Effects of chelating agent additions to an NH4OH-H2O2-H2O wet cleaning solution are examined in terms of metallic contamination on Si surfaces. While ethylenediaminetetraacetic acid and other well-known chelating agents have been shown to reduce Fe adsorption onto an Si surface only by one third, adding a phosphonic acid chelating agent at a concentration of only 1 ppm reduces Fe and Ca contamination by more than one order of magnitude and increases dielectric strength of 11 nm thin oxide.