System and method for controlling droplet timing and steering in an LPP EUV light source

摘要

A method and apparatus for improved control of the trajectory and timing of droplets of target material in a laser produced plasma (LPP) extreme ultraviolet (EUV) light system is disclosed. A droplet illumination module generates a laser curtain, and sensors detect the droplets as they pass through the curtain. One sensor in combination with a controller detects the position of the droplets relative to a desired trajectory to the irradiation site so that a signal can be sent to an actuator of a droplet generator to adjust orientation of the droplet generator and direct subsequent droplets to the irradiation site, as in the prior art. A second sensor, or droplet detection module, also detects each droplet as it passes through the curtain, and in combination with a controller determines when the source laser should generate a pulse so that the pulse will arrive at the irradiation site at the same time as the droplet, and sends a signal to the source laser to fire at the correct time.

主权项

1. A system for timing the firing of a source laser in an extreme ultraviolet laser produced plasma (EUV LPP) light source having a droplet generator which releases a droplet at a known speed, the source laser firing pulses at an irradiation site, comprising:
a droplet illumination module comprising a first line laser configured to generate a first laser curtain between the droplet generator and the irradiation site; a droplet detection module comprising a first sensor configured to detect a flash when the droplet passes through the first laser curtain; a first controller configured to:
determine, based upon the flash as detected by the first sensor, a known distance from the first curtain to the irradiation site, and the known speed of the droplet, a time when the source laser should fire a pulse so as to irradiate the droplet when the droplet reaches the irradiation site; andgenerate a timing signal instructing the source laser to fire at the determined time; a second sensor configured to detect the flash when the droplet passes through the first laser curtain; and a second controller configured to determine, based upon the flash as detected by the second sensor, that the droplet is not on a desired trajectory leading to the irradiation site and providing a signal indicating an adjustment to a direction in which the droplet generator releases a subsequent droplet which will place the subsequent droplet on the desired trajectory.