Imaging optics and projection exposure installation for microlithography with an imaging optics

Abstract

An imaging optics has at least six mirrors, which image an object field in an object plane in an image field in an image plane. An entry pupil of the imaging optics is arranged in the imaging beam path in front of the object field. At least one of the mirrors has a through-opening for the passage of imaging light. A mechanically accessible pupil, in which an obscuration stop is arranged for the central shading of the pupil of the imaging optics, is located in a pupil plane in the imaging beam path between the object field and a first of the through-openings. A first imaging part beam directly after a second mirror in the imaging beam path after the object field and a second imaging part beam directly after a fourth mirror in the imaging beam path after the object field intersect one another in an intersection region. The result is an imaging optics, in which a handleable combination of small imaging errors, manageable production and a good throughput for the imaging light is achieved.

Claims

1. An imaging optics, comprising: at least six mirrors configured to image an object field in an object plane into an image field in an image plane along a path of imaging light, wherein: chief rays of the imaging light, which emanate from points of the object field which are spaced apart from one another, have a mutually diverging beam course; of the at least six mirrors, a mirror has a through-opening which is the first through-opening: a) after the object plane along the path of the imaging light; and b) configured to pass the imaging light along the path of the imaging light; a pupil is located in a pupil plane in the path of the imaging light between the object field and the first through-opening; the imaging light passes once through the pupil along the path of the imaging light; an obscuration stop is arranged in the pupil plane to provide central shading of an exit pupil of the imaging optics; a first imaging part beam is directly after a second mirror in the path of the imaging light after the object field; a second imaging part beam is directly after a fourth mirror in the path of the imaging light after the object field; and the first and second imaging parts intersect each other in an intersection region.

2. The imaging optics of claim 1, wherein the imaging optics comprises exactly eight mirrors.

3. The imaging optics of claim 1, further comprising an aperture stop configured to determine an outer form of the pupil, wherein the aperture stop is in the pupil plane.

4. The imaging optics of claim 1, wherein the plurality of mirrors comprises a third mirror in the path of the imaging light after the object field, and the pupil plane is between the second and third mirrors in the path of the imaging light after the object field.

5. The imaging optics of claim 1, wherein the second mirror in the path of the imaging light is further away from the object plane than is the fourth mirror in the path of the imaging light.

6. The imaging optics of claim 1, wherein two intermediate image planes are in the path of the imaging light between the object field and the image field.

7. The imaging optics of claim 6, wherein the plurality of mirrors comprises a third mirror in the path of the imaging light after the object field, and the first intermediate image plane is between the second mirror and the third mirror in the path of the imaging light.

8. The imaging optics of claim 6, wherein the plurality of mirrors comprises a sixth mirror in the path of the imaging light after the object field, and the second intermediate image plane is between the sixth mirror and a seventh mirror in the path of the imaging light.

9. The imaging optics of claim 6, wherein the imaging optics is a microlithography projection optics.

10. The imaging optics of claim 1, wherein the imaging optics has a central pupil obscuration of at most 30% relative to a diameter of a beam bundle of the imaging light in the pupil plane.

11. The imaging optics of claim 1 wherein the imaging optics has a maximum wavefront error of 70 m.

12. The imaging optics of claim 1, wherein the imaging optics has a maximum distortion of 10 nm.

13. The imaging optics of claim 1, comprising: a first part objective comprising mirrors, all mirrors in the first part objective being without through-openings configured to pass the imaging light; and a second part objective comprising at least one mirror with a through-opening configured to pass the imaging light.

14. The imaging optics of claim 1, wherein the imaging optics is a catoptric optical system.

15. The imaging optics of claim 1, wherein the imaging optics is a microlithography projection optics.

16. An optical system, comprising: a microlithography projection optics having an object field in an object plane and an image field in an image plane; and an illumination optics configured to guide illumination light toward the object field of the microlithography projection optics, wherein: the microlithography projection optics comprises at least six mirrors configured to image the object field in the object plane of the microlithography projection optics into the image field in the image plane of the microlithography projection optics along a path of imaging light; chief rays of the imaging light, which emanate from points of the object field which are spaced apart from one another, have a mutually diverging beam course; of the at least six mirrors, a mirror has a through-opening which is the first through-opening: a) after the object field along the path of the imaging light; and b) configured to pass the imaging light along the path of the imaging light; a pupil is located in a pupil plane in the path of the imaging light between the object field and the first through-opening; the imaging light passes once through the pupil along the path of the imaging light; an obscuration stop is arranged in the pupil plane to provide central shading of an exit pupil of the imaging optics; a first imaging part beam is directly after a second mirror in the path of the imaging light after the object field; a second imaging part beam is directly after a fourth mirror in the path of the imaging light after the object field; and the first and second imaging parts intersect each other in an intersection region.

17. The optical system of claim 16, further comprising a light source configured to provide the imaging light.

18. The optical system of claim 17, wherein the imaging light has a wavelength of between 5 and 30 nm.

19. A method, comprising: providing an optical system according to claim 16; and using the optical system to project a structure of a reticle onto a light-sensitive layer of a wafer to provide an exposed light-sensitive layer on the wafer.

20. The method of claim 19, further comprising developing the exposed light-sensitive layer on the wafer to provide a microstructured component or a nanostructured component.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the disclosure will be described in more detail below with the aid of the drawings, in which:

(2) FIG. 1 schematically shows a projection exposure installation for EUV microlithography;

(3) FIG. 2 shows a configuration of an imaging optics, which can be used as a projection objective in the projection exposure installation according to FIG. 1, the imaging beam path being shown for the chief rays (virtually) and for the upper and lower coma beam of three selected field points;

(4) FIG. 3 shows the imaging optics according to FIG. 2, wherein the real imaging beam path is shown for a variety of individual beams;

(5) FIG. 4 shows, in a view similar to FIG. 2, a further configuration of an imaging optics, which can be used as a projection objective in a projection exposure installation according to FIG. 1; and

(6) FIG. 5 shows the imaging optics according to FIG. 4, in a view similar to FIG. 3.

DETAILED DESCRIPTION

(7) A projection exposure installation 1 for microlithography has a light source 2 for illumination light or imaging light 3. The light source 2 is an EUV light source, which produces light in a wavelength range of, for example, between 5 nm and 30 nm, in particular between 5 nm and 15 nm. The light source 2 may, in particular, be a light source with a wavelength of 6.9 nm or else a light source with a central wavelength of 13.5 nm. Other EUV wavelengths are also possible. In general, any wavelengths, for example, visible wavelengths or else other wavelengths, which can be used in microlithography and are available for suitable laser light sources and/or LED light sources (for example 365 nm, 248 nm, 193 nm, 157 nm, 129 nm, 109 nm) are even possible for the illumination light 3 guided in the projection exposure installation 1. A beam path of the illumination light 3 is shown highly schematically in FIG. 1.

(8) An illumination optics 6 is used to guide the illumination light 3 from the light source 2 toward an object field 4 in an object plane 5. Using a projection optics or imaging optics 7, the object field 4 is imaged in an image field 8 in an image plane 9 at a predetermined reduction scale. The image field 8 has an extent of 13 mm in the x-direction and an extent of 1 mm in the y-direction. One of the embodiments shown in FIG. 2ff. can be used for the projection optics 7. The projection optics 7 according to FIG. 2 reduces by a factor of 8. Other reduction scales are also possible, for example 4x, 5x or else reduction scales which are greater than 8. An imaging scale of 8 is suitable, in particular, for the illumination light 3 with an EUV wavelength as an angle of incidence on the object side on a reflection mask 10 can thereby be kept small. An imaging scale of 8 does not lead to using very large masks either. The image plane 9 in the projection optics 7 in the configurations according to FIG. 2ff. is arranged parallel to the object plane 5. A detail of the reflection mask 10 coinciding with the object field 4 is imaged here, and is also called a reticle.

(9) The imaging by the projection optics 7 takes place on the surface of a substrate 11 in the form of a wafer, which is carried by a substrate holder 12. Shown schematically in FIG. 1 between the reticle 10 and the projection optics 7 is a beam bundle 13, which runs therein, of the illumination light 3, and a beam bundle 14 of illumination light 3 issuing from the projection optics 7 between the projection optics 7 and the substrate 11. A numerical aperture, on the image field side, of the projection optics 7 in the configuration according to FIG. 2 is 0.50. This is not depicted to scale in FIG. 1.

(10) To facilitate the description of the projection exposure installation 1 and the various configurations of the projection optics 7, a Cartesian xyz-coordinate system is given in the drawing, from which the respective position relationship of the components shown in the figures is produced. In FIG. 1, the x-direction runs perpendicularly to the drawing plane and into it. The y-direction extends to the right and the z-direction extends downward.

(11) The projection exposure installation 1 is of the scanner type. Both the reticle 10 and the substrate 11 are scanned during operation of the projection exposure installation 1 in the y-direction. A stepper type of the projection exposure installation 1, in which a stepwise displacement of the reticle 10 and substrate 11 takes place in the y-direction between individual exposures of the substrate 11, is also possible.

(12) FIGS. 2 and 3 show the optical design of a first embodiment of the projection optics 7. The beam path of three respective individual beams 15, which emanate from five object field points spaced apart from one another in FIG. 2 in the y-direction, is shown in FIG. 2. The three individual beams 15, which belong to one of these five object field points, are in each case associated with three different illumination directions for the two object field points. Chief rays or main beams 16, which extend through the centre of a pupil in a pupil plane 17 of the projection optics 7, are drawn in FIG. 2 only for graphical reasons as these are not real, but virtual imaging beam paths of the projection optics 7 because of the central pupil obscuration. These chief rays 16 firstly run divergently, starting from the object plane 5. This will also be called the negative back focus of an entry pupil of the projection optics 7 below. The entry pupil of the projection optics 7 according to FIGS. 2 and 3 does not lie within the projection optics 7, but in the beam path in front of the object plane 5. This makes it possible, for example, to arrange a pupil component of the illumination optics 6 in the entry pupil of the projection optics 7 in the beam path in front of the projection optics 7, without further imaging optical components having to be present between this pupil component and the object plane 5. A mirror acting merely to deflect beams, for example a mirror for grazing incidence, may also be arranged between the pupil component and the object plane 5, for example, in this case of the arrangement of a pupil component of the illumination optics 6 in the entry pupil of the projection optics 7, without intermediate imaging optical components.

(13) The projection optics 7 according to FIGS. 2 and 3 has a total of eight mirrors, which are consecutively numbered in the order of the beam path of the individual beams 15, proceeding from the object field 4, by M1 to M8. FIGS. 2 and 3 show the calculated reflection faces of the mirrors M1 to M8. Only a small region of these calculated reflection faces is used, as can be seen in the view of FIG. 2. Only this actually used region of the reflection faces is present in the real mirrors M1 to M8. These useful reflection faces are carried in a known manner by mirror bodies.

(14) The optical data of the projection optics 7 according to FIGS. 2 and 3 are shown below with the aid of two tables. The first table shows in the column Radius the respective radius of curvature of the mirrors M1 to M8. The third column (Thickness) describes the spacing, proceeding from the object plane 5, in each case from the following surface in the z-direction.

(15) The second table describes the precise surface form of the reflection faces of mirrors M1 to M8, wherein the constants K and A to G are to be inserted in the following equation for the arrow height z:

(16) $z\left(h\right)==\frac{{\mathrm{ch}}^2}{1+\mathrm{SQRT}\left\{1-\left(1+K\right)c^2{h}^2\right\}}++A{h}^4+{\mathrm{Bh}}^6+{\mathrm{Ch}}^8+{\mathrm{Dh}}^{10}+{\mathrm{Eh}}^{12}+{\mathrm{Fh}}^{14}+{\mathrm{Gh}}^{16}$

(17) h is the spacing here from an optical axis 18 of the projection optics 7. h.sup.2=x.sup.2+y.sup.2 thus applies. The reciprocal value of Radius is inserted for c.

(18) TABLE-US-00001 Radius Processing Surface (1/c) Thickness mode Object INFINITE 543.757 plane M1 449.236 211.269 REFL M2 381.481 71.127 REFL STOP INFINITE 678.094 M3 1293.655 878.647 REFL M4 2575.518 1103.024 REFL M5 340.443 577.829 REFL M6 659.115 1250.269 REFL M7 2394.266 642.054 REFL M8 817.414 663.527 REFL Image INFINITE 0.000 plane Surface K A B C M1 0.000000E+00 2.460293E10 1.269784E15 2.803303E21 M2 0.000000E+00 6.386979E08 2.318025E12 6.696092E17 M3 0.000000E+00 9.799571E11 1.514496E15 1.015677E20 M4 0.000000E+00 1.251897E11 1.029828E15 6.301813E21 M5 0.000000E+00 2.958312E08 5.028056E13 8.066658E18 M6 0.000000E+00 2.017168E11 2.275527E17 9.166209E23 M7 0.000000E+00 1.252401E09 4.102615E15 2.060274E20 M8 0.000000E+00 2.416984E11 5.199686E17 8.459189E23 Surface D E F G M1 1.652701E25 0.000000E+00 0.000000E+00 0.000000E+00 M2 4.001704E21 0.000000E+00 0.000000E+00 0.000000E+00 M3 2.679237E26 0.000000E+00 0.000000E+00 0.000000E+00 M4 1.577707E26 0.000000E+00 0.000000E+00 0.000000E+00 M5 4.143857E21 0.000000E+00 0.000000E+00 0.000000E+00 M6 5.861325E28 0.000000E+00 0.000000E+00 0.000000E+00 M7 1.022964E25 1.423250E30 0.000000E+00 0.000000E+00 M8 1.424018E28 1.255450E34 7.241285E40 0.000000E+00

(19) The object field 4 and the image field 8 are arranged in a ring segment-shape around the optical axis 18. The mirrors M1 to M4 are used approximately in a ring segment-shaped manner and off-axis in relation to the optical axis 18. The used optical reflection face of the mirrors M1 to M4 is thus remote from the optical axis 18. The object field 4 and the image field 8 are arranged spaced apart from the optical axis 18. The reflection faces of all the mirrors M1 to M8 are rotationally symmetrical according to the above equation for the arrow height z in relation to the optical axis 18. Alternatively, it is possible for the mirrors M1 to M8 to have deviations from a rotationally symmetrical shape.

(20) The mirrors M1, M3, M4, M6 and M8 are configured as concave mirrors. The mirrors M2, M5 and M7 are configured as convex mirrors.

(21) The mirrors M1 and M6 and M5 and M8 are arranged back-to-back with regard to the orientation of their reflection faces.

(22) The optically used regions of the mirrors M1 to M6 have no through-opening for the passage of imaging light, in other words are not obscured.

(23) In the imaging beam path between the mirrors M6 and M7, the individual beams 15 pass through a through-opening 19 in the mirror M8. The mirror M8 around the through-opening 19 is used. The mirror M8 is thus an obscured mirror. Apart from the mirror M8, the mirror M7 is also obscured and also in each case has a virtually central through-opening 19. The through-opening 19 of the mirror M7 is passed through by the imaging light 3 in the imaging beam path between the mirror M8 and the image field 8, shortly before reaching the image field 8.

(24) The pupil plane 17 is located in the imaging beam path in the projection optics 7 between the mirrors M2 and M3. The pupil plane 17 is located in the imaging beam path between the object field 4 and the through-opening 19 of the mirror M8. Arranged in the pupil plane 17 is an obscuration stop 20 for central shading of a pupil of the projection optics 7. The pupil in the pupil plane 17 is arranged mechanically accessibly for this purpose. The obscuration stop 20 shades that central region of the imaging light 3 in the pupil plane 17 which, because of the through-openings 19, does not contribute to the imaging of the object field 4. An obscuration stop of this type may be held mechanically, for example, by thin metal struts, which block a minimal part of the imaging light (cf FIG. 7d in US 2006/0232867 A1). A further alternative for a mechanical holder is shown in FIG. 7b from the application US 2006/0232867 A1.

(25) The obscuration stop 20 is only indicated in FIGS. 2 and 3. An optical effect of the obscuration stop 20 is illustrated by FIG. 3, in which the real imaging beam path through the projection optics 7 is shown with the aid of a selected variety of the individual beams 15. It can clearly be seen in FIG. 3 that a central region of the variety of the individual beams 15 is shaded in the imaging beam path around the obscuration stop 20. This central shading can also be seen in the region of the further pupil planes in the imaging beam path between the object field 4 and the image field 8. One of these further pupil planes, the pupil plane 21, is located in the imaging beam path between the mirrors M5 and M6. The central shading effect of the obscuration stop 20 in the region of an exit pupil of the projection optics 7 can furthermore be seen in the region of the imaging beam path in the mirrors M7 and M8.

(26) A first intermediate image plane 22 of the projection optics 7 is located in the imaging beam path between the mirrors M2 and M3 after the pupil plane 17. Between the pupil plane 21 and the exit pupil of the projection optics 7, a second intermediate image plane 23 is located in the imaging beam path between the mirrors M6 and M7. The second intermediate image is located in the second intermediate image plane 23 closely adjacent to the through-opening 19 in the mirror M8. As a result, it is possible to make this through-opening 19 very small in comparison to the used reflection face of the mirror M8. A central pupil obscuration in the projection optics 7 is 24% of the diameter of the entire beam bundle of imaging light 3 in the pupil plane 17. Accordingly, only 5.76% of the cross sectional area of the beam bundle of imaging light 3 is shaded there.

(27) A first imaging part beam 24 in the projection optics 7 runs between the mirrors M2 and M3. A second imaging part beam 25 runs between the mirrors M4 and M5. These two imaging part beams 24, 25 intersect one another in an intersection region 26. This intersection region is spatially adjacent to the mirror M6.

(28) In addition to the obscuration stop 20, an aperture stop can also be arranged in the pupil plane 17 to predetermine an outer form of the pupil of the projection optics 7. The obscuration stop 20 may, in particular, additionally have the function of an aperture stop of this type.

(29) The obscuration stop 20 and the aperture stop also arranged in the pupil plane 17 are in each case a stop which is run through precisely once by the imaging beam path.

(30) The second mirror M2 in the imaging beam path is further away from the object plane 5 than the fourth mirror M4 in the imaging beam path. As a result, provided between the second mirror M2 and the object field 4 is an installation space 27 which is shown by dashed lines in FIG. 2, in which, for example, a mirror of the illumination optics 6, in particular a grazing-incidence mirror can be arranged. A cylinder can be written into the installation space 27, the rotational axis of symmetry of which coincides with the optical axis 18. A z-extent of this installation space cylinder is more than 16% of the entire installation length of the projection optics 7, in other words the spacing between the object plane 5 and the image plane 9. A radius of this installation space cylinder has a y-dimension that corresponds to the y-spacing of the object field 4 from the optical axis 18.

(31) The projection optics 7 has a correction of the wavefront of about 13 m at a wavelength of the imaging light of 13 nm.

(32) The projection optics 7 has a maximum distortion of 5 nm.

(33) The projection optics 7 is constructed from a first, unobscured part objective with the mirrors M1 to M6, in other words with mirrors without a through-opening for the imaging light 3, and a second part objective with the mirrors M7, M8 with the through-openings 19 for the imaging light 3.

(34) The projection optics 7 is a catoptric optical system, in other words an optical system exclusively configured with mirrors M1, M8.

(35) FIGS. 4 and 5 show a further embodiment of a projection optics 28, which can be used instead of the projection optics 7 in the projection exposure installation 1. Components and details corresponding to those which have already been described with reference to FIGS. 1 to 3 have the same reference numerals and are not discussed again in detail.

(36) The optical data of the projection optics 28 are shown below with the aid of two tables, which with regard to the structure, correspond to the Tables for the projection optics 7.

(37) TABLE-US-00002 Surface Radius (1/c) Thickness Processing mode Object plane INFINITE 613.559 M1 406.659 187.587 REFL M2 422.395 48.314 REFL STOP INFINITE 609.274 M3 1159.498 861.821 REFL M4 2575.518 1085.195 REFL M5 277.079 573.822 REFL M6 656.425 1245.415 REFL M7 2489.088 641.593 REFL M8 817.507 663.067 REFL Image plane INFINITE 0.000 Surface K A B C D M1 0.000000E+00 4.087938E10 2.211846E15 2.636371E20 4.868396E26 M2 0.000000E+00 8.742259E08 4.355110E12 3.666477E18 9.255361E21 M3 0.000000E+00 2.698572E11 1.517420E16 1.014742E21 3.986399E27 M4 0.000000E+00 1.486765E10 2.068756E16 8.454470E23 3.789880E27 M5 0.000000E+00 2.357073E08 1.037369E13 4.242200E17 3.626310E21 M6 0.000000E+00 1.218200E10 3.610597E16 8.927849E22 1.195427E27 M7 0.000000E+00 9.462055E10 2.671043E15 1.215091E20 6.632766E26 M8 0.000000E+00 1.444201E11 3.962539E17 7.092908E23 9.439764E29 Surface E F G H J M1 1.965381E30 5.703202E35 0.000000E+00 0.000000E+00 0.000000E+00 M2 3.701762E28 5.285209E29 0.000000E+00 0.000000E+00 0.000000E+00 M3 8.916733E33 8.213059E39 0.000000E+00 0.000000E+00 0.000000E+00 M4 2.834304E32 1.746649E38 0.000000E+00 0.000000E+00 0.000000E+00 M5 3.431867E27 1.134085E29 0.000000E+00 0.000000E+00 0.000000E+00 M6 2.779912E32 1.010642E37 0.000000E+00 0.000000E+00 0.000000E+00 M7 1.448402E31 5.788876E36 0.000000E+00 0.000000E+00 0.000000E+00 M8 3.225231E34 4.237434E40 1.980412E45 0.000000E+00 0.000000E+00

(38) In the projection optics 28, the first intermediate image plane 22 in the imaging beam path is closer to the pupil plane 17 than in the projection optics 7.

(39) The projection optics 28 has a numerical aperture on the image side of NA=0.60.

(40) In the projection optics 28, the correction of the wavefront is about 16 m. The projection optics 28 has a maximum distortion of 0.7 nm.

(41) A central pupil obscuration in the projection optics 28, for example in the pupil plane 17, is 23% of the diameter of the beam bundle of imaging light 3 and correspondingly 5.29% of the cross sectional area there of the beam bundle of imaging light 3.

(42) Imaging part beams adjacent to the beam bundle of imaging light 3 in the pupil plane 17 are spaced so far apart form the beam bundle of imaging light 3 passing through the pupil plane 17 that an aperture stop of this type can be arranged mechanically in the pupil plane 17 without the aperture stop obstructing the adjacent imaging part beams.

(43) The installation space cylinder which can be written into the installation space 27, in the projection optics 28, has a z-extent, which is about 18% of the total installation length of the projection optics 28 between the object plane 5 and the image plane 9.

(44) To produce a microstructured or nanostructured component, the projection exposure installation 1 is used as follows: firstly, the reflection mask 10 or the reticle and the substrate or the wafer 11 are provided. A structure on the reticle 10 is then projected onto a light-sensitive layer of the wafer 11 with the aid of the projection exposure installation. By developing the light-sensitive layer, a microstructure or nanostructure is then produced on the wafer 11 and therefore the microstructured component is produced.