Aqueous cleaning solution and method of protecting features on a substrate during etch residue removal

An alkaline wet solution for protecting features on a patterned substrate and a substrate processing method using the alkaline wet solution are described. The method includes providing a patterned substrate containing a low-k material, a metal oxide feature, and an etch residue, performing a treatment process that exposes the patterned substrate to an alkaline wet solution that forms a protective coating on the metal oxide feature, the alkaline wet solution containing a mixture of 1) water, 2) ammonium hydroxide, a quaternary organic ammonium hydroxide, or a quaternary organic phosphonium hydroxide, and 3) dissolved silica, and performing a wet cleaning process that removes the etch residue but not the metal oxide feature that is protected by the protective coating. The patterned substrate can further include a metallization layer and the alkaline wet solution can further contain 4) an inhibitor that protects the metallization layer from etching by the alkaline wet solution.