EP4115481A1 - Système pour empêcher une réinjection de rayonnement et installation laser équipée d'un tel système - Google Patents

Système pour empêcher une réinjection de rayonnement et installation laser équipée d'un tel système

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Publication number
EP4115481A1
EP4115481A1 EP20712842.2A EP20712842A EP4115481A1 EP 4115481 A1 EP4115481 A1 EP 4115481A1 EP 20712842 A EP20712842 A EP 20712842A EP 4115481 A1 EP4115481 A1 EP 4115481A1
Authority
EP
European Patent Office
Prior art keywords
laser beam
arrangement
radiation
laser
fabry
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.)
Pending
Application number
EP20712842.2A
Other languages
German (de)
English (en)
Inventor
Steffen Erhard
Gisbert Staupendahl
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.)
Trumpf Lasersystems for Semiconductor Manufacturing GmbH
Original Assignee
Trumpf Lasersystems for Semiconductor Manufacturing GmbH
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
Application filed by Trumpf Lasersystems for Semiconductor Manufacturing GmbH filed Critical Trumpf Lasersystems for Semiconductor Manufacturing GmbH
Publication of EP4115481A1 publication Critical patent/EP4115481A1/fr
Pending legal-status Critical Current

Links

Classifications

    • 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
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/22—Gases
    • H01S3/223—Gases the active gas being polyatomic, i.e. containing two or more atoms
    • H01S3/2232—Carbon dioxide (CO2) or monoxide [CO]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/064—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/70—Auxiliary operations or equipment
    • B23K26/702—Auxiliary equipment
    • 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
    • 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
    • H01S3/0064—Anti-reflection devices, e.g. optical isolaters
    • 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
    • H01S3/0078—Frequency filtering
    • 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
    • H01S2301/00—Functional characteristics
    • H01S2301/02—ASE (amplified spontaneous emission), noise; Reduction thereof

Definitions

  • the invention relates to an optical arrangement for suppressing radiation feedback.
  • the invention also relates to a laser system with such an arrangement.
  • the situation is even more critical with a Q-switched laser for high peak powers.
  • the Q-switch principle is based on an extreme temporary increase in the population inversion and thus the gain in the active medium as a prerequisite for the targeted generation of the powerful radiation pulses.
  • the system is extremely susceptible to the effect of the smallest undesirable amounts of radiation fed back into the active medium, which can then easily be amplified by a factor of 10 4 to 10 5 on a "round trip" in the resonator It is clear that this has serious effects on the pulse generation, since the desired structure of the population inversion is massively disrupted.
  • the "classic" decoupling described above is no longer sufficient here; additional efficient decoupling variants must be used.
  • Laser amplifier arrangements are similarly sensitive for maximum powers, in which the radiation returning from the laser beam target in the direction of the laser has to pass the amplifier stages even before reaching the laser and is drastically amplified in the process.
  • a current example of this situation are the systems for generating EUV radiation, in which a CO 2 seed laser generates the extraordinarily precisely defined primary radiation pulses, which are then highly amplified and aimed at the laser beam target (typically in the form of of a droplet).
  • the backscattered radiation must not influence the radiation generation process, ie here, too, the highest demands are made on the decoupling.
  • the object of the invention is to provide a highly effective arrangement for decoupling radiation between a laser as the radiation source and a laser beam target to which this radiation is applied.
  • This arrangement should not rely on dynamic components such as fast modulators with complex control and, if necessary, synchronization with pulsed radiation, but rather a fixed, stationary decoupling effect for short pulses in the ns range up to cw radiation own. It is a further object of the invention to provide a laser system with such an arrangement. Description of the invention
  • the arrangement has the following components, through which the beam path of the primary laser beam is guided: a) a wavelength-selective element; b) a first Fabry-Perot interferometer which is arranged at an angle of more than 0 ° and less than 6 ° to the optical axis of the Fabry-Perot interferometer in the beam path of the primary laser beam; c) a polarizer; d) a 1/4 phase shifter.
  • the new approach according to the invention is based on the combination of the "classic" decoupling by means of 1/4 phase shifter and polarization-sensitive decoupling Reflection or transmission component with the effect of a Fabry-Perot interferometer (FPI).
  • FPI Fabry-Perot interferometer
  • the arrangement also has, as it were, an effective improvement in the quality of the radiation traveling to the laser beam target through the use of the specific properties of the integrated FPL
  • the divergence In the case of the wave traveling to the laser beam target, it typically corresponds to the divergence of the pure laser beam and lies in the
  • the returning wave is, firstly, LA. no ideal reflection on an ideally flat laser beam target and, secondly, no completely ideal focus position on the surface of the laser beam target (intentionally or unintentionally), have a noticeably different (“worse”) divergence behavior averaged over the entire intensity profile after the focusing lens,
  • the surface of the laser beam target has a relevant influence, ie the returning beam has a noticeably poorer coherence.
  • Amplifier arrangements can, however, also result in the opposite situation if the point of consideration which should correspond to the arrangement of the decoupling system is between the (relatively low-power) seed laser and the high-performance amplifier , which of course also greatly amplifies the returning radiation.
  • Effect of the plasma Practically all of the processing tasks discussed here are linked to the creation of a plasma spark, which arises directly on the surface of the laser beam target, or even to the transformation of the complete laser beam target / droplet into plasma. Its effect z. B. on the direction of the focused beam is mostly negligible because of its proximity to the laser beam target, but is relevant for the direction, divergence, frequency and power of the returning beam.
  • the wavelength (frequency) If the incoming bundle is scattered or reflected by a very fast moving laser beam target (eg a rapidly expanding plasma), the returning bundle is according to the Doppler effect impresses a certain frequency or wavelength change.
  • the transmission T m of the FPI as a function of the wavelength ⁇ , the plate reflectivity R and the plate spacing a is calculated according to
  • the useful R range can be limited to 0.3 ⁇ R ⁇ 0.9.
  • a very important parameter for the desired decoupling effect of an FPI is its finesse F, which indicates the ratio of the period width to the half-width of the transmission peak:
  • the strong angular dependence of the FPI transmission suggests another advantageous property of the arrangement according to the invention: the improvement of the beam quality of the laser beam generated by the spatial filter effect of the FPI with an optimized plate spacing.
  • the arrangement can be arranged in the form of a unit, in particular in a common housing.
  • the angle of the optical axis of the first Fabry-Perot interferometer to the beam path is preferably less than 5 °, in particular less than 4 °, particularly preferably less than 3 °. As a result, the arrangement can be operated particularly efficiently.
  • the arrangement has a first absorber for absorbing the portion of the primary laser beam reflected by the first Fabry-Perot interferometer.
  • the arrangement can have a second absorber for absorbing the portion of the secondary laser beam reflected by the first Fabry-Perot interferometer. Coupling out of the undesired reflection can be ensured by the absorber or absorbers.
  • the first absorber and / or the second absorber can each be designed in the form of a radiation detector.
  • the aforementioned optical components are preferably arranged in the following order for the primary laser beam:
  • a focusing element can be arranged after the 1/4 phase shifter. Particularly preferably, no further components are arranged between the aforementioned components.
  • the first Fabry-Perot interferometer can have two plates made of transparent material, the opposite sides of which have a reflectivity R between 0.3 and 0.9. The sides preferably have a reflectivity R between 0.5 and 0.8. As an alternative or in addition to this, the plates preferably have a spacing between 1 mm and 1000 mm, in particular between 10 mm and 30 mm. The plates are preferably made of ZnSe or diamond.
  • the wavelength-selective element is also preferably designed in the form of a diffraction grating. The blaze wavelength of the diffraction grating preferably corresponds to the wavelength of the primary laser beam.
  • the polarizer is preferably designed in the form of an absorbing thin film reflector (ATFR) mirror.
  • the 1/4 phase shifter is preferably designed in the form of a 1/4 phase shifter mirror.
  • optical components enable a structurally simple construction of the arrangement with high performance.
  • the arrangement can have a telescope arrangement for expanding the primary laser beam in front of the first Fabry-Perot interferometer. This can the first Fabry-Perot interferometer to be irradiated with particularly high power.
  • the expansion factor is preferably between 1.5 and 5, particularly preferably between 1.5 and 3.
  • the arrangement can have a second Fabry-Perot interferometer, which is arranged downstream of the first Fabry-Perot interferometer. This can significantly increase the decoupling efficiency. More preferably, a third Fabry-Perot interferometer is arranged downstream of the second Fabry-Perot interferometer.
  • the reflectivity R of the plates of the further Fabry-Perot interferometers is preferably between 0.2 and 0.7, particularly preferably between 0.3 and 0.5. Interferometers with different reflectivities R are also preferably used.
  • the object of the invention is also achieved by a laser system with a laser beam source for emitting a primary laser beam, a laser beam target and an arrangement described here for guiding the primary laser beam, the beam path of the arrangement running between the laser beam source and the laser beam target.
  • the laser beam source is preferably designed in the form of a high-power laser beam source for emitting a primary laser beam with an average power of at least 1 kW.
  • the laser beam source is designed in particular in the form of a CO 2 laser beam source.
  • the laser beam source s can be provided for delivery of a primary laser beam in the form of radiation pulses with pulse durations between 10 -9 s and 10 '. 6 This makes the laser system particularly suitable for generating EUV radiation.
  • the laser system can have an amplifier system which is arranged on the beam path between the laser beam target and the laser beam source, the arrangement being arranged between the amplifier system and the laser beam source.
  • the laser system can have a further connection described here. Have order arranged between the amplifier system and the laser beam target.
  • the laser system can have a further 1/4 phase shifter which is arranged between the amplifier system and the further arrangement.
  • a particularly powerful and structurally compact laser system can be implemented by means of one or more of these features.
  • the laser beam target is designed to emit EUV radiation when irradiated with the primary laser beam.
  • the laser beam target can be designed in the form of a droplet.
  • the laser beam target is preferably designed in the form of a tin droplet.
  • the invention further relates to the use of an arrangement described here and / or a laser system described here in a system for generating EUV radiation, in particular an EUV lithography system.
  • Fig. 2 shows the basic structure of a Fabry-Perot interferometer (FPI);
  • Fig. 4 shows schematically the separation of incident and reflected
  • FIG. 6 shows, by way of example, a measurement of the radiation filtering by means of an FPI
  • FIG. 8 shows a structure according to the invention for a laser system in the form of a laser amplifier arrangement
  • 9 shows the expansion of a high-power radiation beam by means of a telescope
  • FIG. 1 shows a characteristic example of the need to suppress the radiation feedback, in which defined pulses should be formed from the cw radiation of a CO 2 laser by means of an interference laser radiation modulator. Without suppression of the feedback, the almost statistical P (t) curve shown in FIG. La resulted; when decoupling by means of the ATFR mirror and 1/4 phase shifter mirror, the clean desired pulse function according to FIG.
  • the example shown in FIG. 1 relates to a special application of defined radiation pulses (method of elementary volume removal - EVA) in fine machining by means of a CO 2 laser.
  • ILM interference laser radiation modulator
  • the desired pulse train was generated from the inherently continuous laser radiation.
  • Fig. 2 shows the basic structure of an FPI 10 with plates 12a and 12b at a distance a to illustrate the properties listed above.
  • an FPI 10 of the structure shown will be used in which there is a decisive difference between the two Areas of reflectivity R air is located. This reduces the harmful effect of the FPI-internal power increase, especially when using larger R (R> 0.5), on the R-coating itself.
  • R the Radio-Coating
  • FIG. 3 shows the theoretical transmission of an FPI 10 as a function of the plate spacing a for three selected reflectivities R. It illustrates the strong R-dependence of contrast and finesse, both of which are decisive for the effect of the FPI 10 to suppress the radiation feedback between the laser beam target and the laser beam source. This concerns both the sensitivity to the smallest angular changes of the radiation incidence on the FPI 10 as well as frequency or wavelength changes of the radiation returning from the laser beam target, which are, for example, reflected or scattered by a rapidly expanding plasma, as is the case for the Generation of EUV radiation is characteristic.
  • a minimum angle d is necessary which, after a predetermined distance s, is sufficient for the separation of the incident and reflected bundle (see FIG. 4).
  • two factors should preferably be taken into account with regard to the FPI function.
  • a sufficiently large plate spacing a is preferred. Its optimal size depends crucially on the respective parameter of the returning radiation, which is primarily effective for the decoupling. Because of the high selectivity of an FPI 10 with respect to the angle of incidence d, plate spacings a in cm are preferred for the suppression of the radiation components in the returning beam with divergences or inclinations towards the FPI axis> 1 mrad if the FPI is finesse of 14 assumes.
  • the parameter influencing the decoupling is a frequency shift due to the Doppler effect at a rapidly moving laser beam target, significantly larger plate spacings a are preferred. If, for example, one takes a Doppler shift of about 100 MHz on the extremely rapidly expanding plasma during EUV generation of the irradiated droplet, a should preferably be at least 10 cm for an efficient decoupling effect (cf. FIG. 5). This requirement is put into perspective, however, if one takes into account that with a frequency shift of 100 MHz, the optical gain of the active media, for example from CO 2 lasers or amplifiers, drops significantly, so that a second effect occurs here, which is for suppression contributes to the returning wave.
  • the boundary conditions to be met here are that, firstly, a clean separation of an incident laser beam 14 with diameter D from the portion 16 reflected at the FPI 10 with approximately the same diameter must be ensured and, secondly, the required distance s is not too large, the angle d so shouldn't be too small. Thirdly, the role of d is relatively complex: In terms of a high filter effect with regard to unwanted radiation and a high efficiency in radiation decoupling, d should not be too small either; on the other hand, as already mentioned above, the maximum transmission worsens with increasing d should of course be close to 1 for the working beam.
  • the laser beam 14 emerges in FIG. 4 from a wavelength-selective element 18.
  • d should therefore preferably be optimized. This optimization is closely linked to the distance a between the FPI plates 12a, 12b, since, in addition to the plate reflectivity R, the two geometric parameters a and d ultimately determine the effectiveness of the arrangement described.
  • FIG Frequency f plotted.
  • FIG. 6 also shows the results of a measurement which clearly illustrates the effect of an FPI 10 optimized in accordance with the invention as a radiation filter.
  • the influence of the gas discharge current I of a low pressure CO 2 laser on the beam quality was examined.
  • the latter is characterized by the quotient P T / PR, which represents the ratio of useful power P T (that is, radiation transmitted by the FPI) to the power component P R to be filtered out, which is reflected by the FPI 10. Since the laser was intentionally operated in a regime that was tively quickly led to overheating of the laser gas, the diagram shows very instructively how the beam quality (i.e.
  • the quotient P T / P R initially assumes a clear maximum at a relatively low current, and in the case of currents exceeding this, and so that overheating will drop dramatically.
  • the amount of radiation filtered out increases from approx. 17% of the incident power to approx. 25%, which ultimately means that the quality of the useful beam remains almost constant (but with decreasing power), although the quality of the "raw beam" of the laser is noticeably lower
  • Continuous monitoring of the filtered out radiation component which is constantly available for measurements during processing, provides an important parameter for diagnosing the processing process.
  • FIG. 7 shows the highly schematic basic structure of an arrangement 20 according to the invention.
  • a laser beam source 22 which here can for example be a Q-switched high-power CO 2 laser, is initially assumed.
  • Their primary laser beam 24 is characterized by a defined wavelength l, a linear polarization of defined direction 26 and a more or less good beam quality K. Since the components according to the invention for beam filtering on the one hand and for suppressing radiation feedback on the other hand for the precisely defined wavelength l mentioned are designed, the system must be prevented from shifting along the beam path "laser beam source - beam guidance and shaping - laser beam target (target)" to another wavelength in order to guarantee their function.
  • a wavelength-selective element 28 (eg a diffraction grating or a prism) ensures that the system is reliably fixed to the specified I.
  • this wavelength-selective element 28 is already in the Laser, that is to say the laser beam source 22, can itself be integrated and is then of course not required again outside the laser.
  • the situation is somewhat different in high-power laser amplifier systems, such as those used in EUV systems (see FIG. 8).
  • Treatment feedback is preferably not dispensed with the wavelength-selective element.
  • the primary laser beam 24 passes a central element of the solution according to the invention, the Fabry-Perot interferometer (FPI) 10 optimized in accordance with the above statements.
  • the first task of this FPI 10 is that of maximum transmission for the wavelength A set consists in filtering out radiation components 30, which consequently reduce the beam quality, the focusability of the radiation and ultimately the quality of processing, which are typically radiation fractions that deviate more or less from the fundamental mode TEM 00th In the simplest case, they are destroyed by an absorber 32 which - as here - can be designed in the form of a radiation detector. Its measurement signal provides information on the size of the parasitic radiation components 30, but also provides important information on the stability of the laser beam source 22 and / or the pulse behavior of the laser when the time course is recorded and can consequently also be used for diagnostic and control purposes.
  • the radiation components 34 transmitted and filtered by the FPI 10 are then sent via a "classic" combination of polarizer 36 and ⁇ / 4 phase shifter 38 for radiation decoupling of laser (laser beam source 22) and target (laser beam target 40)
  • the desired conversion of the linearly polarized into circularly polarized radiation 42 takes place, which can then be sent to the laser beam target 40, for example by means of a focusing element 44.
  • the effect of the elements 36 and 38 is that the secondary laser beam 46 returning from the laser beam target 40 in the direction of the laser beam source 22, which is typically more or less partially circularly polarized, is initially in the A / ⁇ phase shifter 38 in a second conversion is transformed into partially linearly polarized radiation 48, the polarization direction of which is perpendicular to that of the primary laser beam 24.
  • this dilemma is solved by the action of the specially optimized Fabry-Perot interferometer 10.
  • the FPI 10 arranged at the aforementioned small angle d weakens the radiation component 50 in a number of ways to a level that is harmless to the laser function.
  • the differences in the parameters of the incoming radiation component 34 and the returning radiation component 50 are decisive.
  • the most important differences that lead to a high level of reflection at the FPI 10 and thus to the desired elimination of the radiation component 50 have already been mentioned. It has also already been said that an exact quantitative recording of all contributing effects is practically impossible. For qualitative considerations, it makes sense to subdivide the effects into coherence-independent and coherence-bound.
  • the entire radiation component 52 which in the ideal case corresponds more or less to the radiation component 34 in terms of output, is destroyed in a second absorber 54 and ultimately ensures a highly effective blocking of the returning radiation.
  • the overall attenuation of the returning radiation reaches factors that can be between 10 3 and 10 4 . It is therefore at least 1 to 2 orders of magnitude more efficient than the conventional combinations of polarizer and 1/4 phase shifter and suitable for radiation decoupling, which are subject to the highest demands.
  • the preferred order of the elements 10, 36 and 38 should be pointed out again, which is particularly important under the aspect of the power sensitivity of the FPI 10 and is especially decisive for laser amplifier applications is (cf. also the comments on FIGS. 8, 9 and 10).
  • the power load on the FPI 10 is minimized for the following reasons: First, the FPI 10, regardless of its position in front of or behind the elements 36 and 38, is always at full power exposed to the radiation traveling to the laser beam target 40, since it can be assumed to a good approximation that the losses in the elements 36 and 38 are minimal.
  • the differences in the radiation exposure of FPI 10 for the two arrangement variants depend practically exclusively on the power of the returning radiation that hits FPI 10.
  • this is decisively weakened by the decoupling effect of elements 36 and 38, so that even with very powerful reverse radiation components, as can occur in high-power laser amplifier systems , the FPI function 10 is not endangered by this.
  • FIG. 8 shows a laser system 56 according to the invention in the form of a laser amplifier arrangement.
  • An amplifier system 58 can also consist of several stages, for example an additional preamplifier or several high-performance amplifiers.
  • the radiation 24 generated in a laser 22 with precisely defined properties is brought here in the amplifier system 58 to a power level that enables demanding applications.
  • the radiation thrown back by a laser beam target 40 in particular in the form of a droplet, should under no circumstances pass through the amplifier system 58, since otherwise it would be extremely amplified and thus the decoupling from the laser 22 would be made significantly more difficult.
  • that part of the super radiation that runs in the direction of the laser 22 and occurs in any case and independently of the radiation feedback through the laser beam target 40 must be taken into account.
  • the laser radiation 24 first passes through a first arrangement 20a, which takes on all of the tasks discussed in relation to FIG
  • a component that is reflected or scattered by the laser beam target 40 is only imperfectly destroyed by a second arrangement 20b and is highly amplified in the amplifier system 58
  • a component that is also used when the second arrangement 20b occurs namely one-way super-radiation (ASE) of the amplifier system 58 itself.
  • the latter is essentially unpolarized and is therefore made by the unit of polarizer 36 and 1/4 phase shifter 38 (see FIG. 7) of the first Arrangement 20a only reduced to about half.
  • the radiation in the amplifier system 58 is generally amplified to very high values of the peak pulse power, but also the average power.
  • the latter can be, for example, in CO 2 laser amplifier systems for EUV generation in the multi-kW range and therefore requires special precautions for the second arrangement 20b, which is necessary for reliable shielding of the amplifier system 58 from the Laser beam target 40 is intended to provide radiation components 62 returning.
  • the effect of the second arrangement 20b should be completely analogous to that of the first arrangement 20a.
  • amplified, circularly polarized radiation 64 is first converted back into linear polar ized to transform. This is done by means of a 1/4 phase shifter 66.
  • the incident radiation firstly has significantly higher power values and secondly its linear polarization by 90 ° compared to the laser radiation 24 is rotated. The latter is not a problem, in principle only a unit composed of polarizer 36 and 1/4 phase shifter 38 (see FIG. 7) can be rotated through 90 ° for this purpose.
  • FIG. 9 the expansion of the diameter of a beam 68 by means of a telescope arrangement 70 directly in front of an FPI 10, which has a larger free aperture adapted to the expanded beam 72.
  • the intensity on the R surfaces can be set within wide limits in such a way that the FPI function and thus the beam 74 emanating from the FPI 10 is not impaired by thermal effects.
  • a remedy according to the invention can also be provided by an FPI cascade.
  • the basic version, an FPI tandem, is shown in FIG. 10.
  • the solution is based on the division of the FPI effect to suppress the radiation feedback over several FPIs, here a first FPI 10 and a second FPI 76, in particular with a reduced R.
  • a numerical example should illustrate that.
  • This basic principle can be expanded and optimized by using, for example, more than 2 interferometers to further reduce the radiation load or to maximize the decoupling efficiency while minimizing the radiation load.
  • the invention relates in summary to an optical arrangement 20, 20a, 20b for filtering laser radiation.
  • the arrangement 20, 20a, 20b has a wavelength-selective element 28, a first Fabry-Perot interferometer 10, a polarizer 36 and a 1/4 phase shifter 38.
  • the optical axis of the Fabry-Perot interferometer 10 is aligned at an angle of more than 0 ° and less than 6 ° to the laser beam impinging on the Fabry-Perot interferometer 10.
  • the Fabry-Perot interferometer 10 is designed both for coupling out undesired radiation components 30 of the primary laser beam 24 impinging on the Fabry-Perot interferometer 10 and for coupling out undesired radiation components 52 of the secondary laser beam 46 reflected by a laser beam target 40 , 20a, 20b at least one further Fabry-Perot interferometer 76.
  • the arrangement 20, 20a, 20b further preferably comprises a telescope arrangement 70 for expanding the primary laser beam 24 incident on the Fabry-Perot interferometer 10.
  • the invention relates to furthermore a laser system 56 with at least one such arrangement 20, 20a, 20b.
  • the laser system 56 preferably comprises an amplifier system 58 which is arranged between two arrangements 20a, 20b.
  • the laser system 56 is particularly preferably designed to generate EUV radiation.
  • the laser beam target 40 can be in the form of a droplet.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Optics & Photonics (AREA)
  • Electromagnetism (AREA)
  • Plasma & Fusion (AREA)
  • Mechanical Engineering (AREA)
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  • Chemical Kinetics & Catalysis (AREA)
  • Lasers (AREA)

Abstract

L'invention concerne un système optique (20) pour filtrer un rayonnement laser. Ce système (20) comprend un élément de sélection de longueur d'onde (28), un premier interféromètre de Fabry-Pérot (10), un polariseur (36) et un déphaseur A/4 (38). L'axe optique de l'interféromètre de Fabry-Pérot (10) est orienté selon un angle supérieur à 0° et inférieur à 6° vers le faisceau laser rencontrant cet interféromètre de Fabry-Pérot (10). L'interféromètre de Fabry-Pérot (10) est conçu à la fois pour découpler des composantes de rayonnement (30) indésirables du faisceau laser primaire (24) rencontrant cet interféromètre de Fabry-Pérot (10) et pour découpler des composantes de rayonnement (52) indésirables d'un faisceau laser secondaire (46) réfléchi par une cible de faisceau laser (40). De préférence, ledit système (20) comprend au moins un interféromètre de Fabry-Pérot supplémentaire. De préférence encore, le système (20) comporte un ensemble télescope pour étendre le faisceau laser primaire (24) rencontrant l'interféromètre de Fabry-Pérot (10). Cette invention concerne en outre une installation laser équipée d'un tel système (20). De préférence, l'installation laser comprend un système amplificateur agencé entre deux systèmes (20). De préférence encore, l'installation laser est conçue pour générer un rayonnement EUV. La cible de faisceau laser (40) peut se présenter sous la forme d'une gouttelette.
EP20712842.2A 2020-03-03 2020-03-03 Système pour empêcher une réinjection de rayonnement et installation laser équipée d'un tel système Pending EP4115481A1 (fr)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/EP2020/055489 WO2021175412A1 (fr) 2020-03-03 2020-03-03 Système pour empêcher une réinjection de rayonnement et installation laser équipée d'un tel système

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EP4115481A1 true EP4115481A1 (fr) 2023-01-11

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EP20712842.2A Pending EP4115481A1 (fr) 2020-03-03 2020-03-03 Système pour empêcher une réinjection de rayonnement et installation laser équipée d'un tel système

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EP (1) EP4115481A1 (fr)
KR (1) KR20220134656A (fr)
CN (1) CN115244799A (fr)
WO (1) WO2021175412A1 (fr)

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8462425B2 (en) * 2010-10-18 2013-06-11 Cymer, Inc. Oscillator-amplifier drive laser with seed protection for an EUV light source
US8774236B2 (en) * 2011-08-17 2014-07-08 Veralas, Inc. Ultraviolet fiber laser system
CN103067092A (zh) * 2012-12-28 2013-04-24 华为技术有限公司 多波长光源装置
DE102015211426A1 (de) 2015-06-22 2016-12-22 Trumpf Laser Gmbh Verstärkeranordnung

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WO2021175412A1 (fr) 2021-09-10
CN115244799A (zh) 2022-10-25
KR20220134656A (ko) 2022-10-05

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