By-product collecting processes for cleaning processes

An apparatus and a method for operating the same. The method includes providing an apparatus which includes a chamber, wherein the chamber includes first and second inlets, an anode and a cathode structures in the chamber, and a wafer on the cathode structure. A cleaning gas is injected into the chamber via the first inlet. A collecting gas is injected into the chamber via the second inlet. The cleaning gas when ionized has a property of etching a top surface of the wafer resulting in a by-product mixture in the chamber. The collecting gas has a property of preventing the by-product mixture from depositing back to the surface of the wafer.