Substrate processing apparatus and methods

A method for forming a feature on a substrate by etching a trench with high bottom clean efficiency, comprising:

• positioning the substrate in a vacuum processing region of a processing chamber;
• during a first etching cycle, exposing at least one portion of the substrate to an etchant while maintaining the substrate below a temperature threshold;
• subsequently bombarding the at least one portion with ions of an inert gas plasma by providing an RF source power at a power level of 300 W to 1000 W while generating the inert gas plasma, while maintaining the substrate below the temperature threshold, to at least one of:
• activate unreacted etchant by the inert gas plasma,
• physically remove etchant byproducts, formed by reaction of the etchant and regions of the at least one portion, to reduce top trench overhang, or
• anneal away etchant byproducts, formed by reaction of the etchant and regions of the at least one portion, via latent heat of the inert gas plasma to unreacted portions of the substrate reveal fresh surfaces of the substrate at the bottom of a trench and allow more substrate material to be etched at the bottom of the trench;
• and
• subsequently heating the substrate to a second temperature higher than the temperature threshold to sublimate at least one etchant byproduct.

A method for forming a feature on a substrate by etching a trench with high bottom clean efficiency, comprising, in order:

• (a) generating a plasma from a gas or gas mixture within a processing chamber to form a processing gas including an etchant and exposing at least a portion of a material layer disposed on the substrate to the etchant while maintaining the substrate at a first temperature;
• (b) subsequently generating an inert gas plasma within the processing chamber by providing an RF source power at a power level of 300 W to 1000 W while generating the inert gas plasma;
• (c) subsequent to (b), repeating (a);
• and
• (d) only after (c), heating the substrate to a second temperature higher than the first temperature, to sublimate at least one byproduct of reaction between the etchant and a material layer disposed on the substrate.