Wet Chemical Etching of Transparent Conducting Ga-Doped ZnO Thin Films by Oxalic and Formic Acid

Wet etching behaviors of highly crystalline, well-textured Ga-doped zinc oxide (GZO) film with a thickness of 150 nm are investigated by using oxalic and formic acids. These two organic acids showed strikingly different etching characteristics with respect to etch rate and etch profile under 0.02 M of concentration and 30 degrees C of temperature. Under these conditions, a faster vertical etch rate of 90 nm/min and sharp edge lines of the patterned GZO film resulted from a formic acid etchant while an oxalic acid solution generated a slower vertical rate of 22 nm/min and uneven line features. These etching behaviors were schematically described by monitoring the intermediate etching stages for each etchant. The mobility of hydronium ions in the oxalic and formic acid solutions, which should be associated with their chemical structures, presumably plays an important role in determining characteristic etching behaviors. Activation energies for the vertical etching of oxalic and formic acids were also experimentally determined to be 14.60 and 6.58 kcal/mol, respectively. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3121525] All rights reserved.