Light source for lithography exposure process

A method for generating light in a lithography exposure process, comprising:

• generating targets with a fuel target generator;
• detecting a flow velocity of the targets at a first detection position and a second detection position on a moving path;
• adjusting the flow velocity of the targets in response to the detected flow velocity when the detected flow velocity is different from a predetermined value;
• and
• irradiating at least one laser on the targets to generate plasma that emits light;
• wherein the targets supplied by the fuel target generator are separated by a droplet pitch, and a distance between the first detection position and the second detection position is smaller than the droplet pitch;
• wherein the operation of detecting the flow velocity of the targets comprises:
• projecting a first light curtain and a second light curtain at the first detection position and the second detection position, respectively, on a moving path;
• receiving light reflected from one of the targets when the one of the targets passes through the first detection position and the second detection position;
• measuring a time difference between a time when the light reflected from the target at the first detection position is detected and a time when the light reflected from the target at the second detection position is detected;
• and
• determining a flow velocity of the targets by dividing the distance between the first detection position and the second detection position by the measured time difference.

A light source for producing light in a lithography system, comprising:

• a fuel target generator configured to generate a plurality of targets along a moving path, wherein the fuel target generator includes a vessel and a nozzle;
• a monitoring device configured to measure a period of time during which one of the targets passes through two detection positions, wherein the monitoring device includes a transducer and a detector;
• a laser generator configured to generate at least one laser to allow a conversion of the targets into plasma;
• and
• a controller configured to adjust parameters of the fuel target generator and the laser generator according to the measured period of time, when the measured period of time is different from a predetermined value, wherein the parameter of the laser generator which is adjusted according to the measured period of time comprises a frequency for generating a laser for illuminating the targets.