U.S. patent application number 09/810472 was filed with the patent office on 2001-08-02 for differential interference contrast microscope and microscopic image processing system using the same.
Invention is credited to Kusaka, Kenichi.
Application Number | 20010010591 09/810472 |
Document ID | / |
Family ID | 18173952 |
Filed Date | 2001-08-02 |
United States Patent
Application |
20010010591 |
Kind Code |
A1 |
Kusaka, Kenichi |
August 2, 2001 |
Differential interference contrast microscope and microscopic image
processing system using the same
Abstract
A differential interference contrast microscope including an
illuminating light source 61, a polarizer 62 for converting an
illumination light ray into a linearly polarized light, a polarized
light separating means 63 for dividing the linearly polarized light
ray into two linearly polarized light rays having mutually
orthogonal vibrating directions, an illuminating optical system 64,
65 for projecting the two linearly polarized light rays onto an
object 66 under inspection, a polarized light combining means 69
for combining the two linearly polarized light rays on a same
optical path via an inspecting optical system 67, 68, an analyzer
70 for forming a differential interference contrast image on an
imaging plane 71. The polarized light separating means 63 is
constructed such that an amount of wavefront shear between the two
linearly polarized light rays on the object can be changed, and the
polarized light combining means 69 is arranged between the object
66 and the analyzer 70 at such a position that the two linearly
polarized light rays propagate in parallel with each other and is
constructed such that the two linearly polarized light rays can be
combined with each other in accordance with the shear amount of
wavefront introduced by the polarized light separating means
63.
Inventors: |
Kusaka, Kenichi; (Sagamihara
City, JP) |
Correspondence
Address: |
STEVENS, DAVIS, MILLER & MOSHER, LLP
Suite 850
1615 L Street, N.W.
Washington
DC
20036
US
|
Family ID: |
18173952 |
Appl. No.: |
09/810472 |
Filed: |
March 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09810472 |
Mar 19, 2001 |
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09572666 |
May 16, 2000 |
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6229644 |
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09572666 |
May 16, 2000 |
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08986095 |
Dec 5, 1997 |
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6128127 |
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Current U.S.
Class: |
359/371 ;
359/368; 359/386 |
Current CPC
Class: |
G02B 26/00 20130101;
G02B 27/283 20130101; G01B 9/04 20130101; G02B 21/14 20130101 |
Class at
Publication: |
359/371 ;
359/368; 359/386 |
International
Class: |
G02B 021/00; G02B
021/06 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 5, 1996 |
JP |
8-325,184 |
Claims
What is claimed is:
1. A differential interference contrast microscope of transmission
type comprising: an illumination light source means for emitting an
illumination light ray; a first polarizing means for converting the
illumination light ray emitted from the illumination light source
means into a linearly polarized light ray; a polarized light
separating means for separating the linearly polarized light ray
emanating from the first polarizing means into two linearly
polarized light rays having mutually orthogonal vibrating
directions; an illuminating optical system including a condenser
lens and introducing said two linearly polarized light rays having
mutually orthogonal vibrating directions onto an object under
inspection; an inspecting optical system including an objective
lens and inspecting the object under inspection; a polarized light
combining means for combining said two linearly polarized light
rays transmitted through the object under inspection on a same
optical axis; and a second polarizing means for interfering said
two linearly polarized light rays combined on the same optical axis
with each other to form an interference image; wherein said
polarized light separating means is constructed to change an amount
of wavefront shear of the two linearly polarized light rays with
mutually orthogonal vibrating directions on the object under
inspection, and said polarized light combining means is arranged
between said object under inspection and said second polarizing
means at such a position that said two linearly polarized light
rays propagate in parallel with each other and are combined with
each other on the same optical axis in accordance with a variable
amount of wavefront shear introduced by said polarized light
separating means.
2. A microscope according to claim 1, wherein said inspecting
optical system comprises a first lens group including said
objective lens and a second lens group including an imaging lens,
said first and second lens groups being arranged such that a back
focal point of the first lens group is identical with a front focal
point of the second lens group, and said polarized light combining
means is arranged behind the second lens group.
3. A microscope according to claim 1 or 2, wherein said polarized
light separating means is constructed to separate the linearly
polarized light ray into the two linearly polarized light rays
having mutually orthogonal vibrating directions and is arranged at
such a position that said two linearly polarized light rays having
mutually orthogonal vibrating directions are made incident upon
said object under inspection substantially in parallel with each
other and that an amount of wavefront shear is changed in
cooperation with said polarized light combining means.
4. A microscope according to claim 3, wherein said illuminating
optical system comprises a third lens group and a fourth lens
group, said third and fourth lens groups being arranged such that a
back focal point of the third lens group is identical with a front
focal point of the fourth lens group, and said polarized light
separating means is arranged in front of said third lens group.
5. A microscope according to claim 3, wherein said objective lens
in the imaging optical system is constructed to be removably
inserted into the optical axis and said illuminating optical system
is constructed to change a focal length of the illuminating optical
system in accordance with a back focal point of an objective lens
to be inserted into the optical axis.
6. A microscope according to claim 1 or 2, wherein said polarized
light separating means is constructed to separate the linearly
polarized light ray into the two linearly polarized light rays
which have mutually orthogonal vibrating directions and propagate
in parallel with each other and is arranged at such a position that
said two linearly polarized light rays having mutually orthogonal
vibrating directions are made incident upon said object under
inspection substantially in parallel with each other and that an
amount of wavefront shear is changed in cooperation with said
polarized light combining means.
7. A microscope according to claim 6, wherein said illuminating
optical system comprises a third lens group and a fourth lens
group, said third and fourth lens groups being arranged such that a
back focal point of the third lens group is identical with a front
focal point of the fourth lens group, and said polarized light
separating means is arranged in front of said third lens group.
8. A microscope according to claim 6, wherein said objective lens
in the imaging optical system is constructed to be removably
inserted into the optical axis and said illuminating optical system
is constructed to change a focal length of the illuminating optical
system in accordance with a back focal point of an objective lens
to be inserted into the optical axis.
9. A microscope according to claim 1, wherein said polarized light
separating means includes a variable focus optical system arranged
in said illuminating optical system and is contracted to change an
amount of wavefront shear in cooperation with said polarized light
combining means.
10. A differential interference contrast microscope of transmission
type comprising: an illumination light source means for emitting an
illumination light ray; a first polarizing means for converting the
illumination light ray emitted from the illumination light source
means into a linearly polarized light ray; an illuminating optical
system including a condenser lens and illuminating an object under
inspection with said linearly polarized light ray; an inspecting
optical system including an objective lens and inspecting the
object under inspection; a second polarizing means for interfering
two linearly polarized light rays combined on a same optical axis
with each other to form an interference image; a polarized light
separating and combining means for separating the linearly
polarized light ray emanating from the first polarizing means into
two linearly polarized light rays having mutually orthogonal
vibrating directions and combining two linearly polarized light
rays propagating in parallel with each other on a same optical
axis; and a reflection means for projecting said linearly polarized
light ray emanating from said first polarizing means onto the
object under inspection by means of said polarized light separating
and combining means and illuminating optical system as said two
linearly polarized light rays having mutually orthogonal vibrating
directions and propagating in parallel with each other, and
impinging the two linearly polarized light rays transmitted through
the object under inspection, having mutually orthogonal vibrating
directions and propagating in parallel with each other upon said
polarized light separating and combining means by means of said
imaging optical system.
11. A microscope according to claim 10, wherein said linearly
polarized light ray emanating from said first polarizing means is
made incident upon a first portion of said polarized light
separating and combining means and said two linearly polarized
light rays having mutually orthogonal vibrating directions,
propagating in parallel with each other and transmitted through the
object under inspection is made incident upon a second portion of
the polarized light separating and combining means, said second
portion being different from said first portion.
12. A microscope according to claim 10 or 11, wherein said
objective lens in the imaging optical system is constructed to be
removably inserted into the optical axis and said illuminating
optical system is constructed to change a focal length of the
illuminating optical system in accordance with a back focal point
of an objective lens to be inserted into the optical axis.
13. A differential interference contrast microscope of reflection
type comprising: an illumination light source means for emitting an
illumination light ray; a first polarizing means for converting the
illumination light ray emitted from the illumination light source
means into a linearly polarized light ray; an imaging optical
system including an objective lens for irradiating an object under
inspection and inspecting the object under inspection; a reflection
member for introducing said linearly polarized light ray emanating
from the first polarizing means into said imaging optical system; a
polarized light separating and combining means for separating the
linearly polarized light ray emanating from the first polarizing
means into two linearly polarized light rays having mutually
orthogonal vibrating directions and combining the two linearly
polarized light rays reflected by the object under inspection with
other on a same optical axis; and a second polarizing means for
interfering the two linearly polarized light rays combined on a
same optical axis with each other to form an interference image;
wherein said polarized light separating and combining means is
constructed such that said linearly polarized light ray emanating
from the first polarizing means into the two linearly polarized
light rays having mutually orthogonal vibrating directions and
propagating in parallel with each other and an amount of wavefront
of said two linearly polarized light rays can be changed, and said
polarized light separating and combining means is arranged at such
a position that said two linearly polarized light rays with
mutually orthogonal vibrating directions are made incident upon the
object under inspection in parallel with each other.
14. A microscope according to claim 13, wherein said imaging
optical system comprises a first lens group including said
objective lens and a second lens group including an imaging lens,
said first and second lens groups being arranged such that a back
focal point of the first lens group is identical with a front focal
point of the second lens group, and said polarized light separating
and combining means is arranged behind said second lens group.
15. A microscopic image processing system comprising: a
differential interference contrast microscope, in which an object
under inspection is irradiated with two linearly polarized light
rays having mutually orthogonal vibrating directions and the two
linearly polarized light rays transmitted through or reflected by
the object under inspection are combined on a same optical axis to
form a differential interference contrast image of the object under
inspection on an imaging plane; an electronic image sensing means
for picking-up said differential interference contrast image of the
object under inspection to derive an image signal; and an image
processing means for performing selectively a contrast enhancement
for said image signal supplied from said electronic image sensing
means; wherein an amount of wavefront shear of said two linearly
polarized light rays having mutually orthogonal vibrating
directions on said object under inspection is changed in accordance
with an image processing to be performed by said image processing
means.
16. A system according to claim 15, wherein said differential
interference contrast microscope is formed by the microscope as
claimed in claim 1.
17. A microscopic image processing system comprising: a
differential interference contrast microscope, in which an object
under inspection is irradiated with two linearly polarized light
rays having mutually orthogonal vibrating directions and the two
linearly polarized light rays transmitted through or reflected by
the object under inspection are combined on a same optical axis to
form a differential interference contrast image of the object under
inspection on an imaging plane; an electronic image sensing means
for picking-up said differential interference contrast image of the
object under inspection to derive an image signal; and an image
processing means for processing said image signal supplied from
said electronic image sensing means to measure a phase difference
or step structure of the object under inspection; wherein an amount
of wavefront shear of said two linearly polarized light rays having
mutually orthogonal vibrating directions on said object under
inspection is changed.
18. A system according to claim 17, wherein said differential
interference contrast microscope is formed by the microscope as
claimed in claim 1.
19. A microscopic image processing system comprising: a
differential interference contrast microscope of reflection type,
in which an object under inspection is irradiated with two linearly
polarized light rays having mutually orthogonal vibrating
directions and the two linearly polarized light rays reflected by
the object under inspection are combined on a same optical axis to
form a differential interference contrast image of the object under
inspection on an imaging plane; an electronic image sensing means
for picking-up said differential interference contrast image of the
object under inspection to derive an image signal; and an image
processing means for processing said image signal supplied from
said electronic image sensing means to detect a position of a
depressed and protruded pattern of the object under inspection;
wherein an amount of wavefront shear of said two linearly polarized
light rays having mutually orthogonal vibrating directions on said
object under inspection is changed.
20. A system according to claim 19, wherein said differential
interference contrast microscope is formed by the microscope as
claimed in claim 13.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a differential interference
contrast microscope for use in investigating transparent biological
substances or specimens such as cells and bacteria as well as a
fine pattern of projections and depressions formed on a surface of
a semiconductor substrate, e.g. a silicon wafer. The present
invention also relates to a microscopic image processing system
using such a differential interference contrast microscope.
[0003] 2. Related Art Statement
[0004] FIG. 1 shows a known differential interference contrast
microscope of transmission type. The microscope comprises, in
addition to illumination light source 1, condenser lens 2 and
objective lens 3 which are generally provided in a conventional
optical microscope, polarizer 5 and Nomarski prism 6 which are
arranged in this order between the illumination light source 1 and
the condenser lens 2, and Nomarski prism 7 and analyzer 8 which are
arranged in this order between the objective lens 3 and an imaging
plane 4. In such a differential interference contrast microscope,
after a light ray emitted by the light source 1 is converted by the
polarizer 5 into a linearly polarized light ray, the light ray is
divided by the Nomarski prism 6 into ordinary and extraordinary
light rays. Then, these tow linearly polarized light rays are
projected by the condenser lens 2 onto a specimen or object 9 under
inspection. The ordinary and extraordinary light rays transmitted
through the specimen 9 are combined via the objective lens 3 on a
same light path by means of the Nomarski prism 7. Then, the
combined light rays are made incident upon the analyzer 8 to form a
differential interference contrast image on the imaging plane
4.
[0005] Here, an amount of the separation between the ordinary light
ray and the extraordinary light ray on the specimen 9 under
inspection is called an amount of wavefront shear or a shear amount
of wavefront. It has been known that an amount of wavefront shear
is an important parameter for defining the contrast of the
differential interference contract image and the resolving power of
the microscope. For instance, in Japanese Patent Laid-open
Publication Kokai Hei 7-35982, there is described that in order to
obtain a practical contrast under the inspection with naked eye, it
is necessary to increase an amount of wavefront shear to a certain
extent. However, when an amount of wavefront shear is increased
beyond the resolving power of the objective lens of the microscope,
a so-called double image is inspected to decrease the resolution of
the image.
[0006] Therefore, in known differential interference contrast
microscope, in order to investigate various objects, the shear
amount of wavefront between the two linearly polarized light rays
on an object under inspection is usually determined such that the
contrast and the resolution of the image inspected by the naked eye
are balanced suitably.
[0007] However, there has been proposed to change an amount of
wavefront shear in accordance with objects under inspection. For
instance, in a microscopic image processing system using the
transmission type differential interference contrast microscope, a
differential interference contrast image obtained by the microscope
is picked-up by an electronic image sensing device and a contrast
of the image is enhanced by an image processing method. In such a
contrast enhancing method, it is possible to monitor clearly a
differential interference contrast image having a too low contrast
to be seen by the usual inspection with the naked eye. In order to
further increase the resolution of the monitored image, an amount
of wavefront shear has to be decreased below a conventional value
which has been used for inspecting the differential interference
contrast image with the naked eye as described in the above
mentioned Japanese Patent Publication Kokai Hei 7-35982.
[0008] A reflection type differential interference contrast
microscope has been also used to inspect a fine structure such as a
gap portion of a magnetic head. Also in this case, it has been
known that the differential interference contrast microscopic image
can be inspected much more clearly by decreasing an amount of
wavefront shear.
[0009] As explained above, recently it has been desired to obtain a
differential interference contrast image by changing an amount of
wavefront shear and differential interference contrast microscopes
which can offer different amounts of wavefront shear have been
available from almost microscope makers. A similar faculty for
changing an amount of wavefront shear has been also required in a
microscopic image processing system using a differential
interference contrast microscope such as various measuring
equipments. For instance, not only the above mentioned microscopic
image processing system using the contrast enhancing method, but
also a step measuring device for inspecting a step of an object
under inspection by utilizing the differential interference
contrast, a phase difference measuring device for measuring a phase
distribution of a transparent object under inspection by utilizing
the differential interference contrast and a position detecting
device for detection a position of an alignment mark on a
semiconductor wafer have encountered the same problem. In these
devices, the measurement and position detection could be performed
much more precisely by applying a suitable amount of wavefront
shear for objects under inspection.
[0010] However, in known differential interference contrast
microscopes, the ordinary and extraordinary light rays are obtained
by using the Nomarski prism which is made of a birefringent
crystal, and therefore it is necessary to prepare a plurality of
Nomarski prisms which are designed to provide different wavelength
shears. It should be noted that since the Nomarski prism is
manufactured by precisely processing the birefringent crystal, it
is liable to be rather expensive. Therefore, a cost for preparing a
plurality of expensive Nomarski prisms becomes very high. Moreover,
even if a plurality of Nomarski prisms are prepared, each prisms
have their own specific shear amounts of wavefront, an inspection
could not be always possible with an optimum amount of wavefront
shear.
[0011] In "OPTICA ATCA", 1972, vol. 19, no. 12, 1015-1026, M. Pluta
has reported a differential interference contrast microscope with a
variable amount of wavefront shear. In this known differential
interference contrast microscope, first and second sets of 1/2
wavelength plate and Nomarski prism are provided on the objective
lens side and condenser lens side, respectively, and in each of the
first and second sets, the 1/2 wavelength plate and Nomarski prism
are arranged rotatable about an optical axis to change an amount of
wavefront shear.
[0012] However, in this known differential interference contrast
microscope, there is a problem that a positional shift of image
might occur upon the rotation of the Nomarski prisms when surfaces
of the Nomarski prisms are not in parallel with each other.
Moreover, this microscope requires four expensive Nomarski prisms
instead of two Nomarski prisms in the conventional differential
interference contrast microscope, and thus a cost is apparently
increased.
SUMMARY OF THE INVENTION
[0013] The present invention has for its object to provide a novel
and useful differential interference contrast microscope of
transmission type and reflection type, in which an amount of
wavefront shear can be changed by a simple construction in a less
expensive manner.
[0014] It is another object of the invention to provide a novel and
useful differential interference contrast microscope of reflection
type, in which an amount of wavefront shear can be changed by a
simple construction in a less expensive manner.
[0015] It is still another object of the invention to provide a
novel and useful microscopic image processing system using a
differential interference contrast microscope with a variable
amount of wavefront shear.
[0016] According to a first aspect of the invention, a differential
interference contrast microscope of transmission type
comprises:
[0017] an illumination light source means for emitting an
illumination light ray;
[0018] a first polarizing means for converting the illumination
light ray emitted from the illumination light source means into a
linearly polarized light ray;
[0019] a polarized light separating means for separating the
linearly polarized light ray emanating from the first polarizing
means into two linearly polarized light rays having mutually
orthogonal vibrating directions;
[0020] an illuminating optical system including a condenser lens
and introducing said two linearly polarized light rays having
mutually orthogonal vibrating directions onto an object under
inspection;
[0021] an inspecting optical system including an objective lens and
inspecting the object under inspection;
[0022] a polarized light combining means for combining said two
linearly polarized light rays transmitted through the object under
inspection on a same optical axis; and
[0023] a second polarizing means for interfering said two linearly
polarized light rays combined on the same optical axis with each
other to form an interference image;
[0024] wherein said polarized light separating means is constructed
to change an amount of wavefront shear of the two linearly
polarized light rays on the object under inspection, and said
polarized light combining means is arranged between said object
under inspection and said second polarizing means at such a
position that said two linearly polarized light rays having the
mutually orthogonal vibrating directions propagate in parallel with
each other and are combined with each other on the same optical
axis in accordance with a variable amount of wavefront shear
introduced by said polarized light separating means.
[0025] In the differential interference contrast microscope of
transmission type according to the invention, the polarized light
combining means is not formed by a conventional Nomarski prism, and
is arranged at such a position that the two linearly polarized
light rays having the mutually orthogonal vibrating directions
propagate in parallel with each other and are combined with each
other on the same optical axis in accordance with a variable amount
of wavefront shear introduced by the polarized light separating
means. By constructing the polarized light combining means in this
manner, it is possible to decrease the number of Nomarski prisms
upon compared with the above mentioned known differential
interference contrast microscope proposed by M. Pluta.
[0026] The polarized light combining means is constructed to change
an amount of wavefront shear of the two linearly polarized light
rays with mutually orthogonal vibrating directions and is provided
at such a position that these two linearly polarized light rays
propagate in parallel with each other, said position being
different from that of the conventional differential interference
contrast microscope. Therefore, according to the invention, the
polarized light combining means is arranged at such a position
between the object under inspection and the second polarizing means
that the two linearly polarized light rays propagate in parallel
with each other.
[0027] According to a second aspect of the invention, a
differential interference contrast microscope of transmission type
comprises:
[0028] an illumination light source means for emitting an
illumination light ray;
[0029] a first polarizing means for converting the illumination
light ray emitted from the illumination light source means into a
linearly polarized light ray;
[0030] an illuminating optical system including a condenser lens
and illuminating an object under inspection with said linearly
polarized light ray;
[0031] an inspecting optical system including an objective lens and
inspecting the object under inspection;
[0032] a second polarizing means for interfering two linearly
polarized light rays combined on a same optical axis with each
other to form an interference image;
[0033] a polarized light separating and combining means for
separating the linearly polarized light ray emanating from the
first polarizing means into two linearly polarized light rays
having mutually orthogonal vibrating directions and combining two
linearly polarized light rays propagating in parallel with each
other on a same optical axis; and
[0034] a reflection means for projecting said linearly polarized
light ray emanating from said first polarizing means onto the
object under inspection by means of said polarized light separating
and combining means and illuminating optical system as said two
linearly polarized light rays having mutually orthogonal vibrating
directions and propagating in parallel with each other, and
impinging the two linearly polarized light rays transmitted through
the object under inspection, having mutually orthogonal vibrating
directions and propagating in parallel with each other upon said
polarized light separating and combining means by means of said
imaging optical system.
[0035] In this differential interference contrast microscope of
transmission type, since the separation of the linearly polarized
light ray into the two linearly polarized light rays with mutually
orthogonal vibrating directions and the combination of these two
linearly polarized light rays are performed by the single polarized
light separating and combining means, the construction can be
simpler and a cost can be decreased.
[0036] According to a third aspect of the invention, a differential
interference contrast microscope of reflection type comprises:
[0037] an illumination light source means for emitting an
illumination light ray;
[0038] a first polarizing means for converting the illumination
light ray emitted from the illumination light source means into a
linearly polarized light ray;
[0039] an imaging optical system including an objective lens for
irradiating an object under inspection and inspecting the object
under inspection;
[0040] a reflection member for introducing said linearly polarized
light ray emanating from the first polarizing means into said
imaging optical system;
[0041] a polarized light separating and combining means for
separating the linearly polarized light ray emanating from the
first polarizing means into two linearly polarized light rays
having mutually orthogonal vibrating directions and combining the
two linearly polarized light rays reflected by the object under
inspection with other on a same optical axis; and
[0042] a second polarizing means for interfering the two linearly
polarized light rays combined on a same optical axis with each
other to form an interference image;
[0043] wherein said polarized light separating and combining means
is constructed such that said linearly polarized light ray
emanating from the first polarizing means into the two linearly
polarized light rays having mutually orthogonal vibrating
directions and propagating in parallel with each other and an
amount of wavefront of said two linearly polarized light rays can
be changed, and said polarized light separating and combining means
is arranged at such a position that said two linearly polarized
light rays with mutually orthogonal vibrating directions are made
incident upon the object under inspection in parallel with each
other.
[0044] In this manner, in the differential interference contrast
microscope of reflection type according to the invention, an amount
of wavefront shear between the two linearly polarized light rays on
the object under inspection can be changed by using the single
polarized light separating and combining means, and thus the
construction becomes simple and less expensive.
[0045] According to a fourth aspect of the invention, a microscopic
image processing system comprises:
[0046] a differential interference contrast microscope, in which an
object under inspection is irradiated with two linearly polarized
light rays having mutually orthogonal vibrating directions and the
two linearly polarized light rays transmitted through or reflected
by the object under inspection are combined on a same optical axis
to form a differential interference contrast image of the object
under inspection on an imaging plane;
[0047] an electronic image sensing means for picking-up said
differential interference contrast image of the object under
inspection to derive an image signal; and
[0048] an image processing means for performing selectively a
contrast enhancement for said image signal supplied from said
electronic image sensing means;
[0049] wherein an amount of wavefront shear of said two linearly
polarized light rays having mutually orthogonal vibrating
directions on said object under inspection is changed in accordance
with an image processing to be performed by said image processing
means.
[0050] In the system in which the contrast enhancement is carried
out by processing the image signal obtained through the
differential interference contrast microscope, it is preferable to
adjust an amount of wavefront shear to a value smaller than a value
which is conventionally used in the inspection with the naked eye
as described in the above mentioned Japanese Patent Publication
Kokai Hei 7-35982. However, when a shear amount is decreased, a
contrast of the differential interference contrast image might
become lower and the alignment of the object under inspection could
not be performed easily with the naked eye. In the above mentioned
microscopic image processing system according to the invention, an
amount of wavefront shear between the two linearly polarized light
rays on the object under inspection is changed in accordance with
the image processing method to be carried out in the image
processing means. Therefore, an amount of wavefront shear can be
adjusted to optimum values for the inspection with the naked eye
and the contrast enhancement.
[0051] According to a fifth aspect of the invention, a microscopic
image processing system comprises:
[0052] a differential interference contrast microscope, in which an
object under inspection is irradiated with two linearly polarized
light rays having mutually orthogonal vibrating directions and the
two linearly polarized light rays transmitted through or reflected
by the object under inspection are combined on a same optical axis
to form a differential interference contrast image of the object
under inspection on an imaging plane;
[0053] an electronic image sensing means for picking-up said
differential interference contrast image of the object under
inspection to derive an image signal; and
[0054] an image processing means for processing said image signal
supplied from said electronic image sensing means to measure a
phase difference or step structure of the object under
inspection;
[0055] wherein an amount of wavefront shear of said two linearly
polarized light rays having mutually orthogonal vibrating
directions on said object under inspection is changed.
[0056] In the differential interference contrast microscope, when
an object under inspection is transparent, a contrast of a
differential interference contrast image depends on a phase
difference of the object, and when an object is not transparent, a
contrast depends on a step structure of the object. Therefore, the
differential interference contrast microscope can be applied to the
measurement of the phase difference or step structure of the object
by using the fringe scan method. In this case, it is preferable to
make an amount of wavefront shear as large as possible to increase
a contrast, and thus the measurement of phase difference or step
structure with a high precision. However, if the wavefront shear is
larger than a structure of the object to be inspected, the ordinary
and extraordinary light rays could not be made incident upon a
desired portion of the object and the measurement could not be
carried out.
[0057] Therefore, according to the invention, an amount of
wavefront shear between the two linearly polarized light rays on
the object under inspection can be adjusted to optimum values for
the measurement of the phase difference or step structure.
[0058] According to a sixth aspect of the invention, a microscopic
image processing system comprises:
[0059] a differential interference contrast microscope of
reflection type, in which an object under inspection is irradiated
with two linearly polarized light rays having mutually orthogonal
vibrating directions and the two linearly polarized light rays
reflected by the object under inspection are combined on a same
optical axis to form a differential interference contrast image of
the object under inspection on an imaging plane;
[0060] an electronic image sensing means for picking-up said
differential interference contrast image of the object under
inspection to derive an image signal; and
[0061] an image processing means for processing said image signal
supplied from said electronic image sensing means to detect a
position of a pattern of depressions and protrusions formed in a
surface of the object under inspection;
[0062] wherein an amount of wavefront shear of said two linearly
polarized light rays having mutually orthogonal vibrating
directions on said object under inspection is changed.
[0063] By using the above mentioned microscopic image processing
system according to the invention, since an amount of wavefront
shear between the two linearly polarized light rays can be
adjusted, a position of a fine pattern of protrusions and
depressions of several nano meters formed in a surface of a
semiconductor wafer can be detected precisely. That is to say, an
amount of wavefront shear can be increased as large as possible
within a range by which the fine structure of protrusions and
depressions can be detected.
BRIEF DESCRIPTION OF THE DRAWINGS
[0064] FIG. 1 is a schematic view showing a known differential
interference contrast microscope;
[0065] FIG. 2 is an enlarged view of a part of the microscope shown
in FIG. 1;
[0066] FIG. 3 is a schematic view illustrating a first embodiment
of the differential interference contrast microscope of
transmission type according to the invention;
[0067] FIG. 4 is a schematic view depicting an embodiment of the
imaging optical system of the microscope shown in FIG. 3;
[0068] FIG. 5 is a schematic view showing an embodiment of the
illuminating optical system of the microscope illustrated in FIG.
3;
[0069] FIGS. 6A and 6B are schematic views showing the polarized
light separating means and polarized light combining means,
respectively of the microscope of FIG. 3;
[0070] FIG. 7 is a schematic view depicting a second embodiment of
the differential interference contrast microscope of transmission
type according to the invention;
[0071] FIG. 8 is a schematic view illustrating the polarized light
separating and combining means of the microscope shown in FIG.
7;
[0072] FIG. 9 is schematic view showing a third embodiment of the
differential interference contrast microscope of transmission type
according to the invention;
[0073] FIG. 10 is a schematic view showing an embodiment of the
differential interference contrast microscope of reflection type
according to the invention;
[0074] FIG. 11 is a schematic view representing a first embodiment
of the microscopic image processing system according to the
invention;
[0075] FIG. 12 is a schematic view showing a second embodiment of
the microscopic image processing system according to the
invention;
[0076] FIG. 13 is a schematic view depicting a third embodiment of
the microscopic image processing system according to the invention;
and
[0077] FIG. 14 is a schematic perspective view illustrating another
embodiment of the polarized light separating means according to the
invention.
DETAILED EXPLANATION OF THE INVENTION
[0078] FIG. 3 is a schematic view showing a first embodiment of the
differential interference contrast microscope of transmission type
according to the invention. A light ray emitted from an
illuminating light source 61 is converted by a polarizer 62
constituting the first polarizing means into a linearly polarized
light ray, and then the linearly polarized light ray is made
incident upon a polarized light separating means 63 and is divided
into two linearly polarized light rays whose vibrating directions
are mutually orthogonal. According to the invention, the polarized
light separating means 63 is constructed such that an amount of
wavefront shear between said two linearly polarized light rays can
be changed continuously. For instance, the polarized light
separating means 63 may be constructed by a pair of wedge-shaped
crystal plates, at least one of which is movable in a direction
perpendicular to an optical axis.
[0079] In the present embodiment, the two linearly polarized light
rays with orthogonal vibrating directions emanate from the
polarized light separating means 63 in parallel with each other. By
effecting a relative movement of the two crystal plates, the
thickness of the crystal plate or plates is changed continuously so
as to change an amount of wavefront shear of the two linearly
polarized light rays with mutually orthogonal vibrating directions
propagating in parallel with each other.
[0080] The two linearly polarized light rays having the mutually
orthogonal vibrating directions separated by the polarized light
separating means 63 are made incident upon an object 66 under
inspection by means of lens groups 64 and 65 constituting the
illuminating optical system. There lens groups 64 and 65 are
arranged such that a back focal point of the lens group 64 is
identical with a front focal point of the lens group 65. Therefore,
the two linearly polarized light rays with orthogonal vibrating
directions emanating from the polarized light separating means 63
in parallel with each other are made incident upon the object 66
under inspection also in parallel with each other.
[0081] The two linearly polarized light rays with mutually
orthogonal vibrating directions transmitted through the object 66
under inspection are made incident upon a polarized light combining
means 69 by means of a lens group 67 comprising an objective lens
and a lens group 68 comprising an imaging lens, these lens groups
constituting the imaging optical system. The lens groups 67 and 68
are arranged such that a back focal point of the lens group 67 is
identical with a front focal point of the lens group 68, and thus
the two linearly polarized light rays having the mutually
orthogonal vibrating directions, transmitted through the object 66
under inspection and propagating in parallel with each other are
made incident upon the polarized light combining means 69 in
parallel with each other.
[0082] The polarized light combining means 69 is constructed as
illustrated in FIG. 3B and comprises a pair of wedge-shaped crystal
plates, at least one of which is movable in a direction
perpendicular to an optical axis of the imaging optical system. The
thickness of the crystal plate or plates in the optical axis is
changed by relatively moving the crystal plates such that the
incident two linearly polarized light rays having mutually
orthogonal vibrating directions and having the wavefront shear
whose amount is determined by the polarized light separating means
63 are combined on the same optical axis. In other words, an
acceptable amount of wavefront shear of the polarized light
combining means 69 is made equal to that of the polarized light
separating means 63.
[0083] The two linearly polarized light rays combined by the
polarized light combining means 69 on the same optical axis are
made incident upon an analyzer 90 constituting the second
polarizing means to form an interference image. The thus formed
interference image is formed on an imaging plane 91 for the
inspection.
[0084] In a preferable embodiment of the differential interference
contrast microscope of transmission type according to the
invention, said inspecting optical system comprises a first lens
group including said objective lens and a second lens group
including an imaging lens, said first and second lens groups being
arranged such that a back focal point of the first lens group is
identical with a front focal point of the second lens group, and
said polarized light combining means is arranged behind the second
lens group.
[0085] As shown in FIG. 4, a back focal point of an objective lens
11 is positioned at a front focal point of an imaging lens 12, two
linearly polarized light rays having mutually orthogonal vibrating
directions are made incident upon a polarized light combining means
14 in parallel with each other and thus are combined on a same
optical axis. By such a construction, an unevenness of brightness
within a field of view of the differential interference contrast
microscope can be decreased.
[0086] In the known differential interference microscope of
transmission type shown in FIG. 1, an incident angle to the
Nomarski prism 7 is not constant as shown in FIG. 2 which
illustrates a part of the microscope on an enlarged scale. That is
to say, a light ray from a central portion of the field of view is
made incident upon the Nomarski prism 7 perpendicularly thereto,
but a light ray from a peripheral portion of the field of view is
obliquely made incident upon the Nomarski prism 7. Therefore, there
is introduced a non-uniformity between the ordinary light ray and
the extraordinary light ray within the field of view, and thus an
unevenness in brightness occurs.
[0087] In order to correct the above mentioned unevenness in
brightness within the field of view of the differential
interference contrast microscope, Japanese Patent Publication Kokai
Sho 61-181920 has proposed to arrange a crystal plate which
compensates a difference in optical path length between the
ordinary light ray and the extraordinary light ray. However, the
use of the crystal plate in addition to the Nomarski prism
increases a cost of the microscope.
[0088] In the preferable embodiment of the differential
interference contrast microscope of transmission type according to
the invention, as illustrated in FIG. 4, since the back focal point
of the objective lens 11 is identical with the front focal point of
the imaging lens 12 and the polarized light combining means 14 is
arranged behind the imaging lens 12, both the light rays from the
central portion and peripheral portion of the field of view are
made perpendicularly incident upon the polarized light combining
means 14, and thus the unevenness in brightness within the field of
view can be decreased by a simple and less expensive structure.
[0089] In another preferable embodiment of the differential
interference contrast microscope of transmission type according to
the invention, said polarized light separating means for separating
the incident linearly polarized light ray into the two linearly
polarized light rays having mutually orthogonal vibrating
directions is arranged at such a position that the two linearly
polarized light rays are transmitted through the object under
inspection substantially in parallel with each other, and an amount
of wavefront shear is changed in cooperation with said polarized
light combining means.
[0090] In a preferable modification of such an embodiment, said
polarized light separating means is constructed such that the two
linearly polarized light rays having mutually orthogonal vibrating
directions emanate from the polarized light separating means in
parallel with each other.
[0091] In another preferable embodiment, the polarized light
separating means is constructed in a similar manner to the
polarized light combining means. In this case, in order to make the
two linearly polarized light rays separated by the polarized light
separating means incident upon the object under inspection
substantially in parallel with each other, it is preferable to
construct the illuminating optical system as an afocal system.
[0092] In a preferable embodiment of the differential interference
contrast microscope of transmission type according to the
invention, said illuminating optical system comprises a third lens
group and a fourth lens group arranged in this order viewed from
the light source means, a back focal point of the third lens group
is identical with a front focal point of the fourth lens group, and
said polarized light separating means is arranged in front of the
third lens group.
[0093] As illustrated in FIG. 5, a light ray emitted by an
illumination light source 15 is converted by a polarizer
constituting the first polarizing means into a linearly polarized
light ray, and then the linearly polarized light ray is projected
onto the specimen 13 under inspection by means of polarized light
separating means 17, third lens group 18 and fourth lens group 19.
The polarized light separating means 17 is constructed such that
the incident linearly polarized light ray is separated into two
linearly polarized light rays having mutually orthogonal vibrating
directions and is arranged at such a position that said two
linearly polarized light rays transmit the object 13 under
inspection substantially in parallel with each other. Then, an
amount of wavefront shear can be changed in cooperation with the
polarized light combining means not shown in FIG. 5. In the present
embodiment, the back focal point of the third lens group 18 is
coincided with the front focal point of the fourth lens group 19,
and thus the two linearly polarized light rays with mutually
orthogonal vibrating directions are made incident upon the object
13 under inspection in parallel with each other. Therefore, it is
possible to mitigate the unevenness of brightness within a field of
view similar to the embodiment explained above.
[0094] In a preferable embodiment of the differential interference
contrast microscope according to the invention, the polarized light
separating means is constructed such that said two linearly
polarized light rays emanate from the polarized light separating
means in parallel with each other and is arranged at such a
position that these two polarized light rays are made incident upon
the object under inspection substantially in parallel with each
other. Then, a focal length of the illumination optical system is
changed in accordance with a change in a position of the back focal
point of an objective lens which is removably inserted into the
optical axis. Therefore, the two linearly polarized light rays with
mutually orthogonal vibrating directions are made incident upon the
polarized light combining means always in parallel with each
other.
[0095] When the differential interference contrast microscope of
transmission type according to the invention is applied to the
microscopic image processing system, a plurality of objective
lenses having different focal lengths and types are prepared and
any desired objective lens is removably inserted into the optical
axis. In this case, if a focal length of the illumination optical
system is not changed, the two linearly polarized light rays do not
propagate in parallel with each other and could not be combined on
the same optical axis.
[0096] In the above explained preferable embodiment, the focal
length of the illumination optical system is changed in accordance
with a change in a position of a back focal point of an objective
lens. Then, the two linearly polarized light rays can be made
incident upon the polarized light combining means always in
parallel with each other. In this case, the illumination optical
system is preferably formed by an afocal system.
[0097] In still another preferable embodiment of the differential
interference contrast microscope of transmission type according to
the invention, the polarized light separating means comprises a
variable power optical system arranged in the illumination optical
system, and an amount of wavefront shear is changed in cooperation
with the polarized light combining means.
[0098] In such an embodiment, an amount of wavefront is changed by
changing a power of the illumination optical system. In this case,
when the polarized light separating means includes such an optical
element that the incident linearly polarized light ray is separated
into two linearly polarized light rays which have mutually
orthogonal vibrating directions and propagate in parallel with each
other and that the two linearly polarized light rays are
transmitted through the object under inspection in parallel with
each other, said optical system with variable focal length is
preferably formed by an afocal optical system to change an amount
of wavefront shear on the object under inspection. When the
polarized light separating means comprises Wollaston's prism or
Nomarski prism, it is preferable to construct the variable power
optical system such that an amount of wavefront shear on the object
under inspection is change by changing a focal length of the
illumination optical system. It should be noted that the variable
power may be realized by the zoom system or turret system.
[0099] In a preferable embodiment of the differential interference
contrast microscope of transmission type according to the
invention, a phase difference changing means for changing a phase
difference between said two linearly polarized light rays having
mutually orthogonal vibrating directions is provided in the optical
path between the polarized light separating means and the polarized
light combining means.
[0100] In the differential interference contrast microscope, the
inspection is usually carried out with an optimum contrast by
changing a phase difference between the two linearly polarized
light rays. In the present invention, at least the polarized light
separating means is different from the conventional Nomarski prism,
and thus a phase difference between the two linearly polarized
light rays is liable to be very large. Therefore, it is
advantageous to provide the above mentioned phase difference
changing means.
[0101] Further, in the embodiment just explained above, it is
further preferable to form the illumination light source by a
quasi-monochromatic light source.
[0102] By using the quasi-monochromatic light source, the phase
difference changing means may be constructed such that the phase
difference is changed merely within a range from 0 to 2.pi..
Therefore, the phase difference changing means may be formed by a
simple element such as the Snarmont compensator. When the
illumination light source is formed by a white light source, a
variation in the phase difference between the two polarized light
rays with mutually orthogonal vibrating directions upon changing an
amount of wavefront shear becomes large, and therefore it is
difficult to compensate such a large phase difference by means of a
single phase compensator. That is to say, the phase difference
changing means has to be constructed by a combination of a phase
compensator and a plurality of wavelength plates, and the
wavelength plates must be changed in accordance with a phase
difference. In this manner, the phase difference changing means
becomes complicated in construction and could not be handled
easily.
[0103] In another preferable embodiment of the differential
interference microscope of transmission type according to the
invention, at least one of the polarized light separating means and
polarized light combining means is formed by a pair of
wedged-shaped crystal plates, at least one of which is arranged
movably in a direction perpendicular to the optical axis.
[0104] As illustrated in FIG. 6A, the polarized light separating
means 17 is formed by a pair of wedge-shaped crystal plates 21a and
21b, and the crystal plate 21a is arranged movably in a direction
perpendicular to the optical axis as depicted by a double-headed
arrow. The incident linearly polarized light ray can be separated
into two linearly polarized light rays having mutually orthogonal
vibrating directions and propagating in parallel with each other.
When the crystal plate 21a is moved to change a thickness of the
crystal plate 21a, an amount of wavefront shear between the two
linearly polarized light rays can be changed in a continuous
manner.
[0105] FIG. 6B shows an embodiment of the polarized light combining
means 14 comprising a pair of wedge-shaped crystal plates 23a and
23b, the crystal plate 23a being arranged movably in a direction of
the optical axis of the inspection optical system. The crystal
plate 23a is moved to change its thickness in the direction of the
optical axis in accordance with an amount of wavefront shear of the
incident two linearly polarized light rays with mutually orthogonal
vibrating directions such that the these two linearly polarized
light rays are combined on the optical axis.
[0106] It is preferable to make the wedge-shaped crystal plates of
a quartz having a relatively small birefringence, because such a
quartz can be processed relatively easily. According to the
invention, the wedged-shaped crystal plate may be also made of a
calcite which has a relatively large birefringency or any other
birefringent material. In FIGS. 4-6, arrows in the crystal plates
denote directions of optic axes of the crystal plates. In another
drawings, arrows in crystal plates represent directions of optic
axes.
[0107] FIG. 7 is a schematic view showing a second embodiment of
the differential interference contrast microscope of transmission
type according to the invention. In the present embodiment, an
illumination light ray emitted by an illumination light source 31
is converted into a linearly polarized light ray by an analyzer 32
constituting the first polarizing means, and then the thus linearly
polarized light ray is reflected by a half mirror 33 and is made
incident upon a polarized light separating and combining means 34,
in which an amount of wavefront shear can be changed. Then, two
linearly polarized light rays having mutually orthogonal vibrating
directions emanate from the polarized light separating and
combining means 34 in parallel with each other. These linearly
polarized light rays are reflected by a half mirror 35, and are
made incident upon an object 41 under inspection by means of
reflection mirror 36, illuminating lens 37, reflection mirrors 38
and 39 and illuminating lens 40. The two linearly polarized light
rays with mutually orthogonal vibrating directions are transmitted
through the object 41 under inspection and emanate therefrom in
parallel with each other. Then, these two linearly polarized light
rays are made incident upon the half mirror 35 by means of
objective lens 42 and imaging lens 43 and are transmitted through
the half mirror 35. Then, the two linearly polarized light rays
with mutually orthogonal vibrating directions are made incident
upon the polarized light separating and combining means 34 in
parallel with each other and are combined thereby on the same
optical axis. The combined two linearly polarized light rays are
made incident upon a polarizer 44 constituting the second
polarizing means to form an interference image on an imaging plane
45.
[0108] In this manner, the separating operation and combining
operation are performed by the single means 34, and thus it is no
more necessary to effect the adjustment of an amount of wavefront
shear in the previous embodiment. In the embodiment shown in FIG.
7, in order to prevent the two linearly polarized light rays
emanating from the polarized light separating and combining means
34 from being made incident upon the analyzer 44 by means of the
half mirror 35, imaging lens 43, objective lens 42, object 41 under
inspection, illumination lens 40, reflection mirrors 39 and 38,
illumination lens 37, reflection mirror 36, half mirror 35,
polarized light separating and combining means 34 and half mirror
33 in this order, it is desired to provide an optical isolator
comprising a combination of, for instance a rotatary crystal and a
Faraday element.
[0109] In a modification of the second embodiment shown in FIG. 7,
the linearly polarized light ray emanating from the polarizer 32 is
made incident upon the polarized light separating and combining
means 34 at a first surface portion and the two linearly polarized
light rays whose vibrating directions are orthogonal to each other
are made incident upon the polarized light separating and combining
means 34 at a second surface portion which is separated from said
first surface portion. That is to say, as depicted in FIG. 8,
separate parts of the polarized light separating and combining
means 34 are used to separate the polarized light ray and combine
the two linearly polarized light rays, respectively. Also in this
case, an amount of wavefront shear between the two linearly
polarized light rays having mutually orthogonal vibrating
directions emanating from the polarized light separating and
combining means 34 becomes identical with that of the two linearly
polarized light rays impinging upon the same means 34. By using
such a polarized light separating and combining means 34, it is
possible to separate completely the illuminating optical system and
the inspecting optical system, and thus a possible decrease in
contrast due to flare light can be avoided.
[0110] FIG. 9 is a schematic view illustrating a third embodiment
of the differential interference contrast microscope of
transmission type according to the invention, in which the
separation and combination of the two linearly polarized light rays
are carried out by one and same polarized light separating and
combining means. In this embodiment, a light ray emitted by an
illumination light source 81 is converted into a linearly polarized
light ray by an analyzer 82, and then the linearly polarized light
ray is made incident upon a first portion of a polarized light
separating and combining means 84 by means of a mirror 83a and is
separated into two linearly polarized light rays which have
mutually orthogonal vibrating directions and propagate in parallel
with each other. The polarized light separating and combining means
84 may be formed by two wedge-shaped crystal plates like as the
polarized light separating and combining means 34 shown in FIG. 8.
Then, an amount of wavefront shear can be adjusted by moving one of
the crystal plates in the direction perpendicular to the optical
axis.
[0111] The two linearly polarized light rays having mutually
orthogonal vibrating directions and propagating in parallel with
each other are then made incident upon an object 87 under
inspection by means of reflection mirrors 83b and 83c, illuminating
lens group 85, reflection mirrors 83d and 83e and illuminating lens
group 86.
[0112] The two linearly polarized light rays transmitted through
the object 87 under inspection are then made incident upon a second
portion of the polarized light separating and combining means 84 by
means of objective lens group 88 and imaging lens group 89. These
two linearly polarized light rays are combined thereby on the same
optical axis and are made incident upon an analyzer 90 to form an
interference image on an imaging plane 91.
[0113] In modifications of the embodiments shown in FIGS. 7 and 9,
a back focal point of the illuminating optical system is changed in
accordance with a focal length of an objective lens to be inserted
into the optical axis such that the two linearly polarized light
rays having mutually orthogonal vibrating directions are made
incident upon the polarizing separating and combining means always
in parallel with each other.
[0114] In another preferable modification, a phase difference
between the two linearly polarized light rays with mutually
orthogonal vibrating directions is changed by inserting a phase
difference adjusting means in the optical path between the
polarizer and the analyzer.
[0115] In another preferable modification, the illumination light
source is formed by a quasi-monochromatic light source.
[0116] FIG. 10 is a schematic view showing a first embodiment of
the differential interference contrast microscope of reflection
type according to the invention. An illumination light ray emitted
by an illuminating light source 51 is converted into a linearly
polarized light ray by a polarizer 52. The linearly polarized light
ray is reflected a half mirror 53 and then is made incident upon a
polarized light separating and combining means 54. The linearly
polarized light ray is separated into two polarized light rays
having mutually orthogonal vibrating directions, which are then
made incident upon an object 57 under inspection by means of
imaging lens 54 and an objective lens 55. The polarized light
separating and combining means 54 is arranged at such a position
that the two linearly polarized light rays impinge upon the object
57 in parallel with each other.
[0117] The two linearly polarized light rays reflected by the
object 57 under inspection are made incident upon the polarized
light separating and combining means 55 by means of the objective
lens 56 and imaging lens 55 and are combined thereby on the same
optical axis. The thus combined two polarized light rays are made
incident upon an analyzer 58 to form an interference image on an
imaging plane 59.
[0118] In the differential interference contrast microscope of
reflection type according to the present invention, it is possible
to change an amount of wavefront shear by means of the simple
construction using only one polarized light separating and
combining means.
[0119] In a preferable embodiment of the differential interference
contrast microscope of reflection type according to the invention,
the inspecting optical system comprises a first lens group
including the objective lens and a second lens group including the
imaging lens, a back focal point of said first lens group is
coincided with a front focal point of the second lens group, and
the polarized light separating and combining means is arranged
behind the second lens group.
[0120] That is to say, in this preferable embodiment, the
construction shown in FIG. 4 is applied to the differential
interference contrast microscope of reflection type. Then, the two
linearly polarized light rays with mutually orthogonal vibrating
directions emanating from the polarized light separating and
combining means in parallel with each other and reflected by the
object under inspection can be made incident upon the polarized
light separating and combining means in parallel with each other
and can be combined on the same optical axis.
[0121] In another preferable modification, a phase difference
adjusting means is arranged in the optical path between the
polarizer and the analyzer and a phase difference between the two
linearly polarized light rays with mutually orthogonal vibrating
directions is changed.
[0122] In another preferable modification, the illumination light
source is formed by a quasi-monochromatic light source. Then, the
construction can be made simpler.
[0123] In another preferable modification, the polarized light
separating and combining means is formed by two wedge-shaped
crystal plates like as the polarized light separating and combining
means 34 shown in FIG. 6. Then, an amount of wavefront shear
between the two linearly polarized light rays can be adjusted by
moving one of the crystal plates in the direction perpendicular to
the optical axis.
[0124] FIG. 11 is a schematic view showing a first embodiment of
the microscopic image processing system according to the invention.
In the present embodiment, use is made of the differential
interference contrast microscope of transmission type illustrated
in FIG. 3. The interference image formed on the imaging plane 70 is
picked-up by an image sensing element 101 and an image signal from
the image sensing element is supplied to an image processing means
102 to perform the contrast enhancement. Then the image signal
having the enhanced contrast is supplied to an output means 103
such as a display monitor.
[0125] An amount of wavefront shear between the two linearly
polarized light rays on the object 66 under inspection is adjusted
by changing amounts of wavefront shear of the polarized light
separating means 63 and polarized light combining means 69 in
cooperation with each other. When the enhancement of contrast is
not effected in the image processing means 102, an amount of
wavefront shear is increased such that the contrast of the image
inspected by naked eyes, and when the contrast enhancement is
carried out in the image processing means, an amount of wavefront
shear is decreased to increase the resolving power.
[0126] FIG. 12 is a schematic view illustrating a second embodiment
of the microscopic image processing system according to the
invention. In the present embodiment, the differential interference
contrast microscope of reflection type shown in FIG. 10 is combined
with a fringe scanning device for measuring a step structure. To
this end, in the present embodiment, the analyzer 58 shown in FIG.
10 is replaced by a phase changing means of the fringe scanning
device. Furthermore, an electronic image sensing element 110 is
arranged at the imaging plane of the differential interference
contrast microscope of reflection type to pick-up the interference
image. An image signal from the image sensing element 110 is stored
in an image storing means 111, and the stored image signal is
processed in an image processing means 112 by the fringe scan
method to measure a step in the object 57 under inspection.
[0127] The phase changing means is formed by 1/4 wavelength plate
115 and a rotating analyzer 116 having a Snarmont compensator. By
rotating the analyzer 116, a phase difference between the two
linearly polarized light rays with mutually orthogonal vibrating
directions which are made incident upon the analyzer via the 1/4
wavelength plate 115 can be changed. In the present microscopic
image processing system of the present embodiment, an amount of
wavefront shear can be changed by the polarized light separating
and combining means 54 to a suitable value for measuring the step
structure in the object 57 under inspection. Therefore, the
measurement of the step structure can be performed with a high
precision.
[0128] FIG. 13 is a schematic view showing a third embodiment of
the microscopic image processing system according to the invention.
In the present embodiment, use is made of the differential
interference contrast microscope of reflection type illustrated in
FIG. 10 and a position of a pattern having protrusions and
depressions on a surface of a semiconductor wafer is detected. The
interference image formed on the imaging plane of the microscope is
picked-up by an electronic image sensing element 117 and image
signal derived from the image sensing element is supplied to an
image processing means 118. In the image processing means 118, the
image signal is processed to detect a position of the pattern of
protrusions and depressions, and the thus detected position
information is supplied to an output means 119. In the microscopic
image processing system of the present embodiment, an amount of
wavefront shear between the two linearly polarized light rays
impinging upon the object 57 under inspection can be adjusted by
the polarized separating and combining means 54 to an optimum value
for detecting the pattern of protrusions and depressions with a
high precision.
[0129] In preferable embodiments of the microscopic image
processing system according to the invention, the differential
interference contrast microscopes of reflection type shown in FIGS.
3, 7 and 9 can be advantageously used. Also in such preferable
embodiments, an amount of wavefront shear between the two linearly
polarized light rays with mutually orthogonal vibrating directions
on the object under inspection can be adjusted to an optimum value,
and thus it is possible to measure and detect the object with a
high precision.
[0130] The present invention is not limited to the embodiments
explained above, but many modifications and alternations can be
conceived by those skilled in the art within the scope of the
invention. For instance, in the above embodiments, the polarized
light separating means, polarized combining means and polarized
light separating and combining means are formed by a pair of
wedge-shaped crystal plates, at least one of which is arranged
movably in the direction perpendicular to the optical axis.
According to the invention, as illustrated in FIG. 14, they may be
formed by a pair of Savart's plates 121a and 121b, at least one of
which is arranged movable in the direction perpendicular to the
optical axis. Also in this case, an amount of wavefront shear
between the two linearly polarized light rays with mutually
orthogonal vibrating directions can be changed.
[0131] As stated above in detail, in the differential interference
contrast microscope of transmission type and reflection type, an
amount of wavefront shear can be adjusted by a simple construction
and the differential interference contrast inspection can be
performed with a very high precision.
[0132] Further, in the microscopic image processing system
according to the invention, since an amount of wavefront shear can
be adjusted to optimum values for both the inspection with naked
eye and contrast enhancement, the measurement and detection can be
carried out precisely.
* * * * *