Source: https://patents.justia.com/patent/8687289
Timestamp: 2020-03-29 19:32:03
Document Index: 657738084

Matched Legal Cases: ['§119', '§119', 'Application No. 10', 'ART1', 'ART2', 'ART1', 'ART2', 'Application No. 0961109615']

US Patent for Projection objective and projection exposure apparatus with negative back focus of the entry pupil Patent (Patent # 8,687,289 issued April 1, 2014) - Justia Patents Search
Justia Patents With Reflecting ElementUS Patent for Projection objective and projection exposure apparatus with negative back focus of the entry pupil Patent (Patent # 8,687,289)
Projection objective and projection exposure apparatus with negative back focus of the entry pupil
Dec 6, 2011 - Carl Zeiss SMT GmbH
Method for correcting the distortion of a first imaging optical unit of a first measurement system
Vacuum system, in particular EUV lithography system, and optical element
Projection exposure apparatus, and method for reducing deformations, resulting from dynamic accelerations, of components of the projection exposure apparatus
Mirror element, in particular for a microlithographic projection exposure apparatus
This application is a continuation of U.S. application Ser. No. 12/949,985, filed Nov. 19, 2010, now U.S. Pat. No. 8,094,380, which is a continuation of U.S. application Ser. No. 11/689,672, filed Mar. 22, 2007, now U.S. Pat. No. 7,869,138, which claims benefit under U.S.C. §119 to U.S. provisional application 60/786,744, filed Mar. 27, 2006. U.S. application Ser. No. 11/689,672 also claims priority under U.S.C. §119 to German Patent Application No. 10 2006 014 380, filed on Mar. 27, 2006. The full disclosure of these earlier applications is incorporated herein by reference.
An illumination system has been presented in US 2005/0088760, wherein the rays reflected from a reflective object in an object plane enter the projection objective on divergent paths. In the case of an axially symmetric projection objective which has an optical axis, this means that the projection objective has a negative back focus of the entry pupil. For axially symmetric systems, this means that a positive principal ray angle γ is present at the reflective object in the object plane. In the examples presented in US 2005/0088760, the positive principal ray angle γ is less than 7° (e.g., less than 6°).
The back focus is determined by the distance from the object plane to the point where the principal ray directed to the central field point of the illuminated field in the object plane intersects the optical axis. With a positive principal ray angle at the object or at the reticle, for example γ=8°, and with a field radius r=125 mm, the back focus SEP is obtained as SEP=−R/tan γ=−889.4 mm. In systems with a negative back focus of the entry pupil, the principal ray angle γ at the object is positive.
According to a first aspect of the disclosure, a first embodiment of a microlithography projection objective with a negative back focus of the entry pupil is proposed, which includes at least two mirrors, i.e. a first mirror (S1) and a second mirror (S2), wherein the objective is designed in such a way that each principal ray CR originating from a central point of the object field and traversing the objective from the object plane to the image plane intersects the optical axis (HA) at least once in a point of intersection that is specific to that ray, with the respective points of intersection being located geometrically between the image plane of the projection objective and the mirrored entry pupil plane of the mirrored entry pupil of the projection objective. The terms “entry pupil” and “mirrored entry pupil” are explained in more detail in FIG. 1a.
According to the first aspect of the disclosure, all points of intersection of the principal rays with the optical axis of the projection objective lie between the mirrored entry pupil plane and the image plane of the projection objective.
In an advantageous embodiment of the disclosure, the at least one point of intersection has along the optical axis a first distance A1 to the object plane, and the mirrored entry pupil has a second distance A2 to the object plane, wherein the distances A1 and A2 conform to the rule that A2 is always smaller than A1 (e.g., A2<0.9·A1, A2<0.8·A1, A2<0.7·A1, A2<0.5·A1).
In some embodiments of the disclosure it is envisioned that in a projection objective with negative back focus of the entry pupil, an incident principal ray on its way to the first mirror (CRE) of the projection objective travels in the meridional plane of the projection objective on a path between the principal ray reflected from the mirror surface (CRR) and the optical axis (HA) of the projection objective. This is shown in FIG. 1h. Both the incident principal ray (CRE) as well as the reflected principal ray (CRR) are in this case associated with the same field point, for example the central field point.
In some embodiments, the objective according to the disclosure is a catoptric projection objective with a negative back focus of the entry pupil, an image-side wave front aberration WRMS of less than 0.01λ and on each of the mirrors a maximum angle of incidence smaller than 21°. The image-side wave front aberration can be WRMS≦0.07λ (e.g., WRMS≦0.06λ). The maximum angle of incidence in the meridional plane on each of the mirrors can be ≦20°. The symbol λ stands here for the wavelength of the light which traverses the projection objective along an imaging light path from the object plane to the image plane.
A double-facetted illumination system is distinguished by having a first facetted mirror with a multitude of first facets, so-called field facets, as well as a second facetted mirror with a multitude of second facets, so-called pupil facets. As described above, a system of this kind has the second facetted element with pupil facets arranged in or near the mirrored entry pupil of the projection objective. The pupil facet mirror in some embodiments can have about 200 to 300 pupil facets which, as an option, can be designed so that they are switch-controlled whereby the correlation of the first facets to the second facets can be changed. A change in the correlation of the first to the second facets for the adjustment of the setting can be achieved in a double-facetted illumination system for example by exchanging the first facetted optical elements with field facets. In systems that are designed for a wavelength 193 nm (e.g., for wavelengths≦100 nm, for wavelengths in the range of EUV wavelengths of 10 to 30 nm), the facets are designed as reflectors, i.e., mirrors.
FIG. 1a serves to visualize the negative back focus of the entry pupil,
FIG. 1b represents a schematic view of a microlithography projection exposure apparatus,
FIG. 1c represents a cone of rays for the definition of the image-side numerical aperture,
FIG. 1d represents a part of a mirror surface in a meridional section,
FIG. 1e represents a part of a mirror surface in a plane that is orthogonal to the meridional plane,
FIG. 1f shows the shape of a ring field,
FIG. 1g shows a microlithography projection exposure apparatus according to the state of the art as described in US 2005/088760 with a projection objective with negative back focus of the entry pupil,
FIG. 1h is a schematic illustration to explain the geometry of the ray path in the vicinity of the first mirror,
FIG. 2a represents a first example that embodies a projection objective according to the disclosure with a negative back focus of the entry pupil, wherein no intermediate image is formed in the light path from the object plane to the image plane,
FIG. 2b consists of Table 1,
FIG. 3a shows an alternative version of a projection objective according to the first embodiment,
FIG. 3b consists of Table 2,
FIG. 4 shows a microlithography projection exposure apparatus that contains a projection objective according to FIG. 2a,
FIG. 5a shows a second embodiment of a projection objective with negative back focus of the entry pupil, wherein the paths of the light ray cross over themselves in the meridional plane in the first partial objective,
FIG. 5b consists of Table 3,
FIG. 6a represents a first alternative system of a projection objective according to the second embodiment,
FIG. 6b consists of Table 4,
FIG. 6c shows a second alternative system of a projection objective according to the second embodiment,
FIG. 6d consists of Table 5,
FIGS. 1a to 1h will be referred to in the following detailed description of the general concepts which are used in all of the embodiments and relate to all of the illustrated examples.
FIG. 1a serves to visualize the concept which is referred to herein as negative back focus.
FIG. 1a shows the principal ray CRB of an illumination light bundle directed at the central field point of an illuminated field as illustrated for example in FIG. 1f. As shown here, the principal ray CRB of the illumination light bundle reflected on a reflective object REFLOBJ, for example a reticle and, now as principal ray of a projection light bundle, enters into a projection objective of which the first mirror S1 and the second mirror S2 are shown in the drawing. “Negative back focus of the entry pupil” means that the principal ray angle γ at the reflective object, for example the reticle, is positive. The principal ray angle γ is the angle by which the principal ray CRP is inclined relative to the normal direction NO of the reflective object REFLOBJ. For systems with negative back focus of the entry pupil, the angle γ is by definition positive and is measured counterclockwise.
FIG. 1b represents a microlithography projection exposure apparatus 2100. The latter contains a light source 2110, an illumination system 2120, a projection objective 2101 as well as a support structure or work surface 2130. Further shown is a Cartesian coordinate system. The radiation of the light source 2110 is directed to an illumination system 2120. The illumination system 2120 has an influence on the radiation originating from the light source 2110, for example by homogenizing the radiation or by directing a ray bundle 2122 of the radiation for example by means of the illustrated direction-changing mirror 2121 onto a mask 2140 which is positioned in an object plane 2103. The projection objective 2101 projects the radiation that is reflected by the mask 2140 onto a substrate surface 2150 which is positioned in an image plane 2102. The ray bundle 2142 on the object side has according to the disclosure a principal ray CRP with a positive principal ray angle γ. Also indicated in the drawing is the surface-normal direction NO of the object plane 2103 in the vicinity of the mask 2140. The substrate 2150 is supported or carried by a support structure 2130, wherein the support structure 2130 moves the substrate 2150 relative to the projection objective 2101, so that the projection objective 2101 projects images of the mask 2140 onto different areas of the substrate 2150.
The projection objective 2101 includes an optical axis 2105. As shown in FIG. 1a, the projection objective 2101 projects a part of the mask 2140 that does not contain the optical axis of the projection objective 2101 into an image plane 2102. The light source 2110 is selected in such a way that it provides electromagnetic radiation at an operating wavelength λ that is used to operate the microlithography projection exposure apparatus. In some of the examples described, the lights source 2110 is a laser plasma source or a plasma discharge source that emits EUV radiation. As alternatives, it is also possible to use light sources that are used for other wavelengths, such as for example light-emitting diodes (LEDs) which emit radiation in the blue or UV range of the electromagnetic spectrum, for example at 365 nm or 248 nm, respectively. This can be for systems in which broad-band light sources are used together with mirror systems.
FIG. 1c shows the marginal rays 2152 of the light bundle which projects the object into the image plane 2102. The marginal rays 2152 define a cone of rays.
The angle of the cone of rays is related to the image-side numerical aperture (NA) of the projection objective 2101. The image-side numerical aperture can be expressed as NA=n0·sin ΘNA, wherein n0 stands for the refractive index of the medium that lies adjacent to the substrate 2150. This medium can be for example air, nitrogen, water, or a vacuum. The symbol ΘNA stands for the angle that is defined by the marginal rays of the projection objective 2101.
R = k · λ NA ,
wherein R stands for the minimal resolution of the projection objective and k is a dimension-less factor which is referred to as process factor. The process factor k varies as a function of different factors, for example the polarization properties of the image projection or the selected modes of illumination. The process factor k lies typically in the range from 0.4 to 0.8 but can also be below 0.4 or above 0.8 for special applications.
In some embodiments, the projection objective 2101 has very small WRMS-values of the image in the image plane 2102. For example, a projection objective 2101 can have a WRMS-value of about 0.1·λ or less (e.g., 0.07·λ, less than 0.07·λ, less than 0.06·λ, less than 0.05·λ, less than 0.045·λ, less than 0.04·λ, less than 0.035·λ, less than 0.03·λ, less than 0.025·λ, less than 0.02·λ, less than 0.015·λ, less than 0.01·λ, less than 0.008·λ, and less than 0.006·λ).
In general, the part of the radiation that is reflected by a mirror varies as a function of the angle of incidence of the radiation on the mirror surface. As the image-producing radiation is propagated along a multitude of different paths in a catoptric projection objective, the angle of incidence of the radiation can vary between mirrors. This is illustrated in FIG. 1d which shows a part of a mirror 2300 in a sectional view along the meridional plane. The mirror 2300 contains a concave reflective mirror surface 2301. The image-producing radiation which reaches the surface 2301 along different paths includes for example the paths that are represented by the rays 2310, 2320, 2330. The rays 2310, 2320, 2330 fall on a part of the mirror surface 2301. The surface-normal directions on the surface of the mirror vary in this part of the mirror surface 2301 and are represented by the lines 2311, 2321 and 2331 for the points of incidence of the rays 2310, 2320 and 2330. The rays 2310, 2320 and 2330 meet the surface under the angles Θ2310, Θ2310 and Θ2310, respectively.
For every mirror in the projection objective 2100, it is possible to represent the angles of incidence of the image-producing rays in a multitude of ways. One possible form of representation is through the respective maximum angle of the rays that fall on each mirror in the meridional section of the projection objective 2101. This maximum angle is referred to as Θmax. In general, the angle Θmax can vary between different mirrors of the projection objective 2101. In certain embodiments of the disclosure, the overall maximum value (Θmax)max for all mirrors of the projection objective 2101 is 60° or less (e.g., 55° or less, 50° or less, 45° or less). In some examples, the overall maximum angle (Θmax)max is relatively small, for example 40° or less (e.g., 35° or less, 30° or less, 25° or less, 20° or less).
As another possibility, the incident light on a mirror can be characterized through the angle of incidence on each mirror in the meridional section for the principal ray of the central field point of the field to be illuminated in the object plane. This angle is referred to as ΘCR. Concerning the principal ray angle ΘCR, reference is also made to what has been said hereinabove in the introductory part. It is again possible to define a maximum angle ΘCR(max) in the projection objective as the maximum principal ray angle of the central field point. This angle ΘCR(max) can be relatively small, for example smaller than 40° (e.g., smaller than 35°, smaller than 30°, smaller than 25°, smaller than 20°, smaller than 15°).
Each mirror in the projection objective 2101 can further be characterized by a range of the angles of incidence in the meridional section of the projection objective 2101. The range within which the angle Θ varies on each mirror is referred to as ΔΘ. The range ΔΘ for each mirror is defined as the difference between an angle Θ(max) and an angler Θ(min), wherein Θ(min) stands for the minimum angle of incidence of the image-forming rays that fall on a mirror surface in the meridional section of the Projection objective 2101, and Θ(max) stands for the maximum angle of the incident image-forming rays on a mirror surface, as has already been defined above. The range ΔΘ generally varies between mirrors in the projection objective 2101 and can be relatively small for some mirrors, for example smaller than 25° (e.g., smaller than 20°, smaller than 15°, smaller than 10°). On the other hand, ΔΘ can be relatively large for other mirrors in the projection objective 2101. For example, ΔΘ can be 20° or larger, in particular 25° or larger (e.g., 30° or larger, 35° or larger, 40° or larger). In some embodiments, the maximum value ΔΘmax for all ranges ΔΘ, i.e. the maximum over all mirrors of the projection objective 2101 for the respective range of variation ΔΘ on each mirror can be relatively small, for example smaller than 25° (e.g., smaller than 20°, smaller than 15°, smaller than 12°, smaller than 10°, smaller than 8°).
FIG. 1e shows an example of a mirror 2660 of the type used in the projection objective. The mirror 2660 has the shape of a ring segment, i.e., a segment of a circular mirror 2670 with a diameter D. The mirror 2660 has a maximum dimension Mx in the x-direction. In examples of embodiments, the dimension Mx can be 800 mm or less (e.g., 700 mm or less and, 600 mm or less, 500 mm or less, 400 mm or less, 300 mm or less, 200 mm or less, 100 mm or less).
In general, the shape of the field of the projection objective 2101 can vary. FIG. 1f shows a ring segment 2700, also referred to as a ring field. The ring segment 2700 can be characterized by an x-dimension Dx, a y-dimension Dy, and a radial dimension Dr. Dx and Dy are the dimensions of the field as measured, respectively, in the x-direction and in the y-direction. The amounts for these dimensions will be named in the following description. For example in a field of 26×2 mm2 in the image plane, the dimension Dx is 26 mm and Dy is 2 mm. The dimension Dr represents the ring radius measured from the optical axis 2105 to the inner border of the field 2700. The ring field segment 2700 is symmetric relative to a plane indicated by the line 2710, which is parallel to the y/z-plane. In general, Dx, Dy and Dr vary in magnitude, depending on the design of the projection objective 2101. Typically, Dx is larger than Dy. The relative sizes of the field dimensions or field measurements Dx, Dy and Dr in the object plane 2103 and in the image plane 2102 vary as a function of the magnification or reduction ratio of the projection objective 2101. In some examples, Dx in the image plane 2102 is relatively large, for example larger than 1 mm (e.g., larger than 3 mm and, larger than 4 mm, larger than 5 mm, larger than 6 mm, larger than 7 mm, larger than 8 mm, larger than 9 mm, larger than 10 mm, larger than 11 mm, larger than 12 mm, larger than 13 mm, larger than 14 mm, larger than 15 mm, larger than 18 mm, larger than 20 mm, larger than 25 mm, larger than 30 mm). The dimension Dy in the image plane 2102 can lie in the range from 0.5 mm to 5 mm (e.g., up to 1 mm, up to 2 mm, up to 3 mm, up to 4 mm). Typically, Dr in the image plane 2102 is in the range from 10 mm to 50 mm (e.g., 15 mm or more or, 20 mm or more, 25 mm or more, 30 mm or more).
Generally speaking, for other field shapes such as for example a rectangular field, the projection objective 2101 can have a maximum field dimension or field measurement in the image plane 2102 of more than 1 mm (e.g., more than 3 mm and, more than 4 mm, more than 5 mm, more than 6 mm, more than 7 mm, more than 8 mm, more than 9 mm, more than 10 mm, more than 11 mm, more than 12 mm, more than 13 mm, more than 14 mm, more than 15 mm, more than 18 mm, more than 20 mm, more than 25 mm, more than 30 mm). FIG. 1e further shows the central field point Z. The central field point Z defines the origin of a local x-y-z coordinate system. In scanning microlithography systems, the y-direction generally indicates the scanning direction.
FIG. 1g gives a detailed illustration of a state-of-the-art microlithography projection exposure apparatus as disclosed in Patent Application Publication US 2005/088760. The projection objective 1 has a negative back focus. The illumination system includes a primary light source 3 and a light-collecting optical element, a so-called collector 5. The collector 5 is a grazing-incidence collector. The radiation emitted by the light source is filtered by means of the spectral filter element 7 together with the aperture stop 9, so that behind the aperture stop there is only usable radiation of, e.g., 13.5 nm wavelength. The spectral filter in the form of a grid element diffracts the light that falls on the grid element in different directions, for example in the first-order diffraction. The aperture stop is arranged in or near the intermediate image 11 of the primary light source 3 in the first-order diffraction. The projection exposure apparatus further includes a first facetted optical element 13 with first facets, so-called field raster elements which are configured as small facet mirrors, and a second optical element 15 with second facets, so-called pupil raster elements. The first optical element 13 which comprises the field facets breaks up the incident light bundle 17 which arrives from the primary light source 3 into a multitude of light bundles. Each of the light bundles is focused and forms a secondary light source at or near the place where the second optical element 15 with pupil raster elements is arranged.
As can be seen clearly in FIG. 1g, with the configuration of the state-of-the-art projection objective, the light-ray path crosses over itself between the illumination system and the projection objective, and consequently this system is not amenable to a modular configuration which would allow a separation of the illumination system from the projection objective.
FIG. 1h represents the ray path for many of the embodiments of projection objectives that are presented herein, which have a negative back focus in the area of the object plane 51 of the projection objective and of the mirror S1 that comes first in the light path from the object plane to the image plane, with the latter not being shown in FIG. 1h. The symbol CRE in FIG. 1h identifies the incident principal ray falling on the first mirror, and CRR represents the reflected principal ray belonging to one and the same field point, for example the central field point, of the object field. As can be seen in FIG. 1h, in some embodiments of the disclosure the principal ray CRE of the incident light bundle in the meridional plane of the projection objective lies between the principle ray of the light bundle CRR that is reflected from the surface of the mirror S1 and the optical axis HA of the projection objective.
Also shown in FIG. 1h is the local x-y-z coordinate system, the normal direction NO that is perpendicular to the object plane 51 in which an object field is formed, and the positive principal ray angle γ under which the principal ray CRE is reflected by an object (not shown) in the object plane 51.
FIG. 2a illustrates a first embodiment of a six-mirror projection objective which has a negative back focus of the entry pupil, but which is amenable to a modular design configuration of a microlithography projection exposure apparatus. The objective according to FIG. 2a has an object plane 100, an image plane 102, a first mirror S1, a second mirror S2, a third mirror S3, a fourth mirror S4, a fifth mirror S5, and a sixth mirror S6.
As can be clearly seen, no intermediate image is formed in the light path from the object plane 100 to the image plane 102 in the projection objective shown in FIG. 2a. The objective has only a single aperture stop plane 104 which in the illustrated example is located on the fifth mirror, i.e. in the posterior part of the objective which consists of the fifth mirror S5 and the sight mirror S6. By arranging the aperture stop plane 104 in this way, it becomes possible to arrange the mirrors S1 and S2 in the anterior part of the objective at a large distance from the optical axis HA. If a projection objective of this kind is used in a projection exposure apparatus with a reflective object in an object plane, the arrangement where the mirrors in the anterior part of the objective have a large distance from the optical axis makes it possible to place components of the illumination system, specifically a facetted optical element of the illumination system, in this space on the optical axis of the projection system and thus in or near the mirrored entry pupil RE. The projection objective illustrated in FIG. 2a has an image-side numerical aperture of NA=0.25 and a reduction ratio of 4. The field size of the field that is projected into the image plane is 2×26 mm2, which means that the dimension Dy of the field measured along the y-axis (see FIG. 1e) is 2 mm, and the dimension Dx is 26 mm. In the example shown in FIG. 2, the principal ray CRE of the incident ray bundle falling on the mirror surface of the first mirror S1 lies on the meridional plane between the reflected principal ray CRR associated with the same field point of the reflected ray bundle and the optical axis HA of the projection objective. Further shown is the mirrored entry pupil RE of the projection objective, which lies in the plane 103. The point of intersection with the optical axis of the principal ray CR of the light beam 105 propagating from the object plane to the image plane is identified by the label “CROSS”. According to the disclosure, this point of intersection labeled CROSS lies in the posterior part of the objective in the meridional section between the plane 103 in which the mirrored entry pupil RE lies and the plane that contains the point of intersection CROSS. The projection objective in the configuration of FIG. 2a has a resolution of 22 nm, an image-side wave front aberration RMS of 0.008λ, an image-side field curvature of 7 nm and a distortion of 2.5 nm. The objective has no intermediate image, and it possesses an accessible aperture stop plane 104. As described above, the aperture stop B is formed in the accessible aperture stop plane 104—which is also at the same time a pupil plane and which includes the point of intersection CROSS—on the fifth mirror. FIG. 2a further shows the distance A1 of the plane 104 containing the point of intersection CROSS from the object plane 100 along the optical axis HA as well as the distance A2 of the plane 103 containing the mirrored entry pupil RE from the object plane 100. The two distances conform to the rule A2<A1. Also shown in FIG. 2a are a first sub-objective (SUBO1) and a second sub-objective (SUBO2), where the second sub-objective (SUOBO2) includes the aperture stop B.
It can further be seen in FIG. 2a that the projection objective is subdivided into two partial systems, i.e. a first partial system PART1 and a second partial system PART2. The first partial system PART1 with the mirrors S1 and S2 has a distance DIS along the optical axis HA from the second partial system PART2 with the mirrors S3, S4, S5 and S6.
The principal ray angle γ in the first embodiment, i.e. the angle of the principal ray CR associated with the central field point of the field in the object plane 100 is γ=7° in relation to the surface-normal direction. The distance of the central field point from the optical axis is 132 mm. Based on these data, it can be calculated that the mirrored entry pupil RE has a maximum distance of 1075 mm from the object plane. The optical data of the embodiment shown in FIG. 2a are listed in Code V format in Table 1 which is attached as FIG. 2b. The nomenclature of tables in Code V format are well understood by a man skilled in the art. In the Code V tables for reflective systems thickness mean in the context of mirror systems the thickness of the air space between two neighboring optical surfaces, i.e., the distance along the optical axis between two optical surfaces that directly follow each other in the light path
FIG. 3a illustrates a second embodiment of a six-mirror projection objective according to the disclosure without intermediate image and with negative back focus of the entry pupil. This embodiment has an image-side numerical aperture NA of 0.30 and a field size Dy×Dx of 2×26 mm2 as well as a reduction ratio of 4×. The image-side wave front aberration is 0.03λ, the image-side field curvature 18 nm, and the distortion is 4 nm. In the sequence of mirrors from the object plane to the image plane the mirror curvatures follow each other as N-P-P-N-N-P, i.e. convex-concave-concave-convex-convex-concave. The projection objective includes an accessible aperture stop 104. The aperture stop B is arranged in the accessible aperture stop plane 104 on the fifth mirror. The aperture stop plane is at the same time also a pupil plane which contains the point of intersection CROSS of the principal ray CR with the optical axis HA. The distance from the object plane 100 to the image plane 102 is 1600 mm, the maximum dimension My in the meridional section for all mirrors is 176 mm, and the maximum mirror diameter, i.e. the maximum dimension Mx measured in the x-direction for all mirrors is 459 mm.
The principal ray angle at the central field point is γ=7° at the object, and the distance of the central field point from the optical axis is 159 mm. The mirrored entry pupil RE in the plane 103 has an axial distance A2 of 1295 mm from the object plane 100. Components that are analogous to those in FIG. 2a have the same reference symbols. As in FIG. 2a, the principal ray CRE of the incident ray bundle falling on the surface of the first mirror S1 lies in the meridional section between the optical axis and the principal ray CRR of the ray bundle associated with the same field point that is reflected from the surface of the first mirror. The point of intersection CROSS of the principal ray CR of the central field point with the optical axis HA of the projection objective is geometrically located between the plane 103 with the mirrored entry pupil RE of the projection objective and the image plane 102. The distance along the optical axis between the plane 104 which contains the point of intersection CROSS and the object plane is labeled with A1, and the distance along the optical axis between the plane 103 which contains the mirrored entry pupil and the object plane is labeled with A2. In the present embodiment, A2 is smaller than A1, due to the location of the point of intersection CROSS between the mirrored entry pupil RE and the image plane.
As can be seen in FIG. 3a, the principal ray has on its light path from the object plane 100 to the image plane 102 exactly one point of intersection CROSS with the optical axis. Therefore, according to the disclosure, all points of intersection of the projection objective lie between the plane 103 of the mirrored entry pupil RE and the image plane 102.
The system data in Code V format for the second embodiment according to FIG. 3a are listed in Table 2 in FIG. 3b.
FIG. 4 shows a microlithography projection exposure apparatus with a projection objective according to the embodiment of FIG. 2a and FIG. 2b. As can be seen in FIG. 4, there is no cross-over between the ray pattern of the projection system and the ray pattern of the illumination system, which stands in contrast to the system of FIG. 1g. In other words, the illumination ray bundle 211 on its light path from the next-to-last optical component 206 to the object plane 212 where the object such as a reticle is arranged does not cross over the image-producing ray pattern 213 which proceeds in the projection objective from the object plane 212 to the image plane 214, except for the necessary cross-over which occurs at the reticle. The meridional plane in the present case is the plane of the drawing, which includes the optical axis HA. The optical elements of both parts of a projection exposure apparatus, i.e. the illumination system and the projection system, are arranged in separate design envelopes. The optical elements of the illumination system are arranged in a first design space B1, while the optical elements of the projection system are arranged in a second design space B2. The first design space B1 is separated for example by a wall W from the second design space B2. Due to the separation between two different design spaces B1 and B2, one obtains a modular design structure for the projection exposure apparatus. As can further be seen, there is enough space available for example for the installation of the pupil facet mirror 208 of a double-facetted illumination system.
In the following embodiments of microlithography projection objectives with negative back focus of the entry pupil according to FIGS. 5a and 5b and FIGS. 6a and 6b, a free space is created in the microlithography projection exposure apparatus in the area of the mirrored entry pupil RE through a design concept that provides for a cross-over of ray bundles in the anterior part of the objective. The anterior part of the objective is that part of the projection objective which comprises the mirrors which are arranged nearest to the object plane. With this kind of a design it is possible to arrange in particular the second mirror S2 of the six-mirror objective shown in the examples of FIGS. 5a and 6a at a large distance from the optical axis HA of the projection objective. The cross-over of rays in the meridional plane which contains the optical axis HA of the projection objective occurs in the illustrated examples of FIGS. 5a, 5b and 6a, 6b between the ray bundle which proceeds from the object plane 300 to the first mirror S1 and the ray bundle which proceeds from the second mirror S2 to the third mirror S3. The aperture stop B is arranged in the ray path from the second mirror S2 to the third mirror S3. Due to the large distance of the mirrors in the anterior part of the objective from the optical axis, it is possible to design a microlithography projection exposure apparatus in which the ray pattern of the illumination system does not cross over the ray pattern of the projection objective in the meridional plane, so that a separation is possible between the illumination system and the projection objective, as is the case for example in the system in FIG. 4.
In the example shown in FIG. 5a of a six-mirror projection objective with cross-over of the ray bundles in the anterior part of the objective, an intermediate image ZW is formed between the fourth mirror S4 and the fifth mirror S5. The first mirror is labeled as S1, the second mirror as S2, the third mirror as S3, and the sixth mirror in the light path from the object plane 300 to the image plane 302 is labeled as S6. As was already the case in FIGS. 2a and 3a, FIG. 5a shows only the usable portion of each mirror, with the usable portion of the first mirror S1 labeled N1, the usable portion of the second mirror S2 labeled N2, the usable portion of the third mirror S3 labeled N3, the usable portion of the fourth mirror S4 labeled N4, the usable portion of the fifth mirror S5 labeled N5, and the usable portion of the sixth mirror S6 labeled N6. The usable portion of a mirror is the area that meets the rays of the light bundle which travel from the object plane to the image plane. The embodiment according to FIG. 5 has an image-side numerical aperture of NA=0.25, a reduction ratio of 4×, and a field size of 2×26 mm2 of the field in the object plane, i.e. Dy=2 mm and Dx=26 mm. The principal ray angle of the central field point is γ=7° at the object and the distance of the central field point from the optical axis is 93 mm. As can be calculated from these data, the mirrored entry pupil RE has an axial distance of 757 from the object plane. The resolution is 22 nm, the image-side wave-front aberration RMS is 0.006λ, the image-side field curvature is 1.5 nm, and the distortion is 6 nm. The mirrors follow each other in the sequence P-P-N-P-N-P, i.e. concave-concave-convex-concave-convex-concave. Two planes that are conjugate to the entry pupil, so-called pupil planes 312, 314, are formed in the system. The pupil plane 312 contains the point of intersection CROSS1 of the principal ray CR with the optical axis, while the pupil plane 314 contains the point of intersection CROSS2. The projection objective is telecentric on the image side, so that the exit pupil lies at infinity. The system is distinguished by the fact that the exit pupil is not obscured. The term “exit pupil” means the image of the aperture stop produced by the partial objective that follows the aperture stop. An accessible aperture stop B is arranged in one of the two pupil planes 312, 314 which is accessible from at least one side of the projection objective. The aperture stop B in the present example is formed between the second and third mirrors. The maximum mirror diameter, i.e. the maximum dimension My of all mirrors as measured in the meridional section is 157 mm, and the maximum mirror diameter of all mirrors as measured in the x-direction, i.e., the maximum dimension Mx, is 389 mm. The maximum angle ΔΘCR(max) of the principal ray of the central field point for all mirrors is 16.4°, the maximum angle of incidence Θmax(max) on all mirrors in the meridional section is 21°. The maximum bandwidth ΔΘmax of the angles of incidence in the meridional section on each mirror is 17.3° for all mirrors.
The optical data of the example of FIG. 5a are listed in Code V format in Table 3 which is found in FIG. 5b.
FIG. 6a illustrates a further embodiment of a six-mirror projection objective according to the disclosure with an intermediate image and with negative back focus of the entry pupil. This embodiment has an image-side numerical aperture NA of 0.30, a reduction ratio of 4×, and a field size of 2×26 mm2, i.e. Dy=2 mm and Dx=26 mm. The principal ray angle at the central field point is γ=7° at the object, and the distance of the central field point from the optical axis is 106 mm. The distance between the object plane 300 and the image plane 302 is 1520 mm. The mirrored entry pupil RE has an axial distance of 754 mm from the object plane. The system has a resolution of 18 nm, an image-side wave front aberration RMS of 0.018λ, an image-side field curvature of 11 nm, and a distortion of 3.2 nm. The six mirrors follow each other from the object plane to the image plane in the sequence P-P-N-P-N-P, i.e. concave-concave-convex-concave-convex-concave. Two pupil planes are formed in the light path from the object plane to the image plane, with one of the pupil planes being accessible. The aperture stop B is arranged in the accessible pupil plane. The aperture stop plane B is formed between the second and the third mirror. The maximum mirror diameter, i.e. the maximum dimension My of all mirrors as measured in the meridional section is 189 mm, and the maximum mirror diameter of all mirrors as measured in the x-direction, i.e., the maximum dimension Mx, is 423 mm. The maximum angle of incidence ΔΘCR(max) of the principal ray of the central field point for all mirrors is 19°, the maximum angle Θmax(max) for all mirrors in the meridional section is 24.1°, and the maximum range ΔΘmax of the angles of incidence for all mirrors is 19.8°. Components that are analogous to those in FIG. 5a are identified by the same reference numerals. Common to both of the systems of FIG. 5a and FIG. 6a is the spatial arrangement of the mirrors in the anterior part of the objective along the optical axis, namely:
second mirror S2—fourth mirror S4—first mirror S1—third mirror S3.
Furthermore common to both of the systems of FIG. 5a and FIG. 6a, the aperture stop B is arranged between the second mirror S2 and the third mirror S3 in or near the pupil plane 312.
The optical data of the embodiment according to FIG. 6a are listed in Code V format in Table 4 which is presented in FIG. 6b.
The embodiment of FIG. 6c represents an alternative to the systems according to FIGS. 5a and 6a. The aperture stop B in the embodiment of FIG. 6c is located directly on the third mirror S3 in the pupil plane 312. Placing the aperture stop on a mirror has the advantage that the passing ray bundles are not separated as strongly from each other, so that either the angles of incidence can be made smaller or, if the angles of incidence are kept the same, the overall length can be made shorter, as is the case in this example. The system according to FIG. 6c has the further advantage that the angles of incidence are small on all mirrors. The spatial arrangement of the mirrors in the anterior part of the objective is as follows:
fourth mirror S4—second mirror S2—first mirror S1—third mirror S3.
Compared to the embodiment of FIG. 6a, the positions of the mirrors S2 and S4 along the optical axis have been switched.
FIG. 6c shows a lens section of the foregoing system. The optical data for this system are listed in Code V format in Table 5 which is shown in FIG. 6d. The image-side numerical aperture of the system is NA=0.25, and the field size is 2×26 mm2, wherein the field is configured as a ring field segment. The reduction ratio of the system of FIG. 6c is 4×, the image resolution is 22 nm, the RMS value for the image-side wave-front aberration is 0.019λ, the image-side field curvature is 20 nm, and the distortion is 0.8 nm. There are six mirrors in total following each other in the sequence PPNPNP, i.e. concave-concave-convex-concave-convex-concave. Overall, the system has two pupil planes 312, 314, one of which is accessible. The accessible pupil plane is at the same time the plane in which the aperture stop B is arranged. The aperture stop B is arranged on the third mirror. The distance between the object plane 100 and the image plane 102 is 1490 mm, the maximum mirror diameter, i.e. the maximum dimension My of all mirrors as measured in the meridional section is 197 mm, and the maximum mirror diameter of all mirrors as measured in the x-direction, i.e., the maximum dimension Mx, is 464 mm, and the maximum angle of incidence ΔΘCR(max) of the principal ray of the central field point for all mirrors is 16.6°, the maximum angle Θmax(max) for all mirrors in the meridional section is 19.2°, and the maximum range ΔΘmax of the angles of incidence in the meridional section for all mirrors is 16.7°.
A first embodiment of a system of this type is shown in FIG. 7. The system according to FIG. 7 includes a projection objective 1000 with negative back focus which has a first mirror S1, a second mirror S2, a third mirror S3, a fourth mirror S4, a fifth mirror S5, and a sixth mirror S6. Furthermore, the illumination system includes a nested grazing-incidence collector 1002 which is located in the light path downstream of the light source and receives the radiation of the light source 1004 in a half-space with a large aperture of NA 0.7. The illustrated collector in the schematic sketch has only two mirror shells which are rotationally symmetric relative to an axis of rotation, wherein two reflections occur at each of the shells. Of course, a collector with more than two shells and with more than two reflections per shell would likewise be conceivable. In the embodiment shown in FIG. 7, a normal-incidence mirror 1008 is arranged in the light path from the light source 1004 to the object plane 1006. Due to its multi-layered coatings, for example 40 to 70 Mo/Si coatings, the normal-incidence mirror 1008 functions as a narrow-band wavelength filter. The concept of using a normal-incidence mirror which due to its multi-layered coating acts as a narrow-band wavelength filter belongs to the known state of the art. A mirror of this type can be moved into different positions, so that different usable areas 1008.1 and 1008.2 can be positioned in the ray path. In the present example, the move to a different location occurs by turning about the axis of rotation RA. The area of the multi-layered mirror 1008 that is moved out of the ray path can now be cleaned, for example with a cleaning device. In addition, a spectral grid filter can be put on the currently operative usable range 1008.1, 1008.2 of the normal-incidence multi-layered mirror 1008. The way in which the state-of-the-art spectral filter removes light that is not of the usable wavelength is that the light of the light source falls on a grid which has at least one grid period in a grid plane that is significantly larger than the usable wavelength (e.g., 150 to 200 times larger than the usable wavelength). If the usable wavelength is for example around 13.5 nm, the periodicity of a binary grid acting in this manner as a spectral filter is of the order of microns.
The system of FIG. 8 has only 8 mirrors in the light path from the light source to the image plane of the projection objective where the object to be illuminated is arranged, for example a wafer. However, the reflective reticle in the object plane was not counted in the number of mirrors for the system according to FIG. 8. As an alternative possibility in the system according to FIG. 8, the collector 2004 can be replaced by an other collector, for example a grazing-incidence collector. Even with a system of this kind with a grazing-incidence collector, it is possible to specify an EUV projection exposure apparatus with nine or fewer mirrors in which an image-side numerical aperture of NA≧0.25 (e.g., NA≧0.3) is possible with a field size of 2×26 mm2.
With the system according to FIG. 10, a projection exposure apparatus is made available which illuminates a field of 26×2 mm2 with an image-side numerical aperture NA≧0.25 (e.g., NA≧0.3). The projection exposure apparatus has a maximum of 10 or fewer components at which normal-incidence reflections occur.
In addition to the microlithography projection systems with negative back focus of the entry pupil which allow a modular design of the foregoing description to be realized, the disclosure also provides microlithography projection systems with a small number of optical components and with an image-side numerical aperture NA≧0.25 (e.g., A≧0.3) with a maximum dimension (Dx, Dy) of a field on the image side of more than 1 mm (e.g., more than 3 mm, more than 4 mm, more than 5 mm, more than 6 mm, more than 8 mm, more than 10 mm, more than 12 mm, more than 15 mm, more than 20 mm, more than 25 mm). In a system of this type, there are optionally ten or fewer normal-incidence reflections on optical elements between the light source and the image plane, wherein the reflection on the reflective object that is arranged in the object plane, specifically the reflective reticle, is not counted. The size of the image field can be for example 2×26 mm2. Particularly advantageous within this context are microlithography projection systems in which only one optical integrator is required. Among systems with only one optical integrator, a special advantage is held by those systems that are distinguished by the fact that the optical integrator can be placed at an arbitrarily chosen location in the microlithography projection exposure apparatus. Optical integrators which meet these requirements are in particular so-called location-variant or field dependent optical integrators or specular reflectors.
1. A projection objective having an entry pupil, an exit pupil, an object plane, an image plane, and a light path between the object plane and the image plane, the projection objective comprising:
at least five mirrors arranged in the light path,
wherein: the projection objective has a negative back focus of the entry pupil; the projection objective is configured so that, during use of the projection objective, the projection objective has no intermediate image along the light path between the image plane and the object plane; and the projection objective is a microlithography projection objective.
2. The projection objective of claim 1, further comprising an aperture stop arranged in or near a pupil plane of the projection objective.
3. The projection objective of claim 2, wherein:
at least one of the at least five mirrors is located along the light path before the aperture stop; and
at least a different one of the at least five mirrors is located along the light path after the aperture stop.
4. The projection objective of claim 3, wherein at least two mirrors of the at least five mirrors are located along the light path after the aperture stop.
5. The projection objective of claim 4, wherein the at least five mirrors comprise at least six mirrors, and at least four of the at least six mirrors are located along the light path before the aperture stop.
6. The projection objective of claim 3, wherein the at least five mirrors comprise at least six mirrors, and at least four of the at least six mirrors are located along the light path before the aperture stop.
7. The projection objective of claim 1, wherein the projection objective has an image-side numerical aperture of at least 0.2.
8. The projection objective of claim 1, wherein the at least five mirrors comprises first, second, third fourth, fifth and sixth mirrors in sequence along the light path.
9. The projection objective of claim 8, wherein the first mirror is convex-shaped, the second mirror is concave-shaped, the third mirror is concave-shaped, the fourth mirror is convex-shaped, the fifth mirror is convex-shaped, and the sixth mirror is concave-shaped.
10. The projection objective of claim 9, wherein:
the first and second mirrors define a first partial system; and
the third, fourth, fifth and sixth mirrors define a second partial system.
11. The projection objective of claim 10, wherein a geometrical distance between the first and second partial systems along an optical axis of the projection objective is more than 30% of an overall length of the objective.
12. The projection objective of claim 8, wherein:
13. The projection objective of claim 12, wherein a geometrical distance between the first and second partial systems along an optical axis of the projection objective is more than 30% of an overall length of the objective.
14. The projection objective of claim 1, wherein each of the at least five mirrors is rotationally symmetric with respect to an optical axis of the projection objective.
15. The projection of claim 1, wherein the projection objective is a catoptric projection objective.
16. The projection objective of claim 1, wherein the projection objective is a catadioptric projection objective.
17. The projection objective of claim 1, wherein the projection objective is configured to direct radiation of a wavelength of less than or equal to 193 nanometers from the object plane to the image plane.
a projection objective having an entry pupil, an object plane, an image plane, and a light path between the object plane and the image plane, the projection objective comprising at least five mirrors arranged in the light path,
wherein: the projection objective has a negative back focus of the entry pupil; the projection objective is configured so that, during use of the projection exposure apparatus, the projection objective has no intermediate image in the light path; and the projection exposure apparatus is a microlithography projection exposure apparatus.
19. The projection exposure apparatus of claim 18, further comprising an aperture stop arranged in or near a pupil plane of the projection objective.
20. The projection exposure apparatus of claim 19, wherein:
at least another one of the at least five mirrors is located along the light path after the aperture stop.
21. The projection exposure apparatus of claim 20, wherein at least two mirrors are located along the light path after the aperture stop.
22. The projection exposure apparatus of claim 21, wherein the at least five mirrors comprise at least six mirrors, and at least four of the at least six mirrors are located along the light path before the aperture stop.
4650292 March 17, 1987 Baker et al.
4655555 April 7, 1987 Maechler et al.
5003567 March 26, 1991 Hawryluk et al.
5071240 December 10, 1991 Ichihara et al.
5212588 May 18, 1993 Viswanathan et al.
5309276 May 3, 1994 Rodgers
5812309 September 22, 1998 Thoma et al.
6033079 March 7, 2000 Hudyma
6072852 June 6, 2000 Hudyma
6195201 February 27, 2001 Koch et al.
6198793 March 6, 2001 Schultz et al.
6226346 May 1, 2001 Hudyma
6240158 May 29, 2001 Oshino
6244717 June 12, 2001 Dinger
6266389 July 24, 2001 Murayama et al.
6302548 October 16, 2001 Takahashi et al.
6318869 November 20, 2001 Hudyma
6353470 March 5, 2002 Dinger
6359678 March 19, 2002 Ota
6426506 July 30, 2002 Hudyma
6452661 September 17, 2002 Komatsuda
6512641 January 28, 2003 Omura
6549270 April 15, 2003 Ota
6557443 May 6, 2003 Laruc
6577443 June 10, 2003 Dinger
6600552 July 29, 2003 Dinger
6660552 December 9, 2003 Payne et al.
6666560 December 23, 2003 Suzuki
6750948 June 15, 2004 Omura
6850361 February 1, 2005 Nakano et al.
6867913 March 15, 2005 Mann et al.
6894834 May 17, 2005 Mann et al.
6902283 June 7, 2005 Dinger
6922291 July 26, 2005 Sunaga et al.
6929373 August 16, 2005 Yoshikawa
6947210 September 20, 2005 Terasawa
7114818 October 3, 2006 Minakata
7224441 May 29, 2007 Sasaki
7414781 August 19, 2008 Mann et al.
7719772 May 18, 2010 Mann et al.
7869138 January 11, 2011 Mann et al.
8094380 January 10, 2012 Mann et al.
20010002155 May 31, 2001 Takahashi et al.
20010038446 November 8, 2001 Takahashi
20010043391 November 22, 2001 Shafer et al.
20020012100 January 31, 2002 Shafer
20020171048 November 21, 2002 Braat
20030076483 April 24, 2003 Komatsuda
20030147131 August 7, 2003 Terasawa
20040070743 April 15, 2004 Hudyma et al.
20040114217 June 17, 2004 Mann et al.
20040165255 August 26, 2004 Sasaki et al.
20040165282 August 26, 2004 Sunaga et al.
20040252358 December 16, 2004 Kawahara et al.
20050088760 April 28, 2005 Mann et al.
20050134980 June 23, 2005 Mann et al.
20060209302 September 21, 2006 Sasaki
20060232867 October 19, 2006 Mann et al.
20060284113 December 21, 2006 Chang et al.
20070195317 August 23, 2007 Schottner et al.
20070223112 September 27, 2007 Mann et al.
20090262443 October 22, 2009 Mann et al.
20110063596 March 17, 2011 Mann et al.
33 43 868 June 1985 DE
102 12 405 October 2002 DE
103 59 576 July 2005 DE
10 2005 042 005 July 2006 DE
0 730 169 September 1996 EP
0 730 179 September 1996 EP
0 730 180 September 1996 EP
0 779 528 June 1997 EP
0 730 513 August 1997 EP
1 069 448 January 2001 EP
1 093 021 April 2001 EP
1 199 590 April 2002 EP
1 225 481 July 2002 EP
1 335 229 August 2002 EP
1 333 260 August 2003 EP
1 335 228 August 2003 EP
1 450 196 August 2004 EP
1 450 209 August 2004 EP
1 494 056 January 2005 EP
1 376 191 January 2007 EP
3-041328 February 1991 JP
07 036959 February 1995 JP
07 283116 October 1995 JP
11-110791 April 1999 JP
2000-031041 January 2000 JP
2003-107354 April 2003 JP
2003-114387 April 2003 JP
2003-222572 August 2003 JP
2003-233002 August 2003 JP
2004-029625 January 2004 JP
2004 512552 April 2004 JP
2004-170869 June 2004 JP
2004-516500 June 2004 JP
2004-214242 July 2004 JP
2004 525398 August 2004 JP
2004-258541 September 2004 JP
2005-055553 March 2005 JP
2005-166778 June 2005 JP
2005-258457 September 2005 JP
476943 February 2002 TW
594043 June 2004 TW
2004 17758 September 2004 TW
226938 January 2005 TW
WO 02/48796 June 2002 WO
WO 2004/010224 January 2004 WO
Russell Hudyma, “An Overview of Optical Systems for 30nm Resolution Lithography at EUV Wavelengths,” Proceedings of SPIE, vol. 4832, Dec. 2002, pp. 137-148.
Bal, Matthieu Frèdèric, dissertation “Next-Generation Extreme Ultraviolet Lithographic Projection Systems”, pp. 1-139, (Feb. 10, 2003).
National Science Foundation article, “Breakthrough Brings Lasser Light to New Regions of the Spectrum,” NSF PR 03-01; date: Jan. 2, 2003.
T. Jewell “Optical system design issues in development of projection camera for EUV lithography, ” SPIE vol. 2437, p. 340-346, Aug. 1995.
Japanese Office Action, with English translation, for corresponding JP Appl No. 2007-081783, dated Aug. 17, 2012.
English translation of Office Action for corresponding Application No. JP 2008-529565, dated Feb. 21, 2011.
Office Action for corresponding Application No. JP 2008-529565, dated Dec. 7, 2009.
The Taiwanese Office Action, with translation thereof, for corresponding TW Patent Application No. 0961109615, dated Oct. 4, 2013.
Japanese Office Action, with English translation, for corresponding JP Appl No. 2007081783, dated Aug. 19, 2013.
Patent number: 8687289
Patent Publication Number: 20120075608
Inventors: Hans-Juergen Mann (Oberkochen), Wolfgang Singer (Aalen)
Primary Examiner: Darryl J Collins
Application Number: 13/312,196
Current U.S. Class: With Reflecting Element (359/726); Including Concave Or Convex Reflecting Surface (359/727); Plural Mirrors Or Reflecting Surfaces (359/850)
International Classification: G02B 17/02 (20060101);