US Patent 12130556 Plasma position control for extreme ultraviolet lithography light sources

A method includes dispensing a droplet into a vacuum chamber; firing a pre-pulse laser to the droplet; sensing a first image of a return beam of the pre-pulse laser from the droplet; after firing the pre-pulse laser, firing a main-pulse laser to the droplet, wherein when the main-pulse laser hits the droplet, the droplet is vaporized into a plasma that emits extreme ultraviolet radiation; after sensing the first image and firing the main-pulse laser, sensing a second image of a return beam of the main-pulse laser from the droplet; and adjusting a plasma position in the vacuum chamber according to at least the second image.