The organic oxidizing agents 1,4-benzoquinone and its nontoxic derivative 2,3,5,6-tetrachloro-1,4-benzoquinone have been shown to be alternatives to the toxic and carcinogenic hexavalent chromium which is routinely used in most etching solutions. The newly developed etching solutions delineate both grown-in and process-induced defects in silicon-on-insulator substrates fabricated by the Smart-Cut technology and show a good correlation to the defect densities obtained with a dilute Secco (0.04 M) etching solution serving as a reference. In combination with an aqueous solution of the nontoxic fluorinating agent tetrafluoroboric acid, which has been introduced as an alternative to the very toxic solution of hydrofluoric acid (49%), a completely nontoxic etching solution is presented. An etching mechanism will be discussed, explaining the generation of elemental hydrogen which is formed during the etching process. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3505943] All rights reserved.