Gradient etching with microwave oxidation

A method of forming a contact structure on a semiconductor substrate, the method comprising:

• performing a microwave oxidation etch process on the contact structure, wherein the microwave oxidation etch process comprises flowing a first process gas over the contact structure and delivering a microwave energy to the first process gas without generating a plasma in a processing chamber, wherein:
• the contact structure comprises a feature formed in a surface of the semiconductor substrate,
• the feature is defined by a silicon-based portion, a bottom surface, a top-side surface, a first sidewall, and a second sidewall,
• a first liner layer is disposed over at least a portion of the feature, and
• a second liner layer is disposed over at least a portion of the first liner layer;
• and
• depositing a metal gap fill material over the contact structure to fill the feature.

A method of forming a contact structure on a semiconductor substrate, the method comprising:

• forming a first liner layer over the contact structure by maintaining a first temperature of the semiconductor substrate and providing a first carrier gas, a first metal-containing precursor, and a first hydrogen-containing precursor to a first processing chamber, wherein:
• the contact structure comprises a feature formed in a surface of the semiconductor substrate,
• the feature is defined by a silicon-based portion, a bottom surface, a top-side surface, a first sidewall, and a second sidewall, and
• the first liner layer is disposed over at least a portion of the feature;
• and
• performing a microwave oxidation etch process on the contact structure, wherein the microwave oxidation etch process comprises flowing a first process gas over the contact structure and delivering a microwave energy to the first process gas without generating a plasma in a processing chamber.