# US 7,411,686 B2 · Methods and apparatus for aligning an etalon with a photodiode array > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,411,686 B2 - Document ID: US7411686B2 - Status: Granted - Kind: B2 - Application number: 11/452,501 - Filed: 2006-06-14 - Published: 2007-12-20 - Granted: 2008-08-12 - Earliest claimed: 2006-06-14 - Assignees: Cymer, Inc. - Inventors: Robert J. Rafac - Web page: https://patentgrep.com/patent/US7411686B2 ## CPC - G01J 3/02: Details - G01J 3/027: {Control of working procedures of a spectrometer; Failure detection; Bandwidth calculation} - G01J 3/0289: {Field-of-view determination; Aiming or pointing of a spectrometer; Adjusting alignment; Encoding angular position; Size of measurement area; Position tracking} - G01J 3/26: using multiple reflection, e.g. Fabry-Perot interferometer, variable interference filters - 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) ## Abstract A method and apparatus are disclosed for measuring a characteristic, e.g. spectral bandwidth, of a light beam. The apparatus may comprise an etalon for generating an interference pattern having at least one light cone, an arrangement of detector elements, the arrangement receiving a portion of the light cone and producing a signal indicative of the characteristic; and an auxiliary detector positioned to receive a portion of the light cone and produce a signal indicative of an alignment between the etalon and the linear arrangement. ## Claims ### Claim 1 An apparatus for measuring a characteristic of a light beam, the apparatus comprising: an etalon for generating an interference pattern having at least one light cone, an arrangement of detector elements receiving a portion of the light cone and producing a signal indicative of the characteristic; and an auxiliary detector positioned to receive a portion of the light cone and produce a signal indicative of an alignment between the etalon and the arrangement of detector elements. ### Claim 2 (depends on 1) An apparatus as recited in claim 1 wherein the arrangement of detector elements comprises an array of photodiodes. ### Claim 3 (depends on 1) An apparatus as recited in claim 1 wherein the arrangement of detector elements comprises a linear array. ### Claim 4 (depends on 1) An apparatus as recited in claim 1 wherein the etalon is a Fabry Perot interferometer having a plano configuration. ### Claim 5 (depends on 1) An apparatus as recited in claim 1 wherein the auxiliary detector is a single photodiode. ### Claim 6 (depends on 1) An apparatus as recited in claim 1 wherein the characteristic is spectral bandwidth. ### Claim 7 A method for measuring an alignment of an etalon relative to an arrangement of detector elements, the method comprising the steps of: positioning an auxiliary detector at a known location; illuminating the etalon to generate a light cone; adjusting a wavelength of light illuminating the etalon to illuminate the auxiliary detector and at least two locations on the arrangement of detector elements; and using the positions of the two illuminated locations on the arrangement of detector elements and the position of the illuminated auxiliary detector to determine an alignment between the etalon and the arrangement of detector elements. ### Claim 8 (depends on 7) A method as recited in claim 7 wherein the arrangement of detector elements and the auxiliary detector are located in a plane and the using step comprises the sub-step of calculating a position of a light cone center in the plane. ### Claim 9 (depends on 7) A method as recited in claim 7 wherein the arrangement of detector elements comprises an array of photodiodes. ### Claim 10 (depends on 7) A method as recited in claim 7 wherein the arrangement of detector elements comprises a linear array. ### Claim 11 (depends on 7) A method as recited in claim 7 wherein the etalon is a Fabry Perot interferometer having a plano configuration. ### Claim 12 (depends on 7) A method as recited in claim 7 wherein the auxiliary detector is a single photodiode. ### Claim 13 (depends on 7) A method as recited in claim 7 wherein the step of adjusting a wavelength of light illuminating the etalon is accomplished by scanning the wavelength over a range of wavelengths. ### Claim 14 A method for testing whether an etalon remains in a pre-selected alignment relative to an arrangement of detector elements comprising the steps of: illuminating an auxiliary detector with a portion of a light cone generated by the etalon while the etalon and arrangement of detector elements are in the pre-selected alignment; determining the positions of at least two locations on the arrangement of detector elements that are illuminated simultaneously with the auxiliary detector; and thereafter testing whether the pre-selected alignment is still present by: illuminating the auxiliary detector with a portion of a light cone generated by the etalon; and comparing locations on the arrangement of detector elements that are illuminated simultaneously with the auxiliary detector to the locations found in the determining step. ### Claim 15 (depends on 14) A method as recited in claim 14 wherein the step of illuminating the auxiliary detector is accomplished by adjusting a wavelength of light incident upon the etalon. ### Claim 16 (depends on 14) A method as recited in claim 14 wherein the arrangement of detector elements and the auxiliary detector are located in a plane and the using step comprises the sub-step of calculating a position of a light cone center in the plane. ### Claim 17 (depends on 14) A method as recited in claim 14 wherein the arrangement of detector elements comprises an array of photodiodes. ### Claim 18 (depends on 14) A method as recited in claim 14 wherein the arrangement of detector elements comprises a linear array. ### Claim 19 (depends on 14) A method as recited in claim 14 wherein the etalon is a Fabry Perot interferometer having a plano configuration. ### Claim 20 (depends on 14) A method as recited in claim 14 wherein the auxiliary detector is a single photodiode.