JP3304410B2 - Near 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 a microscope, and more particularly to a dry high-magnification objective lens for correcting the chromatic aberration from near ultraviolet to the visible region and for use in the semiconductor market and the like. .

[0002]

2. Description of the Related Art Conventionally, as a near-ultraviolet objective lens, a general high-magnification objective lens for ultraviolet fluorescence and German Patent Publication No. 3915868 are known.

[0003] However, in these conventional examples,
A general ultraviolet fluorescent objective lens simply passes near-ultraviolet light, and does not necessarily have the same focal position from near-ultraviolet to visible.In addition, even if the focal position is shifted, the imaging performance is sufficient. Usually it is not. Furthermore, these objective lenses are generally used for living organisms, and those with high resolution and high resolution are often immersion types, but in the semiconductor market, etc., the immersion type is hardly used because it damages the specimen and has poor workability. . However, in recent years, the necessity of clearly seeing objects on the order of sub-microns has increased in the semiconductor market and the like, and a high resolution of a dry system as well as a liquid immersion system has been demanded.

[0004] Also, German Patent Publication No. 39158
The objective lens described in No. 68 floats according to the wavelength (single wavelength) used in the ultraviolet to visible range, and cannot be used simultaneously in a wide wavelength range. This is suitable for observation at a specific wavelength, but cannot be used for fluorescence confocal microscopes, etc., which require exact same focal position performance at different wavelengths. In addition, floating operation during switching observation at different wavelengths Is troublesome and operability deteriorates.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and an object of the present invention is to enable high-resolution observation with near-ultraviolet light and ultraviolet-fluorescence confocal.
An object of the present invention is to provide a near-ultraviolet objective lens that has been color-corrected in the near-ultraviolet to visible range.

[0006]

The near-ultraviolet objective lens of the present invention comprises, in order from the object side, a meniscus lens having a concave surface facing the object side and a cemented lens, and a first lens unit L1 having a positive power as a whole. Second including two triplet lenses
It comprises a lens unit L2 and a third lens unit L3 comprising a pair of cemented lenses whose concave surfaces face each other, and satisfies the following conditions. (1) 1.5 <| f ₁ /f|<3.5 (2) 0.5 <| R ₃ / D ₃ | <1.5 where f ₁ and f are the first lens unit L1 and the whole, respectively. The focal lengths R ₃ and D _{3 of the system} are respectively the radius of curvature of the object side surface of the most object side lens of the third lens unit L3 and the center thickness thereof.

In this case, it is desirable to use only a glass material having a thickness of 10 mm and an internal transmittance of 50% or more at a wavelength of 350 nm. It is desirable that at least two biconvex lenses including a plano-convex lens are made of fluorite.

[0008]

The reason and operation of the above configuration will be described below. In order to perform color correction in a wide wavelength range from the near ultraviolet to the visible region, a large number of bonding surfaces must be used, and chromatic aberration must be corrected effectively there. First lens group L
1 is for introducing a high-angle light beam emitted from an object into a second lens unit L2 having an effective color correction capability using a triple cemented lens or fluorite while gradually reducing the angle. It is. In order to bend the light beam without causing large spherical aberration or the like, it is necessary to make the angle difference between the normal line of the surface and the incident light beam not so large. Therefore, the first lens has a concave surface facing the object side. It becomes a meniscus lens. Further, the condition set for effectively introducing the light into the second lens unit L2 is the above condition (1). Here, if the lower limit of 1.5 is exceeded, the power of the first lens unit L1 becomes too strong, and the spherical aberration and chromatic aberration generated there cannot be completely corrected by the second and subsequent lens units. When the value exceeds 0.5, the light beam group having a large angle is introduced into the second lens unit L2, and the chromatic aberration and the like generated in the first lens unit L1 cannot be corrected by the second lens unit L2. .

After the color correction by the second lens unit L2, it is necessary to guide to the third lens unit L3 having a strong concave surface in order to correct the field curvature. Here, the field curvature is corrected effectively. In order to do so, the above condition (2) is set. here,
If the lower limit of 0.5 is exceeded, the power on the object side surface of the most object side lens of the third lens unit L3 becomes too strong, where a large positive Petzval value is generated, followed by a negative Petzval value of a concave surface. But it's hard to counter, and
Since the light beam bends too rapidly, the spherical aberration, chromatic aberration, coma aberration, and the like generated there cannot be corrected by other groups. Conversely, if the upper limit of 1.5 is exceeded, the ray height cannot be lowered to lead to a strong concave surface, a negative Petzval value cannot be generated effectively, and field curvature cannot be corrected.

Furthermore, in order to effectively guide light rays to the image side lens of the third lens unit L3 and satisfactorily correct various aberrations, it is desirable to satisfy the following conditions.

(3) 3 <| (d ₃ + d ₄ / n ₄ + d ₅ / n ₅ ) / f | <8, where d ₃ , d ₄ , n ₄ , d ₅ , and n ₅ are the third lens group The distance between the two lens units L3, the center thickness and the refractive index of each sample side lens of the third lens unit L3. Here, if the lower limit of 3 of the condition (3) is exceeded, the distance of the ray falling is short, so that the height of the ray incident on the image side lens of the third lens unit L3 does not decrease, and an effective negative Petzval value is obtained. Can not occur. Conversely, if the upper limit of 8 is exceeded,
The height of the light ray incident on the image side lens of the third lens unit L3 is too low, and an excessive negative Petzval value, coma and the like are generated.

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 50% or more at a wavelength of 350 nm. With this objective lens, color correction is performed over a wide range from near ultraviolet to visible.
The number of lenses is considerably larger than that of a normal objective lens, which is a necessary condition.

Furthermore, in the objective lens of the present invention, it is desirable that at least two of the biconvex lenses including the plano-convex lens are fluorite. In order to perform color correction in a wide range from the near ultraviolet to the visible range, it is necessary to use a lot of anomalous dispersion glass, which is commonly called, and fluorite is the best. In addition, there is anomalous dispersion glass for convex lenses, but in consideration of the color correction ability and the transmittance of ultraviolet rays, fluorite must be used. The reason is that the center thickness is inevitably increased, and the transmittance thereof becomes a problem.)

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments 1 to 3 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 3 show lens cross sections of Examples 1 to 3, respectively. Here, in each of the examples, a magnification of 100
X, numerical aperture (NA) 0.85, all of which are designed to be corrected for dry infinity, and have a focal length of 3.6 mm.

In the arrangement of the lens system, in order from the object (sample) side, in the first embodiment, the first lens unit L1 is
The second lens unit L2 includes a cemented lens of a positive meniscus lens having a concave surface facing the object side, a negative meniscus lens having a concave surface facing the image side, and a biconvex lens. A lens, a negative meniscus lens having a concave surface facing the image side, a biconvex lens, and a triple cemented lens of a negative meniscus lens having a concave surface facing the object side,
The third lens unit L3 includes a cemented lens of a biconvex lens and a biconcave lens, and a cemented lens of a positive meniscus lens having a concave surface facing the object side and a biconcave lens. The fluorite is a biconvex lens on the image side of the first triplet lens of the second lens unit L2,
Are used for the three cemented double-convex lenses and the third cemented lens of the third lens unit L3.

In the second embodiment, the first lens unit L1 and the second lens unit L2 are the same as in the first embodiment, but the third lens unit L3
Is composed of a cemented lens of a plano-convex lens and a plano-concave lens, and a cemented lens of a biconcave lens and a biconvex lens. The fluorite is a biconvex lens on the image side of the first triplet lens of the second lens unit L2, and Are used for two biconvex lenses of the three-element cemented lens.

In the third embodiment, the first lens unit L1
Is composed of a positive meniscus lens having a concave surface facing the object side, a negative meniscus lens having a concave surface facing the image side, and a cemented lens of a biconvex lens. The second lens unit L2 includes a biconvex lens, a biconcave lens, and a biconvex lens. The third lens unit L3 includes a cemented lens, a negative meniscus lens having a concave surface facing the image side, a biconvex lens, and a negative meniscus lens having a concave surface facing the object side. The third lens unit L3 includes a biconvex lens and a biconcave lens. It consists of a cemented lens and a cemented lens of a biconcave lens and a biconvex lens. The fluorite is a biconvex lens on the image side of the first triplet lens of the second lens unit L2, a biconvex lens of the second triplet lens, and a biconvex lens of the first cemented lens of the third lens unit L3. We use for three pieces.

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 ... are the d-line refractive indices of each lens, and v _d1 , v _d2 .

[0019] Example 1 f = 3.6 NA = 0.85 M = 100 × r 1 = -50.000 d 1 = 3.00 n d1 = 1.498 ν d1 = 66.8 r 2 = 7.199 d 2 = 4.83 n d2 = 1.620 ν d2 = 36.3 r _{3 = 35.679 d 3 = 15.88 r} 4 = -5.098 d 4 = 4.62 n d3 = 1.517 ν d3 = 52.4 r 5 = 15.142 d 5 = 7.26 n d4 = ( _{fluorite) ν d4 =. r 6 =} -9.090 d 6 _{= 1.14 r 7 = 25.259 d 7} = 4.00 n d5 = 1.652 ν d5 = 58.5 r 8 = 11.159 d 8 = 8.79 n d6 = ( _{fluorite) ν d6 =. r 9 =} -9.021 d 9 = 2.00 n d7 = 1.652 _{ν d7 = 58.5 r 10 = -29.928} d 10 = 0.29 r 11 = 21.322 d 11 = 7.53 n d8 = ( _{fluorite) ν d8 =. r 12 =} -12.966 d 12 = 2.00 n d9 = 1.652 ν d9 = 58.5 r _{13 = 16.769 d 13 = 8.23 n} d10 = 1.569 ν d10 = 71.3 r 14 = -15.756 d 14 = 0.51 r 15 = 10.935 d 15 = 7.20 n d11 = 1.497 ν d11 = 81.6 r 16 = -14.862 d 16 = 2.53 n _{d12 = 1.741 ν d12 = 52.6 r} 17 = -413.869 d 17 = 0.28 r 18 = 3.683 d 18 = 3.67 n d13 = 1.519 ν d13 = 64.5 r 19 = 5.697 d 19 = 1.57 r 20 = ∞ ( The _{present) | f 1 /f|=2.77 | R 3} / D 3 | = 1.25 | (d 3 + d 4 / n 4 + d 5 / n 5) /f|=6.66

Example 2 f = 3.6 NA = 0.85 M = 100 × r ₁ = 18.703 d ₁ = 2.95 n _d1 = 1.596 ν _d1 = 39.2 r ₂ = -9.306 d ₂ = 2.00 _{nd 2} = 1.498 ν _d2 = 66.8 r _{3 = 10.133 d 3 = 3.74 r} 4 = -5.787 d 4 = 16.42 n d3 = 1.498 ν d3 = 66.8 r 5 = ∞ d 5 = 13.63 n d4 = 1.497 ν d4 = 81.6 r 6 = -15.855 d 6 = 1.79 r _{7 = 43.965 d 7 = 2.00 n} d5 = 1.741 ν d5 = 52.6 r 8 = 10.326 d 8 = 11.77 n d6 = ( _{fluorite) ν d6 =. r 9 =} -18.335 d 9 = 2.00 n d7 = 1.741 ν d7 = _{52.6 r 10 = -35.773 d 10 =} 0.20 r 11 = 14.981 d 11 = 8.97 n d8 = ( _{fluorite) ν d8 =. r 12 =} -19.128 d 12 = 4.03 n d9 = 1.741 ν d9 = 52.6 r 13 = 16.479 _{d 13 = 8.44 n d10 = 1.569} ν d10 = 71.3 r 14 = -20.158 d 14 = 1.71 r 15 = 11.437 d 15 = 7.85 n d11 = 1.497 ν d11 = 81.6 r 16 = -14.259 d 16 = 2.07 n d12 = 1.741 _{ν d12 = 52.6 r 17 = -56.555} d 17 = 0.20 r 18 = 3.225 d 18 = 3.05 n d13 = 1.519 ν d13 = 64.5 r 19 = 3.763 d 19 = 1.79 r 20 = ∞ ( specimen _{| F 1 /f|=2.76 | R 3 /} D 3 | = 1.16 | (d 3 + d 4 / n 4 + d 5 / n 5) /f|=6.61

[0021] Example 3 f = 3.6 NA = 0.85 M = 100 × r 1 = 13.488 d 1 = 2.52 n d1 = 1.596 ν d1 = 39.3 r 2 = -9.164 d 2 = 2.32 n d2 = 1.498 ν d2 = 65.0 r _{3 = 7.716 d 3 = 4.96 r} 4 = -4.529 d 4 = 5.22 n d3 = 1.527 ν d3 = 51.1 r 5 = 12.751 d 5 = 5.98 n d4 = ( _{fluorite) ν d8 =. r 6 =} -7.810 d 6 _{= 20.84 r 7 = 58.790 d 7} = 2.00 n d5 = 1.652 ν d5 = 58.5 r 8 = 14.229 d 8 = 10.26 n d6 = ( _{fluorite) ν d8 =. r 9 =} -7.678 d 9 = 2.00 n d7 = 1.652 _{ν d7 = 58.5 r 10 = -17.908} d 10 = 2.15 r 11 = 18.425 d 11 = 6.00 n d8 = ( _{fluorite) ν d8 =. r 12 =} -11.442 d 12 = 4.44 n d9 = 1.652 ν d9 = 58.5 r _{13 = 18.125 d 13 = 6.00 n} d10 = 1.497 ν d10 = 81.1 r 14 = -13.482 d 14 = 0.91 r 15 = 11.951 d 15 = 5.97 n d11 = 1.497 ν d11 = 81.1 r 16 = -12.381 d 16 = 2.72 n _{d12 = 1.741 ν d12 = 52.6 r} 17 = -40.955 d 17 = 0.16 r 18 = 3.670 d 18 = 3.65 n d13 = 1.516 ν d13 = 64.2 r 19 = 5.992 d 19 = 1.55 r 20 = ∞ ( standard The _{present) | f 1 /f|=2.43 | R 3} / D 3 | = 1.31 | (d 3 + d 4 / n 4 + d 5 / n 5) /f|=3.48

FIGS. 4 to 6 show aberration diagrams showing the spherical aberration, astigmatism, and distortion of the near ultraviolet objective lenses of Examples 1 to 3 described above.

[0023]

As described above, according to the present invention,
It is possible to obtain a dry high-magnification objective lens that is color-corrected satisfactorily from the near ultraviolet to the visible region, and has good image plane flatness and transmittance.

[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 an aberration diagram showing a spherical aberration, an astigmatism, and a distortion of the first embodiment.

FIG. 5 is an aberration diagram similar to FIG. 4 of the second embodiment.

FIG. 6 is an aberration diagram similar to FIG. 4 of the third embodiment.

[Explanation of symbols]

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

Claims (3)

(57) [Claims] 1. A first lens group having a positive power as a whole, and a second lens group including two triple cemented lenses, each of which includes, in order from the object side, a meniscus lens having a concave surface facing the object side and a cemented lens. And a third lens group consisting of a pair of cemented lenses having concave surfaces facing each other, and satisfying the following condition: (1) 1.5 <| f ₁ / f | <3.5 (2) 0.5 <| R ₃ / D ₃ | <1.5 where f ₁ and f are the focal lengths of the first lens unit and the entire system, respectively, and R ₃ and D ₃ are each The radius of curvature of the object side surface of the most object side lens of the third lens group and the center thickness thereof. 2. The near-ultraviolet objective lens according to claim 1, wherein the following condition is satisfied: (3) 3 <| (d ₃ + d ₄ / n ₄ + d ₅ / n ₅ ) / f | < 8 where d ₃ , d ₄ , n ₄ , d ₅ , and n ₅ are the distance between the two lens units of the third lens unit, the center thickness and the refractive index of each sample side lens of the third lens unit. 3. The near-ultraviolet objective lens according to claim 1, wherein only a glass material having a thickness of 10 mm and an internal transmittance at a wavelength of 350 nm of 50% or more is used.