Directional sio2 etch using plasma pre-treatment and high-temperature etchant deposition

A method, comprising:

• positioning a silicon-containing substrate in a processing chamber, the silicon-containing substrate comprising:
• an exposed surface;
• one or more microstructures formed in the exposed surface;
• and
• a native oxide layer formed on the exposed surface;
• biasing the substrate;
• exposing the substrate to a low energy inert plasma to form amorphous silicon oxide on surface perpendicular to the flow of the low energy inert plasma;
• heating the substrate to a first temperature;
• exposing the surface of the substrate to a plasma comprising ammonium fluoride (NH4F) to form one or more volatile products;
• and
• heating the substrate to a second temperature, which is higher than the first temperature, to sublimate the volatile products.