U.S. Pat. No. 5,837,662 discloses a process for cleaning contaminants from the surface of a wafer after the wafer has been lapped, the process including contacting the wafer with an oxidizing agent to oxidize organic contaminants and immersing the wafer in an aqueous bath containing citric acid into which sonic energy is directed to remove metallic contaminants present on the surface of the wafer.