Ion sources and methods for generating an ion beam with controllable ion current density distribution

1. An ion source for a plasma processing apparatus, comprising:

a plasma discharge chamber configured to contain an ignited plasma therein;

an optical grid positioned proximate a first end of the plasma discharge chamber, the optical grid having a plurality of apertures configured such that ions from the plasma within the plasma discharge chamber pass through the apertures of the plurality

and bombard a substrate;

a re-entrant vessel positioned proximate to a second end of the plasma discharge chamber, the second end generally opposing the first end, the re-entrant chamber configured to shape the plasma within the plasma discharge chamber; and

a plasma shaper extending from the re-entrant vessel and into the plasma discharge chamber,

wherein a position of the plasma shaper relative to the optical grid is adjustable between a first position and a second position that is closer to the optical grid than the first position, the position of the plasma shaper being operable to change a plasma density distribution within the plasma discharge chamber.

2. The ion source of claim 1 , further comprising:

a radio frequency source for igniting and sustaining the plasma within the Plasma discharge chamber.

3. The ion source of claim 1 , further comprising:

one or more magnets positioned within the re-entrant vessel.

4. The ion source of claim 1 , further comprising:

An actuator configured to move the plasma shaper between the first and second positions.

5. The ion source of claim 4 , wherein the actuator comprises a bellows.

6. The ion source of claim 1 , wherein the plasma shaper includes a shaped head within the plasma discharge chamber.

7. The ion source of claim 6 , wherein a shape of the shaped head is rectangular, conical, reverse conical, or semispherical.

8. The ion source of claim 6 , wherein the shaped head is off-set with respect to a longitudinal axis of the plasma shaper.

9. The ion source of claim 1 , wherein the plasma shaper is operably coupled to the re-entrant vessel such that movement of the plasma shaper between the first and second position comprises moving the re-entrant vessel between respective first and second positions, the second position being closer to the optical grid than the first position.

10. The ion source of claim 1 , wherein the plasma shaper is moveable between the first and second position and with respect to the re-entrant vessel.

11. The ion source of claim 10 , wherein the first position of the plasma shaper is within the re-entrant vessel.

12. A plasma processing apparatus, comprising:

an evacuated chamber having opposing ends;

the ion source of claim 1 positioned within the evacuated chamber at one of the opposing ends; and

a substrate holder positioned within the evacuated chamber at the other opposing end and configured to support a substrate thereon.

13. A method of operating a radiofrequency ion source that includes a discharge chamber having a discharge space therein, the method comprising:

generating a plasma with a plasma density distribution from a working gas in the discharge space of the discharge chamber;

extracting an ion beam from the plasma with at least one electrode disposed at a first end of the discharge space; and

adjusting the plasma density distribution by moving a plasma shaper with respect to the at least one electrode.

14. The method of claim 13 , further comprising:

determining an actual distribution profile of a density of the ion beam proximate to a wafer processing location;

comparing the actual distribution profile of the ion beam density with a desired distribution profile for the ion beam density; and

based upon the comparison, moving the plasma shaper a selected distance.

15. The method of claim 13 , wherein the plasma shaper is moved between a first position and a second position that is closer to the at least one electrode than the first position.