Abstract: Described herein is a method for selectively cleaning and/or etching a sample. The method includes selectively forming a film in a trench of a substrate such that the trench may be selectively etched. A polymer film is deposited on the bottom surface of the trench without being deposited on the side wall. A second film is selectively formed in the trench without forming the second film on the polymer film. The polymer is then removed from the bottom surface of the trench and then etching is performed on the bottom surface of the trench using an etch chemistry, wherein the second film protects the side wall from being etched.