Patent Number: 
Section: claims

1. A method comprising:directing a first amplified light beam toward a target material droplet, the first amplified light beam having an energy sufficient to form a collection of pieces of target material from the target material droplet, the pieces in the collection of pieces being spatially distributed throughout a volume that is shaped as part of a sphere and is larger than the target material droplet, the volume comprising a planar portion that extends from one edge of the volume to another and faces a direction of propagation of the second amplified light beam; anddirecting a second amplified light beam toward the collection of pieces to convert the pieces of target material to plasma that emits EUV light. 2. The method of claim 1, wherein a normal to the planar portion is parallel to the direction of propagation of the second amplified light beam. 3. The method of claim 1, wherein the volume comprises a rounded portion adjacent to the planar portion, the rounded portion extending along the direction of propagation. 4. The method of claim 3, wherein the second amplified light beam interacts with pieces of target material at the planar portion before interacting with pieces of target material that are in rounded portion. 5. The method of claim 1, wherein the planar portion forms at least part of an outer region of the volume. 6. The method of claim 1, wherein the pieces of target material are disbursed throughout the volume and on one or more surfaces of the volume. 7. The method of claim 1, wherein the planar portion and one or more sides of the volume comprise flat regions. 8. The method of claim 1, further comprising forming the target material droplet prior to directing the first amplified light beam. 9. The method of claim 1, wherein EUV light is emitted from the volume in all directions. 10. The method of claim 1, wherein EUV light is emitted from the volume isotropically. 11. The method of claim 1, wherein the target material droplet comprises a metal, and the collection of pieces comprises pieces of the metal, at least some of which do not make physical contact with another piece of the metal. 12. The method of claim 11, wherein the metal comprises tin. 13. The method of claim 1, whereinthe volume defines a longitudinal axis along a longitudinal direction that is parallel to a direction of propagation of the second amplified light beam and a transverse axis along a transverse direction that is transverse to the direction of propagation of the second amplified light beam,the transverse axis is the greatest extent of the volume along the transverse direction and the longitudinal axis is the greatest extent of the volume along the longitudinal direction and has an extent that is less than the transverse axis, anddirecting the second amplified light beam toward the collection of pieces comprises penetrating into the volume along the longitudinal axis. 14. The method of claim 1, wherein the first amplified light beam comprises a pulse of light having a duration of 150 ps and a wavelength of 1 μm. 15. The method of claim 1, wherein the first amplified light beam comprises a pulse of light having a duration of less than 150 ps and a wavelength of 1 μm. 16. The method of claim 1, wherein the first amplified light beam comprises two pulses of light. 17. The method of claim 16, wherein the two pulses of light are temporally separated from each other. 18. The method of claim 1, wherein a density of the pieces of target material increases along a direction that is parallel to a direction of propagation of the second amplified light beam. 19. A target for an extreme ultraviolet (EUV) light source, the target comprising:pieces of target material distributed throughout volume that is shaped as a portion of a sphere, the target material comprising a material that emits EUV light when converted to plasma, whereinthe volume shaped as a portion of a sphere comprises a planar portion that is adjacent to a round portion, the planar portion being positioned to face a source of an amplified light beam and extending from one edge of the rounded portion to another edge of the rounded portion, whereinthe rounded portion faces away from the source of the amplified light beam. 20. An extreme ultraviolet (EUV) light source comprising:a first source that produces a pulse of light;a second source that produces an amplified light beam;a target material delivery system;a chamber coupled to the target material delivery system; anda steering system that steers the amplified light beam toward a target location in the chamber that receives a target material droplet from the target material delivery system, the target material droplet comprising a material that emits EUV light when converted to plasma, whereinthe target material droplet forms a target when struck by the pulse of light, the target comprising a volume shape as a portion of a sphere and having pieces of the target material throughout the volume, and a planar portion that extends from one edge of the volume to another, the planar portion receiving the amplified light beam.