An euv optical projection system includes at least six reflecting surfaces for imaging an object (OB) on an image (IM). The system is preferably configured to form an intermediate image (IMI) along an optical path from the object (OB) to the image (IM) between a secondary mirror (M2) and a tertiary mirror (M3), such that a primary mirror (M1) and the secondary mirror (M2) form a first optical group (G1) and the tertiary mirror (M3), a fourth mirror (M4), a fifth mirror (M5) and a sixth mirror (M6) form a second optical group (G2). The system also preferably includes an aperture stop (APE) located along the optical path from the object (OB) to the image (IM) between the primary mirror (M1) and the secondary mirror (M2). The secondary mirror (M2) is preferably concave, and the tertiary mirror (M3) is preferably convex. Each of the six reflecting surfaces preferably receives a chief ray (CR) from a central field point at an incidence angle of less than substantially 15°. The system preferably has a numerical aperture greater than 0.18 at the image (IM). The system is preferably configured such that a chief ray (CR) converges toward the optical axis (OA) while propagating between the secondary mirror (M2) and the tertiary mirror (M3).
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1. An euv optical projection system, comprising:
a primary mirror, a secondary mirror, a tertiary mirror, a fourth mirror, a fifth mirror and a sixth mirror, for imaging an object on an image,
wherein said system is configured to form an intermediate image along an optical path from the object to the image between said secondary mirror and said tertiary mirror,
wherein said secondary mirror is concave,
wherein said tertiary mirror is convex, and
wherein said system has a numerical aperture greater than 0.18 at the image.
25. An euv optical projection system, comprising:
a primary mirror, a secondary mirror, a tertiary mirror, a fourth mirror, a fifth mirror and a sixth mirror, for imaging an object on an image; and
an aperture stop located along an optical path from said object to said image between said primary mirror and said secondary mirror,
wherein said secondary mirror is concave,
wherein said tertiary mirror is convex,
wherein said aperture stop is not located on said primary mirror and said aperture stop is not located on said secondary mirror, and
wherein said system has a numerical aperture greater than 0.18 at the image.
16. An euv optical projection system, comprising:
a primary mirror, a secondary mirror, a tertiary mirror, a fourth mirror, a fifth mirror and a sixth mirror, for imaging an object on an image,
wherein said system is configured to form an intermediate image along an optical path from the object to the image between said secondary mirror and said tertiary mirror,
wherein each of said primary mirror, said secondary mirror, said tertiary mirror, said fourth mirror, said fifth mirror and said sixth mirror receives a chief ray from a central field point at an incidence angle of less than about 15°, and
wherein said system has a numerical aperture greater than 0.18 at the image.
28. An euv optical projection system, comprising:
a primary mirror, a secondary mirror, a tertiary mirror, a fourth mirror, a fifth mirror and a sixth mirror, for imaging an object on an image, and
an aperture stop located along an optical path from said object to said image between said primary mirror and said secondary mirror,
wherein said system is configured such that a chief ray from a central field point converges toward said optical axis while propagating between said secondary mirror and said tertiary mirror,
wherein said aperture stop is not located on said primary mirror, and said aperture stop is not located on said secondary mirror, and
wherein said system has a numerical aperture greater than 0.18 at the image.
2. The system according to
3. The system according to
4. The system according to
an optical axis between an object plane and an image plane,
wherein said system is further configured such that a chief ray from a central field point converges toward said optical axis while propagating between said secondary mirror and said tertiary mirror.
5. The system according to
an optical axis between an object plane and an image plane,
wherein said system is further configured such that a chief ray from a central field point propagates approximately parallel to said optical axis while propagating between said secondary mirror and said tertiary mirror.
6. The system according to
7. The system according to
an optical axis between a object plane and a image plane,
wherein said system is further configured such that a chief ray from a central field point diverges away from said optical axis while propagating between said secondary mirror and said tertiary mirror.
8. The system according to
9. The system according to
10. The system according to
wherein each of said primary mirror, said secondary mirror, said tertiary mirror, said fourth mirror, said fifth mirror, and said sixth mirror is disposed between said object and said image, and
wherein said object and said image are separated from one another by a physical distance of less than or equal to about 1500 mm.
11. The system according to
wherein each of said primary mirror, said secondary mirror, said tertiary mirror, said fourth mirror, said fifth mirror, and said sixth mirror is disposed between said object and said image, and
wherein said object and said image are separated from one another by a physical distance of less than or equal to about 1200 mm.
12. The system according to
13. The system according to
14. The system according to
15. The system according to
17. The system according to
18. The system according to
an optical axis between an object plane and an image plane,
wherein said system is further configured such that a chief ray from a central field point converges toward said optical axis while propagating between said secondary mirror and said tertiary mirror.
19. The system according to
20. The system according to
an optical axis between a object plane and a image plane,
wherein said system is further configured such that a chief ray from a central field point diverges away from said optical axis while propagating between said secondary mirror and said tertiary mirror.
21. The system according to
22. The system according
wherein said secondary mirror is concave, and
wherein said tertiary mirror is convex.
23. The system according to
wherein each of said primary mirror, said secondary mirror, said tertiary mirror, said fourth mirror, said fifth mirror, and said sixth mirror is disposed between said object and said image, and
wherein said object and said image are separated from one another by a physical distance of less than or equal to about 1500 mm.
24. The system according to
wherein each of said primary mirror, said secondary mirror, said tertiary mirror, said fourth mirror, said fifth mirror, and said sixth mirror is disposed between said object and said image, and
wherein said object and said image are separated from one another by a physical distance of less than or equal to about 1200 mm.
26. The system according to
27. The system according to
29. The system according to
30. The system of
31. The system of
wherein said primary mirror and said secondary mirror form a first optical group, and
wherein said tertiary mirror, said fourth mirror, said fifth mirror and said sixth mirror for a second optical group.
32. The system of
33. The system of
wherein said primary mirror and said secondary mirror form a first optical group, and
wherein said tertiary mirror, said fourth mirror, said fifth mirror and said sixth mirror for a second optical group.
34. The system of
35. The system of
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The present application is
In a preferred embodiment, the peak-to-valley distance A of the aspheres is limited with respect to the best fitting sphere of the off-axis segments of all mirrors by:
A≦12 μm−64 μm (0.25−NA)−0.3 μm/mm (2 mm−W).
According to yet another embodiment, a projection objective that includes six mirrors is characterized by an image-side numerical aperture NA≧10.15 and an image-side width of the arc-shaped field W≧1 mm, and the angles of incidence AOI are limited for all rays of the light bundle impinging a physical mirror surface on all six mirrors S1, S2, S3, S4, S5, S6 by:
AOI≦23°−35°(0.25−NA)−0.2°/mm (2 mm−W).
wherein the angles of incidence AOI refer to the angle between the incident ray and the normal to the physical mirror surface at the point of incidence. The largest angle of any incident bundle of light rays occurring on any of the mirrors is always given by the angle of a bundle-limiting ray.
Preferably, an embodiment of the invention would encompass all three of the above aspects, e.g., an embodiment in which the free optical working distance would be more than 50 mm at NA=0.20 and the peak-to-valley deviation of the aspheres, as well as the angles of incidence, would lie in the regions defined above.
The asphericities herein refer to the peak-to-valley (PV) deviation, A, of the aspherical surfaces with respect to the best fitting sphere of the physical mirror surface of an specific mirror. The physical mirror surface of a specific mirror is also denoted as the used area of this specific mirror. The aspherical surfaces are approximated in the examples by using a sphere. The sphere has a center on the figure axis vertex of the mirror. The sphere intersects the asphere in the upper and lower endpoint of the used area in the meridian section. The data regarding the angles of incidence always refer to the angle between the incident ray and the normal to the physical mirror surface at the point of incidence. The largest angle of any incident bundle of light rays occurring on any of the physical mirror surfaces is always given by the angle of a bundle-limiting ray. The used diameter or the diameter of the physical mirror surface will be defined here and below as the envelope circle diameter of the physical mirror surface or the used area of a mirror, which is generally not circular.
In a preferred embodiment the free working distance is 60 mm.
The objective can be used not only in the EUV, but also at other wavelengths, without deviating from the scope of the invention. In any respect, however, to avoid degradation of image quality, especially degradation due to central shading, the mirrors of the projection objectives should be arranged so that the light path of the bundle of light rays traveling from the object plane to the image plane is obscuration-free. Furthermore, to provide easy mounting and adjusting of the system, the physical mirror surfaces have a rotational symmetry to a principal axis (PA). Moreover, to have a compact design with an accessible aperture and to establish an obscuration-free light path of the bundle of light rays traveling from the object plane to the image plane, the projection objective device is designed in such a way that an intermediate image of the object situated in the object plane is formed after the fourth mirror. In such systems, it is possible that the aperture stop is situated in the front, low-aperture objective part, with a pupil plane conjugated to the aperture stop imaged in the focal plane of the last mirror. Such a system ensures telecentricity in the image plane.
In an preferred embodiment of the invention, the aperture stop is freely accessible and arranged in the light path from the object plane to the image plane between the second and third mirror. Good accessibility of the aperture stop is ensured when the ratio of the distance between the first and third mirror to the distance between the first and second mirror lies in the range of:
0.5<S1S3/S1S2<2.
As defined for the free working distance in general a distance between two mirrors is the distance of the vertices of the surfaces of these mirrors.
Furthermore, in order to prevent vignetting of the light running from the third to the fourth mirror, by the aperture stop arranged between the second and third mirror, the ratio of the distance between the second mirror and aperture stop to the distance between the third mirror and the aperture stop lies in the range:
0.5<S2 aperture/(S3 aperture)<2.
In such a system, the angles of incidence on the physical mirror surfaces in the front part of the objective are reduced.
An aperture stop which physically lies between the second mirror, S2, and the first mirror, S1, must be formed at least partially as a narrow ring in order to avoid clipping of light moving from S1 to S2. In such a design, there is a danger that undesirable direct light or light reflected on S1 and S2, will pass outside the aperture ring and reach the image plane and thus the wafer. However, if the aperture stop is placed in the light path between the second and third mirror and physically close to the first mirror (which can be easily achieved mechanically), an efficient masking of this undesired light is possible. The aperture stop can be designed both as an opening in the first mirror or an opening which is arranged behind the first mirror.
In another embodiment of the invention, the aperture stop is arranged on or near the second mirror. Arrangement of the aperture on a mirror has the advantage that it is easier to manufacture.
In order to ensure an obscuration-free ray path with simultaneously low angles of incidence, the ratio of the distance between the first and third mirrors (S1S3) to the distance between the first and second mirrors (S1S2) lies in the range:
0.3≦S1S3/S1S2≦2.0,
while the ratio of the distance between the second and third mirrors (S2S3) to the distance between the third and fourth mirrors (S3S4) lies in the range:
0.7≦S2S3/S3S4≦1.4.
In order to be able to make the necessary corrections of imaging errors in the six-mirror systems, in a preferred embodiment, all six mirrors are designed to be aspherical. However, an alternative embodiment whereby at most five mirrors are aspherical can simplify the manufacturing, because it is then possible to design one mirror, preferably the largest mirror, i.e., the quaternary mirror, in the form of a spherical mirror. Moreover, it is preferred that the second to sixth mirror be in a concave-convex-concave-convex-concave sequence.
In order to achieve a resolution of at least 50 nm, the design part of the rms wavefront section of the system should be at most 0.07λ and preferably 0.03λ.
Advantageously, in the embodiments of the invention, the objectives are always telecentric on the image-side.
In projection systems which are operated with a reflection mask, a telecentric light path on the object-side is not possible without illumination through a beam splitter which reduces the transmission strongly. One such device is known from JP 95 28 31 16.
In systems with transmission mask, the projection objective can be telecentric on the object side. In these embodiments, the first mirror is preferably concave.
The telecentericity error in the image plane, where the the wafer is situated should not exceed 10 mrad and is typically between 5 mrad and 2 mrad, with 2 mrad being preferred. This ensures that changes of the imaging ratio remain within tolerable limits over the depth of focus.
In an preferred embodiments of the invention, the six mirror objective could comprise a field mirror, a reducing three-mirror subsystem and a two-mirror subsystem.
In addition to the projection objective also a projection exposure apparatus is shown, that includes at least a projection objective device. In a first embodiment, the projection exposure apparatus has a reflection mask, while in an alternative embodiment, it has a transmission mask. Preferably, the projection exposure apparatus includes an illumination device for illuminating an off-axis arc-shaped field and the system is designed as an arc-shaped field scanner. Furthermore, the secant length of the scan slit is at least 26 mm and the ring width is greater than 0.5 mm.
The invention will be described below with the aid of the drawings as examples.
What follows is a cite list of references which, in addition to that which is described in the background and brief summary of the invention above, are hereby incorporated by reference into the detailed description of the preferred embodiments, as disclosing alternative embodiments of elements or features of the preferred embodiment not otherwise set forth in detail below. A single one or a combination of two or more of these references may be consulted to obtain a variation of the preferred embodiments described below. Further patent, patent application and non-patent references, and discussion thereof, cited in the background and/or elsewhere herein are also incorporated by reference into the detailed description of the preferred embodiments with the same effect as just described with respect to the following references:
U.S. Pat. Nos. 5,063,586, 5,071,240, 5,078,502, 5,153,898, 5,212,588, 5,220,590, 5,315,629, 5,353,322, 5,410,434, 5,686,728, 5,805,365, 5,815,310, 5,956,192, 5,973,826, 6,033,079, 6,014,252, 6,188,513, 6,183,095, 6,072,852, 6,142,641, 6,226,346, 6,255,661 and 6,262,836;
European patent applications no. 0 816 892 A1 and 0 779 528 A; and
“Design of Reflective Relay for Soft X-Ray Lithography”, J. M. Rodgers, T. E. Jewell, International Lens Design Conference, 1990;
“Reflective Systems design Study for Soft X-ray Projection Lithography”, T. E. Jewell, J. M. Rodgers, and K. P. Thompson, J. Vac. Sci. Technol., November/December 1990.
“Optical System Design Issues in Development of Projection Camera for EUV Lithography”, T. E. Jewell, SPIE Volume 2437, pages 340-347;
“Ring-Field EUVL Camera with Large Etendu”, W. C. Sweatt, OSA TOPS on Extreme Ultraviolet Lithography, 1996; and
“Phase Shifting Diffraction Interferometry for Measuring Extreme Ultraviolet Optics”, G. E. Sommargaren, OSA TOPS on Extreme Ultraviolet Lithography, 1996;
“EUV Optical Design for a 100 nm CD Imaging System”, D. W. Sweeney, R. Hudyma, H. N. Chapman, and D. Shafer, SPIE Volume 3331, pages 2-10.
Three specific preferred embodiments relating to this optical projection system are described.
First Preferred Embodiment:
Although there are many ways to characterize this optical system, one convenient way is to break the system into two groups G1 and G2. Starting at the object OB, the first group G1 is comprised the concave mirror pair M1 and M2. This group forms an intermediate image IMI at a magnification of about −0.8× between mirror M2 and mirror M3. The remaining four mirrors (convex mirror M3, concave mirror M4, convex mirror M5 and concave mirror M6) comprise the second imaging or relay group G2. This second group G2 works at a magnification of approximately −0.3×, resulting in 4× reduction (the reduction ratio is the inverse of the absolute value of the optical magnification) of the object OB at the image IM.
The optical prescription of the first embodiment of
where h is the radial coordinate; c is the vertex curvature of the surface (1/R); and A, B, C, D, and E are the 4th, 6th, 8th, 10th, and 12th order deformation coefficients, respectively. These coefficients are listed in Table 2.
The optical system of this first preferred embodiment is designed to project a ring field format that is illuminated with extremely ultraviolet (EUV) or soft X-ray radiation. The numerical aperture NAO at the object OB is 0.050 radians; at a 4× reduction this corresponds to a numerical aperture NA of 0.20 at the image IM. The ring field 21 at the object OB is shown with FIG. 2. It is centered at 118 mm from the optical axis, which contains the vertex of each of the aspheric mirrors. This annular field extends from 114 mm to 122 mm forming an arcuate slit with a width 23 of 8 mm. The extent 25 of the ring field 21 perpendicular to the scan direction 27 becomes 104 mm. The central field point is denoted with the reference sign 29. At 4× reduction, this ring field becomes 2.0 mm wide in the scan direction at the image.
As a result of the distribution of optical power and location of the aperture stop APE, the incidence angles are well controlled so that the design is compatible with EUV or soft X-ray multilayer coatings. As measured by the chief ray CR from the central field point 29, this system exhibits very low incidence angles ranging from 2.9° to 12.5°. The chief ray incidence angles for the chief ray CR from the central field point 29 are: Object: 5.2°; M1: 6.5°; M2: 5.0°; M3: 12.5°; M4: 5.6°, M5: 8.6°, and M6: 2.9°. These low incidence angles are a key enabling element for EUV lithography since (1) they minimize the multilayer induced amplitude and phase errors that have an adverse impact to lithographic performance and (2) enable simplified coating designs that do not rely heavily on the use of laterally graded coating profiles. With poor design (i.e., failure to minimize these incidence angles), these multilayer-induced amplitude and phase errors can lead to critical dimension (CD) errors that are easily greater than 20% of the nominal linewidth, making the system unusable for production applications.
Besides the low incidence angles, a preferred system further enables EUV lithography by utilizing mirrors with low peak aspheric departure. The maximum peak departure, contained on mirror M1, is 25.0 μm. The other mirrors have low-risk aspheres with departures that range from 0.5 μm to 14 μm. The low aspheric departures of the mirror surfaces facilitate visible light metrology testing without a null lens or Computer Generated Hologram CGH, resulting in surface figure testing to a high degree of accuracy. An aspheric mirror with a very large peak departure is unproducible because it cannot be measured to the required accuracy to realize lithographic performance.
Table 3 summarizes the performance of the PPNPNP configuration of FIG. 1. The table demonstrates that this first preferred embodiment is able to achieve lithographic performance with a resolution on the order of 30 nm (assuming a k1-factor of approximately 0.5). The location of the aperture stop APE is selected so that the third order astigmatism contribution from the strong concave secondary mirror M2 is made very small. The strongly undercorrected astigmatic contribution from the primary mirror M1 comes from the aspheric departure on M1 and is balanced by the M3/M4 combination. Considering the system without any aspheres, the location of the aperture stop APE also effectively balances the third-order coma and distortion contributions from the primary mirror M1 and secondary mirror M2. A hyperbolic profile is added to the primary mirror M1 in such a way as to create a large undercorrected spherical contribution, coma contribution, and astigmatism contribution, thus promoting good aberration correction allowing the residual wavefront error (departure from the ideal reference sphere) to remain exceedingly small. In fact, aberration correction and resulting aberration balance reduces the composite RMS wavefront error is only 0.0125λ (0.17 nm), with simultaneous correction of the static distortion to less than 2 nm across the field.
This optical projection system has further benefits in that the system of
Referring to
Second Preferred Embodiment:
In a second of these general embodiments, an optical projection system for extreme ultraviolet (EUV) lithography including six mirrors arranged in a PPNPNP configuration is disclosed. The plan view of this second preferred embodiment is shown in
In addition to the features outlined by the first preferred embodiment, this second preferred embodiment teaches that the tertiary mirror M3′ may be located on the object side of the primary mirror M1′ (i.e., closer to the object OB′ than the primary mirror M1′). This feature departs drastically from the teaches of the prior art that show the tertiary mirror must be located either in close proximity to the primary mirror ('079 patent) or on the image side of the primary mirror('310 patent). This location of mirror M3′ enables a reduction in the overall length from object plane OB to image plane IM (total track length) by some 250 mm. This decrease in total track length is accomplished by shifting the tertiary mirror from the image side of the primary mirror M1′ to the object side of the primary mirror M1′ and then decreasing the distance between mirror M1′ and mirror M6′. This also allows the parent diameter of the tertiary mirror M3′ to be smaller than either the primary mirror M1′ or the secondary mirror M2′. These changes affect the angular condition of the chief rays upon reflection from the secondary mirror M2′. Prior art teaches that the chief ray from the central field point must diverge from the optical axis after reflection from the secondary mirror ('310 patent, '079 patent, etc.), but now the chief ray CR′ assumes a more parallel condition with respect to the optical axis OA′. In this second embodiment, this chief ray CR′ is made identically parallel to the optical axis OA′. This change in chief ray angle impacts the aberration balance in the design enough to form a distinct local minima, so that the residual aberration set seen in a Zernike decomposition of the wavefront differs from that of the first preferred embodiment.
The optical prescription of this second preferred embodiment of
Like the first preferred embodiment, the object OB′ will be projected to the image IM′ at 4× reduction in a ring field format with a telecentric imaging bundle (chief rays parallel to the optical axis OA′ at the image IM′). Table 6 provides a performance summary demonstrating that this preferred embodiment is capable of lithographic performance at a wavelength of 13.4 nm. For comparison to the first embodiment, this second preferred embodiment also utilizes a numerical aperture NA of 0.20 at the image IM′ and projects a 2 mm wide field in the scan direction. The system is compatible with reflective multilayer coatings since the incidence angles at each mirror are relatively small. As measured by the chief ray CR′ from the central field point 29′, the incidence angles range from 3.9° to 14.6°. The exact chief ray incidence angles for the chief ray CR′ from the central field point 29′ are: Object OB′: 5.6°; M1: 7.2°; M2: 4.4°; M3: 14.6°; M4: 8.8°, M5: 9.7°, and M6: 3.9°. Again, these low incidence angles are a key enabling element for EUV lithography since the low incidence angles minimize the multiplayer induced amplitude and phase errors that have an adverse impact to lithographic performance.
The composite RMS wavefront error across the field is 0.0131λ (0.18 nm), ranging from 0.0095λ (0.13 nm) at the best field point to 0.0157λ (0.21 nm) at the worst. The distortion of the chief ray has been reduced to less than 1 nm across the field. Clearly this combination of telecentric imaging, a highly corrected wavefront, and essentially no distortion demonstrates that this system is suitable for modern lithography at soft x-ray or extreme ultratviolet wavelengths.
This preferred embodiment has further advantages in that the system of
The results of another simple scaling experiment demonstrate that this preferred embodiment easily supports increases in field width. Without making any modifications, an analysis of the composite RMS wavefront error was made over a 3 mm wide arcuate slit, which represents a 50% increase to the value shown in Table 6. The composite RMS wavefront error was found to be 0.028λ (0.38 nm), again a level that supports lithographic quality imaging.
Third Preferred Embodiment:
The third preferred embodiment is shown in FIG. 4. Like the first and second preferred embodiments, this system utilizes a re-imaging PPNPNP configuration with a physically accessible aperture stop APE″ that is located between the primary mirror M1″ and secondary mirror M2″. And like the first and second embodiments, the intermediate image IMI″ is located between the secondary mirror M2″ and the tertiary mirror M3″. Similar to the second embodiment, the tertiary mirror M3″ is located on the object side of the primary mirror M1″. This particular embodiment differs from the second preferred embodiment in that the chief ray CR″ from the central field point 29″ converges toward the optical axis OA″ after reflection from the secondary mirror M2″, thus forming another advantageous projection system with distinct characteristics.
The optical prescription for this third embodiment of
Like the first two preferred embodiments, the object OB″, e.g. a pattern on mask or reticle, will be projected to the image IM″ at 4× reduction in a ring field format with a telecentric imaging bundle (chief rays parallel to the optical axis at the image). At the image″ typically a semiconductor wafer is arranged. Table 6 provides a performance summary demonstrating that this preferred embodiment is capable of lithographic performance at a wavelength of 13.4 nm. For comparison purposes, this third preferred embodiment also utilizes a numerical aperture NA of 0.20 at the image IM″ and projects a 2 mm wide field in the scan direction. The system is compatible with reflective multilayer coatings since the incidence angles at each mirror are relatively small. As measured by the chief ray CR″ from the central field point 29″, the incidence angles range from 3.9° to 13.9°. The exact chief ray incidence angles from the central field point are: Object OB″: 6.6°; M1: 8.0°; M2: 4.4°; M3: 13.9°; M4: 8.6°, M5: 9.6°, and M6: 3.9°. Again, these low incidence angles are a key enabling element for EUV lithography since the low incidence angles minimize the multiplayer induced amplitude and phase errors that have an adverse impact to lithographic performance.
The composite wavefront error across the field is 0.0203λ (0.27 nm), ranging from 0.0148λ (0.20 nm) at the best field point to 0.0243λ (0.33 nm) at the worst. The distortion of the chief ray has been reduced to less than 1 nm across the field. Clearly this combination of telecentric imaging, a highly corrected wavefront, and essentially no distortion demonstrates that this system is suitable for modern lithography at soft x-ray or extreme ultratviolet wavelengths. The design can also be scaled in numerical aperture or field like second preferred embodiment.
The optical design descriptions provided above for the first-third embodiments herein demonstrate an advantageous catoptric projection system concept for EUV lithography. While these embodiments have been particularly described for use in a 13.4 nm tool, the basic concept is not limited to use with lithographic exposure tools at this wavelength, either shorter or longer, providing a suitable coating material exists in the soft x-ray region of the electromagnetic spectrum.
While exemplary drawings and specific embodiments of the present invention have been described and illustrated, it is to be understood that that the scope of the present invention is not to be limited to the particular embodiments discussed. Thus, the embodiments shall be regarded as illustrative rather than restrictive, and it should be understood that variations may be made in those embodiments by workers skilled in the arts without departing from the scope of the present invention as set forth in the claims that follow, and equivalents thereof. For example, one skilled in the art may reconfigure the embodiments described herein to expand the field of view, increase the numerical aperture, or both, to achieved improvements in resolution or throughput.
TABLE 1
Optical prescription first preferred embodiment
Vertex
Element number
radius of curvature
Thickness (mm)
Glass
Object OB
INFINITY
806.775
A(1)
−1997.63
−328.184
REFL
Aperture Stop APE
INFINITY
−399.404
A(2)
1148.069
649.7918
REFL
Intermediate
INFINITY
132.9323
image IMI
A(3)
486.7841
−277.569
REFL
A(4)
660.9159
890.6587
REFL
A(5)
393.8628
−476.472
REFL
A(6)
580.3377
501.472
REFL
Image IM
TABLE 2
Aspheric prescription
Aspheric
K
A
B
C
D
E
A(1)
−9.1388E+01
5.4676E−10
7.0301E−15
−1.4409E−19
2.1657E−25
5.5712E−30
A(2)
−6.4930E−01
3.7924E−11
3.2952E−18
−1.1462E−21
8.4115E−26
−4.9020E−30
A(3)
−2.3288E−01
3.3571E−10
1.8240E−14
−1.9218E−19
−4.2667E−23
2.9468E−23
A(4)
−6.4180E−03
3.9345E−11
1.8257E−16
−6.9023E−22
1.3692E−26
−6.2042E−32
A(5)
1.5857E+00
−1.7764E−09
7.7970E−14
−1.2619E−18
5.4017E−22
−3.8012E−26
A(6)
8.9884E−02
−4.2455E−12
1.4898E−17
1.4824E−22
−7.0550E−28
6.6775E−32
TABLE 3
Performance summary first preferred embodiment
Metric
Performance
Wavelength
13.4
nm
Numerical aperture (image)
0.20
Ringfield format (image)
i. Radius
30.0
mm
ii. Width
2.0
mm
iii. Chord
26.0
mm
Reduction ratio (nominal)
4:1
Overall length (mm)
1500
mm
RMS wavefront error
(waves @ λ = 13.4 nm)
i. Composite
0.0125λ
ii. Variation
0.0076λ-0.0167λ
Chief ray distortion (max)
1.9
nm
Exit pupil location
Infinity
Max. aspheric departure across
instantaneous clear aperture (ICA)
i. M1
25.0
μm
ii. M2
0.5
μm
iii. M3
1.4
μm
iv. M4
14.0
μm
v. M5
3.0
μm
vi. M6
3.8
μm
TABLE 4
Optical prescription second preferred embodiment
Vertex
Element number
radius of curvature
Thickness (mm)
Glass
Object Plane OB′
INFINITY
786.7828
A(1)
−1522.9647
−275.3849
REFL
Aperture Stop APE′
INFINITY
−461.3979
A(2)
922.8035
452.3057
REFL
Intermediate
INFINITY
95.0000
image IMI′
A(3)
273.0204
−218.5016
REFL
A(4)
511.1320
834.1959
REFL
A(5)
434.1472
−326.2172
REFL
A(6)
440.9571
363.2172
REFL
Image IM′
TABLE 5
Aspheric prescription second preferred embodiment
Aspheric
K
A
B
C
D
E
A(1)
−6.5661E+04
3.6028E−01
2.7656E−09
1.3237E−14
5.6475E−20
1.4711E−23
A(2)
1.0837E−03
−3.0142E+00
3.384E−18
−6.8499E−16
−1.8748E−20
1.0985E−24
A(3)
3.6627E−03
1.9328E+00
−1.6611E−08
−4.9082E−13
2.9169E−17
−3.8673E−27
A(4)
1.9564E−03
−1.2442E−01
−1.0927E−11
2.7712E−16
−2.0608E−21
3.6395E−26
A(5)
1.3034E−03
8.5377E+00
−6.9001E−09
−2.2929E−13
−8.9645E−18
−2.1791E−27
A(6)
2.2678E−03
1.4526E−01
3.2069E−11
3.3003E−16
5.1329E−21
−1.7296E−25
TABLE 6
Performance summary second preferred embodiment
Metric
Performance
Wavelength
13.4
nm
Numerical aperture (image)
0.20
Ringfield format (image)
i. Radius
30.0
mm
ii. Width
2.0
mm
iii. Chord
26.0
mm
Reduction ratio (nominal)
4:1
Overall length (mm)
1250
RMS wavefront error
(waves @ λ = 13.4 nm)
i. Composite
0.0131λ
ii. Variation
0.0095λ-0.0157λ
Chief ray distortion (max)
0.9
nm
Exit pupil location
Infinity
Max. aspheric departure across
instantaneous clear aperture (ICA)
i. M1′
18.0
μm
ii. M2′
6.2
μm
iii. M3′
8.7
μm
iv. M4′
28.0
μm
v. M5′
7.0
μm
vi. M6′
7.0
μm
TABLE 7
Optical prescription third preferred embodiment
Vertex
Element number
radius of curvature
Thickness (mm)
Glass
Object Plane OB″
INFINITY
708.2875
A(1)
−1351.9353
−222.3328
REFL
Aperture Stop APE″
INFINITY
−435.9047
A(2)
801.1198
389.5537
REFL
Intermediate
INFINITY
85.9324
image IMI″
A(3)
257.6903
−223.6826
REFL
A(4)
508.9915
827.9429
REFL
A(5)
434.7744
−321.5090
REFL
A(6)
436.7586
358.5090
REFL
Image IM″
TABLE 8
Aspheric prescription third preferred embodiment
Aspheric
K
A
B
C
D
E
A(1)
−7.3968E−04
1.8042E+00
2.2388E−09
4.0136E−15
6.8479E−19
−1.2865E−22
A(2)
1.2483E−03
−2.6267E+00
4.4819E−10
−1.7571E−15
5.8143E−20
−3.7874E−24
A(3)
3.8806E−03
−8.5604E−01
2.2165E−08
−6.7204E−12
1.1406E−15
−1.0131E−19
A(4)
1.9647E−03
−7.7387E−02
−3.8053E−11
−1.2483E−15
2.8880E−20
−3.4746E−25
A(5)
2.3000E−03
8.3687E+00
−6.1944E−09
−1.9683E−13
−1.6280E−17
4.8296E−21
A(6)
2.2896E−03
1.3269E−01
5.6594E−11
5.5533E−16
−1.1978E−21
7.3097E−25
TABLE 9
Performance summary third preferred embodiment
Metric
Performance
Wavelength
13.4
nm
Numerical aperture
0.20
(image IM″)
Ringfield format (image IM″)
i. Radius
30.0
mm
ii. Width
2.0
mm
iii. Chord
26.0
mm
Overall length (mm)
1156
Reduction ratio (nominal)
4:1
RMS wavefront error
(waves @ λ = 13.4 nm)
i. Composite
0.0203λ
ii. Range
0.0148λ-0.0243λ
Chief ray distortion (max)
1.5
nm
Exit pupil location
Infinity
Max. aspheric departure across
instantaneous clear aperture (ICA)
i. M1″
17.3
μm
ii. M2″
6.4
μm
iii. M3″
9.7
μm
iv. M4″
32.2
μm
v. M5″
6.7
μm
vi. M6″
6.7
μm
In
In addition the axis extending the object plane, i.e., the x-axis and the y-axis are depicted. As can be seen from
In
In particular,
The physical aperture stop B is arranged between the second mirror S2 and the third mirror S3. And, as is clear from
physical distance from the vertex V5 of the surface of mirror S5 to the image plane 4>used diameter of mirror S5.
Other distance requirements are also possible and may be used, such as the physical distance is (1) greater than the sum of one-third of the used diameter of the mirror next to the wafer, S5, and 20 mm, or (2) greater than 50 mm. In the preferred embodiment, the physical distance is 60 mm.
Such a physical distance guarantees a sufficiently free working distance A, and allows the use of optical components compatible for use with wavelengths<100 nm, and preferably wavelengths of 11 to 13 nm. Optical components in this range include, for example, Mo/Si or Mo/Be multi-layer systems, where the typical multilayer systems for λ=13 nm is Mo/Si layer pairs and for λ=11 nm, is Mo/Be systems, both of approximately 70 layer pairs. Reflectivities attainable in such systems are approximately 70%. In the multi-layer layer systems, layer stresses of above 350 MPa may occur. Stresses of such values may induce surface deformation, especially in the edge regions of the mirror.
The systems according to the invention, as they are shown, for example, in
RES=k1λ/NA.
This results in a nominal resolution of at least 50 nm and 35 nm at a minimum numerical aperture of NA=0.2 for k1=0.77 and λ=13 nm, and for k1=0.64 and λ=11 nm, respectively, where k1 is a parameter specific for the lithographic process.
Furthermore, the light path for a bundle of light rays running from the object plane to the image plane of the objective shown in
Numerous masks can be used in the projection exposure apparatus. The masks or reticle are arranged in the object plane of the projection objective. The masks include transmission masks, stencil masks and reflection masks. The projection objective, which is telecentric on the image side, i.e. in the image plane, can be telecentric or non-telecentric on the object side, i.e. in the object plane depending on which mask is used. For example, if the bundle of light rays is telecentric on the object-side when using a reflection mask a transmission-reducing beam splitter must be employed. If the bundle of light rays is non-telecentric on the object-side, unevennesses of the mask leads to dimensional errors in the image. Therefore, the angle of incidence of the chief ray of the bundle of light rays through the central field point 1500 in the object plane is preferably below 10°, so that the requirements for reticle evenness lies in an achievable range. Moreover, the system of
Due to the high image-side telecentricity, the entrance pupil of the last mirror S6 is at or near the focal plane of this mirror. Therefore, in systems with an intermediate image as described before, the aperture, B, is in the front, low-aperture objective part preferably in the light path between the first and third mirror S1, S3. Thus the pupil plane conjugated with the aperture stop will be imaged in the focal plane of the last mirror.
All mirrors S1-S6 of
The highest angle of incidence of a ray impinging a mirror surface in the six-mirror objective shown in
A freely accessible aperture stop between the second and third mirror as well as no vignetting of the bundle of light rays running from S3 to S4 by the aperture stop is achieved with small angles of incidence of the rays impinging onto the mirror surfaces when the following distance conditions are fulfilled:
0.5<S1S3/S1S2<2
and
0.5<S2 aperture/(S3 aperture)<2.
Here, the abbreviation S1S3 means the mechanical distance or physical distance between the vertices V1 and V3 of the surface of the mirrors S1 and S3. And, “S2 aperture” means the mechanical distance between the vertex V2 of the surface of mirror S2 and the aperture. Furthermore, in order to reduce the angles of incidence on the mirrors in any of the embodiments of
reticle S1<S2S3.
To ensure a sufficient free working distance A not only on the image side but also on the object side the reticle is situated sufficiently far in front of the first mirror next to the object plane, which is in the present case the surface of the second mirror S2. In the present case, for example, the physical distance between the reticle and the vertex V2 of the surface of mirror S2 is 80 mm.
Furthermore, in the embodiments of
0.3 (used diameter S3+used diameter S6)<S3S6.
Here S3S6 denotes the physical distance between the vertex V3 of the surface of mirror S3 and the vertex V6 of the surface of the mirror S6.
In the following table 10, the parameters of the system represented in
TABLE 10
element No.
radius
Thickness
diameter
Type
Object
INF
80.9127
258.1723
413.0257
S1
A(1)
−88.8251
197.5712
REFL
−324.2006
195.6194
0.0000
188.6170
S2
A(2)
324.2006
188.7078
REFL
aperture
67.1796
423.6214
183.2180
0.0000
S3
A(3)
−423.6214
184.7062
REFL
−74.9270
519.0546
S4
A(4)
498.5484
541.0453
REFL
109.8242
248.6244
281.5288
177.5488
S5
A(5)
−281.5288
65.0842
REFL
S6
A(6)
281.5288
187.9549
REFL
78.3999
Image
image width
59.202
53.9889
aspherical constants:
Z = (CURV) Y2/[1 + (1 − (1 + K) (CURV)2Y2)1/2] + (A)Y4 + (B)Y6 + (C)Y8 + (D)Y10
asphere
CURV
K
A
B
C
D
A(1)
0.00031800
−27.686599
0.00000E+00
1.32694E−15
2.00546E−20
−8.49471E−25
A(2)
0.00094928
−3.998204
0.00000E+00
4.03849E−15
−6.15047E−20
2.73303E−25
A(3)
0.00126752
0.424198
0.00000E+00
1.58766E−15
−8.27965E−20
2.80328E−24
A(4)
0.00123850
0.023155
0.00000E+00
2.46048E−17
−1.08266E−22
3.75259E−28
A(5)
0.00329892
2.902916
0.00000E+00
1.55628E−12
−6.71619E−17
−5.30379E−21
A(6)
0.00277563
0.072942
0.00000E+00
2.96285E−16
3.99125E−21
4.55007E−26
Reference wavelength = 13 nm
One difference to the objective of
Another advantage of this embodiment is the spherical design of mirror S4, which presents advantages especially from the point of view of manufacturing, because mirror S4 is the largest mirror of the system. With such a design, the asphericity in the used range is increased slightly to 10.5 μm. The largest angle of incidence occurs on mirror S5 and is approximately 18.6°. The wavefront error of the arrangement is 0.032λ, within a 1.7 mm wide arc-shaped field at λ=13 nm. Furthermore, if the mirror S4 is designed to be slightly aspherical with 0.4 μm, then the wavefront error can be kept to 0.031λ within a 1.8 mm wide arc-shaped field at λ=13 nm. Efficient masking of the undesirable light is obtained not only when the aperture stop is formed directly on mirror S1, but also when it is arranged behind, i.e., after, mirror S1. Preferably, the aperture stop is positioned such that the following relationship is obtained:
S2S1≦0.9×S2 aperture.
S2S1 denotes the mechanical distance of the vertex V2 of the surface of mirror S2 and the vertex V1 of the surface of the mirror S1.
Table 11 shows the constructional data of the 5× objective according to
TABLE 11
element No.
Radius
Thickness
diameter
type
Object
INF
85.2401
256.1389
358.4668
S1
A(1)
0.0024
203.8941
REFL
−358.4691
203.8845
0.0000
201.9677
S2
A(2)
358.4691
201.9942
REFL
aperture
60.7572
390.5456
187.2498
0.0000
S3
A(3)
−390.5456
188.9474
REFL
−104.1273
505.8686
S4
A(4)
494.6729
550.3686
REFL
114.3062
256.9217
281.6969
181.7337
S5
A(5)
−281.6969
64.4286
REFL
S6
A(6)
281.6969
187.8549
REFL
78.1545
Image
image width
60.0041
53.6996
aspherical constants:
Z = (CURV) Y2/[1 + (1 − (1 + K) (CURV)2Y2)1/2] + (A)Y4 + (B)Y6 + (C)Y8 + (D)Y10
asphere
CURV
K
A
B
C
D
A(1)
0.00035280
−58.238840
0.00000E+00
2.14093E−15
2.29498E−20
0.00000E+00
A(2)
0.00097971
−4.160335
0.00000E+00
1.54696E−15
8.15622E−21
0.00000E+00
A(3)
0.00117863
−2.136423
0.00000E+00
−1.78563E−16
3.45455E−20
0.00000E+00
A(4)
0.00124362
0.000000
0.00000E+00
0.00000E+00
0.00000E+00
0.00000E+00
A(5)
0.00338832
2.909987
0.00000E+00
7.90123E−13
7.04899E−17
0.00000E+00
A(6)
0.00278660
0.062534
0.00000E+00
2.79526E−16
7.00741E−21
0.00000E+00
Reference wavelength = 13 nm
Another embodiment is shown in
Table 12 shows the optical parameters of the embodiment of
TABLE 12
element No.
Radius
thickness
diameter
Type
Object
INF
84.0595
205.6642
473.5521
S1
A(1)
−145.8261
147.3830
REFL
−327.7260
136.4700
aperture
112.0176
0.0000
S2
A(2)
473.5521
112.1228
REFL
190.4830
163.5236
0.0000
184.4783
S3
A(3)
−190.4830
185.3828
REFL
−399.1713
358.6720
S4
A(4)
589.6560
654.5228
REFL
207.5220
310.1977
276.2668
175.3066
S5
A(5)
−276.2668
65.2138
REFL
S6
A(6)
276.2668
182.8159
REFL
77.5085
Image
image width
59.0000
53.9968
aspherical constants:
Z = (CURV) Y2/[1 + (1 − (1 + K) (CURV)2Y2)1/2] + (A)Y4 + (B)Y6 + (C)Y8 + (D)Y10
asphere
CURV
K
A
B
C
D
A(1)
0.00015851
441.008070
0.00000E+00
−3.49916E−16
1.27478E−19
−3.37021E−25
A(2)
0.00089932
−5.032907
0.00000E+00
−6.95852E−15
−7.53236E−20
−2.74751E−24
A(3)
0.00188578
0.913039
0.00000E+00
−1.60100E−15
−9.53850E−20
1.30729E−26
A(4)
0.00108147
0.038602
0.00000E+00
2.48925E−18
−5.29046E−24
−4.37117E−31
A(5)
0.00269068
7.253316
0.00000E+00
−5.70008E−13
−9.32236E−17
−6.09046E−21
A(6)
0.00281036
0.150957
0.00000E+00
1.30822E−15
1.86627E−20
5.08158E−25
Reference wavelength = 13 nm
Table 13 shows the optical parameters of the embodiment of
TABLE 13
element No.
Radius
thickness
Diameter
Type
Object
INF
151.2625
194.7605
229.0820
S1
A(1)
−39.4068
162.9862
REFL
−189.6752
147.1426
aperture
65.0637
0.0000
S2
A(2)
229.0820
65.1650
REFL
137.5708
168.3504
0.0000
230.5128
S3
A(3)
−137.5708
234.0072
REFL
−300.3445
386.2567
S4
A(4)
437.9153
630.7784
REFL
133.0981
343.1578
353.0840
257.0225
S5
A(5)
−353.0840
79.9521
REFL
S6
A(6)
353.0840
264.2853
REFL
78.6376
image
image width
44.0000
54.0051
aspherical constants:
Z = (CURV) Y2/[1 + (1 − (1 + K) (CURV)2Y2)1/2] + (A)Y4 + (B)Y6 + (C)Y8 +
(D)Y10 + (E)Y12 + (F)Y14 + (G)Y16 + (H)Y18 + (J)Y20
K
A
B
C
D
asphere
CURV
E
F
G
H
J
A(1)
−0.00080028
0.000000
−3.35378E−09
5.36841E−14
−7.86902E−19
−5.07886E−24
0.00000E+00
0.00000E+00
0.00000E+00
0.00000E+00
0.00000E+00
A(2)
0.00040002
0.000000
1.68178E+08
2.05570E−12
2.42710E−16
5.69764E−20
0.00000E+00
0.00000E+00
0.00000E+00
0.00000E+00
0.00000E+00
A(3)
0.00113964
−2.760663
0.00000E+00
−3.55779E−15
1.03881E−19
−3.64996E−24
0.00000E+00
0.00000E+00
0.00000E+00
0.00000E+00
0.00000E+00
A(4)
0.00128753
0.019273
0.00000E+00
5.82746E−18
−1.77496E−22
1.64954E−27
−6.20361E−33
0.00000E+00
0.00000E+00
0.00000E+00
0.00000E+00
A(5)
0.00373007
11.6888968
0.00000E+00
−5.53902E−12
−4.32712E−16
−1.54425E−19
0.00000E+00
0.00000E+00
0.00000E+00
0.00000E+00
0.00000E+00
A(6)
0.00240387
−0.002567
0.00000E+00
−6.78955E−16
−8.39621E−21
−2.95854E−25
0.00000E+00
0.00000E+00
0.00000E+00
0.00000E+00
0.00000E+00
Reference wavelength = 13 nm
TABLE 14
element No.
radius
thickness
Diameter
type
Object
INF
103.2808
197.1874
219.3042
S1
A(1)
−39.2890
157.6222
REFL
−180.0152
142.1492
aperture
67.2659
0.0000
S2
A(2)
219.3042
67.4347
REFL
131.2051
167.6895
0.0000
228.0182
S3
A(3)
−131.2051
232.3162
REFL
−247.5850
401.4441
S4
A(4)
378.7901
613.5493
REFL
134.4001
355.7774
348.5086
268.3735
S5
A(5)
−348.5086
81.5255
REFL
S6
A(6)
348.5086
269.2435
REFL
75.4983
image
image width
36.1195
53.9942
aspherical constants:
Z = (CURV) Y2/[1 + (1 − (1 + K) (CURV)2Y2)1/2] + (A)Y4 + (B)Y6 + (C)Y8 +
(D)Y10 + (E)Y12 + (F)Y14 + (G)Y16 + (H)Y18 + (J)Y20
K
A
B
C
D
asphere
CURV
E
F
G
H
J
A(1)
−0.00061615
0.000000
−5.19402E−09
1.09614E−13
−3.44621E−18
1.58573E−22
−7.07209E−27
0.00000E+00
0.00000E+00
0.00000E+00
0.00000E+00
A(2)
0.00066911
0.000000
1.69112E−08
2.39908E−12
2.89763E−16
1.00572E−19
1.84514E−29
0.00000E+00
0.00000E+00
0.00000E+00
0.00000E+00
A(3)
0.00140031
0.000000
−8.71271E−10
−1.47622E−15
−3.40869E−20
4.32196E−24
−2.23484E−28
0.00000E+00
0.00000E+00
0.00000E+00
0.00000E+00
A(4)
0.00143731
0.000000
2.18165E+12
2.65405E−17
−2.01757E−22
1.14856E−28
1.49857E−32
−8.61043E−38
0.00000E+00
0.00000E+00
0.00000E+00
A(5)
0.00378996
0.000000
8.54406E−08
2.25929E−12
3.36372E−16
1.92565E−20
5.75469E−24
0.00000E+00
0.00000E+00
0.00000E+00
0.00000E+00
A(6)
0.00246680
0.000000
−3.61754E−12
−8.29704E−16
−1.53440E−20
−2.24433E−25
5.91279E−30
0.00000E+00
0.00000E+00
0.00000E+00
0.00000E+00
Reference wavelength = 13 nm
Thus, the invention provides a six-mirror projection objective with an imaging scale of preferably 4×, 5× or 6× for use in an EUV projection system. Other uses may be employed, however. The six-mirror projection objective has the resolution required for the image field, which is e.g. arc-shaped and has a advantageous structural design, since the aspheres of the mirror surfaces are relatively low, the angles of incidence of the rays of the bundle of light rays impinging the mirror surfaces are small, and there is enough room for mounting the mirrors.
It should be understood by a person skilled in the art, that the disclosure content of this application comprises all possible combinations of any element(s) of any claims with any element(s) of any other claim, as well as combinations of all claims amongst each other.
Hudyma, Russell, Dinger, Udo, Mann, Hans-Jûrgen
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