EP2351170A1 - Procédé et appareil pour commande laser dans un laser à décharge de gaz à deux chambres - Google Patents

Procédé et appareil pour commande laser dans un laser à décharge de gaz à deux chambres

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Publication number
EP2351170A1
EP2351170A1 EP09822307A EP09822307A EP2351170A1 EP 2351170 A1 EP2351170 A1 EP 2351170A1 EP 09822307 A EP09822307 A EP 09822307A EP 09822307 A EP09822307 A EP 09822307A EP 2351170 A1 EP2351170 A1 EP 2351170A1
Authority
EP
European Patent Office
Prior art keywords
energy
laser
control system
dose
voltage input
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP09822307A
Other languages
German (de)
English (en)
Other versions
EP2351170A4 (fr
Inventor
Robert N. Jacques
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Cymer LLC
Original Assignee
Cymer Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US12/255,385 external-priority patent/US7751453B2/en
Priority claimed from US12/255,367 external-priority patent/US7720120B2/en
Priority claimed from US12/255,347 external-priority patent/US7756171B2/en
Application filed by Cymer Inc filed Critical Cymer Inc
Publication of EP2351170A1 publication Critical patent/EP2351170A1/fr
Publication of EP2351170A4 publication Critical patent/EP2351170A4/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70008—Production of exposure light, i.e. light sources
    • G03F7/70025—Production of exposure light, i.e. light sources by lasers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/102—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling the active medium, e.g. by controlling the processes or apparatus for excitation
    • H01S3/104—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling the active medium, e.g. by controlling the processes or apparatus for excitation in gas lasers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/13—Stabilisation of laser output parameters, e.g. frequency or amplitude
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/005—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
    • H01S3/0057—Temporal shaping, e.g. pulse compression, frequency chirping
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/02—Constructional details
    • H01S3/03—Constructional details of gas laser discharge tubes
    • H01S3/034—Optical devices within, or forming part of, the tube, e.g. windows, mirrors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/23—Arrangements of two or more lasers not provided for in groups H01S3/02 - H01S3/22, e.g. tandem arrangements of separate active media
    • H01S3/2308—Amplifier arrangements, e.g. MOPA
    • H01S3/2325—Multi-pass amplifiers, e.g. regenerative amplifiers

Definitions

  • the disclosed subject matter is generally related to laser systems and, more particularly, is related to a laser control system for a two chamber gas discharge laser.
  • FIG. 1 is an illustration of a block diagram of a MOPA (Master Oscillator/Power Amplifier) laser system 10 as is known in the prior art.
  • the MOPA laser system 10 is used, for instance, in the area of integrated circuit lithography.
  • a 193 nm ultraviolet laser beam is provided at the input port of a lithography machine/scanner 2 such as stepper or scanner machines supplied by Canon or Nikon with facilities in Japan or ASML with facilities in the Netherlands.
  • the MOPA laser system 10 includes a laser energy control system 4 for controlling both pulse energy and accumulated dose energy output of the system at pulse repetition rates, for instance, of 4,000 Hz or greater.
  • the MOPA laser system 10 provides extremely accurate triggering of the discharges in the two laser chambers relative to each other with both feedback and feed-forward control of the pulse and dose energy.
  • the MOPA laser system 10 includes a beam delivery unit 6, which provides an enclosed beam path for delivering the laser beam to an input port of scanner 2.
  • the light source includes a seed laser generator, e.g., a master oscillator 11 and an amplifier laser portion, e.g., a power amplifier 12, described in more detail below, and which may also be an oscillator, e.g., a power ring oscillator ("PRA”), also described in more detail below.
  • PRA power ring oscillator
  • the seed laser may be referred to as an MO and the amplifier laser may be referred to as a power amplifier or simply a PA, with the intent to cover other forms of seed laser arrangements and amplifier laser arrangements, such as a power ring amplifier ("PRA”), which is in fact an oscillator, i.e., a power oscillator (“PO”), together forming a MOPO, and unless expressly stated otherwise these terms are meant to be so broadly defined.
  • PRA power ring amplifier
  • PO power oscillator
  • the light source also includes a pulse stretcher 22.
  • the master oscillator 11 and the power amplifier/power oscillator 12 each include a discharge chamber 11A, 12A similar to the discharge chamber of single chamber lithography laser systems.
  • These chambers 11 A, 12A contain two electrodes, a laser gas, a tangential for circulating the gas between the electrodes and water-cooled finned heat exchangers.
  • the master oscillator 11 produces a first laser beam 14A which is amplified, in a PA configuration by two passes through the power amplifier 12, or in the case of a PO/PRA configuration, by oscillation in the PO/PRA, to produce a second laser beam 14B as shown in FIG. 1.
  • the master oscillator 11 includes a resonant cavity formed by an output coupler 11 C and a line narrowing package 11 B.
  • the gain medium for the master oscillator 11 is produced between two elongated electrodes contained within the master oscillator discharge chamber 11A.
  • the power amplifier 12 is basically a discharge chamber 12A and in this preferred embodiment is almost exactly the same as the master oscillator discharge chamber 11 A providing a gain medium between two electrodes, but the power amplifier 12 may have no resonant cavity, unlike a PO/PRA.
  • This MOPA laser system 10 configuration permits the master oscillator 11 to be designed and operated to maximize beam quality parameters such as wavelength stability and very narrow bandwidth; whereas the power amplifier 12 is designed and operated to maximize power output. For this reason the MOPA laser system 10 represents a much higher quality and much higher power laser light source than single chamber systems.
  • the amplifier portion may be configured, e.g., for two beam passages through the discharge region of the amplifier discharge chamber, or for oscillation in the cavity containing the amplifier discharge chamber, as shown in FIG. 1.
  • the beam oscillates within the cavity containing the master oscillation chamber 11 A between LNP 11 B and output coupler 11C (with 30 percent reflectance) of the MO 11 and is severely line narrowed on its passages through LNP 1OC.
  • a wavelength of a laser beam emitted from the output coupler 11C is measured by a line center analysis module 7.
  • the line narrowed seed beam is reflected downward by a mirror in the MO wavelength engineering box (MO WEB) 24 and reflected horizontally at an angle slightly skewed (with respect to the electrodes orientation) through the PA wavelength engineering box (PA WEB) 26 to the amplifier chamber 12.
  • a beam reverser 28 reflects the beam back for a second pass through PA chamber 12, or for oscillation in the PO/PRA chamber, horizontally in line with the electrodes orientation.
  • a bandwidth of a laser emitted from the discharge chamber 12A is measured by a spectral analysis module 9, although the bandwidth of the laser may instead be measured by a bandwidth analysis module.
  • the laser system output beam pulses 14B pass from the PA/PO chamber 12A to a beam splitter 16.
  • the beam splitter 16 reflects about 60 percent of the power amplifier output beam 14B into a delay path created by four focusing mirrors 2OA, 20B 1 2OC and 2OD.
  • the 40 percent transmitted portion of each pulse of beam 14B becomes a first hump of a corresponding stretched pulse of an output beam pulse 14C.
  • the output beam 14C is directed by beam splitter 16 to mirror 2OA which focuses the reflected portion to point 22.
  • the beam then expands and is reflected from mirror 2OB which converts the expanding beam into a parallel beam and directs it to mirror 2OC which again focuses the beam again at point 22.
  • a beam delivery unit delivers the output beam 14C.
  • the BDU may include two beam-pointing mirrors 4OA, 4OB one or both of which may be controlled to provide tip and tilt correction for variations beam pointing.
  • FIG. 2 is an illustration of an energy control block diagram 50 for the MOPA/MOPO Laser System of FIG. 1 , in accordance with the prior art.
  • FIG. 2 illustrates various control elements that control a voltage supply 52 to the MOPA laser system 10.
  • the energy control block diagram 50 includes a static control 54, which provides a basically determined voltage anticipated to achieve an energy target 56 (if there are no other influences for which account need be made).
  • a feed forward block 58 provides a voltage adjustment based on a trigger interval 60. Trigger interval 60 is used to compute repetition rate, shot number and duty cycle, which impact the 'voltage input - energy output' relationship. The voltage adjustment is computed as a function of these values.
  • An energy servo 62 adjusts the voltage input 52 based on a calculated voltage error 64 of the previous shot.
  • a dither cancellation 66 adjusts voltage to cancel energy changes caused by a timing dither 68.
  • an energy dither 70 provides a periodic signal added to the voltage input 52 used to estimate the effects of voltage on MO energy, output energy, and MOPA timing. These five voltage signals are added together to generate the voltage input 52.
  • the energy 72 is measured.
  • the energy target is subtracted from the measured energy 72 to create an energy error signal 74, which is scaled by dV/dE, the laser estimate 76 of the derivative of voltage with respect to energy.
  • the resulting voltage error 64 is used to drive adaptation algorithms 78 which adjust some of the voltage signals in a way that minimizes either energy errors, dose errors, energy sigma, or some combination thereof.
  • the MOPA laser system 10 shown in FIG. 1 is an improvement on the single chamber systems, providing greater beam control, beam power, and stability than the single chamber systems. However, resolving tonal disturbances and further sharpening timing and energy control of the system can significantly improve operation.
  • aspects of embodiments of the disclosed subject matter provide a system and method for controlling a laser system. Briefly described, in architecture, aspects of one possible embodiment of the system, among others, can be implemented as follows.
  • the system contains an oscillator gas chamber and an amplifier gas chamber.
  • a first voltage input is operatively connected to deliver electrical pulses to a first pair of electrodes within the oscillator gas chamber and a second pair of electrodes within the amplifier gas chamber.
  • An output of the gas chambers is an energy dose calculated by a trapezoidal window.
  • a control circuit connects to the first voltage input for modifying the first voltage input.
  • a feedback control loop communicates an output of the gas chambers to the control circuit for modifying the first voltage input.
  • aspects of the disclosed subject matter can also be viewed as providing methods for controlling a laser system.
  • one embodiment of such a method can be broadly summarized by the following steps: delivering a first voltage input operatively in the form of electrical pulses to a first pair of electrodes within a oscillator gas chamber and a second pair of electrodes within a amplifier gas chamber; calculating an energy dose of an output of the gas chambers with a trapezoidal window; modifying the first voltage input with a control circuit; and communicating an output of the gas chambers to the control circuit with a feedback control loop for modifying the first voltage input.
  • FIG. 1 is an illustration of a block diagram of a MOPA/MOPRA Laser System.
  • FIG. 2 is an illustration of an energy control block diagram for the MOPA/MOPRA Laser System of FIG. 1.
  • FIG. 3 is an illustration of a graph representing trapezoidal windows of varying repetition rates, in accordance with a first exemplary embodiment of the disclosed subject matter.
  • FIG. 4 is an illustration of a graph of a frequency response of the dose operator for the windows illustrated in FIG. 3, in accordance with a first exemplary embodiment of the disclosed subject matter.
  • FIG. 5 is an illustration of an energy control block diagram for the MOPA/MOPRA Laser System of FIG. 1, in accordance a first exemplary embodiment of the disclosed subject matter.
  • FIG. 6 is a flowchart illustrating a method of providing the laser control system of FIG. 5, in accordance with the first exemplary embodiment of the disclosed subject matter.
  • FIG. 3 is an illustration of a graph representing trapezoidal windows of varying repetition rates, in accordance with a first exemplary embodiment of the disclosed subject matter.
  • FIG. 4 is an illustration of a graph of a frequency response of the dose operator for the windows illustrated in FIG. 3, in accordance with aspects of a first exemplary embodiment of the disclosed subject matter. Note that while there are a set of zeros that vary for varying window widths, there are clearly zeros for all windows at 20% and 40% of the sample rate. These zeros correspond to the zeros of a 5 pulse moving average. It can be shown that a trapezoidal window is the convolution of a rectangular window having a length equal to the window size, less the trailing edge and a 5 pulse rectangular window.
  • FIG. 5 is an illustration of an energy control block diagram 150 for the MOPA/MOPRA laser system 10 of FIG. 1 , in accordance a first exemplary embodiment of the disclosed subject matter.
  • FIG. 5 illustrates various control elements that control a voltage input 152 to the MOPA/MOPRA laser system 10.
  • the energy control block diagram 150 includes a static control 154, which provides a basically determined voltage anticipated to achieve an energy target 156 (if there are no other influences for which account need be made). Part of a purpose of the static control 154 is to make the energy controller responsive to changes in the energy target 156. If a user adjusts an energy target, the first voltage input 152 for the first shot should be computed to meet the new energy setpoint.
  • the static control 154 may provide the following voltage signal:
  • V (dV/dE) ref * (Et ar get - E re f + e(E targe , - E ref ) 2 + V ref
  • E ref is approximately set to a nominal energy of the laser system 10
  • V re f is the voltage approximately required to fire the laser at E ref .
  • a feed forward block 158 provides a voltage adjustment based on a trigger interval 160.
  • Trigger interval 160 is used to compute repetition rate, shot number and duty cycle, which impact the 'voltage input - energy output' relationship.
  • the voltage adjustment for the trigger interval 160 is computed as a function of these values. More specifically, the voltage signal provided by the feed forward block 158 may be given by: where D is the duty cycle, R is the repetition rate, and n is the shot number. Note that the feed forward voltage has two terms. One term, / 0 , depends on duty cycle and/or burst interval, and another term, /i, depends on shot number and repetition rate. By design, /i is identically zero on the first shot of each burst.
  • /o alone determines the feed forward voltage for the first shot of the burst.
  • This term is intended to adjust the laser for changes in efficiency, which typically persists throughout a burst.
  • the Z 1 term captures the shape of any transients. This law assumes that duty cycle or interburst interval effect just moves the energy vs. shot number up or down equal amounts for all shots in a burst.
  • the shape of the energy transient is assumed to depend only on repetition rate.
  • the /i(R,n) function compensates for the shape of the energy transient.
  • the /i(R,n) function is maintained as a table versus repetition rate and shot number.
  • a simple integrator is used to adapt the bins. In the past, the bins were initialized to zero, requiring several bursts before the laser control was correctly inverting the transient at the repetition rate. Instead of initializing these bins with zero, feed forward bins may be initialized with values of trained bins that are nearest in frequency. Initializing the bins with a value nearer the correct value for the shape of the energy transient allows the laser control more quickly, and with greater accuracy, to invert the transient at the repetition rate.
  • An energy servo 162 adjusts the voltage input 152 based on a calculated voltage error 164 of the previous shot within the same burst.
  • the adjustment from the energy servo 162 may be calculated in at least a couple of different modes.
  • NSquared feedback is a feedback law known to those having ordinary skill in the art. This feedback law feeds back one voltage proportional to an integral of the voltage error (an integral gain) and another proportional to the voltage error integrated twice (an I squared gain).
  • Several sets of gains are provided for the NSquared filter: soft; hard; and MO.
  • Soft gains are used in operational modes when the objective is to minimize shot to shot energy error. Soft gains are selected to minimize energy errors. Hard gains are used in dose and sigma modes.
  • the hard gains are intended to minimize dose (integrated energy error) and tend to be larger than the soft gains.
  • the MO gains are used in MO energy control modes and are also intended to minimize energy errors.
  • An alternative to HSquared feedback is dose feedback. Like the HSquared controller with hard gains, the dose feedback controller is intended to minimize dose, however, it uses a control law that gives better performance with non-rectangular dose windows (e.g., trapezoidal dose windows).
  • Dose feedback is controlled by a dimensioning parameter and a vector of gains.
  • the dose feedback controller is available only in dose and sigma modes and may utilize a Linear Quadratic Regulator to minimize the quadratic sum of energy dose and energy error 172. Utilization of the Linear Quadratic Regulator instead of 100% integral feedback has been shown in tests to reduce energy dose error by approximately 25%.
  • the effect of the laser system 4, as shown in FIG. 5, is to translate the voltage input 152 to energy (evaluated by the energy measurement 172) through a static gain.
  • energy evaluationated by the energy measurement 172
  • the energy servo 162 is directed to providing voltage adjustments responsive to the behavior of the dose operator.
  • the energy dose feedback may be calculated as the inner product of a state feedback vector, K and a vector characterizing the state of the dose operator, xd.
  • Vdose -K xd
  • K is computed as a solution of a linear quadratic regulator which minimizes a weighted sum of the square of the energy error and the square of the energy dose error.
  • a dither cancellation 166 adjusts voltage to cancel energy changes caused by a timing dither 168.
  • u 1/E * dV/dt at constant energy, where E is laser energy, V is voltage and t is MOPA timing, the difference in firing times between the MO and PA chambers.
  • the local slope of the timing versus energy curve is needed. This information is obtained by applying a dither signal to the differential timing commanded to the MO and PA commutator triggers.
  • timing couples into energy this dither signal produces a matching dither in energy.
  • the dither cancellation algorithm adaptively finds a voltage signal which when applied to the laser exactly cancels the dither in energy produced by the timing dither signal. Thus, the timing dither no longer appears in the energy signal and therefore has no impact on energy sigma or energy dose.
  • a by-product of this cancellation algorithm is the derivative of voltage with respect to timing at fixed energy. This by-product is the slope information that the timing dither was applied to identify in the first place.
  • a parameter used in the laser control system for gas control, dMpopdMopa (the derivative of MopaOpPoint with respect to the difference between MO and PA chamber firing times), may be used to make the dither cancellation approximately instantly responsive to changes in MOPA timing (the difference in MO and PA chamber firing times). . If this parameter is off, then on '"large" 1 (1-2 ns) changes in MOPA/MOPRA timing, MopaOpPoint 180 (“Mpop”)will jump to a new value and then over then next several thousand shots, drift to a different value.
  • the amplitude of a dither may be set low normally to reduce the energy dither, but the low amplitude delays calculation of the derivative of the energy dose verses voltage estimate. If the dither is moved under the zero of one of the trapezoidal windows, the amplitude can be raised with diminished negative impact.
  • Mpop compensation 182 adjusts the voltage input 152 to compensate for changes in MOPA timing. This adjustment is primarily to stabilize energy for changes of a DtMopaTarget in excess of approximately 1 nanosecond. If a laser is running with bandwidth control enabled (ASC) and is currently operating away from a resonance, to keep bandwidth up, the control system has decreased the delay between MO and PA triggers. At this point, MopaOpPoint will be a low, negative value because DtMopaTarget is several ns below the value for peak efficiency. Then, the scanner 2 switches repetition rate to one which lies on a bandwidth resonance. Bandwidth goes up and the bandwidth controller advances DtMopaTarget by a few ns to compensate.
  • ASC bandwidth control enabled
  • MopaOpPoint compensation 182 combats this effect. Using the same value used to adjust dither cancellation for changes in Mopa timing, dMpopDMopa, it is possible to compute the amount voltage will need to change for a given change in Mopa timing. When Mopa timing is changed quickly, the MopaOpPoint compensation 182 can predict what voltage change that is also needed and provide an appropriate voltage signal to the voltage input 152 without having to wait for an energy error 174 to appear.
  • the MopaOpPoint compensation 182 may be described as:
  • V Eu 2 /2k
  • E the laser energy
  • u the MopaOpPoint
  • k dMpopDMopa or the derivative of MopaOpPoint with respect to Mopa timing, the difference in firing time between the MO and PA chambers.
  • a disturbance prediction 184 adjusts the voltage input 152 based on a prediction of the voltage error, assuming that the disturbance acting on energy is a DC offset plus several tones.
  • the tones are at frequencies that are multiples of the MO and PA/PO blower speeds. This predicted voltage error is subtracted from the voltage input 152, thus removing the effects due to DC offset or blower blade passage.
  • an energy dither 170 provides a periodic signal added to the voltage input 152 used to estimate the effects of voltage on MO energy, output energy, and MOPA timing.
  • the periodic signal from the energy dither 170 is n shots long and may be described by the equation:
  • A is the dither amplitude
  • n d is the number of cosine periods within one full cycle of the dither.
  • the dither signal is held off for a fixed number of shots before being started in each burst. The delay is provided so that the dither cannot combine with beginning of burst effects to push the laser 4 out of spec.
  • the phase of the dither signal may be randomized. Randomization is done by randomizing the value of k in the above equation to start the dither. For the windows shown in FIG.
  • the dither frequency is 1 fifth of the rep rate (5 shots leading and trailing each trapezoidal window). This is a key frequency for lasers using trapezoidal windows to calculate dose. For windows which have four pulse leading and trailing edges, 20% of the rep rate lies inside a zero of the dose operator. Hence, dithering at this frequency will have no effect on dose.
  • These voltage signals are added together to generate the voltage input 152.
  • the energy is measured 172.
  • the energy target is subtracted from the measured energy to create an energy error signal 174, which is scaled by dV/dE, the laser estimate 176 of the derivative of voltage with respect to energy.
  • the resulting voltage error 164 is used to drive adaptation algorithms 178 which adjust some of the voltage signals in a way that minimizes energy errors, dose errors, or energy sigma, or some combination thereof.
  • FIG. 6 is a flowchart 200 illustrating a method of providing the laser control system 150 of FIG. 5, in accordance with the first exemplary embodiment of the disclosed subject matter.
  • any process descriptions or blocks in flow charts should be understood as representing modules, segments, portions of code, or steps that include one or more instructions for implementing specific logical functions in the process, and alternate implementations are included within the scope of the disclosed subject matter in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the disclosed subject matter.
  • a first voltage input is delivered operatively in the form of electrical pulses to a first pair of electrodes within an oscillator gas chamber and a second pair of electrodes within an amplifier gas chamber.
  • An energy dose of an output of the gas chambers is calculated with a trapezoidal window (block 204).
  • the first voltage input is modified with a control circuit, wherein a frequency response to a dose operator has at least one zero (block 206). At least one of an energy dither and a timing dither is initiated under one of the zeros (block 208).
  • An output of the gas chambers is communicated to the control circuit with a feedback control loop for modifying the first voltage input (block 210).
  • a first voltage input is delivered operatively in the form of electrical pulses to a first pair of electrodes within an oscillator gas chamber and a second pair of electrodes within a amplifier gas chamber.
  • An energy dose of an output of the gas chambers is calculated with a trapezoidal window (block 204).
  • This alternative does not use block 208.
  • An output of the gas chambers is communicated to the control circuit with a feedback control loop for modifying the first voltage input (block 210).
  • a first voltage input is delivered operatively in the form of electrical pulses to a first pair of electrodes within an oscillator gas chamber and a second pair of electrodes within a amplifier gas chamber.
  • An energy dose of an output of the gas chambers is calculated with a trapezoidal window (block 204).
  • K is a state feedback vector computed as a solution of a linear quadratic regulator that minimizes a weighted sum of the square of an energy error and the square of an energy dose error
  • xd is a vector characterizing a state of a dose operator (block 206).
  • An output of the gas chambers is communicated to the control circuit with a feedback control loop for modifying the first voltage input (block 210).

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Optics & Photonics (AREA)
  • General Physics & Mathematics (AREA)
  • Lasers (AREA)

Abstract

Le système de commande laser selon la présente invention contient une chambre de gaz d’oscillateur et une chambre de gaz d’amplificateur. Une première tension d’entrée est connectée de façon fonctionnelle afin de fournir des impulsions électriques à une première paire d’électrodes à l’intérieur de la chambre de gaz d’oscillateur et à une seconde paire d’électrodes à l’intérieur de la chambre de gaz d’amplificateur. La sortie des chambres de gaz est une dose d’énergie calculée par une fenêtre trapézoïdale. Un circuit de commande est connecté à la première tension d’entrée en vue de la modifier. Une boucle de commande à rétroaction communique une sortie des chambres de gaz au circuit de commande afin de modifier la première tension d’entrée.
EP09822307.6A 2008-10-21 2009-10-20 Procédé et appareil pour commande laser dans un laser à décharge de gaz à deux chambres Withdrawn EP2351170A4 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US12/255,385 US7751453B2 (en) 2008-10-21 2008-10-21 Method and apparatus for laser control in a two chamber gas discharge laser
US12/255,367 US7720120B2 (en) 2008-10-21 2008-10-21 Method and apparatus for laser control in a two chamber gas discharge laser
US12/255,347 US7756171B2 (en) 2008-10-21 2008-10-21 Method and apparatus for laser control in a two chamber gas discharge laser
PCT/US2009/005694 WO2010047771A1 (fr) 2008-10-21 2009-10-20 Procédé et appareil pour commande laser dans un laser à décharge de gaz à deux chambres

Publications (2)

Publication Number Publication Date
EP2351170A1 true EP2351170A1 (fr) 2011-08-03
EP2351170A4 EP2351170A4 (fr) 2013-04-10

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JP (2) JP2012506634A (fr)
KR (1) KR101742715B1 (fr)
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US11081852B2 (en) * 2017-04-24 2021-08-03 Cymer, Llc Laser light energy and dose control using repetition rate based gain estimators
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JP7430799B2 (ja) * 2020-03-03 2024-02-13 サイマー リミテッド ライアビリティ カンパニー 光源のための制御システム
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EP2351170A4 (fr) 2013-04-10
KR20110086020A (ko) 2011-07-27
JP2012506634A (ja) 2012-03-15
KR101742715B1 (ko) 2017-06-01
JP2015111718A (ja) 2015-06-18
TW201023462A (en) 2010-06-16
WO2010047771A1 (fr) 2010-04-29
TWI389409B (zh) 2013-03-11

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