Laser mirror with thermal deformation compensation and laser system comprising same

Abstract

The invention relates to a mirror (1) for deflecting laser radiation, in particular a mirror (1) for deflecting an excitation light beam of an EUV driver laser for generating an EUV light-emitting plasma of a target material. The mirror (1) comprises a mirror body (3) having a front side (4) which reflects the laser radiation and at least one upper cooling channel region (11) which is formed therein and in which a flow direction for a cooling medium for cooling the reflecting front side (4) runs below the latter and parallel thereto. Furthermore, the mirror (1) comprises a lower temperature control device (7, 10) for selectively cooling only a central region (12) of the mirror body (3) and / or for selectively heating only an outer region (13) of the mirror body (3) surrounding the central region (12) in each case in a lower region (6, 10) of the mirror body (3). Said lower region (6, 10) is spaced apart from the upper cooling channel region (11) in a direction (y) perpendicular to the front side (4).

Description

[0001] LASER MIRROR WITH THERMAL DEFORMATION COMPENSATION AND LASER SYSTEM

[0002] The present invention relates to a mirror, in particular for deflecting laser radiation, and a laser system equipped therewith.

[0003] Optical devices, such as mirrors, can be used to great effect in a wide variety of applications and fields. Particularly when used to direct laser radiation in industrial applications, such as materials processing or the generation of EUV light, significant amounts of energy and power can impact the mirror. This can lead to uneven heating and, consequently, uneven thermal expansion. The mirror can therefore deform during use, which can negatively impact the precision of the light deflection. A correspondingly deformed mirror can, for example, lead to divergent reflection of a laser beam, thus resulting in undesirable beam expansion.

[0004] As one approach, US Pat. No. 7,740,362 B1 describes a mirror in which a first flow of a heating or cooling fluid is used to temper a front side of the mirror, and a second flow of a heating or cooling fluid is used to temper a back side of the mirror. The fluid is at a constant temperature, and the first flow and the second flow are adjusted by means of a corresponding control system to achieve a desired difference in the thermal expansion of the front and back sides and to set a desired curvature of the mirror. However, even this approach may not always yield optimal results, or it may require considerable measurement and control effort.

[0005] The object of the present invention is to enable a particularly precise and consistent deflection of a laser beam or laser pulse on a mirror in a particularly simple manner.

[0006] The problem is solved by the subject matter of the independent claims. Further possible embodiments of the invention are specified in the subclaims, the description, and the drawings. Features, advantages, and possible embodiments presented in the description for one of the subject matter of the independent claims are to be regarded at least analogously as features, advantages, and possible embodiments of the respective subject matter of the other independent claims, as well as any possible combination of the subject matter of the independent claims, optionally in conjunction with one or more of the subclaims.

[0007] The mirror according to the invention or a corresponding mirror device according to the invention is designed to deflect or reflect laser radiation, in particular to deflect an excitation light beam of an EUV driver laser. Such an excitation light beam has such a high power that, when directed onto a target material, it can generate a target material plasma therefrom, which emits EUV light. However, the mirror according to the invention can also be used in material processing systems.

[0008] The mirror or mirror device according to the invention comprises a mirror body with a mirror side or surface that reflects the laser radiation, i.e., a correspondingly reflective front or top side. The mirror body can be made, for example, of copper or a copper alloy. Furthermore, it is also possible to manufacture the mirror body from silicon carbide (SiC), optionally with diamond components. It is also conceivable to manufacture the mirror body, at least in part, from diamond.

[0009] To create the reflective front side, the mirror body can be polished or coated, for example. An upper cooling channel region or cooling channel section for conducting a cooling medium, for example cooling water or the like, is formed or arranged in the mirror body. In this upper cooling channel region or cooling channel section, an at least primary flow direction for the cooling medium for cooling the reflective front side runs beneath it and at least substantially parallel to it. In other words, the upper cooling channel region extends in an upper plane in which the longitudinal extension direction or flow direction of at least one cooling channel or cooling channel section runs, wherein this upper plane lies or is arranged parallel to the front side. This upper plane can in particular be arranged in an upper or front half of the mirror body facing the front side.To achieve particularly effective, efficient, and rapid cooling of the front side, the upper cooling channel area, or at least one upper cooling channel section therein, can be arranged directly below or behind the reflective front side. Thus, for example, only a material or wall thickness necessary to ensure stability can be present between the interior of the upper cooling channel section and the reflective front side.

[0010] Furthermore, the mirror according to the invention or the mirror device according to the invention comprises a lower temperature control device for selectively cooling only a central region of the mirror body and / or for selectively heating only an edge or outer region of the mirror body surrounding the central region, in each case in a lower or rear or back region or part of the mirror body. This lower region of the mirror body is spaced from the upper cooling channel region in a direction perpendicular to the front side. In other words, the upper cooling channel region and the lower region of the mirror body or the temperature control device arranged there are arranged or formed at different distances or spacings from the reflective front side, viewed in the direction perpendicular to the front side.

[0011] When the mirror according to the invention is used as intended, for example during the intended operation of a laser system equipped therewith, for example an EUV driver laser, the laser radiation can strike the reflective front side and there in particular only or primarily, i.e. with the highest power or with the majority of its total power, the central region of the front side. The central region here therefore means a central region in a plane parallel to the front side or in a radial direction running parallel to the front side or in its plane. During intended operation, no laser radiation, or only a much smaller proportion of the laser radiation than strikes the central region, can strike the edge or outer region surrounding the central region. This means that an at least essentially Gaussian temperature distribution of the front side orof the upper region of the mirror body adjacent to it on the rear, wherein the maximum of this deformation can be in the center of the central region. This could typically lead to a convex deformation of the front side, i.e. a bulging of the central region outwards, i.e. in the direction facing away from the upper cooling channel region. This could cause a laser beam to be further widened by reflection at the front side and / or a shift in the focus position of the laser beam to occur. This problem is countered in the present case by means of the lower temperature control device generating an opposing temperature profile in a second or lower plane on the rear side of the upper cooling channel region or of the corresponding upper region of the mirror body facing away from the front side. By means of the lower temperature control device, the temperature in this lower plane orThis creates a temperature profile in the lower region of the mirror body whose minimum lies in the center of the central region. This would tend to lead to a concave deformation relative to the front side. This compensates for the described convex deformation of the front side. This means that even after extended use of the mirror, the front side can retain its original shape. Depending on the design of the lower temperature control device, it may even be possible to overcompensate for the thermal deformation of the front side caused by the incident laser radiation, in order to cause an overall concave or focusing deformation of the front side as the temperature in the central region of the front side rises. This can, for example, compensate for any beam-expanding influences of other optical elements in the beam path of the respective laser beam.

[0012] In the upper cooling channel area, for example, a spiral course of the upper cooling channel section there can be used to achieve an even distribution of heat, i.e. homogenization. In the lower area, however, the central area can be specifically cooled more than the outer area in order to compensate for the thermally induced expansion of the central area in the upper area of ​​the mirror body, and / or the edge or outer area can be specifically heated more than the central area of ​​the lower area of ​​the mirror body in order to cause additional thermal expansion of the mirror body there. This additional thermal expansion in the lower outer area, i.e. in the outer area in the lower area or in the lower plane of the mirror body, can also compensate for or reduce the described convex deformation of the front side.

[0013] The present invention can achieve inherent self-regulation, particularly when using channels formed or arranged in the lower region of the mirror body, i.e., in the lower plane, for conducting a temperature control medium, in particular a liquid one, as the temperature control device or as part thereof. Thus, solely due to the presently proposed geometric arrangement with two different temperature control planes or regions at different distances from the front side and the different temperature control of the central region and the outer region in the lower plane or in the lower region, thermally induced deformations of the reflective front side that occur when laser radiation is incident can be avoided or reduced, in particular without the need for complex control.The present invention thus makes it possible in a comparatively simple manner to avoid or reduce a divergence of the laser radiation at the mirror which increases with the usage time.

[0014] In one possible embodiment of the present invention, the lower temperature control device comprises a lower cooling channel region with at least one inner lower cooling channel or cooling channel section. This inner lower cooling channel or cooling channel section is arranged - in the lower plane - only in the central region of the mirror body, i.e., only below the central region of the front side. In this lower cooling channel or cooling channel section, an at least primary flow direction for the cooling medium for cooling the central lower region of the mirror body runs parallel to the front side and thus also parallel to the upper cooling channel region or the primary flow direction there. The inner lower cooling channel section or cooling channel is directly connected to at least one inlet or feed, i.e., at least one inlet connection of the mirror or mirror body for fresh cooling medium.The inner lower cooling channel section can therefore be connected to the inlet without a corresponding connecting or connecting line leading through another area to be cooled, in particular not through the upper cooling channel area. This allows fresh cooling medium, i.e. relatively cool cooling medium that has not yet absorbed heat at the front or in the upper cooling channel area, for example coming directly from a heat exchanger or from a reservoir, to initially flow into the inner lower cooling channel section. There, this fresh cooling medium can thus particularly effectively keep the temperature of the central area of ​​the mirror body in the lower level low and thus particularly effectively counteract or compensate for the thermal expansion of the central area of ​​the mirror body in the upper level.The inner lower cooling channel section can be or comprise, for example, a coolant channel running spirally in the central region and / or a region or reservoir with a larger cross-section, for example compared to a supply or connecting line or other cooling channel sections within the mirror body.

[0015] In a possible further development of the present invention, the cooling channel sections or cooling channels can also have individually or partially varying cross-sections, thus forming sections of higher and lower flow velocity within the temperature control device. Thus, a cooling effect can be individually adjusted at specific positions of the mirror.

[0016] In a possible further development of the present invention, the upper cooling channel region or at least one upper cooling channel or upper cooling channel section therein and the lower cooling channel region or at least one lower cooling channel or lower cooling channel section therein, in particular the inner lower cooling channel section mentioned elsewhere, are connected to one another by means of an inner connecting cooling channel or connecting cooling channel section that runs in the central region or below the central region of the front side at least substantially or primarily perpendicular to the front side, i.e., is elongated. Cooling medium supplied to the mirror body can thus initially flow into the inner lower cooling channel section and from there through the inner connecting cooling channel section into the upper cooling channel region.In the simplest case, a single inlet of the mirror body may be sufficient to feed or supply the cooling medium to both the lower cooling channel area and, from there, the upper cooling channel area. This allows for a particularly simple, efficient, and cost-effective design of the mirror and, if applicable, a corresponding cooling circuit connected to it or connectable to it.

[0017] In a possible development of the present invention, the lower temperature control device comprises at least one outer lower cooling channel section. This can be formed in the lower cooling channel region or as part of the lower cooling channel region. The outer lower cooling channel section surrounds the central region of the mirror body and is connected to the upper cooling channel region or to an upper cooling channel or upper cooling channel section there by means of at least one outer connecting cooling channel or connecting cooling channel section which runs at least substantially or primarily perpendicular to the front side in the outer region, i.e. is elongated.Cooling medium heated on the front side flows from the upper cooling channel region through the at least one outer connecting cooling channel section into the at least one outer lower cooling channel section, where it at least partially releases the heat previously absorbed in the upper cooling channel region to the lower outer region of the mirror body. This configuration therefore allows the heat introduced into the upper region of the mirror body by the laser radiation impinging on the front side to be automatically used in the lower outer region of the mirror body to compensate for the thermal deformation of the upper region of the mirror body. This allows a particularly simple and efficient design of the mirror body or of a cooling circuit incorporating it to be realized.

[0018] Furthermore, according to a further advantageous embodiment of the mirror, a central cooling region, which may have a central cooling ring, can be arranged between the upper cooling region and the lower cooling channel region. Such a configuration allows for even better compensation of a locally occurring heat hotspot within the mirror.

[0019] In addition, self-regulating thermal and therefore geometric and optical behavior of the mirror body can be achieved without additional control. If, for example, only relatively low laser radiation powers are radiated onto the front side and thus relatively small amounts of heat are introduced into the mirror body, the cooling medium in the upper cooling channel area heats up accordingly only relatively slightly at a constant volume flow. As a result, relatively little heat is introduced into the outer lower area of ​​the mirror body and thus relatively little thermal expansion is caused there to compensate for the equally relatively small thermally induced deformation of the upper area of ​​the mirror body. With higher radiated laser powers, however, more heat can be generated in the upper area orat the front, a greater temperature gradient arises between the central region and the outer region, and a greater thermal expansion or deformation tendency occurs. This in turn leads to the cooling medium in the upper cooling channel section being heated more strongly, and thus more heat being transported to the outer region of the lower level of the mirror body, so that a correspondingly greater compensating thermal deformation is caused there. In a possible development of the present invention, the mirror body is divided into two parts parallel to the front, into a front or upper part, and a rear or lower part. The upper cooling channel region is formed or arranged in the upper part, while the lower temperature control device is arranged in or on the lower part of the mirror body.The mirror body can therefore be constructed from at least two components which can be arranged against one another or abut one another with their mutually facing surfaces, which can be arranged at least substantially parallel to the front side. This two-part or multi-part construction of the mirror body allows even relatively complex cooling channel shapes or courses to be realized relatively easily. For example, at least part of the lower cooling channel region or a lower cooling channel section can be manufactured as a depression or cutout in the lower part of the mirror body that is open towards the front side. This can then be covered or sealed by the upper part of the mirror body resting thereon. The upper part and the lower part of the mirror body can be connected to one another in a materially bonded manner, in particular soldered together using a solder.While connecting the upper and lower parts of the mirror body using fasteners such as nails, screws, bolts, rivets, and / or clamps is theoretically possible, the mirror body, for which precise shape retention is particularly important, would then deform adversely even without the input of energy or heat generation.

[0020] In a further possible embodiment of the present invention, the upper cooling channel region is fed with the cooling medium through a central or inner inflow or inlet arranged in the central region of the mirror body or the upper cooling channel region. This central or inner inflow of the upper cooling channel region can, for example, be an upper end or an upper outlet of the inner connecting cooling channel section mentioned elsewhere. Starting from this inner inflow, at least one upper cooling channel or upper cooling channel section runs spirally in the upper cooling channel region or as part thereof parallel to the front side up to a respective outer outlet of the upper cooling channel region. This at least one outer outlet is arranged in the upper outer region, i.e. in the outer region of the upper plane or of the upper part of the mirror body.The outer outlet can, for example, be a beginning or an upper end of the outer connecting cooling channel section mentioned elsewhere. Due to the spiral course of the upper cooling channel section proposed here, the heat absorbed by the cooling medium in the upper central region can be distributed evenly across the upper level in a particularly efficient manner. This makes it possible to achieve a correspondingly uniform or symmetrical temperature profile and reduce asymmetrical thermal deformation or a tendency towards deformation of the front side. Because the at least one outer outlet of the upper cooling channel region is arranged in the outer region, this outer region can be heated by the cooling medium flowing thereto, which has absorbed heat in the central region. This can counteract excessively strong thermal deformation that only occurs in the central region.On the other hand, the cooling medium heated in the upper cooling channel area can flow or be transported to the outer area of ​​the lower level of the mirror body via a particularly short and direct route - and thus with particularly low heat loss.

[0021] In a possible further development of the present invention, the upper cooling channel region is also supplied with cooling medium through an external inlet or inlet arranged in the upper outer region of the mirror body. Starting from this external inlet, at least one upper cooling channel or upper cooling channel section extends spirally in the upper cooling channel region or as part thereof, parallel to the front side, until it reaches a central or inner outlet of the upper cooling channel region arranged in the upper central region of the mirror body.The upper cooling channel section, which runs spirally from the inside outwards, and the upper cooling channel section, which runs spirally from the outside inwards, are arranged such that an alternating arrangement of these two cooling channel sections, i.e. the upper cooling channels or upper cooling channel sections running to the outer outlet and to the inner outlet, results along at least one radial line which runs parallel to the front side from the center point of the upper central region to the outer area. The fact that a cooling channel section runs in a specific direction means in particular that a designated primary flow direction of the cooling medium in this cooling channel section points in this direction, i.e. the cooling medium flows in this direction through the cooling channel section during designated operation.For example, fresh cooling medium can be supplied from outside the mirror body to the at least one outer inlet of the upper cooling channel region. For this purpose, the outer inlet can be arranged, for example, on an outer or side wall of the mirror body or of the upper region or part of the mirror body. Such an outer or side wall can, for example, be at least substantially perpendicular to the front side. By arranging the outer inlet in this way, unintentional cooling of the lower outer region of the mirror body by cooling medium flowing into the outer inlet of the upper cooling channel region can be avoided. By means of the interlocking spiral course of several upper cooling channel sections with opposing course or flow directions, as proposed here, a particularly homogeneous temperature distribution in the upper region of the mirror body can be achieved and / or a more precise orMore differentiated control of the temperature profile and thus also of the thermal deformation of the mirror body or the front side can be enabled. For example, a volume flow and / or a temperature of the cooling medium supplied to the outer inlet of the upper cooling channel region can be individually adjusted or controlled, in particular independently of the volume flow and / or the temperature of the cooling medium supplied from outside the mirror body to the lower cooling channel region, which, for example, flows from the lower cooling channel region through the inner inlet of the upper cooling channel region, as described elsewhere.

[0022] In a further possible embodiment of the present invention, the lower temperature control device is or comprises an electrical heating device arranged on the outside of the mirror body and surrounding it parallel to the front side. Such a heating device can be or comprise, for example, a heating wire, a heating coil, a heating mat, a heating cartridge, or the like. This can be wound or laid around an outer side wall of the lower region or the lower plane of the mirror body, for example, perpendicular to the front side. Likewise, this or another heating device can be integrated or embedded in the lower outer region of the mirror body. Such an electrical heating device can, for example, enable faster heating, a wider temperature range, and more precise temperature control compared to temperature control using a liquid or gaseous temperature control medium.The external arrangement of the heating device also allows for a particularly simple and cost-effective mirror design. The electric heating device can, for example, be provided in addition to the cooling channels described elsewhere. This allows, for example, for a demand-controlled, switchable overcompensation—i.e., an at least temporarily concave deformation of the front surface—to be set, in addition to the self-regulating heat or temperature management based on the cooling medium. This allows, for example, the adjustment of the focus or focus position of the laser radiation reflected or deflected by the mirror.

[0023] In a further possible embodiment of the present invention, the mirror has a thermally insulating base body on which the mirror body is mounted or arranged with its rear side opposite the reflective front side. Such a base body can have a thermally and / or mechanically stabilizing effect and thus support a more consistent optical behavior of the mirror. Such a base body can be made of steel, in particular stainless steel, for example.

[0024] In a further possible embodiment of the present invention, the mirror body has a coating, at least or only in the outer area of ​​the front side, which is at least partially transparent, i.e. transmissive, on the front side, i.e. for radiation incident on it from outside, i.e. from the surroundings of the mirror in the direction of the front side. The coating is at least partially reflective on the back side, so that radiation which has passed through the coating in the forward direction and was reflected back in the direction of the front side by the mirror body is reflected back into the mirror body at the back of the coating facing the mirror body. Such a coating can, for example, be a zinc selenide layer on the front side of the mirror body. Such a coating can heat the correspondingly coated area, i.e. in particular the outer area, internally.This allows compensation of the convex deformation of the front side to be supported passively and thus particularly efficiently.

[0025] The present invention also relates to a laser system having at least one mirror according to the invention and a cooling circuit for a cooling medium, into which said at least one mirror or its cooling channel structure is integrated. The laser system according to the invention can in particular be the laser system mentioned in connection with the mirror according to the invention or correspond thereto. The cooling circuit of the laser system can comprise further components, such as a pump and / or a heat exchanger and / or a radiator and / or corresponding connecting coolant lines for the cooling medium and / or the like. The laser system according to the invention can comprise further components, such as a laser radiation source and / or an amplifier for laser radiation and / or an optics or beam guiding device and / or a beam shaping device and / or the like.The laser system according to the invention can be configured, for example, for material processing, such as laser-based separation, cutting, drilling, or welding, or for laser-based additive manufacturing or EUV light generation. In these applications, considerable laser power can be used while simultaneously requiring high precision, so that preventing or compensating for thermal deformation of the at least one mirror according to the invention can be particularly effective and beneficial here.

[0026] Further features of the invention can be derived from the following description of the figures and from the drawings. The features and combinations of features mentioned above in the description, as well as the features and combinations of features shown below in the description of the figures and / or in the figures alone, can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the invention.

[0027] The drawing shows:

[0028] Fig. 1 is a schematic cross-sectional view of a mirror for deflecting laser radiation with a cooling channel structure;

[0029] Fig. 2 is a schematic perspective view of a variant of the cooling channel structure;

[0030] Fig. 3 is a schematic diagram illustrating a geometric behavior of the mirror during operation;

[0031] Fig. 4 is a schematic representation of a variant of an upper part of the cooling channel structure; and

[0032] Fig. 5 is a schematic representation of an upper part of the cooling channel structure in a further variant.

[0033] Identical or functionally equivalent elements are provided with the same reference numerals in the figures. Fig. 1 shows a schematic cross-sectional view of a mirror 1. The mirror 1 here comprises a base body 2, which is thermally insulating and can be made of stainless steel, for example. A mirror body 3 is arranged on this base body 2. The mirror body 3 can be made of a thermally conductive material, such as copper, a copper alloy, or silicon carbide (SiC). A front side 4 of the mirror body 3 facing away from the base body 2 forms a reflective or mirroring surface—in this case for laser radiation.

[0034] The mirror body 3 is here formed in several parts with an upper part 5 facing the front side 4 or having the front side 4 and a lower part 6 facing the base body 2 or arranged on the base body 2. An electrical heating device, which is referred to here as heating ring 7, is also arranged around the lower part 6.

[0035] The mirror 1 can be heated by means of the electrical heating ring 7 and additionally tempered with a liquid cooling medium. For this purpose, the mirror 1 has an external inlet 8 and an external outlet 9. Cool or fresh cooling medium can flow into the mirror 1 or a cooling channel structure formed therein through the external inlet 8. When the mirror 1 is used, i.e. when the front side 4 is irradiated with laser radiation, heat can be introduced into the mirror 1, in particular into the mirror body 3, and absorbed there by the cooling medium. The cooling medium heated in this way can then flow out of the mirror 1 through the external outlet 9. The external outlet 9 and the external inlet 8 can be connected to one another outside the mirror 1 by a cooling circuit (not shown here).

[0036] At least two different cooling or temperature control levels are provided in the mirror body 3 at different distances from the front side 4. In the present case, these are a lower cooling region 10, located in the lower part 6, and an upper cooling channel region 11, located in the upper part 5. In addition to these different temperature control levels, various cooling or temperature control areas or zones are also provided along a direction perpendicular to the front side 4, which are located next to one another in a direction perpendicular thereto, i.e., in the plane of the front side 4, which here, for example, is perpendicular to the plane of the drawing. Specifically, these are a central region 12 and a peripheral or outer region 13 surrounding it.By means of these different temperature control levels and temperature control areas, a thermal deformation or deformation tendency of the front side 4 ultimately caused by the laser radiation incident on the front side 4 when the mirror 1 is used can be reduced or compensated.

[0037] For this purpose, an inner lower cooling channel section 14 is arranged in the central region 12 of the lower cooling channel region 11. Fresh cooling medium can flow directly into this through the outer inlet 8 and thus cool the central region 12 of the lower part 6 or the lower cooling channel region 10. In addition, an outer lower cooling channel section 15 is arranged in the lower cooling channel region 10. This is located in the outer region 13 and surrounds the inner lower cooling section 14, for example at least essentially in a ring shape. The outer lower cooling channel section 15 is directly connected here to the outer outlet 9. During operation, the outer lower cooling channel section 15 can therefore contain already heated cooling medium. In the lower part 6 or the lower cooling channel region 10, a central cooling zone is therefore provided, which is surrounded by an external heating zone.This would lead to a greater thermal expansion of the lower part 6 in the outer region 13 than in the inner region, as indicated here by double arrows.

[0038] Central area 12 and thus tend to cause a concave, i.e. bowl-shaped deformation open towards the front side 4.

[0039] At least one upper cooling channel section 16 is arranged in the upper part 5 or in the upper cooling channel region 11. Relatively cool cooling medium can flow into this section from the inner lower cooling channel section 14 through an inner connecting cooling channel section 17. This cooling medium can then be heated in the central region 12 of the upper cooling channel section 16 and flow thereinto the edge region 13 of the upper cooling channel region 11. From there, the correspondingly heated cooling medium can then flow through an outer connecting cooling channel section 18 into the outer lower cooling channel section 15.

[0040] Since, when the mirror 1 is used as intended, the laser radiation at least primarily falls into the central region 12 of the front side 4, the highest temperature is generated there. This results in a temperature distribution in the upper part 5 that is opposite to that in the lower part 6, which would tend to lead to a convex thermal deformation of the upper part 5. These opposing temperature profiles or deformation tendencies can overall prevent or minimize thermal deformation of the front side 4. To illustrate this, Fig. 2 shows a schematic diagram in which the thermally induced deformation tendencies of the upper part 5 and the lower part 6 are schematically indicated. For the upper part 5, a convex upper part deformation 19 results, the maximum bulge of which points in the direction away from the base body 2 and lies in the center of the central region 12.For the lower part 6, a concave lower part deformation 20 results, the maximum curvature of which in the central region 12 points toward the base body 2. Since the upper part 5 and the lower part 6 are firmly connected to one another, these two deformations 19, 20 overlap or compete, resulting in an overall shape 21 of the mirror body 3 or the front side 4, also indicated here. According to this overall shape 21, the front side 4 can be at least substantially flat or, if appropriate, even concavely curved—less than the lower part 6 or the lower part deformation 20.

[0041] In order to support the compensatory effect of the cooling medium in the lower cooling channel area 10 with respect to the convex deformation of the upper part 5, additional heat can be introduced into the outer area 13 of the lower part 6 by means of the heating ring 7.

[0042] Fig. 3 shows an exemplary schematic perspective view to illustrate the cooling channel structure of the mirror 1 in a possible variant. Here, it can be seen that the inner lower cooling channel section 14 can be designed spirally. For example, the outer inlet 8 can open into an inner lower inlet 22 of the inner lower cooling channel section 14. This inner lower inlet 22 can be located in the central region 12, but does not necessarily have to be arranged centrally there. Instead, a connection or transition of the inner connecting cooling channel section 17 can be located in the center of the central region 12 or of the inner lower cooling channel section 14. However, other shapes, arrangements, or designs are also possible.

[0043] From an upper end of the inner connecting cooling channel section 17, which is designated here as the inner upper inlet 23 to the upper cooling channel region 11 or to at least one upper cooling channel section 16 there, a first upper cooling channel section 16a and a second upper cooling channel section 16b can each extend spirally and open into a respective outer upper outlet 24. The outer upper outlets 24 are arranged, in particular symmetrically distributed, in the outer region 13. The upper cooling channel sections 16a, 16b interlock in a spiral manner. This can result in a particularly close-meshed or dense arrangement of cooling channel sections in the x-direction and, at the same time, a length, i.e. a path traveled by the cooling medium from the inner upper inlet 23 to the outer upper outlets 24, can be kept relatively short.

[0044] In the lower cooling channel area 10, the outer connecting cooling channel sections 18 extending from the outer upper outlets 24 open into an outer lower cooling channel section 25, for example via a respective outer lower inlet. This outer lower cooling channel section 25 is located only in the outer area 13 and can run spirally or annularly around the inner lower cooling channel section 14. For example, several or all parts of the outer lower cooling channel section 25 or several or all outer lower cooling channel sections 25 can lead to a common outer lower outlet 26. Likewise, an individual outer lower outlet 26 can be provided for each plurality of outer lower cooling channel sections 25. Here, the temperature control medium can flow through the common outer lower outlet 26 directly to the outer outlet 9 in order to leave the mirror 1 through this outlet.

[0045] To illustrate another possible design variant of the upper cooling channel region 11 or the upper cooling channel section 16, Fig. 4 shows a schematic plan view. Here, similar to Fig. 3, an inner upper inlet 23 is located in the central region 12, from which the first upper cooling channel section 16a spirals outward to the outer upper outlet 24. Additionally, an outer upper inlet 27 is provided in the outer region 13 in the upper cooling channel region 11. From this, a third upper cooling channel section 16c spirals inward in the opposite flow direction, i.e., into the central region 12 to an inner upper outlet 28 located there.

[0046] Fig. 5 shows a schematic plan view to illustrate another possible variant of the cooling channel structure in the upper cooling channel region 11. Here, similar to Fig. 3, an inner upper inlet 23 is provided. From this, however, not only the first upper cooling channel section 16a and the second upper cooling channel section 16b, but also a fourth upper cooling channel section 16d and a fifth upper cooling channel section 16e each lead spirally outwards to a respective outer upper outlet 24. Here, too, the outer upper outlets 24 are arranged in the outer region 13. By using several, here for example four upper cooling channel sections 16a, 16b, 16d, 16e, which are all fed from the inner upper inlet 23 into the central region 12, a particularly high cooling performance can be achieved in the central region 12.This is the case because the individual upper cooling channel sections 16a, 16b, 16d, 16e can be shorter here with the same coverage or density in the upper level than when using, for example, only the first upper cooling channel section 16a and the second upper cooling channel section 16b as in Fig. 3. In order to achieve the most symmetrical temperature profile possible in the upper part 5, the outer upper outlets 24 can be arranged uniformly or symmetrically distributed.

[0047] Different configurations of the cooling channel structure are therefore possible, with multiple cooling channel sections or cooling spirals and / or differently shaped cooling channel sections being arranged at different levels and / or different flow directions being used. This allows the compensation properties of the cooling channel structure, and ultimately the geometric or optical properties of mirror 1, to be influenced in different ways depending on the application or requirements.

[0048] As a further possibility, for example, externally actively heated temperature control medium, which can therefore have a higher temperature than the cooling medium fed into the external inlet 8, can be fed into the lower cooling channel area 10 and / or the upper cooling channel area 11. This allows additional heat to be introduced into the respective outer region 13 in order to achieve, as required, for example, a temperature difference between the central region 12 and the outer region 13 in the upper part 5, for example in the case of particularly intense laser irradiation in the central region 12 of the front side 4, and / or to effect more effective compensation or overcompensation of the upper part deformation 19 by additional heating of the outer region 13 of the lower part 6.

[0049] Likewise, the upper part 5 or the front side 4, in particular in the outer area 13, can be provided with a transmissively applied coating which has a reflective effect on the back or when the radiation passes twice.

[0050] Overall, the examples described demonstrate how compensation for thermal mirror deformations can be achieved.

[0051] 1 mirror

[0052] 2 base bodies

[0053] 3 mirror bodies

[0054] 4 Front

[0055] 5 Top

[0056] 6 Lower part

[0057] 7 Heating ring

[0058] 8 External inlet

[0059] 9 External drain

[0060] 10 lower cooling channel area

[0061] 11 upper cooling channel area

[0062] 12 Central area

[0063] 13 Outdoor area

[0064] 14 inner lower cooling channel section

[0065] 15 outer lower cooling channel section

[0066] 16 upper cooling channel section

[0067] 16a first upper cooling channel section

[0068] 16b second upper cooling channel section

[0069] 16c third upper cooling channel section

[0070] 16d fourth upper cooling channel section

[0071] 16e fifth upper cooling channel section

[0072] 17 inner connecting cooling channel section

[0073] 18 outer connecting cooling channel section

[0074] 19 Upper part deformation

[0075] 20 Lower part deformation

[0076] 21 Overall shape

[0077] 22 inner lower inlet

[0078] 23 inner upper inlet

[0079] 24 outer upper drain

[0080] 25 outer lower cooling channel section

[0081] 26 outer lower drain

[0082] 27 outer upper inlet 28 inner upper outlet x, y directions

Claims

PATENT CLAIMS 1. Mirror (1) for deflecting laser radiation, in particular mirror (1) for deflecting an excitation light beam of an EUV driver laser for generating an EUV light-emitting plasma of a target material, comprising - a mirror body (3) with a front side (4) reflecting the laser radiation and at least one upper cooling channel region (11) formed therein, in which a flow direction for a cooling medium for cooling the reflecting front side (4) runs below and parallel to the latter, - a lower temperature control device (7, 10) for selectively cooling only a central region (12) of the mirror body (3) and / or for selectively heating only an outer region (13) of the mirror body (3) surrounding the central region (12), in each case in a lower region (6, 10) of the mirror body (3) which is spaced from the upper cooling channel region (11) in a direction (y) perpendicular to the front side (4).

2. Mirror (1) according to claim 1, characterized in that the temperature control device (7, 10) comprises a lower cooling channel region (10) with at least one inner lower cooling channel section (14) which is arranged only in the central region (12) of the mirror body (3) and in which a flow direction for the cooling medium for cooling a central lower region of the mirror body (3) runs parallel to the front side (4), this inner lower cooling channel section (14) being directly connected to an inlet (8) of the mirror body (3) for fresh cooling medium.

3. Mirror (1) according to claim 2, characterized in that the upper cooling channel region (11) and the inner lower cooling channel section (14) are connected to one another by means of an inner connecting cooling channel section (17) running in the central region (12) at least substantially perpendicular to the front side (4), so that cooling medium supplied to the mirror body (3) first flows into the inner lower cooling channel section (14) and from there through the inner connecting cooling channel section (17) into the upper cooling channel region (16).

4. Mirror (1) according to claim 2 or 3, characterized in that the temperature control device (7, 10) comprises an outer lower cooling channel section (25) which surrounds the central region (12) of the mirror body (3) and is connected to the upper cooling channel region (11) by means of at least one outer connecting cooling channel section (18) which runs in the outer region (13) at least substantially perpendicular to the front side (4), so that cooling medium heated in the upper cooling channel region (11) can flow from the upper cooling channel region (11) through the at least one outer connecting cooling channel section (18) into the one outer lower cooling channel section (25) and can release heat absorbed there to the outer region (13) of the mirror body (3).

5. Mirror (1) according to one of claims 2 to 4, characterized in that the mirror body (3) is divided at least in two parallel to the front side (4) into at least one upper part (5), in which the upper cooling channel region (11) is formed, and at least one lower part (6), in or on which the temperature control device (7, 10) is arranged.

6. Mirror (1) according to claim 5, characterized in that the at least one upper part (5) and the at least one lower part (6) are integrally connected to one another.

7. Mirror (1) according to one of the preceding claims, characterized in that the upper cooling channel region (11) is fed with cooling medium through an inner inlet (23) arranged in the central region (12) of the mirror body (3), from which at least one upper cooling channel section (16a, 16b, 16d, 16e) runs spirally to a respective outer outlet (24) of the upper cooling channel region (11) in the outer region (13) of the mirror body (3).

8. Mirror (1) according to claim 7, characterized in that the upper cooling channel region (11) is also fed with cooling medium by an outer inlet (27) arranged in the outer region (13) of the mirror body (3), from which at least one upper cooling channel section (16c) runs spirally to an inner outlet (28) of the upper cooling channel region (11) arranged in the central region (12) of the mirror body (3), so that an alternating arrangement of the upper cooling channel sections (16a; 16c) running to the outer outlet (24) and to the inner outlet (28) results along at least one radial line running from the center point of the central region (12) parallel to the front side (4) into the outer region (13).

9. Mirror (1) according to one of the preceding claims, characterized in that the temperature control device (7, 10) comprises an electric heating device (7) which is arranged on the outside of the mirror body (3) and surrounds it parallel to the front side (4).

10. Mirror (1) according to one of the preceding claims, characterized in that the mirror (1) has a thermally insulating base body (2), made in particular of steel, copper or silicon carbide (SiC), on which the mirror body (3) is arranged with its rear side opposite the reflective front side (4).

11. Mirror (1) according to one of the preceding claims, characterized in that the mirror body (3) has a coating in the outer region (13) of the front side (4) which is at least partially radiation-permeable on the front side and reflective on the back side, so that radiation which has passed through in the forward direction and was reflected in the mirror body (3) back towards the front side (4) is reflected back into the mirror body (3) on the back side of the coating facing the mirror body (3).

12. Laser system, in particular EUV driver laser for generating an excitation light beam for generating an EUV light-emitting plasma of a Target material, comprising a mirror (1) according to one of claims 1 to 11 and a cooling circuit for a cooling medium, in which the mirror (1) is integrated.

Images