Chemical-mechanical planarization (CMP) is a process of oxidizing and chelating the copper overburden present in an interconnect device while mechanically polishing the surface of the wafer. Because the use of condensed CO2 as the solvent for CMP would be environmentally and technically advantageous, several substituted bis(acetylacetonate)ethylenediimine (R(4)BAE, where R = CH3 or CF3) and lithium or sodium dialkyldithiocarbamate (M+(R2DTC-), where M+ = Li+ or Na+ and R = ethyl, n-propyl, n-butyl, or 1,1,1-trifluoroethyl) ligands were used with t-butylperacetate (t-BuPA, as oxidant) for the oxidative dissolution of copper(0) in supercritical (sc) CO2 at 40 degrees C and 170-210 bar or in hexanes at 40 degrees C and atmospheric pressure. The reaction products from the copper etching were determined to be Cu(R(4)BAE) or Cu(R2DTC)(2), respectively. The R2DTC- ligands had higher etch rates than the R(4)BAE ligands with comparable substituents, and the lithium dialkyldithiocarbamate salts gave higher copper etching rates than their sodium counterparts. The highest average etch rates were observed for Li((CF3CH2)(2)DTC): 16.7 nm/min in sc CO2 and 11.2 nm/min in hexanes. While hexanes have similar physical properties when compared to sc CO2, the rates of copper(0) removal with the R2DTC- ligands were 17-49% higher in sc CO2 than in hexanes at comparable temperatures and solvent densities. Scanning electron microscopy (SEM) images of the postreaction copper surfaces using the various ligands showed significant variations in surface roughness. X-ray photoelectron spectroscopy (XPS) measurements indicated that the lower R(4)BAE etch rates may be due to surface passivation by the R(4)BAE ligands and/or the Cu(R(4)BAE) complexes.