Patent Number: 
Section: claims

1. An apparatus for reducing contamination during ion implantation, the apparatus comprising:a platen to hold a workpiece for ion implantation by an ion beam;a mask, located in front of the platen and downstream from a corrector magnet, to block the ion beam and at least a portion of contamination ions having a charge state different than a desired charge state from reaching a first portion of the workpiece during ion implantation of a second portion of the workpiece, wherein a position of the mask relative to the ion beam is chosen based on a likelihood of impact by the contamination ions; anda control mechanism, coupled to the platen, to reposition the workpiece to expose the first portion of the workpiece for ion implantation. 2. The apparatus according to claim 1, wherein the second portion comprises the remaining portion of the workpiece. 3. The apparatus according to claim 1, wherein the first portion comprises one half of the workpiece, and wherein the second portion comprises the other half of the workpiece. 4. The apparatus according to claim 3, wherein the mask has a semi-circular shape. 5. The apparatus according to claim 1, wherein the position of the mask remains in a fixed relative position with respect to the ion beam during the ion implantation of the first portion and the second portion of the workpiece. 6. The apparatus according to claim 1, wherein the mask is made from one or more materials selected from a group consisting of: silicon, carbon, and silicon carbide. 7. The apparatus according to claim 1, wherein the control mechanism repositions the workpiece by rotating the workpiece by a predetermined angle. 8. The apparatus according to claim 1, wherein the ion implantation on the first portion of the workpiece is based on a recipe different from the ion implantation on the second portion of the workpiece. 9. The apparatus according to claim 1, wherein the ion beam is a ribbon beam, and wherein the ion implantation of the first portion and the second portion of the workpiece is performed by translating the workpiece and the mask relative to the ribbon beam. 10. A method for reducing contamination during ion implantation, the method comprising the steps of:positioning a mask in front of a workpiece and downstream from a corrector magnet to block an ion beam and at least a portion of contamination ions having a charge state different than a desired charge state from reaching a first portion of the workpiece during ion implantation of a second portion of the workpiece, wherein a position of the mask relative to the ion beam is chosen based on a likelihood of impact by the contamination ions; andrepositioning the workpiece, after the ion implantation of the second portion, to expose the first portion of the workpiece for ion implantation. 11. The method according to claim 10, wherein the position of the mask remains in a fixed relative position with respect to the ion beam during the ion implantation of the first portion and the second portion of the workpiece. 12. The method according to claim 10, wherein the second portion comprises remaining portion of the workpiece. 13. The method according to claim 10, wherein the first portion comprises one half of the workpiece, and wherein the second portion comprises the other half of the workpiece. 14. The method according to claim 13, wherein the mask has a semi-circular shape. 15. The method according to claim 13, wherein the mask has a rectangular shape. 16. The method according to claim 10, wherein the step of repositioning the workpiece comprises a step of rotating the workpiece by a predetermined angle. 17. The method according to claim 10, wherein the ion implantation on the first portion of the workpiece is based on a recipe different from the ion implantation on the second portion of the workpiece. 18. The method according to claim 10, wherein the ion beam is a ribbon beam, and wherein the ion implantation of the first portion and the second of the workpiece is performed by translating the workpiece and the mask relative to the ribbon beam. 19. The apparatus according to claim 1, wherein the charge state is a singly charged state and the desired charge state is a doubly charged state. 20. The method according to claim 10, wherein the charge state is a singly charged state and the desired charge state is a doubly charged state.