reaction order as well as the temperature dependence of the oxidation and dissolution process with an Arrhenius type expression. In addition, we examinedthe use of several dialkyldithiocarbamates as chelating agents and also determined the reaction kinetics of copper removal for these compounds in carbon dioxide as well as hexane.

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