Selective etch of a substrate

A method comprising:

• placing a substrate into a chamber, the substrate comprising a layer including at least one trench formed therein, the at least one trench having a top surface, a bottom surface, and at least one side wall;
• depositing a polymer film on the bottom surface of the at least one trench without
• depositing the polymer film on the least one side wall of the at least one trench;
• and
• selectively forming a second film on the layer without forming the second film on the polymer film.

A method comprising:

• placing a substrate into a chamber, the substrate comprising a layer including at least one trench formed therein, the at least one trench having a top surface, a bottom surface, and at least one side wall;
• depositing a polymer film on the bottom surface of the at least one trench without depositing the polymer film on the least one side wall of the least one trench;
• and
• selectively forming a second film on the layer without forming the second film on the polymer film,
• removing the polymer film from the bottom surface of the at least one trench,
• performing an etch process, wherein the etch process comprises applying ammonium fluoride to the substrate,
• wherein the performing the etch process selectively interacts with the bottom surface of the at least one trench and does not interact with the top surface and the at least one side wall.