Selective in-situ carbon-based mask protection

A method of etching an underlying layer, the method comprising:

• flowing an oxygen-containing gas to selectively attach oxygen to a patterned carbon-containing layer relative to the underlying layer;
• flowing an oxygen-reactive precursor to form a protection layer on the patterned carbon-containing layer;
• and
• flowing an etchant gas to etch the underlying layer using the patterned carbon-containing layer as an etch mask.

A plasma etching system comprising:

• a chamber configured to contain plasma;
• a substrate support disposed in the chamber and configured to support a substrate comprising a patterned carbon-containing layer having openings exposing an underlying layer;
• an oxygen source fluidically coupled to the chamber and configured to supply an oxygen-containing gas through one or more valves;
• a precursor source fluidically coupled to the chamber and configured to supply an oxygen-reactive precursor through the one or more valves;
• an etchant source fluidically coupled to the chamber and configured to supply an etchant gas through the one or more valves;
• and
• a controller operationally coupled to the one or more valves, the controller comprising a processor and a non-transitory computer-readable medium storing a program including instructions that, when executed by the processor, perform a method comprising cyclically performing the following steps in situ within the chamber;
• performing a pretreatment step comprising flowing the oxygen-containing gas to expose surfaces of a carbon-containing layer to the oxygen-containing gas;
• performing a reaction step comprising flowing the oxygen-reactive precursor to expose the carbon-containing layer to the oxygen-reactive precursor to selectively form a protection layer on the surfaces of the carbon-containing layer;
• and
• performing an etch step comprising flowing the etchant gas and exciting plasma from the etchant gas to etch the underlying layer using the carbon-containing layer as an etch mask.