JPH103033A - Immersion system objective lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To satisfactorily correct spherical aberration of a luminous flux of which numerical aperture exceeds 1 by providing an immersion system objective lens with a front group of an approximately afocal system and a rear group having a positive refraction power and satisfying specific conditions. SOLUTION: This immersion system objective lens has a front group GF of an approximately afocal system and a rear group GR having a positive refraction power, and satisfy three conditions by the condition formulae, 1.5ϕ18<R18/ϕ18<10ϕ18, d4>d2, and |R11|<R10. In the formulae, ϕ18 expresses an effective diameter of the lens surface on a specimen surface side of a positive lens component L9 in the rear group GR, R18 expresses a radius of curvature of the lens surface of the specimen surface side of the positive lens component L9 in the rear group GR, and d2 expresses the length between a positive lens component L1 in the front group GF and a negative lens component L2. The d4 expresses the length between a negative lens component L2 in the front group GF and a positive lens component L3, and R10 expresses a radius of curvature of the specimen surface side of a positive lens component L5 in the rear Group GR, and R11 expresses a radius of curvature of the lens surface on the side of the positive lens component L5 of a negative component L6 in the rear grope GP.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an immersion type objective lens for forming a beam spot in a liquid using ultraviolet light.

[0002]

2. Description of the Related Art There has been remarkable progress in technology utilizing ultraviolet light. Among them, there are various spectroscopic analysis methods by narrowing the diameter of a beam spot to the limit, irradiating the spot into a liquid, generating a refractive index distribution in a medium in the liquid, and utilizing the effect. .

[0003]

In order to obtain an extremely small beam spot as described above, it is necessary for the objective lens to very well correct NA (numerical aperture) exceeding 1 and spherical aberration. . Therefore, the present invention provides a numerical aperture of 1
The objective of the present invention is to satisfactorily correct spherical aberration of a light beam exceeding the above.

[0004]

In order to achieve the above object, for example, as shown in FIG. 1, an immersion type objective lens according to the present invention comprises an immersion type objective lens which focuses substantially parallel light on a sample surface. The objective lens is configured to include, in order from the light incident side, a front group GF that is a substantially afocal system and a rear group GR having a positive refractive power. The front group GF includes, in order from the light incident side, a first positive lens component L1, a negative lens component L2, and a second positive lens component L3.
Has a first positive lens component L5 having a strong convex surface facing the light incident side, and a concave surface facing the sample surface of the first positive lens component L5 and facing the first positive lens component L5. It includes a negative lens component L6 and a second positive lens component L9 disposed closest to the sample surface and having a concave surface facing the sample surface. In this configuration, the following conditions are satisfied. (1) 1.5φ18 <R18 / φ18 <10φ18 (2) d4> d2 (3) | R11 | <R10 where φ18: the lens surface on the sample surface side of the second positive lens component L9 in the rear group GR. Effective diameter, R18: radius of curvature of the lens surface on the sample surface side of the second positive lens component L9 in the rear group GR d2: distance between the first positive lens component L1 and negative lens component L2 in the front group, d4 : The distance between the negative lens component L2 and the second positive lens component L3 in the front group, R10: the radius of curvature of the lens surface on the sample surface side of the first positive lens component L5 in the rear group, R11: in the rear group The radius of curvature of the lens surface of the negative lens component L6 on the first positive lens component L5 side.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a basic configuration of an immersion objective lens according to the present invention will be described. In the present invention,
A system in which the space between the sample surface and the lens surface closest to the sample is filled with a liquid, that is, a liquid immersion system is employed to realize a numerical aperture exceeding one. In an immersion type objective lens as in the present invention, since the refractive index of the liquid is lower than the refractive index of the optical material constituting the objective lens, when the lens surface in contact with the liquid is made flat, a large negative spherical aberration is caused. Occurs. Therefore, in the present invention, the surface in contact with the liquid (the lens surface of the second positive lens component on the sample side) is formed to have a concave surface facing the sample side, thereby suppressing the occurrence of negative spherical aberration. The above condition (1) is given from this point of view. If the value is below the lower limit, the spherical aberration is too positive, which is not preferable. If the value exceeds the upper limit, the spherical aberration is turned to the negative side. It is not preferable because it becomes too much.

Further, in the objective lens of the present invention, the front group is composed of positive, negative and positive, and the lens surface on the rear group side of the negative lens component in the front group raises the incident height of light rays to correct spherical aberration. doing. The condition (2) is given from this viewpoint, and defines a space in which a large divergence action by the negative lens component in the front group is given. If the condition (2) is not satisfied, the incident height of the light beam cannot be sufficiently raised by the negative lens component in the front group, and
It is not preferable because spherical aberration cannot be corrected.

Next, in the rear group, the first positive lens component has a lens surface on the sample surface side and the first positive lens component has a negative lens component on the sample surface side that is closer to the first positive lens component. The directed concave surface forms an air lens, and the air lens satisfactorily corrects spherical aberration. The conditional expression (3) is given from this viewpoint. If conditional expression (3) is not satisfied, it is not preferable because spherical aberration cannot be sufficiently corrected by the air lens.

In the immersion objective according to the present invention, it is desirable that the distance between the front group and the rear group is adjustable. With this configuration, even when the used wavelength is changed, it is possible to adjust the distance between the front group and the rear group to realize almost zero spherical aberration at any wavelength. In the immersion objective according to the present invention, when the focal length of the entire system is fT and the focal length of the front group is fF, it is preferable that the following conditions are satisfied. (4) 0 <| fF | / fT <0.02 Conditional expression (4) defines a preferable range of the focal length of the front group which is almost an afocal system, and the condition (4)
If the front group becomes a complete afocal system beyond the lower limit of (1), it is not preferable because spherical aberration correction cannot be realized by changing the distance between the front group and the rear group. When the value exceeds the upper limit of the condition (4), the focal length of the front group becomes too short, and the change of the spherical aberration with respect to the change of the interval between the front and rear groups becomes too large.

In the immersion type objective lens according to the present invention, it is preferable that the immersion type objective lens is composed of only a non-bonded lens component made of quartz. Glass materials that can withstand the ultraviolet light used in the present invention include quartz and fluorite.
Fluorite is not preferred because it has surface degradation due to temperature change, and the adhesive in this wavelength range is preferably not bonded because of problems of absorption and deterioration.

[0010]

EXAMPLES Numerical examples will be described below. [First Embodiment] FIG. 1 is an optical path diagram of a first embodiment of an immersion objective according to the present invention. In FIG. 1, the front group GF, which is a substantially afocal system, is sequentially arranged from the parallel light incident side.
And a positive rear group GR that condenses light from the front group GF to form a beam spot on the sample surface.
The front group GF includes, in order from the light incident side, a positive meniscus lens (first positive lens component) L1 having a concave surface facing the light incident side, and a biconcave negative lens (negative lens component) L2.
And a biconvex positive lens (second positive lens component) L3 having a strong convex surface facing the sample surface side.

The rear group GR includes, in order from the light incident side, a biconvex positive lens L4 having a strong convex surface facing the light incident side, and a positive meniscus lens (first lens) having a convex surface facing the light incident side. A positive lens component) L5; a biconcave negative lens (negative lens component) L6 with a concave surface facing the light incident side; a positive meniscus lens L7 with a convex surface facing the light incident side; A positive meniscus lens L8 having a convex surface facing the sample surface, and a positive meniscus lens (second positive lens component) L9 disposed closest to the sample surface and having a concave surface facing the sample surface.

Table 1 below summarizes the data. In Table 1, f is the focal length of the entire system, NA is the numerical aperture on the sample surface side, the number at the left end is the order from the parallel light incident side, R is the radius of curvature, D is the lens thickness or lens surface interval, n Is 245 nm
Is the refractive index at. In addition, in the liquid immersion type objective lens of the first embodiment, since water and a cover glass are interposed between the lens surface closest to the sample and the sample, these data are also shown in Table 1.

[0013]

Table 1 [Example 1] f = 1.75 NA = 1.14 R Dn 1 -13.92376 3.60000 1.517450 L1 2 -6.05911 0.96000 1.000000 3 -6.92992 3.00000 1.517450 L2 4 5.80505 2.40000 1.000000 5 94.79946 6.00000 1.517450 L36 -8.83242 (d6) 1.000000 7 7.61020 1.90000 1.517450 L4 8 -825.53364 0.10000 1.000000 9 14.68793 1.90000 1.517450 L5 10 29.83444 0.80000 1.000000 11 -10.68377 2.00000 1.517450 L6 12 40.64282 0.06000 1.000000 13 4.96500 1.50000 1.5174500000 7000 0.07 8.33000 0.07000 1.000000 17 1.26400 1.20000 1.517450 L9 18 3.16200 0.20000 1.387690 Water 19 0.00000 0.17000 1.517450 Cover glass 20 0.00000 0.19600 1.387690 Water FIG. 2 shows the point image light intensity distribution of the immersion objective lens of the first embodiment. In the point image light intensity distribution in FIG. 2, the vertical axis represents the light intensity when the maximum value is normalized to 1, and the horizontal axis represents the distance from the Gaussian image plane along the optical axis direction. Note that FIG.
The point image light intensity distribution shown in (1) shows a state at a wavelength λ = 245 nm (a state at d6 = 30.6).

The following Table 2 shows the spherical aberration at the variable interval.

[0015]

[Table 2] Spherical aberration at 100% 70% 50% 30% at λ = 245nm (d6 = 30.6) 0.00000 0.00000 0.0000 -0.00001 Spherical aberration at λ = 220nm (d6 = 27.8) -0.00015- 0.00008 -0.00009 -0.00005 Spherical aberration at λ = 270 nm (d6 = 31.6) 0.00017 -0.00005 -0.00001 -0.00001 Spherical aberration at λ = 486.1 nm (d6 = 10.5) 0.00001 0.00088 0.00051 0.00018 As is clear from Table 2, the immersion objective according to the first embodiment of the present invention can form an extremely small beam spot in the reference state.
Further, even when the wavelength used changes, the spherical aberration can be suppressed to almost zero by changing the distance between the front group and the rear group. [Second Embodiment] FIG. 3 is an optical path diagram of a second embodiment of the immersion objective lens according to the present invention. In FIG. 3, the front group GF, which is a substantially afocal system, is sequentially arranged from the parallel light incident side.
And a positive rear group GR that condenses light from the front group GF to form a beam spot on the sample surface.
The front group GF includes, in order from the light incident side, a positive meniscus lens (first positive lens component) L1 having a concave surface facing the light incident side, and a biconcave negative lens (negative lens component) L2.
And a biconvex positive lens (second positive lens component) L3 having a strong convex surface facing the sample surface side.

The rear group GR includes, in order from the light incident side, a positive meniscus lens L4 having a convex surface directed to the light incident side, and a positive meniscus lens (first positive lens component) also having a convex surface directed to the light incident side. ) L5, a negative meniscus lens (negative lens component) L6 having a concave surface facing the light incident side, a positive meniscus lens L7 having a convex surface facing the light incident side, and a positive meniscus lens L7 having a convex surface facing the light incident side. It comprises a meniscus lens L8 and a positive meniscus lens (second positive lens component) L9 which is arranged closest to the sample surface and has a concave surface facing the sample surface.

Table 3 below summarizes the data. In Table 3, f is the focal length of the entire system, NA is the numerical aperture on the sample surface side, the number at the left end is the order from the parallel light incident side, R is the radius of curvature, D is the lens thickness or lens surface interval, n Is 245 nm
Is the refractive index at. Further, in the liquid immersion type objective lens of the second embodiment, since water is interposed between the lens surface closest to the sample and the sample, Table 3 also shows this data.

[0018]

[Table 3] [Example 2] f = 1.75 NA = 1.15 RD n 1 -13.86500 3.60000 1.517450 L1 2 -6.03600 0.96000 1.000000 3 -6.93300 3.00000 1.517450 L2 4 5.80000 2.40000 1.000000 5 95.72000 6.00000 1.517450 L36 -8.83700 30.50000 1.000000 7 7.64900 2.40000 1.517450 L4 8 35.34000 0.10000 1.000000 9 15.21800 1.40000 1.517450 L5 10 79.30000 0.90000 1.000000 11 -10.60300 1.40000 1.517450 L6 12 -55.45000 0.06000 1.000000 13 5.15000 2.10000 1.517450 7000 1.0000 00000 1.000000 17 1.25800 1.40000 1.517450 L9 18 2.32400 0.35405 1.387690 Water FIG. 4 shows a point image light intensity distribution of the liquid immersion objective lens of the second embodiment. In the point image light intensity distribution of FIG. 4, the vertical axis represents the light intensity when the maximum value is normalized to 1, and the horizontal axis represents the distance from the Gaussian image plane along the optical axis direction. FIG.
The point image light intensity distribution shown in FIG. 7 represents a state at a wavelength λ = 245 nm.

As is apparent from FIG. 4, the immersion objective according to the second embodiment of the present invention can form an extremely small beam spot. Third Embodiment FIG. 5 is an optical path diagram of a third embodiment of the immersion objective according to the present invention. In FIG. 5, the front group GF, which is a substantially afocal system, is sequentially arranged from the parallel light incident side.
And a positive rear group GR that condenses light from the front group GF to form a beam spot on the sample surface.
The front group GF includes, in order from the light incident side, a positive meniscus lens (first positive lens component) L1 having a concave surface facing the light incident side, and a biconcave negative lens (negative lens component) L2.
And a biconvex positive lens (second positive lens component) L3 having a strong convex surface facing the sample surface side.

The rear group GR includes, in order from the light incident side, a positive meniscus lens L4 having a convex surface facing the light incident side, and a positive meniscus lens (first positive lens component) also having a convex surface facing the light incident side. ) L5, a negative meniscus lens (negative lens component) L6 having a concave surface facing the light incident side, a positive meniscus lens L7 having a convex surface facing the light incident side, and a positive meniscus lens L7 having a convex surface facing the light incident side. It comprises a meniscus lens L8 and a positive meniscus lens (second positive lens component) L9 which is arranged closest to the sample surface and has a concave surface facing the sample surface.

Table 4 below summarizes the data. In Table 4, f is the focal length of the entire system, NA is the numerical aperture on the sample surface side, the number at the left end is the order from the parallel light incident side, R is the radius of curvature, D is the lens thickness or lens surface interval, n Is 245 nm
Is the refractive index at. Further, in the liquid immersion type objective lens of the third example, since water and a cover glass are interposed between the lens surface closest to the sample and the sample, these data are also shown in Table 4.

[0022]

[Third embodiment] f = 1.75 NA = 1.15 RD n 1 -13.94600 3.60000 1.517450 L1 2 -6.03170 0.96000 1.000000 3 -6.96030 3.00000 1.517450 L2 4 5.80400 2.40000 1.000000 5 96.03100 6.00000 1.517450 L36 -8.83130 30.60000 1.000000 7 7.70040 2.40000 1.517450 L4 8 30.94600 0.10000 1.000000 9 12.30100 1.40000 1.517450 L5 10 31.88000 0.90000 1.000000 11 -10.54600 1.40000 1.517450 L6 12 -63.81700 0.06000 1.000000 13 6.20020 2.10000 1.517450 6.200 0.05000080 6.200 2.000 1.000000 17 1.41020 1.20000 1.517450 L9 18 3.13530 0.20000 1.387690 Water 19 0.00000 0.17000 1.517450 Cover glass 20 0.00000 0.18970 1.387690 Water FIG. 6 shows the point image light intensity distribution of the immersion objective lens of the third embodiment. In the point image light intensity distribution in FIG. 6, the vertical axis represents the light intensity when the maximum value is normalized to 1, and the horizontal axis represents the distance from the Gaussian image plane along the optical axis direction. FIG.
The point image light intensity distribution shown in FIG. 7 represents a state at a wavelength λ = 245 nm.

As is clear from FIG. 6, the immersion objective according to the third embodiment of the present invention can form an extremely small beam spot. In the second and third embodiments as well, by changing the distance between the front group GF and the rear group GR, it is possible to correct the fluctuation of the spherical aberration when the used wavelength changes.

Table 5 below shows conditions corresponding to the first to third embodiments.

[0025]

Table 5 Example 1 Example 2 Example 3 Example 3 (1) φ18 1.32000 0.89992 1.33236 R18 / φ18 2.39545 2.58245 2.35319 (2) d2 0.96000 0.96000 0.96000 d4 2.40000 2.40000 2.40000 (3) R10 29.83400 79.30000 31.88000 R11 -10.68400 -10.60300 -10.68400 (4) | fF | / fT 0.0087 0.0087 0.0079

[0026]

As described above, according to the present invention, it is possible to realize an immersion type objective lens capable of suppressing spherical aberration to almost zero while having a numerical aperture exceeding 1.

[Brief description of the drawings]

FIG. 1 is an optical path diagram of an immersion objective lens according to a first embodiment of the present invention.

FIG. 2 is a point image light intensity distribution of the immersion objective lens according to the first example.

FIG. 3 is an optical path diagram of an immersion objective lens according to a second embodiment of the present invention.

FIG. 4 is a point image light intensity distribution of an immersion objective lens of a second example.

FIG. 5 is an optical path diagram of an immersion objective lens according to a third embodiment of the present invention.

FIG. 6 is a point image light intensity distribution of the liquid immersion type objective lens of the third example.

[Explanation of symbols]

 GF: front group GR: rear group

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shoichi Nakamura 471 Nagaodaicho, Sakae-ku, Yokohama-shi, Kanagawa Inside Nikon Engineering Co., Ltd.

Claims (5)

[Claims] An immersion objective lens for converging substantially parallel light on a sample surface, comprising: a front group, which is a substantially afocal system, in order from the light incident side;
A rear group having a positive refractive power, wherein the front group includes, in order from the light incident side, a first positive lens component, a negative lens component, and a second positive lens component; Is a first positive lens component having a strong convex surface directed toward the light incident side, and a negative lens disposed on the sample surface side of the first positive lens component and having a concave surface directed toward the first positive lens component. A liquid immersion objective lens comprising: a component; and a second positive lens component disposed closest to the sample surface and having a concave surface facing the sample surface, and satisfying the following conditions. 1.5 φ18 <R18 / φ18 <10φ18 d4> d2 | R11 | <R10 where φ18: effective diameter of the lens surface on the sample surface side of the second positive lens component in the rear group, R18: in the rear group The radius of curvature of the lens surface on the sample surface side of the second positive lens component d2: the distance between the first positive lens component and the negative lens component in the front group, d4: the negative in the front group The distance between the lens component and the second positive lens component; R10: the radius of curvature of the lens surface on the sample surface side of the first positive lens component in the rear group; R11: the radius of the negative lens component in the rear group. The radius of curvature of the lens surface on the first positive lens component side. 2. An immersion system objective according to claim 1, wherein an interval between said front group and said rear group is adjustable to correct a spherical aberration generated when a used wavelength changes. lens. 3. An immersion objective according to claim 1, wherein the following conditions are satisfied. 0 <| fF | / fT <0.02, where fT is the focal length of the entire system, and fF is the focal length of the front group. 4. An immersion objective according to claim 3, wherein said front group has a negative refractive power. 5. The immersion objective according to claim 1, wherein the immersion objective comprises only a non-bonded lens component made of quartz.