Optical: systems and elements – Compound lens system – Microscope
Reexamination Certificate
2000-10-19
2001-08-28
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Compound lens system
Microscope
C359S368000
Reexamination Certificate
active
06282020
ABSTRACT:
The present application claims the benefit of Japanese Patent Application No.
11-299044
which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laser microscope and a confocal laser scanning microscope.
2. Related Background Art
When a sample with a fine structure is to be observed by a microscope, the critical resolution of the microscope can be expressed by the following:
&dgr;=&lgr;/2NA (1).
In this expression, &dgr;represents the resolution, &lgr; represents the wavelength in use, and NA represents the numerical aperture of an objective lens, respectively.
From the above expression (1), it is suffice in order to enhance the resolution, if the wavelength &lgr; is reduced, or the numerical aperture NA of the objective lens is enlarged, or the wavelength &lgr; is reduced while the numerical aperture NA of the objective lens is enlarged.
When a living sample is to be observed, if the living sample receives a light with a wavelength in the ultraviolet range or lower, the sample itself is damaged due to a photochemical reaction, or the like, so that the resolution can be enhanced by using an objective lens of a liquid immersion type having a large numerical aperture NA.
On the other hand, an inorganic sample (for example, a fine structural member such as an IC) is to be observed by means of an objective lens of the liquid immersion type, impurities may attach to the surface of the IC, or the like. In this case, it is highly probable that the microscope can not be used properly. Thus, the resolution is enhanced by irradiation of a light in the ultraviolet range or lower. In this respect, the inorganic sample itself is seldom damaged by the irradiation of a light in the ultraviolet range or lower.
Incidentally, since the scale of a fine structural member such as an IC is recently rapidly diminishing, it is also demanded to further enhance the resolution of a microscope. Though there exists conventionally a microscope employing an X ray or electron beam as a microscope of high resolution, such microscope is to observe the surface of a sample in a vacuum and the operability thereof is not satisfactory, compared with that of an optical microscope. It is therefore required to enhance the resolution by the use of an optical microscope with an excellent operability.
In order to enhance the resolution in an optical microscope, for example, by two times, if selecting the wavelength of the deep ultraviolet range (273 nm), which is a half of that of an e line (the wavelength of 546 nm) as the representative wavelength of a visible light, a design of the objective lens becomes difficult for the following reasons.
That is, the objective lens is often constituted by combining single lenses with each other since the achromatic method by bonding lenses of different glass materials together which is normally employed in designing a conventional objective lens can not be used, because there is no such adhesive as is not changed in quality in the deep ultraviolet region or there is few glass materials having a sufficient transmittance in the deep ultraviolet region.
In this case, when half width half maximum of the wavelength distribution with respect to the central wavelength is not in the order of picometer (pm) or less, a predetermined optical performance can not be obtained. As a result, an image with an excellent resolution can not be obtained.
It is known that a light source employing a mercury lamp or a xenon lamp also emits a light with the wavelength shorter than the ultraviolet region. However, when only a light having a wavelength with half width half maximum in the order of pm or less is taken out by an interference filter to be used as an illumination light, there arises a problem that a required brightness can not be obtained by means of a conventional image pickup tube or CCD which has no sufficient sensitivity in the deep ultraviolet region.
To cope with this problem, a storage time can be prolonged to securely obtain the required brightness or the half width half maximum can be expanded in proportion to the sensitivity. However, in this case, an image acquiring rate may be sacrificed or the optical performance may be deteriorated.
Accordingly, in order to observe an inorganic sample, a light having a wavelength with a sufficiently small half width half maximum is employed.
In the following, a specific example of a microscopic system employing a light in the deep ultraviolet region.
FIG. 4
is a block diagram for showing the constitution of a confocal laser scanning microscopic system.
A confocal laser scanning microscopic system (a confocal laser scanning microscope)
100
comprises a laser light source
101
, a microscope main body
110
, and an optical image system
130
.
The laser light source
101
emits a laser light of the deep ultraviolet region (the wavelength of 200 nm to 300 nm).
The microscope main body
110
comprises a beam expander
112
for enlarging a laser light
101
a
to a light beam
112
a
which has a sufficient size to cover the pupil plane of an objective lens
111
, a beam splitter
114
which does not transmit the laser light, but transmits therethrough a light reflected by a sample
113
, a two-dimensional scanner unit
115
for two-dimensionally scanning the laser light , a relay lens
116
, a collective lens
117
, a pin hole plate
118
which is disposed at a position conjugate to the focal plane of the objective lens
111
and is formed with a pin hole
118
a
for transmitting therethrough only a light collected by the collective lens
117
, and a photo detector
120
for detecting the light transmitted through the pin hole
118
a
so as to convert such light into an electric signal.
The optical image system
130
comprises an image processing unit
131
, a monitor
132
, and the like, for forming an image of the sample
113
on the basis of the electric signal from the photo detector
120
.
Note that the microscope main body
110
is mounted on an anti-vibration table
140
for making up for a high image quality.
An operation of the confocal laser scanning microscopic system having the aforementioned structure will be described below.
The laser light
101
a
emitted from the laser light source
101
is guided onto an optical path by means of reflection mirrors
102
and
103
, is transmitted through the beam expander
112
, then is reflected by the beam splitter
114
. After that, the laser light is two-dimensionally scanned by the two-dimensional scanner unit
115
, and is irradiated as a spot
119
on the focal plane on the sample
113
by means of the relay lens
116
and the objective lens
111
.
The light reflected by the spot
119
goes back on the optical path to the objective lens
111
, the relay lens
116
and then to the two-dimensional scanner unit
115
, so as to pass through the beam splitter
114
.
The light passing through the beam splitter
114
is collected on the pin hole
118
a
by the collective lens
117
, is converted into an electric signal by the photo detector
120
, and is displayed on the optical image system
130
as an image.
Since only the light on the focal plane of the sample
113
passes through the pin hole
118
a
, an unnecessary diffused light is removed by the pin hole
118
a
, so that it is possible to obtain an image with remarkably improved resolution and contrast in the depth direction in the optical image system
130
.
Incidentally, the laser light source
101
is not so small-sized as to be incorporated in the microscope main body
110
and a single mode optical fiber capable of propagating a deep ultraviolet light has not yet been put to practical use, so that the laser light source
101
is mounted on the anti-vibration table
140
together with the microscope main body
110
.
FIG. 5
is a schematic view of a deep ultraviolet laser light source according to the prior art.
The deep ultraviolet laser light source
101
is provided with a laser radiation source (basic laser light generating means)
105
and a lase
Miles & Stockbridge P.C.
Nikon Corporation
Robinson Mark A.
Spyrou Cassandra
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