KR100532233B1 - Miniature Objective Lenses for Reflected Refractive Microlithography - Google Patents

Abstract

The present invention relates to a reduction objective lens for catadioptric microlithographic having two convex mirrors 21 and 23 facing each other. The concave mirror has a symmetrical structure and has a central bore. Lenses 24 to 60 are mounted behind the mirror on the light path towards the image 61. Preferably, lenses 15 to 20 are moved to the objective lens side and are turned toward the intermediate space between the mirrors 21 and 23 of the central region. The optical path between the convex mirrors can thus be preferably free of lenses. The intermediate image Z is formed at the rear of the mirrors 21 and 23 to have particularly good correction capability.

Description

Miniature Objective Lenses for Refractive Microlithography

The present invention relates to a reduction objective lens for refraction type microlithography having two concave mirrors facing each other. The concave mirror has an axisymmetric structure and has a central bore. BACKGROUND OF THE INVENTION Reflective refracted reduction objective lenses for microlithography in the deep UV (DUV) region are known. Filed April 25, 1997 in US patent application Ser. No. 08 / 845,384, an orthogonally positioned polarizing beam splitter and λ / 4 plate are required for implementation. The beam splitter and λ / 4 plate are a problem for manufacturing in the deep ultraviolet region. In addition, the optical axis about 90 ° deflection is mandatory, so a second deflection is provided to keep the reticle parallel to the wafer.

Other refraction systems have an asymmetric structure. Such a system may be, for example, the Dyson type or known from EP 0,581,585.

U. S. Patent No. 5,488, 229 is directed to a reduced objective lens for microlithography in which the axisymmetric and two concave mirrors face each other. In principle, a central bore is given, but this is not a problem in view of the growing importance of annular aperture illumination.

Both concave mirrors consist of a mangin mirror, the second mirror of which acts as a lens at the center. Thus only iris diaphgrams and wafers are arranged. In an environment of β = 0.1, NA = 0.6 and λ = 193 nm, five lenses and two touch mirrors are sufficient. However, nothing is said about the size of the image filter and the center bore. If the field size of the image obtained in the present invention, a touch mirror having a diameter of up to one meter is required. It is not contemplated that quartz glass or other lens materials could be used at this size while providing adequate quality for deep ultraviolet microlithography. US Pat. No. 5,031,976 shows a similar configuration, but a thick lens with a second mirror flat and separated is provided between the mirrors.

Accordingly, it is an object of the present invention to provide a reduction objective that provides an image field having a size corresponding to the fabrication requirements of a wafer-stepper machine and provides adequate error correction. The present invention provides for a design that allows for manufacturing and, in particular, excludes large and thick lenses.

The reduced objective lens for refraction type microlithography, which is an object of the present invention, defines an optical axis, provides an optical path, and forms an image of an object. The reduction objective lens for refraction type microlithography includes: two concave mirrors mounted on the optical axes facing each other; Each concave mirror having a symmetrical configuration on the optical axis and having a central bore; And a plurality of lenses arranged along the optical axis, facing rearward of the image of the mirror on the optical path.

By the plurality of lenses, the light beam is reduced to a diameter considerably smaller than the diameter of the mirror so that a correction lense having an ideal diameter can be used again.

According to another type of the invention, the lens on the object side is located forward in the intermediate space between the mirrors of the central bore region. Thus, an object-side lens system protrudes into the mirror intermediate space of the central bore region, positively affecting chromatic aberration.

According to another type of the invention, there is no lens in the optical path between the concave mirrors, ie there is no lens in the optical path in the region of the maximum beam diameter. Thus, the purpose of using a small lens is achieved.

An intermediate image is provided on the back of the mirror. In this way, the surface in common with the mirror becomes the region between the intermediate image and the image. In the vicinity of the surface, an element for correcting the image error caused by the mirror may be mounted in an optimal state. Meniscus pairs are suitable for this purpose.

In another aspect of the invention, a correction element is provided, in particular a convex air lens is provided between the two lenses and in this way excellently corrects for astigmatism.

In another aspect of the invention, the diameter of the image field is greater than 20 mm and the numerical aperture NA on the image side is less than 0.06. Further, the field curvature is smaller than 0.06 mu m, and color correction of the bandwidth of at least 6 pm (pico meter) is achieved. With this property, i.e., the characteristics of the large image field, the low image field curvature associated with the large numerical aperture, and the suitable color bandwidth, a useful quality is provided by the present invention.

With reference to the lens sectional view of FIG. 1 and the data in Table 1, a preferred embodiment of the reduced objective lens for the refractive index microlithography of the present invention will be described. Here, a total of 27 lenses, two mirrors 21 and 23, and a flat plate 50/51 are shown. In the 27 mm diameter image field, the diameter of the maximum lens 19/20 is about 173 mm, and the diameter of the maximum mirror 23 is about 707 mm. The central bore reaches about 35% of the mirror diameter. The objective lens is configured for a wavelength of 193.38 nm, and the numerical aperture NA on the image side is 0.70.

An intermediate image plane Z is realized between the surface 29 and the surface 30, and correspondingly, the additional pupils P are provided with masks 46, 47; 48, 49 and 53, 54. Such a meniscus lens is capable of correcting an image error generated by the mirrors 21, 23, in particular an off-axis image error, to an optimal state here.

Flat plates 50 and 51 are provided between the meniscus lenses immediately adjacent to the area of the pupil P. During the manufacture of the objective lens, the flat plate (for the purpose of correcting the residual error of the objective lens through small form correction, which may be generated by, for example, ion ray etching) 50/51) may be used.

The object-side lens groups 1 to 20 are wide angle rectrofocus objective lenses. Lens groups 25 to 29 are symmetrical to the lens groups 1 to 20 and are in front of the intermediate image of this type. Since the meniscus lenses 19, 20 and 24, 25 diverge the light beam largely on the mirror side, the center bore becomes small. The two lens groups 1 to 20 and 24 to 29 extend into the mirror structures 21 and 23. Generating large longitudinal chromatic aberration is the main function of the meniscus lenses 19 and 20. This chromatic aberration is compensated for by all remaining lenses.

The large convex surface 57, together with the glass thickness of the corresponding lens 58, is important for the objective lens described above, and similar structures are commonly used in microscope objectives.

The whole lens is spherical and made of quartz glass. Other materials (calcium fluoride) are also used for operation at low wavelengths of 157 nm.

The mirror is aspheric in accordance with known power series expansion.

[Equation 1]

P (h) = (1 / 2R) h ² + c ₁ h ⁴ +... + c _n h ^{2n + 2}

Where P is sagitta as a function of aspheric constants c ₁ to c _n and radius (h, height to optical axis) provided in Table 1, and R is the vertex radius obtained from Table 1 )to be. The deviation of the mirror surface from the spherical surface is moderate enough to be controlled in the manufacturing process.

The manufacture of aspherical mirrors having a diameter in the range of 0.5 to 1 m is known in the field of astronomy equipment. In the case of continuous manufacturing, it is used for molding techniques such as galvano forming. Conjugated correction surface can be used in the flat plate 50/51 described above or in one of the adjacent meniscus lens surfaces, so the accuracy in manufacturing is not very necessary.

It is also possible to use an elastic mirror. Known alignment cementing can be modified to be adjusted during assembly using the actuator and then secured to the elastic support. On the other hand, such a mirror can control the mirror in an optimum shape online during operation by a piezoelectric actuator to compensate for the thermal lens effect.

As described above, in the present invention, it becomes possible to provide a reduction objective lens that provides an image field having a size corresponding to the size requirement of a wafer-stepper machine and provides proper error correction.

TABLE 1

1 shows a lens cross section of a preferred embodiment.

* Description of the symbols for the main parts of the drawings *

1 to 20, 24 to 60: lens 21 and 23: mirror

61: Image P: Pupil

Z: middle image

Claims (10)

In a reduction objective lens for refraction type microlithography defining an optical axis, providing an optical path, and forming an image of an object, Two concave mirrors mounted on the optical axis such that the concave surfaces face each other; And A first plurality of lenses arranged toward the image behind the concave mirror on the optical path along the optical axis, Each of the concave mirrors has a structure symmetrical with respect to the optical axis and has a central bore. The method of claim 1, The concave mirrors jointly form an intermediate space between the concave mirrors; The reduced objective lens further comprises a second plurality of lenses arranged toward an object on the optical axis in front of the first plurality of lenses, the second plurality of lenses at least partially inside the intermediate space within the central bore region. A reduction objective lens for refraction type microlithography, characterized in that extending to. The method of claim 1, A reduction objective lens for refraction type microlithography, characterized in that no lens exists in the optical path between the concave mirrors. The method of claim 2, A reduction objective lens for refraction type microlithography, characterized in that an intermediate image (Z) is formed on the optical axis behind the concave mirror. The method of claim 4, wherein 2. The reduced objective lens for refraction type microlithography of claim 1, wherein two lenses of the first plurality of lenses form convex air lenses between the two lenses jointly behind the intermediate image. The method of claim 1, A reduction objective lens for refraction type microlithography, characterized in that the reduction objective lens forms an image field having a diameter larger than 20 mm. The method of claim 1, And said numerical aperture of said image side is greater than 0.60. The method of claim 1, And said image field curvature is less than 0.06 [mu] m. The method of claim 1, A pupil P is formed at the rear of the intermediate image Z; And said first plurality of lenses including a meniscus lens are mounted in said pupil (P) region, and said meniscus lens is convex toward said pupil. The method of claim 9, The first plurality of lenses including an optical element is mounted in the area; And said optical element has an aspheric correction surface.