Using positive dc offset of bias rf to neutralize charge build-up of etch features

An etching apparatus, comprising:

• a plasma processing chamber comprising a chamber enclosure and a substrate support within the chamber enclosure;
• a plasma generator coupled to the plasma processing chamber;
• an RF voltage power source configured to cause a negative bias, relative to a plasma in the plasma processing chamber, to form across a surface of a substrate on the substrate support to etch an opening in the substrate;
• and
• a function generator configured to apply a waveform signal to the substrate support, wherein the waveform signal is selected to intermittently cause the negative bias on the substrate surface to change to a positive bias relative to the plasma.

An etching apparatus, comprising:

• a plasma processing chamber comprising a chamber enclosure and a substrate support within the chamber enclosure;
• a plasma generator coupled to the plasma processing chamber;
• an RF voltage power source configured to cause a negative bias, relative to a plasma in the plasma processing chamber, to faun across a surface of a substrate on the substrate support to etch an opening in the substrate;
• and
• a function generator operably coupled with the substrate support and configured to apply a series of pulses alternating between a positive voltage and a voltage that is less than the positive voltage, including a zero voltage, to the substrate support at an amplitude, frequency and duration selected to intermittently cause the negative bias on the substrate surface to change to a positive bias relative to the plasma.