Patent Application
20250147427
The disclosure relates to a projection exposure apparatus for semiconductor lithography.
In relation to their imaging quality, projection exposure apparatuses for semiconductor lithography can exhibit a behaviour that depends significantly on temperature. Both elements not involved directly in the optical imaging, such as, for example, mounts and holders or housing parts, and optical elements themselves, such as for example lenses or, in the case of EUV lithography, mirrors, typically change their extent or their surface shape when heated up or cooled down, which can have a direct effect on the quality of the imaging of a lithography mask, for example a phase mask, a so-called reticle, on a semiconductor substrate, a so-called wafer, as undertaken by the system. In this case, the heating of the individual components of the apparatus during operation can be traced back to the absorption of some of the radiation which is used to image the reticle onto the wafer. This radiation is produced by a light source, which is referred to as a used light source hereinafter. In the case of EUV lithography, the used light source is often a comparatively complex plasma source, with which a plasma that emits electromagnetic radiation in the desired short-wave frequency ranges is generated via laser irradiation of tin particles.
Projection exposure apparatuses are usually designed for a stationary state during operation, which is to say a state in which no substantial fluctuations in the temperature of apparatus components should be expected over time. Thus, the apparatus or its components are typically preheated, especially following a long down time of the apparatus and the cooling of the components typically connected therewith, which is to say it is desirable to establish a state in which the projection exposure apparatus and its individual components are each set to temperatures that come close to the values attained during operation.
In this respect, known systems, especially in the case of EUV systems, have used preheaters which are used to both time-dependently and spatially variably compensate aberrations caused by surface deformations on account of absorption-induced temperature fluctuations. The idea involves externally heating the material when little or no used radiation is absorbed, and of reducing the external heating power by an extent equal to the heating on account of the absorption of the used radiation during operation.
Some known approaches use infrared radiation in the preheaters, the infrared radiation being influenced by an illumination optical unit in such a way that it can be adjusted in terms of its intensity, for example also in terms of its intensity distribution. The illumination optical unit frequently comprises a collimator for producing approximately parallel radiation from the infrared radiation produced by a laser and comprises a tube for adjusting the beam shape. Certain known preheaters use what are known as screw rings for fixing the individual optical elements within a housing of the illumination optical unit. However, particles of different dimensions, for example of between 3 micrometers (μm) and 100 μm, may arise on account of the friction arising between the thread and the screw rings. This can be undesirable because this can significantly increase the probability of such a particle precipitating on an optical element and being able to lead to a damaging of the optical element, and hence to an outage of the preheaters, on account of the significant absorption of the heating radiation by the particle.
The present disclosure to provide a device which eliminates certain disadvantages of known systems.
In an aspect, the disclosure provides a projection exposure apparatus comprising a heating device for heating at least one element of the projection exposure apparatus by means of electromagnetic radiation. In this case, the heating apparatus comprises an illumination optical unit having a housing and at least one optical element, arranged within the housing, for influencing the electromagnetic radiation. According to the disclosure, at least one optical element is fixed within the housing by way of at least one elastic element. As a result of the optical element being fixing according to the disclosure by way of the spring force exerted by the elastic element, it is possible to dispense with screwing of a holding ring. This can help prevent mutually corresponding flanks of threads from sliding on one another as this could lead to a particle exposure of the illumination optical unit.
In this case, the at least one optical element can be arranged in such a way between the elastic element and a receptacle formed in the housing that the elastic element presses the optical element against the receptacle. In other words, the receptacle in this case can serve as an abutment for the spring force exerted on the optical element by the elastic element.
The at least one optical element can be arranged between a first elastic element and a second elastic element. In this case, there is the option of the first elastic element exerting a force on the second elastic element via the optical element. Then, the second elastic element may in turn for example press a further optical element against a receptacle in the housing, and hence fix the optical element in this way.
It is likewise conceivable for the elastic element to be arranged between a first optical element and a second optical element.
Especially in cases where the optical element is the last optical element in the illumination optical unit, it may be desirable for the elastic element to be arranged between the optical element and a holding element. For example, the holding element may be a retaining ring or lid.
In this case, the lid may comprise a lock, for example in the form of a bayonet lock, arranged on an outer surface of the housing. What can be achieved as a result of the lock being arranged on the outer surface of the housing is that a possible particle exposure caused by components of the lock sliding past one another does not reach the interior of the illumination optical unit.
Especially in cases in which a diffractive optical element, for example a diffraction grating, is used as an optical element, it may be desirable for the illumination optical unit to comprise a displacement unit for positioning at least one optical element in a plane perpendicular to the longitudinal axis of the housing. In this case, the optical element may be arranged in a sleeve of the displacement unit.
By way of example, a friction-free mount of the sleeve in the housing can be achieved by virtue of the sleeve being mounted on at least three pins which each have a spherical contact surface on each end, with the ends of the pins opposite the sleeve resting on a receptacle in the housing of the illumination optical unit. Additionally, or in an alternative thereto, it is also conceivable to use leaf springs or a monolithic kinematic system.
In a variant of the disclosure, the heating device may comprise a labyrinth seal. In this case, the labyrinth seal may be formed by two mutually corresponding partial geometries in two different component parts of the illumination optical unit.
Exemplary embodiments and variants of the disclosure will be explained in more detail hereinafter with reference to the drawing, in which:
Certain parts of a microlithographic projection exposure apparatus 1 are described in exemplary fashion below initially with reference to
An embodiment of an illumination system 2 of the projection exposure apparatus 1 has, in addition to a radiation source 3, an illumination optical unit 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 may also be provided as a module separate from the rest of the illumination system. In this case, the illumination system does not comprise the light source 3.
A reticle 7 arranged in the object field 5 is illuminated. The reticle 7 is held by a reticle holder 8. The reticle holder 8 is displaceable, for example in a scanning direction, by way of a reticle displacement drive 9.
A Cartesian xyz-coordinate system is shown in
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 extends parallel to the object plane 6. Alternatively, an angle that differs from 0° between the object plane 6 and the image plane 12 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, for example longitudinally with respect to the y-direction. The displacement, firstly, of the reticle 7 by way of the reticle displacement drive 9 and, secondly, of the wafer 13 by way of the wafer displacement drive 15 can be implemented so as to be mutually synchronized.
The radiation source 3 is an EUV radiation source. The radiation source 3 emits EUV radiation 16, which is also referred to below as used radiation, illumination radiation or illumination light. For example, the used radiation has a wavelength in the range between 5 nm and 30 nm. The radiation source 3 can be a plasma source, for example an LPP (laser produced plasma) source or a GDPP (gas discharge produced plasma) source. It may also be a synchrotron-based radiation source. The radiation source 3 may 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 may be a collector with one or more ellipsoidal and/or hyperboloidal reflection surfaces. The illumination radiation 16 can be incident on the at least one reflection surface of the collector 17 with grazing incidence (GI), which is to say at angles of incidence of greater than 45° relative to the direction of the normal to the mirror surface, or with normal incidence (NI), which is to say 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 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 going beyond a pure deflection effect. As an alternative or in addition, the deflection mirror 19 may be in the form of a spectral filter that separates a used light wavelength of the illumination radiation 16 from stray light of a wavelength deviating therefrom. If the first facet mirror 20 is arranged in a plane of the illumination optical unit 4 that is optically conjugate to the object plane 6 as a field plane, it 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.
The first facets 21 may be embodied as macroscopic facets, such as rectangular facets or as facets with an arcuate edge contour or an edge contour of part of a circle. The first facets 21 may be in the form of plane facets or alternatively as facets with convex or concave curvature.
As is known for example from DE 10 2008 009 600 A1, the first facets 21 themselves can also each be composed of a multiplicity of individual mirrors, such as a multiplicity of micromirrors. The first facet mirror 20 may be in the form of a microelectromechanical system (MEMS system). For details, reference is made to DE 10 2008 009 600 A1.
The illumination radiation 16 travels horizontally, which is to say in the y-direction, between the collector 17 and the deflection mirror 19.
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 can 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 is also referred to as a specular reflector. Specular reflectors are known from US 2006/0132747 A1, EP 1 614 008 B1, and U.S. Pat. No. 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 second facets 23 may likewise be macroscopic facets, which may for example have a round, rectangular or hexagonal boundary, or may alternatively be facets composed of micromirrors. In this regard, reference is likewise made to DE 10 2008 009 600 A1.
The second facets 23 may have plane reflection surfaces or alternatively reflection surfaces with a convex or concave curvature.
The illumination optical unit 4 consequently forms a double-faceted system. This fundamental principle is also referred to as a fly's eye condenser (fly's eye integrator).
It can be desirable 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 10. For example, the pupil facet mirror 22 can be arranged so as to be tilted relative to a pupil plane of the projection optical unit 10, as is described, for example, in DE 10 2017 220 586 A1.
The individual first facets 21 are imaged into the object field 5 using the second facet mirror 22. The second facet mirror 22 is the last beam-shaping mirror or indeed the last mirror for the illumination radiation 16 in the beam path upstream of the object field 5.
In a further embodiment, not illustrated, of the illumination optical unit 4, a transfer optical unit can be arranged in the beam path between the second facet mirror 22 and the object field 5, the transfer optical unit contributing for example to the imaging of the first facets 21 into the object field 5. The transfer optical unit may comprise exactly one mirror, but alternatively also comprise 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 can comprise one or two normal-incidence mirrors (NI mirrors) and/or one or two grazing-incidence mirrors (GI mirrors).
In the embodiment shown in
The deflection mirror 19 can also be dispensed with in a further embodiment of the illumination optical unit 4, and so 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.
The imaging of the first facets 21 into the object plane 6 via the second facets 23 or using the second facets 23 and a transfer optical unit is often only approximate imaging.
The projection optical unit 10 comprises a plurality of mirrors Mx, which are consecutively numbered in accordance with their arrangement in the beam path of the projection exposure apparatus 1.
In the example illustrated in
Reflection surfaces of the mirrors Mx can be in the form of free-form surfaces without an axis of rotational symmetry. Alternatively, the reflection surfaces of the mirrors Mx can be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflection surface shape. Just like the mirrors of the illumination optical unit 4, the mirrors Mx can have highly reflective coatings for the illumination radiation 16. These coatings can be designed as multilayer coatings, for example 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 of approximately the same magnitude as a z-distance between the object plane 6 and the image plane 12.
The projection optical unit 10 may have an anamorphic form. For example, it has different imaging scales βx, βy in the x- and y-directions. The two imaging scales βx, βy of the projection optical unit 10 are preferably (βx, βy)=(+/−0.25, +/−0.125). A positive imaging scale β means imaging without image inversion. A negative sign for the imaging scale β means imaging with image inversion.
The projection optical unit 10 consequently leads to a reduction in size with a ratio of 4:1 in the x-direction, which is to say 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, which is to say in the scanning direction.
Other imaging scales are likewise possible. Imaging scales with the same signs and the same absolute values in the x-direction and y-direction are also possible, for example with absolute values of 0.125 or 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 can be the same or can differ depending on the embodiment of the projection optical unit 10. Examples of projection optical units with different numbers of such intermediate images in the x and y directions are known from US 2018/0074303 A1.
In each case one of the pupil facets 23 is assigned to exactly one of the field facets 21 to form a respective illumination channel for illuminating the object field 5. For example, this can yield illumination according to the Köhler 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.
The field facets 21 are imaged, in each case by way of an assigned pupil facet 23, onto the reticle 7 in a manner such that they are superposed on one another for the purposes of illuminating the object field 5. The illumination of the object field 5 is in general as homogeneous as possible. It preferably has a uniformity error of less than 2%. The field uniformity can be achieved by overlaying different illumination channels.
The illumination of the entrance pupil of the projection optical unit 10 can be geometrically defined by an arrangement of the pupil facets. It is possible to set the intensity distribution in the entrance pupil of the projection optical unit 10 by selecting the illumination channels, for example the subset of pupil facets, which guide light. This intensity distribution is also referred to as illumination setting.
A likewise preferred pupil uniformity in the region of sections of an illumination pupil of the illumination optical unit 4 that are illuminated in a defined manner can be achieved by a redistribution of the illumination channels.
Further aspects and details of the illumination of the object field 5 and for example of the entrance pupil of the projection optical unit 10 are described below.
The projection optical unit 10 may have a homocentric entrance pupil. The latter can be accessible. It can also be inaccessible.
The entrance pupil of the projection optical unit 10 generally cannot be illuminated exactly via the pupil facet mirror 22. The aperture rays often do not intersect at a single point when imaging the projection optical unit 10 which telecentrically images the centre of the pupil facet mirror 22 onto the wafer 13. However, it is possible to find a surface area in which the spacing of the aperture rays, determined in pairwise fashion, is minimal. This surface area represents the entrance pupil or an area in real space that is conjugate thereto. For example, this surface area has a finite curvature.
The projection optical unit 10 might have different positions of the entrance pupil for the tangential beam path and for the sagittal beam path. In this case, an imaging element, for example an optical component part of the transfer optical unit, should be provided between the second facet mirror 22 and the reticle 7. With the aid of this optical element, the different poses 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
The first facet mirror 20 is tilted with respect to an arrangement plane defined by the second facet mirror 22.
The structure of the projection exposure apparatus 101 and the principle of the imaging are comparable with the structure and procedure described in
In contrast to an EUV projection exposure apparatus 1 as described in
The illumination system 102 provides DUV radiation 116 for imaging the reticle 107 on the wafer 113. A laser, a plasma source or the like can be used as the source of this radiation 116. The radiation 116 is shaped in the illumination system 102 via optical elements such that the DUV radiation 116 has the desired properties with regard to diameter, polarization, shape of the wavefront and the like when it is incident on the reticle 107.
Apart from the additional use of refractive optical elements 117, such as lens elements, prisms, terminating plates, the structure of the downstream projection optical unit 110 with the lens housing 119 does not differ in principle from the structure described in
It is self-evident that the optical unit shown in the figure should be understood to be purely exemplary. The principle shown may also be applied to other optical arrangements, for example collimators.
In a schematic illustration,
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2022 207 148.4 | Jul 2022 | DE | national |
The present application is a continuation of, and claims benefit under 35 USC 120 to, international application No. PCT/EP2023/069200, filed Jul. 11, 2023, which claims benefit under 35 USC 119 of German Application No. 10 2022 207 148.4, filed Jul. 13, 2022. The entire disclosure of each of these applications is incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2023/069200 | Jul 2023 | WO |
| Child | 19012047 | US |
