Negative ion extraction: How can that be done?

You must reverse the direction of the electric field by the wall to extract negative ions.
- It ordinarily sets up to repel negative ions (and electrons.)
- Negative ions do NOT have enough energy to overcome it.
You must be able to absorb the electron current to reverse this electric field (in steady state).
- This current can be LARGE. (~ 5000 A/m2 at 1011 cm-3 or 162 A to an 8” wafer.)
- This current reduces as the electron density decreases.
Pulsed plasmas help in extracting negative ions.
- ne decreases quickly during the turn-off and late afterglow.
- As ne decreases, it becomes significantly easier to reverse the electric field direction and extract negative ions!