JP3242426B2 - UV objective lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens for ultraviolet light having a wavelength of about 250 nm.

[0002]

2. Description of the Related Art An objective lens using light in the ultraviolet region having a wavelength of about 250 nm is used for a high-resolution imaging lens, a study of a living body in the ultraviolet region, and a research application of a laser. Although reflective objective lenses are often used for such applications,
When high resolution is required, the refractive system is more advantageous. A refraction type ultraviolet objective lens is described in, for example, O. S.
A. Vol. 38, p. 689, this objective lens has a high magnification, glycerin immersion and high numerical aperture (N
In (A), the spherical aberration is satisfactorily corrected.

The ultraviolet objective lenses described in JP-A-1-319719 and JP-A-1-319720 have a low magnification and a low NA, but the spherical aberration is corrected relatively favorably with a small number of lenses. ing.

Further, German Patent Specification No. 391586
The ultraviolet objective lens described in No. 8 has a high NA and a high magnification, and is color-corrected from visible to ultraviolet.
A part of the objective lens floats according to the wavelength used.

[0005]

SUMMARY OF THE INVENTION O. S.
A. The objective lens described in (1) has a large field curvature, an extremely small effective visual field, and is immersed in glycerin, so that it cannot be used in the semiconductor market or laser applications.

Further, the objective lenses described in the above publications have a small number of components, so that chromatic aberration and curvature of field are not sufficiently corrected despite low magnification and low NA.

Further, German Patent Specification No. 391586
The ultraviolet objective lens described in No. 8 floats a part of the objective lens in accordance with the wavelength used, and has a disadvantage that the working distance (WD) is very short, so that the operability is poor. .

The present invention has been made in view of such a situation, and has as its object to prevent ultraviolet light having a wavelength of about 250 nm from deteriorating the performance around the field of view, having a relatively long working distance, and having a floating function corresponding to the wavelength. It is an object of the present invention to provide a high-resolution objective lens of a refraction system which does not need to be used.

[0009]

The ultraviolet objective lens of the present invention comprises a meniscus lens having a concave surface facing the object side and a meniscus lens having a concave and convex joint, and has a first positive power as a whole.
Lens group L1, including at least two cemented lenses,
The lens group includes a second lens unit L2 having a positive power as a whole, a concave / convex cemented lens, and a third lens unit L3 having a negative power. Each of the lens units is a fixed lens unit and satisfies the following conditions. It is a feature. (1) 3.4 <| f ₁ / f | <5 (2) 5 <| f ₂ / f | <10 (3) 2.5 <| f ₃ /f|<7.5 where f ₁ , f ₂ , f ₃ , and f are the focal lengths of the first lens unit L1, the second lens unit L2, the third lens unit L3, and the entire system, respectively.

[0010]

It is desirable to use fluorite for all the convex lenses. Further, it is desirable to use only a glass material having a thickness of 10 mm and an internal transmittance of 80% or more at a wavelength of 250 nm.

[0012]

The reason and operation of the above configuration will be described below. In an optical system used at a wavelength of about 250 nm,
Due to transmittance problems, the optical materials used are usually fluorite,
Limited to about fused quartz (or synthetic quartz). Each of these materials has a refractive index of 1.42 to 1.51 in the above-mentioned wavelength range, and dispersion (Abbe number) is not distributed in a wide range. It is difficult to design a high-magnification objective lens in which the chromatic aberration has been corrected within a certain range. This tendency becomes more pronounced as the working distance becomes longer.

Lasers are mainly used as light sources in this wavelength range, and they are almost monochromatic light sources. Also, since lasers of different wavelengths are rarely used at the same time, it is not always necessary to correct chromatic aberration over a certain wavelength range, and it is sufficient if aberrational performance is obtained at several laser wavelengths. Floating for focus adjustment every time is complicated and poor in operability.

In the objective lens of the present invention, high resolution can be obtained at several laser wavelengths simply by adjusting the working distance, and by doing so, a much larger working distance than the conventional one can be obtained. It is something that you get.

To obtain such an objective lens, it is not necessary to correct axial chromatic aberration and magnification chromatic aberration.
Various aberrations at each wavelength must be well corrected by one lens system. For that purpose, it is important to guide the light beam to the second lens unit L2 without causing large spherical aberration in the first lens unit L1. In order to bend the light beam without generating a large spherical aberration, it is necessary to make the angle difference between the normal to the lens surface and the incident light beam not so large, and for that purpose, the first lens unit L1 is moved toward the object side. It is more effective if a combination of meniscus lenses with concave surfaces is used, and at least one of them is a cemented lens having irregularities. The condition (1) is set so as to effectively introduce light rays into the second lens unit L2. Here, if the lower limit of 2.5 is exceeded, the power of the first lens unit L1 becomes too strong, and the spherical aberration and curvature of field generated there cannot be completely corrected by the rear group. When the value exceeds 5, the light beam group having a large angle becomes the second lens unit L
Thus, spherical aberration and the like generated in the first lens unit L1 cannot be completely corrected by the second lens unit L2.

The second lens unit L2 includes three cemented lenses,
By including more than one, the spherical aberration and coma of each wavelength are corrected very favorably, and the condition (2) is set in order to maximize the effect. Here, when the lower limit of 5 to condition (2) is exceeded, the second lens unit L
2 becomes too strong, causing large spherical aberration and coma. Conversely, if the upper limit of 10 is exceeded, the ray height cannot be lowered to lead to the third lens unit L3 having negative power. The curvature of field cannot be corrected by the third lens unit L3.

The condition (3) is set so that the third lens unit L3 effectively corrects the curvature of field.
Here, if the lower limit of 2.5 is exceeded, the third lens unit L
3, the power becomes too strong and the spherical aberration that occurs there,
Coma cannot be corrected by the other groups, and conversely, the upper limit of 7.
If it exceeds 5, the negative power becomes too weak, and the field curvature cannot be corrected.

Further, in order to effectively guide the light beam to the third lens unit L3, it is desirable that the following condition is satisfied.

(4) 2 <| d ₃ / f | <6 where d ₃ is a distance between the second lens unit L2 and the third lens unit L3. Here, if the lower limit of 2 is exceeded, the third
The height of the light ray incident on the lens unit L3 cannot be reduced completely, and the curvature of field cannot be corrected effectively. Conversely, if the upper limit of 6 is exceeded, the light ray will be too low and excessive negative Petzval value and coma aberration will occur. Will occur.

Further, the objective lens of the present invention has a size of 10 mm.
It is desirable to use only a glass material having a thickness and an internal transmittance of 80% or more at a wavelength of 250 nm. With this objective lens, the number of lenses is considerably larger than that of a normal objective lens in order to perform aberration correction extremely well at high magnification, high numerical aperture, and long working distance. It is.

Further, when fluorite is used for the objective lens of the present invention, it is desirable to use all convex lenses. To correct chromatic aberration in a certain wavelength range, it is necessary to use fluorite as a concave lens in the rear group, but if correcting various aberrations for each wavelength, it is more effective to use fluorite for a convex lens as usual Because.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments 1 to 4 of the near-ultraviolet objective lens of the present invention will be described below. Although lens data of each embodiment will be described later, FIGS. 1 to 4 show lens cross sections of Examples 1 to 4, respectively. Here, all examples are 100
×, numerical aperture (NA) 0.85, dry infinity correction design, focal length 360 mm.

In the first embodiment, the first lens unit L1 has a concave surface facing the object side in Example 1 in order from the object (sample) side as the arrangement and material of the lens system (the materials are indicated in parentheses). A negative meniscus lens (quartz), a bi-concave lens (quartz), and a cemented meniscus lens of a bi-convex lens (fluorite) are included. (Fluorite) triplet lens, biconvex lens (fluorite), biconcave lens (quartz), biconvex lens (fluorite) triplet lens, biconvex lens (fluorite), biconcave lens (quartz) It consists of two cemented lenses,
The third lens unit L3 includes a cemented lens of a biconcave lens (quartz) and a biconvex lens (fluorite).

In the second embodiment, the first lens unit L1 is in the first embodiment.
The second lens unit L2 includes a triplet lens of a biconvex lens (fluorite), a concave plano lens (quartz), and a plano-convex lens (fluorite), a biconvex lens (fluorite), and a biconcave lens (quartz). ), A triplet lens of a biconvex lens (fluorite), a triplet lens of a biconvex lens (fluorite), a biconcave lens (quartz), and a positive meniscus lens (fluorite) with a concave surface facing the image side, The third lens unit L3 includes a cemented lens of a biconcave lens (quartz) and a positive meniscus lens (fluorite) having a concave surface facing the image side.

In the third embodiment, the first lens unit L1 is the same as in the first and second embodiments, and the second lens unit L2 is a biconvex lens (fluorite), a concave flat lens (quartz), and a plano-convex lens (fluorite). ), A bi-convex lens (fluorite), a bi-concave lens (quartz), a bi-convex lens (fluorite), a positive meniscus lens (quartz) with a concave surface facing the image side, and a bi-convex lens (Fluorite) and a cemented lens of a biconcave lens (quartz) and a cemented lens of a biconvex lens (fluorite) and a biconcave lens (quartz). The third lens unit L3 is the same as that in the first embodiment.

In the fourth embodiment, the first lens unit L1 and the third lens unit L3 are the same as those in the first and third embodiments.
2 is a triple cemented lens of a biconvex lens (fluorite), a concave plano lens (quartz), and a plano-convex lens (fluorite), a biconvex lens (fluorite), and a negative meniscus lens with a concave surface facing the object side (quartz) , A biconvex lens (fluorite), a biconcave lens (quartz), a positive meniscus lens (fluorite) with a concave surface facing the image side, a biconvex lens (fluorite), and a biconcave lens (quartz) ) Consists of a cemented lens.

The lens data of each embodiment is shown below.
Each data is shown in an order reverse to the actual ray traveling direction. In addition, symbols are the above, f is the focal length of the whole system, N
A is the numerical aperture, M is the magnification, r ₁ , r ₂ ... Are the radii of curvature of the respective lens surfaces, d ₁ , d _2, ... _Are the distances between the respective lens surfaces, n _d1 , n
_d2 ... indicates the material of each lens.

[0028] Example 1 f = 360 NA = 0.85 M = 100 × r 1 = 56.370 d 1 = 2.51 n d1 = ( _{fluorite) r 2 = -14.095 d 2 =} 2.00 n d2 = ( quartz) r ₃ = 8.928 _{d 3 = 12.96 r 4 = -48.595} d 4 = 2.51 n d3 = ( _{quartz) r 5 = 11.674 d 5 =} 6.29 n d4 = ( _{fluorite) r 6 = -26.188 d 6 =} 8.57 r 7 = -120.086 d 7 = 4.00 n _d5 = _{(quartz) r 8 = 16.927 d 8 =} 8.47 n d6 = ( _{fluorite) r 9 = -37.143 d 9 =} 3.16 r 10 = 78.866 d 10 = 5.60 n d7 = ( fluorite) r ₁₁ = _{-48.273 d 11 = 4.00 n d8 =} ( _{quartz) r 12 = 19.726 d 12 =} 8.42 n d9 = ( _{fluorite) r 13 = -55.289 d 13 =} 0.20 r 14 = 25.214 d 14 = 4.95 n d10 = ( fluorite R ₁₅ = 15d ₁₅ = 2.50 n _d11 = (quartz) r ₁₆ = 12.119 d ₁₆ = 6.62 n _d12 = (fluorite) r ₁₇ = -118.585 d ₁₇ = 0.20 r ₁₈ = 9.841 d ₁₈ = 7.07 n _d13 = _{(fluorite) r 19 = -17.458 d 19 =} 2.00 n d14 = ( _{quartz) r 20 = 22.237 d 20 =} 0.20 r 21 = 3.347 d 21 = 4.17 n d15 = ( _{English) r 22 = 2.951 d 22 =} 0.92 r 23 = ∞ ( _{specimen) | f 1 /f|=3.47 | f 2} /f|=7.65 | f 3 /f|=5.53 | d 3 /f|=3.6
.

[0029] Example 2 f = 360 NA = 0.85 M = 100 × r 1 = -302.660 d 1 = 3.67 n d1 = ( _{fluorite) r 2 = -8.046 d 2 =} 6.00 n d2 = ( quartz) r ₃ = _{9.999 d 3 = 15.81 r 4 =} -75.381 d 4 = 2.00 n d3 = ( _{quartz) r 5 = 14.686 d 5 =} 5.80 n d4 = ( _{fluorite) r 6 = -21.509 d 6 =} 0.20 r 7 = -37.945 d ₇ = 5.16 n _d5 = _{(fluorite) r 8 = -11.123 d 8 =} 3.91 n d6 = ( _{quartz) r 9 = 19.275 d 9 =} 6.56 n d7 = ( _{fluorite) r 10 = -33.468 d 10 =} 0.55 r _{11 = 57.028 d 11 = 5.39 n} d8 = ( _{fluorite) r 12 = -95.363 d 12 =} 6.00 n d9 = ( _{quartz) r 13 = 18.294 d 13 =} 7.07 n d10 = ( fluorite) r ₁₄ = -47.646 d _{14 = 0.28 r 15 = 24.213 d} 15 = 5.71 n d11 = ( _{fluorite) r 16 = ∞ d 16 =} 2.00 n d12 = ( _{quartz) r 17 = 11.259 d 17 =} 6.80 n d13 = ( fluorite) r ₁₈ = _{-294.258 d 18 = 0.20 r 19 =} 8.796 d 19 = 7.44 n d14 = ( _{fluorite) r 20 = -20.013 d 20 =} 2.22 n d15 = ( quartz) r ₂₁ = 13.242 d _{21 = 0.20 r 22 = 3.323 d} 22 = 3.81 n d16 = ( _{quartz) r 23 = 3.190 d 23 =} 0.86 r 24 = ∞ ( _{specimen) | f 1 /f|=3.8 | f 2} /f|=7.114 | f _{3 /f|=4.71} | d _{3 /f|=4.39}
.

[0030] Example 3 f = 360 NA = 0.85 M = 100 × r 1 = 154.703 d 1 = 2.52 n d1 = ( _{fluorite) r 2 = -12.311 d 2 =} 2.75 n d2 = ( quartz) r ₃ = 9.742 _{d 3 = 12.52 r 4 = -76.830} d 4 = 2.00 n d3 = ( _{quartz) r 5 = 10.937 d 5 =} 5.41 n d4 = ( _{fluorite) r 6 = -29.602 d 6 =} 9.59 r 7 = -146.653 d 7 = 2.00 n _d5 = _{(quartz) r 8 = 16.169 d 8 =} 7.72 n d6 = ( _{fluorite) r 9 = -74.387 d 9 =} 5.00 n d7 = ( _{quartz) r 10 = -41.770 d 10 =} 1.70 r 11 = _{74.643 d 11 = 6.70 n d8 =} ( _{fluorite) r 12 = -16.507 d 12 =} 3.20 n d9 = ( _{quartz) r 13 = 17.339 d 13 =} 7.92 n d10 = ( fluorite) r ₁₄ = -47.678 d ₁₄ = _{0.20 r 15 = 26.822 d 15 =} 4.90 n d11 = ( _{fluorite) r 16 = ∞ d 16 =} 2.00 n d12 = ( _{quartz) r 17 = 11.536 d 17 =} 7.17 n d13 = ( fluorite) r ₁₈ = -126.903 _{d 18 = 0.20 r 19 = 9.815} d 19 = 7.44 n d14 = ( _{fluorite) r 20 = -19.860 d 20 =} 2.00 n d15 = ( quartz) r ₂₁ = 28.715 d _{21 = 0.20 r 22 = 3.508 d} 22 = 4.24 n d16 = ( _{quartz) r 23 = 2.982 d 23 =} 0.99 r 24 = ∞ ( _{specimen) | f 1 /f|=3.50 | f 2} /f|=8.13 | f _{3 /f|=5.39} | d _{3 /f|=3.48}
.

Example 4 f = 360 NA = 0.85 M = 100 × r ₁ = 175.567 d ₁ = 5.35 n _d1 = (fluorite) r ₂ = −7.996 d ₂ = 5.63 n _d2 = (quartz) r ₃ = 9.174 _{d 3 = 15.09 r 4 = -52.756} d 4 = 2.00 n d3 = ( _{quartz) r 5 = 15.358 d 5 =} 5.86 n d4 = ( _{fluorite) r 6 = -18.805 d 6 =} 0.20 r 7 = -36.681 d 7 = 5.24 n _d5 = _{(fluorite) r 8 = -10.479 d 8 =} 5.82 n d6 = ( _{quartz) r 9 = 22.070 d 9 =} 6.11 n d7 = ( _{fluorite) r 10 = -34.954 d 10 =} 3.08 r 11 _{= 60.484 d 11 = 6.00 n d8} = ( _{quartz) r 12 = 21.426 d 12 =} 6.44 n d9 = ( _{fluorite) r 13 = -51.266 d 13 =} 2.27 r 14 = 23.125 d 14 = 5.86 n d10 = ( fluorite _{) r 15 = ∞ d 15 =} 2.14 n d11 = ( _{quartz) r 16 = 11.306 d 16 =} 6.49 n d12 = ( _{fluorite) r 17 = -306.604 d 17 =} 0.25 r 18 = 8.859 d 18 = 6.91 n d13 = _{(fluorite) r 19 = -20.587 d 19 =} 2.00 n d14 = ( _{quartz) r 20 = 12.551 d 20 =} 0.20 r 21 = 3.228 d 21 = 3.82 n d15 = ( stone English) r ₂₂ = 3.155 d ₂₂ = 0.91 r ₂₃ = ∞ (sample) | f ₁ /f|=3.73 | f ₂ /f|=6.33 | f ₃ /f|=4.81 | d ₃ /f|=4.19
.

FIGS. 5 to 8 show aberration diagrams showing the spherical aberration, astigmatism, distortion, and point image intensity distribution of the ultraviolet objective lenses of Examples 1 to 4 described above.

[0033]

As described above, according to the present invention,
It is possible to obtain a dry high-resolution ultraviolet objective lens having a high magnification and a high numerical aperture that can be used in a wavelength range around 250 nm, has good image plane flatness and transmittance, and has a relatively long working distance.

[Brief description of the drawings]

FIG. 1 is a sectional view of a near-ultraviolet objective lens according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a lens according to a second embodiment.

FIG. 3 is a sectional view of a lens according to a third embodiment.

FIG. 4 is a sectional view of a lens according to a fourth embodiment.

FIG. 5 is an aberration diagram showing a spherical aberration, astigmatism, distortion, and point image intensity distribution in Example 1.

FIG. 6 is an aberration diagram similar to FIG. 5 of the second embodiment.

FIG. 7 is an aberration diagram similar to FIG. 5 of the third embodiment.

FIG. 8 is an aberration diagram similar to FIG. 5 of the fourth embodiment.

[Explanation of symbols]

 L1 first lens group L2 second lens group L3 third lens group

Continuation of front page (56) References JP-A-54-11755 (JP, A) JP-A-58-90611 (JP, A) JP-A-59-155822 (JP, A) JP-A-54-79053 (JP) JP-A-59-29216 (JP, A) JP-A-60-159717 (JP, A) JP-A-60-205521 (JP, A) JP-A-63-23119 (JP, A) 4-26813 (JP, A) JP-A-64-249313 (JP, A) JP-A-3-188407 (JP, A)

Claims (2)

(57) [Claims] 1. An object comprising, in order from the object side, a meniscus lens having a concave surface facing the object side and a concave-convex cemented meniscus lens, and includes at least two positive lens first lens units L1 and three cemented lenses as a whole. the second lens group of positive power L2, include irregularities cemented lens and a third lens group L3 having a negative power, both the individual lens units fixed
An ultraviolet objective lens which is a lens group and satisfies the following condition: (1) 3.4 <| f ₁ / f | <5 (2) 5 <| f ₂ / f | <10 ( 3) 2.5 <| f ₃ /f|<7.5, where f ₁ , f ₂ , f ₃ , and f are the first lens unit L1, the second lens unit L2, the third lens unit L3, and the entire system, respectively. Is the focal length. 2. The ultraviolet objective lens according to claim 1, wherein fluorite is used for all convex lenses.