Cu contaminants of similar to 1 x 10(13) atoms/cm(2) on SiO2 surfaces can be removed to less than similar to 3 x 10(9) atoms/cm(2) by immersion in 3 ppm HCN aqueous solutions within 2 min at room temperature. The Cu removal process by HCN aqueous solutions consists of the initial fast and subsequent slow steps. X-ray absorption fine structure (XAFS) measurements with the total reflection X-ray fluorescence (TXRF) geometry (TXRF-XAFS) have been used for determination of chemical states of Cu contaminants before and after cleaning with HCN aqueous solutions. Cu contaminants are composed of Cu+ and Cu (2+) species, latter being present above the former. In the former species, a Cu atom is linearly bound to two oxygen atoms (Cu2O-like species), while in the latter species, a Cu atom is bound to four equatorial oxygen atoms and two axial oxygen atoms [Cu(OH)(2)-like species]. CN- ions react with outer Cu(OH)(2)-like species with a high rate, leading to initial fast removal of Cu contaminants. When the Cu concentration decreases to similar to 1 x 10(10) atoms/cm(2), Cu+ species becomes a main species and its removal rate becomes much lower. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3599832] All rights reserved.