Patent Application
20250021010
This disclosure relates to a device and a method for aligning components, in particular components of a projection exposure apparatus for semiconductor lithography.
Projection exposure apparatuses are subject to extremely high demands in terms of the imaging accuracy, which among other things largely depends on the positioning of the optical elements and thus the components of the projection exposure apparatus.
The achieved accuracy of the positioning of the optical elements is made up of a pre-alignment achieved during the assembly of the optical elements and a subsequent positioning of the optical elements by manipulators. The accuracy that can be achieved by the manipulators also depends, among other things, on a maximum required total travel path, which is also determined by the accuracies achieved during the pre-alignment of the components. The greater the required travel path of the manipulators, the lower is the resolution required for positioning accuracy. Demands placed on projection exposure apparatuses regarding the positioning accuracy of the optical elements, which increase from generation to generation, therefore also lead to ever higher demands placed on the alignment of the optical elements in relation to a global reference in the assembly.
In addition, the increasingly modular design of projection exposure apparatuses, which has the aim of being able to simply exchange defective modules at the customer's site or to replace them with further developed and improved modules, leads to a further increase in the demands regarding the accuracy of the alignment of the optical elements or components during assembly. The accuracies achieved during an exchange at the customer's site are worse than during initial assembly due to a lack of or limited availability of measurement means in the devices and methods used from the prior art.
Furthermore, the demand for a plug-and-play process at the customer's site, i.e. any replacement of components without pairing modules as is frequently used in the prior art, leads to increased demands regarding the accuracy of the alignment of the components with one another. These increased demands can increasingly no longer be met by the devices and methods currently used in the prior art.
In certain aspects, this disclosure is directed to specify a device and a method with which components can be aligned with the required accuracy.
In certain aspects, disclosed is a method for aligning two components of a projection exposure apparatus for semiconductor lithography that comprises the following method steps:
The two components can be designed, for example, as an optical module and a frame of a projection exposure apparatus for semiconductor lithography, wherein in one embodiment, the optical module is mounted on the frame and placed on it. The number of mandrels depends on the design of the mandrels, but is expediently selected in such a way that the alignment of the components relative to one another is determined statically. The interactive procedure when positioning the two components in an x-y plane on the one hand and in a z-direction perpendicular thereto on the other hand has the advantage that a possible generation of particles can be minimized.
Due to the mandrels arranged in the recesses, particles generated at the mandrel or in the recess are initially generated on the rear side of an optical effective surface arranged on the optical component, i.e., the surface exposed to radiation for the purpose of imaging the structures. As a result, the path to the optical effective surface to be overcome by the particles is very large. Furthermore, the relative movement between the components that are in contact during fine positioning can be minimized by the pre-positioning effected by pre-loading of the mandrel. In addition, the particles generated during pre-positioning and fine-positioning are trapped in the contact area between the components during the assembly process.
In particular, the frame can be braced with a contact force of less than 1000 N, preferably less than 100 N and particularly preferably less than 10 N, between the two components. As already explained further above, the risk of particle generation is dependent on the contact force and the distance travelled by the surfaces in contact during fine positioning, and so a lower contact force is advantageous during fine positioning.
In a further embodiment of the method, the at least one mandrel can be loosened once at the end of the method and tightened again to the maximum extent. This has the advantage that tension that is caused by and frozen during the complete loading of the weight of the optical module when it is lowered onto the frame in the optical module can be relaxed. As a result, no parasitic deformations can occur on the optical effective surface already explained above.
In another aspect, disclosed is a device for aligning two components of a projection exposure apparatus for semiconductor lithography is characterized in that the device comprises a mandrel. A mandrel is a clamping means known from the field of machine tools, which effects a radial expansion of the mandrel through an axial movement or feed in the mandrel. The mandrel typically comprises a cone with a clamping sleeve that is arranged thereon and corresponds to the outer geometry of the cone. By moving the cone relative to the clamping sleeve, the latter is pushed onto the cone and expands radially because of it. In the case of a manually actuated mandrel, the relative movement between the cone and the clamping sleeve is achieved by hand using a clamping nut or clamping screw. Alternatively, the mandrel can also be actuated hydraulically, electrically, or pneumatically via a clamping cylinder. In the case of this device, the radial expansion of the mandrel does not act to brace the two components, but rather as a means for aligning the two components with one another.
In particular, the mandrel can be permanently connected to one of the two components. A main body of the mandrel can be aligned with a local or global reference on one of the components.
Furthermore, the other component can have a recess that corresponds to the outer diameter of the mandrel. The recess can be designed as a hollow cylinder in the form of a drilled hole or as another arbitrary inner contour.
In addition, the mandrel can be designed in such a way that it can assume a released and a braced state. In the released state, the mandrel is first inserted into the recess, hereinafter referred to as drilled hole, of the other component. The clearance between the released mandrel and the drilled hole can be chosen such that joining is easily possible and the increased risk of work hardening during joining, in particular in a vacuum environment, such as in an EUV projection exposure apparatus, can be avoided.
In particular, the joint clearance between the drilled hole and the mandrel in a released state can be greater than or equal to 30 μm. After joining, the mandrel can be brought into the braced state, which reduces the clearance between the mandrel and the drilled hole. Depending on the position of the components relative to one another, when the mandrel is braced, there may be a relative movement between the components, i.e., the components may align with one another. The bracing of the mandrel can advantageously increase the accuracy of the alignment of the two components relative to each other. In the event of a manually actuated mandrel, the mandrel is actuated by hand using a clamping nut or clamping screw. Alternatively, the mandrel can also be actuated hydraulically, electrically, or pneumatically via a clamping cylinder.
In the braced state, the joint clearance between the drilled hole and the mandrel can be less than 30 μm, preferably less than 15 μm, and particularly preferably less than 5 μm.
In a further embodiment, a clamping element, for example a clamping screw or a clamping nut of the mandrel, can be connected to a clamping sleeve or a main body in such a way that only axial forces can be transmitted. This decoupling of the force transmission can be realized, for example, by a ball bearing arranged between an intermediate piece and the clamping sleeve.
Furthermore, the clamping sleeve and/or the main body can be coated with a friction-reducing layer. The coating can be, for example, a ceramic layer, such as a what is known as DLC (diamond like carbon) coating, which can lead to less generation of particles. This can be advantageous for the use of the mandrel in a vacuum environment or an environment with high requirements relating to freedom from particles, such as in a clean room.
In a further embodiment of the device, the outer contour of the clamping sleeve or the inner contour of the corresponding recess can have a rounded geometry. This can have the advantage that, for example, only a line contact occurs between the drilled hole and the outer contour of the clamping sleeve, i.e., no overdetermination and thus jamming can occur.
Furthermore, the device can comprise a weight compensation unit for one of the components. The weight compensation unit reduces the frictional force between the components and thus the force that the mandrel has to apply to align the two components with one another.
In particular, the alignment can thus be carried out with a contact force of less than 1000 N, preferably less than 100 N, and particularly preferably less than 10 N. The contact force is here the normal force, acting on the contact surface, between the clamping sleeve and the main body, which directly determines the frictional force. A reduction in the frictional force can advantageously lead to less particle generation. Furthermore, the weight compensation unit of the various components can be aligned in such a way that, regardless of the components' own weight, the force for aligning the components is comparable. As a result, the same mandrel could be used to align all components, achieving savings in development and production costs.
In a further embodiment, the device may include an indicator to indicate successful alignment. This indicator can communicate, using a visual, acoustic or tactile signal, that the alignment of the two components relative to one another has been reliably achieved within the predetermined accuracies. For example, a control pin can be arranged in the mandrel in such a way that the control pin is flush with an outer surface of the mandrel or extends beyond it when the predetermined bracing and thus the alignment accuracy have been achieved.
Furthermore, the mandrel can have a predetermined maximum travel, which can be implemented, for example, via a fixed stop for the clamping screw or the clamping nut.
In particular, the predetermined maximum travel can be settable. This can be an advantage if the tolerances for the travel cannot be observed by simple assembly due to the tolerance chain of the component parts used. The setting can be implemented, for example, using a shim that can be adapted in terms of thickness as required. Alternatively, the stop can also be adapted or reworked after measuring the travel.
In a further embodiment, the mandrel can have a revolving ball bearing. The ball bearing filled with balls connects an intermediate piece of the mandrel to the clamping sleeve and can only transmit axial forces. The clamping sleeve no longer rotates when being braced owing to the balls. The resulting greatly reduced relative movement of the clamping sleeve on the main body advantageously reduces the formation of particles. The particles can be held back in the mandrel by a seal encompassing the gap between the clamping sleeve and the main body and also the partially slotted clamping sleeve. As a result, the mandrel gives off almost no particles to the outside and can be considered suitable for clean rooms and vacuum applications.
In particular, the clamping sleeve can have a stiff and an elastic partial region. A first half of the ball bearing can be arranged in the stiff partial region, and because of it, this half does not change its diameter even when the mandrel is braced. The elastic region can be formed, for example, by decoupling cuts in such a way that an extensive contact surface between the clamping sleeve and a cone on the main body is ensured during bracing.
Furthermore, the clamping sleeve can have a monolithic structure.
In a further embodiment, a thread effecting the travel can be arranged internally. Within the meaning of the application, internal is to be understood as meaning that the thread is arranged within a volume which is almost completely closed off from the environment.
In particular, a volume surrounding the thread can be sealed off from the outside by at least one seal to avoid particle contamination. This embodiment can be suitable in particular for use in areas with high requirements in terms of freedom from particles, as is required, for example, in clean rooms and in many vacuum environments.
Other aspects, embodiments, and advantages follow.
Exemplary embodiments and variants will be explained in more detail below with reference to the drawing, in which
The essential integral parts of a microlithographic projection exposure apparatus 1 are described in exemplary fashion below initially with reference to
One 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 by way of a reticle displacement drive 9 in particular in a scanning direction.
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 in particular 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 may be implemented so as to be mutually synchronized.
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 of 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 can be a collector with one or with a plurality of 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), that 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), that 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. Alternatively or in addition, the deflection mirror 19 may be embodied in the form of a spectral filter that separates a used light wavelength of the illumination radiation 16 from extraneous 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 can be embodied in the form of macroscopic facets, in particular in the form of rectangular facets or in the form of facets with an arcuate peripheral contour or a peripheral contour of part of a circle. The first facets 21 can be embodied as plane facets or, alternatively, as convexly or concavely curved facets.
As known for example from DE 10 2008 009 600 A1, the first facets 21 themselves can also be composed in each case of a multiplicity of individual mirrors, in particular a multiplicity of micromirrors. In particular, the first facet mirror 20 can be embodied as a microelectromechanical system (MEMS system). For details, reference is made to DE 10 2008 009 600 A1.
The illumination radiation 16 travels horizontally, that is to say longitudinally with respect to 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 convexly or concavely curved reflection surfaces.
The illumination optical unit 4 consequently forms a doubly faceted system. This fundamental principle is also referred to as a fly's eye condenser (fly's eye integrator).
It can 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 10. In particular, 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 with the aid of 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 shown) of the illumination optical unit 4, a transfer 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 transfer optical unit may have exactly one mirror, or alternatively have two or more mirrors, which are arranged one behind the other in the beam path of the illumination optical unit 4. The transfer 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
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 by means of the second facets 23 or using the second facets 23 and a transfer optical unit is, as a rule, 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
Reflection surfaces of the mirrors Mi can be embodied as freeform surfaces without an axis of rotational symmetry. Alternatively, the reflection surfaces of the mirrors Mi 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 Mi can have highly reflective coatings for the illumination radiation 16. These coatings can 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 center of the object field 5 and a y-coordinate of the center of the image field 11. This object-image offset in the y-direction can be of approximately the same magnitude as a z-distance between the object plane 6 and the image plane 12. In particular, the projection optical unit 10 can have an anamorphic embodiment. In particular, 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, that 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, that is to say in the scanning direction.
Other imaging scales are likewise 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 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 for forming in each case an illumination channel for illuminating the object field 5. In particular, 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 produce a plurality of images of the intermediate focus on the pupil facets 23 respectively assigned thereto.
By way of an assigned pupil facet 23, the field facets 21 are imaged in each case onto 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 overlaying 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 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 in particular of the entrance pupil of the projection optical unit 10 are described below.
The projection optical unit 10 may have in particular a homocentric entrance pupil. The latter can be accessible. It can also be inaccessible.
The entrance pupil of the projection optical unit 10 cannot, as a rule, be exactly illuminated using the pupil facet mirror 22. In the case of imaging of the projection optical unit 10 which telecentrically images the center of the pupil facet mirror 22 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 spacing of the aperture rays that is 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 the case that the projection optical unit 10 has different poses 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 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 arranged so as to be tilted with respect to an arrangement plane defined by the second facet mirror 22.
The construction of the projection exposure apparatus 101 and the principle of the imaging are comparable with the construction and procedure described in
Identical component parts are designated by a reference sign increased by 100 relative to
In contrast to an EUV projection exposure apparatus 1 as described in
The illumination system 102 provides DUV radiation 116 required for the imaging of 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 by means of 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 construction of the downstream projection optical unit 110 with the lens housing 119 does not differ in principle from the construction described in
The mandrel 50 explained in detail in
This is indicated in
Additional embodiments are within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102022203393.0 | Apr 2022 | DE | national |
| 102022208738.0 | Aug 2022 | DE | national |
The present application claims the priority of the German patent application DE 10 2022 203 393.0 of Apr. 6, 2022 and DE 10 2022 208 738.0 of Aug. 24, 2022, and also International Application No. PCT/EP2023/058458 filed on Mar. 31, 2023, the content of which are fully incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2023/058458 | Mar 2023 | WO |
| Child | 18901513 | US |
