U.S. patent application number 12/910240 was filed with the patent office on 2012-04-19 for simplified particle emitter and method of operating thereof.
This patent application is currently assigned to ICT Integrated Circuit Testing Gesellschaft fur Halbleiterpruftechnik mbH. Invention is credited to Jurgen FROSIEN, Stefan LANIO.
Application Number | 20120091359 12/910240 |
Document ID | / |
Family ID | 43971540 |
Filed Date | 2012-04-19 |
United States Patent
Application |
20120091359 |
Kind Code |
A1 |
LANIO; Stefan ; et
al. |
April 19, 2012 |
SIMPLIFIED PARTICLE EMITTER AND METHOD OF OPERATING THEREOF
Abstract
An emitter assembly for emitting a charged particle beam along
an optical axis is described. The emitter assembly being housed in
a gun chamber and includes an emitter having an emitter tip,
wherein the emitter tip is positioned at a first plane
perpendicular to the optical axis and wherein the emitter is
configured to be biased to a first potential, an extractor having
an opening, wherein the opening is positioned at a second plane
perpendicular to the optical axis and wherein the extractor is
configured to be biased to a second potential, wherein the second
plane has a first distance from the first plane of 2.25 mm and
above.
Inventors: |
LANIO; Stefan; (Erding,
DE) ; FROSIEN; Jurgen; (Riemerling, DE) |
Assignee: |
ICT Integrated Circuit Testing
Gesellschaft fur Halbleiterpruftechnik mbH
Heimstetten
DE
|
Family ID: |
43971540 |
Appl. No.: |
12/910240 |
Filed: |
October 22, 2010 |
Current U.S.
Class: |
250/396R |
Current CPC
Class: |
H01J 37/063 20130101;
H01J 37/09 20130101; H01J 37/16 20130101; H01J 2237/06375 20130101;
H01J 37/08 20130101; H01J 37/06 20130101 |
Class at
Publication: |
250/396.R |
International
Class: |
H01J 3/14 20060101
H01J003/14 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 19, 2010 |
EP |
10 187 979.9 |
Claims
1. An emitter assembly for emitting a charged particle beam along
an optical axis, the emitter assembly being housed in a gun chamber
and comprising: an emitter having an emitter tip, wherein the
emitter tip is positioned at a first plane perpendicular to the
optical axis and wherein the emitter is configured to be biased to
a first potential; an extractor having an opening, wherein the
opening is positioned at a second plane perpendicular to the
optical axis and wherein the extractor is configured to be biased
to a second potential, wherein the second plane has a first
distance from the first plane of 2.25 mm and above.
2. The emitter assembly according to claim 1, further comprising:
an extractor support supporting the extractor, wherein the
extractor support is connected to the extractor and being
connectable to a housing of the gun chamber.
3. The emitter assembly according to claim 2, wherein the extractor
support is an insulating extractor support configured to prevent
arcing only for voltages of 10 kV and below.
4. The emitter assembly according to claim 2, wherein the extractor
support is adapted to separate the gun chamber in a first vacuum
region and a second vacuum region.
5. The emitter assembly according to claim 1, wherein the extractor
has a cup-like shape.
6. The emitter assembly according to claim 5, wherein the extractor
includes a first portion with the opening, which is essentially
perpendicular to the optical axis, and a second portion surrounding
the optical axis and being adapted to shield the first potential
applied to the emitter.
7. The emitter assembly according to claim 1, wherein the emitter
or the extractor is movable such that the first distance can be
varied.
8. The emitter assembly according to claim 1, further comprising: a
suppressor configured to be biased to a suppressor potential,
wherein the suppressor potential can be varied.
9. A gun chamber for a charged particle beam device, comprising: an
emitter assembly, the emitter being housed in the gun chamber and
comprising: an emitter having an emitter tip, wherein the emitter
tip is positioned at a first plane perpendicular to the optical
axis and wherein the emitter is configured to be biased to a first
potential; an extractor having an opening, wherein the opening is
positioned at a second plane perpendicular to the optical axis and
wherein the extractor is configured to be biased to a second
potential, wherein the second plane has a first distance from the
first plane of 2.25 mm and above; and the gun chamber further
comprises: an electrode having an opening for trespassing of the
charged particle beam and being configured to be biased to a third
potential;
10. The gun chamber according to claim 9, comprising: a housing of
the gun chamber having at least one vacuum connection adapted for
connecting a vacuum pump, wherein the extractor support is
connected to the extractor and the housing of the gun chamber.
11. The gun chamber according to claim 10, further comprising: a
second vacuum connection adapted for connecting a vacuum pump,
wherein the vacuum connection is positioned to evacuate the first
vacuum region and the further vacuum connection is positioned to
evacuate the second vacuum region.
12. The gun chamber according to claim 9, wherein the electrode is
positioned at a second plane perpendicular to the optical axis and
wherein the distance between the third plane and the second plane
is smaller than 1.5 times the first distance.
13. The emitter assembly according to claim 1, wherein at least two
of the emitter assemblies are combined to form a charged particle
beam device.
14. The emitter assembly according to claim 13, wherein each of the
emitters of the at least two emitter assemblies is connected to one
power supply for providing the first potential to the emitters.
15. The emitter assembly according to claim 13, wherein the at
least two emitter assemblies are provided within a gun chamber,
wherein the gun chamber further comprises an electrode having an
opening for trespassing of the charged particle beam and being
configured to be biased to a third potential.
16. A method of operating the emitter assembly according to claim
10, wherein the voltage between the first potential and the second
potential is at least 20 kV.
17. The method according to claim 16, further comprising: biasing
an electrode having an opening for trespassing of the charged
particle beam to a third potential, wherein the voltage between the
second potential and the third potential is 15 kV or below,
particularly 10 kV or below.
18. The method according to claim 17, wherein the voltage between
the second potential and the third potential is 10 kV or below.
19. The method according to claim 16, wherein the first potential
is shielded by a portion of the extractor surrounding the optical
axis.
Description
FIELD OF THE INVENTION
[0001] Embodiments of the invention relate to particle sources for
particle beam systems e.g. electron microscopes. Particularly, they
relate to simplified particle emitters, charged particle beam
devices and methods of operating simplified emitters and charged
particle beam devices. More specifically, they relate to an emitter
assembly for emitting a charged particle beam along an optical
axis, a gun chamber for a charged particle beam device, a charged
particle beam device, and a method of operating an emitter assembly
or a charged particle beam device, respectively.
BACKGROUND OF THE INVENTION
[0002] Technologies such as microelectronics, micromechanics and
biotechnology have created a high demand for structuring and
probing specimens within the nanometer scale. Micrometer and
nanometer scale process control, inspection or structuring, is
often done with charged particle beams. Probing or structuring is
often performed with charged particle beams which are generated and
focused in charged particle beam devices. Examples of charged
particle beam devices are electron microscopes, electron beam
pattern generators, ion microscopes as well as ion beam pattern
generators.
[0003] During manufacturing of semiconductor devices or the like, a
plurality of observation steps and sample modification steps are
usually conducted. Common systems include an electron beam column
for observation, imaging, testing or inspecting of a specimen and
an ion beam column for patterning of a specimen or material
modification.
[0004] In light of the increasing desire to improve the resolution
of charged particle beam devices, devices with high energy charged
particle beams are desired, for example electron beams with 15 keV
and above. Thereby, reliable operation at high voltages and simple
and robust mechanical design are to be considered. Further, to
increase the throughput of charged particle beam devices in
applications such as microelectronics, micromechanics and
biotechnology, high beam currents and arraying of emitters at a
narrow pitch should also be provided.
SUMMARY
[0005] In light of the above, an emitter assembly for emitting a
charged particle beam along an optical axis according to
independent claim 1, a gun chamber for a charged particle beam
device according to independent claim 9, a charged particle beam
device according to claim 13, and a method of operating an emitter
assembly according to independent claim 16 are provided.
[0006] According to one embodiment, an emitter assembly for
emitting a charged particle beam along an optical axis is provided.
The emitter assembly being housed in a gun chamber and includes an
emitter having an emitter tip, wherein the emitter tip is
positioned at a first plane perpendicular to the optical axis and
wherein the emitter is configured to be biased to a first
potential, an extractor having an opening, wherein the opening is
positioned at a second plane perpendicular to the optical axis and
wherein the extractor is configured to be biased to a second
potential, wherein the second plane has a first distance from the
first plane of 2.25 mm and above.
[0007] According to another embodiment a gun chamber for a charged
particle beam device is provided. The gun chamber includes an
emitter assembly and an electrode having an opening for trespassing
of the charged particle beam and being configured to be biased to a
third potential. The emitter assembly includes an emitter having an
emitter tip, wherein the emitter tip is positioned at a first plane
perpendicular to the optical axis and wherein the emitter is
configured to be biased to a first potential, an extractor having
an opening, wherein the opening is positioned at a second plane
perpendicular to the optical axis and wherein the extractor is
configured to be biased to a second potential, wherein the second
plane has a first distance from the first plane of 2.25 mm and
above.
[0008] According to a yet further embodiment, a charged particle
beam device is provided. The charged particle beam device includes
one or more, typically at least two emitter assemblies. Each of the
one or more emitter assemblies includes an emitter having an
emitter tip, wherein the emitter tip is positioned at a first plane
perpendicular to the optical axis and wherein the emitter is
configured to be biased to a first potential, an extractor having
an opening, wherein the opening is positioned at a second plane
perpendicular to the optical axis and wherein the extractor is
configured to be biased to a second potential, wherein the second
plane has a first distance from the first plane of 2.25 mm and
above. Thereby, each of the emitters is connected to one power
supply for providing the first potential to the one or more
emitters.
[0009] According to an even further embodiment, a method of
operating an emitter assembly is provided. The method includes
emitting a charged particle beam along an optical axis, biasing an
emitter to a first potential, and biasing an extractor to a second
potential, wherein the voltage between the first potential and the
second potential is at least 15 kV, particularly at least 20
kV.
[0010] Further advantages, features, aspects and details that can
be combined with embodiments described herein are evident from the
depending claims, the description and the drawings.
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] FIG. 1 shows a schematic view of a charged particle beam
device with a common emitter assembly;
[0013] FIG. 2A illustrates a common emitter assembly and the method
of operation thereof;
[0014] FIG. 2B illustrates an emitter assembly according to
embodiments described herein and the method of operation
thereof;
[0015] FIG. 3 shows a schematic view of a charged particle beam
device with an emitter assembly according to embodiments described
herein;
[0016] FIG. 4 shows a schematic view of a yet further charged
particle beam device according to embodiments described herein
utilizing an emitter assembly according to embodiments described
herein;
[0017] FIG. 5 shows a schematic view of a charged particle beam
device with a yet further emitter assembly according to embodiments
described herein;
[0018] FIG. 6 shows a schematic view of another charged particle
beam device according to embodiments described herein utilizing
another emitter assembly according to embodiments described
herein;
[0019] FIG. 7 shows a schematic view of a multi-beam gun chamber
area according to embodiments described herein having a plurality
of emitter assemblies according to embodiments described herein;
and
[0020] FIG. 8 shows a flow chart illustrating methods of operating
emitter assemblies and charged particle beam devices according to
embodiments described herein.
DETAILED DESCRIPTION OF THE INVENTION
[0021] 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. Each example is provided by way of
explanation of the invention and is not meant as a limitation of
the invention. For example, 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 present invention includes such modifications and
variations.
[0022] 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.
[0023] Generally, when referring to corpuscles it is to be
understood as a light signal in which the corpuscles are photons as
well as particles, in which the corpuscles are ions, atoms,
electrons or other particles.
[0024] Within the following description of the drawings, the same
reference numbers refer to the same components. Generally, only the
differences with respect to the individual embodiments are
described.
[0025] A "specimen" as referred to herein, includes, but is not
limited to, semiconductor wafers, semiconductor workpieces, and
other workpieces such as masks, glass substrates, memory disks or
the like.
[0026] According to embodiments described herein, a simplified
emitter assembly for emitting a charged particle beam along the
optical axis is provided. For example, a simplified electron
emitter, such as the cold field emitter or thermal field emitter
can be provided. This is particularly relevant for applications
having a high energy electron beam within the charged particle beam
device. According to the following description, reference is made
to electron beam devices. However, it is to be understood that
corresponding principles can also be applied for other charged
particle beam devices, such as ion microscopes.
[0027] According to typical embodiments, the emitter assembly, the
gun chamber and the charged particle beam device can be used for
field emitters, such as cold field emitters and thermal field
emitters, i.e. emitters having a high brightness, for example above
1.times.10.sup.8 A/(cm.sup.2 sr). For example common hairpin
cathodes can have a brightness of 5.times.10.sup.4 to
5.times.10.sup.6 A/(cm.sup.2 sr), Emitter tips of LaB6 could
typically have a brightness of a few 1.times.10.sup.7
A/(cm.sup.2sr), whereas field emitters can have a brightness of
1.times.10.sup.8 A/(cm.sup.2sr) and above or even 1.times.10.sup.9
A/(cm.sup.2sr) and above.
[0028] FIG. 1 shows an electron beam device 1 having a housing 20
and an objective lens 13. An electron emitter 5 includes an emitter
tip opposite to an extraction electrode 12, which is positively
biased (for the example of electrons) to an extraction voltage Vex.
In order to provide the extraction voltage, power supply 6 is
connected to the extraction electrode 12. The assembly of the
emitter 5 and the extraction electrode is connected with the power
supply for providing the acceleration voltage Vacc, which can
typically be connected to ground. This is indicated by reference
numeral 2. Thus, the acceleration voltage determines the beam
energy of electrons that are travelling in regions of the charged
particle beam device 1 that are on ground potential or when hitting
a grounded target. According to some examples, as shown in FIG. 1,
the landing energy of electrons emitted by the emitter 5 on the
specimen 3 can be defined by biasing the specimen 3. Thereby, the
voltage supply 8 can typically be connected to a portion of the
charged particle beam device which is biased on the acceleration
potential or the acceleration voltage. Thereby, the landing energy
of the electron beam can be adjusted or determined by the power
supply 8. According to yet further options, which can be used for
embodiments of the invention described herein, the beam energy
within the charged particle beam device can further be varied,
typically increased, by applying a voltage Vcol to internal beam
guiding components 9 in the charged particle beam device 1.
Accordingly, the power supply 10 can be connected to ground and the
beam guiding components 9.
[0029] According to typical examples, the emitter is biased to the
acceleration potential provided by the power supply 4. Thereby, the
power supply 4 can be connected to ground (reference numeral 2) and
the high-voltage is provided into the chamber 20 through the
high-voltage feedthrough 23. A further high-voltage, which is
provided by the acceleration voltage and the extraction voltage,
i.e. by the power supply 4 and the power supply 6, is fed in the
chamber through high-voltage feedthrough 24, in order to connect
the extraction electrode 12 with the respective conductor. Further,
the voltage feedthrough 32 is provided in order to connect the beam
guiding components 9 with the potential provided by the power
supply 10.
[0030] Due to the acceleration voltage and the extraction voltage,
an electron beam is emitted by the emitter 5 and guided along the
optical axis within the charged particle beam device 1. The charged
particle beam can then be focused by condenser lens 11 and
objective lens 13 to be focused on the specimen 3. Typically, the
objective lens 13 includes upper and lower pole pieces 26 and a
coil 24. The energy of the electron beam on the specimen 3 can be
adjusted by the power supply 8, which can adjust or provide the
landing energy since the power supply 8 is connected to the
acceleration voltage Vacc and defines the potential difference
between the emitter tip 5 and the specimen 3. On impingement of the
primary electron beam, which is emitted from the emitter, secondary
and/or backscattered particles are generated which can be detected
with detector 15. In order to provide an image of a region of the
specimen, scanning devices (not shown in FIG. 1) can be provided to
scan the electron beam over the desired region of the specimen.
[0031] Common emitter assemblies follow the emitter manufacturer's
recommendations and datasheets and attempt to maintain the voltage
between the emitter tip and the extraction potential constant as
well as the tip to extractor at a constant distance. This is
generally done independent of the acceleration voltage Vacc, which
may vary between some ten kV to some hundred kV. Thereby, two
different designs are mostly used. First, the tip is carried by an
elongated emitter insulator. The emitter insulator is a
high-voltage feedthrough capable of withstanding the required
acceleration voltage and is also used for supplying the high
voltage to the emitter tip. The extractor is carried by a different
extractor insulator, which is attached to the vacuum chamber, for
example a grounded vacuum chamber. Thereby, the extractor voltage
is fed through an additional high-voltage feedthrough capable of
withstanding essentially the same acceleration voltage, i.e. the
acceleration voltage minus the extraction voltage. Secondly, the
approach of the mini module can be used. Thereby, the extractor is
mechanically fixed to the structure carrying the emitter.
Accordingly, the extractor insulator needs to withstand the
comparably small extraction voltage Vex. However, the additional
extraction voltage needs to be fed through the same emitter
insulator, which may result in arcing. This mini module design
needs only one high-voltage feedthrough. If the mini module itself
is well aligned internally, the emitter and the extractor electric
electrode can be aligned together with respect to the following
electrode, such as an anode.
[0032] Both designs can also be described with respect to FIG. 2A.
In FIG. 2A the acceleration voltage is provided to the tip of the
emitter 5 by the power supply 4. The power supply 7 provides a
suppressor voltage to the suppressor electrode 22 and the power
supply 6 provides the extraction voltage to the extraction
electrode 12. The further electrode 9 can, for example, be set on
ground potential or to another potential of a few kV. For example,
the further electrode 9 can be an anode, a first electrode of a
condenser lens, an electrode of a beam guiding component for
guiding the beam on a higher potential through the column, or the
like.
[0033] According to typical optional modification, the suppressor
can for example be in a range of -100 V to -500 V as compared to
the emitter tip. Thereby, the suppressor is used to suppress
thermal emission of the emitter tip.
[0034] In the case of the two above-described designs, the tip can,
for example, be on -30 kV the suppressor can be on -30.3 kV, the
extraction electrode 12 can be on -22 kV and the further electrode
9 can be on ground. Thus, a large potential difference is created
between the extractor aperture and the first electrode. This
voltage drop creates a parasitic lens, which is difficult to
control because usually there are no alignment elements. Typically,
the tip should be close to the condenser lens, which results in the
lack of space for alignment elements, and additional elements would
make it even more difficult to reliably withstand large voltage
drops across the gap. Further, if the voltage drop between the
extractor and ground will be several ten kV, such as 22 kV
according to the above example, the corresponding field will
produce a strong `parasitic` lens and provide many opportunities
for high voltage flashover. This can be avoided by the simplified
emitter assembly according to embodiments described below.
Accordingly, even if the tip of emitter 5 can be aligned with
respect to the extractor the lens, a parasitic lens between the
extractor electrode 12 and the further electrode 9, can often not
be aligned. Further, this design requires two or more high-voltage
feedthroughs. For the mini module design, it would be possible to
align the emitter 5 together with the extraction electrode 12 with
respect to the further electrode 9. However, this does require a
very good alignment between the emitter 5 and the extraction
electrode 12 and still generates strong lens between the extraction
electrode 12 and the further electrode 9.
[0035] The new concept, according to embodiments described herein,
overcomes a technical prejudice such that it is not necessary and
not even advisable to operate an emitter according to the
mechanical setup used by the emitter vendors, which is used to
qualify the emitter performance and the production of data sheets.
The principal set up is shown in FIG. 2B. In FIG. 2B the
acceleration voltage is provided to the tip of the emitter 5 by the
power supply 4. The power supply 7 provides a suppressor voltage to
the suppressor electrode 22. The extraction electrode 112 is at a
low voltage, which can be similar or close to the voltage of the
further electrode 9. Thus, a power supply 106 can provide a
relatively small control voltage for the extraction electrode 112.
The further electrode 9 for example, can be set on ground potential
or to another potential of a few kV. According to typical
embodiments, which can be combined with other embodiments described
herein, the further electrode 9 can be an anode, a first electrode
of a condenser lens, an electrode of a beam guiding component for
guiding the beam on a higher potential through the column, or the
like.
[0036] In the case of the two above-described designs, the tip can,
for example, be on -30 kV and the suppressor can be on -30.3 kV,
the extraction electrode 112 can be on -5 kV and the further
electrode 9 can be on ground. Thus, the large potential difference
which has been created between the extractor aperture and the first
electrode (see FIG. 2A) is significantly reduced. The resulting
parasitic lens is also reduced.
[0037] Accordingly, the extraction electrode 112 is positioned at a
larger distance from the tip of the emitter 5. According to typical
embodiments which can be combined with other embodiments described
herein, this distance can be at least 2.25 mm, at least 2.5 mm, at
least 5 mm or even in the range of 7 mm to 20 mm. Further, the
potential of the extraction electrode 112 can be, e.g. for the
example shown in FIG. 2B, in a range of ground to about 10 kV,
typically it can be 2 kV to 7 kV. Accordingly, the influence of the
parasitic lens between the extraction electrode 112 and the further
electrode 9 can be significantly reduced. As described herein, the
tip-to-extractor spacing can be enlarged as long as the extraction
voltage, i.e. the potential difference between the tip of the
emitter 5 and the extraction electrode 112 is raised accordingly.
Thereby, the field strengths of the electric field at the emitter
apex can be provided as desired, i.e., can be kept essentially
constant as compared to common emitter assembly configurations.
[0038] It is to be understood that even though examples of
potentials are described herein, embodiments of the invention are
also directed to examples where other potentials are used as long
as the relative potentials of the components, i.e. the potential
differences or voltages, are within the described ranges. For
example, the tip of the emitter, the specimen or another component
can be on ground and the remaining components can be raised to
positive potentials or to another potential, respectively.
[0039] Yet according to some embodiments described herein, the beam
guiding components in the column can be biased to ground potential.
This can be in particular used for high speed scanning and
detection, for example for electron beam inspection system (EBI).
If the column itself is set on ground potential, there is no need
to keep elements such as electrostatic scan deflectors or detection
electronics on a floating, high potential, which could result in
noise in scanning or detection signals from partial discharge. Yet
according to other options the column might as well be at high
potentials, e.g. for critical dimension measuring applications,
where the specimen should be on ground. However, also for such
applications, the relative potentials from the tip to the extractor
and the extractor to a further electrode can be advantageously
utilized.
[0040] FIG. 3 shows an electron beam device 300 illustrating
embodiments described herein. The electron beam device 300 has a
housing 20 and an objective lens 13. An electron emitter 5 includes
an emitter tip opposite to an extraction electrode 112, which is
positively biased compared to the tip to a voltage for extracting
the electrons. However, as compared to FIG. 1, in order to extract
the electrons, a comparable small voltage is provided by control
power supply 106, which is connected to the extraction electrode
112. The power supply 4 for providing the acceleration voltage
Vacc, which can typically be connected to ground (reference numeral
2) determines the beam energy of electrons that have been
travelling in regions of the charged particle beam device 300 that
are on ground potential or when hitting a grounded target.
According to some embodiments, which can be combined with other
embodiments described herein, as shown in FIG. 3, the landing
energy of electrons emitted by the emitter 5 on the specimen 3 can
be defined by biasing the specimen 3. Thereby, typically the
voltage supply 8 can be connected to a portion of the charged
particle beam device which is biased on the acceleration
potential/voltage. Thereby, the landing energy of the electron beam
can be adjusted or determined by the power supply 8. According to
yet further options, which can be used for embodiments of the
invention described herein, the beam energy within the charged
particle beam device can be varied further, typically increased, by
applying a voltage Vcol to internal beam guiding components 9 or a
first electrode 9 in the charged particle beam device 300.
Accordingly, the power supply 10 can be connected to ground and the
beam guiding components 9.
[0041] According to typical examples, the emitter is biased to the
acceleration potential provided by the power supply 4. Thereby, the
power supply 4 can be connected to ground (reference numeral 2) and
the high-voltage is provided into the chamber 20 through the
high-voltage feedthrough 23. A further high-voltage feedthrough can
be avoided. The control voltage of the power supply 106, can be fed
in the chamber through low-voltage feedthrough 132, in order to
connect the extraction electrode 112 with the respective conductor.
Further, the voltage feedthrough 32 is provided in order to connect
the beam guiding components 9 with the potential provided by the
power supply 10. Thereby, typically high voltage feedthroughs are
configured to withstand voltages of 20 kV and above, whereas
low-voltage feedthroughs are configured for voltages of 15 kV or
below, even though they can also withstand higher voltages,
[0042] Due to the acceleration voltage and the extraction voltage,
an electron beam is emitted by the emitter 5 and guided along the
optical axis within the charged particle beam device 1. The charged
particle beam can then be focused by condenser lens 11 and
objective lens 13 on the specimen 3. Typically, the objective lens
13 includes upper and lower pole pieces 26 and a coil 24. The
energy of the electron beam on the specimen 3 can be adjusted by
the power supply 8, which can adjust or provide the landing energy
since the power supply 8 is connected to the acceleration voltage
Vacc and defines the potential difference between the emitter tip 5
and the specimen 3. On impingement of the primary electron beam,
which is emitted from the emitter, secondary and/or backscattered
particles are generated which can be detected with detector 15. In
order to provide an image of a region of the specimen, scanning
devices (not shown in FIG. 3) can be provided to scan the electron
beam over the desired region of the specimen.
[0043] As shown in FIG. 2B and FIG. 3, the voltage between the tip
of the emitter 5 and the extraction electrode 112 is raised. Even
though raising a critical voltage may not be considered one first
sight, an increase of the voltage between the emitter and the
extraction electrode can be beneficial, particularly if the
acceleration voltage of the emitter tip is raised and/or if a
charged particle beam device with a high beam energy inside the
column is considered. Thereby, it is to be understood that a
charged particle beam device with a high charged particle beam
energy has a significantly higher beam energy within guiding
components of the column as compared to the landing energy of the
charged particles. For example, the beam energy within the column
can be at least 20 times, or at least 30 times higher compared to
the landing energy of the charged particles.
[0044] As shown in FIG. 4, the tip-to-extractor distance can be
increased such that the voltage between the tip of emitter 5 and
the extraction electrode is increased up to the acceleration
voltage, for example 30 kV in the example shown above. Thereby, as
shown in FIG. 4, the extraction voltage and the further electrode 9
or the beam guiding components 9 in the column can be set to ground
potential. Accordingly, the full voltage drop is between the tip
and the extractor. Nevertheless, in light of the increased
distance, the field strengths of the electric field at the emitter
apex can be provided as desired. Further, the field strengths
between mechanical components of the tip carrier and the extractor
carrier can be reduced by also properly increasing the
corresponding distances. Accordingly, in some embodiments there is
no need for a high-voltage power supply for the extraction voltage
or even for any power supply for the extraction voltage. For
example, the first electrode of the condenser lens, an anode or the
like, can be considered as the extractor for the emitter. Thus, in
the example shown in FIG. 4, the extraction electrode could also be
omitted by positioning the guiding components 9 at the position of
the extraction electrode 112. Nevertheless, even if internal column
components such as an anode, a first electrode of a condenser lens,
or beam guiding components for providing high energy beams within
the column are raised to Vcol, the parasitic lens can be reduced.
Further, if no separate isolated extractor electrode and no Vex
power supply are provided, the emission from the tip can be simply
controlled by Vacc and/or the tip-to-extractor distance.
[0045] Since an omission of a power supply for the extraction
electrode might result in loss of flexibility of control parameters
during operation of the electron beam device, the extraction
electrode might be movable along the optical axis as indicated by
arrow 113 in FIG. 4. However, even though an emitter is usually
operated at nearly the same operating conditions over its entire
lifetime, minor changes in the extraction voltage, i.e. the voltage
between the emitter tip and the extraction electrode can be
necessary to compensate for aging effects. These changes are
usually less than 10% to 15% of the extraction voltage. This can be
compensated by adjusting the tip to extraction electrode distance
and/or by providing a relatively small voltage, such as the control
voltage provided by power supply 106 in FIG. 3. Within FIG. 3 the
movement of the extraction electrode along the optical axis is also
indicated by reference 113. However, if for example a control
voltage is connected to the extraction electrode 112, the movement,
as shown by arrow 113, can be considered optional. According to
typical embodiments, if aging effects of the voltage between the
emitter tip and that extraction electrode are to be compensated
for, it is sufficient to provide a voltage of, for example, 1 kV to
6 kV, such as 3 kV to 4.5 kV to the extractor electrode. According
to typical embodiments, which can be combined with other
embodiments described herein, the control voltage supply can
typically vary the voltage between the tip and the extractor by 10%
to 15%. If, for example, this voltage is reference to ground, the
necessary insulator can be relatively simple structure and the
feedthrough can be made reliable and off-the-shelf
[0046] According to further embodiments, which can be combined with
other embodiments described herein, the power supply for connecting
the extraction voltage can be forced to be unipolar by choosing the
tip to extractor spacing, such that the aging effects can be
compensated for by using one polarity of the voltage supply only.
According to yet further alternative options, aging effects could
also be compensated for by static adjustment of the position of the
extraction electrode along the optical axis, for example, by using
shims during a maintenance procedure.
[0047] Further embodiments can be described with reference to FIG.
5. Therein, a further electron beam device 300 is described.
Similar to FIG. 3, the electron beam device 300 has a housing 20
and an objective lens 13. An electron emitter 5 includes an emitter
tip opposite to an extraction electrode 512, which is positively
biased compared to the tip to a voltage for extracting the
electrons. A suppressor 22, such as a suppressor cup, is provided
for suppressing thermal emission of the tip. Thereby, the tip of
the emitter extends above 0 mm to 0.5 mm, e.g. 0.25 mm below the
opening aperture in the suppressor. The power supply 4 for
providing the acceleration voltage Vacc, which can typically be
connected to ground (reference numeral 2) determines the beam
energy of electrons that are travelling in regions of the charged
particle beam device 300 that are on ground potential. The landing
energy of electrons emitted by the emitter 5 on the specimen 3 can
be defined by biasing the specimen 3. Thereby, typically the
voltage supply 8 can be connected to a portion of the charged
particle beam device which is biased on the acceleration
potential/voltage. The beam energy within the charged particle beam
device can be varied further, typically increased, by applying a
voltage Vcol to internal beam guiding components 9 or a first
electrode 9 in the charged particle beam device 300. The power
supply 4 can be connected to ground (reference numeral 2) and the
high-voltage is provided into the chamber 20 through the
high-voltage feedthrough 23. A further high-voltage can be avoided.
The control voltage of the power supply 106 can be fed in the
chamber through low-voltage feedthrough 132, in order to connect
the extraction electrode 112 with the respective conductor.
Further, the voltage feedthrough 32 is provided in order to connect
the beam guiding components 9 with the potential provided by the
power supply 10. Due to the acceleration voltage and the extraction
voltage, an electron beam is emitted by the emitter 5 and guided
along the optical axis within the charged particle beam device 300.
The charged particle beam can then be focused by condenser lens 11
and objective lens 13 on the specimen 3. Typically, the objective
lens 13 includes upper and lower pole pieces 26 and a coil 24.
[0048] The suppressor is typically biased to about -100 V to about
-1 kV with respect to the emitter tip. The energy of the electron
beam on the specimen 3 can be adjusted by the power supply 8, which
can adjust or provide the landing energy since the power supply 8
is connected to the acceleration voltage Vacc and defines the
potential difference between the emitter tip 5 and the specimen 3.
On impingement of the primary electron beam, which is emitted from
the emitter, secondary and/or backscattered particles are generated
which can be detected with detector 15. In order to provide an
image of a region of the specimen, scanning devices (not shown in
FIG. 3) can be provided to scan the electron beam over the desired
region of the specimen.
[0049] As described above, the extraction electrode is positioned
along the optical axis such that the distance between the emitter
tip and the extraction electrode aperture, i.e. the opening in the
extraction electrode, is at least 2.25 mm, at least 4.5 mm, e.g. in
the range of 4 to 10 mm. The control voltage provided by power
supply 106 is such that aging effects of the emitter assembly can
be compensated for. According to yet further additional or
alternative modification, a compensation of the extraction voltage
or an adjustment of the field strength at the emitter tip can also
be provided by the potential applied to the suppressor. For
example, if the suppressor is typically biased to -300 V as
compared to the tip, which is about the manufacturer
recommendation, a higher suppressor voltage such as about -600 V to
-800 V as compared to the tip can be used to compensate for one kV
to a few kV of a tip to extractor voltage. Thus, aging effects or
fine adjustment of the tip-to-extractor voltage can be conducted by
one or more of the elements selected from the group consisting of:
the control voltage or the respective power supply, the suppressor
voltage or the respective power supply, a movement of the tip to
vary the extractor-tip-distance, and a movement of the extractor to
vary the extractor-tip-distance.
[0050] According to yet further additional or alternative
modifications of embodiments of methods and apparatuses described
herein, the extractor electrode can be mechanically and
electrically connected to the housing of the gun chamber or the
charged particle beam device. Thereby, if, for example, the housing
is grounded, the extractor is grounded as well. Thereby, typically,
aging effects of the tip can be compensated for, or adjustment of
the field strength at the tip can be provided by adjusting the
voltage of the suppressor. According to typical embodiments a
change of the suppressor potential by about 500 V to 1000 V equals
a change of the tip-to-extractor voltage of about 20% to 40%. This
is independent of the acceleration voltage. Thus, if an
acceleration voltage of about 10 kV would be used for a system with
a beam energy in the column of 10 keV, an increase of the
suppressor voltage of e.g. 700 V would compensate for, e.g., about
3 kV tip-to-extractor voltage, and if an acceleration voltage of
about 30 kV would be used for a system with a beam energy in the
column of 30 keV, an increase of the suppressor voltage of e.g. 700
V would compensate for, e.g., about 10 kV tip-to-extractor voltage.
Thus, the suppressor voltage is a beneficial compensation tool,
because it can efficiently be used in the same way as
tip-to-extractor voltages variations, because it compensates for a
percentage of the tip-to-extractor voltage.
[0051] In light thereof, a combination of a variable
tip-to-extractor distance, e.g., by moving the emitter, and of a
suppressor voltage variations can provide a good adjustment.
Particularly the option of setting the extractor on the housing
potential or the potential of internal beam guiding elements
provides for these correction parameters also a further simplified
design.
[0052] According to yet further embodiments, which can be combined
with other embodiments described herein, the above described
influence of the suppressor voltage can also be used for control of
the beam current. Since the same current change would be achieved
with an essentially constant change of the suppressor voltage
independent of the beam energy within the column, no excessive
suppressor voltages would be required even for systems having beam
energies in the columns for 25 kV and above. Yet, on the other
hand, a correction of the beam current with the tip-to-extractor
voltage would be essentially proportional to tip-to-extractor
voltage. Thus, for the embodiments having an increased
tip-to-extractor voltage described herein, a current adjustment
would also require an increased voltage range for adjustment.
[0053] Yet according to some embodiments described herein, which
can be combined with other embodiments described herein, an
acceleration of the electrons within the column can be provided to
a major part, e.g. at least 70% or least 80%, between the tip and
the extraction electrode. Thus, even for high energy beam devices,
which have a high energy electron beam guiding region and/or which
have at least 10 times higher beam energy in the column compared to
the landing energy, an acceleration takes place mainly between the
tip and the extractor. Thereby, it should be noted that the earlier
the charged particles are accelerated to the high energy, the more
energy broadening effects and aberrations due to electron-electron
interaction can be reduced. Since the emitted electrons are
immediately accelerated to essentially their maximum energy across
the smallest possible distance, electron-electron interaction is
reduced to the absolute minimum. This reduces energy broadening and
limits the increase in virtual source size.
[0054] According to yet further embodiments, the following feature
can be provided as an advantageous option for a mechanical design
providing a simplification regarding High Voltage stability. The
extractor structure or extraction electrode can be shaped like a
cup that surrounds the emitter structure. Thereby, the extractor
electrode 512 has a portion, which is essentially perpendicular to
the optical axis and including the extractor aperture or opening.
Further, the extractor electrode 512 has a rim portion surrounding
the optical axis, and particularly a region of the emitter tip,
which is biased to the high acceleration potential. Thereby, the
cup can be shaped to have a sufficient distance to the emitter in
order to avoid arcing. If for example the emitter and/or the
holding structure of the emitter tip has a small radius of
curvature in some region, the cup can be shaped to reduce the risk
of arcing in this region. If a cup-shaped extractor electrode 512
is provided, the volume of high field strength is confined to the
gap between the extractor cup and the emitter and can be easily
controlled by proper shaping and machining of the parts. The
potentially dangerous voltage drop along the emitter insulator is
mainly handled by making the insulator sufficiently long and by
proper surface design. Since the extractor cup is basically at
ground potential, all components of the emitter assembly, all
components of a gun chamber, and/or all components of the charged
particle beam device are outside of the shield region and the
vacuum chamber is in an area of low field strength which simplifies
the mechanical design and reduces the risk of arcing significantly.
This design allows reducing the distance between virtual source and
condenser lens. This automatically leads to better optical
performance.
[0055] According to yet further optional modifications of
embodiments described herein, the extractor electrode or the
extractor cup can be mechanically centered to the condenser lens.
Since the extractor cup is to be biased to a relatively low
potential, i.e. there is a relatively smaller voltage between the
housing 20 and the extractor electrode 512, this alignment can be
more easily accomplished. A mechanical x-y-alignment of the tip
with respect to the extractor allows bringing the beam to the
optical axis of the condenser. This improved mechanical alignment
leads to improved optical performance.
[0056] FIG. 6 illustrates a further advantageous modification,
which can be provided in light of the simplified design of the
emitter assembly. As compared to the embodiments shown in FIGS. 3
to 5, the electron beam device 300 shown in FIG. 6 shows the
insulator 632 for carrying the extractor 512 and shows the
insulator 633 carrying the further electrode 9 or the beam guiding
components 9. The extractor electrode, the insulators and the
further electrodes are formed to provide two sub-chambers in the
gun chamber region. A first connection 644 for a vacuum pump and a
second connection 642 for a vacuum pump are provided.
[0057] Thus, having the emitter tip and the region between the
extractor and the further electrode independent of each other, it
is possible to evacuate the region of the emitter 5. This is inter
alia more easily possible since the regions outside the cup are
shielded by the potential of the extractor 512, which can be
essentially ground (+- a few kV) or essentially the potential of
the housing or the beam guiding components (+- a few kV).
Accordingly, the proposed design allows easy adaptation to emitters
with special vacuum requirements like a lower total pressure (e.g.
in the order of magnitude of 1.times.10.sup.-11 mbar), lower
partial pressure of critical gases (e.g. in the order of magnitude
of 1.times.10.sup.-9 mbar) or even higher partial pressure of
process gases (e.g. in the order of magnitude of 1.times.10.sup.-6
mbar). In common systems, this would usually require inserting an
additional differentially pumped vacuum area between condenser and
emitter, accompanied by a significant increase in tip-to-condenser
distance.
[0058] According to the embodiments described herein, the extractor
can be used as the differential pumping aperture and separate the
volumes below and above the extractor cup by introducing an
insulating barrier between the extractor cup and the vacuum chamber
housing. Since the voltage applied to the extractor cup is small,
there is no risk of arcing.
[0059] According to another embodiment, the simplified emitter
assembly can be advantageously used for a charged particle
multi-beam device, wherein a plurality of emitter tips is arrayed.
FIG. 7 shows a gun region of a multi-beam system. The system 700
includes a housing portion 720 and two or more high voltage
feedthroughs 23 (5 insulating feedthroughs are shown in FIG. 7) for
the acceleration voltage provided by power supply 4. The
acceleration voltage is provided to two or more emitters 5 having
respective emitter tips. Two or more, i.e. a corresponding number,
extractor electrodes 512/712 or extractor cups are provided.
According to the example shown in FIG. 7, two or more low-voltage
feedthroughs 132 can be provided to allow for biasing each of the
two or more extractors to an individual potential. This is
indicated by one power supply 706 having a corresponding number of
outputs (5 in FIG. 7). According to alternatives, each control
voltage for an extractor electrode can be provided by an individual
power supply or a smaller number of power supplies can each provide
some of the required potentials. The further electrode, i.e. an
electrode in beam travelling direction downstream of the extractor
is shown in FIG. 7 by reference numeral 9. For example, the further
electrode 9 can be an anode, a first electrode of a condenser lens,
a beam guiding component for providing high beam energies, or the
like.
[0060] As described above a combination of a variable
tip-to-extractor distance, e.g., by moving the emitter, and of a
suppressor voltage variations can provide a good adjustment for the
beam current and/or a good compensation of tip aging equally usable
to a variation of the tip-to-extractor voltage. Particularly the
option to set the extractor on the housing potential or the
potential of internal beam guiding elements provides for these
correction parameters also a further simplified design, i.e. the
power supply 706, the feedthroughs 132 and the insulators 632, 732
could be omitted. A control of the individual beams and/or a
compensation of the aging of the emitter could be controlled by one
or, preferably, both of the tip-to-extractor distance and the
suppressor voltage. Thus, a multi-beam device can be provided such
that equal currents for all emitters can be adjusted and aging of
the emitters can be compensated. The equal current and the option
to compensated for aging can then be provided with a simplified
design allowing for a particularly narrow pitch, e.g. 50 mm or
smaller, between the emitters as disclosed herein.
[0061] Generally, the simplified emitter assembly according to
embodiments described herein, allows for arraying of many emitters
at a narrow pitch, e.g. at a distance of 60 mm or smaller. In light
of the reduced potential of the extractor electrodes or extractor
cups, and in light of the shielding of the extractor cups, small
insulators 632/732 for carrying the extractor can be provided.
[0062] According to yet further modification thereof, the
individual extractor cups may be reduced to narrow units. For
example, cylindrical cups having a first portion including the
aperture opening and a second portion having a cylindrical portion
surrounding the optical axis, and a conical transition portion
between the first and the second portion can be reduced in one or
both lateral dimensions as long as the first portion providing the
field symmetry is not affected by the reducing the cup dimension in
one or two directions, e.g. in the form of slices. The rotational
symmetry is only required in the vicinity of the tip. The overall
shielding function does not ask for symmetry. A shielding in the
volume surrounding the emitter structure could also be provided by
a common shield.
[0063] The above mentioned control of emission current by a small
extraction voltage provided by power supply 706, which can, for
example, be referred to ground potential, is beneficial in multi
column systems, where the beam currents in the individual columns
need to be precisely matched.
[0064] 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.
[0065] According to embodiments described herein, a simplified
emitter assembly with an emitter having an emitter tip, wherein the
emitter tip is positioned at a first plane perpendicular to the
optical axis and wherein the emitter is configured to be biased to
a first potential, an extractor having an opening, wherein the
opening is positioned at a second plane perpendicular to the
optical axis and wherein the extractor is configured to be biased
to a second potential, wherein the second plane has a first
distance from the first plane of 2.25 mm an above provides at least
one of the following advantages. It can reduce arcing across the
extractor insulator and/or extractor feedthrough as compared to the
common emitter designs, it can reduce arcing inside the mini module
or the emitter insulator/feedthrough, it can reduce arcing between
the extractor structure and the vacuum chamber, it can reduce loss
in optical performance due to the misalignment of the strong
parasitic lens between extractor and the following electrode, such
as an anode and/or the first electrode of a condenser, and/or it
can reduce or avoid loss in optical performance due to avoidable
electron-electron interaction. Yet, a simple and robust mechanical
design which can, for example, be operated reliably at high column
voltage, when the emitter structure is raised to a high voltage
Vacc with respect to the surrounding column parts (vacuum chamber,
liner tubes, insulators, feedthroughs, pumps) can be provided.
Further, the number of high-voltage feedthroughs configured for 20
kV and above can be reduce, the number of components exposed to
high electrical field strength can be reduced and/or the emitter
brightness can be improved. The emitter brightness can, for
example, be improved by reducing energy broadening of the beam due
to an early acceleration, by reducing broadening of the virtual
source, and/or by reducing aberrations of the gun lens by reducing
parasitic lenses, which are difficult to align. The design
practically eliminates the `parasitic` lens between extractor and
condenser. Yet further, it can be possible to improve mechanical
alignment of the emitter components and to reduce the distance of
the tip to the first (condenser) lens of the system. Further, as
described above, arraying of emitters at narrow pitch can be
provided more easily and the possibility to incorporate an
additional differential vacuum chamber to improve emission
stability and/or emitter lifetime can be provided more easily. One
or more of the above aspects can be utilized to better enable a
high beam current operation. Thereby, in addition to the arraying
options, the throughput of a system can be increased.
[0066] As described above, the simplified emitter assemblies
described herein have an increased tip-to-extractor difference as
compared to the mechanical setup used by the emitter vendors, which
is used to qualify the emitter performance and the production of
data sheets. This is provided by correspondingly increasing the
voltage between the tip and the extractor, and/or by
correspondingly decreasing the voltage between the extractor and
the further electrode. An acceleration of the electrons is
conducted in the first region between the tip and the extractor.
Thus, according to embodiments of operating an emitter assembly,
the following steps shown in FIG. 8 are provided. In step 802 a
charged particle beam, e.g. an electron beam, is emitted.
Therefore, in step 804 an emitter is biasing an emitter to a first
potential, an extractor is biased in step 804 to a second
potential, wherein the voltage between the first potential and the
second potential is at least 15 kV, particularly at least 20 kV. As
further optional step 808, a further electrode having an opening
for trespassing of the charged particle beam is biased to a third
potential, wherein the voltage between the second potential and the
third potential is 15 kV or below, particularly 10 kV or below.
According to typical embodiments, which can be combined with other
embodiments described herein, the voltage of the extractor can
typically be 10% to 15% of the acceleration voltage Vacc.
[0067] As described above, a plurality of embodiments has been
described. Thereby, according to one embodiment, an emitter
assembly for emitting a charged particle beam along an optical axis
is provided. The emitter assembly being housed in a gun chamber and
includes an emitter having an emitter tip, wherein the emitter tip
is positioned at a first plane perpendicular to the optical axis
and wherein the emitter is configured to be biased to a first
potential, an extractor having an opening, wherein the opening is
positioned at a second plane perpendicular to the optical axis and
wherein the extractor is configured to be biased to a second
potential, wherein the second plane has a first distance from the
first plane of 2.25 mm and above. According to optional
modifications thereof, at least one of the following features can
be utilized, which are of the group consisting of: the assembly can
further include an extractor support supporting the extractor,
wherein the extractor support is connected to the extractor and
being connectable to a housing of the gun chamber, particularly
wherein the extractor support is an insulating extractor support
configured to prevent arcing only for voltages of 10 kV and below;
for example, the extractor support can be adapted to separate the
gun chamber in a first vacuum region and a second vacuum region;
the extractor can have a cup-like shape, particularly wherein the
extractor includes a first portion with the opening, which is
essentially perpendicular to the optical axis, and a second portion
surrounding the optical axis and being adapted to shield the first
potential applied to the emitter; the emitter or the extractor is
movable such that the first distance can be varied; and the
assembly further includes a suppressor configured to be biased to a
suppressor potential, wherein the suppressor potential can be
varied.
[0068] According to another embodiment a gun chamber for a charged
particle beam device is provided. The gun chamber includes an
emitter assembly and an electrode having an opening for trespassing
of the charged particle beam and being configured to be biased to a
third potential. The emitter assembly includes an emitter having an
emitter tip, wherein the emitter tip is positioned at a first plane
perpendicular to the optical axis and wherein the emitter is
configured to be biased to a first potential, an extractor having
an opening, wherein the opening is positioned at a second plane
perpendicular to the optical axis and wherein the extractor is
configured to be biased to a second potential, wherein the second
plane has a first distance from the first plane of 2.25 mm and
above. According to optional modifications thereof, at least one of
the following features can be utilized, which are of the group
consisting of: the gun chamber can include a housing of the gun
chamber having at least one vacuum connection adapted for
connecting a vacuum pump, wherein the extractor support is
connected to the extractor and the housing of the gun chamber; the
gun chamber can include a second vacuum connection adapted for
connecting a vacuum pump, wherein the vacuum connection is
positioned to evacuate the first vacuum region and the further
vacuum connection is positioned to evacuate the second vacuum
region; and the electrode can be positioned at a second plane
perpendicular to the optical axis and wherein the distance between
the third plane and the second plane is smaller than 1.5 times the
first distance.
[0069] According to a yet further embodiment, a charged particle
beam device is provided. The charged particle beam device includes
one or more, typically at least two emitter assemblies. Each of the
one or more emitter assemblies includes an emitter having an
emitter tip, wherein the emitter tip is positioned at a first plane
perpendicular to the optical axis and wherein the emitter is
configured to be biased to a first potential, an extractor having
an opening, wherein the opening is positioned at a second plane
perpendicular to the optical axis and wherein the extractor is
configured to be biased to a second potential, wherein the second
plane has a first distance from the first plane of 2.25 mm and
above. Thereby, each of the emitters of is connected to one power
supply for providing the first potential to the one or more
emitters. According to optional modifications thereof, the one or
more, typically tow or more, emitter assemblies can be provided
within a gun chamber according to embodiments described herein.
[0070] According to an even further embodiment, a method of
operating an emitter assembly is provided. The method includes
emitting a charged particle beam along an optical axis, biasing an
emitter to a first potential, and biasing an extractor to a second
potential, wherein the voltage between the first potential and the
second potential is at least 15 kV, particularly at least 20 kV.
According to optional modifications thereof, at least one of the
following features can be utilized, which are of the group
consisting of: the method can include biasing an electrode having
an opening for trespassing of the charged particle beam to a third
potential, wherein the voltage between the second potential and the
third potential is 15 kV or below, particularly 10 kV or below; the
first potential can be shielded by a portion of the extractor
surrounding the optical axis; and the beam current can be varied by
varying the tip-to-suppressor voltage.
[0071] 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.
* * * * *