# US 10,502,623 B2 · Line-narrowed KrF excimer laser apparatus > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,502,623 B2 - Document ID: US10502623B2 - Status: Granted - Kind: B2 - Application number: 16/210,097 - Filed: 2018-12-05 - Published: 2019-04-11 - Granted: 2019-12-10 - Earliest claimed: 2016-07-22 - Assignees: Gigaphoton Inc. - Applicants: Gigaphoton Inc. - Inventors: Masato Moriya - Web page: https://patentgrep.com/patent/US10502623B2 ## CPC - G01J 3/26: using multiple reflection, e.g. Fabry-Perot interferometer, variable interference filters - G01J 3/0205: {Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows} - H01J 61/20: mercury vapour - H01J 61/24: Means for obtaining or maintaining the desired pressure within the vessel - H01J 61/28: Means for producing, introducing, or replenishing gas or vapour during operation of the lamp - H01J 61/72: having a main light-emitting filling of easily vaporisable metal vapour, e.g. mercury - H01S 3/1305: {Feedback control systems} - H01S 3/137: for stabilising of frequency - H01S 3/139: by controlling the mutual position or the reflecting properties of the reflectors of the cavity {, e.g. by controlling the cavity length} - H01S 3/225: comprising an excimer or exciplex - H01S 3/2256: {KrF, i.e. krypton fluoride is comprised for lasing around 248 nm} - H01S 3/08009: {using a diffraction grating} - G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N) - H01J: ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS (spark-gaps H01T; electric arc lamps H05B31/00; particle accelerators H05H) - H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL ## Abstract A line-narrowed KrF excimer laser apparatus includes a laser chamber, a line narrow optical system, an actuator, an output coupling mirror, a wavelength detecting unit, and a wavelength controller. The actuator is capable of changing a wavelength of light selected by the line narrow optical system. The wavelength detecting unit includes a low-pressure mercury lamp accommodating mercury, a getter material that adsorbs at least a part of the mercury, and a hot cathode that excites at least a part of the mercury, an etalon provided at a position where reference light emitted from the low-pressure mercury lamp and detected light emitted from the output coupling mirror are incident on the etalon, and a light intensity distribution sensor configured to detect an intensity distribution profile of interference fringes of the reference light and an intensity distribution profile of interference fringes of the detected light. ## Claims ### Claim 1 A line-narrowed KrF excimer laser apparatus comprising: a laser chamber including a first window and a second window, the laser chamber accommodating a pair of discharge electrodes and configured to seal a laser gas including krypton gas and fluorine gas; a line narrow optical system provided in an optical path of light emitted from the first window; an actuator capable of changing a wavelength of light selected by the line narrow optical system; an output coupling mirror constituting an optical resonator with the line narrow optical system, the output coupling mirror being provided in an optical path of light emitted from the second window and configured to emit a part of the light emitted from the second window; a wavelength detecting unit including a low-pressure mercury lamp accommodating mercury, a getter material that adsorbs at least a part of the mercury, and a hot cathode that excites at least a part of the mercury, an etalon provided at a position where reference light emitted from the low-pressure mercury lamp and detected light emitted from the output coupling mirror are incident on the etalon, and a light intensity distribution sensor configured to detect an intensity distribution profile of interference fringes of the reference light and an intensity distribution profile of interference fringes of the detected light; and a wavelength controller configured to perform calculating a cumulative profile by accumulating the intensity distribution profile of the interference fringes of the reference light and calculating a wavelength of the detected light based on the cumulative profile and the intensity distribution profile of the interference fringes of the detected light, and controlling the actuator based on results of calculation of the wavelength of the detected light. ### Claim 2 (depends on 1) The line-narrowed KrF excimer laser apparatus according to claim 1, wherein the wavelength controller accumulates the intensity distribution profile of the interference fringes of the reference light for a time period of at least a part of a predetermined period from time at which the low-pressure mercury lamp starts emitting the reference light. ### Claim 3 (depends on 1) The line-narrowed KrF excimer laser apparatus according to claim 1, wherein the wavelength detecting unit detects the intensity distribution profile of the interference fringes of the reference light more than once, and the wavelength controller accumulates the intensity distribution profile of the interference fringes of the reference light by adding the intensity distribution profile of the interference fringes of the reference light more than once. ### Claim 4 (depends on 1) The line-narrowed KrF excimer laser apparatus according to claim 1, wherein a time period from time at which the low-pressure mercury lamp starts emitting the reference light to time of starting decrease in a quantity of light of the reference light emitted from the low-pressure mercury lamp is 5 seconds or more and 60 seconds or less. ### Claim 5 (depends on 1) The line-narrowed KrF excimer laser apparatus according to claim 1, wherein a time period from time at which the low-pressure mercury lamp starts emitting the reference light to time of an occurrence of a depression in the intensity distribution profile of the interference fringes detected by the light intensity distribution sensor is 10 seconds or more and 30 seconds or less. ### Claim 6 (depends on 1) The line-narrowed KrF excimer laser apparatus according to claim 1, wherein the low-pressure mercury lamp has a characteristic of mercury vapor pressure to temperature including a local maximum value of 0.8 Pa or higher and 1.2 Pa or lower and a local minimum value of 0.6 Pa or higher and 1.0 Pa or lower. ### Claim 7 (depends on 1) The line-narrowed KrF excimer laser apparatus according to claim 1, wherein the getter material is provided in a position shifted from an approximate center of the low-pressure mercury lamp in a direction opposite to a traveling direction of the reference light traveling toward the etalon from the approximate center. ### Claim 8 (depends on 1) The line-narrowed KrF excimer laser apparatus according to claim 1, wherein the getter material is provided in a position where a shortest distance from the hot cathode is 2 mm or more and 6 mm or less. ### Claim 9 (depends on 1) The line-narrowed KrF excimer laser apparatus according to claim 1, wherein the getter material includes an alloy of indium, silver, and mercury. ### Claim 10 (depends on 1) The line-narrowed KrF excimer laser apparatus according to claim 1, wherein the mercury accommodated in the low-pressure mercury lamp includes one isotope at 49% or higher. ### Claim 11 A line-narrowed KrF excimer laser apparatus comprising: a laser chamber including a first window and a second window, the laser chamber accommodating a pair of discharge electrodes and configured to seal a laser gas including krypton gas and fluorine gas; a line narrow optical system provided in an optical path of light emitted from the first window; an actuator capable of changing a wavelength of light selected by the line narrow optical system; an output coupling mirror constituting an optical resonator with the line narrow optical system, the output coupling mirror being provided in an optical path of light emitted from the second window and configured to emit a part of the light emitted from the second window; a wavelength detecting unit including a low-pressure mercury lamp accommodating mercury, a getter material that adsorbs at least a part of the mercury, and a hot cathode that excites at least a part of the mercury, an etalon provided at a position where reference light emitted from the low-pressure mercury lamp and detected light emitted from the output coupling mirror are incident on the etalon, and a light intensity distribution sensor configured to detect an intensity distribution profile of interference fringes of the detected light and an integrated profile obtained by integrating an intensity distribution profile of interference fringes of the reference light for a predetermined period from time at which the low-pressure mercury lamp starts emitting the reference light; and a wavelength controller configured to perform calculating a wavelength of the detected light based on the integrated profile and the intensity distribution profile of the interference fringes of the detected light, and controlling the actuator based on results of calculation of the wavelength of the detected light. ### Claim 12 (depends on 11) The line-narrowed KrF excimer laser apparatus according to claim 11, wherein the low-pressure mercury lamp starts emitting the reference light after the light intensity distribution sensor starts exposure. ### Claim 13 (depends on 11) The line-narrowed KrF excimer laser apparatus according to claim 11, wherein the predetermined period is 5 seconds or more and 30 seconds or less. ### Claim 14 (depends on 11) The line-narrowed KrF excimer laser apparatus according to claim 11, wherein a time period from the time at which the low-pressure mercury lamp starts emitting the reference light to time of starting decrease in a quantity of light of the reference light emitted from the low-pressure mercury lamp is 5 seconds or more and 60 seconds or less. ### Claim 15 (depends on 11) The line-narrowed KrF excimer laser apparatus according to claim 11, wherein a time period from the time at which the low-pressure mercury lamp starts emitting the reference light to time of an occurrence of a depression in the intensity distribution profile of the interference fringes detected by the light intensity distribution sensor is 10 seconds or more and 30 seconds or less. ### Claim 16 (depends on 11) The line-narrowed KrF excimer laser apparatus according to claim 11, wherein the low-pressure mercury lamp has a characteristic of mercury vapor pressure to temperature including a local maximum value of 0.8 Pa or higher and 1.2 Pa or lower and a local minimum value of 0.6 Pa or higher and 1.0 Pa or lower. ### Claim 17 (depends on 11) The line-narrowed KrF excimer laser apparatus according to claim 11, wherein the getter material is provided in a position shifted from an approximate center of the low-pressure mercury lamp in a direction opposite to a traveling direction of the reference light traveling toward the etalon from the approximate center. ### Claim 18 (depends on 11) The line-narrowed KrF excimer laser apparatus according to claim 11, wherein the getter material is provided in a position where a shortest distance from the hot cathode is 2 mm or more and 6 mm or less. ### Claim 19 (depends on 11) The line-narrowed KrF excimer laser apparatus according to claim 11, wherein the getter material includes an alloy of indium, silver, and mercury. ### Claim 20 (depends on 11) The line-narrowed KrF excimer laser apparatus according to claim 11, wherein the mercury accommodated in the low-pressure mercury lamp includes one isotope at 49% or higher.