# US 2014/0151583 A1 · Alignment of light source focus > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0151583 A1 - Document ID: US20140151583A1 - Status: Published application - Kind: A1 - Application number: 14/175,730 - Filed: 2014-02-07 - Published: 2014-06-05 - Earliest claimed: 2010-07-22 - Assignees: ASML Netherlands B.V. - Applicants: Cymer, LLC - Inventors: Matthew R. Graham; William N. Partlo; Steven Chang; Robert A. Bergstedt - Web page: https://patentgrep.com/patent/US20140151583A1 ## CPC - H05G 2/0086: {Optical arrangements for conveying the laser beam to the plasma generation location} - G01B 11/0608: {Height gauges} - G01B 11/26: for measuring angles or tapers; for testing the alignment of axes - H05G: X-RAY TECHNIQUE (investigating or analysing materials by the use of X-rays G01N23/00; apparatus for X-ray photography G03B42/02; X-ray tubes H01J35/00; TV systems having X-ray input H04N5/321) - G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS ## Abstract An extreme ultraviolet light system includes a steering system that steers and focuses an amplified light beam traveling along a propagation direction to a focal plane near a target location within an extreme ultraviolet light chamber, a detection system including at least one detector positioned to detect an image of a laser beam reflected from at least a portion of a target material within the chamber, a wavefront modification system in the path of the reflected laser beam and between the target location and the detection system, and a controller. The wavefront modification system is configured to modify the wavefront of the reflected laser beam as a function of a target focal plane position along the propagation direction. The controller includes logic for adjusting a location of the focal plane of the amplified light beam relative to the target material based on the detected image of the reflected laser beam. ## Claims ### Claim 1 (canceled) ### Claim 2 A method comprising: irradiating a target material with an amplified light beam that travels along a propagation direction, an interaction between the target material and the amplified light beam at least partially consuming and converting the target material to a plasma that emits extreme ultraviolet radiation and producing a reflection of the amplified light beam; modifying a wavefront of the reflection of the amplified light beam, the modification being a function of a location of a focal plane of the amplified light beam along the propagation direction; detecting an image of the modified reflected amplified light beam; and determining the location of the focal plane of the amplified light beam relative to the target material based on the detected image. ### Claim 3 (depends on 2) The method of claim 2, further comprising causing a light source to emit the amplified light beam toward the target material. ### Claim 4 (depends on 3) The method of claim 3, wherein causing the light source to emit the amplified light beam comprises causing the light source to emit a plurality of pulses, the plurality of pulses comprising a main pulse and at least one pre-pulse. ### Claim 5 (depends on 3) The method of claim 3, wherein causing the light source to emit the amplified light beam comprises causing the light source to emit a plurality of main pulses. ### Claim 6 (depends on 2) The method of claim 2, further comprising determining whether the focal plane of the amplified light beam overlaps the target material based on the determined location of the focal plane of the amplified light beam. ### Claim 7 (depends on 6) The method of claim 6, wherein determining whether the focal plane of the amplified light beam overlaps the target material comprises determining a distance between the focal plane of the amplified light beam and the target material along the direction of propagation. ### Claim 8 (depends on 7) The method of claim 7, further comprising: comparing the determined distance to a threshold that comprises a predetermined distance; determining whether the determined distance exceeds the threshold; adjusting the location of the focal plane when the determined distance exceeds the threshold; and irradiating the target material with the amplified light beam having the adjusted focal plane. ### Claim 9 (depends on 6) The method of claim 6, wherein determining whether the focal plane overlaps the target material comprises determining whether the target material is at the focal plane. ### Claim 10 (depends on 2) The method of claim 2, wherein modifying the wavefront includes introducing a separation along the propagation direction between focal planes each having a focus in a respective transverse direction relative to the propagation direction. ### Claim 11 (depends on 2) The method of claim 2, wherein modifying the wavefront includes modifying one or more of a curvature and a shape of a wavefront of the reflected laser beam. ### Claim 12 (depends on 2) The method of claim 2, wherein modifying the wavefront includes introducing an astigmatism in the wavefront of the reflected laser beam. ### Claim 13 (depends on 2) The method of claim 2, wherein determining the location of the focal plane includes fitting the detected image to a metric and determining a center of image intensity and an orientation of the detected image based on the metric. ### Claim 14 (depends on 13) The method of claim 13, wherein determining the location of the focal plane includes fitting the detected image to the metric and determining an ellipticity based on the metric. ### Claim 15 An extreme ultraviolet light system comprising: a target material delivery system that delivers a target material to a target location, the target material comprising a material that emits extreme ultraviolet light when converted to plasma; a light source configured to provide an amplified light beam, at least a portion of the amplified light beam being sufficient to convert the target material to plasma; a detection system comprising at least one detector positioned to detect an image of the amplified light beam reflected from at least a portion of the target material; a wavefront modification system in the path of the reflected amplified light beam, the wavefront modification system configured to modify the wavefront of the reflected amplified light beam as a function of a location of a focal plane of the amplified light beam along a propagation direction of the amplified light beam; and a controller coupled to the detection system and the steering system, the controller configured to: access an image of the reflected amplified light beam, and determine a location of the focal plane of the amplified light beam relative to the target location along the direction of propagation based on the image of the reflected amplified light beam. ### Claim 16 (depends on 15) The extreme ultraviolet light system of claim 15, wherein the light source is a light source that is configured to provide a main pulse and at least one pre-pulse. ### Claim 17 (depends on 15) The extreme ultraviolet light system of claim 15, wherein the wavefront modification system comprises a transmissive optical element. ### Claim 18 (depends on 15) The extreme ultraviolet light system of claim 15, wherein the wavefront modification system comprises an astigmatic optical element. ### Claim 19 (depends on 15) The extreme ultraviolet light system of claim 15, further comprising a steering system configured to direct and focus the amplified light beam to a focal plane near the target location. ### Claim 20 (depends on 19) The extreme ultraviolet light system of claim 19, wherein the focal plane is at the target location.