Technique for improving uniformity of a ribbon beam

1. An apparatus for improving uniformity of a ribbon beam having a plurality of beamlets, the apparatus comprising:

a first corrector-bar assembly having a first set of magnetic core members and a first plurality of coils distributed along the first set of magnetic core members; and

a second corrector-bar assembly having a second set of magnetic core members and a second plurality of coils distributed along the second set of magnetic core members,

wherein the second corrector-bar assembly is located at a predetermined distance from the first corrector-bar assembly;

wherein each of the first plurality of coils is individually excited to deflect at least one beamlet in the ribbon beam, thereby causing the plurality of beamlets to arrive at the second corrector-bar assembly in a desired spatial spread, and

wherein each of the second plurality of coils is individually excited to further deflect one or more beamlets in the ribbon beam, thereby causing the plurality of beamlets to exit the second corrector-bar assembly at desired angles.

2. The apparatus according to claim 1 , wherein the desired spatial spread of the plurality of beamlets at the second corrector-bar assembly is achieved to produce a uniform ion dose associated with the ribbon beam exiting the second corrector-bar assembly.

3. The apparatus according to claim 1 , wherein the desired angles of the plurality of beamlets are achieved for an angle uniformity associated with the ribbon beam exiting the second corrector-bar assembly.

4. The apparatus according to claim 1 , wherein the desired spatial spread of the plurality of beamlets at the second corrector-bar assembly is achieved to produce a non-uniform ion dose associated with the ribbon beam exiting the second corrector-bar assembly.

5. The apparatus according to claim 1 , wherein the desired angles of the plurality of beamlets are achieved to produce a spatially varying angle distribution associated with the ribbon beam exiting the second corrector-bar assembly.

6. The apparatus according to claim 1 , wherein the deflections introduced by each of the first corrector-bar assembly and the second corrector-bar assembly are linear.

7. The apparatus according to claim 1 , further comprising:

a controller that controls the individual excitations of the first plurality of coils and the second plurality of coils.

8. The apparatus according to claim 7 , further comprising:

one or more measurement devices that measure the ribbon beam.

9. The apparatus according to claim 8 , wherein the controller calibrates the first corrector-bar assembly and the second corrector-bar assembly by separately perturbing one or more of the first plurality of coils and the second plurality of coils and by aggregating corresponding changes in the ribbon beam.

10. The apparatus according to claim 7 , wherein the controller causes at least one coil to be excited at a sufficiently high frequency to produce a dithering motion in at least one of the plurality of beamlets.

11. A method for improving uniformity of a ribbon beam, the method comprising the steps of:

providing a first corrector-bar assembly having a first set of magnetic core members and a first plurality of coils distributed along the first set of magnetic core members;

providing a second corrector-bar assembly having a second set of magnetic core members and a second plurality of coils distributed along the second set of magnetic core members, wherein the second corrector-bar assembly is located at a predetermined distance from the first corrector-bar assembly;

passing the ribbon beam through the first corrector-bar assembly;

exciting one or more of the first plurality of coils individually to deflect at least one beamlet in the ribbon beam, thereby causing the plurality of beamlets to arrive at the second corrector-bar assembly in a desired spatial spread; and

exciting one or more of the second plurality of coils individually to further deflect one or more beamlets in the ribbon beam, thereby causing the plurality of beamlets to exit the second corrector-bar assembly at desired angles.

12. The method according to claim 11 , further comprising:

exciting at least one coil with a sufficiently high frequency to produce a dithering motion in at least one beamlet.

13. The method according to claim 11 , wherein a current frequency in at least one of the first plurality of coils and the second plurality of coils is adjusted to control a local beamlet angle distribution.

14. The method according to claim 11 , further comprising:

introducing a plurality of perturbations in one or more coils;

measuring changes in the ribbon beam in response to the plurality of perturbations, each change corresponding to one perturbation;

establishing a computation model by aggregating the measured changes; and

selecting settings for the first plurality of coils and the second plurality of coils by evaluating one or more merit functions calculated based on the computation model.

15. At least one signal embodied in at least one carrier wave for transmitting a computer program of instructions configured to be readable by at least one processor for instructing the at least one processor to execute a computer process for performing the method as recited in claim 11 .

16. At least one processor readable carrier for storing a computer program of instructions configured to be readable by at least one processor for instructing the at least one processor to execute a computer process for performing the method as recited in claim 11 .

17. A method for improving uniformity of a ribbon beam, the method comprising the steps of:

providing one or more tuning elements near a path of a ribbon beam;

introducing a plurality of perturbations in the one or more tuning elements;

measuring changes in the ribbon beam in response to the plurality of perturbations, each change corresponding to one perturbation;

establishing a computation model by aggregating the measured changes; and

selecting settings for the one or more tuning elements by evaluating one or more merit functions calculated based on the computation model.

18. The method according to claim 17 , wherein the settings for the one or more tuning elements are selected to produce a desired ion dose or angle distribution.

19. The method according to claim 18 , wherein the desired ion dose or angle distribution is selected from a group consisting of: a uniform distribution pattern, a non-uniform distribution pattern, and a configurable distribution pattern.

20. The method according to claim 17 , wherein the one or more tuning elements are selected from a group consisting of: corrector-bar assemblies, multipoles, dipoles, coils, and magnetic rods.