JP5504763B2 - Lens array and optical system - Google Patents

Description

  The present invention relates to a lens array in which a plurality of lenses are arranged adjacent to each other and an optical system having the lens array.

  Conventionally, among illumination optical systems used in exposure apparatuses such as photolithography, a lens array using a fly-eye lens (micro fly-eye lens) as an integrator optical system for ensuring illuminance uniformity on the focal plane There is a thing using. Further, as an example of the integrator optical system described above, one having a configuration in which two fly-eye lenses are arranged (see, for example, Patent Document 1). Furthermore, there are some in which both surfaces of the two fly-eye lenses are formed by cylindrical lens surfaces. In the case of the integrator optical system configured as described above, since all the surfaces of the two fly-eye lenses have a convex lens shape, the effective diameters of the entrance surface and the exit surface are reduced with respect to the overall size of each lens. There are many.

JP 2008-191469 A

  Here, when the fly-eye lens as described above is formed using photolithography, in the manufacturing process, solvent or post-bake is performed for smoothing the lens surface. Therefore, by design, the joint portion 201 that is outside the effective diameter of each of the adjacent cylindrical lenses 200 should form a corner portion 201a as indicated by a dotted line in the graph of FIG. 6 by combining the convex surface and the convex surface. Actually, unlike the design shape, the curved portion 201b becomes smooth as shown by the solid line in the graph of FIG.

  As a result, the curved portion 201b of the seam portion 201 has a light emission angle smaller than the designed angle, and as a result, the curved portion 201b is outside the effective diameter that should originally go outside the necessary area in the focal plane. There has been a problem in that light rays enter an area required as stray light and deteriorate the illumination intensity distribution.

  As a method for preventing such a phenomenon, the curved portion 201b of the joint portion 201 has the same shape as the designed corner portion 201a or approaches the designed corner portion 201a as much as possible. Conceivable. However, this method has proved to be very difficult due to the characteristics of manufacturing by photolithography.

  The present invention has been made in view of such circumstances, while ensuring the necessary amount of light and preventing stray light due to rays outside the effective diameter toward the required area in the focal plane, the focal plane It is an object of the present invention to provide a lens array capable of forming a uniform illumination intensity distribution with a light beam having an effective diameter in a necessary area of the lens and an optical system having the lens array.

In order to solve this problem, the present invention provides a lens surface (D) between a plurality of adjacent lenses in a lens array (110, 120) in which a plurality of lenses (111, 121) are arranged adjacent to each other. In addition, each lens has a concave portion (Dc) having a curved shape, and the portions of the lens surface excluding the concave portion in the cross section including the optical axis (K) are inside and outside the effective diameter (Da). The outer curvature is larger than the inner curvature across the boundary (L), and is configured to direct light rays outside the effective diameter of each lens out of the necessary area on the focal plane. It is characterized by having a lens array.

The present invention also provides an optical system (100) having two lens arrays, a first lens array (110) disposed on the light incident side and a second lens array (120) disposed on the light exit side. The two lens arrays are arranged such that a plurality of lenses (111, 121) are adjacent to each other, and a curved concave surface is formed on a lens surface (D) between the adjacent lenses. A portion (Dc), and at least each lens (121) of the second lens array has an effective diameter (Da) except for the concave portion of the lens surface in a cross section including the optical axis (K). ) The outer curvature is larger than the inner curvature across the inner / outer boundary (L), and the rays outside the effective diameter of each lens are directed outside the required area on the focal plane. Configured to Characterized in that the optical system is.

  Here, in order to explain the present invention in an easy-to-understand manner, the description has been made in association with the reference numerals of the drawings representing the embodiments. However, it is needless to mention that the present invention is not limited to the embodiments. .

  According to the present invention, the lens surface in the cross section including the optical axis is formed so that the outer curvature is larger than the inner curvature across the boundary between the inner and outer effective diameters. Can be prevented from entering the required area in the focal plane as stray light, and rays outside the effective diameter are directed outside the required area in the focal plane so that the effective diameter is within the required area in the focal plane. It is possible to form a uniform illumination intensity distribution by the light beams.

It is a schematic front view which shows the structure of the exposure apparatus which concerns on embodiment of this invention. 2 is a schematic perspective view showing one cylindrical lens in the first micro fly's eye lens of the integrator optical system provided in the exposure apparatus of FIG. 1 and one cylindrical lens in the corresponding second micro fly's eye lens. FIG. It is a schematic cross-sectional view which shows the mode of the lens surface of D surface of the 2nd micro fly's eye lens of FIG. It is the figure which represented the result of having compared the measured curvature radius of the design curvature radius of the D surface of one cylindrical lens in the 2nd micro fly's eye lens of FIG. 3 with an actual curvature radius in the graph. (A) It is the schematic for comparing and explaining the light state by the integrator optical system of this Embodiment, and (b) the light state by the conventional integrator optical system. It is the figure which represented the result of having compared the design shape and actual shape of the joint part of the cylindrical lenses in the conventional fly eye lens with the graph.

  Embodiments of the present invention will be described below.

  FIG. 1 is a schematic front view showing a configuration of an exposure apparatus according to an embodiment of the present invention. FIG. 2 is a schematic perspective view showing one cylindrical lens in the first micro fly's eye lens of the integrator optical system provided in the exposure apparatus of FIG. 1 and one cylindrical lens in the corresponding second micro fly's eye lens. . FIG. 3 is a schematic cross-sectional view showing a state of the lens surface of the D surface of the second micro fly's eye lens of FIG. FIG. 4 is a graph showing a result of comparing the measured curvature radius of the design curvature of the D surface of one cylindrical lens of the second micro fly's eye lens of FIG. 3 with the actual curvature radius.

  In this embodiment, as an embodiment of the optical system in the present invention, an integrator optical system provided in an exposure apparatus will be described as an example. In the present embodiment, a micro fly's eye lens constituting an integrator optical system will be described as an example of the lens array according to the present invention.

  First, an outline of an exposure apparatus 10 including a micro fly's eye lens and an integrator optical system according to the present embodiment will be described. As shown in FIG. 1, an exposure apparatus 10 in the present embodiment is an apparatus that exposes a wafer, and includes a light source 11, a beam expander 12, a bending mirror 13, a diffractive optical element 14, an afocal zoom lens 15, It has a diffractive optical element 16, a zoom lens 17, an integrator optical system 100 as an embodiment of the optical system in the present invention, a condenser optical system 18, a mask M, a projection optical system PL, a wafer W, and the like.

  In this embodiment, as the light source 11 for supplying exposure light (illumination light), for example, a KrF excimer laser light source that supplies light with a wavelength of 248 nm or an ArF excimer laser light source that supplies light with a wavelength of 193 nm is provided. Yes. A substantially parallel light beam emitted from the light source 11 along the Z direction has a rectangular cross section extending along the X direction, and is incident on the beam expander 12 including a pair of lenses 12a and 12b. Thus, the light beam is shaped into a light beam having a predetermined rectangular cross section.

  Further, the substantially parallel light beam via the beam expander 12 as a shaping optical system is deflected in the Y direction by the bending mirror 13 and then enters the afocal zoom lens 15 via the diffractive optical element 14. ing. In general, a diffractive optical element is formed by forming a step having a pitch of about the wavelength of exposure light (illumination light) on a glass substrate, and has a function of diffracting an incident beam to a desired angle. Specifically, the diffractive optical element 14 has a function of forming a circular light intensity distribution in the far field (or Fraunhofer diffraction region) when a parallel light beam having a rectangular cross section is incident. Therefore, the light beam passing through the diffractive optical element 14 forms a circular light intensity distribution, that is, a light beam having a circular cross section at the pupil position of the afocal zoom lens 15. The afocal zoom lens 15 is configured so that the magnification can be continuously changed within a predetermined range while maintaining an afocal system (non-focus optical system).

  The light beam that has passed through the afocal zoom lens 15 enters the diffractive optical element 16 for annular illumination. The afocal zoom lens 15 optically substantially conjugates the divergence origin of the diffractive optical element 14 and the diffractive surface of the diffractive optical element 16. The numerical aperture of the light beam condensed on one point of the diffractive surface of the diffractive optical element 16 or a surface in the vicinity thereof changes depending on the magnification of the afocal zoom lens 15. Further, the diffractive optical element 16 for annular illumination has a function of forming a ring-shaped light intensity distribution in the far field when a parallel light beam is incident.

  The light beam that has passed through the diffractive optical element 16 enters the zoom lens 17. In the vicinity of the rear focal plane of the zoom lens 17, in order from the light source side, the first micro fly's eye lens 110 as an embodiment of the first lens array in the present invention and the implementation of the second lens array in the present invention. An incident surface (that is, an incident surface of the first micro fly's eye lens 110) of an integrator optical system (optical integrator) 100 as an embodiment of the optical system in the present invention having the second micro fly's eye lens 120 as a form. It is positioned. The integrator optical system 100 functions to form multiple light sources based on the incident light flux.

  As described above, the luminous flux from the circular light intensity distribution formed at the pupil position of the afocal zoom lens 15 via the diffractive optical element 14 is emitted from the afocal zoom lens 15 and then has various angular components. Is incident on the diffractive optical element 16. That is, the diffractive optical element 14 constitutes an optical integrator having an angle beam forming function. On the other hand, the diffractive optical element 16 has a function of forming a ring-shaped light intensity distribution in the far field when a parallel light beam is incident. Therefore, the light beam that has passed through the diffractive optical element 16 forms an annular illumination field centered on the optical axis K, for example, on the rear focal plane of the zoom lens 17 (and hence on the incident plane of the integrator optical system 100).

  The outer diameter of the annular illumination field formed on the entrance surface of the integrator optical system 100 varies depending on the focal length of the zoom lens 17. Thus, the zoom lens 17 substantially connects the diffractive optical element 16 and the entrance surface of the integrator optical system 100 in a Fourier transform relationship. The light beam incident on the integrator optical system 100 is two-dimensionally divided, and a large number of annular light sources (hereinafter referred to as the illumination field) formed by the light beam incident on the integrator optical system 100 on the rear focal plane of the integrator optical system 100 , Referred to as “secondary light source”).

  The luminous flux from the annular secondary light source formed on the rear focal plane of the integrator optical system 100 is subjected to the light condensing action of the condenser optical system 18 and then superimposed on the mask M on which a predetermined pattern is formed. Illuminate. The light beam that has passed through the pattern of the mask M forms an image of the mask pattern on the wafer W, which is a photosensitive substrate, via the projection optical system PL. Thus, by performing batch exposure or scan exposure while two-dimensionally driving and controlling the wafer W in a plane (XY plane) orthogonal to the optical axis K of the projection optical system PL, each exposure region of the wafer W is masked. M patterns are sequentially exposed.

  As described above, in the exposure apparatus 10 according to the present embodiment, the integrator optical system 100 having the first micro fly's eye lens 110 and the second micro fly's eye lens 120 is used in order to improve the uniformity of illumination light. ing.

  Next, the integrator optical system 100 of the present embodiment will be described in more detail. As described above, the integrator optical system 100 according to the present embodiment includes the first micro fly's eye lens 110 disposed on the light incident side and the second micro fly's eye lens 120 disposed on the light exit side. It has two lens arrays. The first micro fly's eye lens 110 and the second micro fly's eye lens 120 of the present embodiment are arranged such that a plurality of lenses are adjacent to each other. In particular, in the present embodiment, the first micro fly eye lens 110 and the second micro fly's eye lens 120 are formed as cylindrical lenses. A plurality of lenses are arranged next to each other. As shown in FIG. 2, the cylindrical lenses 111 and 121 in the micro fly's eye lenses 110 and 120 are formed and arranged so as to be positioned on the same optical axis K in the configuration of the exposure apparatus 10. ing.

  Further, the cylindrical lens 111 in the first micro fly's eye lens 110 of the present embodiment has an A surface as an incident surface on the light incident side, and a C surface as an output surface on the output side of light incident from the A surface. ing. Furthermore, the cylindrical lens 121 in the second micro fly's eye lens 120 of the present embodiment has a B surface as an incident surface on the light incident side, and a D surface as an output surface on the output side of light incident from the B surface. ing. The two cylindrical lenses 111 and 121 in the present embodiment are formed in parallel with each other between the incident surfaces (A surface and B surface) and the exit surfaces (C surface and D surface). The incident surface (A surface) and exit surface (C surface) of the cylindrical lens 111 of the first micro fly's eye lens 110 and the entrance surface (B surface) and exit surface (D surface) of the cylindrical lens 121 of the second micro fly's eye lens 120. ) Are formed so that the generatrix directions are orthogonal to each other. As a result, the A surface of the first micro fly's eye lens 110 and the B surface of the second micro fly's eye lens 120 act on, for example, light in the Z-axis direction, and the C surface of the first micro fly's eye lens 110 and the second micro fly's eye For example, the lens can be formed on the D surface of the eye lens 120 so as to act on light in the X-axis direction orthogonal to the Z-axis direction.

  In addition, as shown in FIGS. 3 and 4, the D surface that is the exit surface of the cylindrical lens 121 in the second micro fly's eye lens 120 of the present embodiment has a lens surface in a cross section including the optical axis K. The outer curvature is larger than the inner curvature across the inner and outer boundaries L of the effective diameter Da. More specifically, the D surface of the cylindrical lens 121 in the second micro fly's eye lens 120 of the present embodiment has an effective diameter Da in a predetermined range across the optical axis K, and light passing through this range It goes to the necessary area in the focal plane. In addition, a predetermined range outside the effective diameter (a joint portion between the cylindrical lenses 121) located on the opposite side (outside) of the effective diameter Da across the boundary L has a larger curvature than the curvature of the effective diameter Da. Most of the curvatures thus formed are Db. Further, a concave portion Dc is formed in a predetermined range further outside the large curvature portion Db outside the effective diameter.

  With such a lens configuration, as shown in FIG. 5 (b), in the case of a conventional lens in which the curvature does not change inside and outside the effective diameter, light passing outside the effective diameter becomes stray light indicated by a dotted line in the figure. 5A, the lens according to the present embodiment has a larger curvature on the outer side than the inner side of the effective diameter, as shown in FIG. 5A. Then, since the light outside the effective diameter travels outside the necessary area of the focal plane, stray light due to the light outside the effective diameter does not occur, and a uniform illumination intensity distribution can be formed. It should be noted that the ratio and range in which the curvature is changed inside and outside the effective diameter may be appropriately determined depending on the shape and size of the lens, the curvature of the effective diameter of the lens, and the like.

  As described above, according to the integrator optical system 100 in the exposure apparatus 10 of the present embodiment and the second micro fly's eye lens 120 provided in the integrator optical system 100, the cylindrical lens 121 in the cross section including the optical axis K is used. The D surface is formed so that the curvature on the outer side (large curvature Db) is larger than the curvature on the inner side (effective diameter Da) across the boundary L between the inner and outer sides of the effective diameter Da. Can prevent light outside the effective diameter from entering the required area on the focal plane as stray light, and direct light outside the effective diameter outside the required area on the focal plane. A uniform illumination intensity distribution by light rays within the effective diameter can be formed in a necessary area in the focal plane.

  The embodiment described above is described in order to facilitate understanding of the present invention, and is not described in order to limit the present invention.

  For example, in the above-described embodiment, the lens is formed on both surfaces of the micro fly's eye lens. However, the present invention is not limited to this, and the lens may be formed on only one surface.

  In the above-described embodiment, a micro fly's eye lens is used in which a plurality of cylindrical lenses are arranged adjacent to each other. However, the present invention is not limited to this, and a plurality of lenses having other shapes are adjacent to each other. A lens array having a different configuration, such as an array arranged in this manner, may be used.

  In the above-described embodiment, the curvature of the second micro fly's eye lens of the second micro fly's eye lens is changed so that only the D surface of the second micro fly's eye lens has an effective diameter. That is, in the above-described embodiment, stray light from outside the effective diameter is not particularly problematic for the directions acting on the A-plane and the B-plane of the light rays. The configuration of the present invention is not applied to the B surface. In the above-described embodiment, since the effective diameter of the C surface is relatively large with respect to the size of the lens, the portion outside the effective diameter where stray light is generated is small enough to ignore the influence. The configuration of the present invention is not applied to the C plane. As described above, in the above-described embodiment, the curvature is changed inside and outside the effective diameter according to the present invention only on the D surface that the configuration of the present invention is really necessary (the curvature outside the effective diameter across the boundary is increased). This is designed to make the configuration of the optical system as simple as possible, facilitate the manufacture of the optical system, and reduce the cost for manufacturing the optical system.

  However, the present invention is not limited to this, and may have a configuration in which the same curvature is changed on both surfaces of one lens, or the first micro fly's eye of two micro fly's eye lenses. The lens or both micro fly's eye lenses may have a configuration in which the curvature is changed.

  In the above-described embodiment, the integrator optical system having two micro fly's eye lenses has been described. However, the integrator optical system may be applied to other optical systems, a lens array having only one micro fly's eye lens, etc. The present invention may be applied to other configurations.

10 Exposure apparatus 100 Integrator optical system (optical system)
110 First micro fly's eye lens (first lens array)
111 Cylindrical lens (lens)
120 Second micro fly's eye lens (second lens array)
121 Cylindrical lens (lens)
D Lens D surface (lens surface)
Da Effective diameter Db Large part of curvature Dc Concave part K Optical axis L Boundary

Claims (3)

In a lens array in which a plurality of lenses are arranged adjacent to each other,
The lens surface between the plurality of adjacent lenses has a curved concave surface portion,
Wherein each lens has its said portion excluding the concave portion of the lens surface in the cross section including the optical axis, across the effective diameter outside the boundary, and than the inner curvature of the so formed as curvature of the outer increases A lens array configured to direct light rays outside the effective diameter of each lens to outside a necessary area in the focal plane . An optical system having two lens arrays, a first lens array disposed on the light incident side and a second lens array disposed on the light exit side,
Each of the two lens arrays is arranged such that a plurality of lenses are adjacent to each other,
The lens surface between the plurality of adjacent lenses has a curved concave surface portion,
At least each lens of the second lens array has an outer curvature larger than an inner curvature, with a portion of the lens surface excluding the concave portion in a cross section including the optical axis sandwiching the boundary between the inner and outer effective diameters. The optical system is configured so that the light beam outside the effective diameter of each lens is directed outside a necessary area on the focal plane . Each lens of the two lens arrays has an incident surface on which light is incident and an exit surface from which light incident from the incident surface is emitted,
The lens surface of the exit surface between the plurality of adjacent lenses has a curved concave portion,
At least on the exit surface of each lens of the second lens array, the portion excluding the concave portion of the lens surface in the cross section including the optical axis is outside the inner curvature with the boundary inside and outside the effective diameter therebetween. The optical system according to claim 2, wherein the optical system is formed so as to have a large curvature, and is configured to direct a light beam outside the effective diameter of each lens toward a necessary area outside a focal plane. .

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