JPH0720385A - Microscopic objective lens - Google Patents

Abstract

PURPOSE:To provide a microscopic objective lens in which visible light area and a near ultraviolet area are corrected simultaneously, and is provided with remarkably improved operability and possesses super long operating distance. CONSTITUTION:This lens is comprised of a first lens group G1 and a second lens group G2. The first lens group G1 is provided with first and second lens group C1, C2 consisting of a convex lens and a concave lens, or the junction lens of them. The second lens group G2 includes a single convex lens and the junction lens of the convex lens with the concave lens, and at least one of the junction lenses is formed of a three-junction lens. In such a constitution the optical constant of each lens group is set so as to satisfy conditions (1): 2F<D12<10F, (2): F<IF1I<3.5F, (3): n2n-n2p>0.1, and (4): upsilon2p-upsilon2n>20, upsilon2p>80.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a microscope objective lens. More specifically, a so-called retro structure that includes a first lens group that is far from the object side and has a negative refracting power as a whole, and a second lens group that is close to the object side and has a positive refracting power as a whole The present invention relates to an infinity correction type microscope objective lens of a focus optical system.

[0002]

BACKGROUND ART A microscope is used for observing semiconductor IC patterns. Further, laser processing such as repair of semiconductors and semiconductor masks using YAG laser (wavelength; 1064 nm) or the second harmonic (wavelength; 532 nm) of YAG laser is also performed. Recently, high-resolution observation and fine processing using light of shorter wavelength [eg, third harmonic of YAG laser (wavelength: 355 nm)]
Laser processing using photochemical reactions is about to begin.

In these cases, a long working distance of the microscope objective lens is required for convenience of operation. In response to such a demand, the present applicant has previously proposed the objective lens disclosed in JP-A-60-70412 and JP-A-63-23119 as a microscope objective lens having a long working distance. ing.

[0004]

However, the microscope objective lenses disclosed in the above-mentioned respective publications are mainly those whose aberrations are corrected in the visible light region. Therefore, in addition to the observation in the visible light region, when the laser processing by the YAG third harmonic in the near-ultraviolet region or the near-ultraviolet observation is attempted, the following problems occur. For example, even if focusing is performed so that the imaging condition is satisfied in the visible light region, the imaging condition is not satisfied in the near-ultraviolet region, and therefore, the laser spot of the YAG third harmonic is set at an accurate position of the IC pattern. There arises a problem that a laser spot of a YAG third harmonic wave that cannot be irradiated or cannot be observed with the naked eye must be irradiated by trial and error for focusing.

By the way, as an objective lens corrected from the visible light region to the near ultraviolet region, for example, JP-A-62-4
A microscope objective lens disclosed in Japanese Patent No. 9313 is known. However, the working distance of this microscope objective lens is
In an objective lens with a magnification of about 50X, it is extremely short, such as 1 times the focal length.
It was a big problem in operation.

An object of the present invention is to solve the above-mentioned conventional problems, correct the visible light region and the near-ultraviolet region at the same time, and have a very long working distance with a significantly improved operability. It is to provide an objective lens.

[0007]

Therefore, the microscope objective lens of the present invention has a first lens group that is far from the object side and has a negative refracting power as a whole, and a positive lens group that is near the object side and has a positive refractive power as a whole. An infinity correction type microscope objective lens including a second lens group having a refractive power of
The lens group has a first lens group and a second lens group, each group is composed of a convex lens and a concave lens, or a cemented lens of a convex lens and a concave lens, and the second lens group is a single convex lens, A cemented lens of a convex lens and a concave lens, at least one of which is 3
D ₁₂ ; lens distance between the first lens group and the second lens group, F; overall focal length, F ₁ ; focal length of the first lens group, n _2p ; cementing in the second lens group Average refractive index at d line of convex lens of lens, n _2n ; Average refractive index at d line of concave lens of cemented lens in second lens group, ν _2p ; Average Abbe number of convex lens in second lens group , Ν _2n ; the average Abbe number of the concave lens in the second lens group, and the optical constant of each lens group is given by the following equation 2F <D ₁₂ <10F ………… (1) F <IF ₁ I < 3.5F ……………… (2) n _2n −n _2p > 0.1 ………… (3) ν _2p −ν _2n > 20, ν _2p > 80 ………… (4) It is characterized as being.

[0008]

The above equation (1) is based on the first lens group and the second lens group.
It defines the distance from the lens group. In the formula (1), when D ₁₂ exceeds the upper limit (10 F), the power of the first lens group and the second lens group becomes weak for aberration correction, which is advantageous, but the working distance cannot be lengthened. Also,
When D ₁₂ exceeds the lower limit (2F), the power becomes strong and high-order aberrations such as spherical aberration and coma occur, which makes it difficult to correct them.

The above formula (2) defines the focal length of the first lens group. In equation (2), IF
_{When 1} I exceeds the upper limit (3.5 F) and the focal length becomes long,
Aberration correction is advantageous, but there is a disadvantage that the working distance is shortened. Also, if IF ₁ I exceeds the lower limit (F) and the focal length becomes short, it is advantageous to increase the working distance,
The occurrence of aberrations in the first lens group becomes remarkable, and it becomes difficult for the second lens group to completely correct the aberrations generated in the first lens group.

Further, the above equation (3) defines the refractive index of the cemented lens in the second lens group. If the expression (3) is not satisfied, the radius of curvature of the cemented surface must be made tight, spherical aberration, especially higher-order aberrations will occur, and the first lens group, which is another lens group, cannot be completely corrected. In particular,
Aberrations are severely generated in the short wavelength region, the aberrations are out of balance, and it becomes extremely difficult to correct the aberrations.

The above equation (4) defines the Abbe number of the lenses in the second lens group. Ν _{2p in the} following equation>
80 specifies the Abbe number of the convex lens. If this condition is not satisfied, a large deviation will occur in the occurrence of spherical aberration, chromatic aberration, etc. in the short wavelength region and the visible light region, making it difficult to simultaneously correct various aberrations at each wavelength. Ν _2p − in the previous equation
ν _2n > 20 defines the Abbe number of the convex lens and the concave lens. If this condition is not satisfied, the power of the convex lens and the concave lens becomes too strong when chromatic aberration is corrected, and high-order aberrations such as spherical aberration and coma are generated.
In order to reduce this occurrence, the number of lenses must be increased, which causes a large increase in production cost.

According to the present invention, the optical constants of the respective lens groups are set so that the expressions (1) to (4) are simultaneously satisfied, thereby simultaneously correcting various aberrations such as spherical aberration, coma aberration and chromatic aberration at each wavelength. However, the working distance is extremely long, visible range ~
It was possible to obtain a microscope objective lens that can be used up to the near-ultraviolet region.

[0013]

The preferred embodiments of the microscope objective lens of the present invention will be described below.
A suitable example is given and explained in detail based on a drawing.First embodiment The microscope objective lens of the first embodiment is, as shown in FIG.
It is located on the side far from the body and has a negative refracting power as a whole.
1 lens group G₁Is close to the object side and is positive as a whole.
Second lens group G having a refractive power of₂Consists of and
It First lens group G₁Is the first lens group C₁And second len
Close-up C₂And each set C ₁, C₂Is a convex lens L
_1,L₃And concave lens L_2,L_FourConsists of. Second lens group G₂
Is a single convex lens and a combination of convex and concave lenses
Lens and at least one of the cemented lenses is 3
Consists of a cemented lens. Specifically, three independent convex
L_Five,L_13,L₁₄And concave lens L₆And convex lens L
₇Two-piece cemented lens consisting of and a convex lens L₈,concave lens
L₉And convex lens L _TenA three-element cemented lens consisting of
Lens L₁₁And concave lens L₁₂Two-element cemented lens consisting of
It is formed including and.

With the above construction, the focal length of 200 mm
When the image is formed by the imaging lens, the magnification is 50 times,
The numerical aperture NA is 0.42 and the focal length is 4.0 mm.
By satisfying the relations of the expressions (1) to (4),
When the optical constants were set as shown in Table 1, the lens system
From the vertex of the surface closest to the object to the object surface (working distance
Away) WD is 16.97mm, and long working distance can be obtained.
I was able to. Where L₁... L₁₄Is each lens, r₁… R
_{twenty four}Is the curvature of each surface of each lens, d₁... d _{twenty three}Is the thickness of each lens
And lens spacing, n₁... n₁₄Is the refractive index of each lens, ν
₁… Ν₁₄Is the Abbe number of each lens [= (nd-1) / (n
F-nC)].

[Table 1] r ₁ =-8.928 d ₁ = 3.6 n ₁ = 1.62004 ν ₁ = 36.3 L ₁ r ₂ =-4.68 d ₂ = 0.032 r ₃ =-4.55 d ₃ = 1.5 n ₂ = 1.58913 ν ₂ = 61.2 L ₂ r ₄ = 16.277 d ₄ = 4.4 r ₅ = -60.663 d ₅ = 4.2 n ₃ = 1.62004 ν ₃ = 36.3 L ₃ r ₆ =-6.707 d ₆ = 0.043 r ₇ =-6.52 d ₇ = 1.5 n ₄ = 1.51633 ν ₄ = 64.1 L ₄ r ₈ = ∞ d ₈ = 14 r ₉ = -20.602 d ₉ = 5.2 n ₅ = 1.45650 ν ₅ = 90.3 L ₅ r ₁₀ = -11.802 d ₁₀ = 1 r ₁₁ = -48.514 d ₁₁ = 1.5 n ₆ = 1.69680 ν ₆ = 55.5 L ₆ r ₁₂ = 15.24 d ₁₂ = 7.2 n ₇ = 1.49700 ν ₇ = 81.1 L ₇ r ₁₃ = -34.684 d ₁₃ = 1 r ₁₄ = 290.47 d ₁₄ = 7.2 n ₈ = 1.49700 ν ₈ = 81.1 L ₈ r ₁₅ = -18.6 d ₁₅ = 1.4 n ₉ = 1.69680 ν ₉ = 55.5 L ₉ r ₁₆ = 40.06 d ₁₆ = 6.5 n ₁₀ = 1.49700 ν ₁₀ = 81.1 L ₁₀ r ₁₇ =- 33.1 d ₁₇ = 0.3 r ₁₈ = 22.12 d ₁₈ = 9 n ₁₁ = 1.45650 ν ₁₁ = 90.3 L ₁₁ r ₁₉ = -18.831 d ₁₉ = 1.4 n ₁₂ = 1.77250 ν ₁₂ = 49.6 L ₁₂ r ₂₀ = -145.3 d ₂₀ = 0.3 r ₂₁ = 33.1 d ₂₁ = 5.1 n ₁₃ = 1.45650 ν ₁₃ = 90.3 L ₁₃ r ₂₂ = -46.56 d ₂₂ = 0.33 r ₂₃ = 14.003 d ₂₃ = 4.1 n ₁₄ = 1.49700 ν ₁₄ = 81.1 L ₁₄ r ₂₄ = 30.654

The above equations (1) to (4) are obtained on the basis of the optical constants of the above lens systems, and are as follows. (1) ...... D ₁₂ = 3.5F (2) formula _{... IF 1 I = 2.5F (3} ) Equation _{...... n 2n -n 2p = 0.24 (} 4) equation _{...... ν 2p -ν 2n = 31.5,} ν _2p = 85.0

FIG. 2 shows the measurement results of spherical aberration, astigmatism and distortion in this example. This FIG. 2 is obtained by tracing a ray from the image side toward the object plane, and Y ′ represents the image height when an image is formed by an image forming lens having a focal length of 200 mm. As is apparent from the figure, it is understood that various aberrations are well corrected despite the large numerical aperture NA and the long working distance WD.

[0018]Second embodiment The microscope objective lens of the second embodiment is, as shown in FIG.
Similarly to the first embodiment, the first lens group G₁And the second lens group
G₂It consists of and. First lens group G₁Is the first
Lens set C₁And the second lens set C₂And each set C ₁, C
₂Is a convex lens L_1,L₃And concave lens L_2,L_FourConsists of
It is formed by a cemented lens. Second lens group G₂
Is three single convex lenses L_Five,L_13,L₁₄And a convex lens
L₆And concave lens L₇A two-element cemented lens consisting of
Lens L₈, Concave lens L₉And convex lens L_TenConsists of
Three cemented lens and convex lens L₁₁And concave lens L₁₂Or
And a two-lens cemented lens.

With the above-mentioned structure, the magnification is 50 times, the numerical aperture NA on the object side is 0.4, and the focal length is 4.0 mm when the image is formed by the imaging lens having the focal length of 200 mm. When the optical constants of the respective lenses are set as shown in Table 2 by satisfying the relationships of the expressions (1) to (4), the working distance W
D was 16.52 mm, and a long working distance could be obtained.

[0020] Table 2 _{r 1 = - 6.76 d 1 =} 3.5 n 1 = 1.62004 ν 1 = 36.3 L 1 r 2 = - 4.07 d 2 = 1.5 n 2 = 1.58913 ν 2 = 61.2 L 2 r 3 = -444.12 d ₃ = 4.5 r ₄ = -12.245 d ₄ = 4 n ₃ = 1.62004 ν ₃ = 36.3 L ₃ r ₅ =-5.723 d ₅ = 1.5 n ₄ = 1.51633 ν ₄ = 64.1 L ₄ r ₆ = ∞ d ₆ = 12.1 r ₇ = -29.306 d ₇ = 5.5 n ₅ = 1.49700 ν ₅ = 81.1 L ₅ r ₈ = -14.227 d ₈ = 1.15 r ₉ = 118.97 d ₉ = 7.5 n ₆ = 1.45650 ν ₆ = 90.3 L ₆ r ₁₀ =- 14.01 d ₁₀ = 1.5 n ₇ = 1.69680 ν ₇ = 55.5 L ₇ r ₁₁ = -242.23 d ₁₁ = 1.3 r ₁₂ = 54.78 d ₁₂ = 8.5 n ₈ = 1.49700 ν ₈ = 81.1 L ₈ r ₁₃ = -19 d ₁₃ = 1.4 n ₉ = 1.69680 ν ₉ = 55.5 L ₉ r ₁₄ = 27.8 d ₁₄ = 7.5 n ₁₀ = 1.49700 ν ₁₀ = 81.1 L ₁₀ r ₁₅ = -26.929 d ₁₅ = 0.3 r ₁₆ = 28.486 d ₁₆ = 7.5 n ₁₁ = 1.45650 ν ₁₁ = 90.3 L ₁₁ r ₁₇ = -20.88 d ₁₇ = 1.4 n ₁₂ = 1.77250 ν ₁₂ = 49.6 L ₁₂ r ₁₈ = -294.03 d ₁₈ = 0.3 r ₁₉ = 26.5 d ₁₉ = 5.3 n ₁₃ = 1.45650 ν ₁₃ = 90.3 L ₁₃ r ₂₀ = -52.51 d ₂₀ = 0.3 r ₂₁ = 14.79 d ₂₁ = 4.2 n ₁₄ = 1.49700 ν ₁₄ = 81.1 L ₁₄ r ₂₂ = 38.1

The above equations (1) to (4) are calculated based on the optical constants of the respective lens systems as follows. (1) ...... D ₁₂ = 3.0F (2) formula _{... IF 1 I = 2.0F (3} ) Equation _{...... n 2n -n 2p = 0.25 (} 4) equation _{...... ν 2p -ν 2n = 31.5,} ν _2p = 85.0

FIG. 4 shows the measurement results of spherical aberration, astigmatism and distortion in this example. As is apparent from the figure, it is understood that various aberrations are well corrected despite the large numerical aperture NA and the long working distance WD.

[0023]Third embodiment The microscope objective lens of the third embodiment is, as shown in FIG.
Similarly to the first embodiment, the first lens group G₁And the second lens group
G₂It consists of and. First lens group G₁Is the first
Lens set C₁And the second lens set C₂And each set C ₁, C
₂Is a convex lens L_1,L₃And concave lens L_2,L_FourConsists of.
Second lens group G₂Is three single convex lenses L_Five,L_16,
L₁₇And concave lens L₆And convex lens L₇2 sheets consisting of
Cemented lens and convex lens L₈, Concave lens L₉And convex
L_Ten3 cemented lens consisting of, and convex lens L₁₁, Concave
Lens L₁₂And convex lens L₁₃3-element cemented lens consisting of
And the convex lens L₁₄And concave lens L₁₅Joining two pieces
And a lens.

With the above-mentioned structure, the magnification is 100 times, the numerical aperture NA on the object side is 0.5, and the focal length is 2.0 mm when the image is formed by the imaging lens having the focal length of 200 mm.
When the optical constants of the respective lenses were set as shown in Table 3 by satisfying the relationships of the above equations (1) to (4), the working distance WD was 12.89 mm, and a long working distance could be obtained. .

[Table 3] r ₁ =-7 d ₁ = 3.15 n ₁ = 1.62004 ν ₁ = 36.3 L ₁ r ₂ =-3.816 d ₂ = 0.041 r ₃ =-3.654 d ₃ = 1 n ₂ = 1.58913 ν ₂ = 61.2 L ₂ r ₄ = 9.609 d ₄ = 3.15 r ₅ = -11.498 d ₅ = 3.42 n ₃ = 1.62004 ν ₃ = 36.3 L ₃ r ₆ =-4.181 d ₆ = 0.038 r ₇ =-4.07 d ₇ = 1 n ₄ = 1.51633 ν ₄ = 64.1 L ₄ r ₈ = ∞ d ₈ = 17.29 r ₉ = -35.407 d ₉ = 4.5 n ₅ = 1.49700 ν ₅ = 81.1 L ₅ r ₁₀ = -13.402 d ₁₀ = 1.3 r ₁₁ = -29.643 d ₁₁ = 1.4 n ₆ = 1.51633 ν ₆ = 64.1 L ₆ r ₁₂ = 13.402 d ₁₂ = 6 n ₇ = 1.49700 ν ₇ = 81.1 L ₇ r ₁₃ = -62.519 d ₁₃ = 0.3 r ₁₄ = ∞ d ₁₄ = 5.8 n ₈ = 1.49700 ν ₈ = 81.1 L ₈ r ₁₅ = -14.364 d ₁₅ = 1.5 n ₉ = 1.64000 ν ₉ = 60.2 L ₉ r ₁₆ = 28.956 d ₁₆ = 5.6 n ₁₀ = 1.49700 ν ₁₀ = 81.1 L ₁₀ r ₁₇ =- 30.404 d ₁₇ = 0.3 r ₁₈ = 31.998 d ₁₈ = 6.6 n ₁₁ = 1.45650 ν ₁₁ = 90.3 L ₁₁ r ₁₉ = -21.83 d ₁₉ = 1.5 n ₁₂ = 1.69680 ν ₁₂ = 55.5 L ₁₂ r ₂₀ = 31.998 d ₂₀ = 4.8 n ₁₃ = 1.45650 ν ₁₃ = 90.3 L ₁₃ r ₂₁ = -54.009 d ₂₁ = 0.3 r ₂₂ = 29.295 d ₂₂ = 5.7 n ₁₄ = 1.45600 ν ₁₄ = 90.3 L ₁₄ r ₂₃ = -26.811 d ₂₃ = 1.4 n ₁₅ = 1.74100 ν ₁₅ = 52.6 L ₁₅ r ₂₄ = -97.615 d ₂₄ = 0.35 r ₂₅ = 26.811 d ₂₅ = 4.1 n ₁₆ = 1.45650 ν ₁₆ = 90.3 L ₁₆ r ₂₆ = -128.56 d ₂₆ = 0.34 r ₂₇ = 11.802 d ₂₇ = 4.1 n ₁₇ = 1.49700 ν ₁₇ = 81.1 L ₁₇ r ₂₈ = 30.144

The above equations (1) to (4) are obtained based on the optical constants of the above lens systems, and are as follows. (1) ...... D ₁₂ = 8.6F (2) formula _{... IF 1 I = 2.4F (3} ) Equation _{...... n 2n -n 2p = 0.17 (} 4) equation _{...... ν 2p -ν 2n = 27.1,} ν _2p = 85.2

FIG. 6 shows the measurement results of spherical aberration, astigmatism and distortion in this example. As is apparent from the figure, it is understood that various aberrations are well corrected despite the large numerical aperture NA and the long working distance WD.

The present invention relates to an infinity-correction type microscope objective lens, but if a small, well-corrected imaging lens is provided on the image plane side of the first lens group G ₁ , then it is a finite correction type. It is self-evident that it can be used as.

[0029]

As described above, according to the present invention, it is possible to provide a microscope objective lens having an ultra-long working distance in which the visible light region and the near-ultraviolet region are simultaneously corrected and the operability is remarkably improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a lens configuration of a first example of a microscope objective lens according to the present invention.

FIG. 2 is a diagram showing various aberrations of the same example.

FIG. 3 is a diagram showing a lens configuration of a second example of the microscope objective lens according to the present invention.

FIG. 4 is a diagram showing various aberrations of the same example.

FIG. 5 is a diagram showing a lens configuration of a third example of the microscope objective lens according to the present invention.

FIG. 6 is a diagram showing various aberrations of the same example.

[Explanation of symbols]

G ₁ 1st lens group G ₂ 2nd lens group C ₁ 1st lens group C ₂ 2nd lens group L _{1 to} L ₁₇ lens

Claims (1)

[Claims] 1. An infinity lens composed of a first lens group located on the side far from the object side and having a negative refracting power as a whole, and a second lens group located on the side close to the object side and having a positive refracting power as a whole. In the correction type microscope objective lens, the first lens group includes a first lens group and a second lens group, and each group includes a convex lens and a concave lens, or a cemented lens of a convex lens and a concave lens, respectively. The second lens group has a single convex lens and a cemented lens of a convex lens and a concave lens, and at least one of the cemented lenses is composed of three cemented lenses. D ₁₂ ; of the first lens group and the second lens group Lens interval, F; Overall focal length, F ₁ ; Focal length of first lens group, n _2p ; Average refractive index at d line of convex lens of cemented lenses in second lens group, n _2n ; Second lens In the group Average refractive index at the d-line of a concave lens of the focus lens, [nu _2p; average Abbe number of the convex lens in the second lens group, [nu _2n; average Abbe number of the concave lens in the second lens group, and the case, each lens The optical constants of the group are as follows: 2F <D ₁₂ <10F ………… (1) F <IF ₁ I <3.5F ………… (2) n _2n −n _2p > 0.1 …… …………… (3) ν _2p −ν _2n > 20, ν _2p > 80 ……… (4) A microscope objective lens characterized by the above-mentioned.