WO2022069125A1

WO2022069125A1 - Stop apparatus for delimiting a beam path between a light source and an illumination optical unit of a projection exposure apparatus for projection lithography

Info

Publication number: WO2022069125A1
Application number: PCT/EP2021/073847
Authority: WO
Inventors: Michael Patra
Original assignee: Carl Zeiss Smt Gmbh
Priority date: 2020-09-29
Filing date: 2021-08-30
Publication date: 2022-04-07
Also published as: DE102020212229B3; TW202230037A; KR20230075488A; NL2029213A; NL2029213B1

Abstract

A stop apparatus (36) serves to delimit an illumination light beam path between a light source and an illumination optical unit of a projection exposure apparatus for projection lithography. The stop apparatus (36) has a stop (35) which is arranged in the beam path and which has an aperture (34) for the passage of used illumination light (16) that emanates from the light source. At least one displacement device (47) serves to displace the stop (35) transversely to the illumination light beam path. This yields a stop apparatus, the use of which yields an increased EUV throughput of a projection exposure apparatus equipped therewith in the case of an otherwise comparable imaging and structuring performance of the projection exposure apparatus, or an improved structuring and imaging performance at a given EUV throughput.

Description

Stop apparatus for delimiting a beam path between a light source and an illumination optical unit of a projection exposure apparatus for projection lithography

The content of the German Patent Application DE 10 2020 212 229.6 is incorporated by reference herein.

The invention relates to a stop apparatus for delimiting a beam path between a light source and an illumination optical unit of a projection exposure apparatus for projection lithography. Further, the invention relates to a stop system comprising such a stop apparatus, an illumination optical unit comprising such a stop apparatus or comprising such a stop system, an illumination system comprising such an illumination optical unit, an optical system comprising such an illumination optical unit, a projection exposure apparatus comprising such an optical system, a production method for producing microstructured or nanostructured components using such a projection exposure apparatus, and a structured component produced by the method.

A stop apparatus of the type set forth at the outset is known from WO 2019/233 741 Al and US 9,632,422 B2. US 6,175,405 Bl discloses an imaging apparatus.

It is an object of the present invention to develop a stop apparatus of the type set forth at the outset, the use of which yields an increased EUV throughput of a projection exposure apparatus equipped therewith in the case of an otherwise comparable imaging and structuring performance of the projection exposure apparatus, or an improved structuring and imaging performance at a given EUV throughput. This object is achieved according to the invention by means of a stop apparatus having the features specified in Claim 1.

According to the invention, it was identified that at least one displacement device for displacing the stop transversely to the beam path opens up an adjustment degree of freedom which allows a correction or compensation of systematic deviations of an actual position of an illumination light beam between the light source and the illumination optical unit from a target position, or of drift deviations of the beam path. In comparison with the prior art, the stop according to the invention can be implemented with a smaller aperture which, without loss of the EUV throughput as a result of the stop, leads to sharper beam-delimiting effect of the stop and which can simplify the requirements in relation to the further illumination light guidance downstream of the stop apparatus. A heat sink can be in thermal contact with the stop of the stop apparatus. Such a thermal contact can be implemented by way of a mechanical connection. This mechanical connection can be embodied as a metallic mechanical connection. The connection can be embodied as an elastic connection.

A positioning accuracy of the at least one displacement device transversely to the illumination light beam path can be better than 0.1 mm.

The stop apparatus has a stop carrier comprising a passage opening within which the aperture is located, wherein the stop is displaceable relative to the stop carrier via the displacement device. Such a stop carrier facilitates a compact structure of the stop apparatus. The stop carrier can comprise further functional components of the stop apparatus, for example sensors for the illumination light or components for dissipating heat, for example a heat sink.

At least two displacement devices according to Claim 2 improve the adjustment options of the stop apparatus.

An actuator embodiment of the displacement device according to Claim 3 facilitates controlled and, in particular, automated displacement of the stop. As an alternative to a driven displacement device, the displacement device can also be capable of being actuated manually.

A corresponding manual adjustment can also be realized according to the principle of a pipe clamp with a frame rod fastened thereto, the latter carrying the stop in turn. It is possible to obtain a linear displacement of the stop transversely to the beam path by releasing the respective clamp and displacing the frame rod.

The actuator can also be embodied as a piezo actuator and, in particular, as a piezo stack.

An embodiment as a linear actuator according to Claim 4 allows precise specification of the position of the stop. The linear actuator can be embodied as a linear drive, in particular a single column linear drive or as a two-column linear drive. The linear actuator can also be embodied as a piston drive or a spindle drive.

A swivel actuator according to Claim 5 can be used, alternatively or additionally, as an actuator component of the stop apparatus. In particular, the stop apparatus can comprise at least one linear actuator and at least one swivel actuator at the same time. A swivel axis of the swivel actuator can extend parallel to the beam path through the stop of the stop apparatus.

Alternatively, the stop apparatus can comprise only linear actuators or only swivel actuators, for example two linear actuators. In the case of a linear actuator embodiment, the linear actuators can be present in a crossed arrangement or else, if at least three linear actuators are used, in an H- arrangement.

An embodiment of the stop apparatus according to Claim 7 can be adapted well to the symmetry of the beam path. The intermediate carrier and/or the stop carrier and/or the further intermediate carrier can be arranged as carrier components that are arranged relative to the stop with rotational symmetry. Use can be made of exactly one intermediate carrier.

A stepper motor embodiment of the displacement device according to Claim 8 has proven its worth in practice. Use can be made of a reluctance stepper motor, a permanent magnet stepper motor or a hybrid stepper motor.

The stepper motor can drive a linear actuator and/or a swivel actuator.

The advantages of a stop system according to Claim 9 correspond to those which were already explained above with reference to the stop apparatus. Open-loop or closed-loop controlled operation of the displacement device, then embodied as an actuator, can be implemented with the aid of the open- loop/closed-loop control device. If an open-loop controlled operation is present, the stop system can also be realized without the measuring device.

The open-loop or closed-loop control can be, in particular, dynamic within the meaning of drift correction.

Furthermore, the stop system can comprise at least one actuator for displacing at least one component of the illumination optical unit which follows the stop in the beam path of the illumination light and which serves to compensate a change in the course of the beam path on account of the adjustment of the stop. Such an actuator can be signal-connected to the open-loop/closed-loop control device. Such an actuator of the illumination optical unit can be embodied as a tilt and/or translation actuator of a facet of a facet mirror of the illumination optical unit. In particular, it is consequently possible to specify the direction of a respective illumination channel upstream of a respective pupil facet of a pupil facet mirror of an illumination optical unit of the projection exposure apparatus, advantageously allowing the size of a reflection surface for the pupil facet to be reduced.

The advantages of an illumination optical unit according to Claim 10, of an illumination system according to Claim 11, of an optical system according to Claim 12, of a projection exposure apparatus according to Claim 13, of a production method according to Claim 14 and of a structured component according to Claim 15 that was produced according to this method correspond to those which have already been discussed above with reference to the stop apparatus according to the invention and the stop system according to the invention. The object to be illuminated can be a reticle. The component produced can be a microchip, in particular a memory chip.

The stop of the stop apparatus or of the stop system of the illumination optical unit according to Claim 10 can be located in an arrangement plane which is optically conjugate to pupil facets of a pupil facet mirror of the illumination optical unit or optically conjugate to a second faceted element of a specular reflector. In this case, the stop arrangement plane is imaged, at least approximately, onto the pupil facets or the second faceted element of the specular reflector.

An intermediate focus of a beam path emanating from the light source can be located in this arrangement plane of the stop. Such an intermediate focus can be formed by the collector of the illumination system according to Claim 11. The illumination system comprising the illumination optical unit having the stop apparatus or the stop system can be designed so that an intermediate focus is generated in an arrangement region of the stop, with the intermediate focus being imaged into a pupil of the illumination optical unit. A pupil facet mirror of the illumination optical unit can be arranged at the location of the imaged pupil, the intermediate focus being imaged illumination channel by illumination channel onto pupil facets of the pupil facet mirror. Alternatively, a second faceted element of a specular reflector of the illumination optical unit can be arranged at the location of the imaged pupil, said specular reflector being used as an alternative to a pupil facet mirror. The intermediate focus can represent an image of a source volume of the light source of the illumination system.

In particular, a degree of pupil filling of an illumination of the object can be set to be advantageously low with the aid of the projection exposure apparatus. The degree of pupil filling is the area of an illuminated component of an illumination pupil in relation to the overall area of the pupil used. A person skilled in the art can find details in respect of the "degree of pupil filling" parameter in WO 2019/149 462 A.

The stop according to the invention allows optimization of the homogeneity or uniformity of an illumination dose experienced from different illumination directions by the object to be illuminated.

Below, at least one exemplary embodiment of the invention is described on the basis of the drawing. In the drawing:

Fig. 1 schematically shows a meridional section of a projection exposure apparatus for EUV projection lithography;

Fig. 2 likewise schematically shows a meridional section of exemplary beam profiles of a beam path in the case of an embodiment of a collector of the projection exposure apparatus for imaging a source volume of an EUV radiation source to an intermediate focus in an intermediate focal plane in which a stop apparatus for delimiting the beam path between the light source and an illumination optical unit of the projection exposure apparatus is arranged;

Fig. 3 shows, in an illustration similar to Figure 2, a further embodiment of the collector;

Fig. 4 schematically shows imaging of the intermediate focus to a pupil facet of a pupil facet mirror of the illumination optical unit via a field facet of a field facet mirror of the illumination optical unit, wherein the intermediate focus image comes to rest centrally on the pupil facet;

Fig. 5 shows, in an illustration similar to Figure 4, imaging of the intermediate focus via one of the field facets of the field facet mirror onto a sensor as a constituent part of a measuring device for measuring or ascertaining a centroid of EUV radiation, incident thereon, of an illumination channel guided by the field facet, wherein the intermediate focus is decentred in comparison with a centred position according to Figure 4 and wherein an intermediate focus image correspondingly comes to rest off-centre on the sensor;

Fig. 6 shows, in an illustration similar to Figure 5, the guidance of an illumination channel from the intermediate focus to the centroid ascertainment sensor via a measuring facet located in an arrangement plane of the field facet mirror;

Fig. 7 shows, in an illustration similar to Figure 4, a course of an illumination channel from the intermediate focus to the pupil facet via the field facet in the case of a decentred intermediate focus and still uncorrected beam profile such that the intermediate focus image comes to rest on the pupil facet in decentred fashion;

Fig. 8 shows, in an illustration similar to Figure 7, the situation following a correction displacement of the field facet such that, while the relative intermediate focus position still is decentred, the intermediate focus image comes to rest centrally on the pupil facet;

Fig. 9 shows, in an illustration similar to Figure 4, intensity curve conditions transversely to the beam direction of the illumination channel, firstly at the location of the intermediate focus prior to passage through a stop in the intermediate focal plane and secondly at the location of the pupil facet;

Fig. 10 shows, in a cross section, a size and relative position comparison between an intermediate focus stop according to the prior art and an intermediate focus stop according to the invention, in the case of the centred intermediate focus;

Fig. 11 shows, in an illustration similar to Figure 10, the stop size and relative position comparison in the case of a decentred intermediate focus;

Fig. 12 schematically shows, albeit with more detail in comparison with Figures 4 to 9, a longitudinal section through the stop apparatus for delimiting the beam path in the region of the intermediate focal plane, comprising a stop that is displaceable transversely to a stop carrier by means of a displacement apparatus transversely to the beam path;

Fig. 13 shows a perspective view of an embodiment of components of the stop apparatus; Fig. 14 shows a plan view of an embodiment of the displaceable stop comprising a displacement device in the form of two linear actuators arranged in the shape of a plus sign;

Fig. 15 shows, in an illustration similar to Figure 14, a further embodiment of the stop apparatus comprising a further embodiment of the displacement device with three linear actuators, which are arranged in the shape of the letter "H";

Fig. 16 shows a plan view of a further embodiment of the stop apparatus comprising a further embodiment of a displacement device with a total of four linear actuators, two of which are arranged between the displaceable stop and an intermediate carrier and two further linear actuators of which serve to displace the intermediate carrier in relation to the stop carrier;

Fig. 17 shows a further embodiment of a stop apparatus comprising a further embodiment of a displacement device with a linear actuator and a rotation or swivel actuator;

Fig. 18 shows a perspective view of a further embodiment of a stop with a linear actuator;

Figs 19 to

21 show, in illustrations similar to Figure 18, further embodiments of linear actuators for the stop of the stop apparatus; Fig. 22 schematically shows, in a cross section, the stop of the stop apparatus and an intensity profile of EUV illumination light of the projection exposure apparatus in the beam path upstream and downstream of the stop in the case of a centred intermediate focus; and

Fig. 23 shows, in an illustration similar to Fig. 22, the intensity profile conditions upstream and downstream of the stop in the case of an intermediate focus that is decentred relative to the stop.

In the following text, the essential components of a microlithographic projection exposure apparatus 1 are described first by way of example with reference to Figure 1. The description of the basic construction of the projection exposure apparatus 1 and its components should not be understood here as limiting.

An illumination system 2 of the projection exposure apparatus 1 has, besides a radiation source 3, an illumination optical unit 4 for the illumination of an object field 5 in an object plane 6. Here, a reticle 7 arranged in the object field 5 is exposed. The reticle 7 is held by a reticle holder 8. The reticle holder 8 is displaceable by way of a reticle displacement drive 9, in particular in a scanning direction.

A Cartesian xyz-coordinate system is shown in Figure 1 for explanation purposes. The x-direction extends perpendicular to the plane of the drawing. The y-direction extends horizontally, and the z-direction extends vertically. The scanning direction extends along the y-direction in Fig. 1. The z-direction extends perpendicularly to the object plane 6. The projection exposure apparatus 1 comprises a projection optical unit 10. The projection optical unit 10 serves for imaging the object field 5 into an image field 11 in an image plane 12. The image plane 12 runs parallel to the object plane 6. Alternatively, an angle between the object plane 6 and the image plane 12 that differs from 0° is also possible.

A structure on the reticle 7 is imaged onto a light-sensitive layer of a wafer 13 arranged in the region of the image field 11 in the image plane 12. The wafer 13 is held by a wafer holder 14. The wafer holder 14 is displaceable by way of a wafer displacement drive 15, in particular along the y- direction. The displacement on the one hand of the reticle 7 by way of the reticle displacement drive 9 and on the other hand of the wafer 13 by way of the wafer displacement drive 15 can take place in such a way as to be synchronized with one another.

The radiation source 3 is an EUV radiation source. The radiation source 3 emits, in particular, EUV radiation 16, which is also referred to below as used radiation, illumination radiation or illumination light. In particular, the used radiation has a wavelength in the range between 5 rnn and 30 rnn. The radiation source 3 can be a plasma source, for example an LPP (“laser produced plasma”) source or a GDPP (“gas discharged produced plasma”) source. It may also be a synchrotron-based radiation source. The radiation source 3 can be a free electron laser (FEL).

The illumination radiation 16 emerging from the radiation source 3 is focused by a collector 17. The collector 17 can be a collector with one or more ellipsoid and/or hyperboloid reflection surfaces, as will be explained below on the basis of exemplary embodiments. The illumination radiation 16 may be incident on the at least one reflection surface of the collector 17 with grazing incidence (GI), i.e. at angles of incidence of greater than 45°, or with normal incidence (NI), i.e. at angles of incidence of less than 45°. The collector 17 can be structured and/or coated, firstly, for optimizing its reflectivity for the used radiation and, secondly, for suppressing extraneous light.

Downstream of the collector 17, the illumination radiation 16 propagates through an intermediate focus IF in an intermediate focal plane 18. The intermediate focal plane 18 can represent a separation between a radiation source module, having the radiation source 3 and the collector 17, and the illumination optical unit 4.

The illumination optical unit 4 comprises a deflection mirror 19 and, arranged downstream thereof in the beam path, a first facet mirror 20. The deflection mirror 19 may be a plane deflection mirror or, alternatively, a mirror with a beam-influencing effect that goes beyond a purely deflecting effect. As an alternative or in addition thereto, the mirror 19 can be embodied as a spectral filter separating a used light wavelength of the illumination radiation 16 from extraneous light having a wavelength that deviates therefrom. Provided the first facet mirror 20 is arranged in a plane of the illumination optical unit 4 which is optically conjugate to the object plane 6 as a field plane, this facet mirror is also referred to as a field facet mirror. The first facet mirror 20 comprises a multiplicity of individual first facets 21, which are also referred to below as field facets. Some of these facets 21 are shown in Figure 1 only by way of example.

The first facets 21 may be embodied as macroscopic facets, in particular as rectangular facets or as facets with an arcuate peripheral contour or a peripheral contour of part of a circle. The first facets 21 may be embodied as plane facets or alternatively as convexly or concavely curved facets.

As known for example from DE 10 2008 009 600 Al, the first facets 21 themselves may also be composed in each case of a multiplicity of individual mirrors, in particular a multiplicity of micromirrors. The first facet mirror 20 may in particular be formed as a microelectromechanical system (MEMS system). For details, reference is made to DE 10 2008 009 600 Al.

The illumination radiation 16 travels horizontally, i.e., along the y- direction, between the collector 17 and the deflection mirror 19. A different direction of travel is also possible, depending on the embodiment of the illumination optical unit 4.

In the beam path of the illumination optical unit 4, a second facet mirror 22 is arranged downstream of the first facet mirror 20. If the second facet mirror 22 is arranged in a pupil plane of the illumination optical unit 4, it is also referred to as a pupil facet mirror. The second facet mirror 22 may also be arranged at a distance from a pupil plane of the illumination optical unit 4. In this case, the combination of the first facet mirror 20 and the second facet mirror 22 can also be embodied as a specular reflector. Specular reflectors are known from US 2006/0132747 Al, EP 1 614 008 Bl and US 6,573,978.

The second facet mirror 22 comprises a plurality of second facets 23. In the case of a pupil facet mirror, the second facets 23 are also referred to as pupil facets. The explanations provided here also apply accordingly to a specular reflector since an effect of the stop apparatus, described below, for second faceted elements of a specular reflector corresponds to the effect for the second facets 23 of the pupil facet mirror 22. To the extent this is relevant within the scope of the description provided here, the effect of the first faceted element of the specular reflector also corresponds to the effect of the first facet mirror 20 with the field facets 21.

The second facets 23 can likewise be macroscopic facets, which can, for example, have a round, rectangular or hexagonal boundary, or alternatively be facets composed of micromirrors. In this regard, reference is likewise made to DE 10 2008 009 600 Al.

The second facets 23 may have planar or alternatively convexly or concavely curved reflection surfaces.

The illumination optical unit 4 consequently forms a twice-faceted system. This basic principle is also referred to as fly's eye integrator or honeycomb condenser.

It may be advantageous to arrange the second facet mirror 22 not exactly in a plane that is optically conjugate to a pupil plane of the projection optical unit 7.

With the aid of the second facet mirror 22, the individual first facets 21 are imaged into the object field 5 The second facet mirror 22 is the last beamshaping mirror or else, in fact, the last mirror for the illumination radiation 16 in the beam path before the object field 5. In a further embodiment of the illumination optical unit 4 that is not shown, a transmission optical unit contributing in particular to the imaging of the first facets 21 into the object field 5 may be arranged in the beam path between the second facet mirror 22 and the object field 5. The transmission optical unit may have exactly one mirror or else alternatively two or more mirrors, which are arranged one behind the other in the beam path of the illumination optical unit 4. The transmission optical unit may in particular comprise one or two normal-incidence mirrors (NI mirrors) and/or one or two grazing-incidence mirrors (GI mirrors).

In the embodiment shown in Figure 1, the illumination optical unit 4 has exactly three mirrors downstream of the collector 17, specifically the deflection mirror 19, the field facet mirror 20 and the pupil facet mirror 22.

The deflection mirror 19 can also be dispensed with in a further embodiment of the illumination optical unit 4, and the illumination optical unit 4 can then have exactly two mirrors downstream of the collector 17, specifically the first facet mirror 20 and the second facet mirror 22.

As a rule, the imaging of the first facets 21 into the object plane 6 by means of the second facets 23 or using the second facets 23 and a transmission optical unit is only approximate imaging.

The projection optical unit 10 comprises a plurality of mirrors Mi, which are consecutively numbered in accordance with their arrangement in the beam path of the projection exposure apparatus 1.

In the example illustrated in Figure 1, the projection optical unit 10 comprises six mirrors Ml to M6. Alternatives with four, eight, ten, twelve or any other number of mirrors Mi are similarly possible. The projection optical unit 10 is a twice-obscured optical unit. The penultimate mirror M5 and the last mirror M6 each have a through opening for the illumination radiation 16. The projection optical unit 10 has an image-side numerical aperture that is greater than 0.5 and may also be greater than 0.6, and may be for example 0.7 or 0.75.

Reflection surfaces of the mirrors Mi can be embodied as free-form surfaces without an axis of rotational symmetry. Alternatively, the reflection surfaces of the mirrors Mi may be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflection surface form. Just like the mirrors of the illumination optical unit 4, the mirrors Mi may have highly reflective coatings for the illumination radiation 16. These coatings may be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

The projection optical unit 10 has a large object image offset in the y- direction between a y-coordinate of a centre of the object field 5 and a y- coordinate of the centre of the image field 11. In the y-direction, this object-image offset can be approximately the same size as a z-distance between the object plane 6 and the image plane 12.

In particular, the projection optical unit 10 may have an anamorphic form. In particular, it has different imaging scales 0_X, p_y in the x- and y- directions. The two imaging scales 0_X, p_y of the projection optical unit 10 are preferably at (p_x, p_y) = (+/- 0.25, /+- 0.125). A positive imaging scale P means imaging without an image reversal. A negative sign for the imaging scale P means imaging with an image reversal. The projection optical unit 10 consequently leads to a reduction in size with a ratio of 4: 1 in the x-direction, i.e. in a direction perpendicular to the scanning direction.

The projection optical unit 10 leads to a reduction in size of 8: 1 in the y- direction, i.e. in the scanning direction.

Other imaging scales are similarly possible. Imaging scales with the same sign and the same absolute value in the x-direction and y-direction are also possible, for example with absolute values of 0.125 or of 0.25.

The number of intermediate image planes in the x-direction and in the y- direction in the beam path between the object field 5 and the image field 11 may be the same or, depending on the embodiment of the projection optical unit 10, may differ. Examples of projection optical units with different numbers of such intermediate images in the x- and y-directions are known from US 2018/0074303 Al.

In each case one of the pupil facets 23 is assigned to exactly one of the field facets 21 for forming in each case an illumination channel for illuminating the object field 5. In particular, this can yield illumination according to the Kohler principle. The far field is decomposed into a multiplicity of object fields 5 with the aid of the field facets 21. The field facets 21 generate a plurality of images of the intermediate focus on the pupil facets 23 respectively assigned thereto, which will likewise still be explained in more detail below.

By way of respectively assigned pupil facets 23, the field facets 21 are imaged on the reticle 7 in a manner superposed on one another for the purposes of illuminating the object field 5. The illumination of the object field 5 is in particular as homogeneous as possible. It preferably has a uniformity error of less than 2%. The field uniformity can be achieved by way of the superposition of different illumination channels.

The illumination of the entrance pupil of the projection optical unit 10 can be defined geometrically by way of an arrangement of the pupil facets. The intensity distribution in the entrance pupil of the projection optical unit 10 can be set by selecting the illumination channels, in particular the subset of the pupil facets, which guide light. This intensity distribution is also referred to as illumination setting.

A likewise preferred pupil uniformity in the region of defined illuminated sections of an illumination pupil of the illumination optical unit 4 can be achieved by a redistribution of the illumination channels.

Further aspects and details of the illumination of the object field 5 and in particular of the entrance pupil of the projection optical unit 10 are described below.

In particular, the projection optical unit 10 may have a homocentric entrance pupil. The latter may be accessible. It may also be inaccessible.

The entrance pupil of the projection optical unit 10 cannot be exactly illuminated using the pupil facet mirror 22 on a regular basis. In the case of imaging the projection optical unit 10 in which the centre of the pupil facet mirror 22 is telecentrically imaged onto the wafer 13, the aperture rays often do not intersect at a single point. However, it is possible to find an area in which the distance of the aperture rays determined in pairs becomes minimal. This area represents the entrance pupil or an area in real space that is conjugate thereto. In particular, this area has a finite curvature.

It may be that the projection optical unit 10 has different positions of the entrance pupil for the tangential beam path and for the sagittal beam path. In this case, an imaging element, in particular an optical component of the transmission optical unit, should be provided between the second facet mirror 22 and the reticle 7. With the aid of this optical element, the different position of the tangential entrance pupil and the sagittal entrance pupil can be taken into account.

In the arrangement of the components of the illumination optical unit 4 illustrated in Figure 1, the pupil facet mirror 22 is arranged in an area conjugate to the entrance pupil of the projection optical unit 10. The field facet mirror 20 is arranged in tilted fashion with respect to the object plane 6. The first facet mirror 20 is arranged in tilted fashion with respect to an arrangement plane defined by the deflection mirror 19.

The first facet mirror 20 is arranged in tilted fashion with respect to an arrangement plane defined by the second facet mirror 22.

Figure 2 shows exemplary individual beams of a beam path of the illumination light 16 between an embodiment of the collector 17 as an ellipsoid mirror between a source volume 24 of the radiation source 3 and the intermediate focus IF in the intermediate focal plane 18. Firstly, the source volume 24 and, secondly, the intermediate focus IF lie in the two foci of the ellipsoid collector 17. The collector 17 has a central passage opening 25 for the passage of pump radiation 26, which is generated by a pump light source 27 of the radiation source 3. By way of example, a wavelength of the pump light source lies in the region of 10.6 pm.

The illumination light 16 is generated in the source volume 24 by interaction of the pump radiation 26 with a tin droplet 27a, which is shot through the source volume 24 along a trajectory 28. The trajectory 28 extends perpendicular to the beam path of a chief ray of the pump radiation 26. The chief ray can coincide with a rotation axis of symmetry of the ellipsoid collector 17.

The collector 17 can be embodied to image with a magnification by a factor of 5.

Figure 3 shows a further embodiment of the collector 17. The collector 17 according to Figure 3 is embodied as a Wolter collector with a total of four nested mirror shells 29, 30, 31, 32 located within one another, which mirror shells are in turn subdivided into two shell sections, which are provided with indices of "1" and "2" in Figure 3. The respective leading mirror shell section 291 to 32i has an inner reflection surface in the form of a hyperboloid in each case and the respective following mirror section 29 to 32 has an inner reflection surface in the form of an ellipsoid. The source volume 24 is also imaged into the intermediate focus IF using this Wolter collector 17, corresponding to what was explained above with reference to Figure 2.

A distance between the source volume 24 and the intermediate focus IF is in the region of 1500 mm. A diameter of intermediate focus IF ranges between 1 mm and 5 mm. Figure 4 shows components of the projection exposure apparatus 1 in the beam path of an illumination channel 16i of the illumination light 16 between the intermediate focus IF and an intermediate focus image 33 on the pupil facet 23 assigned to this illumination channel 16i. The intermediate focus IF is arranged in centred fashion in an aperture 34 in a stop 35 of a stop apparatus 36. The stop apparatus 36 serves to delimit the beam path of the illumination light 16 between the radiation source or light source 3 and the illumination optical unit 4 of the projection exposure apparatus 1.

On account of the centred (intended) arrangement, i.e., a nominal position, of the intermediate focus IF in the aperture 34, the intermediate focus image 33 is located in centred fashion on the pupil facet 23 in the case of the nominal alignment of the field facet 21, which in turn is assigned to the illumination channel 16i.

Figure 5 shows the beam path of an illumination channel 16i between the intermediate focus IF and a sensor of a measuring device 37 for measuring a position of the illumination channel 16i on the sensor, i.e., of the illumination channel 16i. This position measurement on the sensor of the measuring device 37 serves to measure the position of a beam of the illumination light 16 passing through the stop 35. The sensor of the measuring device 37 can be embodied as a PSD (position sensitive device) sensor.

The situation in which the intermediate focus IF has been decentred relative to the centred nominal position according to Figure 4 is illustrated in Figure 5. As long as the field facet 21 remains in its nominal position according to Figure 4, a decentration of the intermediate focus image 33 on the sensor of the measuring device 37 arises on account of this decentration of the intermediate focus IF, as illustrated in Figure 5.

The measuring device 37 is signal-connected to an open-loop/closed-loop control device 38. The latter is signal-connected, in turn, to an adjustment device actuator 39. The adjustment device actuator 39 in turn has a mechanical operative connection to the field facet 21. The stop apparatus 36, the measuring device 37, the open-loop/closed-loop control device 38 and the adjustment device actuator 39 are components of a stop system 40 for the projection exposure apparatus 1.

Figure 6 shows a variant of the stop system 40, in which the illumination light 16 is reflected not via one of the field facets 21 but via a measuring facet 41 to the sensor of the measuring device 37 via the illumination light channel 16i. The measuring facet 41 is arranged adjacent to the field facets 21 of the field facet mirror 20 and can be arranged, for example, in unused regions of the field facet mirror 20 and, in particular, between the field facets 21 of the field facet mirror 20.

Figure 7 shows the beam guiding conditions in the illumination channel 16i between the intermediate focus IF and the pupil facet 23 in the case of decentred intermediate focus IF in accordance with the intermediate focus arrangement in Figures 5 and 6. In the case of the illumination channel profile according to Figure 7, a decentration of the intermediate focus image 33 on the pupil facet 23 emerges from the decentred (actual) arrangement of the intermediate focus IF in the case of a nominal alignment of the field facet 21 like in Figure 4. In comparison with Figure 7, Figure 8 shows the situation following a correction displacement of the field facet 21 for the purposes of centring the intermediate focus image 33 on the pupil facet 23, i.e., for correcting the decentred relative position of the intermediate focus IF which has remained unchanged in comparison with the situation according to Figure 7. The correction displacement can be a tilt and/or a translation of the field facet 21, which is caused by the adjustment device actuator 39. At least one of the three tilt degrees of freedom or one of the three translation degrees of freedom can be used here in each case.

To compensate a change in direction of the beam direction of the illumination light channel 16i following the reflection of the pupil facet 23, which emerges on account of the repositioning of the associated field facet 21, the pupil facet 23 can also be equipped with a corresponding adjustment device actuator, which then in turn is signal-connected to the open-loop/closed-loop control device 38 and represents a component of the stop system 40.

Figure 9 shows, in an illustration similar to Figure 4, intensity conditions of the illumination light 16 in the case of a centred intermediate focus IF between the stop apparatus 36 and one of the pupil facets 23 assigned via an illumination channel 16i. Upstream of the aperture 34 in the stop 35 of the stop apparatus 36, the illumination light 16, in the case of a centred intermediate focus IF, likewise has an intensity distribution centred in relation to the aperture 34 or an intensity profile I(x,y).

The aperture 34 cuts marginal intensity flanks 42 of this intensity distribution I, and so these intensity flanks 42, which are illustrated schematically using dashed lines at the location of the pupil facet in Figure 9, are not imaged, i.e., are missing as intensity contribution on the pupil facet 23. Thus, only a central intensity section 43, the intensity profile of which is illustrated as a solid line between the intensity flanks 42 in Figure 9, is transferred to the pupil facet 23 via the illumination channel 16i.

In the case of an intermediate focus IF that is centred relative to the aperture 34, the central intensity section 43 carries the majority of the intensity of the illumination light 16 of the illumination channel 16i. Thus, only a small part of the illumination light intensity was cut by way of the intensity flanks 42 using the centred stop 35, for example less than 10% or else less than 5% or else less than 2% or else less than 1%. Regularly, the stop 35 cuts more than 0.1% of the entire illumination light intensity that is incident on the intermediate focal plane 18.

As a result of cutting the margins of the intensity profile I using the stop 35, a smaller intermediate focus image 33 overall arises on the pupil facet. This can be used to reduce a typical required diameter of the pupil facets 23 of the pupil facet mirror 22. In particular, it is possible to realize an illumination setting with a smaller degree of pupil filling. As an alternative or in addition thereto, cutting the intensity flanks 42 can bring about a homogenization of illumination light intensities transported by the various illumination channels 16i.

Figures 10 and 11 show size comparison between an aperture 44 in a rigid stop from the prior art and the aperture 34 in the displaceable stop 35 of the stop apparatus 36. An internal diameter of the aperture 34 of this displaceable stop 35 is as large as or slightly larger than, for example by a few percent, a cross-sectional region 45 to be used for the passage of the central intensity section 43 of the illumination light 16. The relative position conditions according to Figure 10 arise provided that the central intensity section 43 is located in the centre of the aperture 44. The aperture 34 in the displaceable stop 35 is located centrally in the aperture 44 in the rigid stop of the prior art. The aperture 34 can have a diameter ranging from 50% to 90%, ranging from 60% to 90% or else ranging from 60% to 75% of the diameter of the aperture 44 of the prior art.

Figure 11 shows the conditions in the case of a decentred intermediate focus IF and a correspondingly decentred central intensity section 43. The region 45 to be used is displaced in accordance with this decentration and the displaceable aperture 34 has followed this displacement under control of an embodiment of a displacement device, for example an embodiment of an adjustment actuator. Despite the decentration of the central intensity section 43, the latter still passes through the aperture 34 in full. By contrast, the aperture 44 in the rigid stop of the prior art needs to be embodied as large as illustrated in Figures 10 and 11 in order to likewise allow the decentred central intensity section 43 to pass.

Figure 12 shows details of the stop apparatus 36. Component parts and functions which were already explained above on the basis of Figures 1 to 11 have the same reference signs and are not explained again in detail.

The stop 35 of the stop apparatus 36 is displaceable relative to a stop carrier 46 of the stop apparatus 36 in the intermediate focal plane 18, as elucidated in Figure 12 by double-headed arrows. The stop carrier 46 has a passage opening 46a, within which the aperture 34 is located. The passage opening 46a is so much larger than the aperture 34 that it is only the aperture 34 and not the passage opening 46a that delimits the beam path of the illumination light 16 in possible operational positions of the aperture 34 relative to the stop carrier 46.

A second displacement degree of freedom of the stop 35 relative to the stop carrier 46, not illustrated in Figure 12, extends perpendicular to the plane of the drawing of Figure 12.

This displacement of the stop 35 is brought about by way of a displacement device 47 which is embodied as at least one actuator, exemplary embodiments of which will still be explained below. The displacement device 47 is signal-connected to the open-loop/closed-loop control device 38 in a maimer not illustrated here. Instead of a single displacement device 47 for bringing about the displacement of the stop 35 in the two degrees of freedom, provision can also be made of a plurality of displacement devices 47 for displacing the stop 35 through the intermediate focal plane 18 along two independent displacement directional components transverse to the beam path of the illumination light 16, each of which can be embodied as an actuator.

Moreover, Figure 12 once again illustrates the intensity profile I(x,y) of the illumination light 16 which passes through the intermediate focal plane 18 and an intensity profile IF of extraneous light 48, which was deflected perpendicular to the beam path of the illumination light 16 by an optical component of the illumination system 2 upstream of the stop apparatus 36 and which is blocked or absorbed by a beam dump structure 49 of the stop carrier 46. In particular, the extraneous light 48 is radiation at a different wavelength from the used wavelength of the illumination light 16, for example the pump radiation 26.

Figure 13 shows an embodiment of the stop 35 of the stop apparatus 36. The stop 35 is thermally coupled to a heat sink 51 by an elastic thermally conductive connection 50, which is elucidated by a spring in Figure 13. The thermally conductive connection 50 can have a metallic embodiment and can be configured in the form of a spring and/or in the form of a strand.

Figure 14 shows an embodiment of components of the stop apparatus 36 with two linear actuators 52, 53, which form displacement devices for displacing the stop 34 transversely to the beam path of the illumination light 16 through the intermediate focal plane 18. The linear actuator 52 acts directly on the stop 35 and is guided along its displacement direction 54 on a carrier 55, which in turn interacts with the other linear actuator 53 with displacement direction 56. The two displacement directions 54, 56 are perpendicular to one another. As elucidated by Figure 14, the two linear actuators 52, 53 and the associated carriers are arranged in the shape of a plus sign.

Figure 15 shows a further embodiment for displacing the stop 35 along two translation degrees of freedom, which are perpendicular to one another and transverse to the beam path of the illumination light 16, with the aid of three linear actuators. The first of these linear actuators 52 corresponds to the one that was already explained above in conjunction with Figure 14. Instead of one further linear actuator, the embodiment according to Figure 15 has two further linear actuators 531, 53 , each of which corresponds to the embodiment according to Figure 14 on its own, although they are arranged with parallel distance from one another and each guide the stop 35 along the displacement direction 54. The two linear actuators 53 i, 53 are operated synchronously with one another for the purposes of displacing the stop 35 along the displacement direction 56. The three linear actuators 52, 53i and 53 are present in the form of an "H" arrangement, as elucidated by Figure 15.

Figure 16 shows a further embodiment of displacement devices for displacing the stop 35 transversely to the beam path of the illumination light 16 through the intermediate focal plane 18. Components corresponding to those which have already been explained above with reference to Figures 1 to 15 have the same reference signs and will not be discussed in detail again.

The stop apparatus 36 according to Figure 16 has a circular edge and is mechanically connected to an intermediate carrier 59 via two linear actuators 57i, 572 with a horizontal displacement direction 58 in Figure 16. In turn, the intermediate carrier 59 is mechanically connected to the stop carrier 46 via two further linear actuators 60i, 6O2 with a perpendicular displacement direction 61 in Figure 16. The stop 35, the intermediate carrier 59 and the stop carrier 46 are arranged coaxially with respect to one another. The stop 35, the intermediate carrier 59 and the stop carrier 46 are embodied with a rotationally symmetric body in each case as carrier components arranged with rotational symmetry with respect to the stop 35.

A further embodiment of a displaceable stop apparatus 36 is explained on the basis of Figure 17. Components and functions corresponding to those which have already been explained above with reference to Figures 1 to 16 have the same reference signs and will not be discussed in detail again.

The stop apparatus 36 according to Figure 17 has as a first displacement device a linear actuator 62 with two actuator rails 621, 62z, between which the stop 35 is guided, for the purposes of displacing the stop 35 along a displacement direction 63. Overall, the linear actuator 62 is connected to a rotation actuator or swivel actuator 64, which may be arranged, for example, below the two actuator rails 621, 62z in Figure 17. The rotation actuator 64 has a rotor in the basic shape of a sleeve with a rotor opening 65, in which the aperture 34 is located in all practically usable displacement positions of the stop apparatus 36. Thus, the rotor opening 65 is significantly larger than the aperture 34.

The rotation actuator 64 serves for the rotation or pivot displacement of the linear actuator 62 and the stop 35 guided thereby, along a swivel direction 66 indicated in turn in Figure 17 by a double-headed arrow. The associated swivel axis is perpendicular to an arrangement plane of the stop 35.

When the stop apparatus 36 is assembled, the rotor opening 65 is aligned to a nominally centred position of the intermediate focus IF such that this intermediate focus position is centred in the rotor opening 65. By controlling the actuators 62, 64, which are controlled by way of the open- loop/closed-loop control device 38, the aperture 34 can then be displaced within the rotor opening 65 and on the basis of an actual position displacement of the intermediate focus relative to the originally specified nominal position (target position) until the aperture 34 once again corresponds to the intermediate focus position of the illumination light 16. Further variants of linear actuators as displacement devices of the stop apparatus 36 are explained below on the basis of Figures 18 to 21. Components and functions corresponding to those which have already been explained above with reference to the respective preceding figures have the same reference signs and will not be discussed in detail again.

Figure 18 shows a linear actuator 67 that is comparable to the linear actuator 62 according to Figure 17. The linear actuator 67 has two actuator rails 67i, 672, between which the stop 35 is guided along a displacement direction 68. In relation to the displacement direction 68, the two actuator rails 67i, 67 are arranged on both sides of the stop 35.

Figure 19 shows an embodiment of a linear actuator 69 having two pinions 70i, 702, at least one of which is driven and meshes with toothed rack sections 711, 7h in turn securely mechanically connected to the stop 35. These toothed rack sections 7h, 7h convert the rotational movement of the pinions 701, 702 into a linear displacement of the stop 35 along the displacement direction 68. In relation to the displacement direction 68, the two toothed rack sections 7h, 7h are arranged in centred fashion in relation to a stop body of the stop 35.

Figure 20 shows a linear actuator 72 as a variant of the linear actuator 69. In the linear actuator 72 there is a pairing of a pinion 70 and a toothed rack section 71, corresponding to what was explained above in relation to the linear actuator 69. Instead of the second pinion/toothed rack section pairing, the linear actuator 72 has a linear guide 73 with a rail 74 that is secured with respect to the stop and a guide section 75 that is secured with respect to the actuator or frame. Figure 21 shows a variant of a linear actuator 76, in which the stop 35 is clamped between two actuator bodies 77, 78 which can expand or contract in a manner synchronized to one another depending on the control via the open-loop/closed-loop control device 38 and which can consequently bring about a displacement of the stop 35 along the displacement direction 68. The actuator bodies 77, 78 can be embodied as piezo actuators.

Alternative linear actuators correspond to those explained above and can be embodied as piston drives, spindle drives, two-column linear drives or single-column linear drives with a long or short column.

Figures 22 and 23 show intensity conditions of the illumination light 16 upstream and downstream of the stop 35 in the case of a stop 35 centred relative to the central intensity section 43 (Figure 22) and in the case of a stop 35 decentred relative to the central intensity section 43 (Figure 23). An intensity centroid of the illustrated intensity profile is highlighted in each of Figures 22 and 23.

By way of a controlled feedback, carried out by the open-loop/closed-loop control device 38, it is possible to measure the intensity profile I(x,y) downstream of the stop 35, for example by way of a spatially resolving sensor of the measuring device 37, and the stop 35 can be transferred from a position according to Figure 23 that is decentred relative to the maximum of the intensity profile I(x,y) into a centred position according to Figure 22 by controlling the respective at least one displacement device. This control process can be implemented iteratively. This control process can be implemented in real time during the operation of the projection exposure apparatus 1 and can ensure that the position of the aperture 34 in each case tracks the intermediate focus IF of the illumination light 16 in the intermediate focal plane 18. According to this tracking, the open- loop/closed-loop control device 38 then also controls the adjustment device actuators 39 of the field facets 21 so that the respective intermediate focus image of the illumination channel 16i comes to rest again in centred fashion on the respective pupil facet 23. Accordingly, it is then also possible to update the pupil facets 23 with the aid of dedicated adjustment device actuators not illustrated here, which in turn can be controlled by way of the open-loop/closed-loop control device 38. This yields an effective illumination light throughput through the illumination optical unit 4.

The respective displacement device can have a stepper motor or be embodied as a stepper motor.

With the aid of the projection exposure apparatus 1, at least one part of the reticle 7 in the object field 5 is imaged onto a region of a light-sensitive layer on the wafer 13 in the image field 11 for the lithographic production of a micro structured or nano structured component, in particular of a semiconductor component, for example of a microchip. Depending on the embodiment of the projection exposure apparatus 1 as a scanner or as a stepper, the reticle 7 and the wafer 13 are moved in a temporally synchronized maimer in the y direction continuously in scanner operation or step by step in stepper operation.

Claims

- 34 - Claims

1. Stop apparatus (36) for delimiting an illumination light beam path between a light source (3) and an illumination optical unit (4) of a projection exposure apparatus (1) for projection lithography

- comprising a stop (35) which is arranged in the beam path and which has an aperture (34) for the passage of used illumination light (16) that emanates from the light source (3),

- comprising at least one displacement device (47; 52, 53; 53 i, 53 ;

57i, 572, 60i, 6O2; 62i, 622, 64; 67i, 672; 69; 72; 76) for displacing the stop (35) transversely to the illumination light beam path,

- comprising a stop carrier (46) which has a passage opening (46a) within which the aperture (34) is located, wherein the stop (35) is displaceable relative to the stop carrier (46) via the displacement device (47; 52, 53; 53I, 53₂; 57i, 572, 6O1, 60₂; 62i, 62₂, 64; 671, 67₂; 69; 72; 76).

2. Stop apparatus according to Claim 1, comprising at least two displacement devices (52, 53; 57, 60; 62, 64) for displacing the stop (35) along two independent displacement directional components (54, 56; 58, 61; 63, 66) transversely to the illumination beam path.

3. Stop apparatus according to Claim 1 or 2, characterized in that the displacement device (47; 52, 53; 531, 532; 57i, 572, 6O1, 6O2; 62i, 622, 64; 67i, 672; 69; 72; 76) is embodied as an actuator.

4. Stop apparatus according to Claim 3, characterized in that the displacement device (47; 52, 53; 531, 532; 57i, 572, 6O1, 6O2; 62i, 622, 64; 67i, 672; 69; 72; 76) is embodied as a linear actuator. - 35 -

5. Stop apparatus according to Claim 3 or 4, characterized in that the displacement device (64) is embodied as a swivel actuator.

6. Stop apparatus according to any one of Claims 1 to 5, wherein the stop carrier (46) comprises further functional components of the stop apparatus.

7. Stop apparatus according to any one of Claims 4 to 6, characterized in that the stop (35) is connected to an intermediate carrier (59) via at least one of the displacement devices (57i, 57 ) embodied as a linear actuator, wherein the intermediate carrier (59) is connected to the stop carrier (46) or a further intermediate carrier via at least one further displacement device (601, 6O2) embodied as a linear actuator.

8. Stop apparatus according to any one of Claims 1 to 7, characterized in that the displacement device (47; 52, 53; 531, 532; 57i, 572, 6O1, 6O2; 62i, 622, 64; 67i, 672; 69; 72; 76) comprises a stepper motor.

9. Stop system (40)

- comprising a stop apparatus (36) according to any one of Claims 1 to 8,

- comprising a measuring device (37) for measuring a position of an illumination light beam passing through the aperture (34),

- comprising an open-loop/closed-loop control device (38) which is signal connected to the at least one displacement device (47; 52, 53; 53i, 53₂; 57i, 57₂, 6O1, 60₂; 62i, 62₂, 64; 67i, 67₂; 69; 72; 76) and to the measuring device (37). Illumination optical unit (4) for illuminating an object field (5) of the projection exposure apparatus (1), within which at least a section of an object (7) with structures to be imaged is arrangeable, characterized by

- a stop apparatus (36) according to any one of Claims 1 to 8 or

- a stop system according to Claim 9. Illumination system (2) comprising an illumination optical unit (4) according to Claim 10, comprising a light source (3) for the illumination light (16) and comprising a collector (17) for focussing the illumination light (16) in the region of the stop (35). Optical system comprising an illumination optical unit (4) according to Claim 10 and comprising a projection optical unit (10) for imaging the object field (5) into an image field (11), in which at least one section of a wafer (13) on which the object structures are to be imaged is arrangeable. Projection exposure apparatus comprising an optical system according to Claim 12, comprising a light source (3) for the illumination light (16) and comprising a collector (17) for focussing the illumination light (16) in the region of the stop (35). Method for producing a structured component, including the following method steps:

- providing a reticle (7) and a wafer (13),

- projecting a structure on the reticle (7) onto a light-sensitive layer of the wafer (13) with the aid of the projection exposure apparatus according to Claim 13, - producing a micro structure and/or nanostructure on the wafer (13). Structured component, produced according to a method according to Claim 14.