Extreme ultraviolet light generation system utilizing a variation value formula for the intensity

An apparatus comprising:

• a chamber;
• a target supply for supplying a target material to a region inside the chamber;
• a focusing optical system for focusing a laser beam on the region, the laser beams including (1) a pre-pulse laser beam with which the target material is irradiated and (2) a main pulse laser beam with which the target material is irradiated subsequent to the pre-pulse laser beam;
• a laser apparatus configured to generate the pre-pulse laser beam having a pulse duration of less than 1 ns and to generate the main pulse laser beam;
• an intensity control optical system for controlling intensity distribution of the pre-pulse laser beam has a uniform intensity distribution region in a first cross-section with which the target material is irradiated, the uniform intensity distribution region in the first cross-section being perpendicular to a first traveling path of the pre-pulse laser beam, a variation value C={(Imax−Imin)/(Imax+Imin)}×100(%) being equal to or less than 20%, where Imax is the highest beam intensity in the uniform intensity distribution region and Imin is the lowest beam intensity in the uniform intensity distribution region;
• a first detector configured to detect that the target material reaches a predetermined position along the first traveling path;
• a laser trigger generator configured to, responsive to the detection of the first detector, generate a trigger signal to control generation of the pre-pulse laser beam and the main pulse laser beam;
• a second detector configured to detect a second traveling path of the target material;
• and
• a droplet controller configured to control the target supply to adjust the second traveling path when a deviation of the second traveling path is out of a permissible range, wherein:
• an area of the uniform intensity distribution region of the first cross-section the pre-pulse laser beam is larger than an area of the maximum cross section of the target material, the maximum cross section of the target material being perpendicular to the first traveling path of the pre-pulse laser beam, and
• the main pulse laser beam does not have a uniform intensity distribution region in a second cross-section with which the target material is irradiated, the uniform intensity distribution region in the second cross-section being perpendicular to a third traveling path of the main pulse laser beam.