Patent Application
20240085800
The disclosure relates to a component for a projection exposure apparatus for semiconductor lithography and to a method for designing the component, such as for minimizing undesirable effects of parasitic deformations caused by an actuator on the imaging quality of the projection exposure apparatus.
In projection exposure apparatuses for semiconductor lithography, optical elements, such as lens elements and/or mirrors, are used for imaging a lithography mask, such as, for example, a phase mask, also known as a reticle, onto a semiconductor substrate, also known as a wafer.
In order to help achieve a high resolution especially of lithography optical units, EUV light having a wavelength of, for example, between 1 nm and 120 nm, such as in the region of 13.5 nm, has also been used for some years, in comparison with predecessor systems having typical wavelengths of 365 nm, 248 nm or 193 nm.
Some of the optical elements used in that case are manipulated, for example, mechanically in order to improve the imaging quality and in order to correct disturbances that occur during operation, wherein a distinction is drawn between a pure shift of the optical elements and a deformation of the optical elements.
In the case of deformable mirrors, actuators, for example in the form of an actuator matrix, are known to have been adhesively connected or bonded to the rear side of the mirrors to create a mechanical connection for a targeted deformation.
Actuator matrices which are embodied in the form of a quadrangular plate and comprise a plurality of interconnected actuator pads are known. The individual actuator pads typically have a quadrangular or triangular shape and comprise holes typically arranged at the corners or sides of the actuator pads. These can have the function that the actuator pads can be contacted to controllers. A physics-related loss of rigidity of the combination of the actuator with the optical element can occur at all peripheries of the actuator, that is to say at the outer edges of the plate of the actuator matrix and the peripheries of the holes, which loss results in parasitic deformations in the region of the peripheries during the actuation or for example due to different thermal expansions based on different coefficients of thermal expansion. This can negatively influence the imaging quality of the projection exposure apparatus.
Due to the scanning mode of operation of certain modern lithography systems, that is to say the movement of the phase mask underneath an illumination slit and a movement of the wafer in an opposite direction, aberrations, which can be caused by the parasitic deformations described, along the scanning direction can add up, which can makes the undesirable effect more pronounced.
SUMMARY
The present disclosure seeks to provide an improved component. The disclosure also seeks to provide a method for designing the component.
A component according to the disclosure for a projection exposure apparatus for semiconductor lithography comprises an optical element and an actuator. The optical element and the actuator are force-fittingly connected to each other, wherein the actuator is configured to at least locally deform the optical element. According to the disclosure, the actuator can be embodied such that the influence of the loss in rigidity at the peripheries delimiting the actuator on the imaging quality is minimized. The force-fitting connection between the actuator and the optical element, such as a mirror, can be brought about by an adhesive connection or bonding or by a releasable connection, such as a screw connection.
In a first embodiment of the disclosure, the actuator can be embodied in the form of an actuator matrix comprising at least two actuator pads. The actuator matrix typically comprises between 9 and 30 actuator pads.
In particular, the cumulative length of the peripheral sections of the actuator extending on an axis parallel to a scanning direction used in the projection exposure apparatus can be minimized. The scanning exposure method used in projection exposure apparatuses can mean that some optical effects of disturbances extending perpendicular to the scanning direction, such as parasitic deformations, are averaged out by the scanning operation and thus minimized.
Furthermore, the outer peripheries of the actuators can be aligned, at least in sections, at an angle to the scanning direction. As a result, the portion of the sections of the peripheries extending in the scanning direction which is summed through the scanning operation can be minimized.
In particular, the actuator can include a peripheral contour meandering around the scanning direction. The contour can be realized, for example, by a hexagonal shape of the actuator pads and by a shift of the actuator pads arranged in rows by half the width of an actuator pad, wherein protrusions of the actuator pads partially protrude into recesses of adjacent pads.
In addition, a straight peripheral structure of the actuator can be aligned at an angle to the scanning direction. This can mean that no more portions, which are aligned in the scanning direction, of the peripheries delimiting the actuator are present. However, it may be desirable to take into account a possible construction-type-related influence of the inclination of the actuator on the deformation effect of the actuator with respect to an optically effective surface.
In particular, holes for contacting the actuator pads formed in the actuator matrix can be designed such that the cumulative length of the edge sections of the holes extending on an axis parallel to a scanning direction used in the projection exposure apparatus is reduced.
This can be accomplished, for example, in that the area of at least some of the holes is minimized, as a result of which the cumulative overall length of the edges of all holes is reduced. The holes can be formed at the corners, the sides, within the effective surface of the actuator pad or in a combination of these positions. The size of the holes is defined by the space for contacting.
Furthermore, the holes can be arranged such that the number of the holes arranged on an axis extending parallel to the scanning direction is minimal. The parasitic aberration summed by the scanning movement thus becomes minimal. The number of the holes located on an axis can be reduced, for example, by an advantageous arrangement of the holes with respect to the actuator pads, as described further above.
In a further embodiment of the disclosure, the actuator pads can have a triangular, a rectangular or a hexagonal geometry. In addition to the geometry of the actuator pads, the number of the rows and columns of the actuator matrices formed by the actuator pads can also be freely selectable, with the result that for example matrices of three rows and three columns up to five rows and five columns or more are conceivable. Nor does the number of rows and columns need to be identical, and a matrix with four rows and six columns can thus also be formed.
In a further embodiment of the disclosure, the actuator can have a separately controllable section for correcting the loss in rigidity. It thereby can become possible to take into account the rigidity, which deviates in the region of the intermediate spaces, of the overall system composed of actuator pad and mirror material by correspondingly modified control of the section, as a result of which an undesired movement/deformation is counteracted and a resulting possible image error can be avoided.
In particular, the section can be formed as a peripheral actuator pad in an actuator pad arranged in the peripheral region of the actuator matrix and can be controllable independently of the second region of the actuator pad formed as a partial actuator pad and be configured for correcting the parasitic deformations caused by the loss in rigidity. Owing to the peripheral actuator pad, the deformation effect at the periphery can be increased in comparison with a non-divided actuator pad, as a result of which the loss in rigidity can be compensated.
A method according to the disclosure for designing a component of a projection exposure apparatus with an optical element and an actuator for minimizing the effects of parasitic deformations in the case of the deformation of the optical element caused by the actuator on the imaging quality of the projection exposure apparatus comprises the following method steps:
The parasitic deformations can be determined for example by FEM simulations or on the optically effective surface of the optical element via an optical measuring technique. The parasitic aberrations can be determined by simulations based on the parasitic deformations or by measurements on the component level or in the overall system, that is to say in the projection exposure apparatus.
Furthermore, at least a part of a travel of the actuator can be used to correct the parasitic deformations. This self-correction, as it is known, can mean that the errors can be compensated at the site where they occur.
In addition, the projection exposure apparatus can comprise a mechanism for optimizing the imaging quality can be taken into account when determining the resulting parasitic aberrations.
In particular, the mechanism can include manipulators for positioning or deforming further optical elements of the projection exposure apparatus. Typically, almost all optical elements of the projection exposure apparatus are manipulable, and therefore a large selection of additional correction mechanisms may be available.
Furthermore, one approach can involve an algorithm based on simulations for the prediction of the imaging quality while taking into account a multiplicity of influence parameters and the determination of the travels of the manipulators therefor.
Exemplary embodiments and variants of the disclosure are explained in greater detail below with reference to the drawing. In the figures,
Certain integral 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 can 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 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
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 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 can 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 may be a collector with one or with a plurality of ellipsoidal and/or hyperboloidal reflection surfaces. The illumination radiation 16 can impinge 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°, 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 can be a plane deflection mirror or, alternatively, a mirror with a beam-influencing effect that goes beyond the purely deflecting effect. Alternatively or in addition, the deflection mirror 19 can be in the form of a spectral filter which separates a used light wavelength of the illumination radiation 16 from extraneous light with 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 in the form of 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 in the form of 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 may also be composed in each case of a multiplicity of individual mirrors, in particular a multiplicity of micromirrors. The first facet mirror 20 can in particular be formed as a microelectromechanical system (MEMS system). For details, reference is made to DE 10 2008 009 600 A1.
Between the collector 17 and the deflection mirror 19, the illumination radiation 16 travels horizontally, that is to say along the y-direction.
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 can likewise be macroscopic facets, which can for example have a round, rectangular, or hexagonal periphery, or alternatively be facets made up of micromirrors. In this regard, reference is likewise made to DE 10 2008 009 600 A1.
The second facets 23 can have plane 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 else, in fact, 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 can be arranged in the beam path between the second facet mirror 22 and the object field 5. The transfer optical unit can 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 transfer optical unit can 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 via 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 free-form 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 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.
In particular, the projection optical unit 10 can have an anamorphic form. 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 can be (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 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 can be the same or, depending on the embodiment of the projection optical unit 10, can 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 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 respectively assigned pupil facets 23, the field facets 21 are imaged 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 can have 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 sections of an illumination pupil of the illumination optical unit 4 which 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.
In particular, the projection optical unit 10 can have 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 centre 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 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 the case 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 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 positions 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 in tilted fashion 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
In contrast to an EUV projection exposure apparatus 1 as described in
The illumination system 102 provides DUV radiation 116, which is used 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 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 construction of the downstream projection optical unit 110 with the lens housing 119 does not differ in principle from the construction described in
In comparison with the illustration of the parasitic aberrations explained in
The actuator 32, 35, 39.x, 43, 50 is designed in a first method step 61.
In a second method step 62, the parasitic deformations of the optical element 31 caused by an actuation or by different coefficients of thermal expansion of the optical element 31 and the actuator 32, 35, 39.x, 43, 50 are determined.
In a third method step 63, the parasitic aberrations are determined on the basis of the parasitic deformations while taking into account the summing effect of a scanning exposure used in the projection exposure apparatus.
In a fourth method step 64, the actuator is optimized on the basis of the determined parasitic aberrations. In this case, in particular the shape and arrangement of the individual actuator pads and of the holes can be varied.
In a fifth method step 65, at least some of the preceding process steps are repeated until the value for the parasitic aberration falls under a predetermined value.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2021 205 368.8 | May 2021 | DE | national |
The present application is a continuation of, and claims benefit under 35 USC 120 to, international application PCT/EP2022/063972, filed May 24, 2022, which claims benefit under 35 USC 119 of German Application No 10 2021 205 368.8, filed May 27, 2021. The entire disclosure of each these applications is incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2022/063972 | May 2022 | US |
| Child | 18507893 | US |
