Objective lens device, microscope observation method, and optical performance inspection method

Abstract

To provide an objective lens which offers good optical performance both in a vacuum environment and atmospheric environment.SOLUTION: A objective lens device 1 is provided, comprising an infinity-corrected objective lens 2, and an atmosphere-vacuum correction lens 3 with negative refractive power removably provided on the infinity conjugate side of the objective lens 2 and designed to be attached when the surrounding environment changes from a vacuum environment to an atmospheric environment.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an infinity-corrected objective lens suitable for semiconductor inspection and microscopic observation, and in particular to an objective lens that can achieve good optical performance in response to environmental changes between atmospheric and vacuum environments, a microscopic observation method using the same, and a method for inspecting optical performance. [Background technology]

[0002] Various infinity-corrected objective lenses are used in semiconductor inspection equipment, microscopes, and the like.

[0003] In recent years, there has also been an increasing demand for objective lenses that can be used in vacuum environments, such as semiconductor inspection equipment that handles EUV, and observation equipment that combines electron microscopes and optical microscopes. These objective lenses are aberration-corrected to ensure optimal optical performance in vacuum environments.

[0004] On the other hand, it is known that when these objective lenses are placed in an atmospheric environment, the refractive index changes due to the change from a vacuum to the atmosphere, and therefore the optical performance also changes.

[0005] This will be explained using specific numerical values. The refractive index (absolute refractive index) in a vacuum, n abs and the refractive index in air (relative refractive index) n rel There is a relationship between them as shown in the following equation (1). n abs =n air n rel ···(1) where n air is the refractive index of air.

[0006] For example, the refractive index of air for light with a wavelength of 266 nm is approximately 1.00028. Taking quartz, a typical optical material, as an example, the refractive index in air is 1.49972, and in a vacuum it is approximately 1.50015. Changes in this refractive index affect the optical performance of optical systems.

[0007] The simplest method for adjusting and inspecting objective lenses used in a vacuum environment is to actually place the objective lens under test in the vacuum environment. Specifically, this involves placing the optical system under test in a vacuum chamber and preparing equipment to measure the optical performance of the optical system under test or to adjust the optical system under test. However, this increases the complexity of the equipment and raises the issue of increased time and cost.

[0008] Therefore, even objective lenses intended for use in a vacuum environment may be assembled, adjusted, and inspected in an atmospheric environment. Specifically, changes in optical performance due to environmental changes—for example, the amount of change in imaging position and aberration—are calculated in advance, and the objective lens is adjusted in an atmospheric environment taking these changes into account. However, due to manufacturing and adjustment errors, the optical performance may not necessarily change by the calculated amount. Therefore, there is a risk that optical performance may deteriorate significantly more than expected in a vacuum environment. In other words, if optical performance changes significantly in response to environmental changes, high-precision adjustment and inspection will be impossible, and ultimately the objective lens will not be able to perform its intended function during actual use.

[0009] Various objective lenses and observation methods have been proposed that reduce the change in optical performance due to the change in the environment between atmospheric and vacuum (see Patent Documents 1 and 2).

[0010] For example, Patent Document 1 discloses an optical system that combines two imaging optical systems and reduces the deviation of the imaging position caused by changes in atmospheric pressure between atmospheric and vacuum.

[0011] Patent Document 2 proposes compensating for changes in refractive index due to environmental changes by using changes in refractive index caused by changes in the wavelength of the light source. Applying this concept, it is believed that an optical system with robust optical performance can be obtained even when the environment changes between atmospheric and vacuum conditions by performing an optical design that allows good optical performance to be obtained at multiple wavelengths. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Patent No. 4819419 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-109926 [Patent Document 3] Patent No. 3805735 [Patent Document 4] Japanese Patent Application Publication No. 05-196873 [Patent Document 5] Japanese Patent Application Publication No. 10-227977 [Non-patent literature]

[0013] [Non-Patent Document 1] J. Webb et al, Optical Design Forms for DUV&VUV Microlithographic Processes, Optical Microlithography XIV, Proceedings of SPIE Vol.4, 346(2001) [Non-patent document 2] W T Welford, Aberrations of Optical Systems, Adam Hilger (1986) [Non-patent document 3] R. Kingslake, B. Johnson, Lens Design Fundamentals, Academic Press, 2010 Summary of the Invention [Problem to be solved by the invention]

[0014] However, the optical system disclosed in Patent Document 1 requires design and use in combination with an imaging lens, rather than an objective lens alone, which limits the degree of freedom in use. Also, there is a problem in that it cannot be applied in principle to cases where one side of the imaging optical system is used in a vacuum and the other in the atmosphere.

[0015] Next, applying the concept of Patent Document 2, an optical system having robust optical performance against atmospheric pressure changes is considered by performing color correction at multiple wavelengths.

[0016] Generally, the amount of change when converting the refractive index change due to atmospheric pressure change into a wavelength change varies depending on the optical material. Therefore, when using a plurality of optical materials, the optical performance may change due to environmental changes between the atmosphere and the vacuum.

[0017] In addition, objective lenses used in a vacuum environment often handle short wavelengths such as DUV and EUV. Generally, the dispersion of optical materials increases as the wavelength becomes shorter, and in the deep ultraviolet and extreme ultraviolet regions including 266 nm, the materials that can be used are limited due to the transmittance characteristics. Due to such restrictions, as described in Patent Document 3 and Non-Patent Document 1, a significant increase in the number of lens elements is required to achieve color correction in the DUV and EUV regions. When the number of lens elements increases significantly, not only does the size of the objective lens increase, but the cost also increases significantly.

[0018] Therefore, an optical system that replaces the refractive index change due to atmospheric pressure change with a wavelength change and maintains optical performance by color correction within that range is considered to have problems from the viewpoints of performance change, cost, size, etc.

[0019] The present invention has been made in view of such a situation, and an object thereof is to realize an objective lens that can obtain good optical performance in both a vacuum environment and an atmospheric environment, an observation method using the same, and an optical performance inspection.

Means for Solving the Problems

[0020] In order to solve the above problems, an aspect of the present invention is an objective lens device (1), comprising an infinity-corrected objective lens (2), and an air-vacuum correction lens (3) having a negative refractive power, which is detachably provided on the infinity conjugate side of the objective lens and is mounted when changing from a vacuum environment to an atmospheric environment.

[0021] According to this aspect, the aberration of the objective lens can be corrected well in both a vacuum environment and an atmospheric environment, despite the simple configuration.

[0022] In the above aspect, the atmosphere-vacuum compensation lens may be composed of two lenses (L1·L2, L31·L32).

[0023] According to this aspect, the size of the atmosphere-vacuum correction lens can be made smaller than when the atmosphere-vacuum correction lens is made up of three or more lenses.

[0024] Furthermore, in order to solve the above-mentioned problems, one aspect of the present invention is an observation method using a microscope (12), wherein the microscope includes an objective lens device (1) having an objective lens (2) that has been aberration-corrected in a vacuum environment and an air-vacuum corrected lens (3) that corrects aberrations resulting from an environmental change from a vacuum environment to an atmospheric environment, and wherein a sample (S) is observed using the objective lens when observing in a vacuum environment, and using the objective lens device with the air-vacuum corrected lens attached to the infinity conjugate side of the objective lens when observing in an atmospheric environment.

[0025] According to this aspect, a sample can be observed with good aberration correction in both a vacuum environment and an atmospheric environment using an objective lens with a simple configuration.

[0026] Furthermore, in order to solve the above-mentioned problems, one aspect of the present invention is a method for inspecting the optical performance of an infinity-corrected objective lens (2) that has been aberration-corrected in a vacuum environment, characterized in that an air-vacuum corrected lens (3) that corrects aberrations that occur due to environmental changes from a vacuum to air is attached to the infinity conjugate side of the objective lens to form an optical system (1), and the optical system including the objective lens and the air-vacuum corrected lens is placed in an atmospheric environment to measure the optical performance. In measuring the optical performance, it is preferable to measure transmitted wavefront aberrations using an interferometer (20), for example.

[0027] According to this aspect, the optical performance of the objective lens that has been corrected for aberrations in a vacuum environment can be inspected in an atmospheric environment. [Effects of the Invention]

[0028] According to the above aspects, it is possible to realize an objective lens, an observation method, and an optical performance inspection that can obtain good optical performance in both a vacuum environment and an atmospheric environment. [Brief explanation of the drawings]

[0029] [Figure 1] An optical path diagram of the objective lens device according to the first embodiment of the present invention when placed in a vacuum environment. [Figure 2] 1 is a diagram showing an optical path of the objective lens device according to the first embodiment when the objective lens device is placed in an atmospheric environment. [Figure 3] FIG. 1 is a longitudinal aberration diagram of the objective lens device according to the first embodiment when placed in a vacuum environment. [Figure 4] 1 is a diagram showing lateral aberration when the objective lens device according to Example 1 is placed in a vacuum environment. [Figure 5] Longitudinal aberration diagram of the objective lens device according to Example 1 when placed in an atmospheric environment [Figure 6] Transverse aberration diagram of the objective lens device according to Example 1 when placed in an atmospheric environment [Figure 7] 10 is a diagram showing an optical path of an objective lens device according to a second embodiment of the present invention when placed in an atmospheric environment. [Figure 8] FIG. 10 is a longitudinal aberration diagram of the objective lens device according to the second embodiment when placed in a vacuum environment. [Figure 9] 10A and 10B are diagrams showing lateral aberrations of the objective lens device according to the second embodiment when placed in a vacuum environment. [Figure 10] Longitudinal aberration diagram of the objective lens device according to Example 2 when placed in an atmospheric environment [Figure 11] Transverse aberration diagram of the objective lens device according to Example 2 when placed in an atmospheric environment [Figure 12] Schematic diagram of an observation device according to the present invention [Figure 13] Schematic diagram of transmitted wavefront measurement using an interferometer according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. [Example]

[0031] First, an objective lens device 1 according to one embodiment of the present invention will be described with reference to Figures 1 to 6. Also, an observation device 10 and an inspection method according to the present invention will be described with reference to Figures 12 and 13.

[0032] Fig. 1 is a diagram of an optical path when the objective lens device 1 according to this embodiment is placed in a vacuum environment. Fig. 2 is a diagram of an optical path when the objective lens device 1 according to this embodiment is placed in an atmospheric environment. As shown in Figs. 1 and 2, when the placement environment changes from a vacuum environment to an atmospheric environment, a detachable atmospheric-vacuum compensation lens 3 is added to the objective lens 2. By configuring the objective lens device 1 in this way, it is possible to realize an objective lens device 1 that has good aberration correction in both a vacuum environment and an atmospheric environment.

[0033] First, the basic principle of the present invention will be explained.

[0034] Since the refractive index of air is approximately 1.00028, the refractive index in an atmospheric environment is smaller than that in a vacuum environment. Therefore, if the objective lens 2 that has been aberration-corrected in a vacuum environment is placed in an atmospheric environment, the spherical aberration, coma, and other aberrations will change.

[0035] It is known that spherical aberration changes according to the conjugate length of an optical system (see Non-Patent Document 2). Based on this theory, when the refractive index decreases, spherical aberration changes to the overcorrected side. Therefore, when using the objective lens 2 corrected for aberration in a vacuum environment in an air environment, it is sufficient to generate undercorrected spherical aberration. For this purpose, the conjugate length may be changed so that the apparent object point as seen from the objective lens 2 approaches the objective lens 2. This can be achieved by adding an air-vacuum correction lens 3 having a negative refractive power on the infinite conjugate side of the objective lens 2. Thus, the objective lens device 1 can satisfactorily correct the aberration of the objective lens 2 in both a vacuum environment and an air environment while having a simple configuration.

[0036] Even if spherical aberration is corrected by changing the conjugate length, coma aberration still remains. Therefore, the air-vacuum correction lens 3 is composed of two lenses L1 and L2 (in the example shown in FIG. 7, lenses L31 and L32), and the objective lens device 1 is configured as a combined system of the air-vacuum correction lens 3 and the objective lens 2 without generating extra spherical aberration. Thereby, it is possible to secure a degree of freedom for satisfactorily correcting coma aberration.

[0037] Generally, increasing the number of lenses increases the degree of freedom in design and is advantageous for aberration correction. However, increasing the number of lenses increases the cost accordingly, and manufacturing errors and assembly errors of the lenses and mechanical components accumulate, leading to a deterioration in the optical performance of the product. Therefore, it is desirable that the air-vacuum correction lens 3 be composed of two lenses L1 and L2, L31 and L32, which is the minimum number of lenses.

[0038] Next, an observation method as another aspect of the present invention will be described.

[0039] The air-vacuum correction lens 3 and the objective lens device 1 including the same disclosed in this specification can be used in both an air environment and a vacuum environment. Therefore, an observation method capable of maintaining good optical performance can be realized even when the space in which the observation object and the objective lens 2 are arranged changes between an air environment and a vacuum environment.

[0040] The observation method is embodied by an observation apparatus 10 illustrated in FIG. 12. The observation apparatus 10 is a microscope observation apparatus and includes a container 11 capable of selectively creating an internal atmosphere environment and a vacuum environment, an objective lens 2, and an air-vacuum correction lens 3. A sample S and an objective lens device 1 (the objective lens 2 and the air-vacuum correction lens 3) are disposed inside the container 11 (chamber C). An imaging lens 4 is disposed outside the container 11. When the inside of the container 11 changes from a vacuum environment to an atmosphere environment, the objective lens device 1 with the air-vacuum correction lens 3 mounted on the infinity conjugate side of the objective lens 2 is mounted on a microscope 12 equipped with an imaging optical system. With such a configuration, an observation apparatus 10 capable of observing the sample S under good aberration correction can be realized even when the inside of the container 11 changes between an atmosphere environment and a vacuum environment.

[0041] Next, an optical system inspection method as another aspect of the present invention will be described. By using the concept of the air-vacuum correction lens 3 disclosed in this specification, a method for inspecting the optical performance of the objective lens 2 designed and manufactured for a vacuum environment in an atmosphere environment can be realized.

[0042] The inspection method will be schematically described with reference to FIG. 13. First, for the objective lens 2, which is a lens to be inspected with aberration correction in a vacuum environment, an air-vacuum correction lens 3 for correcting the aberration change due to the environmental change between under the atmosphere and under the vacuum is designed and manufactured. In the manufacture of the air-vacuum correction lens 3, eccentricity adjustment of each lens and interval adjustment between the lenses may be performed. Next, the air-vacuum correction lens 3 is mounted on the infinity conjugate side of the objective lens 2, and the entire system is disposed in an interferometer 20 in an atmosphere environment. By measuring the transmitted wavefront aberration with the interferometer 20, it becomes possible to inspect the optical performance of the objective lens 2 for vacuum environment use in an atmosphere environment. Based on the measurement result of the transmitted wavefront aberration with the interferometer 20, eccentricity adjustment of each lens of the objective lens 2 and interval adjustment between the lenses may be performed.

[0043] Here, the differences between similar prior examples (inventions described in prior patent documents) and the invention disclosed in this specification will be described.

[0044] In the objective lens 2 of the microscope 12, it is generally well-known that an optical system responsible for aberration correction is provided separately from the main optical system and is detachable from the main optical system.

[0045] However, many of them are based on usage conditions limited to the atmospheric environment, and the change in aberration when the placement environment of the objective lens 2 changes between the atmosphere and vacuum has not been recognized.

[0046] Among known detachable optical systems, an optical system for correcting aberration caused by a cover glass in a microscope objective lens has been particularly widely studied (see, for example, Patent Document 4 and Patent Document 5).

[0047] However, as theoretically shown in Non-Patent Document 3, spherical aberration changes due to a parallel plane plate such as a cover glass, and in addition, chromatic aberration occurs when there is a wavelength width, and field curvature changes further when it is not telecentric, but coma aberration does not need to be considered. On the other hand, coma aberration also occurs due to the change in atmospheric pressure in the placement environment of the objective lens 2, leading to a deterioration in optical performance, as described in this specification. Therefore, the optical systems disclosed in these prior examples cannot be applied to changes in atmospheric pressure between the atmosphere and vacuum.

[0048] Therefore, the atmospheric-vacuum correction lens 3 disclosed in this specification and the objective lens device 1 equipped with the same newly realize an objective lens device 1 that can obtain good optical performance even in environmental changes between the atmosphere and vacuum.

[0049] Thus, according to the present invention, it becomes possible to realize an objective lens device 1, an observation device 10, and an optical performance inspection method that can obtain good optical performance in both a vacuum environment and an atmospheric environment.

[0050] As shown in FIG. 2, the air-vacuum compensation lens 3 according to this embodiment is composed of two lenses L1 and L2, which are, in order from the infinity conjugate side, a negative lens with a convex surface facing the infinity conjugate side and a positive lens with a convex surface facing the infinity conjugate side.

[0051] 3 and 4 show longitudinal and lateral aberration diagrams of the objective lens device 1 according to this embodiment when placed in a vacuum environment.

[0052] 5 and 6 show longitudinal and lateral aberration diagrams of the objective lens unit 1 according to this embodiment when the objective lens unit 1 is placed in an atmospheric environment with the air-vacuum compensation lens 3 attached.

[0053] Next, the following Tables 1 and 2 show the specifications of the objective lens device 1 according to this embodiment. In this embodiment, the wavelength is 266 nm, the focal length of the objective lens unit is 2.0 mm, the NA is 0.9, the working distance is 2.0 mm, and the field of view is Φ0.23 mm. In the lens data, the refractive index of the gap portion whose material is not specified is 1.00000. Table 2 shows the variable gap data for the back focus BF.

[0054] [Table 1] [Table 2] [Example]

[0055] Next, another embodiment of the objective lens device 1 according to the present invention will be described with reference to FIGS.

[0056] 7 is a diagram of the optical path of the objective lens device 1 in another embodiment of the present invention when an air-vacuum corrected lens 3 is attached to the infinity conjugate side of the objective lens 2. The air-vacuum corrected lens 3 is detachable, and is configured to be attached when the environment in which the objective lens 2 is placed changes from vacuum to atmosphere.

[0057] The atmospheric-vacuum correction lens 3 according to this embodiment is composed of two lenses L31 and L32, namely a biconvex lens and a biconcave lens, arranged in order from the infinite conjugate side.

[0058] Figures 8 and 9 show the longitudinal aberration diagram and the lateral aberration diagram when the objective lens device 1 according to this embodiment is arranged in a vacuum environment.

[0059] Figures 10 and 11 show the longitudinal aberration diagram and the lateral aberration diagram when the objective lens device 1 according to this embodiment is arranged in an atmospheric environment after mounting the atmospheric-vacuum correction lens 3.

[0060] Subsequently, Tables 3 and 4 below show the specifications of the objective lens device 1 according to this embodiment. In this embodiment, the wavelength is 355 ± 0.05 nm, the focal length of the objective lens part is 3.6 mm, the NA is 0.85, and the field of view is Φ0.4 mm. In the lens data, the refractive index of the interval part where the material is not described is 1.00000. Table 4 shows the variable interval data of the back focus BF.

Table 3

[0061]

Table 4

[0062] Figure 12 shows a schematic diagram showing the concept of the observation device 10 embodying the observation method according to the present invention.

[0063] The observation device 10 includes a container 11 (vacuum chamber device) capable of making the interior (chamber C) a vacuum environment, a microscope 12 equipped with an imaging optical system, and an imaging device 13 for acquiring a microscope image.

[0064] The microscope 12 is composed of an objective lens 2, an atmospheric-vacuum correction lens 3, and an imaging lens 4 arranged in order from the sample side. The sample S and the objective lens 2 are arranged in the chamber C.

[0065] The objective lens 2 is of an infinity-corrected type and has a structure in which the air-vacuum correction lens 3 can be attached and detached. When the chamber C changes from a vacuum environment to an air environment, the air-vacuum correction lens 3 is mounted on the infinity conjugate side of the objective lens 2.

[0066] The observation device 10 further includes an XYZ stage 14 for placing the sample S, and at least one of a first illumination device 15 and a second illumination device 16.

[0067] The XYZ stage 14 is movable in three axes in the optical axis direction of the microscope 12 and in a direction orthogonal thereto, and by placing the sample S on the XYZ stage 14, the sample S can be moved to an arbitrary position.

[0068] In this embodiment, the sample S can be illuminated by two methods. One is so-called oblique illumination using the first illumination device 15, and the other is so-called epi-illumination in which the inside of the objective lens device 1 is illuminated by the second illumination device 16.

[0069] The light scattered from the sample S by these illumination lights, or the fluorescence excited by the illumination lights, is taken in by the objective lens device 1, and further, a microscope image of the sample S can be obtained by acquiring an image with the imaging lens 4 and the imaging device 13.

[0070] In addition, in the above configuration, a configuration in which the microscope 12 is fixed and the sample S is moved is shown, but conversely, a configuration in which the sample S is fixed and the microscope 12 is moved can also be adopted.

[0071] With the above configuration, an observation device 10 and a microscope observation method capable of observing the sample S can be realized under good aberration correction whether the inside of the chamber C is an air environment or a vacuum environment.

[0072] FIG. 13 shows a schematic diagram of an inspection method using an interferometer 20 embodying the inspection method according to the present invention.

[0073] In this embodiment, the objective lens 2 is aberration-corrected so as to achieve optimal optical performance in a vacuum environment.

[0074] First, an air-vacuum correction lens 3 is designed and manufactured, and attached to the objective lens 2. The air-vacuum correction lens 3 is attached to the infinity conjugate side of the objective lens 2, which is the lens under test, to correct aberration changes caused by environmental changes between atmosphere and vacuum. The air-vacuum correction lens 3 is designed to be detachable from the objective lens 2. This makes the optical performance equivalent in vacuum and atmosphere, and allows the vacuum environment to be simulated in atmosphere.

[0075] Light from the light source 21 passes through a light source lens 22 to be converted into parallel light having a desired beam diameter, and then enters a beam splitter 23. After passing through the beam splitter 23, this light reaches a reference plane plate 24.

[0076] After passing through the reference flat plate 24, the light reaches the objective lens 2 and is condensed at the focal point of the objective lens 2. The light is then reflected by a high-precision spherical reflecting mirror 25, which has a center of curvature at the focal point, and passes through the objective lens 2 and the reference flat plate 24 again to reach the beam splitter 23.

[0077] On the other hand, the light reflected by the reference plane plate 24 is reflected by the beam splitter 23 and reaches the interference fringe observation device 27 through the interference fringe observation lens 26 .

[0078] Then, the light reflected by the reference flat plate 24 and the light that has passed through the objective lens 2 are superimposed and condensed via an interference fringe observation lens 26, and interference fringes are observed by an interference fringe observation device 27. The interference fringes observed by the interference fringe observation device 27 are analyzed to measure the transmitted wavefront aberration.

[0079] In the present embodiment, an optical performance inspection method by measuring the transmitted wavefront aberration using the interferometer 20 has been described. However, the optical performance inspection method can be appropriately changed without departing from the spirit of the present invention. For example, an evaluation chart may be arranged on the sample surface of a device on which a device under test lens device such as the observation device 10 disclosed in this specification is mounted to inspect the optical performance (resolution).

[0080] With the above configuration, it becomes possible to inspect the optical performance of the lens under test (objective lens 2) whose aberration has been corrected in a vacuum environment in an atmospheric environment.

[0081] As described above, the present invention has been described with respect to its preferred embodiments. However, the present invention is not limited to such embodiments and can be appropriately changed without departing from the spirit of the present invention. Further, not all of the components shown in the above embodiments are necessarily essential, and it is possible to appropriately select and choose them as long as the spirit of the present invention is not departed from.

Explanation of Reference Numerals

[0082] 1: Objective lens device (optical system) 2: Objective lens 3: Air-vacuum correction lens 4: Imaging lens 10: Observation device 11: Container 12: Microscope 13: Imaging device 14: XYZ stage 15: First illumination device 16: Second illumination device 20: Interferometer 21: Light source 22: Lens for light source 23: Beam splitter 24: Reference flat plate 25: Spherical mirror 26: Lens for observing interference fringes 27: Interference fringe observation device BF: Back focus C: Chamber L1·L2: Lens L31·L32: Lens S: Sample

Claims

A objective lens device disposed inside a container capable of selectively creating a vacuum environment and an atmospheric environment inside, comprising: An infinitely corrected objective lens; An air-vacuum correction lens having a negative refractive power that is detachably provided on the infinity conjugate side of the objective lens and corrects aberrations caused by environmental changes, which is mounted when changing from a vacuum environment to an atmospheric environment; and An objective lens device in which both the objective lens and the air-vacuum correction lens are disposed inside the container.

2. The objective lens device according to claim 1, wherein the air-vacuum correction lens is composed of two lenses.

3. An observation method using a microscope, comprising: The microscope includes: A container capable of selectively creating a vacuum environment and an atmospheric environment inside; and An objective lens device disposed inside the container, the objective lens device having an objective lens corrected for aberrations in a vacuum environment and a detachable air-vacuum correction lens having a negative refractive power that corrects aberrations caused by an environmental change from a vacuum environment to an atmospheric environment; and Observing a sample using the objective lens disposed inside the container during observation in a vacuum environment, and using the objective lens device formed by mounting the air-vacuum correction lens inside the container on the infinity conjugate side of the objective lens during observation in an atmospheric environment.

4. An optical performance inspection method for an infinitely corrected objective lens corrected for aberrations in a vacuum environment, comprising: Inside a container capable of selectively creating a vacuum environment and an atmospheric environment inside, an air-vacuum correction lens having a negative refractive power that corrects aberrations generated due to an environmental change from under vacuum to under atmosphere is mounted on the infinity conjugate side of the objective lens to form an optical system; and An optical performance inspection method of measuring the optical performance of the optical system including the objective lens and the air-vacuum correction lens disposed inside the container with the inside of the container being in an atmospheric environment.

Images