Method and apparatus for controlling a shape of a pattern over a substrate

A method of processing a substrate comprising:

• etching and forming a recess in the substrate to form a pattern of the substrate;
• in a first session, performing a hybrid gas application cycle in a chamber that holds the substrate having the recess formed therein, including
• introducing a first gas as a precursor for a first time period in the chamber so the precursor absorbs onto sidewalls of the pattern of the substrate,
• subsequently, introducing a second gas as a reaction gas in a first condition so the reaction gas reacts with the precursor to provide a protective layer on the sidewalls of the pattern of the substrate, and
• subsequently introducing another reaction gas in a second condition for a second time period so as to etch away the protective layer and a portion of the substrate at a bottom portion of the pattern, a ratio of the first time period to the second time period being a use-ratio;
• and
• in a second session, repeating the hybrid gas application cycle with a different use-ratio that corresponds with a vertical dimension of the pattern so as to control a shape along the vertical dimension of the pattern,
• wherein the another reaction gas is different from the second gas and the second condition is different from the first condition.