U.S. patent application number 14/490948 was filed with the patent office on 2015-12-03 for apparatus and method for extreme ultraviolet spectrometer calibration.
The applicant listed for this patent is KOREA INSTITUTE OF SCIENCE AND TECHNOLOGY. Invention is credited to Joon Mo AHN, Young Tae BYUN, Young Min JHON, Jae Hun KIM, Sun Ho KIM, Yong Soo KIM, Seok LEE, Taik Jin LEE, Min-Chul PARK, Min Ah SEO, Deok Ha WOO.
Application Number | 20150346029 14/490948 |
Document ID | / |
Family ID | 53026971 |
Filed Date | 2015-12-03 |
United States Patent
Application |
20150346029 |
Kind Code |
A1 |
KIM; Sun Ho ; et
al. |
December 3, 2015 |
APPARATUS AND METHOD FOR EXTREME ULTRAVIOLET SPECTROMETER
CALIBRATION
Abstract
Disclosed are herein an apparatus and method for extreme
ultraviolet (EUV) spectroscope calibration. The apparatus for EUV
spectroscope calibration includes an EUV generating module, an Al
filter, a diffraction grating, a CCD camera, a spectrum conversion
module, and a control module that compares a wavelength value
corresponding to a maximum peak among peaks of the spectrum
depending on the order of the EUV light converted from the spectrum
conversion module with a predetermined reference wavelength value
depending on an order of high-order harmonics to calculate a
difference value with the closest reference wavelength value, and
controls the spectrum depending on the order of the EUV light
converted from the spectrum conversion module to be moved in a
direction of wavelength axis by the calculated difference value.
Thus, it is possible to accurately measure a wavelength of a
spectrum of EUV light used in EUV exposure technology and mask
inspection technology.
Inventors: |
KIM; Sun Ho; (Seoul, KR)
; KIM; Yong Soo; (Seoul, KR) ; KIM; Jae Hun;
(Seoul, KR) ; PARK; Min-Chul; (Seoul, KR) ;
BYUN; Young Tae; (Guri-si, KR) ; SEO; Min Ah;
(Seoul, KR) ; AHN; Joon Mo; (Seoul, KR) ;
WOO; Deok Ha; (Seoul, KR) ; LEE; Seok; (Seoul,
KR) ; LEE; Taik Jin; (Seoul, KR) ; JHON; Young
Min; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KOREA INSTITUTE OF SCIENCE AND TECHNOLOGY |
Seoul |
|
KR |
|
|
Family ID: |
53026971 |
Appl. No.: |
14/490948 |
Filed: |
September 19, 2014 |
Current U.S.
Class: |
250/252.1 ;
250/372 |
Current CPC
Class: |
G01J 3/28 20130101; G01J
3/0297 20130101; G01J 3/2803 20130101; G01J 2003/282 20130101; G01J
3/10 20130101 |
International
Class: |
G01J 3/02 20060101
G01J003/02; G01J 3/28 20060101 G01J003/28; G01J 3/10 20060101
G01J003/10 |
Foreign Application Data
Date |
Code |
Application Number |
May 29, 2014 |
KR |
10-2014-0065251 |
Claims
1. An apparatus for extreme ultraviolet (EUV) spectroscope
calibration, comprising: an EUV generating module that generates
EUV light by interaction of a laser beam and an inert gas inside a
vacuum chamber; an Al filter that transmits a wavelength of a
specific band among wavelengths of the EUV light generated from the
EUV generating module; a diffraction grating that separates the EUV
light transmitted from the Al filter for each wavelength; a CCD
camera that photographs the EUV light with a specific band
wavelength separated from the diffraction grating; a spectrum
conversion module that converts pixels of an image photographed
from the CCD camera into wavelengths to show the wavelengths in a
spectrum depending on an order of the EUV light; and a control
module that compares a wavelength value corresponding to a maximum
peak among peaks of the spectrum depending on the order of the EUV
light converted from the spectrum conversion module with a
predetermined reference wavelength value depending on an order of
high-order harmonics to calculate a difference value with the
closest reference wavelength value, and controls the spectrum
depending on the order of the EUV light converted from the spectrum
conversion module to be moved in a direction of wavelength axis by
the calculated difference value.
2. The apparatus for EUV spectroscope calibration of claim 1,
wherein, when a Zr filter for transmitting the wavelength of the
specific band among the wavelengths of the EUV light generated from
the EUV generating module and blocking a wavelength band of a
femto-second laser is disposed in the same position as that of the
Al filter in a state in which the Al filter is removed, EUV light
transmitted from the Zr filter is transmitted to the diffraction
grating, the EUV light output from the diffraction grating is
photographed by the CCD camera, pixels of an image photographed
from the CCD camera are converted into wavelengths by the spectrum
conversion module to show the wavelengths in the spectrum depending
on the order of the EUV light, and the spectrum depending on the
order of the EUV light converted from the spectrum conversion
module is controlled, by the control module, to be moved in the
direction of wavelength axis by the calculated difference
value.
3. The apparatus for EUV spectroscope calibration of claim 2,
wherein the Zr filter blocks peripheral wavelengths in a fixed
range with respect to 800 nm that is a peak wavelength of a
femto-second laser beam, and transmits a wavelength of a specific
band in a range of 7 nm to 17 nm.
4. The apparatus for EUV spectroscope calibration of claim 1,
wherein the wavelength of the specific band transmitted by the Al
filter is in a range of 17 nm to 60 nm.
5. An apparatus for EUV spectroscope calibration comprising: an EUV
generating module that generates EUV light by interaction of a
laser beam and an inert gas inside a vacuum chamber; a beam
splitter that splits the EUV light generated from the EUV
generating module into reflected light and transmitted light by
transmitting and reflecting the EUV light at a constant ratio; a
reflector that again vertically reflects the reflected light
vertically split from the beam splitter; a diffraction grating that
separates, for each wavelength, the reflected light reflected from
the reflector and the transmitted light split from the beam
splitter; an Al filter that transmits a wavelength of a specific
band among wavelengths of the transmitted light separated from the
diffraction grating; an Zr filter that transmits a wavelength of a
specific band among wavelengths of the reflected light separated
from the diffraction grating and blocks a wavelength band of a
femto-second laser; a CCD camera that photographs the EUV light
transmitted from each of the Al filter and the Zr filter; a
spectrum conversion module that converts pixels of an image
photographed from the CCD camera into wavelengths to show the
wavelengths in a spectrum depending on an order of the EUV light;
and a control module that compares a wavelength value corresponding
to a maximum peak among peaks of the spectrum depending on the
order of the EUV light converted from the spectrum conversion
module and passing through the Al filter and the Zr filter with a
predetermined reference wavelength value depending on an order of
high-order harmonics to calculate a difference value with the
closest reference wavelength value, and controls the spectrum
depending on the order of the EUV light converted from the spectrum
conversion module and passing through the Al filter and the Zr
filter to be moved in a direction of wavelength axis by the
calculated difference value.
6. A method for EUV spectroscope calibration comprising: (a)
generating EUV light by interaction of a laser beam and an inert
gas inside a vacuum chamber; (b) transmitting, by an Al filter, a
wavelength of a specific band among wavelengths of the EUV light
generated in the (a) generating; (c) separating, by a diffraction
grating, the EUV light transmitted in the (b) transmitting for each
wavelength; (d) photographing, by a CCD camera, the EUV light with
a specific band wavelength separated in the (c) separating; (e)
converting, by a spectrum conversion module, pixels of an image
photographed in the (d) photographing into wavelengths to show the
wavelengths in a spectrum depending on an order of the EUV light;
and (f) comparing, by a control module, a wavelength value
corresponding to a maximum peak among peaks of the spectrum
depending on the order of the EUV light converted in the (e)
converting with a predetermined reference wavelength value
depending on an order of high-order harmonics to calculate a
difference value with the closest reference wavelength value, and
moving the spectrum depending on the order of the EUV light
converted in the (e) converting in a direction of wavelength axis
by the calculated difference value.
7. The method for EUV spectroscope calibration of claim 6, after
the (f) comparing, when a Zr filter is disposed in the same
position as that of the Al filter in a state in which the Al filter
in the (b) transmitting is removed, further comprising: (g)
transmitting, by the Zr filter, the wavelength of the specific band
among the wavelengths of the EUV light generated in the (a)
generating and blocking a wavelength band of a femto-second laser;
(h) separating, by the diffraction grating, the EUV light
transmitted in the (g) transmitting for each wavelength; (i)
photographing, by the CCD camera, the EUV light with a specific
band wavelength separated in the (h) separating; (j) converting, by
the spectrum conversion module, pixels of an image photographed in
the (i) photographing into wavelengths to show the wavelengths in
the spectrum depending on the order of the EUV light; and (k)
moving, by the control module, the spectrum depending on the order
of the EUV light converted in the (j) converting in the direction
of wavelength axis by the difference value calculated in the (f)
comparing.
8. The method for EUV spectroscope calibration of claim 7, wherein
the Zr filter in the (g) transmitting blocks peripheral wavelengths
in a fixed range with respect to 800 nm that is a peak wavelength
of a femto-second laser beam, and transmits a wavelength of a
specific band in a range of 7 nm to 17 nm.
9. The method for EUV spectroscope calibration of claim 6, wherein
the wavelength of the specific band transmitted by the Al filter in
the (b) transmitting is in a range of 17 nm to 60 nm.
10. A method for EUV spectroscope calibration comprising: (a')
generating EUV light by interaction of a laser beam and an inert
gas inside a vacuum chamber; (b') splitting, by a beam splitter,
the EUV light generated in the (a') generating into reflected light
and transmitted light by transmitting and reflecting the EUV light
at a constant ratio; (c') again vertically reflecting, by a
reflector, the reflected light vertically split in the (b')
splitting; (d') separating, by a diffraction grating, the reflected
light reflected in the (c') again vertically reflecting and the
transmitted light split in the (b') splitting for each wavelength;
(e') transmitting, by an Al filter, a wavelength of a specific band
among wavelengths of the transmitted light separated in the (d')
separating; (1) transmitting, by a Zr filter, a wavelength of a
specific band among wavelengths of the reflected light separated in
the (d') separating and blocking a wavelength band of a
femto-second laser; (g') photographing, by a CCD camera, the EUV
light transmitted in the (e') transmitting and the (f')
transmitting; (h') converting, by a spectrum conversion module,
pixels of an image photographed in the (g') photographing into
wavelengths to show the wavelengths in a spectrum depending on an
order of the EUV light; and (i') comparing, by a control module, a
wavelength value corresponding to a maximum peak among peaks of the
spectrum depending on the order of the EUV light converted in the
(h') converting and passing through the Al filter and the Zr filter
with a predetermined reference wavelength value depending on an
order of high-order harmonics to calculate a difference value with
the closest reference wavelength value, and moving the spectrum
depending on the order of the EUV light converted in the (h')
converting and passing through the Al filter and the Zr filter in a
direction of wavelength axis by the calculated difference value.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to and the benefit of
Korean Patent Application No. 2014-0065251, filed on May 29, 2014,
the disclosure of which is incorporated herein by reference in its
entirety.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates to an apparatus and method for
extreme ultraviolet (EUV) spectroscope calibration, and more
particularly, to an apparatus and method for EUV spectroscope
calibration which may accurately measure a spectrum of EUV light
used in EUV exposure technologies and mask inspection
technologies.
[0004] 2. Discussion of Related Art
[0005] In general, electromagnetic radiation (also referred to as
"soft X-ray") having a wavelength of approximately 124 nm or less
while having extreme ultraviolet (EUV) light, for example, light
with a wavelength of approximately 13.5 nm may be used in a
photolithography process for fanning a very small pitch on a
substrate, for example, a silicon wafer.
[0006] That is, EUV and X-rays are included in a region having
wavelengths shorter than those of visible rays, may improve a
measurement resolution by a diffraction limit that is limited by
sizes of wavelengths in a precision measurement using light, and
may be utilized in micromeasurement or nondestructive inspection
related to biotechnologies using excellent transmission
characteristics due to extension up to the X-ray region.
[0007] In particular, simultaneously, when a light source having
excellent coherency can be generated, a variety of applications
using the interference and diffraction phenomenon of light are
possible. In addition, the EUV and X-rays can maintain the
repeatability of entering femto-second laser, and therefore can be
used in precision spectroscopy or frequency standard measurement in
the EUV and X-ray regions.
[0008] Among various methods for generating such EUV and X-rays, a
method using a synchrotron may be used. When generating the EUV and
X-rays using the synchrotron, it is possible to obtain several
different wavelength bands while obtaining a large amount of light
with excellent quality, but the facility itself is very large in
its size and expensive and therefore a laboratory cannot be simply
configured.
[0009] As a method for overcoming the above-mentioned problem, a
high-order harmonic generation (HHG) method using a high output
femto-second pulse laser has been suggested, and therefore coherent
EUV and soft X-rays can be generated using a relatively small
experimental apparatus.
[0010] In the HHG method, by applying a high time-varying electric
field to an inert gas such as Ar, Ne, Xe, or the like, electrons
are ionized, moved along the trajectory, and then are recombined
again, and therefore energy corresponding to a sum of ionization
energy and kinetic energy of the electrons may be generated as EUV
light or light in X-ray bands.
[0011] Conventionally, in order to generate such HHG, it is
designed that the inert gas is injected into a gascell and the used
inert gas naturally flows out of the gascell.
[0012] In addition, EUV may be generated even through lithium, tin,
or a semiconductor device as well as the inert gas such as Ar, Ne,
Xe, or the like, but a gas may be used as a medium due to HHG using
the gascell. This is because a medium for allowing EUV to be
generated by HHG using the gascell is only the inert gas due to the
current technologies. EUV may be generated through other methods as
well as the method of generating EUV using the inert gas.
[0013] Meanwhile, according to demands for ultraminiaturization of
a semiconductor process for high integration, development up to ArF
(193 nm) while passing through G line (436 nm), I line (365 nm),
and KrF (248 nm) has been conducted as a light source used in
exposure technologies.
[0014] Thereafter, new exposure technologies that increase
resolution in a semiconductor process of 90 nm or less have been
required, ArF immersion exposure technology and double-patterning
exposure technology have been developed, and therefore a mass
production up to a process of DRAM of 23 nm and NAND flash of 20 nm
has been succeeded.
[0015] As next generation exposure technologies for overcoming the
ArF exposure technology, several technologies have been studied,
and research and development on EUV exposure technology among these
technologies have been actively conducted worldwide such as
reaching a stage of test production by major semiconductor
companies, and the like.
[0016] Meanwhile, in order to inspect a defect of a mask
manufactured by the EUV exposure technology, EUV light is similarly
needed. In particular, technology in which the defect of the mask
is inspected with the same wavelength as a wavelength used in the
exposure technology is referred to as actinic mask inspection
technology. In order to generate EUV with the same wavelength as an
EUV wavelength used in the exposure technology, an HHG method is
needed. In order to check whether the EUV light generated in the
HHG method is suitable for a wavelength to be used, a spectrum
should be measured using an EUV spectroscope, and in this instance,
calibration of the spectroscope should be performed in order to
measure the accurate spectrum. As a calibration method of the EUV
light, a method using an atomic line which has been traditionally
used may be used. Fluorescence lines which are inherent for each
inert gas are referred to as atomic lines. Since wavelength values
of an atomic line spectrum have been already studied several
decades ago and thereby widely known, calibration may be performed
on EUV light based on the position of the atomic line spectrum and
the wavelength value thereof.
[0017] However, in order to obtain energy with an intensity that
can be measured by a CCD camera of the spectroscope, energy which
is several times higher than energy of a laser used in HHG is
needed. Thus, a laser light source that can output energy higher
than that of a laser for generating high-order harmonics for EUV is
necessarily needed.
[0018] Prior Patent Document 1: Korean Patent Registration No.
10-10789135
SUMMARY OF THE INVENTION
[0019] The present invention is directed to an apparatus and method
for extreme ultraviolet (EUV) spectroscope calibration, which can
accurately measure a wavelength of a spectrum of EUV light used in
EUV exposure technology and mask inspection technology.
[0020] According to a first aspect of the present invention, there
is provided an apparatus for extreme ultraviolet (EUV) spectroscope
calibration including: an EUV generating module that generates EUV
light by interaction of a laser beam and an inert gas inside a
vacuum chamber; an Al filter that transmits a wavelength of a
specific band among wavelengths of the EUV light generated from the
EUV generating module; a diffraction grating that separates the EUV
light transmitted from the Al filter for each wavelength; a CCD
camera that photographs the EUV light with a specific band
wavelength separated from the diffraction grating; a spectrum
conversion module that converts pixels of an image photographed
from the CCD camera into wavelengths to show the wavelengths in a
spectrum depending on an order of the EUV light; and a control
module that compares a wavelength value corresponding to a maximum
peak among peaks of the spectrum depending on the order of the EUV
light converted from the spectrum conversion module with a
predetermined reference wavelength value depending on an order of
high-order harmonics to calculate a difference value with the
closest reference wavelength value, and controls the spectrum
depending on the order of the EUV light converted from the spectrum
conversion module to be moved in a direction of wavelength axis by
the calculated difference value.
[0021] Preferably, when a Zr filter for transmitting the wavelength
of the specific band among the wavelengths of the EUV light
generated from the EUV generating module and blocking a wavelength
band of a femto-second laser is disposed in the same position as
that of the Al filter in a state in which the Al filter is removed,
EUV light transmitted from the Zr filter may be transmitted to the
diffraction grating, the EUV light output from the diffraction
grating may be photographed by the CCD camera, pixels of an image
photographed from the CCD camera may be converted into wavelengths
by the spectrum conversion module to show the wavelengths in the
spectrum depending on the order of the EUV light, and the spectrum
depending on the order of the EUV light converted from the spectrum
conversion module may be controlled. by the control module, to be
moved in the direction of wavelength axis by the calculated
difference value.
[0022] Preferably, the Zr filter may block peripheral wavelengths
in a fixed range with respect to 800 nm that is a peak wavelength
of a femto-second laser beam, and transmit a wavelength of a
specific band in a range of 7 nm to 17 nm.
[0023] Preferably, the wavelength of the specific band transmitted
by the Al filter may be in a range of 17 nm to 60 nm.
[0024] According to a second aspect of the present invention, there
is provided an apparatus for EUV spectroscope calibration
including: an EUV generating module that generates EUV light by
interaction of a laser beam and an inert gas inside a vacuum
chamber; a beam splitter that splits the EUV light generated from
the EUV generating module into reflected light and transmitted
light by transmitting and reflecting the EUV light at a constant
ratio; a reflector that again vertically reflects the reflected
light vertically split from the beam splitter; a diffraction
grating that separates, for each wavelength, the reflected light
reflected from the reflector and the transmitted light split from
the beam splitter; an Al filter that transmits a wavelength of a
specific band among wavelengths of the transmitted light separated
from the diffraction grating; an Zr filter that transmits a
wavelength of a specific band among wavelengths of the reflected
light separated from the diffraction grating and blocks a
wavelength band of a femto-second laser; a CCD camera that
photographs the EUV light transmitted from each of the Al filter
and the Zr filter; a spectrum conversion module that converts
pixels of an image photographed from the CCD camera into
wavelengths to show the wavelengths in a spectrum depending on an
order of the EUV light; and a control module that compares a
wavelength value corresponding to a maximum peak among peaks of the
spectrum depending on the order of the EUV light converted from the
spectrum conversion module and passing through the Al filter and
the Zr filter with a predetermined reference wavelength value
depending on an order of high-order harmonics to calculate a
difference value with the closest reference wavelength value, and
controls the spectrum depending on the order of the EUV light
converted from the spectrum conversion module and passing through
the Al filter and the Zr filter to be moved in a direction of
wavelength axis by the calculated difference value.
[0025] According to a third aspect of the present invention, there
is provided a method for EUV spectroscope calibration including:
(a) generating EUV light by interaction of a laser beam and an
inert gas inside a vacuum chamber; (b) transmitting, by an Al
filter, a wavelength of a specific band among wavelengths of the
EUV light generated in the (a) generating; (c) separating, by a
diffraction grating, the EUV light transmitted in the (b)
transmitting for each wavelength; (d) photographing, by a CCD
camera, the EUV light with a specific band wavelength separated in
the (c) separating; (e) converting, by a spectrum conversion
module, pixels of an image photographed in the (d) photographing
into wavelengths to show the wavelengths in a spectrum depending on
an order of the EUV light; and (f) comparing, by a control module,
a wavelength value corresponding to a maximum peak among peaks of
the spectrum depending on the order of the EUV light converted in
the (e) converting with a predetermined reference wavelength value
depending on an order of high-order harmonics to calculate a
difference value with the closest reference wavelength value, and
moving the spectrum depending on the order of the EUV light
converted in the (e) converting in a direction of wavelength axis
by the calculated difference value.
[0026] Preferably, after the (f) comparing, when a Zr filter is
disposed in the same position as that of the Al filter in a state
in which the Al filter in the (b) transmitting is removed, the
method for EUV spectroscope calibration may further include: (g)
transmitting, by the Zr filter, the wavelength of the specific band
among the wavelengths of the EUV light generated in the (a)
generating and blocking a wavelength band of a femto-second laser;
(h) separating, by the diffraction grating, the EUV light
transmitted in the (g) transmitting for each wavelength; (i)
photographing, by the CCD camera, the EUV light with a specific
band wavelength separated in the (h) separating; (j) converting, by
the spectrum conversion module, pixels of an image photographed in
the (i) photographing into wavelengths to show the wavelengths in
the spectrum depending on the order of the EUV light; and (k)
moving, by the control module, the spectrum depending on the order
of the EUV light converted in the (j) converting in the direction
of wavelength axis by the difference value calculated in the (f)
comparing.
[0027] Preferably, the Zr filter in the (g) transmitting may block
peripheral wavelengths in a fixed range with respect to 800 nm that
is a peak wavelength of a femto-second laser beam, and transmit a
wavelength of a specific band in a range of 7 nm to 17 nm.
[0028] Preferably, the wavelength of the specific band transmitted
by the Al filter in the (b) transmitting may be in a range of 17 nm
to 60 nm.
[0029] According to a fourth aspect of the present invention, there
is provided a method for EUV spectroscope calibration including:
(a') generating EUV light by interaction of a laser beam and an
inert gas inside a vacuum chamber; (V) splitting, by a beam
splitter, the EUV light generated in the (a') generating into
reflected light and transmitted light by transmitting and
reflecting the EUV light at a constant ratio; (c') again vertically
reflecting, by a reflector, the reflected light vertically split in
the (b') splitting; (d') separating, by a diffraction grating, the
reflected light reflected in the (c') again vertically reflecting
and the transmitted light split in the (b') splitting for each
wavelength; (e') transmitting, by an Al filter, a wavelength of a
specific band among wavelengths of the transmitted light separated
in the (d') separating; (f') transmitting, by a Zr filter, a
wavelength of a specific band among wavelengths of the reflected
light separated in the (d') separating and blocking a wavelength
band of a femto-second laser; (g') photographing, by a CCD camera,
the EUV light transmitted in the (e') transmitting and the (f)
transmitting; (h') converting, by a spectrum conversion module,
pixels of an image photographed in the (g') photographing into
wavelengths to show the wavelengths in a spectrum depending on an
order of the EUV light; and (i') comparing, by a control module, a
wavelength value corresponding to a maximum peak among peaks of the
spectrum depending on the order of the EUV light converted in the
(h') converting and passing through the Al filter and the Zr filter
with a predetermined reference wavelength value depending on an
order of high-order harmonics to calculate a difference value with
the closest reference wavelength value, and moving the spectrum
depending on the order of the EUV light converted in the (h')
converting and passing through the Al filter and the Zr filter in a
direction of wavelength axis by the calculated difference
value.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The above and other objects, features, and advantages of the
present invention will become more apparent to those of ordinary
skill in the art by describing in detail exemplary embodiments
thereof with reference to the accompanying drawings, in which:
[0031] FIG. 1 is an overall conceptual diagram illustrating an
apparatus for extreme ultraviolet (EUV) spectroscope calibration
according to an embodiment of the present invention;
[0032] FIGS. 2 to 4 are diagrams illustrating a process of moving,
in a direction of a wavelength axis, a spectrum depending on the
order of EUV light passing through an Al filter or a Zr filter
through a control module applied to an embodiment of the present
invention;
[0033] FIG. 5 is an overall conceptual diagram illustrating an
apparatus for EUV spectroscope calibration according to another
embodiment of the present invention;
[0034] FIGS. 6 and 7 are diagrams illustrating a process of moving,
in a direction of a wavelength axis, a spectrum depending on the
order of EUV light passing through an Al filter or a Zr filter
through a control module applied to another embodiment of the
present invention;
[0035] FIGS. 8 and 9 are graphs illustrating a transmission in
compliance with a wavelength of a Zr filter applied to embodiments
of the present invention; and
[0036] FIGS. 10 and 11 are graphs illustrating a transmission in
compliance with a wavelength of an Al filter applied to embodiments
of the present invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0037] Example embodiments of the present invention are disclosed
herein. However, specific structural and functional details
disclosed herein are merely representative for purposes of
describing example embodiments of the present invention, and
example embodiments of the present invention may be embodied in
many alternate forms and should not be construed as limited to
example embodiments of the present invention set forth herein.
[0038] Accordingly, while the invention is susceptible to various
modifications and alternative forms, specific 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 the invention to the particular fauns
disclosed, but on the contrary, the invention is to cover all
modifications, equivalents, and alternatives falling within the
spirit and scope of the invention. Like numbers refer to like
elements throughout the description of the figures.
[0039] It will be understood that, although the terms first,
second, etc. may be used herein to describe various elements, these
elements should not be limited by these terms. These terms are only
used to distinguish one element from another. For example, a first
element could be termed a second element, and, similarly, a second
element could be termed a first element, without departing from the
scope of the present invention. As used herein, the term "and/or"
includes any and all combinations of one or more of the associated
listed items.
[0040] It will be understood that when an element is referred to as
being "connected" or "coupled" to another element, it can be
directly connected or coupled to the other element or intervening
elements may be present. In contrast, when an element is referred
to as being "directly connected" or "directly coupled" to another
element, there are no intervening elements present. Other words
used to describe the relationship between elements should be
interpreted in a like fashion (i.e., "between" versus "directly
between," "adjacent" versus "directly adjacent," etc.).
[0041] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the invention. As used herein, the singular forms "a," "an," and
"the" are intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood
that the terms "comprises," "comprising," "includes," and/or
"including," when used herein, specify the presence of stated
features, integers, steps, operations, elements, and/or components,
but do not preclude the presence or addition of one or more other
features, integers, steps, operations, elements, components, and/or
groups thereof.
[0042] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
invention belongs. It will be further understood that terms, such
as those defined in commonly used dictionaries, should be
interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and will not be
interpreted in an idealized or overly formal sense unless expressly
so defined herein.
[0043] FIG. 1 is an overall conceptual diagram illustrating an
apparatus for extreme ultraviolet (EUV) spectroscope calibration
according to an embodiment of the present invention.
[0044] Referring to FIG. 1, the apparatus for EUV spectroscope
calibration according to an embodiment of the present invention
roughly includes an EUV generating module 100, an Al filter 200, a
diffraction grating 300, a CCD camera 400, a spectrum conversion
module 500, and a control module 600.
[0045] Here, the EUV generating module 100 is a module for
generating EUV light by interaction of a laser beam and an inert
gas inside a vacuum chamber, and includes a laser beam generating
unit 110, a vacuum chamber 120, a plurality of optical members 130,
and an EUV generating unit 140.
[0046] The laser beam generating unit 110 is a laser oscillator
that outputs a light intensity of approximately 10.sup.11
W/cm.sup.2, and outputs a femto-second laser as a light source for
high-order harmonic generation (HHG) according to embodiments of
the present invention.
[0047] The laser beam generating unit 110 according to an
embodiment of the present invention has a femto-second pulse width
of 35, and outputs a femto-second laser through a laser oscillator
using titanium sapphire as a laser gain medium.
[0048] Obviously, conditions such as a pulse width, a wavelength,
and the like of such femto-second laser can be changed to various
embodiments such as an optical fiber-based femto-second laser and
the like in accordance with the purpose of use or environment.
[0049] In addition, the femto-second laser generated in the laser
beam generating unit 110 is a femto-second laser that has a laser
repeatability of 1 kHz and has energy of several mJ per maximum
pulse.
[0050] The vacuum chamber 120 is a chamber for maintaining an
internal environment of the vacuum chamber 120 in a vacuum state.
Here, a pressure inside the chamber through which EUV light passes
is preferably approximately 10.sup.-5 Torr or less, and a partial
pressure of oxygen and moisture is preferably as low as
possible.
[0051] Meanwhile, almost all environments except the laser beam
generating unit 110 are preferably achieved inside the vacuum
chamber 120. That is, an EUV light source is all absorbed in the
atmosphere and thereby generation of the EUV light source should be
achieved inside the vacuum chamber 120, and when the EUV light
source is generated, characteristic analysis of the generated EUV
light source should be also performed inside the vacuum chamber
120.
[0052] The plurality of optical members 130 are disposed inside the
vacuum chamber 120 and used to appropriately transmit a high-output
laser beam generated from the laser beam generating unit 110. For
example, a path of a laser beam generated from the laser beam
generating unit 110 through first and second optical members (not
shown) constituted of a reflecting mirror is changed and a position
of the laser beam is adjusted, and therefore the laser beam is
directed to a third optical member (not shown) constituted of a
concave mirror. The laser beam changed from the first and second
optical members through the third optical member is reflected and
condensed to a fourth optical member (not shown) constituted of a
reflecting mirror, and the laser beam condensed from the third
optical member through the fourth optical member is reflected to be
transmitted to the EUV generating unit 140. The number and
disposition of such a plurality of optical members can be changed
in various ways in accordance with design by those skilled in the
related art.
[0053] In particular, the EUV generating unit 140 for generating
EUV according to the embodiments of the present invention may
inject an inert gas required for generating the EUV light source
with a wavelength band of about several tens of nanometers to
several nanometers, and maintain a constant pressure by collecting
the inert gas.
[0054] Such an EUV generating unit 140 is disposed inside the
vacuum chamber 120 for generating EUV, constituted of a housing
forming the whole body, and generates EUV light by interaction of
the laser beam and an external inert gas (for example, helium (He),
neon (Ne), argon (Ar), or the like).
[0055] In HHG through the EUV generating unit 140 according to the
embodiments of the present invention configured as above, for
example, by applying a high time-varying electric field to the
inert gas containing helium (He), neon (Ne), or argon (Ar), or
their mixed gas, electrons are ionized, moved along the trajectory,
and then recombined again, and therefore energy corresponding to a
sum of ionization energy and kinetic energy of the electrons may be
generated as the EUV light.
[0056] That is, when the femto-second laser beam is made incident
on atoms of the inert gas condensed to the housing of the EUV
generating unit 140, electrons within the atoms of the inert gas
contained in the housing by a strong electric field of the laser
come out of the atoms by a tunneling effect and are ionized.
[0057] The electrons ionized in this manner are accelerated by the
strong electric field of the applied laser without being affected
by the atoms any longer, and has kinetic energy while being
accelerated. Thereafter, the electrons are combined with the atoms
again while the electric field of the laser is changed. In this
instance, by the kinetic energy obtained by the laser and the
recombination of the atoms and the electrons, energy corresponding
to a sum of the generated ionization energy is emitted as light,
and the light becomes the EUV light source.
[0058] The generated EUV light is absorbed and eliminated by
impurities in the atmosphere, and therefore generation of the EUV
light should be achieved in a vacuum environment, that is, inside
the vacuum chamber 120. In addition, components excluding the laser
beam generating unit 110 and components of the spectrum conversion
module 500 and the control module 600 are preferably provided
inside the vacuum chamber 120.
[0059] Meanwhile, the EUV generating unit 140 according to the
embodiments of the present invention configured as above is
specifically described in the prior art of Korean Patent
Application No. 2012-0095715 (module for generating EUV light)
filed by the same applicant, and for a detailed description
thereof, refer to the prior art. In addition, in addition to the
prior art, the EUV generating unit 140 is not limited to its type
as long as it can generate EUV light with a desired wavelength.
[0060] The Al filter 200 transmits a wavelength of a specific band
among wavelengths of the EUV light generated from the EUV
generating module 100 (for example, transmits .gtoreq.67% light in
a range of approximately 17 nm to 60 nm and transmits <10% light
in a range of approximately 17 nm or less).
[0061] Meanwhile, conventionally, the spectrum of the EUV light is
measured without using the Al filter 200, but in this instance, a
light source (fs laser) having energy of 10 mJ or more is needed to
cause an increase in costs.
[0062] The diffraction grating 300 separates the EUV light
transmitted from the Al filter 200 for each wavelength.
[0063] The CCD camera 400 photographs the EUV light with a specific
band wavelength separated from the diffraction grating 300. The
spectrum conversion module 500 converts pixels of an image
photographed from the CCD camera 400 into wavelengths to show the
wavelengths in a spectrum depending on an order of the EUV
light.
[0064] The control module 600 compares a wavelength value
corresponding to a maximum peak among peaks of the spectrum
depending on the order of the EUV light converted from the spectrum
conversion module 500 with a predetermined reference wavelength
value (theory value, see table of FIG. 4) depending on an order of
high-order harmonics to calculate a difference value with the
closest reference wavelength value, and controls the spectrum
depending on the order of the EUV light converted from the spectrum
conversion module 500 to be moved in a direction of wavelength axis
by the calculated difference value.
[0065] That is, in the spectrum passing through the Al filter 200
due to characteristics of the Al filter 200 (transmission is
rapidly reduced to less than 10% at 17.1 nm or less), the whole
spectrum depending on the order of the EUV light converted from the
spectrum conversion module 500 is moved in accordance with the
reference wavelength value (theory value) depending on a
predetermined order of the high-order harmonics, and then accurate
wavelength values of peaks may be obtained.
[0066] Meanwhile, when a Zr filter (not shown) for transmitting the
wavelength of the specific band among the wavelengths of the EUV
light generated from the EUV generating module 100 and blocking a
wavelength band of a femto-second laser is disposed in the same
position as that of the Al filter 200 in a state in which the Al
filter 200 is removed, it is preferable that EUV light transmitted
from the Zr filter be transmitted to the diffraction grating 300,
the EUV light output from the diffraction grating 300 be
photographed by the CCD camera 400, pixels of an image photographed
from the CCD camera 400 be converted into wavelengths by the
spectrum conversion module 500 to show the wavelengths in the
spectrum depending on the order of the EUV light, and the spectrum
depending on the order of the EUV light converted from the spectrum
conversion module 500 be controlled, by the control module 600, to
be moved in the direction of wavelength axis by the calculated
difference value.
[0067] That is, even when the Al filter 200 is replaced by the Zr
filter, the arrangement state of the optical system is the same.
Thus, when a spectrum obtained by passing through the Zr filter is
moved by the same value as the value for allowing a spectrum
obtained by passing through the Al filter 200 to be moved, it is
possible to obtain accurate wavelengths of the peaks in accordance
with the reference wavelength value depending on the predetermined
order of the high-order harmonics.
[0068] The Zr filter blocks peripheral wavelengths in a fixed range
with respect to 800 nm (preferably, approximately 796 nm) that is a
peak wavelength of a femto-second laser beam, and transmits a
wavelength of a specific band (preferably, in a range of
approximately 7 nm to 17 nm) among wavelengths of the EUV light
generated from the EUV generating module 100. That is, it is
preferable that the Zr filter block a wavelength of approximately
20 nm or more, and transmit a wavelength in a range of
approximately 7 nm to 17 nm.
[0069] Meanwhile, according to an embodiment of the present
invention, the Al filter and the Zr filter are disposed between the
EUV generating module 100 and the diffraction grating 300, but the
present invention is not limited thereto. For example, the Al
filter and the Zr filter may be disposed between the diffraction
grating 300 and the CCD camera 400.
[0070] FIGS. 2 to 4 are diagrams illustrating a process of moving,
in a direction of a wavelength axis, a spectrum depending on the
order of EUV light passing through an Al filter or a Zr filter
through a control module applied to an embodiment of the present
invention. Here, FIG. 2 illustrates a state in which calibration is
not performed on both spectrums passing through the Al filter 200
and the Zr filter, FIG. 3 illustrates a state in which the spectrum
passing through the Al filter 200 is first moved in accordance with
a reference wavelength value depending on a predetermined order of
the high-order harmonics, and FIG. 4 illustrates a state in which
the spectrum passing through the Zr filter is also moved by a value
(x axis-wavelength) for allowing the spectrum passing through the
Al filter 200 to be moved, and then calibration is performed.
[0071] FIG. 5 is an overall conceptual diagram illustrating an
apparatus for EUV spectroscope calibration according to another
embodiment of the present invention.
[0072] Referring to FIG. 5, the apparatus for EUV spectroscope
calibration according to another embodiment of the present
invention roughly includes an EUV generating module 1000, a beam
splitter 2000, a reflector 3000, a diffraction grating 4000, an Al
filter 5000, a Zr filter 6000, a CCD camera 7000, a spectrum
conversion module 8000, and a control module 9000.
[0073] Here, the EUV generating module 1000 is a module that
generates EUV light by interaction of a laser beam and an inert gas
inside a vacuum chamber, and includes a laser beam generating unit
1100, a vacuum chamber 1200, a plurality of optical members 1300,
and an EUV generating unit 1400.
[0074] The EUV generating module 1000 includes the same components
as those of the above-described EUV generating module 100 according
to an embodiment of the present invention, and thus detailed
descriptions thereof will be omitted.
[0075] The beam splitter 2000 splits the EUV light generated from
the EUV generating module 1000 into reflected light and transmitted
light by transmitting and reflecting the EUV light at a constant
ratio (for example, transmitted light 50: reflected light 50).
[0076] The reflector 3000 again vertically reflects the reflected
light vertically split from the beam splitter 2000.
[0077] The diffraction grating 4000 separates, for each wavelength,
the reflected light reflected from the reflector 3000 and the
transmitted light split from the beam splitter 2000.
[0078] The Al filter 5000 transmits a wavelength of a specific band
among wavelengths of the transmitted light separated from the
diffraction grating 4000 (for example, transmits .gtoreq.67% light
in a range of approximately 17 nm to 60 nm and transmits <10%
light in a range of approximately 17 nm or less).
[0079] The Zr filter 6000 transmits a wavelength of a specific band
(preferably, in a range of approximately 7 nm to 17 nm) among
wavelengths of the reflected light separated from the diffraction
grating 4000 and blocks peripheral wavelengths in a fixed range
with respect to 800 nm (preferably, approximately 796 nm) that is a
peak wavelength of a femto-second laser beam.
[0080] The CCD camera 7000 photographs the EUV light transmitted
from each of the Al filter 5000 and the Zr filter 6000.
[0081] The spectrum conversion module 8000 converts pixels of an
image photographed from the CCD camera 7000 into wavelengths to
show the wavelengths in a spectrum depending on an order of the EUV
light.
[0082] The control module 9000 compares a wavelength value
corresponding to a maximum peak among peaks of the spectrum
depending on the order of the EUV light converted from the spectrum
conversion module 8000 and passing through the
[0083] Al filter 5000 and the Zr filter 6000 with a predetermined
reference wavelength value depending on an order of high-order
harmonics to calculate a difference value with the closest
reference wavelength value, and controls the spectrum depending on
the order of the EUV light converted from the spectrum conversion
module 8000 and passing through the Al filter 5000 and the Zr
filter 6000 to be moved in a direction of wavelength axis by the
calculated difference value.
[0084] FIGS. 6 and 7 are diagrams illustrating a process of moving,
in a direction of a wavelength axis, a spectrum depending on the
order of EUV light passing through an Al filter or a Zr filter
through a control module applied to another embodiment of the
present invention. Here, FIG. 6 illustrates a state in which
calibration is not performed on both spectrums passing through the
Al filter 5000 and the Zr filter 6000, and FIG. 7 illustrates a
state in which the spectrum passing through the Al filter 5000 is
moved in accordance with a reference wavelength value (theory
value) depending on a predetermined order of the high-order
harmonics using transmission characteristics of the Al filter 5000
and the spectrum passing through the Zr filter 6000 is also moved
by the same value. That is, a horizontal position (x
axis-wavelength) is the same, and therefore two spectrums can be
simultaneously moved.
[0085] According to the embodiments of the present invention,
calibration is performed on the EUV spectroscope using the spectrum
conversion module 8000 and the control module 9000 while measuring
the EUV spectrum, and therefore it is possible to perform real-time
calibration.
[0086] FIGS. 8 and 9 are graphs illustrating a transmission in
compliance with a wavelength of a Zr filter applied to embodiments
of the present invention, and FIGS. 10 and 11 are graphs
illustrating a transmission in compliance with a wavelength of an
Al filter applied to embodiments of the present invention.
[0087] Referring to FIGS. 8 and 9, the Zr filter applied to the
embodiments of the present invention transmits approximately 0.1%
light at 800 nm (preferably, approximately 796 nm) that is a peak
wavelength of the femto-second laser, and transmits
.gtoreq.approximately 50% light in a wavelength range of
approximately 7 nm to 14 nm.
[0088] Referring to FIGS. 10 and 11, the Al filter applied to the
embodiments of the present invention transmits
.gtoreq.approximately 67% light in a wavelength range of
approximately 17 nm to 60 nm and transmits <approximately 10%
light in a wavelength range of approximately 17 nm or less.
[0089] As described above, according to the embodiments of the
present invention, the apparatus and method for EUV spectroscope
calibration may accurately measure the wavelength of the spectrum
of EUV light used in EUV exposure technology and mask inspection
technology.
[0090] It will be apparent to those skilled in the art that various
modifications can be made to the above-described exemplary
embodiments of the present invention without departing from the
spirit or scope of the invention. Thus, it is intended that the
present invention covers all such modifications provided they come
within the scope of the appended claims and their equivalents.
* * * * *