Patent ID: 8648999

Claim:
An extreme ultraviolet light system comprising: a light source that produces an amplified light beam traveling along a propagation direction; a steering system that steers and focuses the amplified light beam to a focal plane near a target location; a target material delivery system that supplies a target material at the target location, an interaction between the target material and the focused amplified light beam consuming and converting the target material to a plasma that emits extreme ultraviolet radiation and producing a reflection of the amplified light beam; an extreme ultraviolet light chamber including an extreme ultraviolet light collector and the target material at the target location, the extreme ultraviolet light collector in the path of the extreme ultraviolet light that is produced when the target material is irradiated by the amplified light beam; a detection system including at least one detector positioned to detect an image of the amplified light beam that is reflected from at least a portion of the target material; a wavefront modification system in the path of the reflected amplified light beam and between the target location and the detection system and configured to modify the wavefront of the reflected amplified light beam as a function of a target focal plane position along the propagation direction; and a controller coupled to the detection system and to the steering system, the controller including logic for adjusting a location of the focal plane of the amplified light beam relative to the target material along the propagation direction based on the detected image of the reflected amplified light beam.