Oxidative Dissolution of Copper and Zinc Metal in Carbon Dioxide with tert-Butyl Peracetate and a β-Diketone Chelating Agent

• Published in: Inorganic chemistry 2005-01, Vol.44 (2), p.316-324
• Main Authors: Visintin, Pamela M, Bessel, Carol A, White, Peter S, Schauer, Cynthia K, DeSimone, Joseph M
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic049765o

A series of β-diketone ligands, R1COCH2COR2 [tmhdH (R1 = R2 = C(CH3)3); tfacH (R1 = CF3; R2 = CH3); hfacH (R1 = R2 = CF3)], in combination with tert-butyl peracetate (t-BuPA), have been investigated as etchant solutions for dissolution of copper metal into carbon dioxide solvent. Copper removal in CO2 increases in the order tfacH < tmhdH < hfacH. A study of the reactions of the hfacH/t-BuPA etchant solution with metallic copper and zinc was conducted in three solvents:  scCO2 (supercrical CO2); hexanes; CD2Cl2. The etchant solution/metallic zinc reaction produced a diamagnetic Zn(II) complex, which allowed NMR identification of the t-BuPA decomposition products as tert-butyl alcohol and acetic acid. Gravimetric analysis of the amount of zinc consumed, together with NMR studies, confirmed the 1:1:2 Zn:t-BuPA:hfacH reaction stoichiometry, showing t-BuPA to be an overall two-electron oxidant for Zn(0). The metal-containing products of the copper and zinc reactions were characterized by elemental analysis, IR spectroscopy, and, as appropriate, NMR spectroscopy and single-crystal X-ray diffraction [trans-M(hfac)2(H2O)(CH3CO2H) (1, M = Cu; 2, M = Zn)]. On the basis of the experimental results, a working model of the oxidative dissolution reaction is proposed, which delineates the key chemical variables in the etching reaction. These t-BuPA/hfacH etchant solutions may find application in a CO2-based chemical mechanical planarization (CMP) process.