Method for generating and amplifying laser pulses, method for generating a plasma which emits secondary radiation, method for producing microchips or semiconductor intermediate products, and optical assembly

Abstract

The invention relates to a method for generating and amplifying laser pulses (12, 14) by means of an optical amplifier (32), the optical amplifier (32) comprising a laser-active solid body (34) for amplifying the laser pulses (12, 14). The method comprises: generating a laser pulse of a first type (12); generating a laser pulse of a second type (14); generating a population inversion in the laser-active solid body (34); and amplifying the laser pulse of the first type (12) and the laser pulse of the second type (14) by means of the optical amplifier (32) by causing the laser pulse of the first type (12) and the laser pulse of the second type (14) to pass through the laser-active solid body (34) while the laser-active solid body (34) is in the state of population inversion. The laser pulse of the first type (12) and the laser pulse of the second type (14) differ from one another in terms of their wavelength.

Description

[0001] Methods for generating and amplifying laser pulses, methods for generating a plasma emitting secondary radiation, methods for manufacturing microchips or semiconductor intermediates and optical arrangements

[0002] Description

[0003] The invention relates to a method for generating and amplifying laser pulses, a method for generating a plasma emitting secondary radiation, a method for manufacturing microchips or semiconductor intermediates, and an optical arrangement.

[0004] Extreme ultraviolet light (EUV light) enables the precise and highly accurate imaging of fine structures, which is why EUV light is frequently used in lithography, a process that can therefore be called EUV lithography. Due to the advantage of precise and highly accurate imaging of fine structures, EUV lithography is suitable for the production of integrated circuits, especially for the manufacture of microchips.

[0005] EUV light is typically generated by irradiating a target material with a laser pulse. The laser pulse converts the target material into a plasma state, and the target material then emits EUV light. Various methods and / or optical arrangements can be used to generate and / or amplify the laser pulse.

[0006] The invention aims to provide a method for generating and amplifying laser pulses, a method for generating a plasma emitting secondary radiation, a method for manufacturing microchips or semiconductor intermediates, and an optical arrangement, each of which has improved properties, in particular enabling the realization of a compact structure.

[0007] The invention solves this problem by providing a method with the features of claim 1, a method with the features of claim 11, a method with the features of claim 12, and an optical arrangement with the features of claim 13. Advantageous embodiments and further developments of the invention are set forth in the dependent claims.

[0008] A method according to the invention serves to generate and amplify laser pulses using an optical amplifier, in particular for exciting a target material, preferably for generating an EUV light-emitting plasma. The optical amplifier comprises a laser-active solid for amplifying the laser pulses. The method comprises: generating a laser pulse of the first kind; generating a laser pulse of the second kind; generating a population inversion in the laser-active solid; and amplifying the laser pulse of the first kind and the laser pulse of the second kind using the optical amplifier, by having the laser pulse of the first kind and the laser pulse of the second kind pass through the laser-active solid while the laser-active solid has the population inversion. The laser pulse of the first kind and the laser pulse of the second kind differ from each other in their wavelength.

[0009] The two laser pulses, which differ in wavelength, can be amplified using the same laser-active solid. This eliminates the need for separate optical amplifiers to amplify the two laser pulses, thus saving one optical amplifier. Therefore, this method reduces the number of optical components required for amplifying the two laser pulses, allowing for a particularly compact and cost-effective optical arrangement.

[0010] Another aspect is that the laser-active solid enables the amplification of laser pulses to high power levels. In other words, the laser-active solid can therefore be suitable for high-power applications.

[0011] Laser pulse amplification can be achieved using stimulated emission in a laser-active solid. This amplification can involve increasing the peak pulse power and / or the pulse energy of the laser pulses.

[0012] The optical amplifier can include a pump radiation source for generating a pump beam. The pump beam can be a laser beam. The pump beam can be used to pump the laser-active solid, in particular optically.

[0013] Pumping, particularly optical pumping, can be understood as the generation of population inversion in the laser-active solid. Specifically, population inversion can be generated by irradiating the laser-active solid with the pump beam and by absorption of the pump beam by the laser-active solid.

[0014] EUV light can be understood as light with a wavelength in the range of 5 nm (nanometers) to 120 nm, in particular 8 nm to 15 nm.

[0015] The target material can be a metal, for example, tin. The target material can be in the form of a droplet, for example, a tin droplet. Forming the target material as a tin droplet can be particularly advantageous for generating EUV light due to a high yield of EUV light.

[0016] The laser-active solid can be slab-shaped. Slab-shaped means that the laser-active solid is plate-shaped. In other words, the laser-active solid can be cuboid-shaped, with its height being less than its width and length. Such a shape can facilitate better cooling of the laser-active solid, particularly improving heat dissipation from the heat generated by laser pulse amplification. This allows for high power amplification of the laser pulses.

[0017] The generation of a first-order laser pulse can be achieved using a first laser beam source. The generation of a second-order laser pulse can be achieved using a second laser beam source. The first and second laser beam sources can be separate from each other.

[0018] The first and / or the second laser beam source can be a wavelength-stabilized and / or frequency-stabilized laser beam source. The first and / or the second laser beam source can be a diode laser. The first and / or the second laser beam source can include at least one laser diode.

[0019] The term "during" can be understood to mean that another process occurs at the same time or simultaneously. In particular, the passage through the laser-active solid while the laser-active solid exhibits population inversion can be understood to mean that the two laser pulses pass through the laser-active solid and that the laser-active solid exhibits population inversion at the same time or simultaneously. The designations "laser pulse of the first kind" and "laser pulse of the second kind" clarify that the two laser pulses differ in their nature, especially in their properties. Specifically, this designation clarifies that the two laser pulses differ in their wavelengths.

[0020] A laser pulse of the first kind can be described as a laser pulse with a first wavelength, and a laser pulse of the second kind can be described as a laser pulse with a second wavelength. It is also conceivable that the laser pulse of the first kind and the laser pulse of the second kind differ in other properties. In other words, the difference between a laser pulse of the first kind and a laser pulse of the second kind cannot be limited to wavelength.

[0021] The laser pulse of the first kind and / or the laser pulse of the second kind can have a pulse duration with a value in the range of 2 ns (nanoseconds) to 50 ns, in particular 4 ns to 20 ns.

[0022] The laser pulse of the first kind and / or the laser pulse of the second kind can have a pulse energy with a value in the range of 1 mJ (millijoules) to 100 mJ.

[0023] The spectral bandwidth of the laser pulse of the first kind and / or the spectral bandwidth of the laser pulse of the second kind can have a value in the range of 0.01 nm to 1 nm, in particular 0.5 nm to 1 nm.

[0024] A central wavelength of the first type of laser pulse can differ from a central wavelength of a gain bandwidth of the laser-active solid by at least 1 nm, in particular 2 nm, preferably 3 nm. A central wavelength of the second type of laser pulse can differ from the central wavelength of the gain bandwidth of the laser-active solid by at least 1 nm, in particular 2 nm, preferably 3 nm.

[0025] The central wavelength of the laser pulse of the first kind can differ from the central wavelength of the laser pulse of the second kind by a wavelength difference, wherein the wavelength difference has a magnitude in the range of 1 nm to 3 nm, in particular 1 nm to 2 nm. The central wavelength of the laser pulse of the first kind and the central wavelength of the laser pulse of the second kind can lie within the gain bandwidth of the laser-active solid.

[0026] The central wavelength of the laser pulse of the first kind and / or the central wavelength of the laser pulse of the second kind can have a value in the range of 1029 nm to 1032 nm.

[0027] The method can involve generating a type I laser beam by regularly repeating the generation of the type I laser pulse. The type I laser beam can be formed from a multitude of type I laser pulses. The average power of the type I laser beam before passing through the laser-active solid can be less than 50 W (watts). The average power of the type I laser beam after passing through the laser-active solid can be in the range of 50 W to 2500 W.

[0028] The method can involve generating a type II laser beam by regularly repeating the generation of the type II laser pulse. The type II laser beam can be formed from a multitude of type II laser pulses. The average power of the type II laser beam before passing through the laser-active solid can be less than 50 W (watts). The average power of the type II laser beam after passing through the laser-active solid can be in the range of 50 W to 2500 W.

[0029] Another aspect of the method is that the first-order laser pulse and the second-order laser pulse can be spatially separated from each other by means of spectral filtering after passing through the optical amplifier. This allows two laser pulses to be provided independently of each other for one application or for two different applications.

[0030] Another aspect of the process is that the first-order laser pulse and the second-order laser pulse can be spatially separated from each other by spectral filtering after passing through the optical amplifier and then combined into a single laser pulse using a spectral combining device. This allows for particularly high pulse energies to be achieved. In a further development of the process, the laser-active solid is formed from a crystal, an amorphous fiber, or an amorphous rod. Such laser-active solids can be produced particularly easily and cost-effectively.

[0031] If the laser-active solid is formed from a crystal, the laser-active solid can also be called a laser crystal.

[0032] The laser-active solid can be made of a material containing, in particular, Yb:YAG, Nd:YAG, Yb:LuAG, Yb:CaF2, Yb:Lu2O3, Yb:GGG, Nd:YVO4, Nd:GdVO4, Yb:KGW, or Yb:KYW. These materials are particularly suitable for efficient amplification and can exhibit low heat generation during amplification. Yb:YAG or Nd:YAG are especially suitable for this purpose.

[0033] In a further development of the method, the laser-active solid is formed from a crystal. The optical amplifier, in particular, comprises a single laser-active solid. The laser-active solid made of crystal can be advantageous for carrying out the method. In particular, this can make the method suitable for generating and amplifying laser pulses to high power levels. In a further development of the method, the first-order laser pulse and the second-order laser pulse pass through the laser-active solid simultaneously or, particularly in the picosecond or nanosecond range, with a time delay, for the purpose of amplification.

[0034] If the first-order laser pulse and the second-order laser pulse pass through the laser-active solid with a time offset, the interval between the two laser pulses can be used for optical pumping of the laser-active solid. This allows the first-order laser pulse and the second-order laser pulse to be amplified by the laser-active solid with the same gain efficiency.

[0035] If the first-order laser pulse and the second-order laser pulse pass through the laser-active solid simultaneously, a setup can be simplified to direct both laser pulses onto a target area at the same time.

[0036] In a further development of the method, the first-order laser pulse propagates along a first direction of propagation. The second-order laser pulse propagates along a second direction of propagation. The method, particularly prior to the amplification of the first-order and second-order laser pulses, involves: changing the first direction of propagation of the first-order laser pulse and / or the second direction of propagation of the second-order laser pulse, such that the first direction of propagation of the first-order laser pulse and the second direction of propagation of the second-order laser pulse have a congruent path in the laser-active solid. As a result, the first-order laser pulse and the second-order laser pulse propagate along a common or identical beam path through the laser-active solid.In other words, the beam path through the laser-active solid of the first type of laser pulse and the beam path through the laser-active solid of the second type of laser pulse are the same, in particular identical.

[0037] Before at least one of the two propagation directions changes, the first and second propagation directions can differ from each other. After at least one of the two propagation directions changes, the two propagation directions can be the same, in particular, exhibit an identical course.

[0038] In a further development of the method, the process involves coupling a sacrificial pulse into the laser-active solid while the solid is undergoing population inversion. The sacrificial pulse traverses the solid, particularly in the picosecond or nanosecond range, with a time delay between the first-order laser pulse and the second-order laser pulse. This reduces or completely eliminates the occurrence of parasitic radiation. Specifically, the sacrificial pulse prevents the amplifier from generating its own laser beam. Parasitic laser power can be selectively extracted from the solid using the sacrificial pulse. The sacrificial pulse can ensure that no more than 10% of the relevant parasitic power loss occurs.

[0039] The sacrificial pulse can pass through the laser-active solid between the first-order laser pulse and the second-order laser pulse. In other words, the first-order laser pulse, the second-order laser pulse, and the sacrificial pulse can pass through the laser-active solid sequentially. One possible sequence of laser pulses passing through the laser-active solid is: first-order laser pulse, sacrificial pulse, and second-order laser pulse. An alternative sequence of laser pulses passing through the laser-active solid is: second-order laser pulse, sacrificial pulse, and first-order laser pulse.

[0040] The sacrificial pulse can have a wavelength that differs from the wavelength of the laser pulse of the first kind and / or the wavelength of the laser pulse of the second kind. A central wavelength of the sacrificial pulse can lie within the gain bandwidth of the laser-active solid. The optical amplifier can include a modulator, in particular an acousto-optic modulator or an electro-optic modulator, which is arranged in the first or second propagation direction downstream of the laser-active solid. By means of the modulator, the sacrificial pulse can be spatially separated from the laser pulse of the first kind and the laser pulse of the second kind. In particular, by means of the modulator, the sacrificial pulse can be deflected while the laser pulse of the first kind and the laser pulse of the second kind are not deflected, or vice versa. This allows the sacrificial pulse to be spatially separated from the other two laser pulses.

[0041] In a further development of the method, the procedure involves: determining a target temperature based on the first wavelength of the laser pulse of the first kind and the second wavelength of the laser pulse of the second kind; and controlling the temperature of the laser-active solid to the target temperature while the laser-active solid exhibits population inversion. This allows the gain bandwidth of the laser-active solid to be influenced, and in particular controlled, such that the laser pulse of the first kind and the laser pulse of the second kind are amplified as they pass through the laser-active solid. In other words, the gain bandwidth of the laser-active solid can thereby be tuned to the first wavelength of the laser pulse of the first kind and to the second wavelength of the laser pulse of the second kind.

[0042] The gain bandwidth of the laser-active solid can be temperature-dependent. By controlling the temperature of the laser-active solid to the target temperature, the gain bandwidth can be influenced, and in particular, regulated.

[0043] Determining the target temperature can involve calculating the magnitude of the difference between the value of the first wavelength of the laser pulse of the first kind and the value of the second wavelength of the laser pulse of the second kind. Alternatively, it can involve determining the target temperature based on the magnitude of the difference between the value of the first wavelength of the laser pulse of the first kind and the value of the second wavelength of the laser pulse of the second kind. A mapping of different target temperature values ​​to different magnitudes of the difference can be predefined, for example, by means of a table.

[0044] The temperature of the laser-active solid can be controlled by regulating the cooling temperature of the optical amplifier used to cool the laser-active solid. For example, the temperature of the laser-active solid can be controlled by regulating the temperature of a cooling fluid, particularly cooling water, that cools the laser-active solid. Alternatively, the cooling system can include at least one Peltier element attached to the laser-active solid for cooling purposes. The temperature of the laser-active solid can be controlled by actuating the Peltier element.

[0045] The target temperature can be in the range of 18°C ​​to 30°C. Preferably, the temperature can be 25°C.

[0046] In a further development of the method, the process, particularly before the generation of the first-order laser pulse and, in particular, before the generation of the second-order laser pulse, includes specifying the duration of a time interval between the first-order laser pulse and the second-order laser pulse. The generation of the first-order laser pulse and the generation of the second-order laser pulse are carried out in such a way that, depending on the specified duration of the time interval, the first-order laser pulse and the second-order laser pulse pass through an output of the optical amplifier with a time delay corresponding to the duration of the time interval, in particular sequentially. This makes the method suitable for applications requiring two laser pulses with a time delay equal to the specified time interval.

[0047] The output of the optical amplifier can be an output of the optical arrangement. The first-order laser pulse and the second-order laser pulse can exit the optical amplifier and / or the optical arrangement via the output.

[0048] In a further development of the method, the procedure, particularly in terms of timing, includes the following steps before the generation of the first-order laser pulse and before the generation of the second-order laser pulse: receiving a trigger signal. The generation of the first-order laser pulse and the generation of the second-order laser pulse occur depending on the received trigger signal. This allows the first-order laser pulse and the second-order laser pulse to be provided as needed.

[0049] In a further development of the method, the process, particularly with regard to timing, after amplification of the first-order and second-order laser pulses, involves directing the first-order and second-order laser pulses onto a target material to generate a plasma of the target material that emits secondary radiation, in particular EUV light. This makes the method suitable for the fabrication of integrated circuits, especially microchips. Generating the secondary radiation can include irradiating a target material with the first-order and second-order laser pulses. By irradiating the target material with the first-order and second-order laser pulses, the target material can be brought into a plasma state. In this plasma state, the target material can emit the secondary radiation.

[0050] Secondary radiation can occur as a byproduct of converting the target material into the plasma state. This secondary radiation may contain EUV light.

[0051] A method according to the invention serves to generate a plasma of a target material that emits secondary radiation, in particular EUV light. The method comprises the steps of the method described above. The method further comprises: generating units of the target material; directing the laser pulse of the first kind and the laser pulse of the second kind onto the units of the target material; thereby generating a plasma of the target material which emits the secondary radiation, in particular EUV light; collecting the generated secondary radiation, in particular the EUV light, in a secondary radiation collecting optic, in particular an EUV collecting optic, and directing the secondary radiation towards a projection exposure optic.

[0052] Each unit of the target material can be configured as a droplet. The secondary radiation collecting optics can be configured as a concave mirror. The projection exposure optics can be configured to focus the secondary radiation onto the target material.

[0053] A method according to the invention serves to manufacture microchips or semiconductor intermediates. The method comprises the steps of the previously described method for generating and amplifying laser pulses or the steps of the previously described method for generating a plasma emitting secondary radiation. The method further comprises: directing generated EUV light, collected by means of an EUV collecting optic, onto a projection exposure optic, in particular a reflective one; directing the EUV light from the projection exposure optic onto a semiconductor substrate coated with a photosensitive coating.

[0054] The photosensitive coating can be called a photoresist.

[0055] An optical arrangement according to the invention is configured for generating and amplifying a laser pulse of the first kind and a laser pulse of the second kind. The optical arrangement comprises a first laser beam source, a second laser beam source, an optical amplifier, and a control device. The first laser beam source serves to generate a laser pulse of the first kind. The second laser beam source serves to generate a laser pulse of the second kind. The optical amplifier comprises a laser-active solid for amplifying the laser pulse of the first kind and the laser pulse of the second kind. The control device is configured for controlling the first laser beam source and the second laser beam source. The laser pulse of the first kind and the laser pulse of the second kind differ from each other in their wavelength. The first laser beam source and the second laser beam source are configured separately or independently of each other.

[0056] The optical arrangement can be designed and specifically configured to execute one of the previously described methods. The preceding description of the methods can also apply to optical arrangements with identical or functionally equivalent features.

[0057] The control unit may include an electrical processing unit, in particular a computer and / or a microcontroller. The control unit may be configured to trigger, initiate, or initiate the generation of the first type of laser pulse by controlling the first laser beam source and / or the generation of the second type of laser pulse by controlling the second laser beam source.

[0058] In a further development of the optical arrangement, the laser-active solid is formed from a crystal, an amorphous fiber, or an amorphous rod. Such laser-active solids can be manufactured particularly easily and cost-effectively.

[0059] If the laser-active solid is formed from a crystal, the laser-active solid can also be called a laser crystal.

[0060] The laser-active solid can be made of a material containing, in particular, Yb:YAG, Nd:YAG, Yb:LuAG, Yb:CaF2, Yb:Lu2O3, Yb:GGG, Nd:YVO4, Nd:GdVO4, Yb:KGW, or Yb:KYW. These materials are particularly suitable for efficient amplification and can exhibit low heat generation during amplification. Yb:YAG or Nd:YAG are especially suitable for this purpose.

[0061] In a further development of the optical arrangement, the laser-active solid is formed from a crystal. The optical amplifier, in particular, comprises a single laser-active solid. The laser-active solid made of crystal can be advantageous for carrying out the process. In particular, this can make the process suitable for generating and amplifying laser pulses to high power levels.

[0062] In a further development of the optical arrangement, the laser-active solid is shaped in a slab-like form.

[0063] Further advantages and advantageous embodiments of the invention can be seen from the figures, their description, and the claims. All features disclosed in the figures, their description, and the claims can be essential to the invention, both individually and in any combination. The figures show:

[0064] Fig. 1 shows a schematic representation of an optical arrangement.

[0065] Fig. 1 shows an optical arrangement 10. The optical arrangement 10 is designed for generating and amplifying a first-order laser pulse 12 and a second-order laser pulse 14. In Fig. 1, the first-order laser pulse 12 is represented by a solid line and the second-order laser pulse 14 by a dotted line. The first wavelength value of the first-order laser pulse 12 and the second wavelength value of the second-order laser pulse 14 differ from each other.

[0066] The optical arrangement 10 has a first laser beam source 16 for generating the laser pulse of the first kind 12. The optical arrangement 10 has a second laser beam source 18 for generating the laser pulse of the second kind 14. The first laser beam source 16 and the second laser beam source 18 are separate and independent of each other.

[0067] The first laser beam source 16 and the second laser beam source 18 are each wavelength-stabilized laser beam sources. Both the first laser beam source 16 and the second laser beam source 18 are configured as diode lasers.

[0068] The laser pulse of the first kind 12 and the laser pulse of the second kind 14 each have a pulse duration in the range of 2 ns to 50 ns. The spectral bandwidth of the laser pulse of the first kind 12 and the spectral bandwidth of the laser pulse of the second kind 14 each have a value in the range of 0.01 nm to 1 nm. The central wavelength of the laser pulse of the first kind 12 differs from the central wavelength of the laser pulse of the second kind 14 by a wavelength difference with a value in the range of 1 nm to 3 nm.

[0069] In the illustrated embodiment, the central wavelength of the first-order laser pulse is 12 × 1029 nm and the central wavelength of the second-order laser pulse is 14 × 1032 nm. After leaving the first laser beam source 16, the first-order laser pulse 12 propagates along a first propagation direction 20. After leaving the second laser beam source 18, the second-order laser pulse 14 propagates along a second propagation direction 22. The first propagation direction 20 of the first-order laser pulse 12 and the second propagation direction 22 of the second-order laser pulse 14 differ from each other.

[0070] The first-order laser pulse 12 and the second-order laser pulse 14 strike a mirror 24 of the optical arrangement 10, which is configured to transmit the first-order laser pulse 12 with a transmittance of over 95% and to reflect the second-order laser pulse 14 with a reflectance of over 95%. The first-order laser pulse 12 is transmitted by the mirror 24, and the second-order laser pulse 14 is reflected by the mirror 24.

[0071] The first-order laser pulse 12 and the second-order laser pulse 14 strike the mirror 24 in such a way that the second propagation direction 22 of the second-order laser pulse 14 is altered by the mirror 24. The mirror 24 changes the second propagation direction 22 of the second-order laser pulse 14 in such a way that the first-order laser pulse 12 and the second-order laser pulse 14 propagate along a common propagation direction 26. In other words, the path of light along which the two laser pulses 12, 14 propagate after passing the mirror 24 is identical after passing the mirror 24.

[0072] The two laser pulses 12, 14 pass through a preamplifier 28 of the optical arrangement 10, which is primarily optical. The preamplifier 28 can be configured as a ytterbium-doped optical fiber. The preamplifier 28 amplifies the two laser pulses 12, 14. In particular, after amplification by the preamplifier 28, the two laser pulses 12, 14 exhibit a higher peak power and / or a higher pulse energy than before amplification by the preamplifier 28.

[0073] After passing through the preamplifier 28, the two laser pulses 12, 14 encounter a spectral filter 30 of the optical arrangement 10. The spectral filter 30 filters out unwanted spectral components, such as those generated by ASE in the preamplifier 28, from the spectrum of the two laser pulses 12, 14. The two laser pulses 12, 14 then pass through an optical amplifier 32 of the optical arrangement 10. The optical path of the two laser pulses 12, 14 through the optical amplifier 32 is shown with a dashed line in Fig. 1.

[0074] The optical amplifier 32 has a single laser-active solid 34 for amplifying the laser pulse of the first kind 12 and the laser pulse of the second kind 14.

[0075] The laser-active solid 34 is formed from a crystal. In other words, the laser-active solid 34 has a crystal structure, which is why it can be called a laser crystal. The laser-active solid 34 is made of Yb:YAG.

[0076] The laser-active solid 34 is slab-shaped, which is why it is plate-shaped. The laser-active solid 34 is cuboid-shaped, with its height being less than its width and length. Therefore, the laser-active solid 34 can be called a slab amplifier or an Innoslab amplifier.

[0077] The optical amplifier 32 has a pump radiation source 36 for generating a pump beam. The pump beam is a laser beam. The pump beam passes through the laser-active solid 34 and is absorbed by the laser-active solid 34, forming a population inversion within the laser-active solid 34. This optically pumps the laser-active solid 34 by means of the pump beam.

[0078] The two laser pulses 12, 14 pass through the laser-active solid 34 while the laser-active solid 34 exhibits population inversion, causing the two laser pulses 12, 14 to be amplified by the optical amplifier 32. The first propagation direction of the first-order laser pulse 12 and the second propagation direction of the second-order laser pulse 14 have a coincident path within the laser-active solid 34. Therefore, the first-order laser pulse 12 and the second-order laser pulse 14 propagate along the same beam path within the laser-active solid 34.

[0079] After amplification by means of the optical amplifier 32, the two laser pulses 12, 14 exhibit a higher peak power and / or a higher pulse energy than before amplification by means of the optical amplifier 32.

[0080] The amplification of the first-order laser pulse 12 by means of the laser-active solid 34 and the amplification of the second-order laser pulse 14 by means of the laser-active solid 34 are identical. Therefore, both laser pulses 12 and 14 experience the same amplification by the laser-active solid 34.

[0081] The gain bandwidth of the laser-active solid 34 is equal to or greater than the difference between the first wavelength of the laser pulse of the first kind 12 and the second wavelength of the laser pulse of the second kind 14. In other words, the central wavelength of the laser pulse of the first kind 12 and the central wavelength of the laser pulse of the second kind 14 lie within the gain bandwidth of the laser-active solid 34. Therefore, the two laser pulses 12 and 14 can be amplified using the same laser-active solid 34.

[0082] The central wavelength of the first-kind laser pulse 12 differs from a central wavelength of the gain bandwidth of the laser-active solid 34 by 1.5 nm. The central wavelength of the second-kind laser pulse 14 differs from the central wavelength of the gain bandwidth of the laser-active solid 34 by 1.5 nm.

[0083] The optical amplifier 32 has a first Peltier element 38 and a second Peltier element 40. The two Peltier elements 38, 40 are arranged on opposite sides of the laser-active solid 34. The two Peltier elements 38, 40 contact the laser-active solid 34. The two Peltier elements 38, 40 serve to cool the laser-active solid 34. The two Peltier elements 38, 40 are controlled by a control unit 42 of the optical arrangement.

[0084] The control unit 42 is an electronic computing unit in the form of a microcontroller. The control unit 42 is configured to regulate the gain bandwidth of the laser-active solid 34 by controlling its temperature. For this purpose, the control unit 42 is provided with the first wavelength of the laser pulse of the first kind 12 and the second wavelength of the laser pulse of the second kind 14. The control unit 42 calculates the magnitude of the difference between the value of the first wavelength of the laser pulse of the first kind 12 and the value of the second wavelength of the laser pulse of the second kind 14. A table is provided to the control unit 42 in which different values ​​of the magnitude of the difference are assigned to different values ​​of a target temperature of the laser-active solid 34.The target temperature listed in the table indicates the temperature that is optimal for amplifying the two laser pulses 12, 14 with the laser-active solid 34. The control unit 42 determines the magnitude of the 3 nm difference. Using the table, the control unit 42 determines a target temperature of 25 °C.

[0085] The control unit 42 is designed to detect the temperature of the laser-active solid 34. The control unit 42 regulates the temperature of the laser-active solid 34 to the target temperature by controlling the two Peltier elements 38, 40 while the laser-active solid 34 exhibits population inversion. This aligns the gain bandwidth of the laser-active solid 34 with the first wavelength of the first-order laser pulse 12 and with the second wavelength of the second-order laser pulse 14.

[0086] To reduce or completely prevent the occurrence of parasitic radiation in the laser-active solid 34, the control device 42 is configured to control the second laser beam source 18 for generating a sacrificial pulse 44. In Fig. 1, the sacrificial pulse 44 is represented by a solid line.

[0087] The sacrificial pulse 44 has the same second wavelength as the laser pulse of the second kind 14. The wavelength of the sacrificial pulse 44 differs from the first wavelength of the laser pulse of the first kind 12.

[0088] The control device 42 is configured to control the second laser beam source 18 for generating the sacrificial pulse 44 such that the sacrificial pulse 44 is coupled into the laser-active solid 34 while the laser-active solid 34 exhibits population inversion. The control device 42 is configured to control the second laser beam source 18 for generating the sacrificial pulse 44 such that the sacrificial pulse 44 is coupled into the laser-active solid 34 with a time offset relative to the laser pulse of the first kind 12 and relative to the laser pulse of the second kind 14. Therefore, the sacrificial pulse 44 traverses the laser-active solid 34 with a time offset relative to the laser pulse of the first kind 12 and with a time offset relative to the laser pulse of the second kind 14.

[0089] The optical amplifier 32 has a modulator 46 for intercepting the sacrificial pulse 44. The modulator 46 is an electro-optic modulator. The modulator 46 is arranged downstream of the laser-active solid 34 in the common propagation direction 26 of the laser pulses 12, 14, 44. By means of the modulator 46, the sacrificial pulse 44 is spatially separated from the first-order laser pulse 12 and the second-order laser pulse 14 and subsequently removed or eliminated. The control device 42 is configured to trigger the generation of the first-order laser pulse 12 by activating the first laser beam source 16 and the generation of the second-order laser pulse 14 by activating the second laser beam source 18. This allows the first-order laser pulse 12 and the second-order laser pulse 14 to be provided at an output 48 with a predetermined duration of a time interval 50 between the two laser pulses 12, 14.

[0090] In the illustrated embodiment, the control unit 42 controls the first laser beam source 16 and the second laser beam source 18 such that the duration of the time interval 50 between the two laser pulses 12, 14 at the output 48 is equal to a predetermined duration. This causes the two laser pulses 12, 14 to pass through the output 48 with a time offset, in particular one after the other. Additionally, the control unit 42 controls the two laser beam sources 16, 18 such that the laser-active solid 34 is first traversed by the first-order laser pulse 12, then by the sacrificial pulse 44, and then by the second-order laser pulse. This causes the laser pulses 12, 14, 44 to traverse the laser-active solid 34 one after the other, and in particular not simultaneously.

[0091] In the illustrated embodiment, the control unit 42 receives a trigger signal 52. The trigger signal 52 can originate from a signal source that is not part of the optical arrangement 10. The control unit 42 controls the first laser beam source 16 and the second laser beam source 18 depending on the trigger signal 52, so that the first laser beam source 16 generates the first-type laser pulse 12 and the second laser beam source 18 generates the second-type laser pulse 14. In other words, the trigger signal 52 specifies a time for the control unit 42 to generate the two laser pulses 12 and 14. This allows the two laser pulses 12 and 14 to be requested as needed via the trigger signal 52.

[0092] The control device 42 can be configured to adjust the timing of the arrival of the laser pulses 12, 14 at the output 48 with an error of less than 10 ns and a time delay from the reception of the trigger signal 52 until the arrival of the laser pulses 12, 14 at the output 48.

[0093] In an alternative embodiment not shown, the control device can be configured to control the first and second laser beam sources such that the generation of a first-order laser pulse and the generation of a second-order laser pulse are repeated at regular time intervals. This allows a multitude of first-order laser pulses to be generated by the first laser beam source and a multitude of second-order laser pulses to be generated by the second laser beam source. The multitude of first-order laser pulses can form a first-order laser beam, and the multitude of second-order laser pulses can form a second-order laser beam. The average power of the first-order laser beam and the average power of the second-order laser beam can be equal.The mean power of the first type of laser beam and the mean power of the second type of laser beam can each be less than 50 W before passing through the laser-active solid and have a value in the range of 50 W to 52 W after passing through the laser-active solid.

[0094] In an alternative embodiment not shown, a target material can be irradiated using the laser pulse of the first kind and the laser pulse of the second kind for the purpose of generating EUV light.

Claims

Patent claims 1. A method for generating and amplifying laser pulses (12, 14) using an optical amplifier (32), in particular for exciting a target material, in particular for generating an EUV light-emitting plasma, wherein the optical amplifier (32) comprises a laser-active solid (34) for amplifying the laser pulses (12, 14), wherein the method comprises: Generating a laser pulse of the first kind (12), Generating a laser pulse of the second kind (14), Generating a population inversion in the laser-active solid (34), and amplifying the first-kind laser pulse (12) and the second-kind laser pulse (14) by means of the optical amplifier (32), by having the first-kind laser pulse (12) and the second-kind laser pulse (14) pass through the laser-active solid (34) while the laser-active solid (34) has the population inversion, where the laser pulse of the first kind (12) and the laser pulse of the second kind (14) differ in their wavelength.

2. Method according to claim 1, wherein the laser-active solid (34) is formed from a crystal, an amorphous fiber or an amorphous rod.

3. Method according to claim 2, wherein the laser-active solid (34) is formed from a crystal and wherein the optical amplifier (32) in particular comprises a single laser-active solid (34).

4. Method according to any of the preceding claims, wherein the laser pulse of the first kind (12) and the laser pulse of the second kind (14) pass through the laser-active solid (34) simultaneously or, in particular in the pico- or nanosecond range, with a time delay for the purpose of amplification.

5. Method according to any of the preceding claims, wherein the laser pulse of the first kind (12) propagates along a first propagation direction (20), wherein the laser pulse of the second kind (14) propagates along a second propagation direction (22), wherein the method, prior to amplifying the first-kind laser pulse (12) and the second-kind laser pulse (14), comprises the following step: changing the first propagation direction (20) of the first-kind laser pulse (12) and / or the second propagation direction (22) of the second-kind laser pulse (14) such that the first propagation direction (20) of the first-kind laser pulse (12) and the second propagation direction (22) of the second-kind laser pulse (14) have a matching course in the laser-active solid (34).

6. Method according to any of the preceding claims, wherein the method comprises: coupling a sacrificial pulse (44) into the laser-active solid (34) while the laser-active solid (34) exhibits population inversion, wherein the sacrificial pulse (44), particularly in the pico- or nanosecond range, passes through the laser-active solid (34) at a time offset from the laser pulse of the first kind (12) and at a time offset from the laser pulse of the second kind (14).

7. Method according to any of the preceding claims, the procedure exhibits: Determining a target temperature based on a first wavelength of the laser pulse of the first kind (12) and a second wavelength of the laser pulse of the second kind (14), and Controlling the temperature of the laser-active solid (34) to the target temperature while the laser-active solid (34) exhibits population inversion.

8. Method according to any of the preceding claims, wherein the method comprises, prior to generating the laser pulse of the first kind (12) and prior to generating the laser pulse of the second kind (14): specifying a duration of a time interval (50) between the laser pulse of the first kind (12) and the laser pulse of the second kind (14), wherein the generation of the first type of laser pulse (12) and the generation of the second type of laser pulse (14) take place in such a way as to depend on the specified duration of the time interval (50) that the first type of laser pulse (12) and the second type of laser pulse (14) pass through an output (48) of the optical amplifier (32) with a time offset, in particular one after the other, for the duration of the time interval (50).

9. Method according to any of the preceding claims, wherein the method comprises, prior to generating the laser pulse of the first kind (12) and prior to generating the laser pulse of the second kind (14): receiving a trigger signal (52), wherein the generation of the first type of laser pulse (12) and the generation of the second type of laser pulse (14) are dependent on the received trigger signal (52).

10. Method according to any of the preceding claims, wherein the method after amplification of the laser pulse of the first kind (12) and the laser pulse of the second kind (14) comprises: directing the laser pulse of the first kind (12) and the laser pulse of the second kind (14) towards a target material to generate a plasma of the target material emitting secondary radiation, in particular EUV light.

11. Method for generating a plasma of a target material emitting secondary radiation, in particular EUV light, wherein the method comprises the steps of the method according to one of the preceding claims, wherein the method further comprises: Generating units of the target material, Directing the first-kind laser pulse (12) and the second-kind laser pulse (14) towards the units of the target material, This generates a plasma of the target material which emits secondary radiation, especially EUV light, Collecting the generated secondary radiation, in particular the EUV light, in a secondary radiation collecting optic, in particular an EUV collecting optic, and directing the secondary radiation towards a projection exposure optic.

12. A method for manufacturing microchips or semiconductor intermediates, wherein the method comprises the steps of the method according to any one of claims 1 to 10 or the steps of the method according to claim 11, wherein the method further comprises: directing generated and collected EUV light by means of an EUV collecting optic onto a projection exposure optic, in particular a reflective one, Directing the EUV light from the projection exposure optics onto a semiconductor substrate coated with a photosensitive coating.

13. Optical arrangement (10) for generating and amplifying a laser pulse of the first kind (12) and a laser pulse of the second kind (14), wherein the optical arrangement (10) comprises: a first laser beam source (16) for generating a laser pulse of the first kind (12), a second laser beam source (18) for generating a laser pulse of the second kind (14), an optical amplifier (32) with a laser-active solid (34) for amplifying the laser pulse of the first kind (12) and the laser pulse of the second kind (14), and a control device (42) for controlling the first laser beam source (16) and the second laser beam source (18), wherein the laser pulse of the first kind (12) and the laser pulse of the second kind (14) differ in their wavelength, wherein the first laser beam source (16) and the second laser beam source (18) are designed separately from each other.

14. Optical arrangement (10) according to claim 13, wherein the laser-active solid (34) is formed from a crystal, an amorphous fiber or an amorphous rod.

15. Optical arrangement (10) according to claim 14, wherein the laser-active solid (34) is formed from a crystal and wherein the optical amplifier (32) in particular comprises a single laser-active solid (34).

16. Optical arrangement (10) according to claim 15, wherein the laser-active solid (34) is slab-shaped.

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