Optical device for changing the polarisation of a polarised light beam, optical system, EUV driver laser and EUV light generation system

Abstract

The invention relates to an optical device (10) for changing the polarisation (12) of a polarised light beam (14). The optical device (10) has a beam input (16) for the polarised light beam (14), which can enter the beam input (16) of the optical device (10) along a first propagation axis (18), and a beam output (20) for the polarised light beam (14), which can exit the beam output (20) of the optical device (10) along a second propagation axis (22). Furthermore, the optical device (10) has a plurality of deflecting elements (24), each of which is designed to deflect the polarised light beam (14) within the optical device (10), wherein at least one of said deflecting elements (24) is designed to change at least one polarisation component of the polarised light beam (14). The optical device (10) also has a beam path (26), which is formed within the optical device (10) by means of the deflecting elements (24) starting from the beam input (16) to the beam output (20) of the optical device (10). According to the invention, the deflecting elements (24) are arranged in such a way that they can be rotated together about an axis of rotation (28). Furthermore, according to the invention, the first propagation axis (18), the second propagation axis (22) and the axis of rotation (28) are parallel to one another.

Description

[0001] Optical device for changing the polarization of a polarized light beam, optical system, EUV driver laser and EUV light generation system

[0002] BACKGROUND OF THE INVENTION

[0003] 1. Field of the invention

[0004] The invention relates to an optical device for changing the polarization of a polarized light beam, comprising a) a beam input for the polarized light beam, which can enter the beam input of the optical device along a first propagation axis, b) a beam output for the polarized light beam, which can exit the beam output of the optical device along a second propagation axis, c) a plurality of deflection elements, each of which is configured to deflect the polarized light beam within the optical device, wherein at least one of these deflection elements is configured to change at least one polarization component of the polarized light beam, d) a beam path which is formed within the optical device by means of the deflection elements, starting from the beam input to the beam output of the optical device.

[0005] The invention further relates to an optical system with the optical device described above, an EUV driver laser with such an optical system or such an optical device and an EUV light generation system with such an EUV driver laser.

[0006] 2. State of the art

[0007] In the manufacture of integrated circuits, so-called microchips, semiconductor substrates (hereinafter "wafers"), which are often monocrystalline, are coated with a coating in a comparatively early manufacturing step, which is then structured in subsequent manufacturing steps. Such structuring acts as a mask in further downstream manufacturing steps, which makes it possible, for example, to etch a functional layer located beneath the coating, to dope it with foreign atoms (e.g., by ion implantation), or to introduce foreign materials into the structuring (e.g., by LIGA and lift-off).

[0008] The goal of these process steps is, among other things, to produce transistors on the wafers, as well as conductive areas that connect the transistors. The patterning can be incorporated into the coating using various methods.

[0009] In photolithography, for example, the coating is implemented as a photosensitive coating, particularly a photoresist. Here, the photoresist is exposed to light of a specific wavelength, to which the photoresist is sensitive, in a specific pattern. This can influence the chemical properties of the exposed areas of the photoresist, such as its solubility in a developer solution. There are photoresists in which the exposed areas polymerize, meaning the solubility of the exposed areas increases compared to the unexposed areas (so-called negative resists). However, there are also photoresists in which the exposed areas become more soluble than the unexposed areas (so-called positive resists).In any case, in order to form the structuring in the photoresist and thus the masking for the functional layer located beneath the photoresist, the more soluble areas of the photoresist are removed using the developer solution.

[0010] In order to introduce the specific pattern into the photoresist, a masking element (hereinafter "photomask") is usually arranged between the light source and the wafer, which, depending on the photoresist used (negative resist or positive resist), is designed as a negative or positive of the structuring to be formed on the photoresist.

[0011] In conventional photolithography, the photomask either lies directly on the photoresist or is positioned just above the photoresist, i.e., at a distance from it, whereby the photomask and the resulting pattern on the photoresist are in a 1:1 ratio. Since photomasks can only be scaled to a finite size, the size of the pattern is essentially limited to a few hundred nanometers. Because smaller patterns enable microchips with significantly higher performance per unit area or volume (since this allows more transistors to be realized in a consistently small area), there is a general effort to reduce the pattern size to physically absolute limits.For this reason, projection exposure systems are generally used today. These systems usually feature a focusing lens system between the photomask and the photoresist, allowing the photomask to be imaged on the photoresist in a drastically reduced size. This allows photomasks to be produced more cost-effectively, as the photomask structures do not need to be as small. It also allows significantly smaller structures to be imaged on the wafers compared to conventional photolithography. The photomask and the resulting patterning on the photoresist can then be present in a ratio of 5:1 or more, for example. The photomask itself can be designed as an absorptive or reflective photomask.

[0012] Since the reduced image of the photomask on the photoresist cannot cover the entire wafer, the wafer is often exposed in prior art processes using a so-called "step-and-repeat" process at a first exposure position, moved a certain distance, and then exposed again at a second exposure position. This is repeated in these known processes until the wafer is largely covered with instances of the same pattern.

[0013] After the areas of the photoresist that are more soluble than the developer solution have been removed and the underlying functional layer has been treated, for example, by etching, the photoresist is often removed from the functional layer by a process called "stripping."

[0014] For multilayer microchips, the projection exposure process described above can be performed up to a hundred times for one and the same microchip.

[0015] EUV-Li. and EUV

[0016] In addition to reducing the size of the photomask and using focusing optics, another way to reduce the size of the pattern on the wafers is to use light with a shorter wavelength for exposure.

[0017] In methods known from the prior art, extreme ultraviolet light (EUV light) with a wavelength in a range of approximately 8 to approximately 15 nm is generated for this purpose, with a major portion of the EUV light being at 13.5 nm, which is directed onto the photoresist by means of an EUV projection optics and an EUV focusing optics of the projection exposure system.

[0018] An EUV light generation system used for this purpose essentially comprises an EUV driver laser, by means of which at least one excitation light beam can be generated, a target material generator, and an EUV light generation chamber. Typically, a pulsed high-power laser is used as the EUV driver laser, and a droplet generator, by means of which droplets of a target material can be shot into the EUV light generation chamber, serves as the target material generator. To prevent damage to the system due to particle contamination, a high vacuum under a process gas atmosphere can prevail within the EUV light generation chamber in implementations known from the prior art. Hydrogen (H2) or helium (He) are particularly suitable as the process gas.

[0019] Tin (Sb) is often used as the target material in processes known from the prior art. In addition to tin (Sb), target materials that include xenon (Xe), gold (Au), and / or lithium (Li) are also possible. To increase the amount of emitted EUV light, the droplets generated by the droplet generator can, for example, first be excited with a first excitation light beam, the so-called pre-pulse, and then with a second excitation light beam, the so-called main pulse. The two excitation light beams can be generated as two independent light beams, but can also be generated by splitting a single light beam. In principle, the EUV light could be generated using just a single excitation light beam; a second excitation light beam is therefore not absolutely necessary. However, the use of a second excitation light beam increases the so-called conversion efficiency, i.e.the ratio of applied laser power to generated EUV power, increases significantly.

[0020] This is because the excitation with the pre-pulse in this known method causes a preconditioning of the target material droplet. Currently, this preconditioning involves the target material droplet developing an approximately disk-like shape due to the input of energy from the pre-pulse, thereby comparatively enlarging the surface area of ​​the target material droplet that can be excited by the second excitation light beam. The main pulse then impinges on the preconditioned target material droplet, exciting it. In the known methods, this excitation involves the generation of an ionized gas of the target material – if the target material is a tin material, this creates a tin plasma. This tin plasma then emits the EUV light required to form the pattern in the photoresist.

[0021] In another known method, for example, a third excitation light beam in the form of a so-called rarefaction pulse can be used for further preconditioning. This pulse strikes the target material droplet between the pre-pulse and the main pulse. In this known method, the rarefaction pulse causes a dilution or increase in volume of the target material droplet, which has been formed into a disc shape by the pre-pulse, into a target material cloud. The term "cloud" in this context is not synonymous with a gaseous or vapor state of the target material. The use of such a rarefaction pulse further increases the conversion efficiency.

[0022] The dilution pulse can be generated by splitting the first excitation light beam into the pre-pulse and the dilution pulse. It is also possible to use a separate beam source for the dilution pulse or even to split a single excitation light beam into the pre-pulse, the dilution pulse, and the main pulse. Furthermore, the dilution pulse can be configured as a section of the main pulse that precedes the main pulse in terms of time and is distinct from the main pulse in terms of its temporal distribution and intensity distribution over time. In this case, it is often referred to as a "pedestal."

[0023] EUV driver lasers are also conceivable, in which more than three excitation light beams are used to excite the target material and generate EUV light.

[0024] In each of the above cases, the main pulse hits the target material droplet with a power in the range of 20 to 50 kW.

[0025] EUV driver laser

[0026] State-of-the-art EUV driver lasers, sometimes referred to as EUV drive lasers, may have a beam source, a pump source, an amplifier arrangement with a plurality of optical amplifiers, and a focusing unit.

[0027] The beam source can generate the excitation light beam, which is then amplified at a specific point along the optical path by the plurality of optical amplifiers into an amplified excitation light beam.

[0028] If, in the methods known from the prior art, more than one light beam is used to generate the EUV light, individual beam sources, ie a pre-pulse beam source, a dilution pulse beam source and a main pulse beam source, can also be present for each excitation light beam (pre-pulse, dilution pulse and main pulse).

[0029] In the known methods, the term "pulse" refers to a light beam that has a comparatively short duration and therefore a starting time and an end time, is part of a multitude of temporally successive light beams of the same type, and is generated by a pulsed laser. The duration of the pulses can be in the micro-, nano-, pico-, or femtosecond range. Lasers operated in continuous wave (CW) mode must be distinguished from this.

[0030] If one, two, three or more individual beam sources are used to generate the excitation light beam or the pre-pulse, dilution pulse and / or main pulse, these can generate the excitation light beams with the same or different wavelength and the same or different intensity, mode, beam caustics and / or polarization, or the excitation light beams can impinge on the target material droplet with the same or different wavelength and the same or different intensity, mode, beam caustics and / or polarization.

[0031] For example, the use of a solid-state laser as a pre-pulse beam source is known in conventional EUV excitation light generation systems. Such a known solid-state laser generates the pre-pulse with a wavelength in the range of approximately 1 pm. A solid-state laser can also be used as the dilution pulse beam source, which, for metrological purposes, preferably has a different wavelength than the pre-pulse, also in the range of approximately 1 pm.

[0032] A CO2 laser is often used as the main pulse beam source, which generates the main pulse with a wavelength in the range of approximately 10.6 pm.

[0033] State-of-the-art problem

[0034] In optical devices known from the prior art for changing the polarization of a polarized light beam, the beam is guided into a target area for the polarized light beam by means of deflection elements which form a beam path for the polarized light beam.

[0035] At least one of these deflection elements is configured to change at least one polarization component of the polarized light beam, for example, to provide a desired target polarization of the polarized light beam in the target area. In particular, due to manufacturing tolerances of the deflection elements or thermal and / or mechanical influences on the deflection elements, a polarization of the light beam in the target area may result that deviates from the desired target polarization.

[0036] If, for example, due to thermal and / or mechanical stresses within an optical device, the actual polarization of the polarized light beam differs from the desired target polarization, the prior art often involves manually replacing the at least one deflection element configured to change at least one polarization component of the polarized light beam with a deflection element that effects a different polarization of the polarized light beam in the target area, which requires comparatively high effort. Deflection elements with different polarization-changing properties can be provided for this purpose.

[0037] Often, several such deflection elements must be replaced manually, i.e., by maintenance personnel using special tools. By replacing these deflection elements, the desired target polarization in the target area can be approximately achieved.

[0038] In addition to the desired target polarization in the target area, another requirement for the polarized light beam or the optical system and / or optical device is often that the polarized light beam impinges at a specific target position. Therefore, if the deflection element(s) are manually replaced as described above, a manual position adjustment of the deflection elements is often performed to correct the actual target position of the polarized light beam to the target position. This adjustment is often performed manually on the deflection elements in order to approximate the target beam path and thus achieve the desired target position with the highest possible precision.

[0039] Despite the measures described here, an undesirable, comparatively large deviation from the desired target polarization and / or the target position in the target area often remains. Particularly in applications where the polarized light beam must exhibit particularly high power, even the smallest deviations outside a specified tolerance range can have serious consequences for the desired result. In addition, the effort and thus the maintenance costs due to the manual replacement of the deflection elements are particularly high. Furthermore, changes in polarization due to thermal and / or mechanical influences cannot be easily compensated during operation and cannot be compensated without a significant health risk for maintenance personnel.

[0040] Particularly in the case of EUV driver lasers or EUV light generation systems that may incorporate such optical devices, this would mean that a process for generating EUV light would have to be interrupted and the beam path opened for this purpose. In this particular technological area, this would also involve a high risk of failure and contamination. SUMMARY OF THE INVENTION

[0041] The object of the present invention is therefore to provide the optical device mentioned at the outset which counteracts the above-mentioned disadvantages of the prior art.

[0042] This object is achieved according to the invention by means of the optical device mentioned at the outset, in which f) the deflection elements are arranged such that they are jointly rotatable about a rotation axis, and g) the first propagation axis, the second propagation axis and the rotation axis are parallel to one another.

[0043] With this optical device, in which the first propagation axis, the second propagation axis and the rotation axis are parallel to each other and the deflection elements are arranged such that they can be rotated together about a rotation axis, a particularly precise desired polarization in the target area can be achieved.

[0044] In addition, the optical device according to the invention allows the deflection elements to be adjusted jointly with respect to the rotation axis, namely by rotating them jointly around the rotation axis, during operation and without the beam path being open. In other words, depending on the position of the deflection elements with respect to the rotation axis, the polarized light beam at the beam output of the optical device can have a different polarization than the polarized light beam at the beam input of the optical device.

[0045] Since the first propagation axis, the second propagation axis, and the rotation axis are parallel to each other, angular deviations between the polarized light beam entering the optical device and the polarized light beam exiting the optical device are largely avoided when the deflection elements are positioned differently relative to the rotation axis. This allows a particularly precise target position in the target area to be achieved for different positions of the deflection elements relative to the rotation axis.

[0046] The rotation axis is preferably a common rotation axis for the deflecting elements. The deflecting elements are therefore preferably rotatable together about a single common rotation axis. The polarized light beam as a whole, i.e., the sum of all polarization components of the polarized light beam, can be linearly polarized, circularly polarized, or elliptically polarized.

[0047] In this case, polarization components of the polarized light beam can be understood to mean an S and / or a P polarization component. Accordingly, a polarization component of the polarized light beam can be the S polarization component or the P polarization component. The S and P polarization components of the polarized light beam are commonly defined with respect to a polarization plane. The polarization plane is in turn defined by an incident light beam portion of the polarized light beam, in this case incident on the deflecting element, and an exit light beam portion of the polarized light beam emerging from the deflecting element, i.e. deflected by the deflecting element. The P polarization component is polarized within the polarization plane, i.e. oscillates within and parallel to the polarization plane.The S-polarization component, in turn, is polarized perpendicular to the plane of polarization, i.e., it oscillates perpendicular to the plane of polarization. Consequently, the P- and S-polarization components are orthogonal to each other.

[0048] If the deflecting elements are now rotated together about the rotation axis, at least one polarization component of the polarized light beam, ie specifically the outgoing light beam portion in comparison to the incident light beam portion, can be changed as a result of this and due to the at least one deflecting element configured to change the polarization.

[0049] The optical device can be designed in a comparatively simple manner with comparatively few deflection elements. For example, the optical device can have at least three, four, five, six, or more deflection elements.

[0050] The at least one deflection element, which is configured to change at least one polarization component of the polarized light beam, can advantageously be designed as a phase-shifting mirror. Phase-shifting mirrors are particularly suitable for light beams with comparatively high powers, such as those provided by EUV driver lasers. Phase-shifting mirrors are therefore particularly well-suited for EUV driver lasers, since birefringent materials are not available for the power levels and wavelength ranges generated by EUV driver lasers.

[0051] A phase-shifting mirror is understood here to be a mirror that reflects the polarized light beam with a phase shift between the P-polarization component and the S-polarization component with respect to the polarization plane. The phase shift refers to the difference between the polarization components of the outgoing light beam compared to the incident light beam of the polarized light beam. A phase-shifting mirror can, for example, cause a phase shift of 90° in the polarized light beam, although any other phase shift amounts are also conceivable and possible. A phase shift of 90° is understood here to mean a phase shift of λ / 4.Thus, a phase shift mirror that causes a phase shift of 90° can reflect a linearly polarized light beam that is incident on the phase shift mirror in such a way that the P-polarization component and the S-polarization component are equal in their amounts, as a circularly polarized light beam.

[0052] Advantageously, the first propagation axis, the second propagation axis, and the rotation axis are congruent with a common reference axis. In this case, the polarized light beam exiting the optical device does not change its position and / or orientation relative to the rotation axis. In other words, the position and / or orientation of the light beam exiting the optical device remains essentially unchanged at different positions of the deflection elements relative to the rotation axis.

[0053] Preferably, the beam path is formed within a beam plane. In this case, the beam plane also extends through the deflection elements by means of which the beam path is formed within the optical device, from the beam input to the beam output. Since the beam path is formed within a beam plane, the optical device can be designed to be particularly compact and space-saving in a direction perpendicular to the beam plane.

[0054] Furthermore, it is advantageous if the deflection elements are arranged on a common rotating body that is configured to rotate about the rotation axis. Arranging the deflection elements on a common rotating body allows for comparatively simple joint rotation of the deflection elements about the rotation axis, for example, using a mechanical and / or electrically operated positioning device.

[0055] Advantageously, the rotating body is formed in one piece. In other words, the rotating body can be formed as a monolithic body. Such a rotating body is particularly easy to manufacture, in particular by means of machining processes, a casting process, for example, an injection molding process, or a 3D printing process. Tolerances in the position and / or orientation of the deflection elements relative to one another, which can practically only be controlled up to a certain minimum degree of resolution, can thus be kept comparatively low, and a comparatively high position and / or orientation accuracy of the deflection elements can be achieved.

[0056] The rotating body preferably has a cooling device designed to dissipate heat from the deflecting elements. By deflecting the light beam at the deflecting elements, a comparatively high heat input from the polarized light beam into the deflecting elements can occur. This is particularly the case with polarized light beams of an EUV driver laser. A cooling device can dissipate heat from the deflecting elements and thereby reduce thermally induced deformations of the deflecting mirrors and the risk of damage to the deflecting mirrors. The cooling device can be designed, in particular, as a water cooling system. Water cooling can dissipate comparatively high heat inputs from the deflecting elements. This heat dissipation can preferably occur directly via the water cooling system. With such direct cooling, the heat is dissipated from the deflecting mirrors directly to the cooling water of the water cooling system.In other words, the deflection elements can be in direct contact with the cooling water or be surrounded by it. In principle, the cooling system can also be designed as an air cooling system.

[0057] It is advantageous if at least one deflecting element is connected to the rotating body by a connecting device such that the at least one deflecting element can expand axially and radially. Heat inputs into the deflecting elements can lead to thermally induced deformations and / or expansions of the deflecting elements. If at least one deflecting element cannot expand axially and radially, these deformations and / or expansions can be further amplified or even reduced. Suitable connecting devices for allowing axial and radial expansion of the at least one deflecting element can, for example, comprise spring elements. Such spring elements can include, for example, coil springs, gas springs, and disc springs.Spring elements in the present sense are understood to mean elements which comprise at least one non-positive connecting means which can connect the deflection element to the rotating body in a non-positive manner and thereby allow an axial and a radial expansion of the deflection element.

[0058] Preferably, at least one deflecting element is adjustable with respect to an alignment of this deflecting element with respect to a desired beam path by means of a correction device. By means of such a correction device, the alignment of the at least one deflecting element can be adjusted, in particular by changing the location and / or position, such that the actual beam path can be adapted to the desired beam path. This can avoid the need to remove this at least one deflecting element in the event of a change in location and / or position and to install a new deflecting element corresponding to the desired beam path. In this context, it is also advantageous if this adjustment of the at least one deflecting element can be carried out without tools, for example by means of an actuator controlled by a control device, so that no maintenance personnel is required.

[0059] Advantageously, a temperature monitoring device is assigned to at least one deflection element. A temperature monitoring device can detect the thermal state of the deflection element and critical overtemperatures at the deflection element. For example, if a critical overtemperature is reached, the power of the polarized light beam can be reduced, or the beam source can be put into sleep mode or shut down completely to reduce the risk of damage to this deflection element. Furthermore, if the at least one deflection element has experienced a critical overtemperature, it can be identified and replaced.

[0060] It is advantageous if a polarization measuring device is assigned to the optical device. Using such a polarization measuring device, the polarization can be measured, particularly in a measuring range within the optical device or in a target range for the polarized light beam, and compared with a desired polarization in the measuring range or target range. Deviations from the desired polarization can be corrected by rotation, i.e., by changing the position relative to the rotation axis of the deflection elements.

[0061] It will be clear to a person skilled in the art that all statements made above with respect to merely "at least one" element of a certain type may also refer to some or even all elements of the same type. In this respect, these developments are of course also encompassed by the invention.

[0062] According to a further aspect of the invention, the problem mentioned at the outset is solved by an optical system comprising a first optical device and a second optical device, comprising some or all of the features mentioned above for the optical device, wherein the optical devices are arranged so as to be rotatable independently of one another and the axes of rotation of the optical devices are parallel to one another. By means of such an optical system, a larger polarization range can be set by rotation about the axis of rotation compared to an individual optical device. In addition to a larger adjustment range, a desired polarization can also be achieved by a comparatively short rotation, i.e. a rotation in which a particularly small adjustment distance is covered starting from a specific reference point, of the first and / or second optical device about the axes of rotation.Advantageously, in the optical system, a sealing and / or shielding device is arranged between the first optical device and the second optical device, which is designed to substantially prevent the escape of a process gas and / or stray light between the optical devices. If a gas laser, in particular a CO2 laser, is used as the beam source for the polarized light beam, the escape of an active laser gas acting as a process gas between the first optical device and the second optical device can be significantly reduced by means of the sealing and / or shielding device. In addition, the risk of contamination of the active laser gas by the ingress of substances can be reduced. In addition to the active laser gas, the process gas can also be a cooling gas or an inert gas, for example for creating a particularly low-reactivity atmosphere.In addition, an atmospheric condition, an overpressure condition, or a negative pressure condition may also exist within the optical devices or the optical system.

[0063] According to yet another aspect of the invention, the problem mentioned at the outset is also solved by an EUV driver laser comprising an optical device or an optical system having some or all of the features mentioned above for the optical device or the optical system.

[0064] According to yet another aspect of the invention, the problem mentioned at the outset is also solved by an EUV light generation system comprising an EUV driver laser, a target material generator and an EUV light generation chamber, comprising some or all of the features mentioned above for the EUV driver laser.

[0065] Character list

[0066] An embodiment of the invention is explained in more detail below with reference to the drawings. These show:

[0067] Fig. 1 is a longitudinal sectional view along an XY plane of an embodiment of an optical device according to the invention;

[0068] Fig. 2 is an enlarged view of an area II marked in Fig. 1 of the optical device according to the invention according to Fig. 1, wherein Fig. 2 shows in particular a connecting device;

[0069] Fig. 3 shows an embodiment of an optical system according to the invention in a perspective view;

[0070] Fig. 4 shows an embodiment of an EUV light generation system according to the invention in a schematic representation.

[0071] The invention is not limited to the embodiments shown. The embodiments shown in the figures merely represent concrete examples of the invention. Within the scope of their specialist knowledge, it is possible for a person skilled in the art to recognize embodiments of the invention that are not explicitly shown.

[0072] List of reference symbols

[0073] 10 optical device

[0074] 10.1 first optical device

[0075] 10.2 second optical device

[0076] 12 Polarization

[0077] 12.1 first polarization

[0078] 12.2 second polarization

[0079] 14 polarized light beam

[0080] 16 Beam entrance

[0081] 18 first propagation axis

[0082] 20 beam exit

[0083] 22 second propagation axis

[0084] 24 Deflection element

[0085] 26 Beam path

[0086] 27 beam area

[0087] 28 Rotation axis

[0088] 28.1 first axis of rotation

[0089] 28.2 second axis of rotation

[0090] 30 common reference axis

[0091] 32 beam plane

[0092] 33 Contact surface

[0093] 34 common rotation bodies

[0094] 35 housings

[0095] 36 Cooling device

[0096] 37 O-ring

[0097] 38 Connecting device

[0098] 39 Axial spring

[0099] 40 Correction device

[0100] 42 Temperature monitoring device

[0101] 44 Polarization measuring device

[0102] 46 optical system

[0103] 48 Sealing and / or shielding device

[0104] 50 EUV driver lasers

[0105] 52 EUV light generation system

[0106] 54 Target material generator 56 EUV light generation chamber

[0107] DESCRIPTION OF PREFERRED EMBODIMENTS

[0108] Fig. 1 shows a longitudinal section along an XY plane of an embodiment of an optical device 10 according to the invention. The optical device 10 is configured to change the polarization 12 of a polarized light beam 14. The polarized light beam 14 in this case has a particularly high power and is configured and intended to be directed onto a target material such as tin (Sb), lithium (Li), or gold (Au) to generate EUV light. A polarized light beam 14 directed onto such a target material causes the generation of a target material plasma, which in turn emits the EUV light. In relation to EUV light, one occasionally speaks of so-called secondary sources. EUV light is understood here as light with a wavelength of approximately 7.5 nm to approximately 15 nm.

[0109] The polarized light beam 14 can, of course, also have a comparatively lower power and be used, for example, for laser marking or cutting processes.

[0110] The optical device 10 has a beam input 16 for the polarized light beam 14, which can enter the beam input 16 of the optical device 10 along a first propagation axis 18. Furthermore, the optical device 10 has a beam output 20 for the polarized light beam 14, which can exit the beam output 20 of the optical device 10 along a second propagation axis 22.

[0111] Furthermore, the optical device 10 has a plurality of deflection elements 24, each of which is configured to deflect the polarized light beam 14 within the optical device 10. At least one of these deflection elements 24 is configured to change at least one polarization component of the polarized light beam 14.

[0112] By means of the deflection elements 24, a beam path 26 is formed within the optical device 10, extending from the beam inlet 16 to the beam outlet 20 of the optical device 10. The beam path 26 is shown as a dotted line in the illustrated embodiment.

[0113] According to the invention, the deflection elements 24 in the optical device 10 are arranged such that they are jointly rotatable about a rotation axis 28. Furthermore, according to the invention, the first propagation axis 18, the second propagation axis 22, and the rotation axis 28 in the optical device 10 are parallel to one another. By means of these inventive features, a particularly precise desired polarization of the polarized light beam 14 can be achieved in a target area. In addition, by means of the optical device 10 according to the invention, a joint adjustment of the deflection elements 24 with respect to the rotation axis 28, namely by means of joint rotation about the rotation axis 28, can take place during operation and without the beam path 16 being open.In other words, depending on the position of the deflection elements 24 with respect to the rotation axis 16, the polarized light beam 14 at the beam output 20 of the optical device 10 may have a different polarization than the polarized light beam 14 at the beam input of the optical device 10.

[0114] Since the first propagation axis 18, the second propagation axis 22, and the rotation axis 28 are parallel to one another, angular deviations between the polarized light beam 14 entering the optical device 10 and the polarized light beam 14 exiting the optical device are largely avoided for different positions of the deflection elements 24 relative to the rotation axis 28. This allows a particularly precise target position in the target area to be achieved for different positions of the deflection elements 24 relative to the rotation axis 28.

[0115] In the present case, the first propagation axis 18, the second propagation axis 22 and the rotation axis 28 are, for example, congruent in a common reference axis 30. The common reference axis 30 lies on the X-axis of the XY section plane in the embodiment of Fig. 1.

[0116] In the present embodiment, the beam path 26 of the optical device 10 is formed, for example, within a beam plane 32. The beam plane 32 is congruent with the XY plane.

[0117] In addition, the deflecting elements 24 of the optical device 10 are arranged in the present case on a common rotating body 34, which is configured to rotate about the rotation axis 28. In the present case, the rotating body 34 is, for example, formed in one piece. However, the rotating body 34 can also be formed in multiple pieces, and individual sections of the rotating body 34 can be connected to one another via common connecting means. In contrast, with the one-piece design of the rotating body 34, it has proven advantageous that such a rotating body 34 is cheaper to manufacture and less susceptible to thermal stresses. In general, the deflecting elements 24 can therefore be aligned particularly precisely if they are arranged on the common rotating body 34, since this body is rotatable about the common rotation axis 28. This eliminates the need to provide a separate rotation mechanism for each deflecting element 24.

[0118] The polarized light beam 14 has a first polarization 12.1 before entering the optical device 10. After the polarized light beam 14 exits the optical device 10, the polarized light beam 10 has a second polarization 12.2. In the present case, the first polarization 10.1 and the second polarization 10.2 are different, although the first polarization 10.1 and the second polarization 10.2 can also be the same. The first polarization 10.1 can be changed into a second polarization 12.2, which is different from the first polarization 12.1, by means of a joint rotation of the deflection elements 24 about the rotation axis 28. In this way, a desired target polarization of the polarized light beam 14 exiting the optical device 10 can be set using the optical device 10.

[0119] The exemplary embodiment of the optical device 10 has, for example, a cooling device 36 which is configured to dissipate heat from the deflection elements 24. The cooling device 36 is designed here as active fluid cooling, wherein in exemplary embodiments not specifically shown, the cooling device is designed, for example, as passive cooling in the form of a heat-dissipating component with a comparatively high thermal conductivity coefficient. Heat occurring in the deflection elements 24 is dissipated in this case by means of a cooling fluid of the active fluid cooling. The cooling fluid is furthermore water, for example, and the fluid cooling is consequently water cooling. In exemplary embodiments not specifically shown, however, the cooling fluid is designed as cooling oil, in particular based on hydrocarbons, or as a gas. The deflection elements 24 are therefore in direct contact with the cooling water.By means of the cooling device 36, cooling water which has absorbed the heat from the deflection elements 24 is discharged and cooling water with a lower temperature than that of the discharged cooling water is supplied.

[0120] In embodiments not specifically illustrated, the entire rotating body 34 is cooled by means of the cooling device 36. In these embodiments, the rotating body 34 has cooling channels, whereby, due to the direct contact of the deflecting elements 24 with the rotating body 34, the heat from the deflecting elements 24 can be passively dissipated via these cooling channels or via a cooling fluid present therein.

[0121] Furthermore, in the exemplary embodiment, the optical device 10 is assigned a polarization measuring device 44. The polarization measuring device 44 enables the measurement of the second polarization 12.2 of the polarized light beam 14. By means of this measurement of the second polarization 12.2, the actual polarization after the polarized light beam 14 exits the optical device 10 is determined. The actual polarization is then compared with a desired polarization. If an impermissible deviation of the actual polarization from the desired polarization occurs, the second polarization 12.2 can be approximated to the desired polarization by means of joint rotation of the deflection elements 24 about the rotation axis 28.

[0122] In the exemplary embodiment of the optical device 10, at least one deflecting element 24 is connected to the rotating body 34 by a connecting device 38 in such a way that the deflecting element 24 can expand axially and radially. In particular, in the present exemplary embodiment, all deflecting elements 24 are each connected to the rotating body 34 by such a connecting device 38. How many of the deflecting elements 24 are connected to the rotating body 34 by such a connecting device 38 depends essentially on the thermal energy input into the deflecting elements 24. If a polarized light beam 14 with particularly high power is deflected, it is advantageous to deflect all deflecting elements in such a way that they can expand radially and axially. For a polarized light beam 14 with comparatively lower power, it may be sufficient to connect only one of the deflecting elements 24 to the rotating body 34 in this way.

[0123] The deflection elements 24 are embodied as silicon mirrors in the present case. In embodiments not specifically shown, the deflection mirrors can also be embodied as copper (Cu) or gold (Au) coated deflection mirrors, or made from a copper (Cu) or gold (Au) monoblock. In further embodiments not specifically shown, the deflection elements 24 can also be embodied as an optical grating, for example, a diffraction grating.

[0124] Fig. 2 now shows an enlarged view of the area II of the connecting device 38 of the embodiment of the optical device shown in Fig. 1.

[0125] The connecting device 38 is connected to the rotating body 34 via a housing 35. In the present case, this connection is designed as a connection that can be released using a tool, wherein the removable connection is a screw (not shown). In embodiments not specifically shown, the connecting device is connected to the rotating body 34 by means of a rivet, screw with a lock nut, or pin. Further embodiments not specifically shown have an adhesive or cement, a material bond such as a weld seam or a soldered connection, or a clamp connection as the connection between the connecting device 38 and the housing 35.

[0126] The deflection element 24 is arranged within the housing 35 in the present case and is guided and / or sealed relative to the housing 35 with respect to the radial extent of the deflection element 24 by means of an O-ring 37. Such a seal retains cooling fluid, in particular cooling water, and prevents the cooling fluid from penetrating a beam region 27 of the optical device 10. The beam region 27 is exposed to a process gas, and contamination of the process gas is greatly reduced by the sealing by means of the O-ring 37. The O-ring 37 allows the deflection element 24 to expand radially. In this way, warping and / or deformation of the deflection element 24, for example due to thermal stresses, is significantly reduced.

[0127] In addition, the deflection element 24 is pressed against a contact surface 33 of the rotating body 34 by an axial spring 39, which is supported on the housing 35. In this way, a precise positioning of the deflection element 24 relative to the rotating body 34 can be achieved. The contact surface 33 is manufactured using comparatively precise manufacturing processes, such as precision milling. The deflection element 24 can expand axially in the direction of the axial spring 38. In this way, distortion and / or deformation of the deflection element 24 is further significantly reduced.

[0128] In the optical device 10 according to the exemplary embodiment, at least one deflecting element 24 is adjustable with respect to a desired beam path by means of a correction device 40. The alignment of the deflecting element 24 with respect to the rotating body 34 can be adjusted by means of the correction device 40. A misalignment of the deflecting element 24 with respect to the rotating body 34 leads to a deviation of the beam path 26 from the desired beam path. The beam path 26 is approximated to the desired beam path by means of the correction device 40.

[0129] Furthermore, at least one deflection element 24 is assigned a temperature monitoring device 42. In the present embodiment of the optical device 10, all deflection elements 24 are assigned a temperature monitoring device 42. A temperature monitoring device 42 detects a temperature of the deflection element 24 assigned to it in each case and is also configured to detect an excess temperature at the respective deflection element 24. As already explained above with regard to the connecting device 38 or the connecting devices 38, here too, for a polarized light beam 14 with comparatively low power, a single temperature monitoring device 42 for just one deflection element 24 may be sufficient. If, as is the case here, a polarized light beam 14 with particularly high power is deflected, it is advantageous to assign a temperature monitoring device 42 to each deflection element 24.

[0130] Fig. 3 shows an embodiment of an optical system 46 according to the invention.

[0131] The optical system 46 comprises a first optical device 10.1 and a second optical device 10.2, wherein each optical device 10.1, 10.2 has the features of the optical device 10 according to the invention. The first optical device 10.1 and the second optical device 10.2 are arranged to be rotatable independently of one another, and the first axis of rotation 28.1 of the first optical device 10.1 and the second axis of rotation 28.2 of the second optical device 10.2 are parallel to one another. A first rotational path of the first optical device 10.1 about the rotational axis 28.1 can thus be different from a second rotational path of the second optical device 10.2 about the rotational axis 28.2. Likewise, a first direction of rotation of the first optical device 10.1 and a second direction of rotation of the second optical device 10.2 can be different from one another.In other words, the rotation directions can be opposite to each other.

[0132] Furthermore, a sealing and / or shielding device 48 is arranged between the first optical device 10.1 and the second optical device 10.2, which is designed to substantially prevent the escape of a process gas and / or stray light between the first optical device 10.1 and the second optical device 10.2.

[0133] Fig. 4 shows an embodiment of an EUV light generation system 52, comprising an EUV driver laser 50, a target material generator 54, and an EUV light generation chamber 56. According to the invention, the EUV driver laser comprises an optical system 46 according to Fig. 3.

Claims

Patent claims 1. An optical device (10) for changing the polarization (12) of a polarized light beam (14), comprising a) a beam input (16) for the polarized light beam (14), which can enter the beam input (16) of the optical device (10) along a first propagation axis (18), b) a beam output (20) for the polarized light beam (14), which can exit the beam output (20) of the optical device (10) along a second propagation axis (22), c) a plurality of deflection elements (24), each of which is configured to deflect the polarized light beam (14) within the optical device (10), wherein at least one of these deflection elements (24) is configured to change at least one polarization component of the polarized light beam (14), d) a beam path (26),which is formed within the optical device (10) by means of the deflection elements (24) starting from the beam inlet (16) to the beam outlet (20) of the optical device (10), characterized in that e) the deflection elements (24) are arranged such that they are jointly rotatable about a rotation axis (28), and f) the first propagation axis (18), the second propagation axis (22) and the rotation axis (28) are parallel to one another.

2. Optical device (10) according to claim 1, characterized in that the first propagation axis (18), the second propagation axis (22) and the rotation axis (28) are congruent in a common reference axis (30).

3. Optical device (10) according to one of the preceding claims, characterized in that the beam path (26) is formed within a beam plane (32).

4. Optical device (10) according to one of the preceding claims, characterized in that the deflection elements (24) are mounted on a common rotation body (34) which is arranged to rotate about the axis of rotation (28).

5. Optical device (10) according to claim 4, characterized in that the rotating body (34) is formed in one piece.

6. Optical device (10) according to claim 4 or 5, characterized in that the rotating body (34) has a cooling device (36) which is designed to dissipate heat from the deflection elements (24).

7. Optical device (10) according to claims 4 to 6, characterized in that at least one deflection element (24) is connected to the rotation body (34) by a connecting device (38) such that the at least one deflection element (24) can expand axially and radially.

8. Optical device (10) according to one of the preceding claims, characterized in that at least one deflection element (24) is adjustable with respect to an alignment of this deflection element with respect to a desired beam path by means of a correction device (40).

9. Optical device (10) according to one of the preceding claims, characterized in that at least one deflection element (24) is assigned a temperature monitoring device (42).

10. Optical device (10) according to one of the preceding claims, characterized in that a polarization measuring device (44) is assigned to the optical device (10).

11. Optical system (46) comprising a first optical device (10.1) and a second optical device (10.2) according to one of the preceding claims, characterized in that the optical devices (10.1, 10.2) are arranged to be rotatable independently of one another and the axes of rotation (28.1, 28.2) of the optical devices (10.1, 10.2) are parallel to one another.

12. Optical system (46) according to claim 11, characterized in that a sealing and / or shielding device (48) is arranged between the first optical device (10.1) and the second optical device (10.2), which is designed to substantially prevent an escape of a process gas and / or stray light between the optical devices (10.1, 10.2).

13. EUV driver laser (50), comprising an optical device (10) according to one of the Claims 1 to 10 or an optical system (46) according to one of claims 11 or 12.

14. EUV light generation system (52) comprising an EUV driver laser (50) according to claim 13, a target material generator (54) and an EUV light generation chamber (56).

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