Abstract
A method for characterizing a lithography apparatus, in particular, a method for characterizing a lithography apparatus configured to cause an obscuration of radiation, as well as a lithography apparatus and a computer program product configured to carry out the methods. A method for characterizing a lithography apparatus; detecting first diffracted radiation of the lithography apparatus, wherein the first diffracted radiation was diffracted at a characterization element; determining a diffraction property of the characterization element based on at least in part the first substantially undiffracted radiation and the first diffracted radiation.
Claims
1. A method for characterizing a lithography apparatus configured to cause an obscuration of radiation, comprising: detecting a first substantially undiffracted radiation of the lithography apparatus; detecting a first diffracted radiation of the lithography apparatus, the first diffracted radiation having been diffracted at a characterization element; determining a diffraction property of the characterization element, based at least in part on the first substantially undiffracted radiation and the first diffracted radiation.
2. The method as claimed in claim 1, wherein said determining of the diffraction property is based further on a compensation.
3. The method as claimed in claim 2, wherein the compensation compensates an appearance of the diffraction property associated with the obscuration.
4. The method as claimed in claim 2, wherein the compensation comprises an interpolation and/or an extrapolation.
5. The method as claimed in claim 1, wherein the diffraction property is based at least in part on a relationship of the first diffracted radiation to the first substantially undiffracted radiation.
6. The method as claimed in claim 1, wherein the diffraction property comprises a diffraction efficiency of the first diffracted radiation in relation to the first substantially undiffracted radiation in an angular space.
7. The method as claimed in claim 1, wherein said detecting of the first substantially undiffracted radiation comprises detecting an intensity of the first substantially undiffracted radiation in a pupil of the lithography apparatus; and/or wherein said detecting of the first diffracted radiation comprises detecting an intensity of the diffracted radiation in the pupil.
8. The method as claimed in claim 1, wherein the first substantially undiffracted radiation comprises a plurality of first substantially undiffracted radiation beams; and wherein the first diffracted radiation comprises a plurality of first diffracted radiation beams, each of which was diffracted at the characterization element.
9. The method as claimed in claim 1, wherein said determining of the diffraction property comprises determining at least one order of diffraction of the first diffracted radiation.
10. The method as claimed in claim 8, wherein said determining of the diffraction property comprises determining at least one order of diffraction of the first diffracted radiation; and wherein the order of diffraction is determined for at least one first diffracted radiation beam from the plurality of diffracted radiation beams.
11. The method as claimed in claim 10, wherein a corresponding first substantially undiffracted radiation beam from the plurality of first substantially undiffracted radiation beams is determined for the at least one first diffracted radiation beam.
12. The method as claimed in claim 11, wherein the diffraction property is determined for the at least one first diffracted radiation beam.
13. The method as claimed in claim 1, wherein the lithography apparatus is configured such that a subset of the first substantially undiffracted radiation is exposed to the obscuration and thereby forms an obscured subset.
14. The method as claimed in claim 13, further comprising determining at least one part of the obscured subset, based at least in part on the diffraction property and the first diffracted radiation.
15. The method as claimed in claim 13, wherein the lithography apparatus is further configured such that a subset of the first diffracted radiation is not exposed to the obscuration and thereby forms an unobscured subset.
16. The method as claimed in claim 14, wherein the lithography apparatus is further configured such that a subset of the first diffracted radiation is not exposed to the obscuration and thereby forms an unobscured subset; and wherein said determining of the obscured subset part is also based at least in part on the part of the unobscured subset which is associated via an order of diffraction with the part of the obscured subset.
17. The method as claimed in claim 16, wherein said determining of the obscured subset part further comprises: determining at least one first substantially undiffracted radiation beam comprised in the obscured subset, based at least in part on a corresponding first diffracted radiation beam of at least one order of diffraction comprised in the unobscured subset.
18. The method as claimed in claim 17, wherein said determining of the obscured subset part further comprises: determining an intensity of the at least one first substantially undiffracted radiation beam based at least in part on the diffraction property and the intensity of the corresponding first diffracted radiation beam.
19. The method as claimed in claim 1, further comprising: detecting a second substantially undiffracted radiation of the lithography apparatus; detecting a second diffracted radiation of the lithography apparatus, the second diffracted radiation having been diffracted at the characterization element; and determining a subset of the second substantially undiffracted radiation which is exposed to the obscuration, based at least in part on the diffraction property and the second diffracted radiation.
20. The method as claimed in claim 19, wherein the second substantially undiffracted radiation is associated with a beam path of the first substantially undiffracted radiation, with the second diffracted radiation being associated with a beam path of the first diffracted radiation.
21. The method as claimed in claim 13, further comprising adjusting a radiation emitting element of the lithography apparatus, based at least in part on said determining of the obscured subset of the first substantially undiffracted radiation.
22. The method as claimed in claim 1, wherein the characterization element is arranged in a reticle plane of the lithography apparatus.
23. The method as claimed in claim 1, wherein the characterization element comprises a diffraction structure.
24. The method as claimed in claim 1, wherein the obscuration is associated with a radiation projecting element of the lithography apparatus and/or an obscuration stop of the lithography apparatus.
25. The method as claimed in claim 1, wherein the first substantially undiffracted radiation comprises radiation reflected at a reticle plane of the lithography apparatus; and/or wherein the first diffracted radiation comprises radiation diffracted at the reticle plane.
26. A lithography apparatus, comprising: a radiation detecting element; a diffraction property determining element of a characterization element, wherein the lithography apparatus is configured to perform a method as claimed in claim 1.
27. The lithography apparatus as claimed in claim 26, wherein the lithography apparatus is configured to carry out the method automatically.
28. A non-transitory computer readable medium comprising instructions which, when executed by a computer apparatus and/or a lithography apparatus, cause the computer apparatus and/or the lithography apparatus to carry out the method as claimed in claim 1.
29. The lithography apparatus comprising a memory storing a computer program comprising the instructions as claimed in claim 28.
30. The method as claimed in claim 19, further comprising adjusting a radiation emitting element of the lithography apparatus, based at least in part on said determining of the subset of the second substantially undiffracted radiation.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0059] The detailed description that follows describes technical background information and exemplary embodiments of the invention with reference to the figures, which show the following:
[0060] FIG. 1 schematically illustrates an exemplary lithography apparatus which can be configured to carry out the method.
[0061] FIG. 2 illustrates a simulation result of a substantially undiffracted radiation of an exemplary lithography apparatus, with the substantially undiffracted radiation containing an obscured subset.
[0062] FIG. 3 illustrates simulation results of a diffracted radiation of an exemplary lithography apparatus in an exit pupil, the calculated diffracted radiation in an entrance pupil, and the determined diffraction efficiency of the diffracted radiation.
[0063] FIG. 4 illustrates simulation results of diffraction efficiencies of diffracted radiations.
[0064] FIG. 5 schematically illustrates the association of an unobscured subset of a diffracted radiation in relation to the corresponding obscured subset of a substantially diffracted radiation.
DETAILED DESCRIPTION
[0065] FIG. 1 schematically illustrates an exemplary lithography apparatus in a plan view. The exemplary lithography apparatus corresponds in part to FIG. 1 of DE 10 2018 207 384 A1 and may contain the details described there. To provide an overview, the exemplary lithography apparatus is explained briefly within the scope of the present application. In this case, the characterization element (as described herein) may correspond to the measurement structure 60 which can be arranged on a measurement reticle 58. The measurement reticle 58 might be aligned along a reticle plane 38 in this case. FIG. 1 illustrates a measuring mode for detecting the radiation of the lithography apparatus 10 diffracted at the measurement structure 60. With regards to the measurement structure 60, a region of incidence of radiation is present on the one hand. The radiation which can be incident on the measurement structure is based e.g. on the radiation of a beam source 12. In this case, the beam source 12 can emit an exposure radiation 14 into an illumination system 18. In this case, the illumination system 18 can also be regarded as an illumination unit. In the illumination system 18, the exposure radiation 14 can initially be incident on a first mirror 20. In this case, the first mirror 20 can comprise a plurality of first facet mirrors 22-1 to 22-5. Each facet mirror 22-1 to 22-5 may comprise an actuator 24 allowing this facet mirror to be adjusted on an individual basis, e.g. be tilted about two mutually orthogonal tilt axes. The actuators 24 can be driven by a control device.
[0066] The illumination system 18 may further comprise a second mirror 28 which can comprise a plurality of second facet mirrors 30-1 to 30-5 (the number and arrangement of five mirrors is purely by way of example), which can be arranged in a pupil plane 26. In this case, the first and second facet mirrors can be arranged in a matrix arrangement. In this case, a first facet mirror 22-3 of the first mirror 20 can selectively direct a part of the exposure radiation 14 to a (e.g. corresponding) second facet mirror 30-3 of the second mirror 28. In this case, the second facet mirror 30-3 can direct this part of the exposure radiation as a first substantially undiffracted radiation beam 56 to the measurement structure 60. Accordingly, any desired combination and number of radiation beams which are radiated into the reticle plane 38 can be formed with the plurality of first and second facet mirrors. Accordingly, the first and second facet mirrors can form different radiation channels in the illumination system 18, wherein the various radiation channels can be radiated on the measurement structure 60. The incident first substantially undiffracted radiation beam can experience a diffraction with a diffraction structure (not depicted in detail) on the measurement structure 60 (e.g. a diffraction grating). For example, the measurement structure 60 can accordingly emit a corresponding first diffracted radiation beam of plus first order 66 and a corresponding first diffracted radiation beam of minus first order 68 into the exit region. These emerging orders of diffraction and their beam paths should be considered to be schematic and exemplary. Further, a first diffracted radiation beam of the zeroth order can be emitted, and also a first diffracted radiation beam of any desired other order of diffraction, depending on the diffraction effect of the measurement structure. In this case, the diffracted radiation beams 66, 68 can be incident on a projection lens 40 of the lithography apparatus. The projection lens can image the diffracted radiation beams 66, 68 onto a wafer plane 53. In this example, the projection lens 40 comprises an obscuration 46 in an obscuration plane 44. Accordingly, the obscuration 46 can cause a radiation (e.g. a radiation beam) incident on the obscuration to not be present in the wafer plane or not be able to be detected in this region. For example, the obscuration 46 may comprise an obscuration stop which can absorb a radiation of the lithography apparatus. The first diffracted radiation beams 68, 66 are diffracted such that, in the example of FIG. 1, they propagate next to the obscuration 46 and are consequently able to be incident on the wafer plane 53. The first diffracted radiation beams 68, 66 can be detected offset in a detection plane (not explicitly depicted here), in which the detector 70 is arranged. Detection in the detection plane offset from the wafer plane can enable a detection of the first diffracted radiation 68, 66 in the distribution of an angular space (e.g. an angular space of an exit pupil). In this case, the detector can detect e.g. the intensity of the radiation.
[0067] The lithography apparatus may comprise a diffraction property determining element-as described herein. The element can be designed to obtain the corresponding input variables with an appropriately designed user interface. However, it can also be configured to automatically read out the input variables. The element can comprise e.g. a computer or a computer system. The computer and/or the computer system can further be configured to prompt the apparatus to at least partly automatically carry out one of the methods described herein.
[0068] However, for the method described herein, it is also possible to detect the first substantially undiffracted radiation (or the first substantially undiffracted radiation beam). To this end, a reflective element (e.g. a mirror element) can be arranged in the reticle plane 38 in place of the measurement structure 60. In this case, the reflective element can radiate the first substantially undiffracted radiation beam 56 at the reticle plane 38 into the optical path of the projection lens 40. Depending on the optical setting of the illumination system 18, the first substantially undiffracted radiation beam may or may not be exposed to the obscuration 46. In the case of a plurality of first substantially undiffracted radiation beams, it is accordingly possible for a subset to be exposed to the obscuration 46, while the other part of the radiation beams are not exposed to the obscuration 46, and hence are detected. The first substantially undiffracted radiation beams are henceforth also referred to as undiffracted radiation channels. Accordingly, some undiffracted radiation channels cannot be detected at the detector as a result of the obscuration.
[0069] This is depicted e.g. in FIG. 2. FIG. 2 illustrates a simulation result of a substantially undiffracted radiation of an exemplary lithography apparatus, with the substantially undiffracted radiation containing an obscured subset X. In this case, the simulation result can represent the intensity distribution of the undiffracted radiation channels I_blank in the exit pupil of the lithography apparatus (e.g. the detected signal in the detection plane). In this case, the representation corresponds to the representation of the intensity in the angular space with the wave vector kx on the x-axis and the wave vector ky on the y-axis, the wave vectors specifying the exit wave vectors in relation to the reticle plane. In this case, the obscured subset X comprises undiffracted radiation channels which cannot be detected through the obscuration and accordingly are inaccessible.
[0070] However, it is helpful to also know the information from the undiffracted radiation channels comprised in the obscured subset X for the purpose of characterizing the lithography apparatus 10. In this case, FIG. 2 illustrates a pixel-structured pattern, wherein a pixel can correspond to an undiffracted radiation channel which e.g. is detected at the detector. In the simulation relating to FIG. 2, a noise was introduced via the facet mirrors in order to illustrate how deviations in the illumination system 18 (and/or the source optical unit) of the lithography apparatus may have an influence on the intensity distribution of the undiffracted radiation channels. In practice, the brightness variations in the radiation channels may also be caused e.g. by the source optical unit of the lithography apparatus. For example, these brightness variations may result from the (e.g. optical) non-idealities of the source optical unit. What may arise in this context is that these non-idealities can vary over time. The source optical unit may e.g. comprise a plasma for emitting radiation, wherein this radiation can be emitted into the illumination unit via one or more optical elements of the source optical unit (e.g. a parabolic mirror).
[0071] In this case, FIG. 3 illustrates simulation results of a diffracted radiation of an exemplary lithography apparatus in an exit pupil, simulation results of the calculated diffracted radiation in an entrance pupil, and the determined diffraction efficiency of the diffracted radiation. In this case, the simulation results illustrated in FIG. 3 are based on the noise and the undiffracted radiation channels from FIG. 2. In this respect, FIG. 3 can be visualized as the undiffracted radiation channels from the illumination unit being incident on the measurement structure 60 rather than a reflective element, with the result that corresponding first diffracted radiation beams are diffracted out of the measurement structure 60. These first diffracted radiation beams can be depicted in the exit pupil according to FIG. 3 and e.g. correspond to the intensity distribution in the detection plane of the detector 70. The first diffracted radiation beams are henceforth also referred to as diffracted radiation channels. Thus, the first line in FIG. 3 with the intensity distribution of the exit pupil I_AP specifies the intensities of the diffracted radiation channels for various orders of diffraction (with kx being depicted on the abscissa and ky being depicted on the ordinate). The zeroth order of diffraction B0, the plus first order of diffraction B+1 and the minus first order of diffraction B1 of the diffracted radiation channels are depicted. Once again, the influence or the noise of the illumination unit is identifiable in the intensity distribution of the exit pupil I_AP. The obscuration 46 in the center of the intensity distribution of the exit pupil I_AP is also identifiable (the obscuration manifesting itself as a central obscuration in this case).
[0072] It should be mentioned that a position of a diffracted radiation channel of zeroth order of diffraction corresponds in angular space to the position of the corresponding undiffracted radiation channel. Further, the diffracted radiation channels e.g. of the plus first order are displaced with regards to the zeroth order, and also with regards to the corresponding undiffracted radiation channels, in terms of position in angular space (or analogously on the detector). This displacement corresponds to the displacement of the diffraction maxima of an order of diffraction differing from zero in relation to the e.g. zeroth order of diffraction. However, it is generally not possible to image all diffraction maxima on account of the numerical aperture, and so a portion of the diffraction maxima of the diffracted radiation channels are not detected, e.g. as is identifiable in FIG. 3 for the first order of diffraction B+1 and B1. As a result of the displacement of the position of the diffracted radiation channels in the exit angular space on account of the diffraction, the (e.g. detected) diffracted radiation channels cannot readily be related to a corresponding undiffracted radiation channel. However, this must be implemented in order to determine the diffraction property. The second line of FIG. 3 thus depicts the intensity distribution of the entrance pupil I_EP. In this case, the entrance pupil represents the entrance angular space in relation to the measurement structure 60 or the plane of the measurement structure 60 (e.g. the reticle plane). The intensity distribution of the entrance pupil I_EP can e.g. take account of reflective factors, e.g. of the reflective element. In this case, a mathematical transformation can be used to convert the diffracted radiation channels into the entrance angular space. There is no displacement in the case of the zeroth order of diffraction since the angle of entrance corresponds to the exit angle in this case. However, there is a displacement in the case of the plus first order of diffraction B+1 and in the case of the minus first order of diffraction B1, as identifiable in FIG. 3. As a result of the transformation into the entrance angular space, wave vector and radiation channel correspond for both diffracted and undiffracted radiation channels, independently of an order of diffraction. Accordingly, it is possible to compare the diffracted and undiffracted radiation channels at the same wave vector coordinates in the entrance angular space. For example, in the case of the intensity distribution of the entrance pupil I_EP, the same diffracted radiation channel for all orders of diffraction B0, B+1, B1 is present at kx=0.5 and ky=0.5. Likewise, the wave vector of a diffracted radiation channel corresponds to the wave vector of a corresponding undiffracted radiation channel in this case, with the result that the intensity distribution I_blank of the undiffracted radiation channels of FIG. 2 can be compared at the same coordinates to the intensity distribution of the diffracted radiation channels in the entrance angular space. Likewise, a diffracted radiation channel in the entrance pupil can be compared with an undiffracted radiation channel at the same coordinate. Accordingly, the diffracted radiation can be related to the undiffracted radiation in order to determine the diffraction property of the measurement structure 60. For example, the diffraction efficiency B_EF is specified in the third line of FIG. 3; it corresponds to the ratio of the intensity of the diffracted radiation channel to the intensity of the corresponding undiffracted radiation channel. Accordingly, it is evident that the central obscuration is identifiable again in the case of the zeroth order of diffraction B0 since the position of a diffracted radiation channel of zeroth order corresponds to the position of the undiffracted radiation channel in the entrance and exit angular space. However, two undefined regions in the diffraction efficiency arise for the first orders of diffraction, as identifiable in FIG. 3. This is related to the fact that the obscured undiffracted radiation channels do not correspond to the obscured diffracted radiation channels (which may arise due to the displacement of the diffraction maxima). For example, a first undefined region therefore arises in the region of kx=ky=0 for the order of diffraction B+1, which arises due to the obscured undiffracted radiation channels. Further, a second undefined region arises by way of example in the region of kx=0, ky=0.6 for the order of diffraction B1, which arises due to the obscured diffracted radiation channels. Accordingly, the diffraction efficiencies for lithography apparatuses with an obscuration may be incomplete.
[0073] Further, it should be observed that the influence of the illumination unit lessens when the diffraction efficiency is formed since the intensities of corresponding radiation channels are divided by one another. A noise which could be comprised in the illumination unit accordingly has no influence on the correct determination of the diffraction property.
[0074] In this case, FIG. 4 illustrates simulation results of diffraction efficiencies of diffracted radiations. In this case, the first column in FIG. 4 corresponds to the diffraction efficiency B_EF1, which is depicted for the diffracted radiation channels of the zeroth order of diffraction B0, the plus first order of diffraction B+1 and the minus first order of diffraction B1. In this case, the first column of FIG. 4 corresponds to the third line of FIG. 3. Accordingly, this depicts the incomplete diffraction efficiencies caused by the obscuration. The second column in FIG. 4 likewise specifies a diffraction efficiency B_EF2 of the orders of diffraction. However, the influence of the obscuration was removed during the simulation in this case. Thus, the determination of the diffraction efficiency B_EF2 was based on complete information. In this simulation case, the intensity distributions of the undiffracted and diffracted radiation channels did not have regions with obscuration. The third column depicts a diffraction efficiency B_EF3 of the orders of diffraction, wherein in this case the diffraction efficiency was compensated (as described herein) for the undefined region or regions of the obscuration from the first column of the diffraction efficiency B_EF1. Subsequently, the diffraction efficiency B_EF2 without obscuration could be compared to the diffraction efficiency B_EF3, in which an obscuration appearance was compensated. As evident from FIG. 4, no difference is identifiable between the diffraction efficiencies B_EF2 and the diffraction efficiency B_EF3. Accordingly, the compensation can sufficiently enable the determination of the diffraction efficiency (or the determination of the diffraction property). Inter alia, this is enabled by the continuity of the diffraction property. However, it is also conceivable that discontinuities of the diffraction property may arise in the general case. In this case, however, the structure on the measurement reticle can be chosen (or designed) such that the discontinuity is suppressed (e.g. in the case of a diffraction grating as a structure).
[0075] FIG. 5 schematically illustrates the association of an unobscured subset of a diffracted radiation in relation to the corresponding obscured subset of a substantially undiffracted radiation. As described herein, the diffraction property can be used to determine the obscured subset of the undiffracted radiation or undiffracted radiation beams. In this case, FIG. 5 schematically shows the intensity spots of the undiffracted radiation beams E in the entrance pupil EP (or in the entrance angular space) in relation to the reticle plane 38 which causes a diffraction and in which e.g. the measurement structure 60 (or the characterization element) can be arranged. In this case, the undiffracted radiation beams E irradiate the measurement structure 60 (not depicted in FIG. 5) and are diffracted out of the reticle plane 38 such that corresponding diffracted radiation beams are radiated into the projection lens of the lithography apparatus. Some of these diffracted radiation beams may have been exposed to the obscuration of the lithography apparatus in the case. Further, the exit pupil AP (or the exit angular space) is depicted, which detects the diffracted radiation beams downstream of the obscuration. In this case, e.g. diffracted radiation beams corresponding to the zeroth order of diffraction B0 or the first order of diffraction B1 are identifiable in the exit pupil. In this case, the position of the diffracted radiation beams of the zeroth order of diffraction B0 can also correspond to the position of the undiffracted radiation beams BU, which were radiated purely reflectively into the projection lens without diffraction at the measurement structure. The obscuration O results in some undiffracted radiation beams S1, S2, S3 being undetectable in the exit pupil even though the corresponding radiation beams S1, S2, S3 were present in the entrance pupil. The undiffracted radiation beams exposed to the obscuration can be referred to here as obscured undiffracted radiation beams S1, S2, S3. According to the invention, these can be determined with the diffraction property (as described herein). Within the scope of the method (described herein), it might e.g. be determined that, as they are detected, corresponding unobscured diffracted radiation beams S1, S2, S3 (e.g. of the first order of diffraction B1) are present for the obscured undiffracted radiation beams S1, S2, S3. The obscured undiffracted radiation beams S1, S2, S3 can be considered to be the obscured subset while the unobscured diffracted radiation beams S1, S2, S3 are in this case associated via an order of diffraction with the obscured subset. Further, e.g. the position of the obscured undiffracted radiation beams S1, S2, S3 can be determined with the method (described herein). To this end, it is possible to use e.g. an unobscured undiffracted radiation beam SN and/or a corresponding unobscured diffracted radiation beam SN e.g. from the surroundings of the obscuration. According to the invention, the diffraction property can be determined for all diffracted radiation beams with the compensation. Accordingly, the diffraction property for the unobscured diffracted radiation beams S1, S2, S3 is available and can be correspondingly used to determine the intensity of the obscured undiffracted radiation beams S1, S2, S3. For example, the intensity of the obscured undiffracted radiation beams S1, S2, S3 can be determined with the ratio of the intensity of the corresponding unobscured diffracted radiation beams S1, S2, S3 divided by their diffraction efficiency (or diffraction property).
