Methods for etching a substrate

A method for etching a substrate in a plasma etch reactor comprising:

• (a) depositing a polymer on surfaces of a feature formed in a substrate disposed in the etch reactor using a first reactive species formed from a first process gas comprising a polymer forming gas;
• (b) etching the bottom surface of the feature of the substrate in the etch reactor using a third reactive species formed from a third process gas including an etching gas, wherein a composition of gases introduced into the etch reactor changes between (a) and (b);
• and
• (c) bombarding a bottom surface of the feature with a second reactive species formed from a second process gas comprising an inert gas and at least one of an oxidizing gas or a reducing gas while depositing the polymer to remove at least some of the polymer disposed on the bottom surface, about wherein a duration of each bombardment of the bottom surface of the feature is about 5 to about 50 percent of a duration of depositing the polymer.

A method for etching a substrate in a plasma etch reactor comprising:

• (a) depositing a polymer on surfaces of a feature formed in a substrate disposed in the etch reactor using a first reactive species formed from a first process gas comprising a polymer forming gas;
• (b) etching the bottom surface of the feature of the substrate in the etch reactor using a third reactive species formed from a third process gas including an etching gas, wherein a composition of gases introduced into the etch reactor changes between (a) and (b);
• and
• (c) bombarding a bottom surface of the feature with a second reactive species formed from a second process gas comprising an inert gas and at least one of an oxidizing gas or a reducing gas while etching the bottom surface to at least one of chemically or physically damage the bottom surface, wherein a duration of each bombardment of the bottom surface of the feature is about 5 to about 50 percent of a duration of etching the bottom surface.