EUV condenser for EUV projection exposure apparatus

Abstract

The EUV condenser for an EUV projection exposure apparatus is used to transmit usable EUV light emitted from a source volume (19) into a condenser volume (28) separated from the source volume (19). The source volume (19) has a first source length z along a connection axis (z) between the center of the source volume (19) and the center of the condenser volume (28). s The source volume (19) has a second cross-sectional source length (x s , y s ) along cross-sectional axes (x, y) perpendicular to the connection axis (z). The EUV condenser is designed to image the source volume (19) into the condenser volume (28). Such imaging has a first imaging ratio (z c / z s ) along the connection axis (z) and a second imaging ratio (x c / x s , y c / y s ) along the cross-sectional axes (x, y). The first imaging ratio (z c / z s ) is at least 10% different from the second imaging ratio (x c / x s , y c / y s ). As a result, an EUV condenser is provided that has a higher throughput of usable EUV light to an optical system in a subsequent EUV light path of the EUV projection exposure apparatus.

Description

Technical Field

[0001] This application claims the priority of U.S. Patent Application No. 63 / 367149 and DE102022207374.6, the contents of which are incorporated herein by reference.

[0002] The present invention relates to an EUV condenser for an EUV projection exposure apparatus.

Background Art

[0003] This type of EUV condenser is known from DE102019200698A1 and WO2009 / 036957A1. Additional EUV condensers are known from DE102013204441A1 and DE102013218128A1.

Summary of the Invention

[0004] The object of the present invention is to produce an EUV condenser that provides a higher throughput of usable EUV light to the optical system in the subsequent EUV light path of an EUV projection exposure apparatus.

[0005] Such an object is achieved by an EUV condenser having the features described in claim 1 and an EUV condenser having the features described in claim 2.

[0006] According to the present invention, it has been found that the reason why the throughput of usable EUV light is limited is that the source volume of the light source that emits the usable EUV light collected by the EUV condenser often deviates significantly from a sphere. Having a condenser with different imaging scales in the direction along the connection axis and the direction transverse to the connection axis enables the collection of such aspherical or anisotropic source volumes into the collection volume, which is better adapted to the subsequent optical components of the EUV projection exposure apparatus as in the case of such imaging scales with no difference.

[0007] In particular, the EUV condenser may have an anisotropic imaging characteristic that compensates for the anisotropic shape of the source volume.

[0008] The design of such a condenser with different imaging ratios can be carried out, for example, with the help of the analytical methods described in the paper "Focusing of an elliptical mirror based system with aberrations", J. Liu et al., J. Opt. 15 (2013) 105709 (7pp) (doi: 10.1088 / 2040-8978 / 15 / 10 / 105709) and the publication "Elliptical mirrors - Applications in microscopy, ed. J. Liu, chapter 6: Aberration analysis of an elliptical mirror with a high numerical aperture", C. Liu et al., IOP Publishing Ltd 2018 (doi: 10.1088 / 978-0-7503-1629-3ch6).

[0009] The length (extension) of the source volume along the connection axis may be in the range of 400 μm to 2 mm, for example in the range of 500 μm to 2 mm or in the range of 400 μm to 1.5 mm. The cross-sectional source length may be in the range of 100 μm to 1 mm, particularly in the range of 500 μm to 1 mm. The limits of each source length and / or cross-sectional source length may be given by the measured size of the 100% enclosed measurement energy volume or EUV emission volume.

[0010] According to claim 1, the EUV condenser has a basic ellipsoidal shape, and the difference between the first imaging ratio and the second imaging ratio is due to the shape deviation from such a basic ellipsoidal shape. The condenser shape of the EUV condenser can be described by a Zernike polynomial expansion. The shape deviation between the actual condenser shape and the basic ellipsoidal shape includes the contributions of the Zernike polynomials Z4 and / or Z9 and / or Z16. Starting from the basic ellipsoidal shape, it has been proven that it is particularly appropriate to implement the difference in the imaging ratio due to the shape deviation from such a basic ellipsoidal shape. The analytical concepts obtained from the above-mentioned literature are well-suited to such shape concepts.

[0011] It has been proven that optimizing the shape deviation by the Zernike polynomial contributions Z4 / Z9 / Z16 as described in claim 1 is particularly useful. These Zernike polynomials are described as Scaled Prolate Spheroidal Zernike polynomials (SPS ZFR) or Zernike Fringe Expanded polynomials (ZFE). In that regard, the CODE V 10.4 Reference Manual, Appendix C refers to it. The Fringe Zernike polynomials Z4, Z9, and Z16 are the first Fringe Zernike polynomials that depend only on the radius and are independent of the azimuth angle. The Fringe Zernike polynomial Z4 corresponds to defocus-field curvature. The Fringe Zernike polynomial Z9 corresponds to the first-order contribution of spherical aberration. The Fringe Zernike polynomial Z16 corresponds to the second-order contribution of spherical aberration.

[0012] That the condenser volume aspect ratio is smaller than the source volume aspect ratio as described in claim 2 is well-suited to a source volume shape that is larger along the connection axis and thus smaller along the cross-sectional axis. For example, the source volume may have a shape of a cigar or an ellipsoid extended along the connection axis.

[0013] The difference in imaging ratios according to claim 3 has been proven to be well adapted to a typical plasma source volume shape. The difference between the first imaging ratio and the second imaging ratio may be greater than 20%, greater than 25%, greater than 50%, greater than 100%, greater than 150%, greater than 200%, greater than 250%, and may even be greater than 300%. Generally, such a difference in imaging ratios is less than 1,000%.

[0014] The reflective surface shape according to claim 6 reduces production costs.

[0015] The reflective surface shape according to claim 7 can be adapted to an irregular source volume shape.

[0016] The advantages of the illumination system according to claim 8 and the projection exposure apparatus according to claim 9 correspond to the advantages already described above with respect to the condenser of the present invention.

[0017] The advantages of the manufacturing method according to claim 10 and the nano or microstructured component according to claim 11 correspond to the advantages described above. Such a component may be a semiconductor microchip, particularly a high-density memory chip.

[0018] Next, exemplary embodiments of the present invention will be described in more detail with reference to the drawings.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0020] The projection exposure apparatus 1 for microlithography includes a light source 2 for illumination light and / or imaging light 3. The light source 2 will be described in more detail later. The light source 2 is, for example, an EUV light source that generates light in a wavelength range between 5 nm and 30 nm, particularly between 5 nm and 15 nm. Hereinafter, the illumination light and / or imaging light 3 is also referred to as EUV light used.

[0021] In particular, the light source 2 may be a light source having a used EUV wavelength of 13.5 nm, or a light source having a used EUV wavelength of 6.9 nm or 7 nm. Other used EUV wavelengths are also possible. In FIG. 1, the beam path of the illumination light 3 is shown very schematically.

[0022] The illumination optical unit 6 serves to guide the illumination light 3 from the light source 2 to the object field 4 in the object plane 5. The illumination optical unit includes a field facet mirror FF shown very schematically in FIG. 1 and a pupil facet mirror PF arranged on the downstream side of the beam path of the illumination light 3, and the pupil facet mirror PF also shown very schematically. An off-axis field-forming mirror 6b (GI mirror; off-axis mirror) is arranged in the beam path of the illumination light 3 between the pupil facet mirror PF arranged in the pupil plane 6a of the illumination optical unit and the object field 4. Such a GI mirror 6b is not essential.

[0023] The pupil facets of the pupil facet mirror PF (not shown in more detail) are part of the transmission optical unit, which transmits the field facets of the field facet mirror FF (also not shown) into the object field 4 in a specific image so that they overlap each other. Embodiments known from the prior art may be used for the field facet mirror FF on the one hand and for the pupil facet mirror PF on the other hand. As an example, such an illumination optical unit is known from DE102009045096A1.

[0024] Using a projection optical unit or an imaging optical unit 7, the object field 4 is imaged into the image field 8 of the image plane 9 at a predetermined scale. Projection optical units that may be used for this purpose are known, for example, from DE102012202675A1.

[0025] To facilitate the description of the various embodiments of the projection exposure apparatus 1 and the projection optical unit 7, a Cartesian xyz coordinate system is shown in this figure, from which the positional relationship of each of the components shown in the figure is clear. In FIG. 1, the x direction extends into the plane of the figure perpendicular to the plane of the figure. The y direction extends to the left in FIG. 1, and the z direction extends upward in FIG. 1. The object plane 5 extends parallel to the xy plane.

[0026] The object field 4 and the image field 8 are rectangular. Instead, it is also possible for the object field 4 and the image field 8 to have a bent or curved embodiment, i.e., in particular, to have the shape of a partial ring. The object field 4 and the image field 8 have an x / y aspect ratio greater than 1. Thus, the object field 4 has a longer object field dimension in the x direction and a shorter object field dimension in the y direction. These object field dimensions extend along the field coordinates x and y.

[0027] One of the exemplary embodiments known from the prior art may be used for the projection optical unit 7. In this case, the object imaged is the part of the reflective mask 10, also called a reticle, that coincides with the object field 4. The reticle 10 is carried by a reticle holder 10a. The reticle holder 10a is displaced by a reticle displacement drive 10b.

[0028] Imaging through the projection optical unit 7 is performed on the surface of the substrate 11 in the form of a wafer carried by a substrate holder 12. The substrate holder 12 is displaced by a wafer or substrate displacement drive 12a.

[0029] FIG. 1 schematically shows a light beam 13 of the illumination light 3 entering the projection optical unit between the reticle 10 and the projection optical unit 7, and a light beam 14 of the illumination light 3 emitted from the projection optical unit 7 between the projection optical unit 7 and the substrate 11. In FIG. 1, the image field side numerical aperture (NA) of the projection optical unit 7 is not reproduced at a constant ratio.

[0030] The projection exposure apparatus 1 is a scanner-type apparatus. During the operation of the projection exposure apparatus 1, both the reticle 10 and the substrate 11 are scanned in the y direction. A stepper-type projection exposure apparatus 1 is also possible in which a stepwise displacement of the reticle 10 and the substrate 11 in the y direction is performed between individual exposures of the substrate 11. These displacements are carried out synchronously with each other by appropriate operation of the displacement drives 10b and 12a.

[0031] FIG. 2 shows the details of the light source 3. Components and functions corresponding to those described above with reference to FIG. 1 are denoted by the same reference numerals and will not be discussed in further detail.

[0032] The light source 3 is a laser-produced plasma (LPP) source type light source. In order to generate plasma, tin droplets 15 are generated as a continuous droplet train by a tin droplet generator 16. The trajectory of the tin droplets 15 extends across the principal ray direction 17 of the usable illumination light 3. The tin droplets 15 fly freely between the tin droplet generator 16 and the tin droplet receiver 18, and pass through the plasma source volume 19 during that time. The usable EUV illumination light 3 is emitted from the plasma source volume 19.

[0033] Within the source volume 19, the pump light 20 of the pump light source 21 impinges on the arriving tin droplets 15. The pump light source 21 may be an infrared laser source, for example a CO2 laser. The pump light source 21 may also be another laser source, particularly another infrared laser source, for example a solid-state laser, particularly a Nd:YAG laser.

[0034] The pump light 20 is transmitted into the source volume 19 by the mirror 22 and the focusing lens 23. The mirror 22 may be a controllable tiltable mirror. A control signal for controlling such a mirror 22 may be generated in response to each sensor signal of a sensor that monitors light source parameters, particularly the parameters of the pump light source 21.

[0035] Due to the impingement of the pump light, plasma is generated from the tin droplets 15 that have reached within the source volume 19. Such generated plasma emits the usable illumination light 3 from the source volume 19. FIG. 2 shows the beam path of the usable illumination light 3 between the source volume 19 and the field facet mirror FF, and in FIG. 2, the field facet mirror FF is only schematically shown according to its position and arrangement. Such an illumination light beam path or optical path is shown as long as the illumination light 3 is reflected from the reflecting surface 24 of the condenser mirror 25 of the EUV condenser 26.

[0036] The condenser mirror 25 has a central through-opening 27 through which the pump light 20 focused on the source volume 19 by the focusing lens 23 passes.

[0037] The EUV condenser 26 serves to transmit the usable EUV light 3 from the source volume 19 into the condenser volume 28 implemented as the intermediate focus of the EUV light 3. The condenser volume 28 is separated from the source volume 19 along the connection axis between the center of the source volume 19 and the center of the condenser volume 28. Such a connection axis coincides with the chief ray direction 17 and extends along the z-axis in FIG. 2.

[0038] The condenser volume 28 is located in the intermediate focus plane 29 of the illumination optical unit 6.

[0039] In the subsequent beam path of the illumination light 3, in order to suppress unnecessary erroneous light having a wavelength different from the EUV wavelength of the illumination light 3 used to illuminate the reticle 10, the reflective surface 24 of the condenser mirror 25 may carry a grating structure. Such erroneous wavelengths may be in the IR wavelength range and / or the DUV wavelength range.

[0040] The field facet mirror FF is arranged in the far-field of the illumination light 3 in the beam path after the condenser volume 28.

[0041] The additional components of the EUV condenser 26 and the light source 2, in particular the tin droplet generator 16, the tin droplet receiver 18 and the focusing lamp 23, are located in the vacuum chamber 30. The vacuum chamber 30 has a through-opening 31 surrounding the condenser volume 28. The vacuum chamber 30 has a pump light inlet window 32 located where the pump light 20 enters the vacuum chamber 30.

[0042] FIGS. 3 to 5 show typical dimensions important with respect to the imaging characteristics of the condenser mirror 25 of the EUV condenser 26. Since the dimensions discussed in that regard have rotational symmetry with respect to the z-axis, there is no difference with respect to the coordinates x and y which both extend vertically in FIGS. 3 to 5. The z-axis in FIGS. 3 to 5 extends horizontally. To represent the far-field, a far-field plane 33 is shown in FIG. 3.

[0043] The distance A between the back surface of the substrate of the condenser mirror 25 and the center of the source volume 19 may be in the range of 150 mm to 300 mm.

[0044] The distance B between the center of the source volume 19 and the center of the condenser volume 28 may be greater than 1 m, or may be in the range of 1 m to 1.5 m.

[0045] The distance C between the center of the condenser volume 28 and the far-field plane 33 may be greater than 500 mm, or may be in the range of 500 mm to 1,500 mm.

[0046] For the tin droplet / pump light interaction, the source volume 19 has a first source length z along the connection axis z between the center of the source volume 19 and the center of the condenser volume 28 s such that the z source length z s may be in the range of 200 μm to 1.5 mm, particularly in the range of 300 μm to 1 mm.

[0047] Furthermore, the source volume 19 has a second cross-sectional source length x along its cross-sectional axes x and y perpendicular to the connection axis z s , y s such that the cross-sectional source length x s , y s may be in the range of 100 μm to 1 mm, particularly in the range of 200 μm to 600 μm, and may be, for example, about 500 μm.

[0048] The ratio z s / x s (=z s / y s ) may be in the range of 1.5 to 5, particularly in the range of 2 to 4, and may be, for example, in the range of 3.

[0049] The condenser volume 28 has a first condenser volume length z along the connection axis z c , as well as a second cross-sectional condenser length x along the cross-sectional axes x and y c , y c and has.

[0050] x c (=y c and z c ) may be in the range of 1 mm to 5 mm.

[0051] The EUV condenser mirror 25 is designed to transfer the source volume 19 into the condenser volume 28 with different imaging ratios with respect to the z-axis on the one hand and different imaging ratios with respect to the x- and y-axes on the other hand. Such imaging by the condenser mirror 25 results in a first imaging ratio i z (i z =z c / z s ) along the connection axis z and a second cross-sectional imaging ratio i x (=i y =x c / x s =y c / y s ) along the cross-sectional axes x and y. The first imaging ratio i z is at least 10% different from the second imaging ratio i x , i y . In particular, the ratio of the first imaging ratio i z to the second imaging ratio i x , i y is in the range of 1.5 to 5, in particular in the range of 2 to 4, for example in the range of 3. In particular, as shown in FIGS. 4 and 5, the ratio of such imaging ratios i z / i x ,y is complementary to the ratio z s / x s ,y s , as a result of which the length anisotropy of the source volume 19 is compensated by the condenser imaging into the condenser volume 28.

[0052] In the schematic views of FIGS. 4 and 5, the source volume is shown as a cuboid with a rectangular cross-section and the condenser volume is shown as a cube with a square cross-section. In reality, the volumes 19 and 28 do not have a faceted shape and have a smoother outer shape, which may resemble an ellipsoid or a deformed ellipsoid with respect to the source volume and may resemble a sphere or a deformed sphere in the case of the condenser volume.

[0053] In particular, the imaging characteristics of the condenser mirror 25 are such that the z / x and z / y condenser volume aspect ratios are smaller than the z / x and z / y source volume aspect ratios. In the illustrated embodiments of FIGS. 4 and 5, the z / x condenser volume aspect ratio is 1 and the z / x source volume aspect ratio is 3.

[0054] The reflecting surface 24 of the condenser mirror 25 has a basic ellipsoidal shape having a first focus located within the source volume 19 and a second focus located within the condenser volume 28.

[0055] The first imaging ratio i z and the second imaging ratio i x i y The difference from is due to the shape deviation of the reflecting surface 24 from such a basic ellipsoidal shape.

[0056] The shape of the reflecting surface 24 of the condenser mirror 25 can be described by a Zernike polynomial expansion. The shape deviation of the reflecting surface 24 from the basic shape, particularly the basic ellipsoidal shape, represents the contribution of the Zernike polynomials Z4 and / or Z9 and / or Z16.

[0057] The reflecting surface 24 of the condenser mirror 25 is rotationally symmetric about the connection axis z.

[0058] In an alternative embodiment, the reflecting surface 24 of the condenser mirror 25 is implemented as a free-form surface without a rotational symmetry axis.

[0059] On the one hand, the imaging ratio i z and on the other hand, the imaging ratio i x,y Each adaptation of results in a reduction of unnecessary clipping of the available EUV light 3 at the aperture located near the condenser volume 28, i.e., at the aperture located at the through-opening 31. Such an aperture serves to suppress unnecessary external light, pump light and / or debris.

[0060] To fabricate microstructured or nanostructured components, the projection exposure apparatus 1 is used as follows: First, a reflective mask 10 or reticle and a substrate or wafer 11 are prepared. Subsequently, with the aid of the projection exposure apparatus 1, the structure on the reticle 10 is projected onto the photosensitive layer of the wafer 11. Then, by developing the photosensitive layer, a microstructured or nanostructured body on the wafer 11, and thus a microstructured component, is fabricated.

Claims

1. An EUV condenser (26) for an EUV projection exposure apparatus (1) for transmitting usable EUV light (3) emitted from a source volume (19) into a condensing volume (28) separated from the source volume (19), - The source volume (19) has a first source length z along the connection axis (z) between the center of the source volume (19) and the center of the light-gathering volume (28) s It has, - The source volume (19) has a second cross-sectional source length x along a cross-sectional axis (x, y) perpendicular to the connection axis (z). s , y s It has, - The EUV condenser (26) is designed to image the source volume (19) within the condensing volume (28), and the image is formed -- The first imaging ratio (z) along the aforementioned connection axis (z) c / z s )and, -- The second imaging ratio (x c / x s , y c / y s ) along the cross-sectional axes (x, y) and It has, -- The first imaging ratio (z c / z s ) is the second imaging ratio (x c / x s , y c / y s ) differs by at least 10%, - The light condenser (26) has a basic ellipsoid shape, and the first imaging ratio (z c / z s ) and the second imaging ratio (x c / x s , y c / y s The difference between this and the basic ellipsoid shape is due to the shape deviation from the basic ellipsoid shape. - The shape of the light concentrator can be described by a Zernike polynomial expansion, and the shape deviation includes the contributions of the Zernike polynomials Z4 and / or Z9 and / or Z16. EUV concentrator (26).

2. An EUV condenser (26) for an EUV projection exposure apparatus (1) for transmitting usable EUV light (3) emitted from a source volume (19) into a condensing volume (28) separated from the source volume (19), - The source volume (19) has a first source length z along the connection axis (z) between the center of the source volume (19) and the center of the light-gathering volume (28) s It has, - The source volume (19) has a second cross-sectional source length x along a cross-sectional axis (x, y) perpendicular to the connection axis (z). s , y s It has, - The EUV condenser (26) is designed to image the source volume (19) within the condensing volume (28), and the image is formed -- The first imaging ratio (z) along the aforementioned connection axis (z) c / z s )and, -- The second imaging ratio (x, y) along the aforementioned cross-sectional axis (x, y) c / x s , y c / y s )and It has, -- The first imaging ratio (z c / z s ) is the second imaging ratio (x c / x s , y c / y s ) differs by at least 10%, - The first imaging ratio (z c / z s ) is the second imaging ratio (x c / x s , y c / y s ) is smaller than, and as a result, - Length of the focusing volume (28) along the connecting axis (z) c ) and the length (x, y) of the light-gathering volume (28) along the cross-sectional axis (x, y) c , y c The aspect ratio of the light-gathering volume (28) is the ratio to (z c / x c , z c / y c )but, - Length of the source volume (19) along the connection axis (z) s ) and the length (x, y) of the source volume (19) along the cross-sectional axis (x, y) s , y s The source volume aspect ratio (z) of the source volume (19) is the ratio of to ). s / x s , z s / y s Smaller than ) EUV concentrator (26).

3. The first imaging ratio (z c / z s ) is the second imaging ratio (x c / x s , y c / y s The EUV concentrator according to claim 1 or claim 2, which differs from ) by more than 10%.

4. The EUV condenser according to claim 3, wherein the first imaging ratio differs from the second imaging ratio by more than 50%.

5. The EUV condenser according to claim 4, wherein the first imaging ratio differs from the second imaging ratio by more than 100%.

6. The EUV concentrator according to claim 1 or 2, wherein the reflective surface (24) of the concentrator (26) is implemented in a rotationally symmetric manner with respect to the connecting axis (z).

7. The EUV concentrator according to claim 1 or 2, wherein the reflective surface (24) of the concentrator (26) is implemented as a free-form surface without a rotational symmetry axis.

8. - Radiation source (2), - The light concentrator according to claim 1 or 2 An EUV lighting system equipped with [specific features / features].

9. - The EUV lighting system according to claim 8, - A projection objective lens (7) for forming an image of the object field (4) illuminated by the EUV illumination system into the image field (8) in the image plane (9) and An EUV projection exposure system equipped with [the following features].

10. The following steps, namely, - The step of preparing the projection exposure apparatus (1) described in claim 9, - Steps to prepare the reticle (10), - A step of projecting the surface of the reticle (10) placed within the object field (4) onto the photosensitive layer of the wafer (11) A method for fabricating microstructured components according to [the specified method].

11. A microstructured component manufactured according to the method of claim 10.

Images