JP2014145839A - Optical system, phase plate employing optical system and optical system manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical system that can obtain a three-dimensional observation image less in deterioration by a color of high resolution without requiring an expensive optical element for a differential interference microscope.SOLUTION: An optical system is configured to: arrange an aperture diaphragm limiting direct light (0-order diffraction light) incident to an image-formation system at a position conjugate with a light source in an illumination system illuminating an object with light from the light as parallel light; and have a structure in which an A area where total 0-order diffraction light passes through, a B area where first-order diffraction light passes through, and a C area where negative first-order diffraction light passes through are arranged at a position (a pupil position) of the aperture diaphragm in the image-formation system allowing light from an object to be image-formed at a predetermined magnification, the B area and the C area have an axially symmetric relation with respect to a symmetric axis including a cross point of the pupil surface and an optical axis, the B area or the C area allows the A area to generate a predetermined phase difference, and the B area and the C area have no area in common with the A area.

Description

  The present invention relates to an optical system that enhances the contrast of the boundary of an object to be imaged.

<Nomarski differential interference microscope>
The conventional Nomarski-type differential interference microscope emphasizes slight differences in the level of objects and differences in refractive index when it is desired to eliminate the halo of a phase contrast microscope, or when observing a thick sample or a sample with a multilayer structure. Used to observe an object in three dimensions. In a Nomarski type differential interference microscope, the amount of image shift (shear amount) due to two polarized lights defined by the Nomarski prism is constant when any specimen is observed. Therefore, in a differential interference microscope that uses a Nomarski prism to shift an image by polarization, a phase plate used in a phase contrast microscope is not used.

<Bright-field observation microscope: an example of an optical system>
With conventional microscopes for bright field observation, it has been difficult to clearly observe specimens (samples) such as biological cells that are nearly colorless and transparent. For this reason, observation has been performed after the sample is stained and colored. However, when stained, the living cells are killed, and it is difficult to observe living cells and the like that are alive.

<Phase contrast microscope: another example of optical system>
A phase contrast microscope has come to be used for observing colorless and transparent living cells without staining or the like. In a phase contrast microscope, for example, an aperture (ring slit) opened in a ring shape is placed between the condenser lens and the light source of the microscope, and the ring is positioned at a position where a real image of the ring aperture can be obtained (for example, the pupil plane of the objective lens). A phase plate having a ring-shaped phase film conjugate with the slit portion of the slit is added. With this configuration, the phase-contrast microscope causes the attenuated direct light to interfere with the diffracted light that is diffracted by the sample and has a different phase, and changes the phase difference of each phase to bright and dark, thereby contrasting the observed image. Increase. This conventional phase-contrast microscope has the function that even if it is a thin sample, it can be observed as a difference in brightness up to the internal structure even without staining, but it has a halo (bright border) around the border of the sample. There was a problem of generating.

  In addition, the phase contrast microscope emphasizes a slight difference in refractive index of a specimen and diffraction at a boundary by converting it into a contrast of light and darkness in order to observe a sample that is almost colorless and transparent without staining. As a more detailed principle of the phase-contrast microscope, there is a phase difference between direct light (0th order diffracted light) that passes straight through the sample and diffracted light (first order diffracted light, −1st order diffracted light, etc.) diffracted by the sample. When the direct light and the diffracted light are overlapped to form an image, a contrast of light and dark due to interference is generated. Therefore, in the conventional phase contrast microscope, only the phase of the direct light (0th order diffracted light) is changed by the phase plate.

  Further, in the phase contrast microscope, in order to obtain the phase difference between the direct light and the diffracted light, a phase film region similar to the aperture region of the aperture stop is formed on the phase plate. The sample is irradiated with illumination light having a limited irradiation range by passing through the aperture stop. When the illumination light passes through the sample, it is divided into direct light traveling straight and diffracted light traveling at different angles. The direct light emitted from the sample reaches the phase film region of the phase plate, while the diffracted light emitted from the sample reaches the region other than the phase film of the phase plate.

  Further, the phase film is formed of a thin film of a predetermined substance and has a dispersion phenomenon, so that not all incident light can be advanced or delayed in phase by a quarter. Therefore, a filter is generally used in the illumination optical system so that only a predetermined wavelength that can shift the wavelength by a quarter is selected and transmitted (see, for example, Patent Document 1).

<Hoffman modulation contrast method: yet another example of optical system>
The Hoffman modulation contrast method is known as a microscopic method for observing a material that is nearly transparent without using polarized light like a Nomarski type differential interference microscope. This method is an invention in which intensity modulation is performed by installing three types of intensity conversion filters at the pupil position of the imaging optical system to emphasize the boundary of an object. This method has an effect of making an object appear stereoscopically by making illumination light incident obliquely (see, for example, Patent Document 2).

<Phase plate used in phase contrast microscope>
In addition, the phase plate of the conventional phase contrast microscope uses a phase film, but because the substance constituting the phase film has a dispersion phenomenon, the phase is the same for a plurality of illumination lights having different wavelengths ( For example, it was difficult to shift by 1/4 wavelength). Therefore, when the sample is observed with illumination light having a broad wavelength such as the entire visible light band, the contrast is lowered. In order to avoid this, the conventional phase plate uses a filter that transmits only light of a predetermined bandwidth of monochromatic (monochrome) so that the ratio of the wavelength to shift does not vary. However, since the conventional phase plate loses information on the color of the sample, there is a problem that the sample can be observed only as a monochrome shade image.

  The inventor of the present invention is a phase plate in which a layer of a first optical medium and a layer of a second optical medium having a refractive index are stacked, and the first optical medium serving as a base portion thereof By controlling the thickness of the medium and the thickness of the second optical medium layer partially stacked on the first optical medium layer, the contrast is reduced even when the sample is observed with light having a broad wavelength. In addition, a phase plate that can be observed with a plurality of colors or broadband wavelengths (for example, F-line (485 nm) to C-line (636 nm)) has been proposed (for example, see Patent Document 3).

Japanese Patent Laid-Open No. 9-230247 JP 51-29149 A JP 2009-2111010 A

  However, in the conventional Nomarski differential interference microscope, the image obtained by the wavelength is significantly different due to the dispersion of the Nomarski prism used to divide the light into two polarized light, so that the color balance in which the object is normally observed as an actual transmission object Had the problem of appearing different colors.

  In addition, since the Nomarski differential interference microscope uses two orthogonal linearly polarized light, a special and expensive optical element such as a Nomarski prism polarizer is required, and the objective lens used is also sensitive to polarization. There is a problem that a special and expensive objective lens without optical distortion inside must be used. Further, when observing an object in a resin container, there is a problem that clear observation cannot be performed due to internal distortion remaining in the resin.

  In addition, the conventional phase-contrast observation method using a phase-contrast microscope generates halo as described above, so that direct light changes on the phase plate in samples with a multilayer structure in which thick samples or samples with different refractive indexes are stacked. Before starting, a phase difference is generated inside the sample, the halo becomes too strong, and the contrast of the image of the object to be observed is significantly lowered and cannot be seen.

  In the Hoffman modulation contrast method, the means for obtaining a three-dimensional image is simply an intensity conversion filter, and in order to form a three-dimensional image, it is necessary to attenuate a large amount of light in the pupil with the filter. There is a problem that the intensity of the image is greatly reduced as compared with the bright field image of the above.

  The present invention has been made in view of the above-described problems, and the object thereof is a relatively simple configuration that does not use expensive optical elements such as an objective lens for a differential interference microscope and a Nomarski prism polarizer. , An optical system for obtaining a three-dimensional observation image with little deterioration in a wide wavelength range (for example, F-line (485 nm) to C-line (636 nm)) with high resolution, and a phase plate used in the optical system and its manufacturing method It is to provide.

  (1) In order to solve the above-mentioned problem, in one embodiment of the optical system of the present invention, an illumination system that illuminates an object using light from a light source as parallel light, and a result of imaging light from the object at a predetermined magnification. In an optical system having an image system, an aperture stop that restricts direct light (0th-order diffracted light) incident on the imaging system at a position conjugate with a light source in the illumination system, and an aperture stop position in the imaging system ( (A pupil position) has an A region through which all 0th-order diffracted light is transmitted, a B region through which 1st-order diffracted light is transmitted, and a C region through which -1st-order diffracted light is transmitted. Regarding the symmetry axis to be included, the B region and the C region are in an axial-to-image relationship, and the B region or the C region has a structure that generates a predetermined phase difference with respect to the A region. And a phase plate having no common area.

  Hereinafter, for example, a case where the phase film is provided only in the B region and the phase film is not present in the C region and the A region will be described.

  The light that has passed through both the B region and the C region at the pupil position becomes interference light by interference of the 0th-order light that has passed through the A region. A case where only the B region can be given a phase difference will be described as an example. One interference light (a portion transmitted through the B region) transmitted through the B region passes through the phase film (a structure that generates a predetermined phase difference). Shift sideways. On the other hand, the other interference light transmitted through the C region (the C region transmission) does not pass through the phase film and thus does not shift. As a result, the two images of the slightly laterally shifted image (B region transmission) and the non-shifted interference light (C region transmission) image are superimposed on the objective lens image plane, so that the brightness of the image is particularly high. The image has an enhanced contrast at the boundary of the part.

  Therefore, in this embodiment, since the Nomarski prism is not used unlike the conventional Nomarski type differential interference microscope, a relatively simple configuration that does not require expensive parts can be achieved, and the color balance of the image can be achieved by the dispersion of the prism. It is possible to suppress the difference from the actual object. Furthermore, even when an object is observed through an object having an internal distortion that remains, such as a resin container, since polarized light is not used, the object to be seen can be clearly observed without being affected by the distortion.

  Further, in the present embodiment, unlike the conventional phase difference observation method, no halo is generated, so that the contrast of the image of the observation object can be prevented from being lowered and difficult to see.

  Further, in this embodiment, intensity conversion is not performed to obtain a stereoscopic image unlike the Hoffman modulation contrast method, and therefore, the attenuation of the light intensity is small and the decrease in the intensity of the image from the original bright-field image is suppressed. Is done.

(2) In one embodiment of the optical system of the present invention, when the phase difference of the B region with respect to the A region or the C region with respect to the A region is Δ,
Δ may satisfy the condition of the following formula (Equation 1).

  In the optical system of this embodiment, the range of | Δ | in the mathematical formula (Equation 1) is, for example, an image formed from the C light of only the first optical material and a phase difference generation layer (which generates a predetermined phase difference). An upper limit and a lower limit shift amount of an image formed from B light including a structure (for example, a phase film) are defined. When the shift amount is a value lower than the lower limit value 0.05π, the image shift amount is too small, and the occurrence of interference when combined is reduced, resulting in an image substantially equivalent to bright field observation. On the contrary, when the shift amount is a value exceeding the upper limit value 0.95π, the brightness of the shifted image is almost reversed, so that the intensity of the light of the two combined images becomes almost zero and interference occurs. Therefore, it makes no sense to generate a phase difference.

(3) In one embodiment of the optical system of the present invention, when the phase difference of the B region with respect to the A region or the C region with respect to the A region is Δ,
Δ may satisfy the condition of the following mathematical formula (Formula 2).

  In the optical system of the present embodiment, the range of | Δ | in Equation (Equation 2) is, for example, an upper limit for the optimum value of the shift amount of the phase difference between two images with respect to the range of Equation (Equation 1). From Formula (2), which defines a range of 0.5π and a lower limit of 0.25π, it is the optimum value of the slight image shift amount, and the lower limit for an object having a periodic structure is the shift amount of 1/8 pitch, the upper limit The value corresponds to ¼ pitch as a shift amount.

  (4) In one embodiment of the optical system of the present invention, the A region through which the 0th-order diffracted light passes may have a point-symmetric shape with respect to the intersection of the optical axis and the pupil plane.

  In the optical system of this embodiment, when the number of symmetry axes is increased in the case of having the above-described plurality of line symmetry axes, point symmetry is obtained. Arrange the A area in a point-symmetrical shape with respect to the optical axis, and arrange so that the positional relationship is point-symmetric with respect to the optical axis, and arrange the B and C areas so as to have a positional relationship that is symmetrical with respect to the optical axis. Thus, a three-dimensional image can be obtained like a conventional differential interference microscope.

  (5) In one embodiment of the optical system of the present invention, the A region through which the 0th-order diffracted light passes may be a circle including the intersection of the optical axis and the pupil plane.

  In the optical system of the present embodiment, since the A region is circular, the aperture stop and the phase plate can be designed and manufactured in the same manner as in the past. Therefore, the design and manufacture are easy, and the manufacturing cost is reduced. The required period can be shortened.

  (6) In one embodiment of the optical system of the present invention, the A region through which the 0th-order diffracted light passes may be a rectangle including the intersection of the optical axis and the pupil plane.

(7) Further, in one embodiment of the optical system of the present invention, if the phase differences of the B region and the C region with respect to the A region are ΔB and ΔC, respectively, the following equation (Equation 3) is satisfied. May be.

  By satisfying Equation (Equation 3), the image that has interfered through the A and B regions and the image that has interfered through the A and C regions are slightly the same in the opposite direction from the original image. The image is shifted by an amount. As a result, an image in which an original image that has passed through an area other than the A area, the B area, or the C area and an image that is shifted in a direction opposite to each other by a small amount are generated on the image plane, and has a constant spatial frequency. An image in which only the structure is emphasized is formed.

The application range of the phase plate in the optical system of this embodiment is not limited to a microscope, but can be applied to a projection optical system and the like. For example, in the case of a projection optical system, there is no distortion or the like in the projected image, for example, the symmetry in the x-axis direction is secured when the horizontal direction in FIGS. There is a need to be. Therefore, it is desirable that (aa) the phase difference of the B region with respect to the A region and (bb) the phase difference of the C region with respect to the A region have the same value. And it is desirable to be satisfied by selecting the thickness.
This is because of the shift amount of the image obtained by interference with the 0th order diffracted light after the diffracted light passes through the B region, and the shift amount of the image obtained by interference with the 0th order diffracted light after the diffracted light passes through the C region. This means that the absolute values are the same and the signs are reversed, and that symmetry in the x-axis direction is ensured.

(8) In one embodiment of the optical system of the present invention, the B region or the C region has a structure for attenuating light, and when the transmittance is T, the following equation (Equation 4) is satisfied. You may do it.

  In the optical system of this embodiment, the transmittance T in Equation (4) is determined from the image formed from the light transmitted through the region of only the first optical material and the light transmitted through the region including the phase difference generation layer. It defines a range in which the stereoscopic effect of the image is enhanced when the formed image is combined. In order to enhance the stereoscopic effect of the images obtained by the interference between the two images that are combined and overlapped, the light intensity of either of the two images is changed so that the value of the transmittance T is slightly reduced. In addition, it is possible to enhance the stereoscopic effect more than the observation image obtained by a conventional differential interference microscope. If the value of the transmittance T is below the lower limit of the above range, the intensity of the light of one image becomes too low, and the other image approaches the normal bright-field image, making it meaningless to combine and interfere with it. . Further, when the value of the transmittance T exceeds the upper limit of the above range, the intensity of the two images becomes substantially equal, so that the images are very close to the conventional differential interference observation image, and further to the conventional differential interference microscope. The effect is weakened.

  (9) In one embodiment of the optical system of the present invention, the structure that generates a predetermined phase difference is a phase film that gives a constant phase difference Δ to two or more wavelengths, and the phase difference Δ is: The condition Δ may be satisfied in a relatively wide wavelength band.

  The phase plate of the optical system according to the present embodiment can obtain an effect with respect to light having a relatively wide wavelength band such as visible light. For example, a substantially constant phase difference Δ with respect to two or more wavelengths of visible light. When the material and thickness are selected so as to give a solid, the color tone of the real substance is faithfully reproduced, and the image is observed with a stereoscopic effect. Image observation is possible with a configuration similar to a phase contrast microscope that does not have a prism or the like. In addition, when observing stained cells and materials with various colors that were not suitable for observation with conventional Nomarski-type differential interference microscopes, differential interference is achieved after faithfully reproducing the colors of the object. It is possible to obtain an image similar to that of a type microscope. Moreover, a comparatively wide wavelength is a width including two or more different wavelengths such as C line (636 nm) and F line (486 nm) in visible light, and in this embodiment, the wide wavelength is used. On the other hand, the condition of the phase difference Δ of the present invention is satisfied.

  (10) In one embodiment of the optical system of the present invention, the structure that generates the predetermined phase difference is transparent to the light used, and generates the phase difference between the 0th-order diffracted light and the first-order light. The portion may have a layer structure made of a single substance in the direction of the optical axis along which light travels.

  In the optical system of the present embodiment, the phase difference generating layer is made of a material that can be transmitted as described above with respect to illumination light (for example, visible light) having a predetermined wavelength emitted from the light source (a material that transmits at least part of the light). ) From a transparent material, the generation of the phase difference becomes clear, and the diffracted light with the final phase difference and the diffracted light without the phase difference (B light and C light) are combined. This interference phenomenon can be clearly reflected in the formed image, and an image with high resolution can be obtained.

  (11) In one embodiment of the optical system of the present invention, the B region and the C region are outside a pair of opposing sides of the rectangle of the A region and are arcuate with line symmetry with respect to the symmetry axis. May be.

  In the optical system of the present embodiment, two images, an image of interference light with a phase difference (B region transmission) and an image of interference light with no phase difference (C region transmission) are formed satisfactorily. It is possible to obtain an image in which the boundary contrast is well enhanced.

  In the present invention, an optical system that does not require an expensive optical element for a differential interference microscope, and can obtain an observation image that is three-dimensional and has little deterioration in a wide wavelength band with a high resolution, a phase plate used therefor, and A manufacturing method thereof can be provided.

It is a figure which shows the schematic structure of the optical system in the new differential interference type | mold microscope as an example of the optical system of the 1st Embodiment of this invention, and the optical path of illumination light. It is a top view which shows the outline | summary of the phase plate as an example of 1st Embodiment, (a) is a top view which shows each area | region of a phase plate, (b) is AA of the phase plate of (a). It is sectional drawing, (c) is AA sectional drawing of the phase plate of (a) of an application example. (A) is an image of a diatom observed with the new differential interference microscope of the first embodiment, and (b) is an image of a diatom observed with a normal bright-field microscope as a comparative example. Is. It is a top view which shows the outline | summary of the phase plate as an example of the 2nd Embodiment of this invention, (a) is a top view which shows each area | region of a phase plate, (b) is a phase plate of (a). It is BB sectional drawing. It is a top view which shows the outline | summary of the phase plate as an example of the 3rd Embodiment of this invention, (a) is a top view which shows each area | region of a phase plate, (b) is a phase plate of (a). It is CC sectional drawing. It is a top view which shows the outline | summary of the phase plate as an example of the 4th Embodiment of this invention, (a) is a top view which shows each area | region of a phase plate, (b) is a phase plate of (a). It is DD sectional drawing. It is a figure which shows the general | schematic structure of the optical system in the new epi-illumination type differential interference microscope as an example of the optical system of the 5th Embodiment of this invention, and the optical path of illumination light. It is a figure which shows the schematic structure of the optical system in the projection exposure apparatus as an example of the optical system of the 6th Embodiment of this invention, and the optical path of illumination light.

<<<< first embodiment >>>>
An outline of the new differential interference microscope 1 as an example of the optical system according to the first embodiment of the present invention will be described below with reference to FIGS. 1 and 2.
The new differential interference microscope 1 according to the first embodiment of the present invention includes a light source 5, an illumination optical system 10, an imaging optical system 40, an object plane, schematically along the optical axis 100 as shown in FIG. 51 and an objective lens image plane 71. In the optical path of the illumination optical system 10, one of the illumination lights emitted from the light source 5 is positioned at a position 21 conjugated with the objective lens exit pupil on the light source 5 side (hereinafter referred to as an exit pupil conjugate position in the illumination optical system) 21. An aperture stop 22 that transmits the part is disposed. The illumination light emitted from the light source 5 is, for example, the wavelength of visible light. The illumination optical system 10 includes a lens 11 closer to the light source 5 than the aperture stop 22, a lens 12 closer to the objective lens 41 than the aperture stop 22, and a condenser lens 13 that focuses the illumination light on the object plane 51. included.

  The aperture stop 22 is formed with a light-transmitting region that demarcates the optical path region of the illumination light (or defines the thickness of the light beam). This light-transmitting region is a limited region having a shape including an opening shape and a notch shape, and the light of the illumination light can be limited to the limited region and transmitted. Illumination light limited by being transmitted through the light transmitting region is emitted toward the condenser lens 13, and is focused on the sample 61 to be observed on the object plane 51 by the condenser lens 13.

  The imaging optical system 40 includes an objective lens 41, a phase plate 43 as an example of this embodiment, and an imaging lens 49. In the objective lens 41, transmitted light from the observed sample 61 or the object surface 51 is incident from the lower surface of FIG. 1, and the transmitted light is emitted from the upper surface toward the phase plate 43. The phase plate 43 will be described later with reference to FIG. The imaging lens 49 images the transmitted light on the objective lens image surface 71.

  The phase plate 43 is disposed at the exit pupil conjugate position 42 of the objective lens 41. The base 48 of the phase plate 43 is formed of a first optical material that can transmit illumination light having a predetermined wavelength emitted from the light source 5. Preferably, the first optical material is a material that is as transparent as possible with respect to the predetermined wavelength, that is, a material that is less attenuated. The phase difference generating layer (place) is a material capable of transmitting illumination light having a predetermined wavelength emitted from the light source 5 and further generating a phase difference so that the phase is different from that of the light transmitted through the first optical material. A structure that generates a constant phase difference (for example, a phase film) is disposed only in one of the B region 45 and the C region 47. In the phase plate 43 of this embodiment, the phase difference generation layer is not disposed in the A region 44, and the phase difference generation layer is disposed only in either the B region 45 or the C region 47. With this configuration, for example, when a phase difference generation layer is disposed in the B region 45, the phase difference between the A light 500 and the B light 501 is not significant, and the phase difference between the A light 500 and the C light 502 is not significant. Both light will be emitted.

  The shape and arrangement of the A region 44, the B region 45, and the C region 47 shown in FIGS. 1 and 2 are examples of the phase plate according to the present embodiment, and are not limited thereto. It may be in shape and arrangement. For example, (1) an image slightly shifted from the original image by interfering with the A region and the B region on the image plane, and (2) interference with passing through the A region and the C region. The image slightly shifted by the same amount in the opposite direction to the case of the A region and the B region from the image of (3) overlaps with the original image that has passed through the region other than the A region, the B region, or the C region. The A region, the B region, and the C region may have other shapes and arrangements as long as the shape and the arrangement are such that an image in which only a certain spatial frequency structure is emphasized is generated. .

  In the phase plate 43 of the present embodiment, the shape of the 0th-order diffracted light (A light) 500 that is incident direct light (the shape limited by the first light-transmitting region 23 of the aperture stop 22) is left as it is. A region (or 112) that is transmitted and output as light 500, B region 45 (or 114) through which incident first-order diffracted light (B light) 501 is transmitted, and incident minus first-order diffused light − A C region 47 (or 116) through which the first-order diffracted light (C light) 502 is transmitted is set. In addition, a phase difference generation layer that has a phase different from that of the light transmitted through the first optical material is disposed only in one of the B region 45 and the C region 47. In this embodiment, the case where the phase difference generation layer is arranged on the upper surface in the B region 45 is shown. Further, a region between the A region 44 and the B region 45 or the C region 47 that transmits neither direct light nor diffracted light is referred to as a non-translucent region 118.

  That is, in the phase plate 43 of the present embodiment, the phase difference generation layer is disposed only in the B region 45 that is in a line symmetry position with respect to the line symmetry axis 102 that passes through the optical axis 100, and the phase difference is present in the C region 47. The generation layer is not disposed, and only the first optical material is used. Thereby, interference can be generated when the B light 501 in which the phase difference from the A light 500 is generated and the C light 502 in which the phase difference from the A light 500 is not generated, and differential interference can be generated. A stereoscopic image like a microscope can be obtained. The diffracted light in this case is B light 501 and C light 502, one B light 501 has a phase difference with A light 500, and the other C light 502 has a phase difference with A light 500. It is not.

  Further, the phase difference generation layer of the phase plate 43 is made of a material that can transmit illumination light having a predetermined wavelength emitted from the light source 5 (a material that transmits at least a part of light), in other words, has a light-transmitting property with respect to the illumination light. The material is preferably a material that is transparent to illumination light.

  In this way, the phase difference generation layer is transparent from the above-described material (a material through which at least a part of light is transmitted) with respect to illumination light (for example, visible light) having a predetermined wavelength emitted from the light source 5. By using the material, the occurrence of the phase difference becomes clear, and the interference phenomenon at the time of combining the B light 501 in which the phase difference has occurred with the C light 502 in which the phase difference has not occurred is clearly reflected in the formed image. A high resolution image can be obtained.

  In the phase plate 43, a thin phase film may be formed as in a conventional phase contrast microscope. However, as an option, the phase plate 43 has a predetermined thickness in the direction of the optical axis 100 so as to generate a phase difference as shown in FIG. The phase difference generating layer formed in a layer shape is disposed on the base material portion 48, or the phase difference generating layer such as an adhesive or resin is cured on the base material portion 48 as shown in FIG. By forming a layer with the amount and thickness, the manufacturing can be facilitated and the cost can be reduced as compared with a thin film or the like.

  That is, in the phase plate 43, the phase difference generation layer is not disposed in the A region 44 through which the A light 500 is transmitted. Further, the phase difference generation layer is not disposed also in the C region 47, and the phase difference generation layer is disposed only in the B region 45. On the other hand, in the conventional phase contrast microscope, a phase film (corresponding to the phase difference generation layer in the present invention) is arranged with respect to the A region 44, and the phase of the diffracted light region such as the B region 45 or the C region 47 is phase. The membrane was not placed. That is, in the new differential interference microscope 1 of the present embodiment, the arrangement of the material generating the phase difference is different from the region 44 in the phase plate of the conventional phase contrast microscope, and either the B region 45 or the C region 47 is used. The only thing that is different is the arrangement.

  As described above, in the phase plate 43, the A region 44 is arranged at the center near the optical axis 100, so that the phase difference between the light transmitted through the B region 45 and the C region 47 (B light 501 and C light 502) is obtained. The A region (A region 44) for generation is made common, and the arrangement of each region can be made efficient and easy. Further, in the phase plate 43, the A region 44 is arranged in a line symmetric shape with respect to the line symmetric axis 102 and line symmetric with respect to the line symmetric axis 102, whereby light from the A region 44 (A By causing the light 500) to have an even distribution in order to generate a phase difference with respect to the light in the B region 45 and the C region 47, a three-dimensional image can be obtained satisfactorily like a conventional differential interference microscope. Can do. Further, in the present embodiment, the B region 45 where the phase difference generation layer is disposed and the C region 47 where the phase difference generation layer is not disposed are axially symmetric on both sides divided by the line symmetry axis 102 passing through the optical axis 100. Further, it is formed as a large area and is arranged at a position on the outer peripheral side with respect to the A area 44.

  In the phase plate 43 of the present embodiment, the A region 44, the B region 45, and the C region 47 through which the A light 500 is transmitted are arranged on the phase plate 43 so as not to overlap each other. . The A region 44 of the present embodiment has a rectangular shape that is line-symmetric with respect to the line symmetry axis 102, and is disposed so as to have a line-symmetric positional relationship with respect to the line symmetry axis 102. From this, the pupil shape of the A region 44 in FIG. 2 has a differential interference effect with respect to the vertical line and the vertical line is emphasized. More preferably, the A region 44 is disposed at a position close to the line symmetry axis 102 at the center of the phase plate 43 close to the optical axis 100, and has a rectangular shape that is point-symmetric to the optical axis 100 including the optical axis 100. Or arranged so as to have a point-symmetrical positional relationship with respect to the optical axis 100.

  By making the A region 44 of the phase plate 43 rectangular, the shortest distance from the center of the B region 45 and the C region 47 arranged in line symmetry to the A region 44 and the end portions of the B region 45 and the C region 47. Since the difference in the shortest distance from the region A to the region A is reduced and the effect in the entire region is obtained, the action of interfering at the time of generation of the phase difference and the synthesis is improved, and it is three-dimensional like a conventional differential interference microscope. An image can be obtained satisfactorily.

  In addition, the principle of the differential interference microscope method of the present invention is that a three-dimensional observation image using the new differential interference microscope 1 of the present embodiment is the primary B light 501) that transmits the B region 45 and the A region. The image obtained by the interference with the 0th-order diffracted light (A light 500) transmitted through 44, the −1st-order C light 502 transmitted through the C region 47, and the 0th-order diffracted light (A light 500) transmitted through the A region 44. This means that a three-dimensional image is obtained by superimposing the image obtained by interference. Therefore, when the B region 45 and the C region 47 are in a symmetric relationship with respect to the A region 44 through which the 0th-order diffracted light (A light 500) is transmitted on the pupil of the imaging system, the two images always shifted. Are observed in a superimposed manner, so that the contrast becomes the highest. Therefore, conversely, when the B region 45 and the C region 47 are in an asymmetric relationship with respect to the A region 44, the B light 501 and C that pass through the region corresponding to the portion where the B region 45 and the C region 47 do not overlap each other. In the portion of the image generated by the light 502) and the 0th-order diffracted light (A light 500), the two images do not overlap, so the contrast is reduced.

  Also, the shape of the pupil is a rectangular shape like the A region 44 shown in FIG. 2 of the present embodiment, and the B region 45 and the C region 47 are parallel to the long side of the rectangle as shown in FIG. When the line is separated and defined between the phase plate 43 and the circular periphery, the boundary line of the B region 45 or C region 47 with the phase film is moved in a direction perpendicular to the optical axis 100. Thus, the area of the region can be changed freely. In that case, it is possible to arbitrarily change the lower limit of the spatial frequency for enhancing the contrast.

  Further, the A region 44 can be a figure that is point-symmetric with respect to the optical axis 100. The A region 44 may have a point-symmetric shape with respect to the optical axis 100, and the B region 45 and the C region 47 may be disposed so as to have a point-symmetric positional relationship with respect to the optical axis 100. In this way, a three-dimensional image can be obtained as in a conventional differential interference microscope with a configuration similar to a phase contrast microscope.

  In the B region 45 where the retardation generation layer is arranged as an example, a recess for arranging the retardation generation layer is formed with a thickness t1 smaller than the total thickness t2 of the base material portion 48, and the recess is positioned in the recess. A phase difference generating layer is disposed. In this case, by forming the concave portion, a phase difference due to the first optical material is generated in the concave portion in the base material portion 48 formed of the first optical material and in the other portions. By adding to the phase difference caused by the phase difference generation layer, the phase difference can be increased.

  In addition, the processing for forming the recesses in the phase plate 43 can be performed by a conventional processing technique, and can be easily manufactured in the same manner as a conventional phase-contrast microscope. The cost can be greatly reduced as compared with a conventional differential interference microscope for obtaining a typical observation image.

  Further, as shown in FIG. 2C, when a cover glass 117 having substantially the same shape as the phase plate 43 is used to protect the surface of the phase plate 43, the thickness t1 is formed on the base material portion 48. After forming the recesses for disposing the phase difference generating layer, an adhesive having characteristics after curing is applied to the entire surface of the base material portion so as to have a predetermined thickness after curing, and the top is substantially the same as the phase plate 43. By covering with the cover glass 117 having the same shape, an adhesive layer having characteristics may be finally formed between the entire surface including the recesses on the phase plate 43 and the cover glass 117. In this case, the B region 45 and the C region 47 can be easily obtained only by forming the recesses, and the phase difference generation layer is disposed on the B region 45 and the C region 47, so that the substrate 48 of the phase plate 43 at the time of manufacture is formed. Can be easily arranged.

  In the phase plate 43, the phase difference of the B light 501 (light transmitted through the region where the phase difference generation layer is disposed) with respect to the A light 500 is the first difference that the incident light forms the A region 44 by the configuration described above. From the difference between the phase that has changed when passing through the layer of optical material and the phase that has changed when incident light has passed through the layer (or the laminated structure of the first optical material and the phase difference generating layer) can get. On the other hand, the C region 47 in which the phase difference generation layer is not disposed has a layer configuration formed of only the first optical material, similarly to the A region 44, and the transmitted light (C light 502) has a phase difference. There is no phase difference due to the generation layer.

  From the above, in the new differential interference microscope 1, the B light 501 in which the phase difference between the A light 500 is generated by the layer of the phase plate 43 and the C light 502 in which the phase difference between the A light 500 due to the layer is not generated Therefore, the part where incremental interference occurs is bright and the part where destructive interference occurs is dark, making it possible to obtain a three-dimensional image like a conventional differential interference microscope. Yes.

  A conventional differential interference microscope required for observing a stereoscopic image has been expensive because it has an expensive prism or the like. However, in the present invention, a stereoscopic microscope has a configuration of a phase contrast microscope that does not have a prism or the like. Image can be observed. Moreover, when observing stained cells and materials with various colors that were not suitable for observation with conventional Nomarski differential interference microscopes, the colors of the object were faithfully reproduced. An image similar to that of a differential interference microscope can be obtained.

  Further, in the new differential interference microscope 1, the arrangement of the optical material (phase difference generation layer, phase film) for generating the phase difference in the phase plate 43 is changed from the conventional direct light portion to a predetermined position in the diffused light portion. The effect is obtained only by such a configurational change. As an effect of the new differential interference microscope 1, the halo inherent in phase difference observation can be reduced, and further, differential interference can be applied to a thick sample or a multilayer sample without using a prism or the like. Like the observation method, bright and dark contrasts can be given to the portions with different thicknesses of the sample, and an observation image with a three-dimensional effect can be obtained like a conventional differential interference microscope.

<< Description of Principle of Present Invention >>
The present invention will now be described using the re-diffraction theory proposed by Abbe.
A striped object having a sinusoidal amplitude transmittance having a certain pitch P is expressed by the following equation (Equation 5). (X is the coordinate on the object surface)

(Reference: “Optical equipment optics II, written by Yoshimasa Hayami, published by the Japan Opto-Mechatronics Association, 2000”. Also, the following formulas (Equation 6), (Equation 7 ), (Equation 8) is also based on the same reference)

The medium that gives the phase difference Δ to the light exists only in the region where the first-order diffracted light of the Fourier transform plane (that is, the pupil plane) of this object is transmitted. At this time, the image U ′ on the image plane of the optical system is expressed by the following equation (Equation 6).

Therefore, when there is an object that causes a phase difference Δ on the pupil plane, the first-order diffracted light is transmitted therethrough, so that the sinusoidal object is on the image side in the x-axis direction from the optical axis (Expression 7) Only shifted image.

For example, when the phase difference Δ = π / 2, the shift amount x0 ′ on the image side is expressed by the following equation (Equation 8).

From this equation (Equation 8), it can be seen that the pattern shifts in the 1/4 pitch x direction.

On the other hand, there is a region where no phase difference occurs on the same pupil plane, and even if the first-order diffracted light is transmitted there, no image shift occurs. The image U ″ in this case is expressed as the following formula (Equation 9).

  Therefore, in the image of the new differential interference microscope of the present invention, U ′ having a slight amount of deviation and an image of U ″ having no deviation overlap on the image plane. The image of the microscope is very similar to the image of a conventional Nomarski differential interference microscope.

  However, it should be noted here that the conventional Nomarski differential interference microscope has a remarkably different color balance of the image obtained depending on the wavelength due to the dispersion of the Nomarski prism used to divide the light into two polarizations. It is. Therefore, in the conventional Nomarski type differential interference microscope, the color of the object looks different from the color balance normally observed from an actual object through which light is transmitted by the bright field microscope.

  On the other hand, in the new differential interference microscope of the present invention, as shown in the above equation (Equation 7), it is suggested that the image shift amount can be made constant according to the wavelength unless the phase difference Δ changes with the wavelength. ing.

  Further, in the conventional Nomarski type differential interference microscope, the shift amount (shear amount) of the image due to the two polarized lights defined by the Nomarski prism is constant when observing any specimen.

  On the other hand, in the new differential interference microscope of the present invention, the shift amount automatically changes depending on the fine structure (spatial frequency) of the sample, as shown in the above formula (Equation 7). Compared with a differential interference microscope, a sharper image can be observed.

<< Material and thickness selection method 1 >>
Further, in the phase plate 43, the phase difference generating layer is made of a material and a material such that the phase difference Δ satisfies the following formula (Equation 1), where Δ is the phase difference generated by the phase difference generating layer. The thickness can be selected.

In this case, the range of | Δ | in the expression (Equation 1) is, for example, an image formed from light transmitted through the C region 47 of only the first optical material and the B region 45 including the phase difference generation layer. An upper limit and a lower limit shift amount of the phase difference of the image formed from the reflected light are defined. In other words, the equation (Equation 1) defines the relative shift amount of the phase difference between the two images generated by the equation (Equation 7).
When the shift amount is a value lower than the lower limit value 0.05π of the mathematical formula (Equation 1), the shift amount of the image is too small, and the occurrence of interference when combined is reduced. Equivalent image. On the contrary, when the shift amount is a value exceeding the upper limit value 0.95π of the mathematical formula (Equation 1), the brightness of the shifted image is almost reversed, so that the intensity of the light of the two synthesized images becomes almost zero. Thus, no interference occurs and the meaning of generating a phase difference is lost.

<< Material and thickness selection method 2 >>
Further, in the phase plate 43, the material and thickness can be selected so that the phase difference Δ generated by the phase difference generating layer satisfies the following mathematical formula (Formula 2).

  In this case, the range of | Δ | in the equation (Equation 2) is, for example, an upper limit value 0 as a condition for giving an optimum value of the shift amount of the phase difference between the two images to the range of the equation (Equation 1). The range of 0.5π and the lower limit of 0.25π is specified. From the mathematical formula (Equation 7), the lower limit value of the optimum value corresponds to 1/8 pitch of the shift amount, and the upper limit value corresponds to 1/4 pitch of the shift amount.

<< Material and thickness selection method 3 >>
Further, in the phase plate 43, the phase difference between the phase of the light transmitted through the A region 44 and the phase of the light transmitted through the B region 45 having the second optical material is a phase difference ΔB, and the light transmitted through the A region 44. When the phase difference of the C region 47 of the second optical material is the phase difference ΔC with respect to the phase of the light to be transmitted, the material and the phase difference ΔB and the phase difference ΔC satisfy the following formula (Equation 3): The thickness can be selected.

  Moreover, there is a case where the image of the new differential interference microscope 1 has no distortion or the like, for example, symmetry in the x-axis direction when the horizontal direction in FIGS. In that case, (aa) the phase difference of the B region 45 having the second optical material with respect to the A region 44 and (bb) the phase difference of the C region 47 of the second optical material with respect to the A region 44 are the same value. It is desirable that

  Therefore, the symmetry in the x-axis direction can be obtained by selecting the material and thickness so as to satisfy the above mathematical formula (Equation 3). That is, the above mathematical formula (Equation 3) is obtained by the following equation. The shift amount of the image obtained by interference with the 0th-order diffracted light after the diffracted light passes through the B region (B region 45 of the present embodiment) having the second optical material, The shift amount of the image obtained by interference with the 0th-order diffracted light after the diffracted light passes through the C region (C region 47 of the present embodiment) of the second optical material has the same absolute value and the opposite sign. This means that the symmetry in the x-axis direction is ensured by selecting the material and thickness so as to satisfy the equation.

  In particular, in the projection optical system as in the sixth embodiment to be described later, in order to obtain the symmetry of the projected image in the x-axis direction, the phase difference of the region B with respect to the region A and the position of the region C with respect to the region A are determined. Since it is desirable that the phase difference is the same value, it is desirable that the mathematical formula (Equation 3) is satisfied.

<< Material and thickness selection method 4 >>
In the phase plate 43, the material and thickness of the phase difference generating layer can be selected so as to give a substantially constant phase difference Δ for two or more wavelengths of light.

  The phase plate 43 can obtain an effect with respect to light having a relatively wide wavelength band such as visible light. For example, the phase plate 43 will be described later in <<<< First optical material and thickness determination method >> of the phase plate >>. The material and thickness can be selected so as to give a substantially constant phase difference Δ to two or more wavelengths of visible light. When the phase plate is formed by a method to be described later, it is possible to observe in a state where the color tone of an actual substance is faithfully reproduced.

<< Material and thickness selection method 5 >>
In the phase plate 43, the material and thickness of the B region 45 are set so that the light transmittance is attenuated so as to satisfy the following formula (Equation 4), where T is the transmittance of the region. Can be selected.

  In this case, the transmittance T in Expression (4) is the image formed from the C light 502 transmitted through the C region 47 of only the first optical material, and B transmitted through the B region 45 including the phase difference generation layer. A range in which the stereoscopic effect of the image is emphasized when the image formed from the light 501 is combined is defined.

  The transmittance T in Equation (4) is used so as to slightly reduce the value of the light transmittance T of one of the two images that are combined and overlapped. As a result, the intensity of the light of one of the two images is reduced, and the composite image can be caused to interfere with the shadow due to the difference in intensity, thus enhancing the stereoscopic effect of the obtained image. The degree of emphasis of the three-dimensional effect in this case can further enhance the three-dimensional effect than the observation image obtained by the conventional Nomarski type differential interference microscope.

  When the transmittance T is below the lower limit of the above range, the intensity of the light of one image is too low, and the other image approaches a normal bright field image. This makes it meaningless to combine and interfere. Further, when the value of the transmittance T exceeds the upper limit of the above range, the intensity of the two images becomes almost equal, so that the images are very close to the observation image of the conventional differential interference, and the conventional Nomarski type differential interference is obtained. By combining and interfering with the microscope according to the method of the present invention, the effect of further enhancing the stereoscopic effect is reduced.

  When the phase plate 43 of the new differential interference microscope 1 described above is manufactured, first, the first optical material, which is a material through which the illumination light having a predetermined wavelength emitted from the light source 5 can pass through the base member 48. After that, the light that is transmitted through the first optical material and that is capable of transmitting illumination light having a predetermined wavelength emitted from the light source 5 only in one of the B region 45 and the C region 47 Includes a step of arranging a phase difference generating layer for generating a phase difference so that the phases are different.

  In that case, for example, before the phase difference generation layer is arranged, the phase difference generation layer is arranged in the light transmitting region (B region 45) where the phase difference generation layer in the base material portion 48 of the phase plate 43 is arranged. In order to achieve this, a recess having a shape that matches the shape is formed. Then, a retardation generation layer is disposed in the recess.

  After forming a recess in the base material portion 48 of the phase plate 43, a phase difference generating layer is disposed at least in the recess. When the phase difference generating layer is solid, the concave portion and the phase difference generating layer are formed in conformity with the B region 45, and the phase difference generating layer is disposed in the concave portion.

  Moreover, when using the cover glass 117 for protecting the surface of the phase plate 43, for example, an adhesive having characteristics after curing can be used as the retardation generation layer. In that case, the adhesive is applied to the entire surface including the recesses of the phase plate 43 so as to have a predetermined thickness after curing. Then, an adhesive layer that is a phase difference generating layer is formed between the entire surface including the concave portion of the phase plate 43 and the cover glass 117.

  In the manufacturing method of the new differential interference microscope 1 described above, since a three-dimensional observation image is obtained, a prism is not required unlike a conventional differential interference microscope, so that the manufacturing cost of the microscope and the cost required for observation are reduced. Can be lowered. Thereby, arrangement and positioning are facilitated, and manufacturing time and manufacturing cost can be reduced.

<< First Optical Material and Thickness Determination Method of Phase Plate >>
The following is a case where two wavelengths of illumination light are incident as an example. (The following contents have been filed as Japanese Patent Application No. 2008-056783 by the same inventor as the present invention.) Each material of the phase plate and its thickness are expressed by the following three formulas (Equation 10), It is possible to determine so that the mathematical formula (Formula 11) and the mathematical formula (Formula 12) hold. In the present embodiment, each optical material has one layer, but each numerical formula also takes into account the case where each layer has a plurality of layers.

However:
t ₁ : thickness of the first optical material,
t ₂ : thickness,
t _1i : the thickness of the i-th layer of the first optical material,
λ1: wavelength of first light (visible light) of incident illumination light,
λ2: wavelength of the second light (visible light) of the incident illumination light,
n ₁ (i, 1): refractive index for light of wavelength λ1,
n ₁ (i, 2): refractive index for light of wavelength λ2,
t _2j : the thickness of the j-th layer,
n ₂ (j, 1): refractive index for light of wavelength λ 1
n ₂ (j, 2): refractive index for light of wavelength λ 2
C1: A constant independent of the wavelength of the first optical material.
C2: A constant that does not depend on the wavelength.

However, for the explanation of the symbols, see the mathematical formula (Equation 10).

However,
C1: A constant independent of the wavelength of the first optical material.
C2: A constant that does not depend on the wavelength.

Further, the total thickness t of the phase plate of the present invention can be determined so that the following two formulas (Formula 13) and Formula (Formula 14) are satisfied in addition to the above formula (Formula 12). .

However,
n ₁ (1,1): refractive index of the first optical medium region with respect to the first wavelength λ1,
n ₂ (1,1): Refractive index of the second optical medium region with respect to the first wavelength λ1.

However,
n ₁ (1,2): refractive index of the first optical medium region with respect to the second wavelength λ2,
n ₂ (1, 2): Refractive index of the second optical medium region with respect to the second wavelength λ2.

Further, the total thickness of the phase plate of the present invention can be determined so that the following formula (Equation 15) holds.

However, for the explanation of the symbols, see the mathematical formula (Formula 13) and the mathematical formula (Formula 14).

Further, the total thickness of the phase plate of the present invention can be determined so that the following formula (Equation 16) is established.

However, C1 or C2 in Equation (Equation 1) to Equation (Equation 1) 4 is C, and | C | represents the absolute value of C.

  By selecting the phase difference generation layer of the first optical material and the second optical material so as to satisfy the above-described formulas (Equation 10) and (Equation 11), the wavelength λ2 can be obtained even for the light flux with the wavelength λ1. The phase of the light beam emitted from the first optical material may be advanced or delayed by a predetermined constant C with respect to the phase of the light beam emitted from the second optical medium region. it can. Thus, since the phase can be shifted with respect to a plurality of wavelengths, the phase of the light beam can be adjusted including the frequency information of the light beam.

  Based on the contents of the present invention described above, the aperture stop 22 and the phase plate 43 were created and incorporated in a conventional phase contrast microscope, and an image of diatom << FIG. 3 (a) >> was taken as a sample. Moreover, the image of the same sample diatom << FIG.3 (b) >> by the conventional bright field microscope was also image | photographed as a comparative example of an image.

<< Experimental result 1 >>
As can be seen from the comparison between FIG. 3 (a) and FIG. 3 (b), the image of the diatom by the new differential interference microscope of the present invention in FIG. An image having a high resolution of details is obtained as compared with the normal bright-field observation image of FIG.

  From the above experimental results, in the optical storage using the above-described phase plate of the present invention, the above-described A region of the present invention is arranged at the center of the phase plate, and a phase difference is generated in either the B region or the C region. It has been confirmed by experiments that the configuration in which the region to be arranged is the configuration that can obtain the effect of the present invention most.

  As described above, the phase difference plate 43 of the present embodiment generates the phase difference of the second optical material that generates a phase difference in the direct light (A light 500) transmission region as in the conventional phase contrast microscope method. Rather than disposing the layer, the material is disposed only on one side of the transmission region of the diffracted light on both sides divided by the axis of line symmetry (in this embodiment, the transmission region 45 of the first-order diffracted light 501), and the phase difference is obtained. It is configured to have. Note that the arrangement for generating the phase difference can obtain the effect of the present invention even with only a part of the transmission region on one side. In contrast to the present embodiment, the material may be disposed only in the transmission region 47 of the −1st order diffracted light 502 to give a phase difference.

  Further, the differential interference microscopic method of the present embodiment is a method for obtaining a stereoscopic observation image without using two polarized lights defined by a prism, unlike the conventional differential interference microscopic method. The new differential interference microscope of this embodiment includes an image having a phase difference obtained by the interference between the first-order diffracted light 501 due to the diffraction phenomenon and the A light 500 that is direct light, the −1st-order diffracted light 502 and the A light due to the diffraction phenomenon. 5 is a microscope configured to superimpose an image having a phase difference obtained by interference with 500 on the objective lens image plane 71. In the present invention, when the object is observed, an image can be formed on the objective lens image plane 71 by emphasizing the refractive index difference at the object boundary and the step difference at the object boundary. it can.

  Therefore, by using the new differential interference microscope of the present embodiment, a stereoscopic observation image can be obtained without using an expensive objective lens and a Nomarski prism polarizer, which are essential for the conventional differential interference microscope. It is done. Further, the stereoscopic observation image can be obtained with a high resolution with little image change and a color close to the color tone of the actual object.

  In addition, the stereoscopic observation image using the new differential interference microscope of the present embodiment has less attenuation of light amount and less decrease in image intensity when compared with a bright field image obtained by a conventional bright field microscope. Thus, it is possible to obtain the effects that the contrast of the image of the observation object is less lowered, the lack of information on the color of the sample is small, and the change in the color balance is small.

  In addition, when the differential interference microscope method of the present embodiment is compared with the conventional phase contrast microscope method, the conventional phase contrast microscope method is located between the A light 500 and other diffracted light. In contrast to the idea of giving a phase difference, the present invention is a completely new idea of giving a phase difference to only a part of the diffracted light. Furthermore, the differential interference microscopic image of this embodiment selects only a portion having a fine structure based on a conventional bright-field image by controlling a region having a phase difference on the pupil. Therefore, there is an advantage that even a nearly transparent object can be easily observed.

<<< Second Embodiment >>>
In the phase plate as an example of the second embodiment of the present invention shown in FIGS. 4A and 4B, the first embodiment is provided in that the B region and the C region are provided on both sides of the line symmetry axis 102. In the first embodiment, “there is a differential interference effect with respect to the vertical line and the vertical line is emphasized” with respect to both the X axis and the Y axis orthogonal to each other on the phase plate. In this embodiment, the above-described effect can be obtained. The shapes and arrangements of the A region, the B region, and the C region shown in FIGS. 4A and 4B are also examples of the phase plate of the present embodiment, and are not limited thereto. Other shapes and arrangements obtained in the same manner as in the first embodiment may be used.

  For that purpose, in the retardation plate 120 (43) of the second embodiment, the original line symmetry axis 102 passing through the optical axis 100 is inclined 45 degrees counterclockwise in the drawing, and the retardation plate 120 (43). The boundary line is set so as to draw a square inscribed around the circle of the phase difference plate 120 (43) at 45 degrees on both sides with respect to the line symmetry axis 102 from the intersection of both the circle circumference and the line symmetry axis 102 Then, the A region 122 (44) is set in a circle around the optical axis 100. In this case, the original line-symmetrical axis 102 is effective when the phase plate 43 is manufactured. However, in the first embodiment, “the differential line has an effect of differential interference with the vertical line and the vertical line is emphasized. As the line symmetry axis for obtaining the effect of “R”, the line symmetry axis in the X axis direction is set at the position of the BB line, and the line symmetry axis in the Y axis direction is set so as to be orthogonal to the X axis.

  Therefore, in the new differential interference microscope 1 of the second embodiment, in the phase plate 120 (43), a plurality of line symmetry axes that pass through the optical axis 100 are provided at predetermined center angles with the optical axis 100 as the center ( In this case, the original line-symmetrical axis 102 is added with two perpendicular X-axis and Y-axis directions), and the pair of axes on both sides divided by the respective line-symmetrical axes (X-axis and Y-axis) In any one of the translucent areas (in this case, the B area 124 (45)) of the image areas (B area 124 (45) and C area 126 (47)), the corresponding line symmetry axis 102 + X axis + Y The retardation generation layer 125 (46) is formed by arranging the retardation generation layer of the second optical material at a position line-symmetric with the other light transmission region with respect to the axis.

  That is, the new differential interference microscope 1 of the present embodiment is formed as shown in FIG. 6 even when it has two line symmetry axes corresponding to the X axis and Y axis orthogonal to each other on the plane of the formed image. Then, by setting the B region 125 (45) and the C region 126 (47) on both sides of each line symmetry axis (X axis and Y axis), a three-dimensional image can be obtained like a conventional differential interference microscope. be able to.

  Thus, the line symmetry axis (X axis and Y axis) passing through the optical axis 100 is not limited to one of the line symmetry axes 102 shown in FIG. 1, and can be increased to two or more. For example, two line symmetry axes (X axis and Y axis) can be arranged orthogonally as shown in FIG. 4, but two or more line symmetry axes are set around the optical axis 100 at equal angles. You can also In this case, the A region 122 (44) is a line-symmetric figure with respect to all line-symmetrical axes, for example, a circle. Further, the B region 124 (45) and the C region 126 (47) are arranged so as to have a line-symmetric positional relationship with respect to at least one line-symmetric axis.

  Further, in the new differential interference microscope 1 of the present embodiment, the A region 122 (44) is a circle including the optical axis 100. Thereby, the pupil shape of the phase plate 43 of the present embodiment can obtain a differential interference effect in both directions of the horizontal line (X axis) and the vertical line (Y axis), and the horizontal line is emphasized in addition to the vertical line. The type is obtained.

  Further, in the new differential interference microscope 1 of this embodiment, the A region 122 (44) is circular, so that the circular aperture stop 22 and the phase plate 120 (43) are designed and manufactured as in the conventional bright field microscope. Therefore, design and manufacturing are easy, manufacturing costs can be reduced, and a period required for manufacturing can be shortened.

<<< Third Embodiment >>>
In the phase plate as an example of the third embodiment of the present invention shown in FIGS. 5A and 5B, the B region and the C region are provided on both sides of the line symmetry axis 102, and X is orthogonal on the phase plate. A point in which the effect of “the differential interference effect with respect to the vertical line and the vertical line being emphasized” of the first embodiment can be obtained with respect to both the axis and the Y axis. Then, although it is the same as that of 2nd Embodiment, A area | region 132 (44) is made into the ring zone shape centering on the optical axis 100 in this embodiment. The shapes and arrangements of the A region, the B region, and the C region shown in FIGS. 5A and 5B are also examples of the phase plate of the present embodiment, and are not limited thereto. Other shapes and arrangements obtained in the same manner as in the first embodiment may be used.

  Thereby, the pupil-shaped A region 132 (44) through which the A light 500 of the phase plate 130 (43) of the present embodiment is transmitted has an annular shape.

  In the new differential interference microscope 1 of the present embodiment, the shape of the aperture stop 22 can be made the same as the phase plate of the conventional phase microscope by forming the A region 132 (44) in a ring shape, so that the design and manufacture can be performed. Therefore, design and manufacture are easy, the manufacturing cost can be reduced, and the period required for manufacturing can be shortened.

<<< Fourth Embodiment >>>
In the phase plate as an example of the second embodiment of the present invention shown in FIGS. 6A and 6B, the first embodiment is provided in that the B region and the C region are provided on both sides of the line symmetry axis 102. However, the A region 142 (44) is circular, the non-translucent region is eliminated, and the (B region) 144 (45) and the C region 146 (47) are located just outside the A region 142 (44). ). The shapes and arrangements of the A region, the B region, and the C region shown in FIGS. 6A and 6B are also examples of the phase plate of the present embodiment, and are not limited thereto. Other shapes and arrangements obtained in the same manner as in the first embodiment may be used.

  The new differential interference microscope 1 of the present embodiment is the same as that of the first embodiment with respect to both the X axis and the Y axis orthogonal to each other on the phase plate, as in the second embodiment and the third embodiment. Rather than obtaining the effect of “the differential interference effect with respect to the vertical line and the vertical line being emphasized”, a line in almost all directions with the optical axis 100 as the center is taken as the line symmetry axis, With respect to the axis of line symmetry, an effect that “there is a differential interference effect with respect to the vertical line and the vertical line is emphasized” can be obtained.

<<< Fifth Embodiment >>>
FIG. 7 shows a schematic configuration of an optical system and an optical path of illumination light when the retardation plate of the present invention is applied to an episcopic phase contrast microscope as an example of the optical system of the fifth embodiment of the present invention. Has been.
In the epi-illumination type new phase contrast microscope 2 of the fifth embodiment, the epi-illumination optical system 10, the half mirror 31, and the connection are roughly compared with the phase contrast microscope 1 of the new system of the first embodiment. The difference is in the image optical system (objective lens optical system) 40. Further, in the optical path of the epi-illumination optical system 10, an aperture stop 22 is disposed at a position 21 (hereinafter referred to as an exit pupil conjugate position in the illumination optical system) that is conjugate with the objective lens exit pupil on the light source 5 side. . The illumination light transmitted through the light transmitting region 23 of the aperture stop 22 is emitted toward the half mirror 31.

  The half mirror 31 reflects the illumination light emitted from the light source 5 and transmitted through the aperture stop 22 to the objective lens side, and transmits the reflected light from the observed sample 61 to the objective lens image plane 71 side.

  In the objective lens 41 in the imaging optical system (objective lens optical system) 40, the illumination light from the half mirror 31 is incident from the upper surface, and the illumination light is emitted from the lower surface toward the observed sample 61 or the object surface 51. Reflected light from the observed sample 61 or the object surface 51 is incident from the lower surface, and the reflected light is emitted to the half mirror 31. A phase plate 43 is provided at the exit pupil conjugate position 42. Further, the phase plate 43 is the same as that of the first embodiment, but the shape and arrangement of the A region, the B region, and the C region shown in FIG. 7 are also examples of the phase plate of the present embodiment. It is not limited, and other shapes and arrangements obtained in the same manner as in the first embodiment may be used.

  Next, in the objective lens 41, the reflected light incident from the lower surface is transmitted through the objective lens 41 from the lower side to the upper side in FIG. The reflected light reaches the phase plate 43, is phase-operated in the phase film region 45, and is emitted toward the half mirror 31. In the phase film region 45, the phase of the reflected light is emitted by being advanced or delayed by, for example, a quarter wavelength operation by the phase film (in the case of a quarter wavelength plate).

  Thus, the phase difference plate 43 of the present invention can also be applied to the epi-illumination type phase contrast microscope 2 as described above without any problem as in the first to fourth embodiments. Therefore, the epi-illumination type phase contrast microscope 2 of the present embodiment can also obtain the same effects as those of the first to fourth embodiments.

<<< Sixth Embodiment >>>
FIG. 8 shows a schematic configuration of an optical system and an optical path of illumination light when the retardation plate of the present invention is applied to a projection exposure apparatus as an example of an optical system of a sixth embodiment of the present invention. Yes.

  The present invention can also be used in an optical system of an exposure apparatus that projects and exposes an image of a mask as in this embodiment. More specifically, the application range of the optical system including the phase plate 43 of the present invention is not limited to the microscope as in the first to fifth embodiments, and can be applied to a projection optical system such as an exposure apparatus. is there. The phase plate 43 of the present embodiment is the same as that of the first embodiment, but the shapes and arrangements of the A region, the B region, and the C region shown in FIG. 8 are also examples of the phase plate of the present embodiment. However, the present invention is not limited to this, and other shapes and arrangements obtained in the same manner as in the first embodiment may be used.

For example, in the case of the new projection optical system 3 shown in FIG. 8, there is no distortion or the like in the image projected on the image plane 71 that is transmitted through the reticle surface 81 and projected, for example, FIGS. It is necessary to ensure symmetry in the x-axis direction when the horizontal direction in FIG. Therefore, it is preferable that (aa) the phase difference of the B region 45 having the second optical material with respect to the A region 44 and (bb) the phase difference of the C region 47 with respect to the A region 44 have the same value. It is desirable to satisfy (Equation 3) by selecting the material and thickness.
This is because the shift amount of the image obtained by interference with the A light 500 after the diffracted light passes through the B region and the shift amount of the image obtained by interference with the A light 500 after the diffracted light passes through the C region. This means that the absolute values are the same and the signs are reversed, and that symmetry in the x-axis direction is ensured.

  As described above, the retardation plate 43 of the present invention can be applied to the projection exposure apparatus 3 as described above without any problem as in the first to fourth embodiments. Therefore, the new projection optical system 3 of the present embodiment can also obtain the same effects as those of the first to fourth embodiments.

  As shown in each of the above embodiments, the optical system of the present invention has an aperture stop that transmits a part of illumination light from the light source along the optical axis and direct light that is transmitted directly through the aperture stop. The optical system has at least a phase plate through which folded light, diffused light, and first-order diffracted light and −1st-order diffracted light are transmitted, and the light transmitted through the phase plate is imaged. The phase plate is formed of a first optical material that is a material that allows the base material portion to transmit illumination light having a predetermined wavelength emitted from a light source. The phase plate is made of a material that can transmit illumination light having a predetermined wavelength emitted from the light source, and the phase difference generation layer has the first-order diffracted light so that the phase is different from the light transmitted through the first optical material. It is arranged only in either the B region that transmits or the C region that transmits −1st order diffracted light.

  In the phase plate of the present invention, the A region, the B region, and the C region are arranged on the device design so that they do not overlap each other. Further, the light-transmitting region where the phase difference generation layer is arranged is arranged in one of the two axially-paired regions divided by the line symmetry axis passing through the optical axis on the phase plate. Is done.

  In the phase plate of the present invention, the phase difference generation layer is disposed only in one of the B region and the C region that are in a line-symmetrical position with respect to the line-symmetric axis passing through the optical axis. Only the first optical material is not disposed in the other region. Thereby, the diffracted light (one of the first-order diffracted light << B light >> or the -1st-order diffracted light << C light >>) having a phase difference with the A light and the diffracted light with no phase difference between the A light ( -1st order diffracted light << C light >> or 1st order diffracted light << B light >> and the effect of interference at the appropriate level becomes a three-dimensional image like a conventional Nomarski differential interference microscope. Can be obtained satisfactorily.

  In the phase plate of the present invention, the A region is disposed at a position close to the line symmetry axis, and the translucent region (B region or C region) in which the phase difference generation layer is disposed is located on the outer peripheral side of the A region. It may be arranged at the position. In addition, by arranging the A region in the central part close to the optical axis, the A region for generating a phase difference in the light transmitted through the B region and the C region (B light and C light) is made common to each region. Can be made more efficient and easier. Further, the region A may have a line-symmetric shape with respect to the line symmetry axis, and may be arranged so as to have a line-symmetric positional relationship with respect to the line symmetry axis.

  Moreover, the phase plate of the present invention arranges the A region in a line symmetric shape with respect to the line symmetric axis and line symmetric with respect to the line symmetric axis, so that light (A light) from the A region is In order to generate a phase difference with respect to the light in the B region and the C region, it is possible to influence with equal distribution. Thereby, a three-dimensional image can be satisfactorily obtained like a conventional Nomarski type differential interference microscope. Further, the region A may have a ring shape centered on the optical axis. Further, by making the A region into a ring shape, the shape of the aperture stop can be made the same as that of a phase plate of a conventional phase microscope, so that design and manufacture are possible. Thereby, design and manufacture are easy, manufacturing cost can be reduced, and a period required for manufacturing can be shortened.

  In addition, the base part of the phase plate of the present invention has, for example, a light-transmitting region (B region or C region) in which the phase difference generating layer is disposed, and a concave portion for arranging the phase difference generating layer is formed. A retardation generation layer may be disposed in the recess. In the phase plate of the present invention, by forming the concave portion, a phase difference due to the first optical material occurs in the concave portion in the base material portion formed of the first optical material and other portions. Here, the phase difference can be increased by adding to the phase difference due to the phase difference generation layer. Moreover, the arrangement | positioning operation | work on the base-material part of the phase plate at the time of manufacture can be made easy by arrange | positioning a phase difference generation layer in the recessed part.

  Further, in order to protect the surface of the phase plate, the phase plate of the present invention has a cover glass having substantially the same shape as the phase plate, for example, between the entire surface including the concave portion of the phase plate and the cover glass, An adhesive layer of adhesive having properties after curing may be formed. The adhesive is applied on the base material portion so as to have a predetermined thickness after curing, and is covered with a cover glass having substantially the same shape as the phase plate so that the B region and the C region can be easily obtained. May be.

  In the phase plate of the present invention, the phase difference generating layer may be formed in a layer shape having a predetermined thickness in the optical axis direction in order to generate a phase difference. For example, instead of forming a thin phase film, a phase difference generating layer in which a solid having a predetermined thickness is formed in a layer shape is disposed on the base material part, or a liquid such as an adhesive or a gel phase difference generating layer is provided. By coating the base material portion with a predetermined thickness and thickness so as to form a layer after curing, manufacturing can be facilitated and cost can be reduced as compared with a thin film or the like.

  Further, the phase plate of the present invention is formed of a first optical material whose material is capable of transmitting illumination light having a predetermined wavelength emitted from the light source, and the first-order diffracted light in the base material base material portion is A material that can transmit illumination light of a predetermined wavelength emitted from the light source only in one of the B region that transmits and the C region that transmits the −1st order diffracted light, and the light that transmits the first optical material; The phase difference generating layer is arranged so that the phases are different. That is, the phase difference generation layer is not disposed in the A region where the 0th-order diffracted light is transmitted through the phase plate, and the phase difference generation layer is disposed only in either the B region or the C region. Thereby, for example, when the phase difference generation layer is arranged in the B region, both the light having a remarkable phase difference between the A light and the B light and the light having no significant phase difference between the A light and the C light are emitted. can do.

  The optical system of the present invention is an aperture stop that transmits a part of illumination light from a light source along the optical axis, 0th-order diffracted light that is direct light that has passed through the aperture stop, and 1 that is diffused light. It is an optical system that has at least a phase plate that transmits the first-order diffracted light and the −1st-order diffracted light, and images the light that has passed through the phase plate. At the time of manufacturing the phase plate, first, the base material portion is formed of a first optical material that is a material capable of transmitting illumination light of a predetermined wavelength emitted from the light source, and then the B region or − A material capable of transmitting illumination light having a predetermined wavelength emitted from the light source only in one of the C regions through which the first-order diffracted light is transmitted, and having a phase different from that of the light transmitted through the first optical material. A step of disposing a phase difference generating layer;

  Further, in the optical system of the present invention, since a three-dimensional observation image is obtained, a prism is not required unlike a conventional differential interference microscope, so that the manufacturing cost of the microscope and the cost necessary for observation can be reduced. it can. Before arranging the phase difference generating layer, for example, a recess for arranging the phase difference generating layer may be formed in a light transmitting region where the phase difference generating layer is arranged in the base part of the phase plate. . Processing to provide a recess in the phase plate can be performed using conventional processing technology, and can be easily manufactured in the same way as conventional phase contrast microscopes, with minimal increase in manufacturing costs. The cost can be greatly reduced as compared with the conventional differential interference microscope.

  In the optical system of the present invention, for example, after forming a concave portion in the base portion of the phase plate, a phase difference generating layer may be disposed in at least the concave portion of the phase plate. Thereby, it becomes easy to arrange | position and position a phase difference generation layer, and can reduce manufacturing time and manufacturing cost. In addition, when a cover glass for protecting the surface of the phase plate is provided, for example, an adhesive having characteristics after curing is used as the phase difference generation layer, and the entire surface including the concave portion of the phase plate is predetermined after curing. You may apply | coat so that it may become thickness and may form an adhesive bond layer between the cover glass and the whole surface including the recessed part of a phase plate. When an adhesive layer is formed between the cover glass and the cover glass, the surface of the adhesive can be flattened, and deterioration of the flatness of the subsequent surface can be prevented by the cover glass.

1 Optical system (new differential interference microscope),
2 Optical system (new epi-illumination-differential interference microscope),
3 Optical system (new projection optical system),
5 light source,
10 Illumination optics,
11, 12, 13, 14 Lens (of illumination optical system) 21 Exit pupil conjugate position in illumination optical system (position conjugate with exit pupil of objective lens in illumination optical system),
22 Aperture stop device (aperture stop,
23 (aperture stop device side) translucent region,
31 half mirror,
40 Imaging optics,
41, 46 lens (in the imaging optical system) 42 exit pupil conjugate position (in the imaging optical system) (position conjugate with the exit pupil of the objective lens),
43 phase plate,
44, 112, 122, 132, 142 area A,
45, 114, 124, 134, 144 B region,
46, 115, 125, 135, 145 phase difference generation region,
47, 116, 126, 136, 146 C region,
48 base material part,
51 Object plane (exit pupil position of objective lens),
61 sample to be observed),
71 Objective lens image plane,
81 Reticle surface (mask surface)
100 optical axes,
102 line symmetry axis,
104 on the first side of the line symmetry axis,
106 the second side of the line symmetry axis,
117 cover glass,
118, 128, 138 non-translucent region,
500 first transmitted light (transmitting through region A),
501 second transmitted light (transmitting through region B),
502 Third transmitted light (transmitted through region C).

Claims (11)

In an optical system having an illumination system that illuminates an object using light from a light source as parallel light, and an imaging system that forms an image of light from the object at a predetermined magnification,
An aperture stop that limits direct light (0th order light) incident on the imaging system at a position conjugate with the light source in the illumination system, and all 0th order light at the position of the aperture stop (pupil position) in the imaging system. A region through which the first order diffracted light passes, and a C region through which the −1st order diffracted light passes, and the B region and the C region with respect to the symmetry axis including the intersection of the pupil plane and the optical axis Is a phase plate in which the B region or the C region has a structure that generates a predetermined phase difference with respect to the A region, and the B region and the C region have no common region with the A region. And an optical system. If the phase difference of the B region relative to the A region or the C region relative to the A region is Δ,
The optical system according to claim 1, wherein Δ satisfies the following condition.
0.05π ≦ | Δ | ≦ 0.95π If the phase difference of the B region relative to the A region or the C region relative to the A region is Δ,
The optical system according to claim 2, wherein Δ satisfies the following condition.
0.25π ≦ | Δ | ≦ 0.5π 4. The optical system according to claim 2, wherein the A region through which the zero-order light passes has a point-symmetric shape with respect to the intersection of the optical axis and the pupil plane. The optical system according to claim 4, wherein the A region through which the zero-order light passes is a circle including an intersection of the optical axis and the pupil plane. The optical system according to claim 4, wherein the A region through which the zero-order light passes is a rectangle including an intersection of the optical axis and the pupil plane. 7. The optical system according to claim 2, wherein the following conditions are satisfied, where ΔB and ΔC are the phase differences of the B region and the C region with respect to the A region.
ΔB = ΔC The optical system according to any one of claims 2 to 6, wherein the B region or the C region has a structure for attenuating light, and the transmittance is T, and the following condition is satisfied.
0.1 <T <0.9   The structure for generating a predetermined phase difference is a phase film that gives a constant phase difference Δ to two or more wavelengths, and the phase difference Δ satisfies the condition of Δ in a relatively wide wavelength band. 9. The optical system according to any one of 1 to 8.   The structure that generates the predetermined phase difference is transparent to the light to be used, and the portion that generates the phase difference between the zero-order light and the first-order light is a single substance in the optical axis direction in which the light travels. The optical system according to claim 2, wherein the optical system has a layer structure as follows.   The B region and the C region are outside a pair of opposing sides of the rectangle of the A region, and are arcuate line-symmetric with respect to the symmetry axis. The optical system described.