Pressure purge etch method for etching complex 3-D structures

A method for etching a substrate and removing byproducts includes (a) setting process parameters of a processing chamber for a selective dry etch process; (b) setting process pressure of the processing chamber to a first predetermined pressure in a range from 1 Torr to 10 Torr for the selective dry etch process; (c) selectively etching a first film material of a substrate relative to a second film material of the substrate in the processing chamber during a first period; (d) lowering pressure in the processing chamber to a second predetermined pressure that is less than the first predetermined pressure by a factor greater than or equal to 4; and (e) purging the processing chamber at the second predetermined pressure for a second period.