Use of Substituted Bis(acetylacetone)ethylenediimine and Dialkyldithiocarbamate Ligands for Copper Chelation in Supercritical Carbon Dioxide

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 CO 2 as the solvent for CMP would be environmentally and technically advantageous, several substituted bis(acetylacetonate)ethylenediimine (R 4 BAE, where R = CH 3 or CF 3 ) and lithium or sodium dialkyldithiocarbamate (M + (R 2 DTC - ), 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) CO 2 at 40 °C and 170−210 bar or in hexanes at 40 °C and atmospheric pressure. The reaction products from the copper etching were determined to be Cu(R 4 BAE) or Cu(R 2 DTC) 2, respectively. The R 2 DTC - 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((CF 3 CH 2 ) 2 DTC): 16.7 nm/min in sc CO 2 and 11.2 nm/min in hexanes. While hexanes have similar physical properties when compared to sc CO 2, the rates of copper(0) removal with the R 2 DTC - ligands were 17−49% higher in sc CO 2 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.