Control of directionality in atomic layer etching

A method for performing atomic layer etching (ALE) on a substrate, comprising:

• performing a surface modification operation on a substrate surface, the surface modification operation including exposing the substrate surface to a first plasma that converts at least one monolayer of the substrate surface to a modified layer, wherein a bias voltage is applied during the surface modification operation, the bias voltage being configured to control a depth of the substrate surface that is converted by the surface modification operation, wherein the bias voltage is configured to accelerate ions from the first plasma towards the substrate surface without substantially etching the substrate surface;
• performing a removal operation on the substrate surface, the removal operation including removing at least a portion of the modified layer from the substrate surface, wherein removing the portion of the modified layer includes applying thermal energy to effect desorption of the portion of the modified layer;
• performing a clean operation on the substrate surface, the clean operation including removing residues generated by the removal operation from the substrate surface, the clean operation further including exposing the substrate surface to a second plasma, wherein the residues are volatilized by the exposure to the second plasma.

A method for performing atomic layer etching (ALE) on a substrate, comprising:

• performing a surface modification operation on a substrate surface, the surface modification operation including exposing the substrate surface to a halogen-containing plasma that converts at least one monolayer of the substrate surface to a modified layer, wherein a bias voltage is applied during the surface modification operation, the bias voltage being configured to control a depth of the substrate surface that is converted by the surface modification operation, wherein the bias voltage is configured to accelerate ions from the first plasma towards the substrate surface without substantially etching the substrate surface;
• performing a removal operation on the substrate surface, the removal operation including removing at least a portion of the modified layer from the substrate surface, wherein removing the portion of the modified layer includes a ligand exchange reaction and applying thermal energy to effect desorption of the portion of the modified layer;