JP2003161881A - Objective lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an objective lens which is easily manufactured and has a surface shape easily measured and relatively moderate eccentric tolerance when it is assembled, and of which aberration has been well corrected. <P>SOLUTION: The objective lens has a numerical aperture of 0.85 or more and is used for lights having wavelengths of 300 nm or less. The objective lens is provided with a meniscus lens directing its concave to an object, a first positive refractive power lens group (G1) facing the image side and including a surface with negative refractive power and a second negative refractive power lens group (G2) facing the image side and including a surface with negative refractive power. An effective diameter of an image side surface of the meniscus lens is ED. A curvature radius of the image side surface of the meniscus lens is r. A condition of ED/|r|<1.90 is satisfied. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens, and more particularly to an objective lens used in the far ultraviolet region having a wavelength of 300 nm or less.

[0002]

2. Description of the Related Art Conventionally, in an objective lens having a numerical aperture of 0.85 or more and a wavelength of 300 nm or less in the far ultraviolet region, a meniscus lens arranged near an object,
In particular, aberration correction is generally performed by setting the radius of curvature of the image side surface of the meniscus lens arranged closest to the object side to be small.

[0003]

However, in the case of a lens having a surface with a small radius of curvature, particularly in a lens in which the value obtained by dividing the effective radius by the absolute value of the radius of curvature exceeds 1.90, the lens is manufactured and the surface shape is measured. However, the eccentricity tolerance during assembly becomes difficult.

The present invention has been made in view of the above problems, and it is easy to manufacture a lens and measure a surface shape,
An object of the present invention is to provide an objective lens in which the eccentricity tolerance when assembled is relatively gentle and the aberration is well corrected.

[0005]

In order to solve the above-mentioned problems, the present invention has a numerical aperture of 0.85 or more and 300
In an objective lens used for light having a wavelength of nm or less, a meniscus lens having a positive refracting power as a whole and having a concave surface facing the object side and a surface having a negative refracting power facing the image side are provided. A first lens group including a second lens group, and a second lens group including a surface having a negative refracting power as a whole and having a negative refracting power toward the image side.
ED / | r | <1.90, where ED is the effective diameter of the image-side surface of the meniscus lens and r is the radius of curvature of the image-side surface of the meniscus lens. An objective lens characterized by satisfying.

According to a preferred aspect of the present invention, all the lens components constituting the objective lens are made of a single kind of optical material. Further, it is preferable that all the lens components forming the objective lens are formed as a single lens.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a diagram schematically showing a lens configuration of an objective lens according to an embodiment of the present invention. In the present embodiment, the present invention is applied to an objective lens used for light having a wavelength of 193.4 nm. Referring to FIG. 1, the objective lens of the present embodiment includes, in order from the object side, a first lens group G1 having a positive refractive power and a second lens group G2 having a negative refractive power.

The first lens group G1 includes, in order from the object side, a positive meniscus lens L11 having a concave surface facing the object side, a positive meniscus lens L12 having a concave surface facing the object side, and a positive meniscus lens having a concave surface facing the object side. A lens L13, a positive meniscus lens L14 having a concave surface facing the object side, a negative meniscus lens L15 having a convex surface facing the object side, and a biconvex lens L
16 and a negative meniscus lens L1 having a convex surface facing the object side
7 and a biconvex lens L18.

The second lens group G2 includes, in order from the object side, a positive meniscus lens L21 having a concave surface facing the object side.
And a biconcave lens L22. A cover glass P having the form of a plane parallel plate is arranged in the optical path between the first lens group G1 and the observation object (not shown). In the first lens group G1, the image-side surface of the negative meniscus lens L15 and the negative meniscus lens L17.
The surface on the image side of "is the surface facing the image and having negative refractive power."
Are configured. Further, in the second lens group G2, the image-side surface of the biconcave lens L22 constitutes a “surface having a negative refractive power toward the image side”.

In this embodiment, all the optical members including the cover glass P are made of quartz. Quartz is 50% at a thickness of 5 mm for light with a wavelength of 193.4 nm.
It is an optical material having the above internal transmittance. The refractive index of quartz is 1.56 with respect to the used wavelength of 193.4 nm.
It is 01954. Further, since the objective lens of this embodiment is designed to be infinity, it is 20 mm on the image side of the objective lens.
An image forming lens (second objective lens) having a focal length of 200 mm is arranged with an air space between, and a finite optical system is formed by a combination of the objective lens and the image forming lens.

The following table (1) lists values of specifications of the objective lens according to the present embodiment. In Table (1), F is the focal length of the objective lens, NA is the object-side numerical aperture of the objective lens, and β is the magnification of the synthetic optical system in which the objective lens and the imaging lens are combined. Furthermore, the surface number is the order of each surface from the object side, and r is the radius of curvature (m
m), d is the distance between each surface (mm), ED is the effective diameter of each surface (mm), and n is the wavelength used (λ = 193.4 nm).
The refractive index for each is shown.

[0012]

[Table 1] F = 2mm NA = 0.9 β = 100 Surface number rd ED n       (Object surface) 0.280000  1 ∞ 0.150000 1.190 1.5601954 (Cover glass P)  2 ∞ 0.385000 1.401  3 -1.27647 1.199918 1.682 1.5601954 (Lens L11)  4 -1.67308 0.060000 3.091  5 -4.91003 1.500000 4.392 1.5601954 (Lens L12)  6 -3.31330 0.080000 5.426  7 -9.78073 1.700000 6.584 1.5601954 (Lens L13)  8 -4.86335 0.120000 7.252  9 -38.44176 1.800000 8.060 1.5601954 (Lens L14) 10 -8.76734 0.200000 8.451 11 24.87585 0.900000 8.546 1.5601954 (Lens L15) 12 8.96724 1.200000 8.404 13 40.08148 2.500000 8.595 1.5601954 (lens L16) 14 -8.55869 0.200000 8.835 15 22.58227 0.900000 8.239 1.5601954 (lens L17) 16 6.98054 1.100000 7.668 17 13.61855 2.000000 7.765 1.5601954 (L18 lens) 18 -23.46477 9.773051 7.659 19 -19.63926 1.200000 4.249 1.5601954 (lens L21) 20 -11.20698 0.180000 4.095 21 -26.26048 0.900000 3.965 1.5601954 (L22 lens) 22 6.21830 20.000000 3.688

2 and 3 are graphs showing various aberrations in this embodiment. In the astigmatism of FIG. 2, the solid line shows the sagittal image plane, and the broken line shows the meridional image plane. In the lateral aberration of FIG. 3, Y is the image height (mm)
Is shown. As is clear from each aberration diagram, it is understood that various aberrations are favorably corrected in this embodiment.
The aberration diagrams shown in the present embodiment are aberration diagrams when the axial air distance between the objective lens and the imaging lens is 20 mm, but even if the axial air distance changes over a wide range. The present inventor has verified that there is almost no variation in aberration.

By the way, referring to FIG. 1, in the first lens group G1, positive meniscus lenses (L11 to L1) are positioned relatively close to the object and have a concave surface toward the object side.
It can be seen that the radius of curvature of the image-side surface of 3) tends to be small. In this embodiment, in the positive meniscus lens L11 arranged closest to the object side, the effective diameter ED of the image side surface thereof is 3.091 mm, and the radius of curvature r thereof is −1.
It is 67308 mm. Therefore, for the positive meniscus lens L11, the ratio ED / | r | between the effective diameter and the absolute value of the radius of curvature is 1.85.

In the second positive meniscus lens L12 from the object side, the effective diameter ED of the image side surface is 5.4.
26 mm and its radius of curvature r is -3.3133 mm
Is. Therefore, for the positive meniscus lens L12, the ratio ED / | r | between the effective diameter and the absolute value of the radius of curvature is 1.64. Further, in the third positive meniscus lens L13 from the object side, the effective diameter ED of the image side surface thereof is 7.252 mm, and the radius of curvature r thereof is -4.863.
It is 35 mm. Therefore, the positive meniscus lens L1
For 3, the ratio of the effective diameter to the absolute value of the radius of curvature ED /
| R | is 1.49.

As described above, in the present embodiment, the ratio ED / | of the positive meniscus lens L11 arranged closest to the object side.
In order to prevent only r | from protruding and becoming large, the action of bending the marginal ray inward is imposed on the surface farther from the object. That is, the ratio ED / | r | of the positive meniscus lens L11 arranged closest to the object side is suppressed as compared with the conventional case,
Instead, the second positive meniscus lens L from the object side
Ratio ED of 12th and 3rd positive meniscus lens L13
// r | is set to be larger than the conventional one. as a result,
The ratio ED / | r | of the image side surface of all the meniscus lenses constituting the first lens group G1 can be suppressed to be smaller than 1.90.

Further, as described above, the first lens group G1
In, the image-side surface of the negative meniscus lens L15 and the image-side surface of the negative meniscus lens L17 form “a surface having a negative refractive power toward the image side”. Furthermore, in the second lens group G2, the image-side surface of the biconcave lens L22 constitutes a “surface having a negative refractive power toward the image side”. As a result, the sine condition can be satisfactorily corrected by providing the surface having the negative refractive power facing the image side.

As described above, in the objective lens of the present embodiment, the ratio ED / | r | of the image side surface of all meniscus lenses constituting the first lens group G1 is 1.9.
Since it is kept smaller than 0, it is easy to fabricate the lens and measure the surface shape, and the eccentricity tolerance when assembled is relatively loose. Further, since the first lens group G1 and the second lens group G2 are provided with the surface of negative refractive power facing the image side,
The sine condition can be satisfactorily corrected, and various aberrations can be satisfactorily corrected.

[0019]

As described above, according to the present invention, it is possible to easily manufacture the lens and measure the surface shape, and to realize an objective lens in which the eccentricity tolerance when assembled is relatively loose and the aberration is satisfactorily corrected. be able to.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a lens configuration of an objective lens according to an embodiment of the present invention.

FIG. 2 is a diagram of various types of aberration in the present embodiment.

FIG. 3 is a diagram of various types of aberration in the present embodiment.

[Explanation of symbols]

G1 first lens group G2 Second lens group L lens P cover glass

Claims (3)

[Claims] 1. Having a numerical aperture of 0.85 or more and 300 n
In an objective lens used for light having a wavelength of m or less, a meniscus lens having a positive refractive power as a whole and a concave surface facing the object side and a surface having a negative refractive power facing the image side are provided. An effective diameter of the image-side surface of the meniscus lens, and a first lens group including the first lens group and a second lens group including a surface having a negative refracting power as a whole and having a negative refracting power toward the image side. Is the ED, and r is the radius of curvature of the image-side surface of the meniscus lens, the objective lens satisfies the condition of ED / | r | <1.90. 2. The objective lens according to claim 1, wherein all the lens components forming the objective lens are made of a single kind of optical material. 3. The objective lens according to claim 1, wherein all the lens components forming the objective lens are formed as a single lens.