Method of running an etch process in higher selectivity to mask and polymer regime by using a cyclic etch process

A method for selectively etching a patterned structure into a substrate, the method comprising the steps of:

• a) in an etching chamber, performing a first partial etching by exposing the substrate to an etching gas or etching gas mixture and an oxidizing gas, under conditions and for a period of time sufficient to preferentially etch a first substrate material over a second substrate material, wherein a polymer of the etching gas is deposited on the substrate, and wherein the first partial etching produces an intermediate patterned structure on the substrate that can be further etched to yield a final intended patterned structure on the substrate,
• b) performing a first polymer removal step by exposing the substrate to a polymer removal gas or polymer removal gas mixture under conditions and for a period of time sufficient to remove some or all of the polymer formed in step a), and
• c) repeating steps a) and b) at least once,
• wherein the polymer removal gas or polymer removal gas mixture comprises one or more of Kr, Xe, NF3, SF6, IF7, IF5, and CF4.