Dc bias in plasma process

A method for sequential plasma treatments with a single DC bias, comprising:

• placing a substrate on a pedestal in a processing chamber;
• applying a negative DC bias voltage to the pedestal using a bias source;
• performing a first plasma treatment on the substrate, comprising:
• generating a first plasma containing negatively charged oxygen ions,
• exposing the substrate to the first plasma, and
• maintaining the negative DC bias voltage to repel the negatively charged oxygen ions from the substrate;
• performing a second plasma treatment on the substrate, comprising:
• generating a second plasma containing positively charged hydrogen ions and negatively charged fluorine ions,
• exposing the substrate to the second plasma, and
• maintaining the negative DC bias voltage to remove the negatively charged fluorine ions from the substrate;
• and
• wherein the negative DC bias voltage is continuously applied during both the first and second plasma treatments.

A method for combined photoresist removal and surface treatment, comprising:

• placing a substrate with a photoresist layer on a pedestal in a processing chamber;
• generating a plasma containing positively charged hydrogen ions, negatively charged oxygen ions, and neutral oxygen radicals;
• exposing the substrate to the plasma;
• applying a pulsed DC bias voltage to the pedestal using a bias source, wherein each pulse cycle comprises:
• a first portion with a negative DC bias voltage to repel the negatively charged oxygen ions from the substrate and remove negatively charged fluorine ions from the substrate, and
• a second portion with a positive DC bias voltage to attract the negatively charged oxygen ions to the substrate;
• wherein the neutral oxygen radicals remove the photoresist layer, and
• wherein the pulsed DC bias voltage simultaneously promotes removal of negatively charged fluorine ions from the substrate and controlled oxidation of a surface of the substrate.