Optical: systems and elements – Compound lens system – Microscope
Reexamination Certificate
2001-01-24
2002-09-10
Nguyen, Thong (Department: 2872)
Optical: systems and elements
Compound lens system
Microscope
C359S368000, C359S385000, C356S370000, C250S201300
Reexamination Certificate
active
06449087
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims the benefit of Japanese Patent Application No. 2000-013622 which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a microscope which is capable of observing a super fine structure of a specimen, and particularly, to a microscope which is capable of obtaining an image with the maximum contrast by adjusting an aperture stop to the optimal in accordance with the degree of unevenness of the surface of the specimen.
2. Description of the Related Art
When a super fine structure of a specimen is to be observed by a microscope, the resolution &dgr; thereof can be obtained by the following expression (1):
&dgr;=&lgr;/2NA (1),
where &lgr; is the wavelength of an illumination light of the microscope, and NA is the numerical number of the objective lens. As seen from the expression (1), in order to improve the resolution &dgr; of the microscope, it is required to reduce the wavelength &lgr; of the illumination light, or to enlarge the numerical aperture NA of the objective lens.
When an object to be observed is a living specimen such as a cell, if the wavelength &lgr; of the illumination light is reduced to be below the ultraviolet spectral range, the living specimen itself is damaged due to a photochemical reaction, or the like. For this reason, it is not advantageous to reduce the wavelength &lgr; of the illumination light but instead the resolution &dgr; can be enhanced by enlarging the numerical aperture NA of the objective lens.
On the other hand, if an object to be observed is an inorganic substance such as a material and the resolution &dgr; is required to be greatly enhanced, the numerical aperture NA of the objective lens is enlarged and the wavelength of the illumination light is reduced, at the same time.
For instance, in the field in which a semiconductor wafer or the like is to be observed, the scale of a fine structure, typically of an integrated circuit, is gradually reducing. Thus, a repeating periodic structure of the fine structure called a line-and-space in a semiconductor process can reach a range below 0.25 &mgr;m.
Currently, in order to observe such a fine structure, a microscope using deep ultraviolet rays having the wavelength &lgr; of 300 nm or less as the illumination light is used. For instance, a laser continuously emitting deep ultraviolet rays having the wavelength &lgr; of 266 nm, which are higher harmonics, four times as high as those emitted from Nd-YAG laser, is used as a light source, and an objective lens having a high numerical aperture NA of about 0.9 is employed, so as to obtain a resolution of about 0.10 &mgr;m.
In such a conventional microscope, if a flat specimen having less unevenness on a surface is to be observed, an image with large resolution &dgr; and an excellent contrast can be obtained by reducing the wavelength &lgr; of the illumination light and by maximizing the numerical aperture NA of the objective lens.
However, when the surface of the specimen has an unevenness in height, which is substantially equivalent to a width of the specimen in a plane direction, an image with excellent contrast can be obtained more frequently with a reduced aperture stop, which is not a problem limitedly related to a microscope using deep ultraviolet rays, but becomes particularly conspicuous with a microscope having a high resolution for observing a super fine structure by employing the deep ultraviolet rays.
FIG. 10
illustrates the above case.
FIG. 10
is a cross-sectional view of a specimen
704
with the surface having unevenness (including convex portions and concave portions) in height h substantially equal to the width w thereof in the plane direction. For observing the specimen
704
by a microscope, ambient light rays of a light flux
701
having a high numerical aperture are intercepted by convex portions of a specimen (sample)
704
and fail to reach a focusing surface
703
. Also, the ambient light rays of a light flux
701
are scattered on the surface of the specimen
704
, so as to decrease the contrast of the image.
Accordingly, by adjusting the numerical aperture NA of the light flux
701
with an aperture stop, it is possible to enhance the contrast and the comprehensive quality of the image since, if a light flux
702
, as shown in the drawing, is employed as the illumination light, there is no scattered light on the surface of the convex portions of the specimen
704
.
However, a value for the numerical aperture obtaining the optimal contrast depends on a width w and a height h of the unevenness of the structure of the specimen
704
. For this reason, the observer has to adjust the aperture stop through trial and error for each specimen having different width w and height h, which provides a great burden on the observer.
Moreover, in the case of a microscope having a high resolution and utilizing deep ultraviolet rays, the specimen
704
is damaged by the deep ultraviolet rays so that reducing the time for adjusting the aperture stop to the minimum is necessary.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a microscope of high resolution for observing a super fine structure of a specimen, in which the aperture stop is set to correspond to the height of the unevenness of the surface of the specimen, so as to obtain an image with the maximum contrast in a short period of time.
In order to achieve the above object, according to one aspect of the present invention, there is provided a confocal microscope for observing, by scanning a spot light for illuminating an object to be observed through an objective lens, an image of said object to be observed, which comprises: an aperture stop adjusting the numerical aperture of the objective lens; and a control unit calculating the contrast of the image of the object in accordance with each focal position while varying the focal position of the objective lens along the direction of the optical axis to obtain the height of the unevenness of the surface of the object from a fluctuation of said contrast, thereby setting the aperture stop in such a manner that the depth of focus is substantially equal to the height of said unevenness.
According to the present invention, an image can be acquired with the optimal contrast in a short period of time since the height of the unevenness of the surface of the object is measured and the aperture stop is automatically set to have the depth of focus corresponding to the height of the unevenness of the object by using the sectioning function of the confocal microscope.
In order to achieve the above object, according to another aspect of the present invention, there is provided a wide field microscope for illuminating an object to be observed with uniform light through an objective lens to observe the image of the object, which comprises: an aperture stop adjusting the numerical aperture of the objective lens; and a control unit calculating a contrast of the image of the object while varying the aperture stop and the focal position of the object lens so as to set the aperture stop and the focal position at the positions at which the contrast becomes the maximum.
According to the present invention, since the contrast of the image of the object to be observed is calculated by varying the aperture stop and the focal position so as to automatically set the aperture stop and the focal position at the positions at which the contrast reaches the maximum, an image can be obtained with the optimal contrast: in a short period of time.
In order to achieve the above object, according to still another aspect of the present invention, there is provided a microscope for observing an image to be observed through an objective lens, which comprise: an aperture stop adjusting the numerical aperture of the objective lens; and a control unit receiving the height of the unevenness of the surface of the object so as to set the aperture stop to have the depth of focus substantially equ
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