JP4418263B2 - Microscope objective lens - Google Patents

Description

  The present invention relates to a microscope objective lens. In particular, the magnification is about 100 ×, a long working distance and a large numerical aperture (NA) are combined, and an infinite correction type in which aberrations are favorably corrected from the visible light region to the near ultraviolet light region. The present invention relates to a microscope objective lens.

  In recent years, the development of semiconductor and liquid crystal technologies has been remarkable, and the degree of integration has been increasing.

  In these observation, measurement, repair, etc., it is desirable that the working distance (WD) of the microscope objective lens is large for the convenience of operation. Further, at the time of observation, in the fields such as observation with higher resolution and repair using a microscope objective lens and a laser, there is a demand for further precise processing. Therefore, a high-performance microscope objective lens that has both high resolution and a long working distance and can be used for laser processing has become necessary. Further, the laser to be used is not limited to the near infrared and visible light regions so far, and a near ultraviolet laser having a shorter wavelength and suitable for precision machining and photochemical reaction has been generally used.

  Under the recent development of such observation, measurement, and repair, the market can use from visible light to near-ultraviolet light region, which can realize high-resolution observation, precision processing by near-ultraviolet laser, processing by photochemical reaction, etc. There is a growing demand for microscope objective lenses having both a long working distance and a large numerical aperture.

  Up to now, the applicant of the present application has proposed Japanese Patent Laid-Open No. 63-23119 and Japanese Patent No. 2975905 as a microscope objective lens having a long working distance, and has a relatively small numerical aperture but a visible light region. Japanese Patent Laid-Open No. 7-20385 in which aberration correction is made from the near-ultraviolet light region, and Japanese Patent Laid-Open No. 2003-167199 that has a long working distance and a large numerical aperture that can be used in the visible to near-infrared light region are proposed. .

JP 63-23119 A Japanese Patent No. 2975905 Japanese Patent Laid-Open No. 7-20385 JP 2003-167199 A

  However, in JP-A-63-23119, Japanese Patent No. 2975905, and JP-A-2003-167199, as described above, although it is a long working distance microscope objective lens, it is mainly only in the visible light region or from visible light to near-red. Aberration correction was performed for the outside light region. Therefore, the imaging position of visible light or near-infrared light does not coincide with the imaging position of near-ultraviolet light, and it does not correct the influence of transmittance in the short wavelength region. It is not intended for repair using a near-ultraviolet laser (wavelength 355 nm) or high-resolution observation using near-ultraviolet light.

  The microscope objective lens disclosed in Japanese Patent Application Laid-Open No. 7-20385 has a long working distance and is well corrected for aberrations from the visible light region to the near ultraviolet light region. However, in this embodiment, the numerical aperture of the 100 × objective lens is about 0.5, which is difficult to say high resolution, and the depth of focus becomes deep, so that there has been an unsatisfactory surface in recent precision processing with a near ultraviolet laser.

  In such precision processing using a near-ultraviolet laser, the microscope objective lens has a high magnification, a long working distance and a high numerical aperture, and can correct aberrations over a wide wavelength range from the visible light region to the near-ultraviolet light region. It is required to be done well.

  The present invention has been made in view of such problems, and its purpose is to improve the operability in which chromatic aberration and various aberrations are well corrected over a wide wavelength range from the visible light region to the near ultraviolet light region. It is an object of the present invention to provide an infinitely corrected microscope objective lens having a good long working distance and a high numerical aperture and a magnification of about 100x.

In order to achieve the above object, the present invention provides:
In order from the object side, it consists of two sets of two-lens cemented lenses, a two-lens cemented lens consisting of a convex lens and a concave lens, and a meniscus two-lens cemented lens having a concave surface facing the object side as a whole. a first group having negative refracting power as a whole, the farthest from the object side, a convex meniscus lens having a convex surface directed toward the object side, a cemented doublet lens of a concave lens and a convex lens, a convex lens, a cemented triplet of concave and convex lens A lens, a cemented two-lens lens of a concave lens and a convex lens, a three-lens cemented lens of a convex lens, a concave lens and a convex lens, and four single convex lenses on the most object side, and among these single convex lenses, the object side The three objective lenses consist of a convex meniscus lens having a concave surface directed toward the object side, and a second objective having a positive refractive power as a whole. The radius of curvature of the object side surface of the double cemented lens located farthest from the object side of the first group is r11r, and the convex meniscus lens located farthest from the object side of the second group The radius of curvature of the object side surface is r21r, the radius of curvature of the object side surface of the convex meniscus lens located closest to the object side is r2r, the Abbe number of all the convex lenses in the first group is ν1p, and in the second group Assuming that the Abbe number of all concave lenses is ν2n, the partial dispersion ratio is θig2n, and the focal length of the entire microscope objective lens is F, the following equations (1) to (4)

The said subject is solved by satisfy | filling.

  However, the Abbe number ν is the refractive index of each wavelength of the d-line (587.56 nm), F-line (486.13 nm), and C-line (656.27 nm), respectively, nd, nF, and nC.

The partial dispersion ratio θig is defined as ni and ng, respectively, for the refractive index of each wavelength of i-line (365.01 nm) and g-line (435.84 nm).

It is represented by

  The diverging light beam emitted from one point on the object surface is incident on the lens on the object side of the second group, converged, emitted from the second group, and incident on the first group. The light beam incident on the first group becomes a parallel light beam by the first group and is emitted from the first group.

Next, each conditional expression will be described.
Equation (1) is
The radius of curvature r11r of the object-side surface (hereinafter referred to as the r11r surface) of the two-piece cemented lens located on the farthest side from the object side of the first group, and the farthest from the object side of the second group This defines the value of the radius of curvature r21r of the object side surface of the convex meniscus lens located on the side (hereinafter referred to as the r21r surface).

In the formula (1-1),
If the value of r11r increases beyond the upper limit of this equation, the correction amount of coma and astigmatism on the r11r surface decreases, and higher-order aberrations increase when correction is made on other surfaces. On the other hand, when the value is smaller than the lower limit, converse aberration and astigmatism are excessively generated on the r11r surface, and this aberration cannot be corrected on the other surfaces.

Equation (1-2) is
In the range of the value of r11r in the expression (1-1), the value of r21r is specified. This balances the negative coma generated on the r21r surface and the positive coma generated on the r11r surface, and controls the generation of third-order and higher-order spherical aberrations on the r21r surface. Correction of spherical aberration and coma aberration of the entire objective lens can be performed by realizing the expression (1-2).

  If the value exceeds the upper limit of this expression, spherical aberration, coma and astigmatism will occur remarkably on the r21r surface, and it will be difficult to correct aberrations on the r11r surface and other surfaces. If this is forcibly corrected for aberrations on another surface, higher-order aberrations occur, and as a result, a large numerical aperture cannot be obtained as a microscope objective lens.

On the other hand, if the lower limit of this equation is exceeded, correction of positive coma that occurs mainly on the r11r surface becomes difficult, and at the same time, because of the large third-order spherical aberration that occurs on the r21r surface, the entire microscope objective lens As a result, it becomes impossible to balance the third-order and higher-order spherical aberrations, and similarly, a large numerical aperture cannot be obtained as a microscope objective lens.
Expression (1) is a condition necessary for correcting spherical aberration, coma aberration, astigmatism, and higher-order aberrations in a well-balanced manner and obtaining a high numerical aperture as a microscope objective lens.

Equation (2) is
This is for defining the radius of curvature r2r of the object side surface of the convex meniscus lens located closest to the object side in the second group (hereinafter, this surface will be referred to as the r2r surface).

  If the upper limit of equation (2) is exceeded, the occurrence of spherical aberration and the like on the r2r surface is reduced, which is advantageous for aberration correction, but at the same time, the working distance is shortened, and the long working distance that is the object of the present invention is maintained. Can not be. If the lower limit is exceeded, spherical aberration, coma aberration, and higher-order aberration that occur on the r2r surface become large, and it is difficult to correct this on other surfaces. Therefore, equation (2) is a necessary condition for obtaining a long working distance and a high numerical aperture at the same time.

Equation (3) is
It defines the Abbe number ν1p of all convex lenses in the first group.
If the Abbe number of the convex lens in the first group exceeds the lower limit of this formula, it becomes advantageous to correct chromatic aberration of magnification, and the difference in Abbe number from the concave lens can be increased, so that the power of each concave lens is reduced. This is convenient for correcting various aberrations, but since a glass material having a large dispersion is used, chromatic spherical aberration occurs.
Accordingly, the shape of the spherical aberration differs for each wavelength, and in particular, aberration correction is performed over a wide wavelength region from the visible light region to the near ultraviolet region, which is the object of the present invention, and a high numerical aperture is maintained. Things become difficult. This cannot be corrected elsewhere.

  If the Abbe number of the convex lens in the first group exceeds the upper limit of this formula, it is convenient for correcting the spherical aberration of the color, but not only the chromatic aberration of magnification cannot be corrected, but also the Abbe of the convex lens and the concave lens. Since the difference between the numbers becomes small, the power of each of the convex lens and the concave lens has to be increased, and various aberrations and their higher-order aberrations become prominent and cannot be corrected elsewhere.

Equation (3) is a condition necessary for the microscope objective lens to correct aberrations over a wide wavelength region from the visible light region to the near ultraviolet region, and to realize a high numerical aperture.
Equation (4) is
It defines the Abbe number and partial dispersion ratio of all concave lenses in the second group.
If a glass material having an Abbe number exceeding the lower limit of the equation (4-1) is used for the concave lens in the second lens group, a glass material having a large dispersion is used, and chromatic spherical aberration occurs. Accordingly, it is impossible to correct aberrations over a wide wavelength region and maintain a high numerical aperture as in the description of the above-described equation (3).

  When a glass material having a partial dispersion ratio exceeding the upper limit of the expression (4-2) is used for the concave lens in the second lens group, it becomes out of the super-achromatic condition, and so-called secondary spectrum is remarkably generated. In particular, the occurrence of chromatic aberration of the secondary spectrum appears more prominently in a wide wavelength range from the visible light range to the near ultraviolet range, which is the object of the present invention.

  Equation (4) is a necessary condition for correcting the spherical aberration of color and preventing the generation of the secondary spectrum over a wide wavelength range from the visible light region to the near ultraviolet region. That is, by satisfying the formulas (1) to (4), a chromatic aberration can be corrected well in a wide wavelength range from the visible light region to the near ultraviolet region, and an infinitely corrected microscope objective lens having a high numerical aperture is realized. it can.

  Since the present invention is configured as described above, it has a high magnification (100x) in which chromatic aberration and other various aberrations are well corrected over a wide wavelength range from the visible light region to the near ultraviolet region. However, an infinity-corrected microscope objective lens having a high numerical aperture (high NA) and a long working distance can be obtained, and the working efficiency under the microscope can be remarkably increased.

  FIG. 1 shows an embodiment of an infinitely corrected microscope objective lens according to the present invention. This microscope objective lens is composed of a first group having negative refractive power and a second group having positive refractive power as a whole in order from the object side.

  The first group is composed of two sets of two cemented lenses, a two-lens cemented lens composed of a convex lens L1 and a concave lens L2, and a meniscus two-lens cemented lens having a convex surface facing the object side as a whole. It is configured.

  The second group includes, in order from the object side, a convex meniscus lens L5 having a convex surface facing the object side, a double cemented lens of a concave lens L6 and a convex lens L7, and a triple cemented lens of a convex lens L8, a concave lens L9 and a convex lens L10. , A concave lens L11 and a convex lens L12, a cemented lens, a convex lens L13, a concave lens L14, a convex lens L15, a cemented lens L16, a convex lens L16, and three convex meniscus lenses L17, L18 having a concave surface facing the object side. L19.

  In such a configuration, the optical constants of the respective lenses are such that when the image is formed by an imaging lens having a focal length of 200 mm, the magnification is 100 times, the numerical aperture (NA) on the object side is 0.67, and the focal length is 2 mm. Is set as shown in Table 1, the working distance (WD), which is the distance from the apex of the surface of the convex meniscus lens L19 located closest to the object side of the lens system to the object surface, is 11.11 mm, which is a long operation. A high-performance infinity-corrected microscope objective lens that has both a distance and a high numerical aperture (high NA) has been realized.

In Table 1, r1 to r30 are the radius of curvature of each surface of each lens. d1 to d29 are the thickness of each lens and the lens interval. All units are (mm). n1 to n19 are refractive indexes at the d-line of the glass materials used for the lenses L1 to L19, ν1 to ν19 are Abbe numbers of the glass materials used for the lenses L1 to L19, and θig6, θig9, θig11, and θig14 are respectively Partial Dispersion Ratio θig of Glass Material Used for Lenses L6, L9, L11, and L14
It is.

Specified magnification of infinity corrected microscope objective in Table 1 100x
Focal length 2.0 mm
Numerical aperture (NA) 0.67
Working distance (WD) 11.11 mm
(Magnification: Magnification when using an imaging lens with a focal length of 200 mm)
(Working distance: Distance from the apex of the most object-side surface of the lens system to the object surface)

The value of each conditional expression in the example

  The above value satisfies the conditional expression (1).

  The above value satisfies the conditional expression (2).

  The above value satisfies the conditional expression (3).

  The above value satisfies the conditional expression (4).

  On the other hand, FIG. 2 shows spherical aberration (FIG. 2A), astigmatism (FIG. 2B), and distortion aberration (FIG. 2C) of the infinity-corrected microscope objective lens of this example. It is shown. Spherical aberration shows aberration at each wavelength of d-line, F-line, C-line and 355 nm.

Astigmatism shows aberrations on the sagittal surface S and the meridional surface M, and the value of the d-line is shown as in the case of distortion. Here, Y ′ is an image height (15 mm) when being imaged by an imaging lens having a focal length of 200 mm.
From these aberration diagrams, the infinity-corrected microscope objective lens of the present embodiment has been well corrected for aberrations from the visible light region to the near ultraviolet region, while having a high magnification (100 ×), a high numerical aperture, and a long working distance. It can be understood that a high-performance microscope objective lens having the above has been realized.

  The present invention has been described with reference to a preferred embodiment. However, the present invention is not limited to this embodiment, and various improvements and design changes can be made within the scope of the technical idea of the present invention. is there. For example, it is possible to change the number of lenses in the first group and the second group and to change the arrangement of convex lenses, concave lenses, and cemented lenses without departing from the scope of the gist of the present invention. Furthermore, although the infinity correction type microscope objective lens has been described in the above embodiment, it can be used as a finite correction type microscope objective lens by providing a small corrected image forming lens on the image plane side of the first group. Needless to say.

It is a structure sectional view of the microscope objective lens of a present Example. It is an aberration diagram of the microscope objective lens of the present example.

Explanation of symbols

G1 1st group G2 2nd group L1-L19 Lens r1-r30 The curvature radius of a lens

Claims (1)

In order from the object side, it consists of two sets of two-lens cemented lenses, a two-lens cemented lens consisting of a convex lens and a concave lens, and a meniscus two-lens cemented lens having a concave surface facing the object side as a whole. a first group having negative refracting power as a whole, the farthest from the object side, a convex meniscus lens having a convex surface directed toward the object side, a cemented doublet lens of a concave lens and a convex lens, a convex lens, a cemented triplet of concave and convex lens A lens, a cemented two-lens lens of a concave lens and a convex lens, a three-lens cemented lens of a convex lens, a concave lens and a convex lens, and four single convex lenses on the most object side, and among these single convex lenses, the object side The three objective lenses consist of a convex meniscus lens having a concave surface directed toward the object side, and a second objective having a positive refractive power as a whole. The radius of curvature of the object side surface of the double cemented lens located farthest from the object side of the first group is r11r, and the convex meniscus lens located farthest from the object side of the second group The radius of curvature of the object side surface is r21r, the radius of curvature of the object side surface of the convex meniscus lens located closest to the object side is r2r, the Abbe number of all the convex lenses in the first group is ν1p, and in the second group Assuming that the Abbe number of all concave lenses is ν2n, the partial dispersion ratio is θig2n, and the focal length of the entire microscope objective lens is F, the following equations (1) to (4)
Microscope objective lens characterized by being.