# US 2014/0191132 A1 · Method of Timing Laser Beam Pulses to Regulate Extreme Ultraviolet Light Dosing > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0191132 A1 - Document ID: US20140191132A1 - Status: Published application - Kind: A1 - Application number: 13/738,918 - Filed: 2013-01-10 - Published: 2014-07-10 - Earliest claimed: 2013-01-10 - Assignees: Cymer, Inc. - Applicants: Cymer, Inc. - Inventors: Alexander Schafgans; James Crouch; Matthew R. Graham; Steven Chang; Paul Frihauf; Andrew Liu; Wayne Dunstan - Web page: https://patentgrep.com/patent/US20140191132A1 ## CPC - G21K 5/00: Irradiation devices (discharge tubes for irradiating H01J37/00) - H05G 2/0084: {Control of the laser beam} - G21K: HANDLING OF PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES - H05G: X-RAY TECHNIQUE (investigating or analysing materials by the use of X-rays G01N23/00; apparatus for X-ray photography G03B42/02; X-ray tubes H01J35/00; TV systems having X-ray input H04N5/321) ## Abstract 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. ## Claims ### Claim 1 A method of regulating a dose of energy produced during stroboscopic firing of an EUV light source configured to generate an energy dose target within one or more packet comprising: (a) setting by a laser controller a dose servo value for a current packet; (b) timing by the laser controller a trigger to pulse a laser beam to irradiate a droplet during the current packet; (c) sensing EUV energy generated by irradiation of the droplet; (d) accumulating by the laser controller the sensed EUV energy with EUV energy generated by irradiation of one or more preceding droplet during the current packet; (e) repeating steps (b), (c), and (d) when the accumulated EUV energy within the current packet is less than an adjusted dose target based on the energy dose target and an accumulated dose error; and (f) mistiming by the laser controller the trigger to pulse the laser beam to not irradiate another droplet during the current packet. ### Claim 2 (depends on 1) The method of claim 1 wherein the dose servo value is equal to 0. ### Claim 3 (depends on 1) The method of claim 1 wherein the dose servo value is not equal to 0. ### Claim 4 (depends on 1) The method of claim 1 wherein the adjusted dose target is equal to the dose target plus the dose servo value. ### Claim 5 (depends on 1) The method of claim 1 further comprising: (g) calculating by the laser controller a dose error for the current packet; (h) accumulating by the laser controller the dose error for the current packet with a dose error for one or more preceding packet; (i) calculating by the laser controller a new adjusted dose target for a next packet based on the energy dose target and the accumulated dose error; and (j) calculating by the laser controller a new dose servo value for the next packet. ### Claim 6 (depends on 5) The method of claim 5 wherein the dose error for the current packet is equal to the dose target for the current packet minus the accumulated EUV energy for the current packet. ### Claim 7 (depends on 5) The method of claim 5 wherein the accumulated dose error comprises the dose error for the current packet and the dose error for one or more preceding packet. ### Claim 8 (depends on 5) The method of claim 5 further comprising repeating steps (a)-(j) for the next packet wherein the adjusted dose target for the next packet is the new adjusted dose target. ### Claim 9 (depends on 5) The method of claim 5 further comprising repeating steps (a)-(j) for the next packet wherein the dose servo value for the next packet is the new dose servo value. ### Claim 10 (depends on 9) The method of claim 9 wherein the new dose servo value is equal to the dose error for the current packet multiplied by a gain. ### Claim 11 A system for regulating a dose of energy produced during stroboscopic burst-firing of an EUV light source configured to generate an energy dose target within one or more packet comprising: a drive laser configured to pulse a laser beam when a trigger is received; a sensor configured to sense EUV energy generated by irradiation of a droplet; and a controller configured to: (a) set a dose servo value for a current packet; (b) time the trigger to pulse the laser beam to irradiate a droplet during the current packet; (c) accumulate sensed EUV energy generated by irradiation of the droplet with EUV energy generated by irradiation of one or more preceding droplet during the current packet; (d) repeat steps (b) and (c) when the accumulated EUV energy within the current packet is less than an adjusted dose target based on the energy dose target and an accumulated dose error; and (e) mistime the trigger to pulse the laser beam to not irradiate another droplet during the current packet. ### Claim 12 (depends on 11) The system of claim 11 wherein the dose servo value is equal to 0. ### Claim 13 (depends on 11) The system of claim 11 wherein the dose servo value is not equal to 0. ### Claim 14 (depends on 11) The system of claim 11 wherein the adjusted dose target is equal to the dose target plus the dose servo value. ### Claim 15 (depends on 11) The system of claim 11 wherein the controller is further configured to: (f) calculate a dose error for the current packet; (g) accumulate the dose error for the current packet with a dose error for one or more preceding packet; (h) calculate a new adjusted dose target for a next packet based on the energy dose target and the accumulated dose error; and (i) calculate a new dose servo value for the next packet. ### Claim 16 (depends on 15) The system of claim 15 wherein the dose error for the current packet is equal to the dose target for the current packet minus the accumulated EUV energy for the current packet. ### Claim 17 (depends on 15) The system of claim 15 wherein the accumulated dose error comprises the dose error for the current packet and the dose error for one or more preceding packet. ### Claim 18 (depends on 15) The system of claim 15 further comprising repeating steps (a)-(i) for the next packet wherein the adjusted dose target for the next packet is the new adjusted dose target. ### Claim 19 (depends on 15) The system of claim 15 further comprising repeating steps (a)-(i) for the next packet wherein the dose servo value for the next packet is the new dose servo value. ### Claim 20 (depends on 19) The system of claim 19 wherein the new dose servo value is equal to the dose error for the current packet multiplied by a gain.