Method of Timing Laser Beam Pulses to Regulate Extreme Ultraviolet Light Dosing

摘要

Described herein are embodiments of a method to control energy dose output from a laser-produced plasma extreme ultraviolet light system by adjusting timing of fired laser beam pulses. During stroboscopic firing, pulses are timed to lase droplets until a dose target of EUV has been achieved. Once accumulated EUV reaches the dose target, pulses are timed so as to not lase droplets during the remainder of the packet, and thereby prevent additional EUV light generation during those portions of the packet. In a continuous burst mode, pulses are timed to irradiate droplets until accumulated burst error meets or exceeds a threshold burst error. If accumulated burst error meets or exceeds the threshold burst error, a next pulse is timed to not irradiate a next droplet. Thus, the embodiments described herein manipulate pulse timing to obtain a constant desired dose target that can more precisely match downstream dosing requirements.

主权项

1. A method of regulating a dose of energy produced during continuous burst mode of an EUV light source comprising:
(a) beginning a burst having a predetermined energy dose target; (b) timing by the laser controller a trigger to pulse a laser beam to irradiate a droplet during the burst; (c) sensing EUV energy generated by the droplet; (d) calculating by the laser controller a current dose error for the droplet based on the sensed EUV energy and the energy dose target; (e) accumulating by the laser controller a burst error based on the current dose error and a running burst error calculated for one or more preceding droplet during the burst; (f) repeating steps (b)-(e) for a next droplet when the burst is not finished and the accumulated burst error does not meet or exceed a threshold burst error; (g) mistiming by the laser controller the trigger to pulse the laser beam to not irradiate the next droplet when the burst is not finished and the accumulated burst error meets or exceeds the threshold burst error; and (h) repeating steps (c)-(g) until the burst is finished.