Pupil stop, illumination optics unit and metrology system

Abstract

A pupil stop (7) is used for the illumination optics unit of a metrology system for determining the spatial image of an object to be measured, as a result of illumination and imaging under conditions corresponding to the illumination and imaging conditions of an optical production system. The pupil stop (7) has two polar channel openings (10, 11) for specifying the corresponding poles of illumination of the illumination optics unit designated by the pupil stop (7; 20). At least one stop web (17, 18) passes through the respective polar channel openings (10, 11), thereby dividing the polar channel openings (10, 11) into multiple partial polar openings (10a, 10b; 11a, 11b). This creates a pupil stop that improves the convergence accuracy of the illumination and imaging conditions of the optical production system to the illumination and imaging conditions of the optical measurement system.

Description

[0001] The contents of German patent application DE10 2021 203 961.8 are incorporated herein by reference. Technical Field

[0002] This invention relates to a pupil stop for an illumination optical unit in a metrology system for determining a spatial image of an object to be measured, as a result of illumination and imaging under conditions corresponding to the illumination and imaging conditions of an optical production system. Furthermore, this invention relates to an illumination optical unit for such a metrology system including such a pupil stop, and to such a metrology system including such an illumination optical unit. Background Technology

[0003] The measurement system is known from US 2017 / 0131 528 A1 (parallel documents WO 2016 / 012 425 A2), WO 2016 / 012426 A1 and US 2017 / 0132782 A1.

[0004] The purpose of this invention is to improve the convergence accuracy of the illumination and imaging conditions of an optical production system to the illumination and imaging conditions of an optical measurement system, which can be part of a metrology system, especially when using a multi-polar illumination setup. Summary of the Invention

[0005] According to the present invention, this objective is achieved by a convergence method having the features described below.

[0006] This invention relates to a pupil stop for an illumination optical unit in a metrology system for determining a spatial image of an object to be measured, as a result of illumination and imaging under illumination and imaging conditions corresponding to the illumination and imaging conditions of an optical production system.

[0007] - Includes at least two pole channel openings for specifying the corresponding pole of the multi-pole illumination of the illumination unit designated by the pupil stop.

[0008] Each includes at least one aperture web, the aperture web passing through the corresponding polar channel opening and thereby dividing the polar channel opening into a plurality of partial polar openings.

[0009] Multi-polar illumination setups are typically similar to mask exposure in projection lithography. Therefore, the corresponding multi-polar illumination situations require high-precision metrology of the exposed objects, i.e., in particular, good convergence between metrological imaging and illumination conditions and production imaging and illumination conditions.

[0010] Surprisingly, a pupil aperture with at least one aperture web in each of the corresponding polar channel openings was identified as improving the convergence of the metering lighting setup with the corresponding multi-polar production lighting setup, even though the polar shadow corresponding to such a web does not need to exist in the production lighting setup.

[0011] For parameters that are crucial to metrology, such as, in particular, NILS (normalized image log slope, derivative of the spatial image intensity curve at the edge location of the imaging structure) and CD (critical size), parameter values ​​can be adapted in metrology to well match the corresponding parameters of the production system.

[0012] The two polar channel openings of the pupil stop can be spaced apart from each other along the polar direction. This polar direction can extend parallel to a direction perpendicular to the object displacement direction of the production projection exposure apparatus, and the metering illumination setup is designed to converge to the illumination setup of the production projection exposure apparatus. If the object plane of the production projection exposure apparatus is spanned by coordinates x and y, and the object displacement direction extends along the y coordinate, then the pupil stop according to the invention can therefore be implemented, for example, as an x-dipole pupil stop, or a C-quad pupil stop (a superposition of x-dipole and y-dipole). This quadrupole superposition of two dipoles in the x and y directions is also called C-quad (refer to WO 2021 / 028 303 A1; especially...). Figure 3 a).

[0013] It is also possible to specify pupil stops with different numbers of poles than two (x-dipole) or four (e.g., C-quad), such as tripole, pentapole, or more than five poles, such as hexapole or octapole. At least two of these poles (which are further subdivided into multiple partial pole openings) may be spaced apart from each other along the x-coordinate.

[0014] Alternatively or additionally, the pupil stop may be arranged such that the two poles of the illumination setting, as specified by the pupil stop, are designated as having a dipole direction, i.e., extending along the direction of the interval between the two poles of the dipole, perpendicular to the object structure of the object to be measured.

[0015] In one embodiment, the aperture web is arranged symmetrically with respect to the center of the pupil aperture. This symmetrical aperture web arrangement has been found to be particularly advantageous for good convergence to illumination and imaging conditions. When the pupil aperture is arranged in the illumination optics unit, the center of the pupil aperture can correspond to the pupil center of the illumination optics unit.

[0016] In one embodiment, exactly one aperture web is arranged in each polar channel opening. The fact that exactly one aperture web is arranged in each polar channel opening has proven its value in practice.

[0017] In one embodiment, the polar channel opening has a first larger aperture width and a second smaller aperture width in two mutually perpendicular directions in the arrangement plane, the aspect ratio between the larger aperture width and the smaller aperture width being greater than 2, and the aperture web extending along the second smaller aperture width.

[0018] In one embodiment, the two polar channel openings are spaced apart from each other along the dipole direction, and the aperture web extends along the dipole direction.

[0019] The extension direction of the aperture web, as described above, particularly ensures good convergence of measurement parameters related to imaging of vertical object structures, i.e., structures aligned with a dipole direction perpendicular to the dipole, where the dipole is specified by the two poles of multipole illumination designated by the pupil aperture. In this case, the dipole direction is along the distance between the two poles of the dipole.

[0020] The present invention also relates to an illumination optical unit for a metrology system for determining a spatial image of an object to be measured, as a result of illumination and imaging under illumination and imaging conditions corresponding to the illumination and imaging conditions of an optical production system, wherein the illumination optical unit includes a pupil stop as described above.

[0021] The present invention also relates to a metrology system for determining a spatial image of an object to be measured, as a result of illumination and imaging under illumination and imaging conditions corresponding to the illumination and imaging conditions of an optical production system.

[0022] -Including the illumination optics unit as described above,

[0023] - Includes an imaging optics unit for imaging a portion of the object onto the measurement plane.

[0024] -Including a spatial resolution detection device arranged in the measurement plane.

[0025] The advantages of the above-described illumination optical unit and the above-described metrology system correspond to the advantages already described above with reference to the pupil aperture.

[0026] These advantages are particularly effective when considering a metrology system according to the following, which includes an imaging optics unit with a large image-side numerical aperture. In one embodiment, the imaging optics unit has an image-side numerical aperture greater than 0.5.

[0027] The metrology system can be used to measure the lithographic mask provided for projection exposure in order to produce semiconductor components with very high structural resolution, such as better than 30 nm, and especially better than 10 nm.

[0028] The metrology system may include a quick-change tool holder for replacing the corresponding dipole pupil stop with a variable stop that specifies an optional measurement illumination setting. This increases the flexibility of the metrology system. Attached Figure Description

[0029] Exemplary embodiments of the present invention will now be explained in more detail with reference to the accompanying drawings. In the drawings:

[0030] Figure 1 A metrological system is schematically illustrated for determining a production space image of an object to be measured, as a result of illumination and imaging under illumination and imaging conditions corresponding to the illumination and imaging conditions of an optical production system, wherein a planar diagram of the object field and a planar diagram of the measurement field at the current z-position are also additionally shown.

[0031] Figure 2 A plan view of the dipole pupil stop of the illumination optics unit for the metrology system is shown; and

[0032] Figure 3 With similar Figure 2 The illustration shows another embodiment of the dipole pupil stop, and also illustrates the parameters used to characterize the position and size of the polar channel opening of the dipole pupil stop. Detailed Implementation

[0033] Figure 1 An imaging optical unit 3 (composed of) is shown in the plane corresponding to the meridional section. Figure 1 The box in the diagram schematically represents the beam path of the EUV illumination light or EUV imaging light 1 in the metering system 2. The illumination light 1 is generated in the illumination system 4 of the projection exposure device 2.

[0034] To facilitate the representation of positional relationships, the Cartesian xyz coordinate system will be used in the following text. Figure 1 The x-axis in the figure extends perpendicularly to the plane of the figure and extends beyond the plane of the figure. Figure 1 The y-axis extends toward the light. Figure 1 The z-axis extends upwards.

[0035] The illumination system 4 includes an EUV light source 5 and an illumination optics unit 6, which are schematically illustrated. The light source can be a laser plasma source (LPP; laser-generated plasma) or a discharge source (DPP; discharge-generated plasma). In principle, a synchrotron-based light source, such as a free-electron laser (FEL), can also be used. The wavelength of the illumination light 1 can be in the range of 5 nm to 30 nm. In principle, in variations of the projection exposure device 2, a light source for a different wavelength can be used, such as one for a wavelength of 193 nm.

[0036] The illumination light 1 is adjusted in the illumination optics unit 6 of the illumination system 4 to provide a specific illumination setting, i.e., a specific illumination angle distribution. This illumination setting corresponds to a specific intensity distribution of the illumination light 1 in the illumination pupil of the illumination optics unit of the illumination system 4. A pupil stop 7, arranged in the pupil plane 8 of the illumination optics unit 6, is used to provide the corresponding illumination setting.

[0037] The pupil stop 7 is held in the pupil stop holder 7a. This can be a quick-change pupil stop holder, which facilitates the replacement of the pupil stop 7 currently used in the lighting with at least one different pupil stop. Such a quick-change holder may include a housing with multiple pupil stops 7 (in particular different pupil stops) for specifying various lighting settings.

[0038] The image-side numerical aperture of the imaging optical unit 3 is 0.7. Depending on the embodiment of the imaging optical unit 3, the image-side numerical aperture may be greater than 0.5, and may also be 0.55, 0.6, 0.65, 0.75, 0.8, or even larger. This image-side numerical aperture of the imaging optical unit 3 is adapted to the image-side numerical aperture of the production projection exposure apparatus to be simulated by imaging through the metrology system. Therefore, the illumination setting of the dipole pupil stop 7 is also adapted to the production illumination setting of the production projection exposure apparatus.

[0039] Figure 2 An embodiment of the pupil stop 7, designed as a dipole pupil stop, is shown in an xy-plane diagram. The usable pupil 9 of the illumination optics unit 6 is... Figure 2 The maximum usable pupil 9 is shown through a circular edge. It can have a circular edge, but it can also have an edge that deviates from a circular shape, such as an elliptical edge. The pupil coordinates spanning the pupil (which correspond to the x and y coordinate directions) are also referred to below as σ. x , σ y These pupil coordinates σ x , σ y Normalized so that the maximum available pupil 9 covers the two coordinates σ respectively. x , σ y The range of values ​​in [-1, 1].

[0040] The dipole pupil stop 7 has two polar channel openings 10 and 11, and its entire outer contour is approximately segmental. Figure 2 The polar channel opening 10 on the left side has a partially circular edge portion 12 that protrudes toward the center Z of the pupil 9.

[0041] The edge profiles of the polar channel openings 10 and 11 are mirror-symmetric with respect to the symmetry plane 13, which is parallel to the yz plane and has σ. xThe coordinates = 0 are sufficient to describe the edge shape of one of the two polar channel openings 10 and 11 below.

[0042] The two polar channel openings 10 and 11 are used to specify the corresponding poles of the dipole illumination of the illumination optical unit 6, as designated by the dipole pupil stop 7. Illumination light 1 can pass through the pupil plane 8 through the two polar channel openings 10 and 11. Illumination light 1 is blocked away from the polar channel openings 10 and 11 by the dipole pupil stop 7. This blocking can be achieved by absorbing and / or reflecting and / or scattering illumination light 1.

[0043] The polar channel opening 10 in negative σ x The edge portion 14, opposite to edge portion 12 in the coordinate direction, has a straight line design and is approximately in coordinate σ. x =Extends at 0.75.

[0044] At the maximum positive and negative σ x In the coordinate region, the two edge portions 12 and 14 are adjacent to each other not through sharp corners but through beveled portions 15 and 16. These beveled portions 15 and 16 are shorter than the other edge portions 12 and 14, and are located at +0.7 and -0.7σ. x The region of coordinates.

[0045] Each polar channel opening 10, 11 has an aperture web 17, 18 that passes through the corresponding polar channel opening 10, 11 and thereby divides the corresponding polar channel opening 10, 11 into multiple partial polar openings, specifically two partial polar openings 10a, 10b and 11a, 11b.

[0046] The two aperture webs 17 and 18 are along with σ y =0 coordinates aligned with σ x Coordinate extension. Due to the mirror symmetry of the polar channel openings 10 and 11, the aperture webs 17 and 18 also extend symmetrically with respect to the plane of symmetry 13, and the center Z of the pupil 9 is located in this plane of symmetry 13. The center Z of the pupil 9 coincides with the center of the dipole pupil aperture 7 (i.e., the centroid of the aperture).

[0047] According to Figure 2 In this embodiment, exactly one aperture web 17, 18 is assigned to each pole channel opening 10, 11. That is, exactly one aperture web 17, 18 is arranged in each pole channel opening 10, 11.

[0048] In the pupil plane 8, that is, in the plane in which the dipole pupil stop 7 is arranged, the polar channel openings 10 and 11 are along σ y The coordinates have a larger aperture width W G And along the pupil coordinate σ perpendicular to it x With the second smallest aperture width WK For larger aperture widths W G Pupil coordinate range σ y Approximately 1.4 (-0.7 to +0.7), at smaller aperture widths W K In the case of σ x The aperture width in the pupil coordinate direction is approximately 0.4 (-0.8 to -0.4, or +0.4 to +0.8). A larger aperture width W... G and smaller aperture width W K The aspect ratio between them is approximately 3.5, therefore greater than 2.

[0049] The aperture webs 17 and 18 each extend along the narrower aperture width W. K extend.

[0050] The webs of the aperture 17 and 18 are at σ y The thickness in the direction of the pupil coordinates is approximately 0.05 (σ y = -0.025 to +0.025).

[0051] The two pole channel openings 10 and 11 specify the x-dipole, i.e., the x-dipole illumination setting of the illumination optics unit 6. Therefore, the x-direction is the dipole direction of this setting. The aperture webs 17 and 18 extend along this dipole direction x.

[0052] The two polar channel openings 10 and 11 are spaced apart from each other along the dipole direction x, specifically, according to σ x Represented by coordinate values, approximately 0.8 (σ x = -0.4 to +0.4).

[0053] Instead of x-dipole, the pupil stop in the dipole pupil stop type 7 can also be implemented as a quadrupole pupil stop, such as the C-quad type. An embodiment of the C-quad with undivided pole channel openings is from WO 2012 / 028 303 A1. Figure 3 a is known.

[0054] exist Figure 2 In the middle, together with the two polar channel openings 10 and 11, two additional polar channel openings 10 are generated for the corresponding C-quad pupil stop. y 11 y Shown using dashed lines. Two additional polar channel openings 10 y 11 y Each is also divided into two parts with a maximum opening of 10. a y 10 b y and 11 a y 11 by This is as explained above in conjunction with the polar channel openings 10 and 11 of the dipole pupil stop 7. The explanations already given regarding polar channel openings 10 and 11 and their aperture webs 17 and 18 apply to polar channel opening 10. y 11 y and the associated aperture web 17 y 18 y The geometry of which is then along σ y Coordinate extension. Two aperture webs 17 y 18 y Along with σ x =0 coordinates aligned with σ y Coordinate extension.

[0055] Figure 3 Another embodiment of the dipole pupil stop 20, which can be used to replace the dipole pupil stop, is shown.

[0056] The following description focuses only on the differences between the dipole pupil stop 20 and the dipole pupil stop 7. Components and functions already explained above in conjunction with the pupil stop 7 share the same reference numerals and will not be discussed further.

[0057] With the dipole pupil stop 20, the stop webs 17 and 18 have a smaller σ. y The range, which is approximately equal to the range based on Figure 2 In the embodiment, the σ of the aperture webs 17 and 18 y Half of the range.

[0058] also, Figure 3 Some parameters are specified for measuring the relative positions of the polar channel openings 10 and 11 of the pupil stop 20.

[0059] ys represents σ y The range of the aperture web 17 and 18 in the direction.

[0060] xm represents the edge portion 14 of the straight line and the center coordinate σ. x =0.

[0061] d represents the circular edge portion 12 of the polar channel opening 10 and σ. x / σ y The distance between the farthest pupils at coordinates [1, 0].

[0062] The measurement system 2 is used as follows: Initially, the imaging optical unit 3 is set on the one hand by the corresponding pupil stop 7 or 20, and on the other hand by the image-side numerical aperture and illumination settings, the latter corresponding to the most likely range of illumination and imaging conditions of the production projection exposure equipment to be measured.

[0063] With the corresponding lighting settings, illumination light 1 illuminates the object field 21 of the object plane 22 of the metering system 2. Therefore, the photolithography mask 23, also known as the mask master, is arranged in the object plane 22 and serves as the object to be illuminated during production. Above the object plane 22, which extends parallel to the xy plane, the structural cross-section of the photolithography mask 23 is... Figure 1 The diagram is schematically shown. The cross-section of the structure is represented such that it is located at... Figure 1 In the attached plane, the actual arrangement of the photomask 23 is perpendicular to the object plane 22. Figure 1 The attached plan view.

[0064] Illumination light 1 is reflected from photolithography mask 23, such as Figure 1 Schematic illustration shows the entrance pupil 24 of the imaging optical unit 3 entering the entrance pupil plane 25. The entrance pupil 24 used by the imaging optical unit 3 is circular, or as shown in the diagram. Figure 1 As schematically shown, it has an elliptical edge.

[0065] Within the imaging optical unit 3, illumination or imaging light 1 propagates between the entrance pupil plane 25 and the exit pupil plane 26. The circular exit pupil 27 of the imaging optical unit 3 is located in the exit pupil plane 26. The imaging optical unit 3 may have modified embodiments, and a circular exit pupil 27 is generated from a circular or elliptical entrance pupil 24.

[0066] Imaging optical unit 3 images the object field 21 onto the image plane 29 or image field 28 of projection exposure device 2. Below the image plane 29, Figure 1 The image light intensity distribution I is schematically shown, which is spaced apart from the image plane 29 in the z-direction by a value z. W The defocus value z is measured in the plane. W The intensity of the imaging light at that location.

[0067] Image light intensities I(x, y, z) at various z values ​​around plane 29 w It is also known as the 3D spatial image of projection exposure device 2.

[0068] A spatial resolution detection device 30 (which can be a CCD camera or a CMOS camera) is arranged in the image plane 29, which represents the measurement plane of the metrology system 2. The detection device 30 records the imaging light intensity I(x, y, z). W ).

[0069] When the object field 21 is imaged onto the image field 28, the imaging optical unit 3 can have a magnification ratio greater than 100. This imaging ratio can be greater than 200, 250, 300, 400, or 500. The imaging ratio of the imaging optical unit 3 is typically less than 2000.

[0070] The shading created by the aperture webs 17 and 18 within the polar channel openings 10 and 11 causes the dipole illumination within the metering system 2 to better correspond to the corresponding dipole illumination of the production system, and should converge to this corresponding dipole illumination in terms of illumination and imaging conditions. Surprisingly, this situation still applies even though the production system lacks a corresponding web or shading within the dipole of the dipole illumination.

[0071] In particular, it achieves good correspondence with the NILS (Normalized Image Logarithmic Slope, the derivative of the spatial image intensity curve at the edge of the imaging structure) parameter. The definition of this NILS parameter can be found in US 2015 / 0 042 974A1.

[0072] It can also reduce the deviation (ΔCD) between critical dimensions (CD), which can be imaged first using the imaging optics of the metrology system and then using the imaging optics of the production system. These deviations are typically normalized to a critical dimension that the production system can image. Reduction of deviation is particularly effective for ΔCD. V The value refers to the change in the critical dimension in the case of a vertically extending structure (in the y-direction). Specifically, the value ΔCD V It can be better than 5%.

[0073] The definition of parameter CD is referenced in US 9,176,390 B.

[0074] Specifically, the deviation in the ratio between the change in critical dimension on the wafer and the change in critical dimension on the mask is:

[0075] MEEF = ΔCD Wafer / ΔCD Mask

[0076] It is advantageous to reduce the size by using a dipole pupil stop of 7 or 20.

[0077] Normalized value:

[0078]

[0079] It can be advantageous to keep it relatively small.

[0080] This applies, especially to the vertical component ΔMEEF. V It can be kept less than 20%, less than 15%, or even less than 10%. For a critical target size of 10% ΔMEEF and minimum resolvable defect size ΔCD = 10%, the measurement error ΔCD of metrology system 2 is 1% of the critical target size.

Claims

1. A pupil stop (7; 20) for an illumination optical unit (6) of a metrology system (2) for determining a spatial image of an object (23) to be measured, as a result of illumination and imaging under illumination and imaging conditions corresponding to the illumination and imaging conditions of an optical production system, wherein the pupil stop... - Includes at least two pole channel openings (10, 11) for designating the corresponding pole of the multi-pole illumination of the illumination optical unit (6) designated by the pupil stop (7; 20), Each includes at least one aperture web (17, 18) that passes through the corresponding polar channel opening (10, 11) and thereby divides the polar channel opening (10, 11) into a plurality of partial polar openings (10a, 10b; 11a, 11b). -in, The pupil stop (7; 20) is implemented in the pupil plane of the illumination optical unit.

2. The pupil stop as described in claim 1, characterized in that, The web of the aperture (17, 18) is arranged symmetrically with respect to the center of the pupil aperture (7; 20).

3. The pupil stop as described in claim 1 or 2, characterized in that, An aperture web (17, 18) is positioned in each polar channel opening (10, 11).

4. The pupil stop as described in claim 1 or 2, characterized in that, The polar channel openings (10, 11) are in two mutually perpendicular directions (σ) in the arrangement plane (8). y , σ x Each of them has the largest aperture width (W) G ) and the second smaller aperture width (W) K The larger aperture width (W) G ) and the smaller aperture width (W) K Aspect ratio (W) between G / W K The aperture width (W) is greater than 2, and the aperture webs (17, 18) are respectively along the second smaller aperture width (W) K )extend.

5. The pupil stop as described in claim 1 or 2, characterized in that, Two of the polar channel openings (17, 18) are spaced apart from each other along the dipole direction (x), and the aperture web (17, 18) extends along the dipole direction (x).

6. An illumination optical unit (6) of a metrology system (2), the metrology system being used to determine a spatial image of an object (23) to be measured, as a result of illumination and imaging under illumination and imaging conditions corresponding to the illumination and imaging conditions of an optical production system, the illumination optical unit comprising a pupil stop (7; 20) as described in claim 1 or 2, wherein, The pupil stop is arranged in the pupil plane of the illumination optical unit.

7. A metrology system (2) for determining a spatial image of an object (23) to be measured, as a result of illumination and imaging under illumination and imaging conditions corresponding to the illumination and imaging conditions of an optical production system, the metrology system -Including the illumination optical unit (6) as described in claim 6, -Includes an imaging optics unit (3) for imaging a portion of an object (23) onto a measurement plane (29), -Including a spatial resolution detection device (30) arranged in the measurement plane (29).

8. The metering system (2) as described in claim 7, characterized in that, The imaging optical unit (3) has an image-side numerical aperture greater than 0.5.

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