System and method for controlling source laser firing in an LPP EUV light source

摘要

Methods and systems for improved timing of a source laser in a laser produced plasma (LPP) extreme ultraviolet (EUV) generation system are disclosed. Due to forces within the plasma chamber, a velocity of a droplet can slow as it approaches the irradiation site. Because the droplet is slowed, a source laser fires prematurely relative to the slowed droplet, resulting in only a leading portion of the droplet being irradiated. The resulting amount of EUV energy generated from the droplet is proportional to the slowed velocity of the droplet. To compensate, the firing of the source laser is delayed for a next droplet based on the generated EUV energy. Because the firing of the source laser is delayed for the next droplet, the next droplet is more likely to be in position to be more completely irradiated, resulting in more EUV energy being generated from the next droplet.

主权项

1. A method for modifying timing of firing a source laser in an extreme ultraviolet (EUV) laser produced plasma (LPP) light source having a droplet generator which releases a sequence of droplets, the source laser firing pulses at an irradiation site, the method comprising:
obtaining a first amount of EUV energy generated from a first pulse of the pulses that impacted a first droplet of the sequence of droplets; determining, from the detected first amount of EUV energy, an anticipated delay of a second droplet of the sequence of droplets reaching the irradiation site; and modifying timing of firing the source laser for a second pulse of the pulses based on the anticipated delay of the second droplet so as to irradiate the second droplet when the second droplet reaches the irradiation site.