Patent Number: 
Section: claims

1. An extreme ultraviolet (EUV) radiation source, comprising:a fuel droplet generator configured to provide a plurality of fuel droplets to an EUV source vessel along a first trajectory;a primary laser configured to generate a primary laser beam along a second trajectory that intersects the first trajectory at a non-perpendicular angle, wherein the primary laser beam has a sufficient energy to ignite a plasma that emits extreme ultraviolet radiation from the plurality of fuel droplets; anda collector mirror located between the primary laser and the first trajectory and having a concave curvature configured to focus the extreme ultraviolet radiation to an exit aperture of the EUV source vessel that is not linearly aligned with the second trajectory of the primary laser beam. 2. The EUV radiation source of claim 1, further comprising:a protection element linearly aligned with the primary laser beam and configured to absorb remnants of the primary laser beam passing through the first trajectory of the plurality of fuel droplets. 3. The EUV radiation source of claim 2, wherein the protection element is located outside of a path of the EUV radiation focused by the collector mirror to the exit aperture. 4. The EUV radiation source of claim 2, wherein the collector mirror has an opening extending through the collector mirror at a location that is offset from a center of the collector mirror. 5. The EUV radiation source of claim 2, further comprising:a second fuel droplet generator configured to provide a second plurality of fuel droplets to the EUV source vessel along a third trajectory;a second primary laser configured to generate a second primary laser beam along a fourth trajectory that intersects the third trajectory at a second non-perpendicular angle; anda second protection element linearly aligned with the second primary laser beam on an opposite side of the second trajectory as the second primary laser. 6. The EUV radiation source of claim 5, wherein the second trajectory and the fourth trajectory are not parallel. 7. The EUV radiation source of claim 5, wherein the protection element and the second protection element are disposed onto opposite sides of the exit aperture of the EUV source vessel. 8. The EUV radiation source of claim 1, wherein the collector mirror is configured to focus the EUV radiation a downstream scanner comprising a plurality of mirrors configured to convey the extreme ultraviolet radiation to a semiconductor workpiece. 9. The EUV radiation source of claim 8, further comprising:an intermediate focus unit comprising a cone shaped aperture arranged within the exit aperture between the EUV source vessel and the scanner. 10. The EUV radiation source of claim 1, further comprising:a pre-pulse laser configured to generate a pre-pulse laser beam, having a lower energy than the primary laser beam, along a fifth trajectory that is not perpendicular to the first trajectory, wherein the pre-pulse laser is arranged so that the pre-pulse laser beam deforms the plurality of fuel droplets prior to the primary laser beam hitting the plurality of fuel droplets. 11. An EUV radiation source, comprising:a tin droplet generator configured to provide a plurality of tin droplets to an EUV source vessel along a first trajectory extending in a first direction;a collector mirror having a concave curvature and an opening that extends through the collector mirror at a location offset from a center of the collector mirror;a carbon dioxide (CO2) laser configured to generate a primary laser beam along a second trajectory extending through the opening in a second direction that is not perpendicular to the first direction; anda protection element linearly aligned with the primary laser beam and configured to absorb remnants of the primary laser beam passing through the first trajectory of the plurality of tin droplets. 12. The EUV radiation source of claim 11, wherein the protection element is located outside a path of the EUV radiation focused by the collector mirror to a focal point of the collector mirror. 13. The EUV radiation source of claim 11, further comprising:a second fuel droplet generator configured to provide a second plurality of tin droplets to the EUV source vessel along a third trajectory extending in a third direction;a second primary laser configured to generate a second primary laser beam along a fourth trajectory extending in a fourth direction that is not perpendicular to the third direction; anda second protection element linearly aligned with the second primary laser beam on an opposite side of the second trajectory as the second primary laser. 14. The EUV radiation source of claim 13, further comprising:an intermediate focus unit comprising a cone shaped aperture arranged within an exit aperture of the EUV source vessel at a location between the EUV source vessel and a downstream scanner. 15. The EUV radiation source of claim 14, wherein the protection element and the second protection element are disposed onto opposite sides of an exit aperture of the EUV source vessel. 16. The EUV radiation source of claim 11, further comprising:a pre-pulse laser configured to generate a pre-pulse laser beam, having a lower energy than the primary laser beam, along a fifth trajectory extending in a fifth direction that is not perpendicular to the first direction, wherein the pre-pulse laser is arranged so that the pre-pulse laser beam deforms the plurality of tin droplets prior to the primary laser beam hitting the plurality of tin droplets. 17. The EUV radiation source of claim 11, wherein the first direction and the second direction are separated by an obtuse angle. 18. A method of generating extreme ultraviolet (EUV) radiation, comprising:providing a plurality of fuel droplets along a first trajectory extending in a first direction; andstriking the fuel droplets with a primary laser beam following a second trajectory extending in a second direction and intersecting the first trajectory at a non-perpendicular angle, wherein the primary laser beam ignite a plasma that emits EUV radiation. 19. The method of claim 18, further comprising:focusing the EUV radiation at a focal point separated from the plasma along a third direction different than the second direction. 20. The method of claim 19, further comprising:providing a second plurality of tin droplets along a third trajectory extending in a third direction; andstriking the fuel droplets with a second primary laser beam along a fourth trajectory extending in a fourth direction that is not perpendicular to the third direction.