U.S. patent application number 13/405759 was filed with the patent office on 2013-08-22 for charged particle beam device with dynamic focus and method of operating thereof.
This patent application is currently assigned to ICT Integrated Circuit Testing Gesellschaft fur Halbleiterpruftechnik GmbH. The applicant listed for this patent is Igor Petrov, Dieter Winkler. Invention is credited to Igor Petrov, Dieter Winkler.
Application Number | 20130214155 13/405759 |
Document ID | / |
Family ID | 45592268 |
Filed Date | 2013-08-22 |
United States Patent
Application |
20130214155 |
Kind Code |
A1 |
Winkler; Dieter ; et
al. |
August 22, 2013 |
CHARGED PARTICLE BEAM DEVICE WITH DYNAMIC FOCUS AND METHOD OF
OPERATING THEREOF
Abstract
A retarding field scanning electron microscope is described. The
microscope includes a scanning deflection assembly configured for
scanning an electron beam over a specimen, one or more controllers
in communication with the scanning deflection assembly for
controlling the electron beam scanning pattern, and a combined
magnetic-electrostatic objective lens configured for focusing the
electron beam including an electrostatic lens portion. The
electrostatic lens portion includes a first electrode with a high
potential bias, and a second electrode disposed between the first
electrode and the specimen plane with a potential bias lower than
the first electrode, wherein the second electrode is configured for
providing a retarding field. The microscope further includes a
voltage supply connected to the second electrode for biasing the
second electrode and being in communication with the controllers,
wherein the controllers synchronize a variation of the potential of
the second electrode with the scanning pattern.
Inventors: |
Winkler; Dieter; (Munich,
DE) ; Petrov; Igor; (Holon, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Winkler; Dieter
Petrov; Igor |
Munich
Holon |
|
DE
IL |
|
|
Assignee: |
ICT Integrated Circuit Testing
Gesellschaft fur Halbleiterpruftechnik GmbH
Heimstetten
DE
|
Family ID: |
45592268 |
Appl. No.: |
13/405759 |
Filed: |
February 27, 2012 |
Current U.S.
Class: |
250/307 ;
250/310 |
Current CPC
Class: |
H01J 37/28 20130101;
H01J 37/21 20130101; H01J 37/1474 20130101; H01J 2237/28 20130101;
H01J 37/145 20130101 |
Class at
Publication: |
250/307 ;
250/310 |
International
Class: |
H01J 37/04 20060101
H01J037/04 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 20, 2012 |
EP |
12156233.4 |
Claims
1. A retarding field scanning electron microscope for imaging a
specimen provided in a specimen plane, comprising: a scanning
deflection assembly configured for scanning an electron beam over
the specimen; one or more controllers in communication with the
scanning deflection assembly for controlling a scanning pattern of
the electron beam; a combined magnetic-electrostatic objective lens
configured for focusing the electron beam, wherein the objective
lens includes a magnetic lens portion and an electrostatic lens
portion, the electrostatic lens portion comprises: a first
electrode configured to be biased to a high potential; and a second
electrode disposed between the first electrode and the specimen
plane, the second electrode being configured to be biased to a
potential lower than the first electrode, wherein the second
electrode is configured for providing a retarding field of the
retarding field scanning electron microscope, wherein the second
electrode comprises: a substrate; a through hole extending through
the substrate; and an electrode surrounding the through hole,
wherein the electrode is arranged on a surface of the substrate; a
voltage supply being connected to the second electrode for biasing
the second electrode to a potential and being in communication with
the one or more controllers, wherein the one or more controllers
synchronize a variation of the potential of the second electrode
with the scanning pattern of the electron beam.
2. The microscope according to claim 1, wherein the scanning
deflection assembly is configured for scanning with a pixel rate of
1 GHz or above.
3. The microscope according to claim 1, wherein the scanning
deflection assembly is configured for scanning with a pixel rate of
3 GHz to 50 GHz.
4. The microscope according to claim 1, wherein the scanning
deflection assembly is configured for a field of view of 50 .mu.m
or above.
5. The microscope according to claim 2, wherein the scanning
deflection assembly is configured for a field of view of 50 .mu.m
or above.
6. The microscope according to claim 1, wherein the scanning
deflection assembly is configured for a field of view of 50 .mu.m
to 500 .mu.m.
7. The microscope according to claim 1, wherein the first and the
second electrode are configured to decelerate the electron beam in
the retarding field to reduce the beam energy by a factor of 5 or
more.
8. The microscope according to claim 1, wherein the voltage supply
for the second electrode is configured for varying the potential of
the second electrode by at least .+-.0.1 V and/or by not more than
.+-.50 V.
9. The microscope according to claim 8, wherein the voltage supply
for the second electrode is configured for varying with a variation
frequency of 1 MHz or more.
10. (canceled)
11. The microscope according to claim 1, wherein the substrate is
comprised of a material having a specific electrical resistivity in
a range from about 10.sup.6 .OMEGA.cm to about 10.sup.12
.OMEGA.cm.
12. The microscope according to claim 1, wherein the second
electrode further comprises: an electrical connection for
connecting the electrode with the voltage supply, the electrode
comprising a lower specific electrical resistivity than the
conductive substrate.
13. The microscope according to claim 1, wherein the microscope is
a multi-beam microscope for two or more electron beams, comprising:
two or more emitter tips, each emitting one electron beam.
14. The microscope according to claim 13, wherein the two or more
beams are each scanned with a respective individual scanning
assembly and the two or more beams are each decelerated with a
respective individual second electrode being configured for
providing a retarding field of the retarding field scanning
electron microscope for the respective electron beam of the two or
more beams, or wherein the two or more beams are scanned with the
scanning assembly being a common scanning assembly for the two or
more beams and the two or more beams are decelerated with the
second electrode being a common second electrode for the two or
more beams.
15. A method of imaging a specimen, comprising: generating an
electron beam in a retarding field scanning electron microscope;
scanning the electron beam over a specimen for image generation;
and focusing the electron beam on the specimen with a combined
magnetic-electrostatic objective lens, wherein the objective lens
includes a magnetic lens portion and an electrostatic lens portion,
and wherein the electrostatic lens portion comprises: a first
electrode; and a second electrode disposed between the first
electrode and the specimen, wherein the second electrode comprises:
a substrate; a through hole extending through the substrate; and an
electrode surrounding the through hole, wherein the electrode is
arranged on a surface of the substrate; biasing the second
electrode to a varying potential; and synchronizing the variation
of the potential of the second electrode with the scanning of the
electron beam.
16. The method according to claim 15, wherein the scanning is
conducted with a pixel rate of 1 GHz or above.
17. The method according to claim 15, wherein the scanning is
conducted over field of view of 50 .mu.m or above.
18. The method according to claim 15, wherein the electron beam is
decelerated by the first and second electrode such that the beam
energy is reduced by a factor of 5 or more.
19. The method according to claim 15, wherein the potential of the
second electrode is varied by at least .+-.0.1 V and/or by not more
than .+-.50 V.
20. The method according to claim 19, wherein the potential of the
second electrode is varied with a variation frequency of 1 MHz or
more.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] Embodiments of the present invention relate to a retarding
field scanning microscope using a charged particle beam and to a
method of imaging a specimen by scanning a charged particle
beam.
BACKGROUND OF THE INVENTION
[0002] Charged particle beam apparatuses have many functions, in a
plurality of industrial fields, including, but not limited to,
critical dimensioning of semiconductor devices during
manufacturing, defect review of semiconductor devices during
manufacturing, inspection of semiconductor devices during
manufacturing, exposure systems for lithography, detecting devices
and testing systems. Thus, there is a high demand for structuring,
testing and inspecting specimens within the micrometer and
nanometer scale.
[0003] Micrometer and nanometer scale process control, inspection
or structuring is often done with charged particle beams, e.g.
electron beams, which are generated and focused in charged particle
beam devices, such as electron microscopes or electron beam pattern
generators. Charged particle beams offer superior spatial
resolution compared to, e.g. photon beams due to their short
wavelengths.
[0004] Thereby, some applications require a high resolution, e.g.
of 10 nm or below, a large field of view and a high scanning speed.
When a charged particle beam such as an electron beam is scanned
over a flat surface, it is typically continuously refocused. The
focal distance between the lens and the position to be imaged
increases when the beam is deflected away from the axis (field
curvature correction). In order to allow for high resolution and
large field of view, the beam is therefore refocused during
deflection. However, the application of a high scanning speed is an
additional challenge.
[0005] For scanning the beam off the optical axis in order to
achieve the required field of view, a magnetic or electrostatic
deflector can be used. Additionally, due to the field curvature,
correction of the focus length can be used. This has often been
done by readjusting the magnetic field of the objective lens and/or
by adjusting the beam energy in the objective lens. Another
theoretical possibility would be to apply a common voltage to all
electrodes in the microscope or to insert an additional electrode
and changing potential of these electrodes or the additional
electrode. However, it has been found that the latter would
necessitate high voltages up to 1 kV for fields of view in the 100
.mu.m area. Such high voltages are difficult to switch with the
required speed and furthermore require electrical insulation which
is difficult to achieve for these high voltages. Yet further, such
electrodes represent relatively large capacitances, which are also
difficult to switch quickly.
[0006] In view of the above, it is an object of the present
invention to provide an improved retarding field scanning
microscope using a charged particle beam, particularly an electron
beam that would overcome at least some of the above problems.
SUMMARY OF THE INVENTION
[0007] In light of the above, a retarding field scanning electron
microscope according to independent claim 1, and a method of
imaging a specimen according to claim 11, are provided. Further
aspects, advantages, and features of the present invention are
apparent from the dependent claims, the description and the
accompanying drawings.
[0008] According to one embodiment, a retarding field scanning
electron microscope for imaging a specimen is provided. The
microscope includes a scanning deflection assembly configured for
scanning an electron beam over the specimen, one or more
controllers in communication with the scanning deflection assembly
for controlling a scanning pattern of the electron beam, and a
combined magnetic-electrostatic objective lens configured for
focusing the electron beam, wherein the objective lens includes a
magnetic lens portion and an electrostatic lens portion. The
electrostatic lens portion includes a first electrode configured to
be biased to a high potential, and a second electrode disposed
between the first electrode and the specimen plane, the second
electrode being configured to be biased to a potential lower than
the first electrode, wherein the second electrode is configured for
providing a retarding field of the retarding field scanning
electron microscope. The retarding field scanning electron
microscope further includes a voltage supply being connected to the
second electrode for biasing the second electrode to a potential
and being in communication with the one or more controllers,
wherein the one or more controllers synchronize a variation of the
potential of the second electrode with the scanning pattern of the
electron beam,
[0009] According to another embodiment, a method of imaging a
specimen is provided. The method includes generating an electron
beam in a retarding field scanning electron microscope, scanning
the electron beam over a specimen for image generation and focusing
the electron beam on the specimen with a combined
magnetic-electrostatic objective lens, wherein the objective lens
includes a magnetic lens portion and an electrostatic lens portion,
and wherein the electrostatic lens portion includes a first
electrode and a second electrode disposed between the first
electrode and the specimen. The method further includes biasing the
second electrode to a varying potential, and synchronizing the
variation of the potential of the second electrode with the
scanning of the electron beam.
[0010] Embodiments are also directed at apparatuses for carrying
out the disclosed methods and include apparatus parts for
performing each described method step. These method steps may be
performed by way of hardware components, a computer programmed by
appropriate software, by any combination of the two or in any other
manner. Furthermore, embodiments are also directed at methods by
which the described apparatus operates. It includes method steps
for carrying out every function of the apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] So that the manner in which the above recited features of
the present invention can be understood in detail, a more
particular description of the invention, briefly summarized above,
may be had by reference to embodiments. The accompanying drawings
relate to embodiments of the invention and are described in the
following:
[0012] FIGS. 1A and 1B illustrate a schematic partial view of a
retarding field scanning charged particle beam device with a
synchronization according to embodiments described herein.
[0013] FIG. 2A illustrates a schematic view of an optionally used
electrode of an immersion lens of a retarding field scanning
charged particle beam device with a synchronization according to
embodiments described herein.
[0014] FIG. 2B illustrates a schematic view of an optionally used
electrode of an immersion lens of a retarding field scanning
charged particle beam device according to embodiments described
herein.
[0015] FIG. 2C illustrates a schematic view of an optionally used
electrode of an immersion lens of a retarding field scanning
charged particle beam device according to embodiments described
herein.
[0016] FIG. 3 illustrates a schematic view of a retarding field
scanning charged particle beam device according to embodiments
described herein.
[0017] FIG. 4 illustrates a schematic view of a retarding field
scanning charged particle beam device having two or more beams
according to embodiments described herein.
[0018] FIGS. 5A and 5B illustrate schematic views of an optionally
used electrode of an immersion lens for a retarding field scanning
charged particle beam device having two or more beams according to
embodiments described herein.
[0019] FIG. 6 illustrates a method of operating a retarding field
scanning charged particle beam device according to embodiments
described herein.
DETAILED DESCRIPTION OF EMBODIMENTS
[0020] Reference will now be made in detail to the various
embodiments of the invention, one or more examples of which are
illustrated in the figures. Within the following description of the
drawings, the same reference numbers refer to same components.
Generally, only the differences with respect to individual
embodiments are described. Each example is provided by way of
explanation of the invention and is not meant as a limitation of
the invention. Further, features illustrated or described as part
of one embodiment can be used on or in conjunction with other
embodiments to yield yet a further embodiment. It is intended that
the description includes such modifications and variations.
[0021] Without limiting the scope of protection of the present
application, in the following the charged particle beam device or
components thereof will exemplarily be referred to as a charged
particle beam device including the detection of secondary
electrons. The present invention can still be applied for
apparatuses and components detecting corpuscles, such as secondary
and/or backscattered charged particles in the form of electrons or
ions, photons, X-rays or other signals in order to obtain a
specimen image. Generally, when referring to corpuscles they are to
be understood as light signals in which the corpuscles are photons
as well as particles, in which the corpuscles are ions, atoms,
electrons or other particles.
[0022] A "specimen" as referred to herein, includes, but is not
limited to, semiconductor wafers, semiconductor workpieces, and
other workpieces such as memory disks and the like. Embodiments of
the invention may be applied to any workpiece on which material is
deposited or which is structured. A specimen includes a surface to
be structured or on which layers are deposited, an edge, and
typically a bevel. According to some embodiments, which can be
combined with other embodiments described herein, the apparatus and
methods are configure for or are applied for critical dimensioning
applications and defect review, where the microscopes and methods
according to embodiments described herein, can be beneficially used
in light of the desires of these applications.
[0023] In the context of the here described embodiments, without
limiting the scope of protection thereto, an intermediate beam
acceleration system intends to describe a charged particle beam
apparatus with initial high acceleration of the charged particles,
which will be decelerated to a landing energy shortly before
striking the specimen. The energy or velocity ratio
v.sub.va/v.sub.landing between the acceleration velocity v.sub.ac,
at which the charged particles are guided through the column and
the landing velocity v.sub.landing, at which the charged particles
strikes the specimen can be about at least 5 or higher.
Furthermore, the landing energy can be 2 kV or less. These are
approximate values which might be adapted according to
circumstances.
[0024] Furthermore, in the following description, it is mostly
referred to scanning electron beam microscopes (SEM), which can
particularly profit from the embodiments described herein. However,
there might be special circumstances, where the embodiments can
also be applied for ion beam scanning systems, where an image is
generated by scanning an ion beam over a specimen.
[0025] According to some embodiments described herein, an E-beam
inspection, critical dimensioning (CD) tool, and/or defect review
(DR) tool can be provided, wherein high resolution, large field of
view and high scanning speed can be achieved. The field curvature
correction is conducted with a fast focusing or with a fast
re-focusing, respectively. Thereby, the decelerating electrode of
the immersion lens being part of the objective lens is utilized to
re-focus the beam, wherein the potential of the decelerating
electrode is synchronized by a controller with the scanning
deflection system.
[0026] The beam is thereby scanned over an essentially flat
surface. It is continuously refocused while the refocusing is
synchronized with the scanning of the beam for correction of the
field curvature. As the focal distance between lens and specimen
plane increases when the beam is deflected away from the axis, the
re-focusing is conducted synchronized with the scanning, e.g.
scanning of lines, particularly for high scanning speeds, e.g.
pixel rates in the GHz region and line speeds in the MHz
region.
[0027] According to some embodiments, which can be combined with
other embodiments described herein, the fast correction of field
curvature, i.e. the increased distance between the objective lens
and the specimen plane due to scanning deflection of the beam, can
be utilized for vector field addressing of the measurement pixels.
Thereby, the electron beam is typically not scanned along lines to
scan an area of the specimen, but the electron beam is scanned to
individual positions or to individual smaller areas. Accordingly,
the voltage corrections function can also be an arbitrary function
without a predetermined modulation frequency. For example, if
individual pixels are addressed randomly, the correction function
can include a plurality of steps of any size between zero
correction and maximum correction. Thereby, the fast switching is
particularly important because the step like functions correspond
to very fast response frequencies of the second electrode.
[0028] Further, embodiments relate to retarding field microscopes,
e.g. low-voltage high-resolution SEM's, where low landing energies
of the primary beam (e.g. 2 keV or below such as 1 keV or below)
are used to limit the load on the sample and to avoid damage.
Thereby, in order to achieve small beam diameters for maximum
resolution, the beam is guided through the microscope column at
high energies. Accordingly, a scanning electron microscope with
intermediate beam acceleration can be used, where the electron beam
is extracted from the source and accelerated to a high energy, e.g.
20 kV. In the final objective lens the beam is slowed down to the
required low landing energy of e.g. 1 kV.
[0029] According to embodiments described herein, the final
objective lens for an electron beam system includes a
magnetic-electrostatic lens. The latter consists typically of an
upper electrode, which lies on a high potential in reference to the
primary electrons, and a lower electrode, which lies on a potential
close to the sample voltage. These electrodes contribute to
focusing, as well as to slowing down the beam to the required low
primary beam voltage. This kind of immersion lens allows focusing
the beam with minor loss of resolution compared to high beam
voltage systems.
[0030] FIG. 1A shows a portion of a scanning electron microscope
100. The objective lens 60 includes the magnetic lens portion
having an upper pole piece 63, a lower pole piece 64 and a coil
(not shown in FIGS. 1A and 1B). The objective lens 60 further
includes an electrostatic lens portion having a first electrode
110, i.e. upper electrode in the figures, and a second electrode
130, i.e. lower electrode in the figures.
[0031] The objective lens 60 focuses the electron beam 12, which
travels in the column along optical axis 2, on the specimen 52,
i.e. in a specimen plane. The specimen 52 is supported on a
specimen support table 50. According to some embodiments, which can
be combined with other embodiments described herein, scanning of an
area of the specimen can be conducted by movement of the table in a
first direction essentially perpendicular to the optical axis, and
by scanning lines in another, second direction essentially
perpendicular to the optical axis and essentially perpendicular to
the first direction.
[0032] If the beam is scanned according to a predetermined scan
pattern, e.g. adjacent lines are scanned, the beam travels off the
optical axis 2 in order to scan the required field of view.
Thereby, a scanning deflector assembly 120 is used. According to
different embodiments, the scanning assembly can be electrostatic,
magnetic or combined electrostatic-magnetic. Typically, at least
one scanning direction essentially perpendicular to the optical
axis 2 (e.g. z-direction) is provided. Often two scanning
directions (e.g. x-direction and y-direction) and the corresponding
scanning assemblies are provided. The one or more scanning
deflection assemblies are thereby configured for high speed
scanning, e.g. to achieve a pixel rate in the GHz region (e.g. 3
GHz or above) and/or a line rate in the MHz region (e.g. 3 MHz or
above).
[0033] Additionally, due to field curvature, correction of the
focus length is required as illustrated by the focus points 112a
and 112b in FIG. 1A. According to embodiments described herein, the
field curvature is corrected continuously during scan, i.e. in a
synchronized manner with the scanning pattern. For modern, high
throughput systems, which can be of MHz per line for modern systems
with pixel acquisition rates in the GHz region, correction of the
field curvature is challenging and the correction voltage and/or
the capacity or induction of correction elements has to be
considered.
[0034] In light of the above, embodiments described herein use the
second (lower) electrode 130 for re-focusing in a synchronized
manner with the scanning. The second electrode can be on ground
potential or on a potential relatively close to the sample
potential for focusing in a position on the optical axis. As the
beam velocity is already slow when the beam passes this electrode,
already small variations of its potential lead to a sufficiently
large change of focusing properties. A 100 .mu.m field of view
would thus require a dynamic focus voltage of a few volts only.
According to embodiments, typical correction voltages can be in the
range of 0.1 V to 50 V, e.g. about 5 V for a maximum value of a
full .+-.50 .mu.m scan deflection. The small voltages are easier to
switch at high speeds. Furthermore, it is easier to design this
electrode to have a small capacitance, as it is located outside the
lens structure and can be reduced and/or adjusted in capacitance as
described in more detail below. Thereby, examplarily a 100 .mu.m
field of view is understood as a field of view having a scanning
range in at least one direction of +50 .mu.m, typically of .+-.50
.mu.m in two directions such that a 100 .mu.m.times.100 .mu.m
square is measured. It can be understood that the diagonal of such
square or rectangle (in case of one direction) is larger than 100
.mu.m.
[0035] According to embodiments described herein, the scan
deflection assembly 120 and the second electrode 130 are connected
to a controller 140 or a controller assembly, wherein a
synchronization of the focus correction is conducted. For example,
a beam position on the optical axis would correlate with no
correction voltage, whereas a maximum deflection of the electron
beam 12 to the left and right in FIG. 1A would correlate to a
maximum voltage correction of a few volts. For example, a scanning
line frequency of 10 MHz would result in a variation of the
potential of the second electrode 130 with a corresponding
frequency. In embodiments described herein, the focus correction
signal is delivered to the voltage driver of the lower
electrode.
[0036] FIG. 1B shows another scanning electron microscope according
to some embodiments described herein. As compared to FIG. 1A, the
controller 140 or controller assembly includes controllers 142 and
144. The controller 142 drives and/or controls the scanning
deflector and the controller 144 drives/controls the correction
potential applied to the second electrode 130. The controllers 142
and 144 form a portion of the controller 140, which provides
synchronization. Accordingly, more than one controller can be
provided to synchronize the focus correction potential applied to
the second electrode 130 with the scanning pattern of the electron
beam.
[0037] According to yet further embodiments, which can be combined
with other embodiments described herein, the second electrode can
be provided by a body 131, and an electrode unit 133 provided on
the body. Thereby, the capacitance can be further reduced to
improve the capability to correct in a synchronized manner with the
high speed scanning.
[0038] According to typically embodiments, the electrode unit can
be provided on an electrically non-conductive body or a body having
a small electrical conductivity in order to reduce the size of the
electrically conductive portion and, thus, the capacitance.
[0039] As illustrated in FIGS. 2A and 2B, the electrode unit 133
can surround the through hole 132 in the body 131. Electrode unit
133 can be arranged on the surface of the body 131, e.g. a ceramic
body, which faces, when in use, the specimen. In further
embodiments, electrode unit 133 is arranged on the opposite surface
of ceramic body 131. The function of electrode unit 133 will be
described in detail further below.
[0040] In yet other embodiments, the electrode 130 can also include
an electrical connection 134 and 135 for connecting the electrode
unit 133 and, optionally also a conductive ceramic body 131 with
one or more voltage supplies. The electrode unit 133 can have a
lower specific electrical resistivity than the ceramic body 131.
This allows for fast switching of the electrode. According to some
embodiments, ceramic body 131 and electrode 133 can be separately
connected to different voltage supplies.
[0041] According to embodiments described herein, the second
electrode can be provided by a body and an electrode unit. Thereby,
the capacitance of the electrode 130 can be further reduced to
allow for fast switching of the electrode in a manner synchronized
with the fast scanning.
[0042] According to some other embodiments, which can be combined
with other embodiments described herein, the electrode 130 does not
include an electrode unit 133. Instead, a conductive ceramic 131
can be electrically connected to the voltage supply for biasing the
electrode 130.
[0043] According to an embodiment, electrode 133 is insulated from
ceramic body 131. This allows providing ceramic body 131 and
electrode 133 with independent voltage supplies. According to other
embodiments, which can be combined with other embodiments described
herein, electrode unit 133 is in electrical connection with the
ceramic body 131. Electrode unit 133 including its electrical
connection line 134 can be formed directly on the ceramic body 134.
Therefore, only one electrical terminal is needed to connect both
the electrode unit 133 and the ceramic body 131. Typically,
electrode unit 133 is connected through connection line 134 with a
terminal formed on ceramic body 131. Since connection line 134 and
electrode unit 133 are in electrical contact with ceramic body 131,
ceramic body 131 will also be on the same electrical potential as
electrode unit 133. The direct electrical connection between
electrode unit 133 and ceramic body 131 does not significantly
influence switching behavior of the electrode unit 133 since
ceramic body 131 has a significantly higher resistivity than
electrode unit 133. Hence, fast switching of electrode unit 133
does not affect the electrical potential of ceramic body 131, which
will be substantially constant. This also means that the
decelerating and re-focusing effect of electrode 130 remains
effective during switching of the electrode unit 133.
[0044] The above described low-pass capability of ceramic body 131
can be understood when considering the ceramic body as large
capacity, which is connected to electrode unit 133 through a large
resistor formed by the conductive ceramic material of ceramic body
131.
[0045] FIG. 2A illustrates an embodiment of an electrode 230 having
a ceramic body 231, a through hole 232, an electrode unit 233, a
terminal 235, and a connection line 234, which electrically
connects terminal 235 with electrode unit 233. As illustrated in
FIG. 2A, electrode unit 233 can be formed on both sides of ceramic
body 231. Furthermore, electrode unit 233 is axially centered
around through hole 232. Typically, electrode unit 233 has a
rotationally-symmetric shape with respect to the axis of through
hole 232.
[0046] Electrode unit 233 extends through the through hole 232 and
covers the sidewalls of through hole 232. Electrode unit 233 and
connection line 234 are formed by a metal, which is deposited
directly onto ceramic body 231 so that they are in electrical
contact. According to embodiments, electrical connection line 234
can also be partially or completely electrically insulated from
ceramic body 231. This reduces the contact area and increases the
resistance between electrode unit 233 and ceramic body 231. By so
doing, the low-pass characteristic of the ceramic body is improved.
The contact area between electrode unit 233 and electrical
connection line 234 and ceramic body 231 can be adapted to tailor
the electrical behavior of electrode 230.
[0047] Electrode 230 is furthermore adapted to be held by holders
which keeps electrode 230 in a predefined position with respect to
the column. The holders also electrically insulate the electrode
230 against the column. The holders can be, for example, fixed to
the electrode 230 by a screw joint, wherein the holders are screwed
in to an internal thread 236.
[0048] Referring back to FIG. 2A, electrode 230 can be
manufactured, for example by providing a conductive ceramic body
231 and forming the through hole 232 in the ceramic body 231 so
that the through hole 232 extends through the ceramic body 231.
Through hole 232 can be formed when ceramic body 231 is provided as
green body. Before or after firing the green ceramic body,
electrode unit 233 surrounding the through hole 232 and connection
line 234 in electrical connection with the electrode unit 233 are
formed. The material of electrode unit 232 is chosen to have a
lower specific electrical resistivity than the fired ceramic body
231. Electrode unit 233 and connection line 234 can be a metal
coating.
[0049] According to an embodiment, electrode unit 233 and/or
connection line 234 can be formed by vapor deposition. According to
an embodiment, electrode unit 233 can be a metal ring or a
preformed metal electrode which is inserted into through hole 232.
In this case, through hole 232 in ceramic body 131 can be made
larger, for example up to 20 mm, to provide sufficient space for
the metal ring. The actual through hole for the charged particles
are then defined by the aperture of the ring.
[0050] According to an embodiment, which can be combined with other
embodiments described herein, an electrode 330, as illustrated in
FIG. 2B, includes a carrier 335 comprised of an insulating material
and a conductive substrate 331 which at least partially covers
portions of carrier 335. Conductive substrate 331 can be comprised
of a material having a specific electrical resistivity in a range
from about 106 .OMEGA.cm to about 1012 .OMEGA.cm. Examples thereof
are conductive ceramics such as SiC and doped aluminum oxide and
diamond-like carbon (DLC). Carrier 335 is electrically insulating.
A through hole 332 is provided in the conductive substrate 331 and
carrier 335. Substrate 331 can be formed on carrier 335, for
example, by deposition or pasting.
[0051] According to an embodiment, electrode 330 includes an
electrode unit 333 which can be comprised of, for example, metal.
An electrical connection 334 can be provided to contact electrode
unit 333 and conductive substrate 331.
[0052] According to an embodiment, as illustrated in FIG. 2C,
electrode 330 does not include a separate electrode unit, but uses
the conductive ceramic as the electrode.
[0053] Further embodiments can be described with respect to FIG. 3.
FIG. 3 shows a charged particle beam device 300. The charged
particle beam column 20 provides a first chamber 21, a second
chamber 22 and a third chamber 23. The first chamber, which can
also be referred to as a gun chamber, includes the charged particle
source 30 having an emitter 31 and suppressor 32. A charged
particle beam is generated by the charged particle beam source 30,
is aligned to the beam limiting aperture 250, which is dimensioned
to shape the beam, i.e. blocks a portion of the beam, passes
through opening 12 of the detector 40 and is focused on the
specimen 52 positioned on a specimen position on the specimen stage
50. On impingement of the charged particle beam, for example,
secondary or backscattered electrons are released from the specimen
50, which can be detected by the detector 40.
[0054] According to some embodiments, which can be combined with
other embodiments described herein, a condenser lens 320 and a beam
shaping or beam limiting aperture 250 is provided. The two-stage
deflection system 240 is provided between the condenser lens and
the beam shaping aperture 250 for alignment of the beam to the
aperture.
[0055] As shown in FIG. 3, according to some embodiments, a
detector 40 can be provided above the objective lens such that the
primary charged particle beam passes through the opening 12 in the
detector. The objective lens 60 having pole pieces 64/63 and a coil
62 focuses the charged particle beam on a specimen 52, which can be
positioned on a specimen stage 50. The objective lens 60 shown in
FIG. 3 includes the upper pole piece 63, the lower pole piece 64
and the coil 62 forming a magnetic lens portion of the objective
lens, as well as the first (upper) electrode 110 and the second
(lower) electrode 130 forming an electrostatic portion of the
objective lens.
[0056] Further, a scanning deflector assembly 120 is provided. The
scanning deflector assembly is connected to controller 142 and the
electrode 130 is connected to controller and/or corresponding
voltage supply 144. The controller 142 and the controller/voltage
supply 144 is connected to a yet another controller 340, which
achieves synchronization between the scanning pattern of scanning
the electron beam and the biasing potential of the electrode 130.
Thereby, a field curvature for a large field of view can be
corrected for, even for high speed scanning applications, because a
comparable small voltage adjustment at a low capacitance component
can be achieved.
[0057] In FIG. 3 the upper electrodes 110 of the electrostatic
immersion lens is provided in the form of a tube. As explained
above, for an objective lens, when imaging negative charged
particles, this tube is preferably on positive potential above
three kV, e.g. 10 keV, 15 keV or 20 keV. Thereby, a beam boost
potential is provided, i.e. the beam travels with high energy
through the column. The embodiment of FIG. 3 shows a lower
electrode 130 below the lower pole piece 64. The lower electrode
being the deceleration electrode of the immersion lens component of
the objective lens is typically at a potential (without correction)
to provide a landing energy of the charged particles on the
specimen of 2 keV or below, e.g. 500 V or 1 keV.
[0058] FIG. 4 illustrates yet further embodiments, wherein the
retarding field scanning microscope 400 is provided as a multi-beam
device. Typically two or more beams can be provided in a multi-beam
device. As an example, FIG. 4 shows five emitters 5 such that 5
electron beams are emitted in the gun chamber 420. The emitter tips
are biased to an acceleration potential V.sub.acc by voltage supply
4, which provides a potential to the tips as compared to ground 2.
Electrodes 412, e.g. suppressors, extractors or anodes are
provided, e.g. in a cup-like shape. These electrodes are
electrically insulated by insulators 432 with respect to each other
and with respect to the gun chamber 420. According to some
embodiments, which can be combined with other embodiments described
herein, also two or more of the electrodes selected from the group
consisting of suppressor, extractor, and anode can be provided.
Typically, these electrodes 412 are biased to potentials by voltage
supplies (not shown) in order to control the two or more electron
beams.
[0059] The charged particle beams travel in a further chamber 430,
in which a specimen 52 is provided. The objective lens 460 focuses
the beams on the specimen or in a specimen plane, respectively.
Thereby, the objective lens can have a common magnetic lens
portion, i.e. a magnetic lens portion acting on two or more of the
charged particle beams. Thereby, for example, one common excitation
coil is provided to a pole piece unit or a pole piece assembly,
wherein several openings for passing of the two or more electron
beams through the pole piece unit are provided. The one common
excitation coil excited the pole piece unit, such that for example
one beam is focused per opening.
[0060] As shown in FIG. 4, the objective lens 460 further includes
an electrostatic lens portion. For example, an electrostatic lens
portion has a first electrode 110 and a second electrode 130. For
example, the second electrodes 130 can individually be connected to
a controller 144 or a respective power supply being controlled by a
controller such that the potentials provided to the electrodes 130
can be synchronized with the scanning deflection of the scanning
deflector assemblies 120, which act on the corresponding charged
particle beams. The scanning deflector assemblies are controlled by
scanning controller 142, which controls the scanning pattern of the
deflectors. The controller 340 is connected to the
controller/voltage supply 144 for the retarding electrodes 130 and
the scan controller 142, such that synchronization is provided.
[0061] As shown in FIG. 4, the electrodes 412, optionally the first
electrodes 110, the second electrodes 130 and the scanning
assemblies 120, are provided individually for the two or more
electron beams. However, it can be understood that if a common
scanning motion of the two or more beams is provided either by a
common scanning deflection assembly or by a common scanning control
signal, the second electrode 130 can also be provided as a common
electrode, while the re-focusing for field curvature correction is
provided for high speed scanning. Yet further, according to some
embodiments, which can be combined with other embodiments described
herein, one or more of the components, which have been described as
individual components above, can be provided as a common component
for the two or more charged particle beams. According to yet
further embodiments, which can be combined with other embodiments
described herein, the two or more beams can also be provided by
having two or more columns 20 (as shown, e.g., in FIG. 3) arranged
next to each other.
[0062] In FIG. 4, lower electrodes 130 are provided such that the
potential for focusing each electron beam can be adjusted
individually. Thereby, one solution might be to provide a common
potential to all lower electrodes 130 or sub-areas of one electrode
130. Additionally, controller 144 provides a correction potential
to the sub areas or the electrodes, respectively. For the
realization of this embodiment, it is required to have a sufficient
resistance between the individual (sub-)electrodes 130. Under this
condition, individual correction potentials can be applied.
Alternatively, it is possible to have completely independent
electrodes 130. Using electrically disconnected electrodes,
controller 144 provides an individual potential for each electrode.
Thus, controller 144 might be used as a controller for correction
purposes and as a controller for providing each electrode with an
individual potential.
[0063] According to some embodiments, the second electrodes 130 for
a multi-beam, device can be provided as explained in more detail
with respect to FIGS. 5A and 5B. FIGS. 5A and 5B illustrate
electrodes according to an embodiment which can be combined with
other embodiments described herein. Electrode assembly 500 includes
a plurality of individual electrodes 530, one of them is
illustrated in an enlarged view in FIG. 5B. Each electrode 530 can
be designed as described in connection with FIGS. 2A to 2C.
[0064] The electrodes 530 are arranged in two rows in this
embodiment so that the connection lines 534 are arranged parallel
to each other. The sides on which the through holes 532 are formed
are positioned towards each other as illustrated in FIG. 5A. A
skilled person will appreciate that other arrangements are also
possible. Each electrode 530 can be positioned and aligned
individually with respect to the respective column of a
multi-column charged particle beam apparatus. Each electrode 530,
particularly the through hole 532 of each electrode 530, is
centered and aligned with respect to the respectively assigned
column so that for each column an individual electrode 530 is
provided. In further embodiments, electrodes 530 can be arranged in
one row, three or more rows. In yet other embodiments, four
electrodes 530 can be provided with terminals extending to all
sides of the electrode assembly.
[0065] Each electrode 530 includes a ceramic body 531, for example
as described above. Since the main component of electrode 530 is
the ceramic body 531, electrode 530 can also be referred to as
ceramic tile. The thickness of ceramic body 531 can be about 1 mm.
The spacing between adjacent electrodes 530 can be about 1 mm. A
skilled person will appreciate that these values are only exemplary
values and that the dimensions of ceramic body 531 can be adapted
according to specific needs.
[0066] The ceramic body 531 can be comprised of, for example SiC.
Other conductive ceramic materials can also be used. Electrode unit
533 including connection line 534 can be a metal coating which is
directly formed on ceramic body 531 to be in electrical contact
with ceramic body 531. For example, Ti can be used as metal for
forming electrode unit 533 and connection line 534.
[0067] A terminal in electrical connection with connection line 534
can be arranged on the side of ceramic body 531 which faces the
column. Connection lines 534 can be formed on the side facing the
stage. This situation is illustrated in FIGS. 5A and 5B. Terminals
are provided to connect the electrode units 533 of each electrode
530 with a voltage supply. Each electrode unit 533 and hence each
electrode 530 can be individually connected. This allows for
individual switching of the electrode units 533 independently of
the other electrode units 533. Each electrode unit 533 can
therefore be connected with a separate voltage supply. According to
embodiments, which can be combined with other embodiments described
herein, each electrode unit 533 is connected to a common voltage
supply through a switching unit which is adapted to individually
and independently connect the electrode units 533 with the voltage
supply. The voltage supply is adapted to provide a potential being
controlled to re-focus the beam in a manner synchronized with the
scanning of the beam.
[0068] Electrode assembly 500 can also include dummy electrodes
530' which are electrically connected to any voltage supply
supplying the bias voltage V.sub.bias but which, unlike electrodes
530, do not include electrode units to protect the sample from
arcing from the outer areas of the column or columns set up
[0069] The embodiments described herein, may as well include
additional components (not shown) such as condenser lenses,
deflectors of the electrostatic, magnetic or compound
electrostatic-magnetic type, such as Wien filters, scanning
deflectors of the electrostatic, magnetic or compound
electrostatic-magnetic type, stigmators of the electrostatic,
magnetic or compound electrostatic-magnetic type, further lenses of
the electrostatic, magnetic or compound electrostatic-magnetic
type, and/or other optical components for influencing and/or
correcting the beam of primary and/or secondary charged particles,
such as deflectors or apertures. Indeed, for illustration purposes,
some of those components are shown in the figures described herein.
It is to be understood that one or more of such components can also
be applied in embodiments of the invention.
[0070] According to some embodiments, a method of imaging a
specimen is provided as illustrated in FIG. 6. Thereby,
particularly a retarding field scanning microscope is utilized,
wherein a charged particle beam, e.g. an electron beam is used. In
step 602 a charged particle beam, preferably an electron beam, is
generated in the retarding field scanning microscope. In step 604
the beam is scanned over the specimen for image generation. As
described above, this can be done in a high speed scanning pattern,
where a pixel rate in the GHz range and/or a line rate in the MHz
rate are provided. The charged particle beam is focused on the
specimen with a combined magnetic-electrostatic objective lens in
step 606. The objective lens includes a magnetic lens portion and
an electrostatic lens portion, and wherein the electrostatic lens
portion includes a first electrode and a second electrode disposed
between the first electrode and the specimen. Typically, the second
electrode decelerates the charged particles for impingement on the
specimen, i.e. an immersion lens is provided by the first and the
second electrode. Accordingly, the second electrode is biased to a
potential. In order to correct for the field curvature,
particularly for a large field of view, the potential provided to
the second electrode is varied and the variation is synchronized
with the scanning of the electron beam in step 608.
[0071] According to yet further embodiments, which can be combined
with other embodiments described herein, the re-focusing due to a
varying potential provided to the retarding electrode of the
immersion lens component of the objective lens can particularly be
provided for a scanning being conducted with a pixel rate of 1 GHz
or above, particularly with a pixel rate of 3 GHz to 50 GHz. Yet
further, the scanning can additionally or alternatively be
conducted over a field of view of 50 .mu.m or above, particularly
of 50 .mu.m to 500 .mu.m. Thereby, the embodiments can be applied
for a retarding field microscope, wherein the electron beam is
decelerated by the first and second electrode such that the beam
energy is reduced by a factor of 5 or more, particularly by a
factor of 10 or more.
[0072] While the foregoing is directed to embodiments of the
invention, other and further embodiments of the invention may be
devised without departing from the basic scope thereof, and the
scope thereof is determined by the claims that follow.
* * * * *