# US 2014/0153596 A1 · Semiconductor Inspection And Metrology System Using Laser Pulse Multiplier > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0153596 A1 - Document ID: US20140153596A1 - Status: Published application - Kind: A1 - Application number: 13/711,593 - Filed: 2012-12-11 - Published: 2014-06-05 - Earliest claimed: 2012-12-05 - Assignees: KLA-Tencor Corporation - Applicants: Kla-Tencor Corporation - Inventors: Yung-Ho Alex Chuang; Justin Dianhuan Liou; J. Joseph Armstrong; Yujun Deng - Web page: https://patentgrep.com/patent/US20140153596A1 ## CPC - H01S 3/005: {Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping (shaping laser beam for working metal or other materials B23K26/06; optical elements, systems or apparatus in general G02B)} - C23C 16/00: Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes (reactive sputtering or vacuum evaporation C23C14/00) - G01N 21/8806: {Specially adapted optical and illumination features} - G02B 17/00: Systems with reflecting surfaces, with or without refracting elements - G02B 17/0848: {off-axis or unobscured systems in which not all of the mirrors share a common axis of rotational symmetry, e.g. at least one of the mirrors is warped, tilted or decentered with respect to the other elements} - G02B 27/00: Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 - G02B 27/108: {for sampling a portion of a beam or combining a small beam in a larger one, e.g. wherein the area ratio or power ratio of the divided beams significantly differs from unity, without spectral selectivity} - H01S 3/00: Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range (semiconductors lasers H01S5/00) - H01S 3/10: Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating - G01N 21/9501: {Semiconductor wafers (manufacturing processes per se of semiconductor devices implementing a measuring step H10P74/20)} - G01N 2021/8838: {Stroboscopic illumination; synchronised illumination} - 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 - C23C: COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL (making metal-coated products by extrusion B21C23/22; covering with metal by connecting pre-existing layers to articles, see the relevant places, e.g. B21D39/00, B23K; metallising of glass C03C; metallising mortars, concrete, artificial stone, ceramics or natural stone C04B41/00; enamelling of, or applying a vitreous layer to, metals C23D; treating metal surfaces or coating of metals by electrolysis or electrophoresis C25D; single-crystal film growth C30B; by metallising textiles D06M11/83; decorating textiles by locally metallising D06Q1/04) - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS ## Abstract A pulse multiplier includes a beam splitter and one or more mirrors. The beam splitter receives a series of input laser pulses and directs part of the energy of each pulse into a ring cavity. After circulating around the ring cavity, part of the pulse energy leaves the ring cavity through the beam splitter and part of the energy is recirculated. By selecting the ring cavity optical path length, the repetition rate of an output series of laser pulses can be made to be a multiple of the input repetition rate. The relative energies of the output pulses can be controlled by choosing the transmission and reflection coefficients of the beam splitter. This pulse multiplier can inexpensively reduce the peak power per pulse while increasing the number of pulses per second with minimal total power loss. ## Claims ### Claim 1 A pulse multiplier comprising: a beam splitter for receiving a laser pulse; and one or more mirrors forming a ring cavity including the beam splitter; wherein the beam splitter directs a first fraction of energy of the laser pulse as an output of the pulse multiplier, and directs a second fraction of the energy of the laser pulse into the ring cavity. ### Claim 2 (depends on 1) The pulse multiplier of claim 1, wherein the beam splitter further directs substantially the second fraction of the energy of the laser pulse out of the ring cavity after the laser pulse has traversed the ring cavity once, while directing substantially the first fraction of energy of that laser pulse back into the ring cavity. ### Claim 3 (depends on 1) The pulse multiplier of claim 1, wherein the first fraction is approximately one third. ### Claim 4 (depends on 1) The pulse multiplier of claim 1, wherein the second fraction is approximately two thirds. ### Claim 5 (depends on 1) The pulse multiplier of claim 1, wherein the first fraction and the second fraction are chosen so that substantially equal energy output pulses are generated from a regular repeating stream of laser pulses. ### Claim 6 (depends on 1) The pulse multiplier of claim 1, wherein each laser pulse is substantially refocused each time that the laser pulse traverses the ring cavity. ### Claim 7 (depends on 1) The pulse multiplier of claim 1, wherein the ring cavity further comprises a prism. ### Claim 8 (depends on 1) The pulse multiplier of claim 1, wherein said one or more mirrors comprise at least two curved mirrors. ### Claim 9 (depends on 8) The pulse multiplier of claim 8, wherein at least two of the mirrors have substantially similar radii of curvature. ### Claim 10 (depends on 1) The pulse multiplier of claim 1, wherein said one or more mirrors comprise four mirrors. ### Claim 11 (depends on 9) The pulse multiplier of claim 9, wherein the ring cavity comprises a Herriott cell or a White cell. ### Claim 12 (depends on 1) The pulse multiplier of claim 1, wherein the pulse multiplier is further configured to double a repetition rate of a substantially regular repeating stream of laser pulses by configuring the ring cavity to have an optical path length that is equivalent to approximately half of, or approximately an odd integer times half of, a time interval between successive laser pulses. ### Claim 13 (depends on 12) The pulse multiplier of claim 12, wherein the optical path length of the ring cavity is longer or shorter than the equivalent of the odd integer times half of the time interval between successive laser pulses by an amount that is approximately equal to half a width of a laser pulse. ### Claim 14 A pulse multiplier comprising: a first ring cavity including: a first beam splitter; a set of one or more mirrors; and a second ring cavity including: a second beam splitter; and a second set of one or more mirrors; wherein the first beam splitter directs a first fraction of each input laser pulse to the second beam splitter, and directs a second fraction of each input laser pulse into the first ring cavity, and wherein the second beam splitter directs a third fraction of each pulse incident on it to an output of the pulse multiplier, and directs a fourth fraction of energy of each pulse incident on it into the second ring cavity. ### Claim 15 (depends on 14) The pulse multiplier of claim 14, wherein the first beam splitter further directs substantially the second fraction of the energy of each pulse out of the first ring cavity to the second beam splitter after the pulse has traversed the first ring cavity once, while directing substantially the first fraction of the energy of that pulse back into the first ring cavity. ### Claim 16 (depends on 14) The pulse multiplier of claim 14, wherein the third fraction is substantially equal to the first fraction. ### Claim 17 (depends on 14) The pulse multiplier of claim 14, wherein the fourth fraction is substantially equal to the second fraction. ### Claim 18 (depends on 14) The pulse multiplier of claim 14, wherein an optical path length of the second ring cavity is approximately an odd integer times half an optical path length of the first ring cavity. ### Claim 19 A system comprising: a pulse multiplier including: a beam splitter for receiving a laser pulse; and a set of mirrors for creating a ring cavity including the beam splitter, wherein the beam splitter directs a first fraction of energy of the laser pulse as an output of the pulse multiplier, and directs a second fraction of the energy of the laser pulse into the ring cavity. ### Claim 20 (depends on 19) The system of claim 19, wherein the system implements one of an unpatterned wafer inspection system, a patterned wafer inspection system, a mask inspection system, and a metrology system. ### Claim 21 (depends on 20) The system of claim 20, wherein the system further comprises a detector configured to simultaneously detect two images or channels of data. ### Claim 22 (depends on 19) The system of claim 19, wherein the system further comprises an electro-optic modulator and/or dispersive element configured to reduce coherence of each laser pulse. ### Claim 23 A method of generating pulses for a system, the method comprising: generating a regular repeating series of laser pulses from a laser; optically splitting each laser pulse using a beam splitter and directing a first fraction of the laser pulse to an output and directing a second fraction of the laser pulse into a ring cavity comprising one or more mirrors; optically splitting each pulse after it has travelled around the ring cavity so that substantially the second fraction is directed to the output and substantially the first fraction is recirculated around the ring cavity; wherein an optical path length of the ring cavity is set so that a time for a pulse to travel once around the ring cavity is approximately equal to an odd integer times half a time interval between the laser pulses and wherein the first fraction and the second fraction are chosen so that output pulses are of approximately equal energy; and transmitting the output pulses to the system. ### Claim 24 (depends on 23) The method of claim 23, wherein each pulse is substantially refocused each time that it traverses the ring cavity. ### Claim 25 (depends on 23) The method of claim 23, wherein the ring cavity further comprises a prism. ### Claim 26 (depends on 23) The method of claim 23, wherein said one or more mirrors comprise at least two curved mirrors. ### Claim 27 (depends on 26) The method of claim 26, wherein at least two of the mirrors have substantially similar radii of curvature. ### Claim 28 (depends on 23) The method of claim 23, wherein said one or more mirrors comprise four mirrors. ### Claim 29 (depends on 27) The method of claim 27, wherein the ring cavity comprises a Herriott cell or a White cell. ### Claim 30 (depends on 23) The method of claim 23, wherein the method further comprises using a second ring cavity to double a repetition rate of the output of the ring cavity, thereby transmitting output pulses to the system at four times a repetition rate of the laser. ### Claim 31 (depends on 1) The pulse multiplier of claim 1, wherein the ring cavity is further characterized in that it does not contain a wave plate. ### Claim 32 (depends on 14) The pulse multiplier of claim 14, wherein at least one ring cavity is further characterized in that it does not contain a wave plate. ### Claim 33 (depends on 19) The system of claim 19, wherein the ring cavity is further characterized in that it does not contain a wave plate. ### Claim 34 (depends on 23) The method of claim 23, wherein the ring cavity is further characterized in that it does not contain a wave plate. ### Claim 35 (depends on 30) The method of claim 30, wherein at least one ring cavity is further characterized in that it does not contain a wave plate.