Multi-step pre-clean for selective metal gap fill

A method of pre-cleaning a substrate, the method comprising:

• exposing a substrate having a dielectric field and a surface structure with a metal bottom and dielectric sidewalls to a strong reductant to remove oxide and/or nitride from the metal bottom and create surface defects in the dielectric sidewalls and/or dielectric field;
• exposing the substrate to an oxidizer to repair the surface defects in the dielectric sidewalls and/or dielectric field and oxidize the metal bottom of the surface structure to form a metal oxide bottom of the surface structure;
• and
• exposing the substrate to a weak reductant to reduce the metal oxide bottom to a pure metal bottom without substantially damaging the dielectric.