System and Method for Creating and Utilizing Dual Laser Curtains From a Single Laser in an LPP EUV Light Source

A method for timing the firing of a source laser in an EUV LPP light source having a droplet generator which releases a droplet at an estimated speed, the source laser firing pulses at an irradiation site, comprising:

• generating from a single laser source a first laser curtain and a second laser curtain, the first and second laser curtains having polarizations orthogonal to each other and located between the droplet generator and the irradiation site;
• detecting by a first sensor a flash when the droplet passes through the first laser curtain;
• determining from the flash as detected by the first 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;
• detecting by a second sensor the flash when the droplet passes through the second laser curtain;
• and
• determining, based upon the flash as detected by the second sensor, a known distance from the first curtain to the irradiation site, and the estimated 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, and generating a timing signal instructing the source laser to fire at the determined time.

A non-transitory computer readable storage medium having embodied thereon instructions for causing a computing device to execute a method for timing the firing of a source laser in an EUV LPP light source having a droplet generator which releases a droplet at an estimated speed, the source laser firing pulses at an irradiation site, the method comprising:

• generating from a single laser source a first laser curtain and a second laser curtain, the first and second laser curtains having polarizations orthogonal to each other and located between the droplet generator and the irradiation site;
• detecting by a first sensor a flash when the droplet passes through the first laser curtain;
• determining from the flash as detected by the first 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;
• detecting by a second sensor the flash when the droplet passes through the second laser curtain;
• and
• determining, based upon the flash as detected by the second sensor, a known distance from the first curtain to the irradiation site, and the estimated 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, and generating a timing signal instructing the source laser to fire at the determined time.