U.S. patent application number 17/317174 was filed with the patent office on 2021-09-09 for optical measurement system.
The applicant listed for this patent is Chia-Bin Tsen, Yu-Yen Wang, Bor-Jen Wu. Invention is credited to Chia-Bin Tsen, Yu-Yen Wang, Bor-Jen Wu.
Application Number | 20210278198 17/317174 |
Document ID | / |
Family ID | 1000005608619 |
Filed Date | 2021-09-09 |
United States Patent
Application |
20210278198 |
Kind Code |
A1 |
Wang; Yu-Yen ; et
al. |
September 9, 2021 |
Optical Measurement System
Abstract
An optical system includes a collimated light source, a beam
splitter, two mirrors and two lenses, a focus lens, and a detector.
An initial light beam is generated by the light source and then
separated by the beam splitter into a first light beam and a second
light beam. The two mirrors respectively direct the first and
second light beams on a sample with symmetrical paths and the two
lenses focus the first and second light beam on the sample
respectively. The first and second light beams are reflected from
the sample and along the counterpart paths to the beam splitter. An
interfered light beam is then generated by combining the reflected
first and second light beams, and focused by a focus lens on a
detector. A Dove prism can be configured between one mirror and one
lens of the two for contrast enhancement. It can produce the photon
combination with same of direction in this setup to enhance
contrast.
Inventors: |
Wang; Yu-Yen; (Taoyuan City,
TW) ; Wu; Bor-Jen; (New Taipei City, TW) ;
Tsen; Chia-Bin; (New Taipei City, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Wang; Yu-Yen
Wu; Bor-Jen
Tsen; Chia-Bin |
Taoyuan City
New Taipei City
New Taipei City |
|
TW
TW
TW |
|
|
Family ID: |
1000005608619 |
Appl. No.: |
17/317174 |
Filed: |
May 11, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
16528945 |
Aug 1, 2019 |
11041711 |
|
|
17317174 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 5/04 20130101; G02B
27/106 20130101; G01B 9/02041 20130101; G01B 9/02091 20130101 |
International
Class: |
G01B 9/02 20060101
G01B009/02; G02B 5/04 20060101 G02B005/04; G02B 27/10 20060101
G02B027/10 |
Claims
1. An optical system, comprising: a collimated light source for
generating an initial light beam; a beam splitter, receiving the
initial light beam, for dividing the initial beam into two incident
light beams symmetrical to a splitting plane of said beam splitter;
two mirrors and two lenses directing the two incident light beams
being focused onto a surface of the sample respectively to generate
an interference pattern on the surface, and receiving two reflected
light beams from the sample back to said beam splitter, thereby
generating an interfered light beam by combining the two reflected
light beams at the beam splitter; a focus lens for focusing the
interfered light beam; and a detector for receiving the focused
interfered light beam to form an image.
2. The optical system according to claim 1, wherein the splitting
plane is normal to the surface.
3. The optical system according to claim 2, further comprising a
Dove prism for inverting one of the two incident light beams before
being focused on the surface, and inverting the other of the two
incident light beams after being focused on the surface.
4. The optical system according to claim 1, wherein the light
source is a low-coherent light source.
5. The optical system according to claim 1, wherein the light
source is a coherent light source.
6. The optical system according to claim 3, wherein said collimated
light source provides a white initial light beam, and further
comprising: a dispersive optical element, receiving the interfered
white light beam from said beam splitter, for dispersing the
interfered white light into spectroscopic components; a pinhole
array for picking up the spectroscopic components into a plurality
of interfered beams; and a projection lens for projecting the
plurality of interfered beams on said detector.
7. The optical system according to claim 3, wherein said collimated
light source provides a white initial light beam, and further
comprising: a dispersive optical element, receiving the white light
beam from said light source, for dispersing the white light into
spectroscopic components; a pinhole array for picking up the
spectroscopic components into a plurality of beams; and a beam
block for picking a specific beam with a specific wavelength from
the plurality of beams.
8. The optical system according to claim 3, wherein said collimated
light source provides a plurality of light beams with different
wavelengths.
9. The optical system according to claim 3, wherein two paths of
the two incident light beams are symmetrical to the splitting
plane.
10. The optical system according to claim 3, further comprising a
computer for processing information from said detector.
11. The optical system according to claim 3, further comprising a
first lens and a second lens for focusing the two incident light
beams onto the surface of the sample.
Description
CLAIM OF PRIORITY
[0001] This application is a Divisional Application of U.S patent
application Ser. No. 16/528,945 filed on Aug. 1, 2019, which is
incorporated by reference as if fully set forth herein.
FIELD OF THE INVENTION
[0002] The invention relates to an optical measurement system, and
particularly to a method and a system for illuminating dual beams
on a sample to generate a stronger interference.
BACKGROUND OF THE INVENTION
[0003] The following descriptions and examples are not admitted to
be prior art by virtue of their inclusion in this section.
[0004] It is important to inspect a surface of micro structures in
many current industries. For example, virus or some other
contamination must be inspected for health consideration. Nano
features and foreign objects must be inspected in semiconductor
industry, in particular when the semiconductor process nodes
approach 10 nm or below. For those micro or nano meter scaled
objects to be inspected, electron microscopes are the most commonly
used commercially available solutions. In biology or medical
industries, cultivated viruses or red blood cells are taken from
body by some invasion means and then prepared as a specimen so that
viruses or red blood cells can be "seen" in vacuum environment of
the electron microscopy. That means vivid virus or red blood cells
can't be seen in any electron microscopy. Further, for the purpose
of progress of the medical industry, it is valuable to see the
vivid virus or red blood cells with non-invasion means.
[0005] Optical interference can be one of the mainstream
non-invasive optical inspection systems for medical and biological
industries. In the field of optical interference, interference
occurs when path lengths of a reference beam and a scanning beam
are coincident with each other. More specifically, interference
generation condition is light source coherence length. When path
length differences are shorter than light source coherence length,
the optical interference will occur. Non-transparent specimens can
be inspected by Michelson interferometer or Mirau interferometer.
Transparent samples can also be measured by interferometry.
[0006] Michelson interferometer is one of the most commonly used
configurations in the optical interferometry. By using a beam
splitter, a light source is split into two paths. Both of the two
light beams are reflected back toward the beam splitter which then
combine and result in interference. The resulted interference
pattern that is not directed back toward the source is typically
directed to some type of photoelectric detector or camera. For
different applications of the interferometer, the two light paths
can be with different lengths or incorporate optical elements or
even materials under test. Please refer to FIG. 1, a light source
LS provides an initial light beam to a beam splitter BS which
separates the initial light into two beams. One of the two beams is
illuminated onto a sample S, and the other beam is illuminated into
a mirror to form a reference path RP. After the two beams reflected
back to the beam splitter BS, they will be combined and directed to
a detector D and interferential patterns are thus generated on the
detector D.
[0007] Mirau interferometer is another commonly used optical
interferometry configuration. A Mirau interferometer works on the
same basic principle as a Michelson interferometer. The difference
between the two is in the physical location of the reference arm.
The reference arm of a Mirau interferometer is located within a
microscope objective assembly. Please refer to FIG. 2, a light
source generates an initial light beam to a lens L which refracts
the beam to a beam splitter BS to generate two beams. One beam is
illuminated into a sample S and the other is reflected back to a
half mirror HM on the lens L. Another optical system can be applied
to combine the two beams to generate interference pattern. For
example, if the sample S can be transparent, another optical system
is configured below the sample S. If the sample S is
non-transparent, an optical system with mirror to collect both
beams should be configured above the sample S.
[0008] Although both Michelson interferometer and Mirau
interferometer are very widely used, only one light beam is used to
probe on the specimen, and interference is occurred by using the
reference light beam. Therefore in both cases at most half of
lights from the light source LS can reach sample surface. This
significantly limits the capability of detecting fine features on
the sample surface. Further, reference path is critical to the
system which will incur complexity in the Michelson
interferometers. Although interference result can be obtained by
using the Mirau interferometers, in non-transparent specimen, due
to back scattered light must be used for interference, optical
intensity illuminated on the specimen is further reduced, and
information of depth and thickness of the specimen can be easily
lost.
[0009] Accordingly, it is necessary to build a new optical system
such that it will be more advantageous to improve the
interferometer than the prior art.
BRIEF SUMMARY OF THE INVENTION
[0010] The object of this invention is to provide a
self-interfering technology that there is no reference path in the
interferometer compared to conventional Michelson or Mirau
interferometers. Thus, incident light intensity on the sample can
be increased, and the amount of light incident on the sample is
substantially higher than the other technologies.
[0011] The object of the present invention is to provide an
equivalent path length for dual beams of the self-interfering
technology. The equivalent path length in the present invention
refers to the dual beams will travel the same path length from
light source to the detector.
[0012] The object of the present invention is to irradiate or
illuminate light beams on the sample with oblique incident for dark
field image.
[0013] The object of the present invention is to provide a Dove
prism for image contrast enhancement.
[0014] The object of the present invention is to provide a low
coherent light source for optical coherence tomography (OCT).
[0015] The object of the present invention is to utilize a no
reference arm configuration to achieve a vibration-proof structure
for the interferometry.
[0016] The object of the present invention is to provide a full
color image obtained by using the self-interfering technology.
[0017] Accordingly, the invention provides an optical system, which
comprises a collimated light source for generating an initial light
beam, a beam splitter for dividing the initial light beam into two
comparable light beams and symmetrical to a splitting plane of the
beam splitter, two mirrors and two lenses, a focus lens, and a
detector. The two mirrors and two lenses direct the two light beams
and focus them onto a surface of the sample respectively to
generate an interference pattern on the surface. The two mirrors
and the two lenses receive two reflected light beams from the
sample back to the beam splitter, thereby generating an interfered
light beam by combining the two reflected light beams at the beam
splitter. The focus lens focuses the interfered light beam on the
detector to form an image.
[0018] In one embodiment of the optical system of the present
invention, the splitting plane is normal to the sample surface.
[0019] In one embodiment of the optical system of the present
invention, the system further comprises a Dove prism for inverting
one of the two incident light beams before being focused on the
surface, and inverting the other of the two incident light beams
after being focused on the surface.
[0020] In one embodiment of the optical system of the present
invention, the light source can be low-coherence light source.
[0021] In one embodiment of the optical system of the present
invention, the light source can be coherence light source.
[0022] In one embodiment of the optical system of the present
invention, the collimated light source provides a white initial
light beam, and the optical system further comprises a dispersive
optical element for dispersing the interfered white light into
spectroscopic components, a pinhole array for picking up the
spectroscopic components into a plurality of interfered beams, and
a projection lens for projecting the interfered beams on the
detector.
[0023] In one embodiment of the optical system of the present
invention, the collimated light source provides a white initial
light beam, and the optical system further comprises a dispersive
optical element for dispersing the white light into spectroscopic
components, a pinhole array for picking up the spectroscopic
components into a plurality of beams, and a beam block for picking
a specific beam with a specific wavelength from the plurality of
beams.
[0024] In one embodiment of the optical system of the present
invention, the collimated light source provides a plurality of
light beams with different wavelengths.
[0025] In one embodiment of the optical system of the present
invention, two paths of the two incident light beams are
symmetrical to the splitting plane.
[0026] In one embodiment of the optical system of the present
invention, the optical system further comprises a computer for
processing information from the detector.
[0027] The present invention also provides an optical system which
comprises a low coherent collimated light source for generating an
initial light beam, a beam splitter receives the initial light beam
to generate a first light beam and a second light beam, a first
mirror directs the first light beam tilt incident to a surface
region of a sample and a second mirror directs the second light
beam tilt incident to the surface region of the sample, a first
lens focuses the first light beam on the surface region and a
second lens focuses the second light beam on the surface region, a
Dove prism between the second mirror and the second lens, a focus
lens, and a detector. The focused first light beam is reflected by
the surface region along a path of the second light beam to the
beam splitter, and the focused second light beam is reflected by
the surface region along a path of the first light beam to the beam
splitter, thereby generating an interfered light beam at the beam
splitter. The focus lens focuses the interfered light beam on the
detector to generate an image.
[0028] In one embodiment of the present optical measurement system,
a first path of the first light beam is symmetrical to a second
path of the second light beam.
[0029] In one embodiment of the present optical measurement system,
a first path of the first light beam is equivalent to a second path
of the second light beam.
[0030] The present invention also provides a method for
illuminating a sample, which comprises steps of generating an
initial collimated light beam; dividing the initial light beam into
a first light beam and a second light beam; projecting and focusing
the first and second light beams onto a surface region of the
sample; inverting images of the second light beam and a reflected
first light beam from the surface region; receiving the reflected
first light beam and a reflected second light beam from the sample
along a path of the second light beam and a path of the first light
beam respectively; combining the reflected first and second beams
to an interfered light beam; and focusing the interfered light beam
to a detector.
[0031] In one embodiment of the present illuminating method, the
light source is a low-coherent light source.
[0032] In one embodiment of the present illuminating method, the
generating step provides a white initial light beam and the method
further comprises steps of dispersing the white initial light beam
into spectroscopic components; picking up the spectroscopic
components into a plurality of beams with respective wavelengths;
and selecting one of the plurality of beams to the beam
splitter.
[0033] The present invention also provides a method for
illuminating a sample, which comprises steps of generating a white
initial collimated light beam; dividing the white initial light
beam into a first light beam and a second light beam; projecting
and focusing the first and second light beams onto a surface region
of the sample; inverting images of the second light beam and a
reflected first light beam from the surface region; receiving the
reflected first light beam and a reflected second light beam from
the sample along a path of the second light beam and a path of the
first light beam respectively; combining the reflected first and
second beams to an interfered light beam; dispersing the interfered
light beam into spectroscopic components; picking up the
spectroscopic components into a plurality of interfered beams with
respective wavelengths; and projecting the plurality of beams to a
detector.
[0034] In one embodiment of the present illuminating method, the
light source is a low-coherent light source.
[0035] In one embodiment of the present invention, the method
further comprises a step of combining each image of the plurality
of interfered beams projected on the detector to form a full color
image.
[0036] In one embodiment of the present illuminating method, a
first path of the first light beam is symmetrical to a second path
of the second light beam.
[0037] Other advantages of the present invention will become
apparent from the following description taken in conjunction with
the accompanying drawings wherein are set forth, by way of
illustration and example, certain embodiments of the present
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] Further advantages of the present invention may become
apparent to those skilled in the art with the benefit of the
following detailed description of the preferred embodiments and
upon reference to the accompanying drawings in which:
[0039] FIG. 1 is a schematic illustration of conventional Michelson
interferometer;
[0040] FIG. 2 is a schematic illustration of conventional Mirau
interferometer;
[0041] FIG. 3 is a schematic illustration of a collimation lens for
the optical system of the present invention;
[0042] FIG. 4 is a schematic illustration of a beam splitter for
the optical of the present invention;
[0043] FIG. 5 is a schematic illustration of a Dove prism for the
optical system of the present invention;
[0044] FIG. 6 is a schematic illustration of an optical system in
accordance with one embodiment of the present invention;
[0045] FIG. 7A to FIG. 7D are schematic illustration of each path
of individual light beams in the optical system in accordance with
one embodiment of the present invention;
[0046] FIG. 8 is a schematic illustration of an optical system in
accordance with one embodiment of the present invention;
[0047] FIG. 9 is a schematic illustration of an optical system with
white light source in accordance with one embodiment of the present
invention;
[0048] FIGS. 10A and 10B are schematic illustrations of an optical
system with white light source in accordance with another
embodiment of the present invention;
[0049] FIGS. 11A and 11B are schematic illustrations of multiple
LED with different wavelengths as light source in accordance with
another embodiment of the present invention;
[0050] FIG. 12 is a flow chart showing the steps of a method for
illuminating a sample in accordance with one embodiment of the
present invention;
[0051] FIG. 13 is a flow chart showing the steps of a method for
illuminating a sample by white light source in accordance with one
embodiment of the present invention;
[0052] FIG. 14 is a flow chart showing the steps of a method for
illuminating a sample by white light source in accordance with
another embodiment of the present invention; and
[0053] FIG. 15 is a flow chart showing the steps of a method for
illuminating a sample by multiple light sources with different wave
lengths in accordance with one embodiment of the present
invention.
[0054] While the invention is susceptible to various modifications
and alternative forms, specific embodiments thereof are shown by
way of example in the drawings and may herein be described in
detail. The drawings may not be to scale. It should be understood,
however, that the drawings and detailed description thereto are not
intended to limit the invention to the particular form disclosed,
but on the contrary, the intention is to cover all modifications,
equivalents and alternatives falling within the spirit and scope of
the present invention as defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
[0055] Accordingly, while example embodiments of the invention are
capable of various modifications and alternative forms, embodiments
thereof are shown by way of example in the drawings and will herein
be described in detail. It should be understood, however, that
there is no intent to limit example embodiments of the invention to
the particular forms disclosed, but on the contrary, example
embodiments of the invention are to cover all modifications,
equivalents, and alternatives falling within the scope of the
invention.
[0056] As used herein, the term "lens" generally refers to a
transparent optical device to a light beam that focuses or
disperses the light beam by means of refraction. Example of such a
lens include, but are not limited to, focus lens, objective lens,
and projection lens. Such lenses can be commonly found and/or
processed in optical industry.
[0057] As used herein, the term "interferometer" or
"interferometry" generally refers to an optical system in which
optical waves or electromagnetic waves are superimposed to cause
the phenomenon of interference, which is used to extract
information.
[0058] As used herein, the term "coherence" generally refers to
that two wave sources are perfectly coherent if they have a
constant phase difference, the same frequency, and the same
waveform. Optical coherence is the ability of light to generate
interference, either temporal or spatial, and refers to the
property of light of keeping the same behavior at different times
or different places.
[0059] As used herein, the term "symmetry" generally refers to
mirror symmetry such as two things are the same respect to a plane.
For example, the two beams are symmetric if there is a symmetric
plane such that the two beams are mirror symmetry. The first
optical lens and mirror is symmetrical to the second optical lens
and mirror if there is a symmetric plane.
[0060] As used herein, the term "equivalent path length" generally
refers to two beams have the same travelling paths. In the present
invention, two beams may experience different paths before arrive
the sample. However, the two beams will have the same path length
from light source to the detector. As used herein, the term "sample
surface" generally refers to an area on the sample illuminated by
two beams. The micro structure of the sample surface may not be
flat, but the sample surface in macro scale may be deemed flatness
to the optical system of the present invention.
[0061] In the drawings, relative dimensions of each component and
among every component may be exaggerated for clarity. Within the
following description of the drawings the same or like reference
numbers refer to the same or like components or entities, and only
the differences with respect to the individual embodiments are
described.
[0062] The present invention would be suitable for, but not limited
to, biological and medical industry, for example skin detection.
The exiting skin detector just has the function of detection for
epidermis, and its optical characteristics have yet to be applied
to bring about a new medical detector for three-dimensional images.
Optical coherence tomography (OCT) is a 3D imaging modality based
on light reflected back from within the sample and has become
indispensable in biomedical applications with many advantages such
as non-invasiveness, high resolution, high imaging speed, and
relatively low cost. In this invention, low-coherence light source
would be preferred for OCT due to too much unnecessary interference
may be generated when Laser is applied to the biological and
medical applications, and this new setup improves low coherence
tomography technology, while conventional interferometers are not
stable. In this art a new technology with self-interferometer is
invented. It not only produces optical interference but also has
doubled confocal characteristics. This new interferometry can
combine the other technologies to achieve non-invasive medical
image, such as high resolution endoscopy, 3D tomography, and blood
glucose measurement, etc. It is also applicable to other fields
when nano or micro critical characteristics are necessary to be
inspected, such as defects/contaminations inspection and metrology
in semiconductor processes. The sensitive characteristics of low
coherence interference are improved, and the interference of the
combined optical beams is stable for the high resolution image.
This invention improves the sensitivity interferences of low
coherence and stability.
[0063] In order to better understand the concept of the present
invention, some optical elements are introduced first.
[0064] Please refer to FIG. 3, a collimated light source is
generated when a collimated lens CL is configured to a light source
LS. A collimated beam of light or other electromagnetic radiation
has parallel rays, and therefore will spread minimally as it
propagates. A perfectly collimated light beam, with no divergence,
would not disperse with distance. Such a beam cannot be created,
due to diffraction. Light can be approximately collimated by a
number of processes, for instance by means of a collimator or
collimated lens CL. Perfectly collimated light is sometimes deemed
to be focused at infinity. Thus, as the distance from a point
source increases, the spherical wave fronts become closer to plane
waves, which are perfectly collimated.
[0065] Unlike the prior arts, the light source in the present
invention can be of low-coherence light source, such as LED (Light
Emitting Diode), RCLED (Resonant Cavity LED), SLED or SLD
(superluminescent diode) which is an edge-emitting semiconductor
light source based on superluminescece. The light source in the
present invention can be coherence or high-coherence light source,
such as LASER, VECSEL. For the light source of low-coherence, the
emitted light is usually generated isotropically, and thus a
collimated lens of telocentric lens is provided to project a light
source into infinity. Thus, a parallel beam can be generated.
[0066] Please refer to FIG. 4, a beam splitter (BS) is provided
that an optical device splits a beam of light into two. It is a
crucial part of most interferometers. In its most common form, a
cube, is made from two triangular glass prisms, and preferred
isosceles right triangle, which are glued together at their base
using polyester, epoxy, or urethane-based adhesives. The thickness
of the resin layer is adjusted such that (for a certain wavelength)
half of the light incident through one "port" (i.e., face of the
cube) is reflected and the other half is transmitted due to total
internal reflection.
[0067] Please refer to FIG. 5, a Dove prism is provided to invert
an image. Dove prisms are shaped from a truncated right-angle
prism. A beam of light travelling parallel to the longitudinal
axis, entering one of the sloped faces 30 of the prism undergoes
one total internal reflection from the inside of the longest
(bottom) face 32 and emerges from the opposite sloped face 31.
Image 40 passing through the prism is flipped (mirrored) 42, and
because only one reflection takes place, the image 40 is also
inverted but not laterally transposed. Thus the Dove prism is used
almost exclusively for images appearing at infinity.
[0068] In the present invention, self-interferometry can be
generated by using the concept of the Bessel beam, in which two
identical beams, generated or separated from a collimated coherence
light beam, interfere with each other at sample surface. The
interfered light beam will be reflected and illuminated on a
detector such that an interference pattern can be obtained and
imaged.
[0069] The collimated light source can also be LASER or LED. In the
present invention, low coherence light source is preferred for the
biological and medical industries. However, in some applications,
the LASER is preferred.
[0070] The collimated light source is divided into two paths of
beams by using a beam splitter in the present invention, and the
two beams may be identical or nearly identical in intensity. The
two divided beams will be directed onto the sample at a tilted
incident angle to generate an interfered pattern by using mirrors
and lenses respectively. The interfered pattern may be similar as
the formation of Bessel beam. Then, the two beams will be reflected
toward the counterpart path to the beam splitter, and will be
merged and interfere with each other at the beam splitter again.
The merged beam is then focused via a focus lens onto a detector to
form images.
[0071] Various embodiments of the present invention will now be
described more fully with reference to the corresponding drawings
in which some example embodiments of the invention are shown.
Without limiting the scope of the protection of the present
invention, all the descriptions and drawings of the embodiments
will exemplarily be referred to optical devices and flow charts
with low-coherence light source. However, the embodiments are not
be used to limit the present invention to specific low-coherence
light source.
[0072] Please refer to FIG. 6, a light source LS provides a
collimated light beam to a beam splitter BS. Light source LS in the
present invention would generate initial coherence light or low
coherence light, such as LASER, SLD, or LED. The beam splitter BS
then divides the initial light beam into a first light beam and a
second light beam.
[0073] The first light beam is reflected by a first mirror M1 with
a first angle .theta.1 and focused by a first lens L1 to a sample
S. Then, the first beam is reflected back to a second mirror M2 to
the beam splitter BS. The second light beam is reflected by the
second mirror M2 with a second angle .theta.2 and focused by a
second lens L2 to the sample S. The two lenses L1 and L2 will
independently focus the first light beam and second light beam onto
the sample S respectively to generate an interfered pattern on the
sample S. Then, the second light beam is reflected toward the first
mirror M1 to the beam splitter BS, while the first light beam is
reflected toward the second mirror M2 to the beam splitter BS. In
one embodiment of present invention, in order to keep the first
path of the first beam symmetrical to the second path of the second
beam which is the counter path of the first path, the first angle
.theta.1 should be equal to the second angle .theta.2. The first
angle .theta.1 and second angle .theta.2 should be varied
accordingly such that angle of the first and second beam incident
to the sample surface can be adjusted. The first angle .theta.1 and
the second angle .theta.2 are combined incident and reflection
angles and can be ranged from 45.degree. to 135.degree.. Further,
the splitting plane of the beam splitter BS should be normal to the
sample surface. Hence, the first beam path is symmetrical to the
second beam path, or the first beam is symmetry to the second
beam.
[0074] The incident angle of the first and second beams on the
sample is tilted or inclined, and may be ranged from 0.degree. to
90.degree.. The image of the present self-interferometer is
dark-field.
[0075] A Dove prism DP is configured between the second mirror M2
and the second lens L2 for image contrast enhancement. The Dove
prism is a type of reflective prism which is used to invert an
image. The Dove prism DP can also be configured between the first
mirror M1 and the first lens L1.
[0076] The first beam and the second beam reflected back at the
beam splitter BS will be merged and generate an interfered pattern
at the beam splitter. The merged beam will be focused by a lens L10
to a detector D. The information received by the detector D will be
processed by computer such that image can be obtained.
[0077] Detailed paths of individual beams in this optical system
can be explained in FIG. 7. In FIG. 7A, some of the initial light
beam from the light source LS may pass through the beam splitter BS
to arrive the mirror M2 and reflected to sample S. Then, some of
the beam may be reflected by the sample S to the mirror M1 and
finally reflected back to the beam splitter BS to arrive the
detector D. In FIG. 7B, some of the initial light beam from the
light source LS may be reflected by the beam splitter BS to the
mirror M1 first and reflected again by the mirror M1 to the sample
S. Some of the beam may be then reflected by the sample S to the
mirror M2 and again reflected by the mirror M2 to the beam splitter
BS. Then, the beam will be reflected by the beam splitter to the
detector D.
[0078] In FIG. 7C, some of the initial light beam from the light
source LS may pass through the beam splitter BS to the mirror M2
and reflected by the mirror M2 to the sample S. However, unlike the
beam-path in FIG. 7A, some of the light beam may be reflected back
by the sample S along the original path to the mirror M2 and
reflected to the beam splitter BS to arrive the detector D. In this
drawing, the light beam does not travel to the mirror M1. In FIG.
7D, some of the initial light beam from the light source LS may be
reflected by the beam splitter BS to the mirror M1 and reflected to
the sample S. Similar to the beam-path in FIG. 7C, the light beam
may be reflected back by the sample S along the original path to
the mirror M1 and reflected by the mirror M1 again to the beam
splitter BS to arrive the detector D.
[0079] Another embodiment of the present invention can be referred
to FIG. 8. Two mirrors M3 and M4 are configured such that light
source LS and detector D can be configured in a better position for
commercial concern. Further, a set of mirrors 20 can be optionally
configured to increase path length of the second beam for some
particular applications, if the interference is generated with
different path lengths. In this embodiment, the two beams will have
equivalent path length.
[0080] Another embodiment of the present invention for full color
image can be referred to FIG. 9. A white light source WLS is
provided in the present invention. The white light source can be
prepared by using a blue LED combined with yellow phosphor, Halogen
lamp, Deuterium lamp, or gas-discharge lamp. It is important for
biological and medical applications. For example, some tissues may
present specific color when infected by virus or lack of some
important chemicals. Then, after the two reflected beams are merged
at the beam splitter, a dispersion optical element DOE is
configured to disperse the white light beam into several
spectroscopic components or individual monochromatic light beams.
Then a pinhole array PA is provided to sample every monochromatic
light beam individually. Then, a projection lens P10 is provided to
project each monochromatic light beam into detector D. The
information received by the detector D is processed by a computer.
In this embodiment of the present invention, a full color image can
be obtained when all images of each individual monochromatic light
beam are superimposed. For example, vivid images of live cells,
such as red blood cells, can be obtained by the present invention
instead of conventional grey level image by using electron
microscopy.
[0081] Another embodiment of the present invention for full color
image can be referred to FIG. 10A. In this embodiment, the
dispersion optical element DOE is configured such that white light
beam emitted from the white light source WLS will be dispersed
immediately. Then a pinhole array PA is provided to sample each
monochromatic light beam individually. A beam block BB is provided
to pick up a specific beam with a specific wavelength to be passed
therethrough. Another embodiment of the present invention is to use
single pinhole PH instead of pinhole array PA, as shown in FIG.
10B. After an image of the specific beam is processed, another beam
is selected by the pinhole PH till all images of all beams are
processed. Thus, a full color image can be obtained.
[0082] Still another embodiment of the present invention for full
color image can be referred to FIG. 11A and FIG. 11B. The light
source comprises several LEDs 12 of different wavelengths on a
board and a collimation lens CL is provided. The multiple LEDs 12
at least include red, green, and blue LED, and can further include
other LED that can be properly designated to cover the full visible
spectrum or beyond if necessary, such as yellow light LED, cyan
light LED, orange LED, and even UV LED. The board 10 can be rotated
or indexed such that every LED 12 can be provided as light source
for the embodiment in FIG. 6. After all images of every LED is
processed and combined, a full color image can be obtained.
[0083] For some patterns with characteristic dimension less than
resolution of visible light, the color is not defined, because the
red, green and blue lights correspond to the human cone cell and
such small patterns can't be seen by using visible light. For
example, most viruses are seen by using electron microscopy and an
image of a virus always shows grey level pattern. However, in the
present invention, if the interference pattern is processed into an
image with white light source or multiple light sources with
different wavelengths, a full color image can be obtained even the
features or patterns in the image is under resolution of visible
light. It is because the patterns or features can be presented by
computation of the interference patterns of the patterns or
features. Similarly, different responses will be shown in the image
when variant wavelengths are illuminated on different materials or
surface characteristics. Different absorptions and reflections can
be revealed by different wavelengths illuminating different
materials, surface roughness, or structure. The full color image
thus can provide more information.
[0084] The operation of the optical system or self-interferometer
provided in the present invention, such as embodiment in FIG. 6,
can be referred to FIG. 12. First, an initial collimated light beam
is generated as shown in step S12-1. Then, the initial light beam
is divided into a first light beam and a second light beam by using
a beam splitter, as shown in step S12-2. Next, the first and second
light beams are projected and focused onto a sample by a first and
second mirror/lens respectively, as shown in step S12-3. Images of
the second light beam and the reflected first light beam from the
sample are inverted by a dove prism, as shown in step S12-4. The
first light beam and the second light beam are reflected toward the
path of the second light beam and the path of the first light beam
respectively, as shown in step S12-5. Then, the reflected first
light beam and the reflected second light beam are combined or
merged at the beam splitter, as shown in step 12-6. The combined,
interfered light beam is then focused onto a detector by a focus
length, as shown in step S12-7.
[0085] The operation of the optical system or self-interferometer
by using a white light source, such as embodiment in FIG. 9, in the
present invention can be referred to FIG. 13. A white initial
collimated light beam is generated first as shown in step S13-1.
The white initial light beam is divided into a first light beam and
a second light beam by a beam splitter, as shown in step S13-2. The
first and second light beams are projected and focused onto a
sample by a first and second mirror/lens respectively, as shown in
step S13-3. Images of the second light beam and reflected first
light beam from the sample are inverted by a Doze prism, as shown
in step S13-4. The first light beam and the second light beam are
reflected toward a path of the second light beam and a path of the
first light beam respectively, as shown in step S13-5. The
reflected first light beam and the reflected second light beam are
combined or merged at the beam splitter, as shown in step S13-6.
The combined light beam is dispersed in spectroscopic components or
individual chromatic light beams by a dispersion optics element, as
shown in step S13-7. The spectroscopic components or individual
chromatic light beams are pickup into a plurality of interfered
beams with respective wavelengths by a pinhole array, as shown in
step S13-8. The plurality of interfered beams is projected onto a
detector, as shown in step S13-9. Each image of the plurality of
beams projected on the detector is combined or superimposed with
adjusted focal length of each wavelength from the image plane, as
shown in step S13-10.
[0086] The operation of the optical system or self-interferometer
by using a white light source, such as embodiment in FIG. 10A, in
the present invention can be referred to FIG. 14. A white initial
collimated light beam is generated first as shown in step S14-1.
The white initial collimated light beam is dispersed into
spectroscopic components by a dispersive optics element as shown in
step S14-2. The spectroscopic components or individual chromatic
light beams are pickup into a plurality of interfered beams with
respective wavelengths by a pinhole array, as shown in step S14-3.
One of the plurality of initial beams is selected to a beam
splitter as an emitting light beam by using a beam block as shown
in step S14-4. Then, the emitting light beam is divided into a
first light beam and a second light beam by a beam splitter, as
shown in step S14-5. The first and second light beams are projected
and focused onto a sample by a first and second mirror/lens
respectively, as shown in step S14-6. Images of the second light
beam and reflected first light beam from the sample are inverted by
a Doze prism, as shown in step S14-7. The first light beam and the
second light beam are reflected toward a path of the second light
beam and a path of the first light beam respectively, as shown in
step S14-8. The reflected first light beam and the reflected second
light beam are combined or merged at the beam splitter, as shown in
step S14-9. The combined, interfered light beam is then focused
onto a detector by a focus length, as shown in step S14-10. Step
S14-4 to step S14-10 are repeated till all plurality of initial
beams being formed images, as shown in step S14-11. And each images
of the plurality of initial beams are combined to form a full color
image as shown in step S14-12.
[0087] The operation of the optical system or self-interferometer
by using a white light source, such as embodiment in FIG. 10, in
the present invention can be referred to FIG. 15. A plurality of
initial beams with different wavelengths is provided, as shown in
step S15-1. Then, one of the plurality of initial light beams is
selected, as shown in step S15-2. The one of plurality of the
initial light beams is collimated into an initial collimated light
beam, as shown in step S15-3.
[0088] Then, the initial collimated light beam is divided into a
first light beam and a second light beam by a beam splitter, as
shown in step S15-4. The first and second light beams are projected
and focused onto a sample by a first and second mirror/lens
respectively, as shown in step S15-5. Images of the second light
beam and reflected first light beam from the sample are inverted by
a Dove prism, as shown in step S15-6. The first light beam and the
second light beam are reflected toward a path of the second light
beam and a path of the first light beam respectively, as shown in
step S15-7. The reflected first light beam and the reflected second
light beam are combined or merged at the beam splitter, as shown in
step S15-8. The combined, interfered light beam is then focused
onto a detector by a focus length, as shown in step S15-9. Step
S15-2 to step S15-9 are repeated till all plurality of initial
beams being formed images, as shown in step S15-10. And each images
of the plurality of initial beams are combined to form a full color
image as shown in step S15-11.
[0089] In summary, the present invention provides an optical
system, more particularly to a self-interferometer in optical
measurement or inspection, and operation method thereof. This
invention can be applied to OCT in bio-medical application.
Moreover, this invention can also be applied to defect inspection
and metrology in the semiconductor manufacturing industry.
Conventional optical inspection tools can't identify defects at 22
nm process node and beyond. This invention can catch defects about
1 nm. In addition, current metrology tool in semiconductor industry
is CD-SEM in which only five points of a wafer is probed to
represent wafer's process uniformity, but full wafer's critical
dimensions can't be measured due to severe low SEM's throughput. In
this invention, whole wafer's critical dimension thus can be
obtained due to high throughput of optical characteristic.
Furthermore, flatness of a thin film surface can also inspected by
using present invention.
[0090] The present invention provides stable images without very
high intensity light source, because both beams for interferometry
are used to illuminate sample. That means there is no reference
beam and the optical system is simpler in construction. Further,
although both LED and LASER can be provided as light source in this
invention, the LED has superiority in cost when low coherence
interferometry can be easily achieved. In the present invention,
dark field image is provided such that image contrast is higher
compared with those of the existing technologies. Moreover, by
using dispersive optical element, pinhole array, and projector,
white light source can be applied to the present invention and full
color image can be obtained. For conventional interferometer,
vibration is detrimental to the system performance and stability.
In contrast, due to there is no reference arm, the
self-interferometer in the present invention can be
vibration-proof.
[0091] Although the present invention has been described in
accordance with the embodiments shown, one of ordinary skill in the
art will readily recognize that there could be variations to the
embodiments and those variations would be within the spirit and
scope of the present invention. Accordingly, many modifications may
be made by one of ordinary skill in the art without departing from
the spirit and scope of the appended claims.
* * * * *