A liquid mixture formed from two benign chemicals, urea and choline chloride, in the molar ratio of 2:1 has been evaluated for post etch residue (PER) removal from copper surface. Residue films were prepared by etching DUV photoresist films coated on copper in CF4/O-2 plasma. Film removal was evaluated under immersion cleaning conditions using X-ray photoelectron spectroscopy and scanning electron microscopy and verified using electrochemical impedance spectroscopy measurements. The residue film was effectively removed in the temperature range of 40-70 degrees C. The results of this study show that choline chloride and urea based DES system has the potential to function as a back end of line cleaning formulation. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3597656] All rights reserved.