JPH09281402A - Object observing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the rotation of a phase remaining in an optical system and to observe the differential interference image of ideal contrast in arbitrary size of the aperture diaphragm of an illuminating system. SOLUTION: The phase difference of light beams EO and OE in orthogonal polarization directions is adjusted by a polarizer 10 and a 1/4 wavelength plate 12, and is sheared by a Nomarski prism 14 to irradiate an object. Transmitted or reflected light through/by the object is synthesized by the Nomarski prism 20, and a coherent polarization component is taken out by a polarizing beam splitter 22. The adjustment of an intensity ratio is performed for the first and second images of the coherent polarized light component in first and second directions obtained, and also a differential interference image is obtained from a difference signal. Thus, the rotation of the remaining phase of the optical system is eliminated, so that the differential interference image of the ideal contrast is observed by the arbitrary size of the aperture diaphragm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an object observing device such as a differential interference microscope, and more specifically to improving the contrast with respect to phase rotation and aperture stop remaining in an optical system.

[0002]

2. Description of the Related Art In an object observing apparatus, for example, a differential interference microscope, the intensity of an interference image by an ideal optical system when an object to be observed does not exist is generally zero. However, for light rays other than the chief ray, an additional phase difference due to the objective lens or the like remains. An optical rectifier is one method for removing the phase rotation remaining in such an optical system. The rotation of the residual phase is also improved by narrowing the aperture stop of the illumination system.

However, the method using an optical rectifier has a disadvantage that it is difficult to use it for a differential interference microscope of epi-illumination. Further, the method of narrowing the aperture stop cannot be applied to a laser scanning microscope that uses the entire aperture of the illumination system, and as a result, good contrast cannot be obtained. Further, there is also a disadvantage that the loss of the amount of light becomes large when the aperture stop of the illumination system is narrowed down.

The present invention focuses on the above points,
It is possible to remove the phase rotation remaining in the optical system and observe the differential interference image of ideal contrast with the size of the aperture stop of the arbitrary illumination system, which simplifies the imaging and laser scanning microscopes. The object of the present invention is to provide an object observing device that can be configured by a simple optical system.

[0005]

The present invention relates to an illumination means (50, 54) for supplying light for illuminating an object; first and second polarization directions orthogonal to each other of the light supplied thereby. Difference adjusting means (10,1
2,14,20,24); The light that irradiates the object to be observed by relatively shading the optical axes of the light of the first polarization direction and the light of the second polarization direction whose phase difference is adjusted by this. Separation means (14,2
4); Light combining means (20, 2) for combining the light of the first polarization direction and the light of the second polarization direction transmitted or reflected by the object.
4); Filter means (22) for respectively obtaining coherent polarization components in the first and second different directions from the light supplied from the light combining means; the first and second directions obtained thereby. First based on the coherent polarization components of
And image pickup means (70, 74) for obtaining a second image; arithmetic means (76, 78) for adjusting the intensity of the first and second images obtained thereby to obtain a differential interference image. It is characterized by that.

Another invention is an illumination means (100) for supplying light for illuminating an object; out of the light supplied by this means, the phase difference between the light in the first and second polarization directions orthogonal to each other is adjusted. Phase difference adjusting means (10, 12, 14, 20, 24) for adjusting the phase difference of the light of the first polarization direction and the light of the second polarization direction relative to each other. And a light separating means (14, 24) for irradiating the object to be observed; a light combining means (20, 24) for combining the light of the first polarization direction and the light of the second polarization direction transmitted or reflected by the object. A filter means (110) for obtaining coherent polarization components from the light supplied from the photosynthesis means; an image pickup means (114) for obtaining an image based on the coherent polarization components thus obtained;
Image storage means (116) for storing the image obtained by the above; the first image stored when adjusted to the first phase by the phase difference adjusting means, and the second image adjusted to the second phase The second image stored at this time is provided with a calculating means (66) for performing intensity adjustment to obtain a differential interference image.

According to a main mode, the phase difference adjusting means includes a rotatable polarizer (10) and a quarter wave plate (1).
2) A liquid crystal whose refractive index is controllable by a voltage, and means (64) for moving at least one of the light separating means and the light combining means in a direction crossing the optical axis.

At least one of the light separating means and the light synthesizing means is constituted by, for example, a birefringent prism (14, 20, 24). The filter means is composed of, for example, a polarization beam splitter (22) or an analyzer (110). The illumination means is, for example, a laser light source (50),
It includes a scanning means (54) for scanning the laser beam outputted therefrom. The scanning means is arranged, for example, in the optical path of light transmitted or reflected by the object, and pinholes (90, 92) are provided at positions conjugate with the object point. Further, the arithmetic means is a signal ratio adjusting means (76) for adjusting a signal intensity ratio of the first and second images; a difference signal for obtaining a difference signal of the two signals adjusted to have a predetermined intensity ratio by the signal ratio adjusting means (76). Calculation means (7
8); is provided. The signal ratio adjusting means is
The intensity ratio adjustment corresponding to the additional phase difference of the rays other than the principal ray is performed.

The main aspects of the present invention include the following. (1) An object observation device for observing a light-transmissive object, wherein a laser light source that emits a first light beam and two linearly polarized light beams having a first polarization state and a second polarization state And a light beam splitting means for splitting the light beam into light beams traveling in different directions, and collecting the two linearly polarized light beams to form two beam spots in the first region in the light transmissive object. A condenser lens, a scanning means for two-dimensionally scanning the two beam spots in the first region, an objective lens capable of condensing light rays generated in the transmission direction from the light-transmissive object, and the light transmission Ray combining means for transmitting the two linearly polarized light rays that have been transmitted through a transparent object and are refracted by the objective lens into a second light ray having a third polarization state, and a first light ray combining means for the second light ray. Two linear polarizations of polarization state and second polarization state The phase difference adjusting means for adjusting the first phase difference which is the relative phase difference amount of the light ray, and the second light ray, two linearly polarized light rays of the fourth polarization state and the fifth polarization state. To separate the polarized light separation means, a first photoelectric conversion element photoelectrically converting the light beam of the fourth polarization state, a second photoelectric conversion element photoelectrically converting the light beam of the fifth polarization state, A first photoelectric conversion element, a signal ratio adjusting means for adjusting a ratio of signal strengths of photoelectric conversion signals of each of the second photoelectric conversion elements, and two of which have a predetermined intensity ratio by the signal ratio adjusting means. An object observation apparatus having a difference signal output means for outputting a difference signal which is a signal difference.

(2) An object observation device for observing a light-reflecting object, wherein a laser light source for emitting a first light beam,
An objective lens arranged along an optical axis capable of condensing a light beam generated in the reflection direction from the light-reflecting object, and the first light beam to the objective lens arranged along the optical axis. A first half-mirror for reflecting the first half-mirror and a first light ray reflected by the first half-mirror in two directions of linearly polarized light having a first polarization state and a second polarization state, which are different from each other. The objective lens collects the two linearly polarized light rays to form two beam spots in a first region in a light-reflecting object, The two linearly polarized light beams of the first polarization state and the second polarization state, which travel in different directions, pass through the objective lens, collide with the light reflective object, are reflected, and are again reflected. It is incident on the objective lens and is re-entered by the beam separating means. The light beam is incident, becomes a second light beam having a third polarization state, exits the light beam separating means, is transmitted through the first half mirror, and further, the two beam spots are reflected by the second beam spot in the first region. A scanning means for dimensionally scanning, a phase difference adjusting means for adjusting a first phase difference which is a relative phase difference amount of two linearly polarized light rays of the first polarization state and the second polarization state, and A first polarization separation means for separating the second light ray into two linearly polarized light rays having a fourth polarization state and a fifth polarization state, and a first polarization separation means for photoelectrically converting the light ray having the fourth polarization state. A photoelectric conversion element, a second photoelectric conversion element that photoelectrically converts the light beam in the fifth polarization state, the first photoelectric conversion element, and the signal strength of each photoelectric conversion signal of the second photoelectric conversion element. Signal ratio adjusting means for adjusting the ratio of the Object observation apparatus characterized by having a difference signal output means for outputting a difference signal which is the difference between the two signals becomes.

(3) The object observation apparatus according to (1) or (2), wherein the first phase difference is an integral multiple of π. (4) The fourth polarization state is linearly polarized light, and is an integral multiple of 90 ° with respect to the plane of polarization of the linearly polarized light in the first polarization state (1) to (3) The object observation device according to any one of 1. (5) The fifth polarization state is linearly polarized light, and is orthogonal to the plane of polarization of the linearly polarized light of the fourth polarization state (1) to (4) Object observation device.

(6) An object observation device for observing a light-transmissive object, wherein a light source for emitting a first light beam and a first light beam from the light source are linearly polarized light parallel to the polarizer angle. A rotatable polarizer, and a light beam separating means for separating the first light beam transmitted through the polarizer into two linearly polarized light beams having a first polarization state and a second polarization state and traveling in mutually different directions, A condenser lens that collects the two linearly polarized light rays and collectively transmits and illuminates the first region inside the light transmissive object, and a light ray that is generated in the transmission direction from the light transmissive object. An objective lens capable of emitting light,
A light beam combining means for transmitting the two linearly polarized light beams that have been transmitted through the light transmissive object and refracted by the objective lens into a second light beam having a third polarization state, and the first polarization state. And a phase difference adjusting means for adjusting the relative phase difference amount of the two linearly polarized light rays of the second polarization state, the second light beam of the third polarization state into a light beam of the fourth polarization state. An analyzer, an image pickup device for photoelectrically converting the light beam in the fourth polarization state, and an image storage means for storing the image signal output from the image pickup device in a readable state,
In the case of images of the same object, when the relative phase difference amount of the two linearly polarized light rays of the first polarization state and the second polarization state by the phase difference adjusting means is the first phase difference A first image and a second image in the case of a second phase difference are stored in the image storage means, and are images of the same object from the image storage means, and the first image by the phase difference adjustment means. Relative phase difference amount of the two linearly polarized light of the polarization state and the second polarization state, the first image in the case of the first phase difference and the second image in the case of the second phase difference Further, the signal ratio adjusting means for adjusting the signal intensity ratio of the first image and the second image, and the difference between the two image signals having a predetermined intensity ratio by the signal ratio adjusting means. An object observation apparatus having a difference image output means for outputting a certain difference image.

(7) An object observing device for observing a light-reflective object, the light source emitting a first light beam and light capable of condensing a light beam generated in the reflection direction from the light-reflective object. An objective lens disposed along an axis, a rotatable polarizer that makes the first light beam linearly polarized parallel to a polarizer angle, and the first light beam that is arranged along the optical axis. The half mirror that reflects toward the objective lens and the first light beam reflected by the half mirror are converted into two linearly polarized light beams of a first polarization state and a second polarization state that travel in different directions. Rays having a ray splitting means for splitting, the rays of the two linearly polarized light of the first polarization state and the second polarization state, which travel in different directions, pass through the objective lens and Hit an object,
It is reflected, again enters the objective lens, enters the light beam separating means again, becomes a second light beam of a third polarization state, exits the light beam separating means, and passes through the half mirror,
Further, a phase difference adjusting means for adjusting the relative amount of phase difference between the two linearly polarized light beams of the first polarization state and the second polarization state, and the second light beam of the third polarization state, An analyzer for converting the light into a light beam in a fourth polarization state, an image sensor for photoelectrically converting the light beam in the fourth polarization state, and an image storage means for storing the image signal output from the image sensor in a readable state. In the images of the same object, the relative phase difference amount of the two linearly polarized light beams of the first polarization state and the second polarization state by the phase difference adjusting means is the first position. The first image in the case of a phase difference and the second image in the case of a second phase difference are stored in the image storage means, and the images of the same object from the image storage means are stored by the phase difference adjusting means. Of the two linearly polarized rays of the first polarization state and the second polarization state The relative phase difference amount is the first image in the case of the first phase difference and the second image in the case of the second phase difference are read out, and further the signals of the first image and the second image. An object comprising: a signal ratio adjusting means for adjusting a ratio of intensities; and a difference image output means for outputting a difference image which is a difference between two image signals having a predetermined intensity ratio by the signal ratio adjusting means. Observation device.

(8) In the above (6) or (7), the first phase difference and the second phase difference are odd multiples of π.
The object observation device described. (9) The object observation device according to any one of (1) to (8), wherein one or both of the light beam splitting unit and the light beam combining unit is a birefringent prism. (10) The object according to any one of (1) to (9), wherein the phase difference adjusting means is a combination of a quarter-wave plate and a polarizer rotatable about an optical axis. Observation device. (11) The phase difference adjusting means can adjust the phase difference by moving one or both of the light beam separating means and the light beam combining means in a direction crossing the optical axis. The object observation device according to any one of 1) to (9).

(12) The object observation device according to any one of (1) to (11), wherein the polarized light separating means is a polarized beam splitter.

According to the present invention, of the light supplied from the illuminating means, the phase difference between the light in the first and second polarization directions orthogonal to each other is adjusted by the phase difference adjusting means. The adjusted optical axes of the light of the first polarization direction and the light of the second polarization direction are applied to the object to be observed while being relatively sheared by the light separating means. The light of the first polarization direction and the light of the second polarization direction transmitted or reflected by the object are combined by the light combining means, and the coherent polarization components in the first and second different directions are extracted by the filter means. Be done.

The image pickup means obtains the first and second images based on the obtained coherent polarization components in the first and second directions. The first and second images thus obtained are subjected to intensity adjustment by the calculating means to obtain a differential interference image.
This removes the phase rotation that remains in the optical system,
A differential interference contrast image with ideal contrast can be observed with any aperture size of the illumination system.

The above and other objects, features and advantages of the present invention will be apparent from the following detailed description and the accompanying drawings.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to Examples. The object observation device according to the present invention is suitable for, for example, a differential interference microscope, particularly a laser scanning microscope.

[0020]

[First Basic Form] First, a first basic form of the embodiment will be described with reference to FIG. It should be noted that, for each element in the figure, the Cartesian coordinates (X1, Y1) to
(X4, Y4) are set so as to be orthogonal to the optical axis AX and have the same azimuth. Similarly, the Cartesian coordinates (X
5 and Y5) are set so as to be orthogonal to the reflection side optical axis AX1 obtained by folding the optical axis AX and have the same azimuth as the orthogonal coordinates (X1, Y1) to (X4, Y4). That is, the coordinates are set so that the coordinate axes overlap when viewed from the illumination side. Hereinafter, those directions will be simply expressed as (x, y).

A light ray i00 for illumination emitted from a light source (not shown) is rotatable by a polarizer 10 and a quarter-wave plate 1
2. The light passes through the Nomarski prism 14 in order and enters the condenser lens 16. The polarizer 10 is a polarization direction of the transmitted light with an azimuth angle θ1 with respect to the x-axis, and this angle θ1 can be changed by rotating the polarizer 10. The quarter-wave plate 12 has a fast axis ne as an optical axis and a slow axis no orthogonal to the optical axis ne. The azimuth angle of the fast axis ne is 45 ° with respect to the x axis, and the azimuth angle of the slow axis no is x.
It is set at -45 ° to the axis. Of the incident light
The linear polarization component of the plane of polarization parallel to the slow axis no is fast axis ne
1/4 wavelength (9
0 °) phase delay occurs. The rays that have passed through the quarter-wave plate 12 are rays EO and OE that are sheared by 2σ on the (X3, Y3) coordinate plane that is the object plane S by the Nomarski prism 14 and the condenser lens 16. Ray EO
Is a linearly polarized light with a plane of polarization parallel to the Y3 axis, and the ray OE
Is a linearly polarized light having a plane of polarization parallel to the X3 axis.

For example, the azimuth angle θ1 of the polarizer 10 is 1
When it coincides with the fast axis ne of the / 4 wave plate 12, the polarized light in the fast axis ne direction of the light ray i00 is transmitted as it is. The azimuth angle θ1 of the polarizer 10 is a quarter wave plate 12
Of the ray i00, the polarized light in the slow axis no direction of the ray i00 is 90% by the ¼ wavelength plate 12.
Transmitted after phase delay. In this way, the Polarizer 1
By the action of the 0 and 1/4 wavelength plates 12, the phase difference between the two linearly polarized light components EO and OE orthogonal to each other can be arbitrarily adjusted. Specifically, the relative phase difference α between the light rays EO and OE can be changed as shown in Expression (2) described below by changing the polarizer angle θ1.

Next, the light rays transmitted through the object on the object surface S are again combined into one light ray by the action of the objective lens 18 and the Nomarski prism 20. When the object is a perfect parallel plate having no phase difference, the Nomarski prism is adjusted so that the phase difference given between the illumination lights EO and OE between the two Nomarski prisms 14 and 20 is an integral multiple of 2π. The positions of 14 and 20 are adjusted in the direction crossing the optical axis AX.

The Nomarski prism 20 again sets 1
The combined light rays enter the polarization beam splitter 22. Of the light rays reaching the polarization beam splitter 22, x
The component of the plane of polarization parallel to the azimuth of θ2 = 45 ° with respect to the axis is transmitted and becomes the ray i1, and the component of the plane of polarization parallel to the azimuth of θ3 = 135 ° with respect to the x-axis is reflected to the ray i2. , Along the optical axis AX1. As a result, the amplitude interference components are extracted from the illumination lights OE and EO.
Then, as will be described later, a differential interference image is obtained from the difference between the two interference components.

Next, assuming that the influence of the OTF of the lens is not taken into consideration, the intensity of the differential interference image by the light rays i1 and i2 at the step position of the object such as the reticle is obtained. In addition,
Since the step of the object to be observed is basically a one-dimensional structure, the following analysis will be performed in all one-dimensional including the optical system. Although the actual optical system is two-dimensional, in the following discussion, one-dimensional assumption is perfectly acceptable. Further, in the following description, the intensity of the point image on the image plane of the image-forming differential interference microscope will be described. However, except that the depth of focus also differs depending on the differential interference microscope of the laser scanning optical system, the image-forming differential If the σ value of the illumination system in the interference microscope is appropriately set, the same differential interference contrast image can be obtained, so that it is basically applicable to the scanning type.

Further, this embodiment has a structure of a laser scanning microscope which follows the optical system of the differential interference microscope. Therefore, the Nomarski prism 14 which is the light beam separating means
Amplitude and phase information of the two beams on the object generated by the above are stored in one light beam generated by the interference of the two light waves in the Nomarski prism 20, which is the light beam combining means. Therefore, the differential interference contrast image can be obtained also by a photoelectric conversion element installed at a position other than the image plane, for example, near the pupil conjugate plane. The image pickup means (for example, a photoelectric conversion element) for obtaining the interference image may be installed at any position after the light beam combining means.

One image point obtained by the differential interference microscope shown in FIG. 1 corresponds to two object points which are separated from each other by the interval 2σ due to the shear of the Nomarski prism 14. If these are O (+ δ) and O (−δ) and the relative phase difference between them is Ψ, the following equation (1) is obtained.
The expression (1) is a complex representation, where a and b represent amplitude components and exp (jΨ) represent phase components. “J” is an imaginary unit.

[0028]

[Equation 1]

Assuming that the phase difference added by the differential interference microscope is α1 and α2, the relationship with the azimuth angle θ1 of the polarizer 10 is given by the following equation (2). And the ray i1,
Intensity Ii of the interference image in an ideal optical system corresponding to i2
1 (α1) and Ii2 (α2) are expressed by the following equation (3) with C as a constant.

[0030]

[Equation 2]

(Equation 3)

Here, the azimuth angle θ1 of the polarizer 10 = −
Assuming π / 4, the intensity Ii1 (α of the interference image by the ideal optical system on the two image planes corresponding to the rays i1 and i2
1) and Ii2 (α2) are expressed by the following equations (4) and (5), respectively.

[0032]

(Equation 4)

(Equation 5)

From the equation (4), when there is no object,
Since a = b and Ψ = 0, the intensity Ii1 (α1) of the interference image by the ideal optical system becomes zero. However, an additional phase difference due to the objective lens 18 and the like remains in the rays other than the chief ray. For example, in a transillumination type differential interference microscope,
By reducing the aperture stop of the illumination system when there is no object, only the chief rays are made to interfere, and the interference image intensity Ii1 (α1) in the equation (4) can be made almost zero. However, as the aperture stop is opened, the phenomenon that the background gradually becomes brighter can be observed experimentally. This is due to the residual residual phase difference described above.

Here, the additional phase difference of the remaining rays other than the principal ray is determined by the phase object O0 which does not depend on the position of the object.
And then define as in the following equation (6). In this equation, "a0" represents the amplitude of the illumination light, and Φ is the average value of the additional phase difference of the rays other than the principal ray. Note that "j"
Is an imaginary unit as in the equation (1).

[0035]

(Equation 6)

The additional phase difference of the rays other than the chief ray is not actually a single value but varies depending on the position on the pupil plane of the objective lens 18 as it passes through the pupil plane.
Therefore, even if the phase difference is adjusted by the Nomarski prism 20 or the like, the intensity Ii1 (α1) (equation (4)) when there is no object in the state where the aperture stop is opened cannot be made completely zero. However, since the additional phase difference of rays other than the principal ray is generally a small value, it may be represented by an average value. Therefore, the intensity when observing the phase object O0 with an ideal optical system, that is, the background intensities Ii1 (O0, α1) and Ii2 (O0, α when the aperture stop is opened.
2) is obtained by the following equations (7) and (8). They are,
It is obtained by substituting the amplitude and phase of the equation (6) into the equations (4) and (5).

[0037]

(Equation 7)

(Equation 8)

Next, the differential output S0 of the background intensity is defined by the following equation (9), where k is a constant. By substituting the equations (7) and (8) into the equation (9), the following equation (10) is obtained. From this equation, if the differential output of background intensity S0 = 0, the background can be made completely zero. At this time
When the relationship between cosΦ and the constant k is obtained, the following expression (11) is obtained. In this way, it is possible to obtain, as an image, an effect equivalent to that when the additional phase difference of light rays other than the principal ray, in other words, the rotation of the phase remaining in the optical system is eliminated.

[0039]

[Equation 9]

(Equation 10)

[Equation 11]

Next, when observing the object represented by the above formula (1) with the aperture stop open, if the object considering the average value Φ of the additional phase difference is expressed as Or, the following ( It becomes like the formula 12). The differential signal Sr corresponding to the equation (9) at this time is represented by the following equation (13) by the same constant k as in the equation (9).

[0041]

(Equation 12)

(Equation 13)

On the other hand, by substituting the equation (12) into the equations (4) and (5), the following equations (14) and (15) are obtained. By substituting these into the equation (13), the following equation (16) is obtained. The approximation of the equation (16) is accurately established, since the average value Φ of the additional phase difference due to the objective lens 18 or the like is usually about 1 to 2 °. Therefore, according to the above observation method, the rotation of the phase remaining in the optical system is satisfactorily eliminated, and even when the aperture stop is opened, (4)
An image equivalent to the ideal interference image Ii1 (α1) of the optical system shown by the formula can be obtained.

[0043]

[Equation 14]

(Equation 15)

[0044]

(Equation 16)

[0045]

[Second Basic Form] Next, the second basic form will be described with reference to FIG. In this mode, the above-described first mode is implemented by an epi-illumination method. In this epi-illumination method, the condenser lens 16
And the objective lens 18 are shared by the objective lens 26, and the Nomarski prisms 14 and 20 also become one Nomarski prism 24. Also, the reflected light from the object is
It is extracted by the half mirror 28 in a direction different from the optical axis AX0 of the illumination optical system.

More specifically, the light ray i00 is transmitted by the polarizer 10
Is linearly polarized in the plane of polarization having an azimuth angle θ1 with respect to the x (X1) axis, passes through the quarter-wave plate 12, and undergoes phase modulation. Then, it advances along the optical axis AX0 and enters the half mirror 28. The light beam reflected by the half mirror 28 travels along the optical axis AX and passes through the Nomarski prism 24 and the objective lens 26 in order. By the actions of the Nomarski prism 24 and the objective lens 26, the illumination light EO, OE which is 2δ sheared on the object plane S which is the (X3, Y3) coordinate plane is obtained. Illumination light EO is Y3
The linearly polarized light having the plane of polarization parallel to the axis and the illumination light OE are the linearly polarized light having the plane of polarization parallel to the X3 axis. Similarly, the illumination light EO, O
The relative phase difference α between E is the azimuth angle θ of the polarizer 10.
It can be changed by changing 1 (see the above formula (2)).

The illumination light reflected by the object on the object surface S is again combined into one light beam by the action of the objective lens 26 and the Nomarski prism 24. When the object is a perfect mirror surface having no phase difference, the phase difference given between the illumination light EO and OE between the object and the Nomarski prism 24 is an integer multiple of 2π so that the Nomarski prism 24 has a phase difference. The position is adjusted across the optical axis AX. The rays of light that have been combined again by the Nomarski prism 24 enter the half mirror 28. Then, the light rays that have passed through this enter the polarization beam splitter 22. The subsequent operation is similar to that of the above-described first embodiment.

[0048]

First Embodiment Next, a first embodiment of the present invention will be described with reference to FIG. The basic structure is the same as that shown in FIG. In FIG. 3, the light beam emitted from the laser light source 50 is linearly polarized light having an azimuth of −45 ° when the Y axis is positive with respect to the X axis. This light beam becomes parallel light by the beam expander 52, is reflected by the reflection mirror 53, and enters the XY scanning unit 54. The light beam is spatially scanned and deflected by the XY scanning unit 54. The light beam after scanning is the first
After passing through the relay lens 56 and the second relay lens 58, the light enters the ¼ wavelength plate 12 and the Nomarski prism 14 located near the pupil position of the condenser lens 16. After passing through the Nomarski prism 14, the two linearly polarized lights whose polarization directions are orthogonal to each other are separated into light beams having a slight relative angle, and are incident on the condenser lens 16. Each light beam refracted by the condenser lens 16 forms a beam spot on the object 62 on the glass slide 60.

On the object 62, the Nomarski prism 1
By the action of 4, the two spots slightly displaced from each other are formed close to each other. These spots two-dimensionally scan the object 62 by the action of the XY scanning unit 54. The XY scanning unit 54 is driven via the synchronizing device 80 and the actuator 88.

The light beam transmitted through the object 62 is the objective lens 1
It is incident on 8 to be refracted and is combined into one parallel light velocity by the Nomarski prism 20 located near the pupil position of the objective lens 18. The combined light rays enter the polarization beam splitter 22. The light ray i1 transmitted through the polarization beam splitter 22 becomes linearly polarized light having an azimuth of 45 ° with respect to the x-axis. Light ray i reflected by the polarization beam splitter 22
2 is linearly polarized light with an azimuth of 135 ° with respect to the x-axis.

With respect to the azimuth angle with respect to the x-axis centering on the optical axis AX of each of the above-mentioned optical elements, assuming that the y-axis direction is positive, the optical axis of the quarter-wave plate 12 is + 45 °, the Nomarski prism 14, The direction of the wedge of 20 is 0 °, and the analyzer angle (θ2) of the polarization beam splitter 22 is + 45 °. Note that these are the same as those in FIG.

Further, as described above, the slide glass 6
If there is nothing that causes a phase difference between two beams on 0 or the object 62, for example, in the case of a parallel plate, the two Nomarski prisms 14, 20
The position of the Nomarski prism 14 is adjusted by the actuator 64 in the direction crossing the optical axis AX so that the initial value of the phase difference given to the two light beams between the two is an integral multiple of 2π. The actuator 64 is controlled by the computer 66.

The light ray i1 transmitted through the polarization beam splitter 22 is refracted by the lens 68 and photoelectrically converted by the photoelectric conversion element 70 composed of CCD or the like to output a video signal. The light ray i2 reflected by the polarization beam splitter 22 is refracted by the lens 72 and photoelectrically converted by the photoelectric conversion element 74 to output a video signal.
The video signal output from the photoelectric conversion element 74 is a light ray i2.
Which is a photoelectric conversion signal relating to an attenuator (multiplier) 76
Thus, the coefficient k is multiplied according to the equation (11). The coefficient k may be experimentally set such that the differential signal when the object does not exist is zero.

A pair of video signals output from the photoelectric conversion element 70 and the attenuator 76 are input to the differential amplifier 78, and the differential amplifier 78 outputs the differential signals of both. This differential signal corresponds to Sr shown in the equation (13) or (16). The differential signal Sr is displayed on the image display unit 82 via the synchronizer 80. The synchronization device 80 captures signals in synchronization with the scanning of the XY scanning unit 54.

On the other hand, in the computer 66, the differential signal S
r is D / A converted and stored as image data as required. The observer can display the data accumulated through the interface 84 on the image display unit 82 and can perform image calculation based on a known image processing technique. In this embodiment, there is no problem even if the quarter wave plate 12 is not provided.

[0056]

Second Embodiment Next, a second embodiment will be described with reference to FIG. The second embodiment is an example in which the first embodiment is configured by the epi-illumination method, and corresponds to the second basic form. In the figure, the light beam emitted from the laser light source 50 becomes parallel light by the beam expander 52, and is further spatially scanned and deflected by the XY scanning unit 54. The light beam after scanning passes through the first relay lens 56 and the second relay lens 58, and then passes through the quarter-wave plate 12 located in the vicinity of the plane conjugate with the pupil plane of the objective lens 26. 1/4
The light ray that has passed through the wave plate 12 is refracted by the pupil projection lens 86, reflected by the half mirror 28 in the direction along the optical axis AX, and enters the Nomarski prism 34. After passing through the Nomarski prism 24, the two linearly polarized lights whose polarization directions are orthogonal to each other are separated into light rays having a slight relative angle and proceed, and then enter the objective lens 26. Each light beam refracted by the objective lens 26 is
A beam spot is formed on the object 62 on the slide glass 60.

On the object 62, the Nomarski prism 2
By the action of 4, the two spots slightly displaced from each other are formed close to each other. These spots two-dimensionally scan the object 62 by the action of the XY scanning unit 54.

The light beam reflected by the object 62 again enters the objective lens 26 and is refracted, passes through the Nomarski prism 24 located near the pupil position of the objective lens 26 again, and enters the half mirror 28. A part of the total amplitude is transmitted through the half mirror 28 and the polarization beam splitter 2
Reach 2. The subsequent operation is similar to that of the first embodiment described above, and the differential signal Sr is obtained in the differential amplifier 78. Note that, also in this embodiment, the quarter-wave plate 12 is
There is no problem at all.

[0059]

Third Embodiment Next, a third embodiment will be described with reference to FIG. The third embodiment is almost the same as the second embodiment, but the position of the XY scanning unit 54 is different in the present embodiment. That is, the reflected light from the object 62 is arranged so as to pass through the XY scanning unit 54 again, which is the optical configuration of a so-called confocal microscope.

Therefore, the light beam incident on the photoelectric conversion elements 70 and 74 is always stationary regardless of the two-dimensional scanning of the laser beam on the object 62. Therefore, the lens 68,
The light is condensed by 72, and pinholes 90 and 92 are provided at the condensing point (a point conjugate with the object point) to reduce unnecessary light such as flare. Of course, also in the present embodiment, the quarter wave plate 12 may not be provided as in the second embodiment.

[0061]

Fourth Embodiment Next, a fourth embodiment will be described with reference to FIG. Although the above-mentioned embodiments are all examples of scanning type in which a laser beam is scanned, the following examples are examples of imaging type, and this example has a transmissive configuration corresponding to FIG. There is.

In FIG. 6, a mercury lamp is used as the light source 100, and the optimum wavelength of the light beam emitted from this is selected by the interference filter 102. The light transmitted through the interference filter 102 is collected by the collector lens 10
4, first relay lens 106, second relay lens 108
Through the polarizer 10, the quarter-wave plate 12, and the Nomarski prism 14 located near the pupil position of the condenser lens 12. As a result, the two linearly polarized light beams whose polarization directions are orthogonal to each other are separated into light beams having a slight relative angle to travel, and the condenser lens 12
The object 62 on the glass slide 60 is refracted by
Illuminate through.

The light beam transmitted through the object 62 is the objective lens 18
Is incident on and refracted, is transmitted through the Nomarski prism 20 located near the pupil position of the objective lens 18, and is incident on the analyzer 110. Some rays are analyzer 1
The light passes through 10 and becomes a linearly polarized light beam having a polarization plane parallel to the analyzer angle. As light rays, i1 and i2 are obtained according to the azimuth angle of the polarizer 10 as described later. The analyzer angle is similar to the analyzer angle θ2 of the polarization beam splitter 22 described above. The light beam transmitted through the analyzer 110 is refracted by the lens 112, and forms an interference image on an image plane conjugate with the object plane of the objective lens 18. Then, similarly to the above-described embodiment, photoelectric conversion is performed by the two-dimensional image pickup device 114 in which the light detection surface is located on the image plane, and a video signal is output from the two-dimensional image pickup device 114.

The two image signals obtained corresponding to the two polariser azimuths are A / D converted in the image storage section 116 and stored as two image data. That is,
First, the azimuth angle θ1 of the polarizer 10 is − with respect to the x direction.
The intensity image corresponding to the light ray i1 is set to π / 4 by the actuator 118, and the intensity image corresponding to the light ray i1 is captured by the two-dimensional image sensor 114 and stored in the image storage unit 116. next,
The azimuth angle θ1 of the polarizer 10 is + π / 4 with respect to the x direction.
Is set by the actuator 118, the intensity image corresponding to the light ray i2 is captured by the two-dimensional image sensor 114, and the intensity image is stored in the image storage unit 116.

In the computer 66, the image storage section 116
Of the two image data stored in the image data, the intensity of the image by the ray i2 is multiplied by the coefficient k according to the equation (11), and then the image by the ray i1 is subtracted by the equations (13) and (16). The image data is calculated, and this is the image storage unit 11.
It is accumulated in 6. The difference image data is D / A converted and output to the display unit 82 for display. It should be noted that the observer can select the display of the accumulated data or other image calculation through the interface 84, as in the above embodiment.

The quarter-wave plate 12 in this embodiment is used.
Similarly, it may not be necessary. However, in this case, an arbitrary phase difference cannot be given to the sheared rays OE and EO by the rotation of the polarizer 10.

[0067]

Fifth Embodiment Next, a fifth embodiment will be described with reference to FIG. The fifth embodiment is an example in which the fourth embodiment is configured by the lost person lighting method. The light beam emitted from the light source 100 passes through the collector lens 104, the first relay lens 106, the second relay lens 108, the polarizer 10 and the quarter wavelength plate 12 in order after wavelength selection by the interference filter 102, and pupil projection The light is refracted by the lens 86 and enters the half mirror 28. Optical axis A by half mirror 28
The rays reflected along X are the Nomarski prism 2
Pass 4. As a result, the light beams whose polarization directions are perpendicular to each other are separated and travel, and are refracted by the objective lens 26 to epi-illuminate the object 62 on the slide glass 60.

The light beam reflected by the object 62 is the objective lens 2
6, the Nomarski prism 24, and the half mirror 28 are sequentially transmitted to enter the analyzer 110. The subsequent operation is the same as that of the fourth embodiment.

[0069]

Other Embodiments The present invention has many embodiments and can be variously modified based on the above disclosure. For example, the following is also included. (1) In the above embodiment, a two-dimensional image pickup device such as a CCD was used, but any image pickup means may be used. In addition, a relay optical system or a mirror may be used if necessary. As the light source, various ones other than the mercury lamp may be used. The shear amounts of the two beams may be variable.

(2) In the above-described embodiment, the present invention is mainly applied to a microscope, but the present invention is applicable to general observation of objects. For example, it is effective for measuring the level difference of an object, inspecting a defect of a magnetic head, a wafer, a reticle, etc., and measuring the position in consideration of the surface shape of the object.

(3) In the above embodiment, the quarter-wave plate and the rotatable polarizer were used as the phase difference adjusting mechanism, but the same effect can be achieved by moving the Nomarski prism in the direction transverse to the optical axis. It is possible. Alternatively, the phase difference may be adjusted using an element such as a liquid crystal having a variable refractive index.

[0072]

As described above, according to the present invention,
Since the light with two polarization directions with adjusted phase differences is sheared and applied to the object and the intensity of the interference image obtained from the combined light is adjusted to obtain the differential interference image, it remains in the optical system. Rotation of the phase to be satisfactorily removed, and the differential contrast image of ideal contrast can be observed with the aperture size of any illumination system. There is an effect that can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view showing a first basic form of an embodiment of the present invention.

FIG. 2 is a perspective view showing a second basic form of the embodiment of the present invention.

FIG. 3 is a diagram showing Embodiment 1 of the present invention.

FIG. 4 is a diagram showing a second embodiment of the present invention.

FIG. 5 is a diagram showing a third embodiment of the present invention.

FIG. 6 is a diagram showing a fourth embodiment of the present invention.

FIG. 7 is a diagram showing a fifth embodiment of the present invention.

[Explanation of symbols]

 10 ... Polarizer 12 ... Quarter wave plate 14, 20, 24 ... Nomarski prism 16 ... Condenser lens 18, 26 ... Objective lens 22 ... Polarization beam splitter (analyzer) 28 ... Half mirror 50 ... Laser light source 52 ... Beam expander 54 ... XY scanning unit 56, 58 ... Relay lens 60 ... Slide glass 62 ... Object 64, 88, 118 ... Actuator 66 ... Computer 68, 72, 112 ... Lens 70, 74, 114 ... Photoelectric conversion element 76 ... Attenuator 78 ... differential amplifier 80 ... synchronization device 82 ... display unit 84 ... interface 86 ... pupil projection lens 90, 92 ... pinhole 100 ... mercury lamp 102 ... interference filter 104 ... collector lens 106, 108 ... relay lens 110 ... analyzer 116 ... image Accumulator

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location G01N 21/88 G01N 21/88 E G02B 21/00 G02B 21/00

Claims (11)

[Claims] 1. Illumination means for supplying light for illuminating an object; first of the lights supplied thereby orthogonal to each other
And a phase difference adjusting means for adjusting the phase difference between the light in the second polarization direction; and the optical axes of the light in the first polarization direction and the light in the second polarization direction, the phase differences of which are adjusted by the phase difference adjusting means. Light separating means for irradiating an object to be observed after shearing; light combining means for combining the light of the first polarization direction and the light of the second polarization direction transmitted or reflected by the object; supplied from the light combiner Filter means for respectively obtaining coherent polarization components in the first and second different directions from the light respectively; first and second based on the coherent polarization components in the first and second directions obtained thereby An object observation apparatus comprising: an image pickup unit for obtaining two images; a calculation unit for adjusting the intensity of the first and second images obtained thereby to obtain a differential interference image. 2. Illuminating means for supplying light for illuminating an object; first of the lights supplied thereby orthogonal to each other
And a phase difference adjusting means for adjusting the phase difference between the light in the second polarization direction; and the optical axes of the light in the first polarization direction and the light in the second polarization direction, the phase differences of which are adjusted by the phase difference adjusting means. Light separating means for irradiating an object to be observed after shearing; light combining means for combining the light of the first polarization direction and the light of the second polarization direction transmitted or reflected by the object; supplied from the light combiner Filter means for respectively obtaining coherent polarization components from light; imaging means for obtaining an image based on the coherent polarization components obtained thereby; image storage means for storing the image thus obtained; The first stored when adjusted to the first phase by the phase difference adjusting means.
Object and the second image stored when adjusted to the second phase, the object observation apparatus comprising: arithmetic means for performing intensity adjustment to obtain a differential interference image. 3. The object observing device according to claim 1, wherein the phase difference adjusting means includes a rotatable polarizer and a quarter-wave plate. 4. The phase difference adjusting means is a liquid crystal whose refractive index can be controlled by a voltage.
Or the object observation device according to 2. 5. The object observation apparatus according to claim 1, wherein the phase difference adjusting unit is a unit that moves at least one of the light separating unit and the light combining unit in a direction crossing an optical axis. . 6. The object observing apparatus according to claim 1, wherein at least one of the light separating means and the light synthesizing means is a birefringent prism. 7. The filter means is a polarization beam splitter or an analyzer, according to claim 1,
The object observation device according to 2, 3, 4, 5 or 6. 8. The object according to claim 1, wherein the illuminating means includes a laser light source and a scanning means for scanning a laser beam output from the laser light source. Observation device. 9. The object observing apparatus according to claim 8, wherein the scanning means is arranged in an optical path of light transmitted or reflected by the object, and a pinhole is provided at a position conjugate with an object point. . 10. The calculation means is a signal ratio adjusting means for adjusting a signal intensity ratio of the first and second images; a difference signal for obtaining a difference signal of two signals adjusted to have a predetermined intensity ratio by the signal ratio adjusting means. 10. The object observing device according to claim 1, 2, 3, 4, 5, 6, 7, 8 or 9, further comprising a computing means. 11. The object observing apparatus according to claim 11, wherein the signal ratio adjusting means adjusts the intensity ratio corresponding to an additional phase difference of light rays other than the chief ray.