U.S. patent application number 13/913723 was filed with the patent office on 2013-10-17 for method for producing a representation of an object by means of a particle beam, as well as a particle beam device for carrying out the method.
The applicant listed for this patent is Carl Zeiss Microscopy GmbH. Invention is credited to Andreas Adolf, Rainer Arnold, Josef Biberger, Ernst Draszba, Klaus Hegele, Harald Niebel, Ralph Pulwey.
Application Number | 20130270437 13/913723 |
Document ID | / |
Family ID | 43978050 |
Filed Date | 2013-10-17 |
United States Patent
Application |
20130270437 |
Kind Code |
A1 |
Biberger; Josef ; et
al. |
October 17, 2013 |
METHOD FOR PRODUCING A REPRESENTATION OF AN OBJECT BY MEANS OF A
PARTICLE BEAM, AS WELL AS A PARTICLE BEAM DEVICE FOR CARRYING OUT
THE METHOD
Abstract
A method for producing a representation of an object using a
particle beam, as well as a particle beam device for carrying out
the method are disclosed. The system described herein is based on
the object of specifying the method and the particle beam device
for producing a representation of an object such that images which
are produced, in particular including FFT images, are as free as
possible of artifacts which are not caused by the object to be
examined. This is achieved in particular in that pixel lives, line
flyback times and pixel pause times are varied in raster
patterns.
Inventors: |
Biberger; Josef;
(Wildenberg, DE) ; Pulwey; Ralph; (Aalen, DE)
; Draszba; Ernst; (Wittislingen, DE) ; Hegele;
Klaus; (Aalen, DE) ; Niebel; Harald;
(Oberkochen, DE) ; Adolf; Andreas; (Aalen, DE)
; Arnold; Rainer; (Ulm, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Carl Zeiss Microscopy GmbH |
Jena |
|
DE |
|
|
Family ID: |
43978050 |
Appl. No.: |
13/913723 |
Filed: |
June 10, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12930046 |
Dec 22, 2010 |
8471202 |
|
|
13913723 |
|
|
|
|
61398146 |
Jun 21, 2010 |
|
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Current U.S.
Class: |
250/307 ;
250/310 |
Current CPC
Class: |
H01J 37/222 20130101;
H01J 37/28 20130101; H01J 2237/223 20130101; H01J 2237/1536
20130101 |
Class at
Publication: |
250/307 ;
250/310 |
International
Class: |
H01J 37/28 20060101
H01J037/28 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 23, 2009 |
DE |
102009055271.5 |
Claims
1-10. (canceled)
11. A method for producing a representation of an object using a
particle beam, wherein the particle beam is made available by a
particle beam device having at least one particle beam column,
wherein the particle beam column has a beam generator for
generating a particle beam, and has an objective lens for focusing
the particle beam onto the object, the method comprising: defining
at least one raster area on the object, wherein the raster area has
at least one first raster point, at least one second raster point
and at least one third raster point; defining a raster pattern,
wherein the raster pattern defines guidance of the particle beam
through the raster area; generating the particle beam; passing the
particle beam to a start point, which is defined by at least one of
the following raster points: the first raster point, the second
raster point or the third raster point; guiding the particle beam
from the start point over the raster area in accordance with the
raster pattern, wherein the particle beam is guided to the first
raster point at a first time, to the second raster point at a
second time, and to the third raster point at a third time;
detecting at least one of: interaction particles or interaction
radiation, wherein the at least one of: interaction particles and
the interaction radiation are or is created by interaction of the
particle beam with the object, wherein the first time, the second
time and the third time are chosen such that a first time interval,
which is defined by a first difference between the first time and
the second time, and a second time interval, which is defined by a
second difference between the first time and the third time, are
different.
12. The method according to claim 11, wherein the particle beam
remains at the first raster point for a first time period, at the
second raster point for a second time period and at the third
raster point for a third time period, and wherein the method
further comprises at least one of the following features: the first
time period, the second time period and the third time period are
identical to one another, or at least one of the following time
periods, specifically the first time period, the second time period
and the third time period, are different to one of the further ones
of the following time periods, specifically the first time period,
the second time period and the third time period.
13. The method according to claim 11, wherein the defining a raster
pattern comprises defining a spiral or a rectangular raster
pattern.
14. The method according to claim 11, wherein the particle beam is
guided over the raster area at least a first time in order to
produce a first representation, and is guided over the raster area
at least a second time in order to produce a second representation,
and wherein the first representation and the second representation
are combined using an averaging method or integration method to
form a final representation.
15. The method according to claim 11, wherein the particle beam is
guided over the raster area at least a first time in order to
produce a first representation and over the raster area at least a
second time in order to produce a second representation, wherein
the first representation and the second representation are produced
using different raster parameters, and wherein the first
representation and the second representation are combined using an
averaging method to form a final representation.
16-20. (canceled)
21. A particle beam device, comprising: at least one first particle
beam column, wherein the first particle beam column has a first
beam generator for generating a first particle beam, and a first
objective lens for focusing the first particle beam onto an object;
at least one first control unit for defining a first raster area on
the object and for defining a first raster pattern, wherein the
first raster area has at least one first raster point, at least one
second raster point and at least one third raster point, and
wherein the first raster pattern defines guidance of the first
particle beam through the first raster area; at least one first
raster device for guiding the first particle beam over the object
in accordance with the first raster pattern, wherein the first
raster device provides that the particle beam is guided to the
first raster point at a first time, to the second raster point at a
second time and to the third raster point at a third time; at least
one first detection unit for detection of at least one of:
interaction particles or interaction radiation, wherein the first
control unit provides that the first time, the second time and the
third time are chosen such that a first time interval, which is
defined by a first difference between the first time and the second
time, and a second time interval, which is defined by a second
difference between the first time and the third time, are
different.
22. The particle beam device according to claim 21, further
comprising: at least one third control unit for defining a second
raster area on the object and for defining a second raster pattern;
at least one second particle beam column, wherein the second
particle beam column has a second beam generator for generating a
second particle beam, a second objective lens for focusing the
second particle beam onto the object, and at least one second
raster device for guiding the second particle beam over the object
in accordance with the second raster pattern; and at least one
second detection unit for detection of at least one of: the
interaction particles or the interaction radiation.
23. The particle beam device according to claim 22, wherein the
third control unit provides that the second raster area is defined
by a multiplicity of raster lines, wherein the multiplicity of
raster lines have at least one third raster line and at least one
fourth raster line, wherein the third raster line has a
multiplicity of raster points, which have at least one fifth raster
point and at least one sixth raster point, wherein the fourth
raster line has a multiplicity of further raster points, which have
at least one seventh raster point and at least one eighth raster
point, and wherein the second particle beam remains at at least one
of: the fifth raster point for a seventh time period, the sixth
raster point for an eighth time period, the seventh raster point
for a ninth time period or the eighth raster point for a tenth time
period, wherein there is an eleventh time period between guidance
of the second particle beam over the third raster line and guidance
of the second particle beam over the fourth raster line, wherein
the multiplicity of raster lines define a multiplicity of eleventh
time periods, and wherein there is a twelfth time period during
guidance of the second particle beam between scanning of at least
one of the following raster points, specifically the fifth raster
point, the sixth raster point, the seventh raster point and the
eighth raster point, using the second particle beam, and scanning
of a further and different one of the following raster points,
specifically the fifth raster point, the sixth raster point, the
seventh raster point and the eighth raster point, using the second
particle beam, wherein the multiplicity of raster points define a
multiplicity of twelfth time periods, and wherein the particle beam
device is provided with at least one fourth control unit for
varying at least one of the following time periods, specifically
the seventh time period, the eighth time period, the ninth time
period, the tenth time period, the eleventh time period and the
twelfth time period.
24. The particle beam device according to claim 22, wherein the
third control unit provides that the second raster area is defined
by at least one fifth raster point, at least one sixth raster point
and at least one seventh raster point, and wherein the second
raster pattern is defined to have a rectangular or spiral
shape.
25. The particle beam device according to claim 21, wherein the
particle beam device further comprises at least one of the
following features: the first particle beam column is in the form
of an electron beam column, and the second particle beam column is
in the form of an ion beam column, the first particle beam column
is in the form of an ion beam column, and the second particle beam
column is in the form of an electron beam column, or the first
particle beam column is in the form of an ion beam column, and the
second particle beam column is in the form of an ion beam
column.
26. (canceled)
Description
RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional App.
No. 61/398,146 filed Jun. 21, 2010, which is incorporated herein by
reference.
TECHNICAL FIELD
[0002] This application relates to a method for producing a
representation of an object using a particle beam and to a particle
beam device for carrying out the method.
BACKGROUND OF THE INVENTION
[0003] Electron beam devices, in particular a scanning electron
microscope (also referred to in the following text as SEM) and/or a
transmission electron microscope (also referred to in the following
text as TEM), are used to examine objects (samples) in order to
obtain knowledge about the characteristics and behavior of objects
in specific conditions.
[0004] In the case of an SEM, an electron beam (also referred to in
the following text as a primary electron beam) is produced using a
beam generator and is focused by a beam guidance system onto an
object to be examined. The primary electron beam is guided in a
raster shape using a deflection device over a surface of the object
to be examined. The electrons in the primary electron beam in this
case interact with the object to be examined. As a consequence of
the interaction, in particular electrons are emitted from the
surface of the object to be examined (so-called secondary
electrons) and electrons in the primary electron beam are scattered
back (so-called back-scattered electrons). The secondary electrons
and back-scattered electrons are detected and are used for image
production. An image of the surface of the object to be examined is
thus obtained.
[0005] Furthermore, it is known from the prior art for combination
devices to be used to examine objects, in which both electrons and
ions can be passed to an object to be examined. By way of example,
it is known for an SEM to additionally be equipped with an ion beam
column. An ion beam generator which is arranged in the ion beam
column is used to produce ions which are used for preparation of an
object (for example etching of the object or application of
material to the object), or else for imaging. In this case, the SEM
is used in particular to observe the preparation, or else for
further examination of the prepared or unprepared object.
[0006] In the case of a TEM, a primary electron beam is likewise
produced using a beam generator and is passed to an object to be
examined using a beam guidance system. The primary electron beam
passes through the object to be examined. When the primary electron
beam passes through the object to be examined, the electrons in the
primary electron beam interact with the material of the object to
be examined. The electrons passing through the object to be
examined are imaged onto a phosphor screen using a system
comprising an objective and a projection lens, or are detected by a
position-resolving detector (for example a camera). In addition,
for this purpose, it is possible to provide for back-scattered
electrons on the object to be examined and/or secondary electrons
emitted from the object to be examined to be detected using a
further detector, in order to image an object to be examined. The
abovementioned imaging is in this case carried out in the scanning
mode of a TEM. In this case, the primary electron beam of the TEM
is focused on the object to be examined, in a similar manner to
that in the case of an SEM, and is guided in a raster shape over
the object to be examined, using a deflection device. A TEM such as
this is generally referred to as an STEM. Analogously, in the case
of an object to be examined through which radiation can be passed,
an SEM can also be operated as an STEM.
[0007] By way of example, it is possible to use the TEM to
determine the structure of a crystal in more detail. For this
purpose, in particular, the images or diffraction patterns produced
using the electrons passing through the object are evaluated. In
principle, a diffraction pattern is a Fourier transform of the
object to be examined and has structures whose position in the
diffraction pattern is governed by the distances and spatial
frequencies of the lattice structure of the crystal. It is also
possible to use the intensity of the structures to make deductions
about the content of an elementary cell of a crystal. The
abovementioned diffraction pattern can be obtained without a
scanning mode, or in the scanning mode of the TEM.
[0008] In the prior art, a standard raster process is carried out
for the scanning mode of a particle beam device. In this standard
raster process, a raster pattern is predetermined having a
multiplicity of raster lines which are arranged parallel to one
another, with each of the multiplicity of raster lines comprising
an identical number of raster points (pixels). The primary electron
beam in the standard raster process is guided to a first end of a
first raster line. The primary electron beam is then guided,
starting from the first end of the first raster line, in the
direction of a second end of the first raster line from one raster
point to another, until the second end of the first raster line is
reached. The primary electron beam is then guided to the first end
of a second raster line. An identical process is carried out with
the second raster line to that with the first raster line. During
the process, the time for which the primary electron beam remains
at each raster point is identical, and can be predetermined in a
fixed form by a control system for a specific imaging mode.
[0009] By way of example, the imaging mode defines a chosen
magnification and the speed at which the primary electron beam is
scanned over the object. During the abovementioned guidance of the
primary electron beam from the second end of the first raster line
to the first end of the second raster line, it is known from the
prior art for a further dwell duration to be provided. This further
dwell duration is predetermined in a fixed form, for example by the
control system, as a function of a chosen imaging mode. A fixed
flyback time is predetermined as a function of the chosen imaging
mode, with this being the time which is intended to exist between
reaching and dwelling at the second end of the first raster line on
the one hand and the guidance of the primary electron beam to the
first end of the second raster line, on the other hand. A further
known embodiment provides for the primary electron beam to be
guided from the second end of the first raster line to the first
end of the second raster line, where the primary electron beam
remains during the further dwell duration, until the primary
electron beam passes over the second raster line, following a
trigger signal. By way of example, this trigger signal is coupled
to the power supply system frequency.
[0010] The guidance of the primary electron beam from one raster
point to a next raster point is also referred to as raster guidance
or else rastering.
[0011] In a high-resolution mode, an STEM can be used to make
atomic structures visible, and to image them. Furthermore, it is
also possible to image a spatially periodic crystal structure of
crystalline samples. During the evaluation of images such as these,
the Fourier transform is used to represent the spatial frequencies
present in a respective image. The intensity of a point in a
Fourier-transformed image (also referred to in the following text
as an FFT image) of the respective image indicates the amplitude
with which a specific spatial frequency (periodicity based on
frequency and direction) is present in the respective image.
[0012] However, it has been found that disturbances which influence
the image of very small structures (for example atomic structures
of a crystalline object) lead to artifacts in the respective image.
Even minor periodic disturbances (for example fluctuations in the
position of the primary electron beam, fluctuations in the
intensity of the primary electron beam and/or fluctuations in the
intensity of a detection signal) can lead to undesirable artifacts
being visible both in the respective image and in the corresponding
FFT image. The artifacts make it harder to evaluate the FFT
image.
[0013] Accordingly, it would be desirable to provide a method and a
particle beam device for producing a representation of an object,
in which images which are produced, in particular also FFT images,
are as free as possible of artifacts which are not caused by the
object to be examined.
SUMMARY OF THE INVENTION
[0014] According to the system described herein, a method is used
to produce a representation of an object using a particle beam,
wherein the particle beam is made available by a particle beam
device having at least one particle beam column. The particle beam
column has a beam generator for producing a particle beam, and an
objective lens for focusing the particle beam onto the object. In
the method according to the system described herein, a raster area
is defined on the object. This is the area over which the particle
beam is guided in order to obtain a representation of the object.
The raster area provided here has a multiplicity of raster lines,
wherein the multiplicity is provided with at least one first raster
line and at least one second raster line, wherein the first raster
line has a multiplicity of raster points, wherein the multiplicity
of raster points have at least one first raster point and at least
one second raster point, and wherein the second raster line has a
multiplicity of further raster points, wherein this multiplicity
are provided with at least one third raster point and at least one
fourth raster point. In this case, in the text above and that
below, a raster line may be, for example, an arrangement of raster
points along a straight line. However, the system described herein
is not restricted to an arrangement of raster points along a
straight line. In fact, the raster points may be arranged along a
line which has a different shape, for example a circular or spiral
shape.
[0015] Furthermore, in the method according to the system described
herein, a raster pattern is defined, wherein the raster pattern
defines guidance of the particle beam through the raster area. For
example, the particle beam is passed sequentially through the
individual raster points in the first raster line and in the second
raster line. However, the system described herein is not restricted
to this raster pattern. In fact, any raster pattern which is
suitable for the system described herein can be used, for example
spiral guidance of the particle beam through the raster area or
even individual raster points in the first raster line and in the
second raster line being passed through on the random-number
principle.
[0016] Furthermore, the method according to the system described
herein provides for the particle beam to be produced and for the
particle beam to be passed to one of the following raster points:
the first raster point, the second raster point, the third raster
point or the fourth raster point. Furthermore, it is envisaged that
the particle beam be guided in accordance with the raster pattern
over the raster area, wherein the particle beam remains at the
first raster point for a first time period, at the second raster
point for a second time period, at the third raster point for a
third time period, and/or at the fourth raster point for a fourth
time period. The first time period to the fourth time period are
the time periods in which it is possible to use a detection device
to detect interaction particles and/or interaction radiation, which
are or is created by an interaction of the particle beam with the
object, and, for example, to integrate the signals detected using
the detection device and associated with one of the first to fourth
raster points. The first time period to the fourth time period are
also respectively referred to as the pixel life or raster point
life.
[0017] Furthermore, in the method according to the system described
herein, there is a fifth time period between guidance of the
particle beam over the first raster line and guidance of the
particle beam over the second raster line. The multiplicity of
raster lines also result in a multiplicity of fifth time periods.
The fifth time period is also referred to as the line flyback
time.
[0018] Furthermore, there is a sixth time period during guidance of
the particle beam between scanning of one of the following raster
points, specifically the first raster point, the second raster
point, the third raster point and the fourth raster point, using
the particle beam and scanning of a further and different one of
the following raster points, specifically the first raster point,
the second raster point, the third raster point as well as the
fourth raster point. In other words, there is a sixth time period
between the scanning of one of the abovementioned raster points
(for example the first raster point) and the scanning of a further,
but different, one of the abovementioned raster points (for example
the second raster point). The multiplicity of raster points also
result in a multiplicity of sixth time periods. The sixth time
period is also referred to as the pixel pause time.
[0019] The method according to the system described herein also
provides for detection of, interaction particles and/or interaction
radiation.
[0020] The method according to the system described herein
furthermore provides for variation of at least one of the following
time periods: the first time period, the second time period, the
third time period, the fourth time period, the fifth time period
and the sixth time period.
[0021] The system described herein is based, at least in part, on
the following idea. The standard raster method explained above is
in principle a linear image (that is to say a correlation) between
a time profile of a signal detected in a particle beam device and
the respective position associated with the detected signal on the
object. For this reason, fluctuations which are periodic over time
(for example fluctuations in the position of the primary electron
beam and/or fluctuations in the intensity of the primary electron
beam) in a representation of the object produced using detected
signals appear as spatially periodic fluctuations in the form of
disturbing patterns (artifacts). These disturbing patterns can be
seen particularly well in an FFT image. Deliberations have now
revealed that better representations of the object can be achieved
by canceling out the correlation between the time profile of the
detected signal (which has the fluctuations that are periodic over
time) and the respective position associated with the detected
signal on the object, in which better representations the
disturbing artifacts are now only very restricted or are even no
longer perceptible at all. This is achieved by varying at least one
of the abovementioned time periods. The abovementioned correlation
is canceled in this way. The more completely the cancellation is
implemented, the more uniformly will any disturbing patterns that
occur be distributed in the representation, as a result of which
they are less pronounced in the representation.
[0022] In a first exemplary embodiment of the method according to
the system described herein, provision is additionally or
alternatively made for at least one of the following time periods,
specifically the first time period, the second time period, the
third time period, the fourth time period, the fifth time period
and the sixth time period, to be randomly varied deterministically
or non-deterministically. In yet another exemplary embodiment of
the method according to the system described herein, provision is
made for the method to have at least one of the following features:
[0023] the first time period, the second time period, the third
time period and the fourth time period form a first sequence for
the raster area, wherein the first sequence is subdivided into at
least one first area of the first sequence and at least one second
area of the first sequence, wherein at least the time periods which
are included in the first area of the first sequence are randomly
varied deterministically or non-deterministically, [0024] the
multiplicity of fifth time periods form a second sequence for the
raster area, wherein the second sequence is subdivided into at
least one first area of the second sequence and at least one second
area of the second sequence, wherein at least the fifth time
periods which are included in the first area of the second sequence
are randomly varied deterministically or non-deterministically, and
[0025] the multiplicity of sixth time periods form a third sequence
for the raster area, wherein the third sequence is subdivided into
at least one first area of the third sequence and at least one
second area of the third sequence, wherein at least the sixth time
periods which are included in the first area of the third sequence
are randomly varied deterministically or non-deterministically.
[0026] A further embodiment of the method according to the system
described herein alternatively or additionally provides that the
raster pattern is defined such that the particle beam is first of
all passed over the first raster line and then over the second
raster line in the raster area. By way of example, the first raster
point and the second raster point in the first raster line are
scanned sequentially. The third raster point and the fourth raster
point in the second raster line are then scanned sequentially, for
example. Furthermore, provision is additionally or alternatively
made that the raster pattern is defined such that the particle beam
is guided through the raster area in the following sequence: first
of all to the first raster point in the first raster line, then to
the second raster point in the first raster line, then to the
fourth raster point in the second raster line, and then to the
third raster point in the second raster line. A further embodiment
of the method according to the system described herein
alternatively or additionally provides that the raster pattern is
defined such that it has a rectangular and/or spiral shape. As has
already been mentioned further above however, the system described
herein is not restricted to a specific raster pattern. In fact, any
raster pattern which is suitable for the system described herein
can be used, for example even with individual raster points in the
first raster line and in the second raster line being passed
through on the basis of the random-number principle.
[0027] In principle, the abovementioned fifth time period is
nothing more than a pause between the guidance of the particle beam
over the first raster line and the guidance of the particle beam
over the second raster line. One embodiment of the method according
to the system described herein additionally or alternatively
provides for the fifth time period to be varied using a first
random-number generator. As an alternative to this, the system
described herein provides for the fifth time period to be varied
such that the fifth time period is up to 5%, up to 10%, up to 20%,
up to 30%, up to 40%, up to 50% or up to 70% shorter than the sum
of the first time period and the second time period, and/or the sum
of the third time period and the fourth time period. By way of
example, the abovementioned variations are defined using the first
random-number generator. In particular, the system described herein
provides for the first random-number generator to be in the form of
a deterministic random-number generator. Furthermore, this
embodiment additionally or alternatively provides for the fifth
time period always to be redefined, for two successive raster
lines, for example in a raster area with more than two raster
lines.
[0028] In yet another embodiment of the method according to the
system described herein, additionally or alternatively to this, the
sixth time period is varied using a second random-number generator.
Once again, as an alternative to this, the sixth time period is
varied such that the sixth time period is up to 10%, up to 20%, up
to 30%, up to 40%, up to 50%, up to 60%, up to 70%, up to 80% or up
to 90% shorter than the first time period, the second time period,
the third time period and/or the fourth time period. As an
alternative to this, the system described herein provides that the
sixth time period is varied such that the sixth time period
corresponds to the first time period, to the second time period, to
the third time period and/or to the fourth time period.
[0029] In yet another embodiment of the method according to the
system described herein, the system described herein provides that
the method additionally or alternatively has at least one of the
following features: [0030] the first time period, the second time
period, the third time period and/or the fourth time period are/is
varied such that the first time period is different to the second
time period, to the third time period and to the fourth time
period, [0031] the first time period, the second time period, the
third time period and/or the fourth time period are/is varied such
that the second time period is different to the first time period,
to the third time period and to the fourth time period, [0032] the
first time period, the second time period, the third time period
and/or the fourth time period are/is varied such that the third
time period is different to the first time period, to the second
time period and to the fourth time period, or [0033] the first time
period, the second time period, the third time period and/or the
fourth time period are/is varied such that the fourth time period
is different to the first time period, to the second time period
and to the third time period.
[0034] The system described herein also relates to a further method
for producing a representation of an object using a particle beam.
By way of example, this further method can be provided with one of
the abovementioned features or with a combination of the
abovementioned features. The particle beam is made available by a
particle beam device having at least one particle beam column,
wherein the particle beam column has a beam generator for producing
a particle beam, and has an objective lens for focusing the
particle beam onto the object. The further method provides that at
least one raster area is defined on the object, wherein the raster
area has at least one first raster point, at least one second
raster point and at least one third raster point. Furthermore, a
raster pattern is defined wherein the raster pattern defines
guidance of the particle beam through the raster area. The further
method also comprises generating the particle beam and the particle
beam being passed to a start point which is defined by one of the
following raster points: the first raster point, the second raster
point or the third raster point. The particle beam is guided from
the start point in accordance with the raster pattern over the
raster area wherein the particle beam is guided to the first raster
point at a first time, to the second raster point at a second time,
and to the third raster point at a third time. The interaction
particles and/or interaction radiation are/is detected at the
abovementioned times, wherein the interaction particles and/or the
interaction radiation are/is created by interaction of the particle
beam with the object. The first time, the second time and the third
time are chosen such that a first time interval, which is defined
by a first difference between the first time and the second time,
and a second time interval, which is defined by a second difference
between the first time and the third time, are different.
[0035] The further method is based, at least in part, on the
following idea. In a raster pattern, the particle beam passes
through a predetermined number of raster points. As a result of the
movements which are predetermined by the raster pattern, there are
different time intervals between one raster point and its adjacent
raster points, wherein a time interval is defined by the difference
between the respective times at which two adjacent raster points
are in each case scanned. The different time intervals are likewise
not correlated, as a result of which, even in the case of a
representation which is produced using this method, disturbing
artifacts in an FFT image are now perceptible only to a very
restricted extent, or even not at all.
[0036] One exemplary embodiment of the further method additionally
or alternatively provides that the particle beam remains at the
first raster point for a first time period, at the second raster
point for a second time period and at the third raster point for a
third time period. Furthermore, the further method has one of the
following features: [0037] the first time period, the second time
period and the third time period are identical to one another, or
[0038] at least one of the following time periods, specifically the
first time period, the second time period and the third time
period, are different to one of the further ones of the following
time periods, specifically the first time period, the second time
period and the third time period.
[0039] Yet another exemplary embodiment of the further method
additionally or alternatively provides that the definition of a
raster pattern comprises the definition of a spiral and/or
rectangular raster pattern.
[0040] One exemplary embodiment of each method as described above
additionally or alternatively provides that the particle beam is
guided over the raster area at least a first time in order to
produce a first representation, and is guided over the raster area
at least a second time in order to produce a second representation.
The first representation and the second representation are then
combined using an averaging method or integration method to form a
final representation. Further embodiments provide for the particle
beam to be guided over the raster area more than twice, and for
each of the representations produced in this way to be combined
with one another. It is also additionally or alternatively possible
to provide for the first representation and the second
representation to be produced using different raster parameters
(for example different pixel lives). This results in particularly
good low-noise representations of the object.
[0041] The system described herein also relates to a computer
program product having a program code which can be run and which,
when run in a processor (for example a computer processor), carries
out the steps of a method which has at least one of the
abovementioned features or a combination of at least two of the
abovementioned features.
[0042] Furthermore, the system described herein relates to a
particle beam device, for example to an electron beam device in the
form of a TEM or an SEM. The particle beam device according to the
system described herein has at least one first particle beam
column, wherein the first particle beam column is provided with a
first beam generator for generating a first particle beam, and with
a first objective lens for focusing the first particle beam onto an
object. Furthermore, the particle beam device according to the
system described herein has at least one first raster device for
guiding the first particle beam over the object, at least one first
detection unit for detection of interaction particles and/or
interaction radiation, and at least one monitoring unit with a
processor in which an abovementioned computer program product is
loaded.
[0043] Furthermore, the system described herein relates to a
further particle beam device, for example to an electron beam
device in the form of a TEM or an SEM. The further particle beam
device according to the system described herein is provided with at
least one first particle beam column, wherein the first particle
beam column has a first beam generator for generating a first
particle beam, and a first objective lens for focusing the first
particle beam onto an object. Furthermore, the further particle
beam device has at least one first control unit for defining a
first raster area on the object, and for defining a first raster
pattern. The first raster area is provided with a multiplicity of
raster lines, with the multiplicity have at least one first raster
line and at least one second raster line. The first raster line in
turn has a multiplicity of raster points, wherein the multiplicity
of raster points have at least one first raster point and at least
one second raster point. Furthermore, the second raster line has a
multiplicity of further raster points, wherein the multiplicity of
further raster points have at least one third raster point and at
least one fourth raster point. The first raster pattern defines
guidance of the first particle beam through the first raster area.
Furthermore, at least one first raster device is provided on the
further particle beam device in order to guide the first particle
beam over the object, wherein the first particle beam remains at
the first raster point for a first time period, at the second
raster point for a second time period, at the third raster point
for a third time period and/or at the fourth raster point for a
fourth time period, wherein there is a fifth time period between
guidance of the first particle beam over the first raster line and
guidance of the first particle beam over the second raster line,
wherein the multiplicity of raster lines define a multiplicity of
fifth time periods, and wherein there is a sixth time period during
guidance of the particle beam between scanning of at least one of
the following raster points, specifically the first raster point,
the second raster point, the third raster point and the fourth
raster point, using the first particle beam and scanning of a
further and different one of the following raster points,
specifically the first raster point, the second raster point, the
third raster point and the fourth raster point, wherein the
multiplicity of raster points define a multiplicity of sixth time
periods. Furthermore, the further particle beam device is provided
with at least one first detection unit for detection of interaction
particles and/or interaction radiation.
[0044] Furthermore, at least one second control unit is provided in
the further particle beam device in order to vary at least one of
the following time periods: the first time period, the second time
period, the third time period, the fourth time period, the fifth
time period and the sixth time period.
[0045] Additionally or alternatively, the second control unit is
designed such that at least one of the following time periods,
specifically the first time period, the second time period, the
third time period, the fourth time period, the fifth time period
and the sixth time period, is randomly varied deterministically or
non-deterministically. Furthermore, additionally or alternatively,
the second control unit is designed such that at least one of the
following features is provided: [0046] the first time period, the
second time period, the third time period and the fourth time
period form a first sequence for the raster area, wherein the first
sequence is subdivided into at least one first area of the first
sequence and at least one second area of the first sequence,
wherein at least the time periods which are included in the first
area of the first sequence are randomly varied deterministically or
non-deterministically, [0047] the multiplicity of fifth time
periods form a second sequence for the raster area, wherein the
second sequence is subdivided into at least one first area of the
second sequence and at least one second area of the second
sequence, wherein at least the fifth time periods which are
included in the first area of the second sequence are randomly
varied deterministically or non-deterministically, and [0048] the
multiplicity of sixth time periods form a third sequence for the
raster area, wherein the third sequence is subdivided into at least
one first area of the third sequence and at least one second area
of the third sequence, wherein at least the sixth time periods
which are included in the first area of the third sequence are
randomly varied deterministically or non-deterministically.
[0049] Additionally or alternatively, a further particle beam
device is given by the following features. The further particle
beam device has at least one first particle beam column, wherein
the first particle beam column has a first beam generator for
generating a first particle beam, and a first objective lens for
focusing the first particle beam onto an object. Furthermore, at
least one first control unit is provided in order to define a first
raster area on the object and in order to define a first raster
pattern, wherein the first raster area has at least one first
raster point, at least one, second raster point and at least one
third raster point, and wherein the first raster pattern defines
guidance of the first particle beam through the first raster area.
Furthermore, at least one first raster device is provided for
guiding the first particle beam over the object in accordance with
the first raster pattern, wherein the first raster device is
designed such that the particle beam is guided to the first raster
point at a first time, to the second raster point at a second time
and to the third raster point at a third time. In addition, the
particle beam device has at least one first detection unit for
detection of interaction particles and/or interaction radiation.
The first control unit is designed such that the first time, the
second time and the third time are chosen such that a first time
interval, which is defined by a first difference between the first
time and the second time, and a second time interval, which is
defined by a second difference between the first time and the third
time, are different.
[0050] Additionally or alternatively, in a further exemplary
embodiment of one of the abovementioned particle beam devices, the
particle beam device has at least one second particle beam column.
The second particle beam column is provided with a second beam
generator for generating a second particle beam, and with a second
objective lens for focusing the second particle beam onto the
object. The particle beam device has at least one third control
unit for defining a second raster area on the object, and for
defining a second raster pattern. Furthermore, the second particle
beam column is provided with at least one second raster device for
guiding the second particle beam over the object in accordance with
the second raster pattern. In addition, the particle beam device
has, for example, at least one second detection unit for detection
of interaction particles and/or interaction radiation.
[0051] Additionally or alternatively, in yet another embodiment of
the abovementioned particle beam device, the third control unit is
designed such that the second raster area is defined by a
multiplicity of raster lines, wherein the second raster area is
provided with at least one third raster line and at least one
fourth raster line, wherein the third raster line has a
multiplicity of raster points, wherein the multiplicity of raster
points have at least one fifth raster point and at least one sixth
raster point, wherein the fourth raster line is provided with a
multiplicity of further raster points, wherein the multiplicity of
further raster points have at least one seventh raster point and at
least one eighth raster point, and wherein the second particle beam
remains at the fifth raster point for a seventh time period, at the
sixth raster point for an eighth time period, at the seventh raster
point for a ninth time period and/or at the eighth raster point for
a tenth time period, wherein there is an eleventh time period
between guidance of the second particle beam over the third raster
line and guidance of the second particle beam over the fourth
raster line, wherein the multiplicity of raster lines define a
multiplicity of eleventh time periods, and wherein there is a
twelfth time period during guidance of the second particle beam
between scanning of at least one of the following raster points,
specifically the fifth raster point, the sixth raster point, the
seventh raster point and the eighth raster point, using the second
particle beam, and scanning of a further and different one of the
following raster points, specifically the fifth raster point, the
sixth raster point, the seventh raster point and the eighth raster
point, using the second particle beam, wherein the multiplicity of
raster points define a multiplicity of twelfth time periods.
Furthermore, the particle beam device has at least one fourth
control unit for varying at least one of the following time
periods, specifically the seventh time period, the eighth time
period, the ninth time period, the tenth time period, the eleventh
time period and the twelfth time period. By way of example, the
variation can be carried out as described above.
[0052] Additionally or alternatively, a further exemplary
embodiment of one of the abovementioned particle beam devices
provides that the third control unit is designed such that the
second raster area is defined by at least one fifth raster point,
at least one sixth raster point and at least one seventh raster
point, and such that the second raster pattern is defined to have a
rectangular and/or spiral shape.
[0053] Additionally or alternatively, yet another exemplary
embodiment of one of the abovementioned particle beam devices
provides that the particle beam device has one of the following
features: [0054] the first particle beam column is in the form of
an electron beam column, and the second particle beam column is in
the form of an ion beam column, [0055] the first particle beam
column is in the form of an ion beam column, and the second
particle beam column is in the form of an electron beam column, or
[0056] the first particle beam column is in the form of an ion beam
column, and the second particle beam column is in the form of an
ion beam column.
BRIEF DESCRIPTION OF THE DRAWINGS
[0057] Embodiments of the system described herein will be explained
in more detail in the following text with reference to the figures,
in which:
[0058] FIG. 1 shows a schematic illustration of a particle beam
device in the form of a TEM that may be used in connection with an
embodiment of the system described herein;
[0059] FIG. 2 shows a simplified flowchart of a method for
producing a representation of an object according to an embodiment
of the system described herein;
[0060] FIG. 3 shows a schematic representation of an object with a
raster area according to an embodiment of the system described
herein;
[0061] FIG. 4 shows a schematic illustration of the raster area
with raster lines as shown in FIG. 3;
[0062] FIG. 5A shows a schematic illustration of a further
exemplary embodiment of a raster line according to an embodiment of
the system described herein;
[0063] FIG. 5B shows a schematic illustration of yet another
exemplary embodiment of a raster line according to an embodiment of
the system described herein;
[0064] FIG. 6A shows a schematic illustration of a first raster
pattern according to an embodiment of the system described
herein;
[0065] FIG. 6B shows a schematic illustration of a second raster
pattern according to an embodiment of the system described
herein;
[0066] FIG. 6C shows a schematic illustration of a third raster
pattern according to an embodiment of the system described
herein;
[0067] FIG. 7 shows an FFT image of an object, which was produced
using a standard raster method according to the prior art;
[0068] FIG. 8 shows an FFT image of an object, which was produced
using a first exemplary embodiment of the method according to the
system described herein;
[0069] FIG. 9 shows an FFT image of an object, which was produced
using a second exemplary embodiment of the method according to the
system described herein;
[0070] FIG. 10 shows a further FFT image of an object which was
produced using a standard raster method according to the prior
art;
[0071] FIG. 11 shows an FFT image of an object which was produced
using a third exemplary embodiment of the method according to the
system described herein;
[0072] FIG. 12 shows an FFT image of an object which was produced
using a fourth exemplary embodiment of the method according to the
system described herein;
[0073] FIG. 13 shows an FFT image of an object which was produced
using a fifth exemplary embodiment of the method according to the
system described herein;
[0074] FIG. 14 shows an FFT image of an object which was produced
using a sixth exemplary embodiment of the method according to the
system described herein;
[0075] FIG. 15 shows an FFT image of an object which was produced
using a seventh exemplary embodiment of the method according to the
system described herein;
[0076] FIG. 16 shows an FFT image of an object which was produced
using an eighth exemplary embodiment of the method according to the
system described herein; and
[0077] FIG. 17 shows a further particle beam device according to an
embodiment of the system described herein.
DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS
[0078] The system described herein will be further explained in the
following text in particular with reference to a particle beam
device 1 in the form of a TEM. However, it should be noted at this
stage that the system described herein is not restricted to a TEM,
and in fact the system described herein can be used for any
particle beam device.
[0079] FIG. 1 shows a schematic illustration of a particle beam
device 1. The particle beam device 1 has an electron source 2 in
the form of a thermal field emission source. However, a different
particle beam source can invariably also be used. An extraction
electrode 3 is arranged behind the electron source 2 along the
optical axis OA of the particle beam device 1, and the potential on
this extraction electrode 3 extracts electrons from the electron
source 2. Furthermore, a first electrode 4 is provided for focusing
the source position, as well as at least one second electrode 5 in
the form of an anode for accelerating the electrons. Due to the
second electrode 5, the electrons emerging from the electron source
2 are accelerated to a desired and adjustable energy, using an
electrode voltage. The electrons form a particle beam in the form
of an electron beam.
[0080] A two-stage condenser is arranged further on on the optical
axis OA, has a first magnetic lens 6 and a second magnetic lens 7,
and a first raster device 8 and a second raster device 9 are
connected following the condenser. Both the first raster device 8
and the second raster device 9 are connected to a first control
unit 10. The control unit 10 is provided with a control processor
which produces control signals. The first raster device 8 and the
second raster device 9 can be used to scan the particle beam over
an object which is arranged on an object plane 12. Furthermore, the
particle beam device 1 has an objective 11, which is in the form of
a magnetic lens. The object plane 12 is arranged at the objective
11, and the object to be examined is arranged on the object plane
12 using a sample manipulator.
[0081] In the opposite direction to the electron source 2, the
objective 11 is followed by a projection lens system having a first
lens 13 and a second lens 14. The first lens 13 and the second lens
14 then produce a representation on a detector 15 of the object
which is arranged on the object plane 12. The representation is,
for example, an image or a diffraction pattern of the object.
[0082] FIG. 2 shows a schematic illustration of a simplified
procedure for one exemplary embodiment of the method according to
the system described herein. First of all, a raster area on the
object arranged on the object plane 12 is defined in a method step
S1. This is illustrated in more detail in FIG. 3. A raster area 17
which is intended to be examined in more detail using the particle
beam is defined on the object 16. The raster area 17 has a first
raster line 18A, a second raster line 18B, a third raster line 18C
and a fourth raster line 18D. FIG. 4 shows the arrangement of the
first raster line 18A, of the second raster line 18B, of the third
raster line 18C and of the fourth raster line 18D, illustrated
enlarged. Each of the abovementioned raster lines 18A to 18D has
raster points. The first raster line 18A has a first raster point
19, a second raster point 20, a third raster point 21, a fourth
raster point 22, a fifth raster point 23, a sixth raster point 24,
a seventh raster point 25 and an eighth raster point 26.
Furthermore, the second raster line 18B is provided with a ninth
raster point 27, a tenth raster point 28, an eleventh raster point
29, a twelfth raster point 30, a thirteenth raster point 31, a
fourteenth raster point 32, a fifteenth raster point 33 and a
sixteenth raster point 34. The third raster line 18C in turn has a
seventeenth raster point 35, an eighteenth raster point 36, a
nineteenth raster point 37, a twentieth raster point 38, a twenty
first raster point 39, a twenty second raster point 40, a twenty
third raster point 41 and a twenty fourth raster point 42. Finally,
the fourth raster line 18D is provided with a twenty fifth raster
point 43, a twenty sixth raster point 44, a twenty seventh raster
point 45, a twenty eighth raster point 46, a twenty ninth raster
point 47, a thirtieth raster point 48, a thirty first raster point
49 and a thirty second raster point 50.
[0083] The abovementioned raster lines 18A to 18D as well as the
abovementioned raster points 19 to 50 are arranged in the form of a
grid in the exemplary embodiment illustrated in FIGS. 3 and 4. It
should explicitly be noted that the system described herein is not
restricted to a raster area such as this. In fact, individual or
all of the abovementioned raster lines may be configured
differently. By way of example, FIG. 5A shows the first raster line
18A in the form of a sawtooth. By way of example, FIG. 5B shows the
first raster line 18A in the form of a spiral.
[0084] A raster pattern is now defined in a further method step S2,
as shown in FIG. 2. The raster pattern defines the guidance
(position movement) of the particle beam when the particle beam is
scanned over the raster area 17 as shown in FIG. 3. FIGS. 6A to 6C
show exemplary embodiments of raster patterns.
[0085] For example, FIG. 6A shows a first raster pattern. For
clarity reasons, only the first raster line 18A and the second
raster line 18B are shown. The first raster pattern includes
unidirectional guidance of the particle beam over each of the
abovementioned raster lines 18A to 18D in one direction. Thus, in
the first raster pattern, the particle beam is first of all guided
to the first raster point 19 on the first raster line 18A. The
particle beam is then guided in the direction of the arrow A along
the first raster line 18A such that the abovementioned raster
points 20 to 26 in the first raster line 18A are scanned
successively. After the eighth raster point 26 on the first raster
line 18A has been scanned, the particle beam is guided to the ninth
raster point 27 in the second raster line 18B. The particle beam is
then guided along the second raster line 18B in the direction of
the arrow A, such that the abovementioned raster points 27 to 34 in
the second raster line 18B are scanned successively.
[0086] FIG. 6B shows a second raster pattern. Once again, for
clarity reasons, only the first raster line 18A and the second
raster line 18B are illustrated. The second raster pattern includes
bidirectional guidance of the particle beam over each of the
abovementioned raster lines 18A to 18D. In the second raster
pattern, the particle beam is therefore first of all guided to the
first raster point 19 in the first raster line 18A. The particle
beam is then guided over the first raster line 18A in the direction
of the arrow A such that the abovementioned raster points 20 to 26
in the first raster line 18A are scanned. After scanning the eighth
raster point 26 in the first raster line 18A, the particle beam is
guided to the sixteenth raster point 34 in the second raster line
18B. The particle beam is then guided over the second raster line
18B in the direction of the arrow B, such that the abovementioned
raster points 33 to 27 in the second raster line 18B are scanned
successively.
[0087] FIG. 6C shows a third raster pattern with raster points. For
clarity reasons, only some of the abovementioned raster points are
provided with reference symbols. The third raster pattern includes
a spiral scan of the raster area 17. The guidance of the particle
beam over the raster area 17 is indicated by arrows. In the third
raster pattern, the particle beam is therefore guided first of all
to the eighth raster point 26. The particle beam is then guided to
the sixteenth raster point 34, then to the twenty fourth raster
point 42 and finally to the thirty second raster point 50. From
there, the particle beam is guided such that the abovementioned
raster points 49 to 43 are scanned. The particle beam is then first
of all guided to the seventeenth raster point 35, then to the ninth
raster point 27 and then to the first raster point 19. From there,
the particle beam is guided such that the abovementioned raster
points 20 to 25 are scanned. The particle beam is then first of all
guided to the fifteenth raster point 33, and then to the twenty
third raster point 41. The particle beam is then guided such that
the abovementioned raster points 40 to 36 are scanned. From there,
the particle beam is guided to the tenth raster point 28. The
particle beam is then guided such that the abovementioned raster
points 29 to 32 are scanned.
[0088] At this point, it is explicitly noted that the system
described herein is not restricted to the abovementioned raster
patterns. In fact, any desired raster pattern can be used which is
suitable for the system described herein. In particular, further
exemplary embodiments provide for the raster pattern to be
generated by a random-number generator. In this case, any desired
ones of the abovementioned raster points 19 to 50 can be scanned
successively independently of the association with one of the
abovementioned raster lines 18A to 18D, for example with each of
the abovementioned raster points 19 to 50 each being scanned only
once.
[0089] In a further method step S3 as shown in FIG. 2, the particle
beam is generated once the raster pattern has been defined (for
example the first raster pattern, the second raster pattern or the
third raster pattern). The particle beam is then moved in a method
step S4 to one of the raster points, which corresponds to the start
point of the raster pattern. By way of example, in the first raster
pattern and the second raster pattern, this is the first raster
point 19 in the first raster line 18A. By way of example, this is
the eighth raster point 26 in the third exemplary embodiment. The
particle beam is then guided over the raster area 17 in accordance
with the defined raster pattern.
[0090] Interaction particles are now detected using the detector 15
in yet another method step S5. Furthermore, the method is continued
after a check in method step S6.
[0091] At least one time period is now varied in a method step S7
as shown in FIG. 2. This will now be explained in more detail in
the following text.
[0092] One variable which can also define the method according to
the system described herein is the dwell duration of the particle
beam in one of the abovementioned raster lines 18A to 18D. A first
raster line time period is the dwell duration in which the particle
beam remains in the first raster line 18A. A second raster line
time period is the dwell duration in which the particle beam
remains in the second raster line 18B. The particle beam remains in
the third raster line 18C for a third raster line time period. The
particle beam remains in the fourth raster line 18D for a fourth
raster line time period. In one exemplary embodiment, the first
raster line time period, the second raster line time period, the
third raster line time period and/or the fourth raster line time
period are/is varied such that each of the abovementioned raster
line time periods is different to at least one or more of the
further abovementioned raster line time periods. In yet another
embodiment, at least one of the abovementioned raster line time
periods is varied with respect to at least one further of the
abovementioned raster line time periods such that the at least one
of the abovementioned raster line time periods is up to 5%, up to
10%, up to 15%, up to 20%, up to 25%, up to 30%, up to 35%, up to
40%, up to 45%, or up to 50% shorter than the at least one further
of the abovementioned raster line time periods. In a further
embodiment, at least one or more (for example all) of the
abovementioned raster line time periods is or are chosen randomly
using a random-number generator, which is contained in the control
unit 10 shown in FIG. 1.
[0093] A further variable which can additionally or alternatively
also define the method according to the system described herein is
the time period between a complete scan of (that is to say the
complete pass over) one of the abovementioned raster lines 18A to
18D and a further one of the abovementioned raster lines 18A to
18D. In principle, this is a pause between the complete scan of
(that is to say the complete pass over) one of the abovementioned
raster lines 18A to 18D and a further one of the abovementioned
raster lines 18A to 18D. This time period is therefore also
referred to in the following text as the line pause time period. In
one embodiment, the line pause time period can be defined using the
random-number generator in the control unit 10 as shown in FIG. 1.
In yet another embodiment, the line pause time period can be varied
to be up to 5%, up to 10%, up to 15%, up to 20%, up to 25%, up to
30%, up to 35%, up to 40%, up to 50% or up to 70% shorter than at
least one of the abovementioned raster line time periods.
Furthermore, in a further embodiment, the line pause time period
between two of the abovementioned raster lines 18A to 18D can be
chosen such that it is always different. For example, a first line
pause time period between guidance of the particle beam over the
first raster line 18A and guidance of the particle beam over the
second raster line 18B is different to a second line pause time
period between the guidance of the particle beam over the second
raster line 18B and the guidance of the particle beam over the
third raster line 18C.
[0094] Additionally or alternatively, in yet another exemplary
embodiment, the dwell duration of the particle beam on at least one
or more (possibly even all) of the abovementioned raster points 19
to 50 can be varied. The dwell duration is referred to in the
following text as the raster point time period.
[0095] This exemplary embodiment will be explained using the
abovementioned raster points 19 to 26 in the first raster line 18A.
It is noted at this point that the following statements also apply,
of course, to all the other abovementioned raster points 27 to
50.
[0096] The particle beam remains at the first raster point 19 for a
first raster point time period, at the second raster point 20 for a
second raster point time period, at the third raster point 21 for a
third raster point time period, at the fourth raster point 22 for a
fourth raster point time period, at the fifth raster point 23 for a
fifth raster point time period, at the sixth raster point 24 for a
sixth raster point time period, at the seventh raster point 25 for
a seventh raster point time period, and at the eighth raster point
26 for an eighth raster point time period. The first raster point
time period to the eighth raster point time period are each varied
such that at least one of the first raster point time period to the
eighth raster point time period is different to at least one or
more of the further ones of the first raster point time period to
the eighth raster point time period. In particular, in one
embodiment, the first raster point time period to the eighth raster
point time period are each different to one another. In particular,
the abovementioned raster point time periods can be varied by a
random-number generator deterministically or non-deterministically,
for example by the control unit 10 shown in FIG. 1.
[0097] A further variable which defines the method additionally or
alternatively is the time period between scanning one of the
abovementioned raster points 19 to 50 and scanning a subsequent one
of the abovementioned raster points 19 to 50. In principle, this is
a pause between the scanning of one of the abovementioned raster
points 19 to 50 and a further one of the abovementioned raster
points 19 to 50, as a result of which this time period is referred
to in the following text as the point pause time period. In one
embodiment, the point pause time period between one of the
abovementioned raster points 19 to 50 and a further one of the
abovementioned raster points 19 to 50 is varied by the
random-number generator in the control unit 10 shown in FIG. 1. It
is therefore possible for the point pause time period between one
of the abovementioned raster points 19 to 50 and a further one of
the abovementioned raster points 19 to 50 to always be chosen to be
different. In a further embodiment, as an alternative to this, the
point pause time period between one of the abovementioned raster
points 19 to 50 and a further one of the abovementioned raster
points 19 to 50 can be chosen such that the point pause time period
is up to 10%, up to 20%, up to 30%, up to 40%, up to 50%, up to
60%, up to 70%, up to 80% or up to 90% shorter than one of the
raster point time periods. As an alternative to this, the point
pause time period is chosen such that it corresponds to at least
one of the raster point time periods.
[0098] In a further method step S8 as shown in FIG. 2, the particle
beam is now guided to a further, one of the raster points 19 to 50.
The method steps S5 to S8 are carried out again, until the method
ends in method step S9.
[0099] Results of test examinations which were carried out using a
particle beam device 1 as shown in FIG. 1 will be explained in the
following text. In this case, an object in the form of an Si110
sample was examined in the STEM mode, in extremely high resolution
conditions. Furthermore, magnetic disturbances were produced at a
frequency of 50 Hz using an air-cored coil and a function
generator. These magnetic disturbances simulated periodic
disturbances which could lead to artifacts in an FFT image of the
examined object.
[0100] FIG. 7 shows the Fourier transform of an image (FFT image)
of the Si110 sample, which was produced using the standard raster
method according to the prior art. The recorded image of the Si110
sample includes 1024 raster lines, each with 1024 raster points.
The raster point time period for each of the 1024 raster points was
20 .mu.s. The raster line time period for each raster line was
therefore also identical. The FFT image shown in FIG. 7 shows the
central reflex and the four characteristic main reflexes, which are
arranged around the central reflex, for the Si110 sample. In
addition to these five abovementioned reflexes, numerous further
reflexes can be identified, which were produced by the
disturbance.
[0101] In contrast, FIG. 8 shows the FFT image of the same object,
in this case using a line pause period between two raster lines of
at most 20% of the raster line time period. The reflexes which
could previously be seen as a result of the disturbance in the FFT
image are smeared along a vertical, as a result of which vertically
aligned strips can be seen. The reflexes actually associated with
the examined object, however, can clearly be seen in the FFT
image.
[0102] FIG. 9 shows a further exemplary embodiment of an FFT image
of the examined object based on the method according to the system
described herein. FIG. 9 is fundamentally based on FIG. 8, but with
the difference that a line pause period between two raster lines of
at most 60% of the raster line time period was used. The reflexes
previously produced by the periodic disturbance in the FFT image
are smeared to an even greater extent along the vertical than in
the exemplary embodiment shown in FIG. 8.
[0103] FIG. 10 shows an FFT image of the examined object, in which
the standard raster method according to the prior art was used. The
recorded image once again contains 1024 raster lines, each having
1024 raster points. The raster point time period of the particle
beam at each raster point was 18 .mu.s. The FFT image shown in FIG.
10 exhibits reflexes at the upper image edge and at the lower image
edge, which reflexes originate from the periodic disturbance. FIG.
11 shows an FFT image of the object, in which the raster point time
period was varied such that these values were up to at most 100% of
the original raster point time period (18 .mu.s). The reflexes at
the upper image edge and at the lower image edge have virtually
completely disappeared. It has been found that variation of the
raster point time period in particular reduces reflexes of
disturbances which are at a frequency of considerably more than 50
Hz.
[0104] A further exemplary embodiment is illustrated in FIGS. 12 to
15, which show FFT images of the examined object. FIG. 7 is the
reference image from the prior art relating to FIGS. 12 to 15. The
further exemplary embodiments shown in FIGS. 12 to 15 are based on
the exemplary embodiment shown in FIG. 11. However, in addition,
the maximum possible raster point time period along the line was
also modulated periodically, as a result of which the time
variation also has even greater fluctuations between pixels which
are a long distance apart from one another within one line. FIG. 12
shows an FFT image of the examined object, in which the raster
point time period was varied such that this was lengthened at most
by 25% of the original raster point time period (20 .mu.s). FIG. 13
shows an FFT image of the examined object, in which the raster
point time period was varied such that this was lengthened by at
most 50% of the original raster point time period (20 .mu.s). FIG.
14 shows an FFT image of the examined object in which the raster
point time period was varied such that it was lengthened by at most
75% of the original raster point time period (20 .mu.s). FIG. 15
once again shows an FFT image of the examined object, in which the
raster point time period was varied such that this was lengthened
at most by 100% of the original raster point time period (20
.mu.s). As can be seen in all the exemplary embodiments shown in
FIGS. 12 to 15, the reflexes which are caused by the periodic
disturbance have decreased in comparison to the FFT image shown in
FIG. 7.
[0105] Each of the abovementioned exemplary embodiments can be
combined with a further one of the abovementioned exemplary
embodiments. For example, in one exemplary embodiment, variation of
the line pause time period and raster point time period are
combined. FIG. 16 shows the result of this combination, wherein the
line pause time period was varied such that this was lengthened by
up to at most 20% of the original raster line time period. The
raster point time period was lengthened by values up to at most 70%
of the original raster point time period (20 .mu.s). FIG. 10
represents the reference according to the prior art for FIG.
16.
[0106] The abovementioned exemplary embodiments of the method
according to the system described herein serve to cancel out the
correlation between the time profile of the detected signal (which
has the fluctuations which are periodic over time) and the
respective position associated with the detected signal on the
object. Better representations of the object can be achieved, in
which the disturbing artifacts are now only greatly restricted or
are even no longer perceptible at all. This is achieved by varying
at least one of the abovementioned time periods.
[0107] A further exemplary embodiment of the method according to
the system described herein will now be explained with reference to
FIG. 6C. In this exemplary embodiment, it is not essential to vary
the line pause time period, the raster point time period and/or the
point pause time period. The abovementioned time periods may also
all be kept constant. As already explained above, the third raster
pattern shown in FIG. 6C includes a spiral scan of the raster area
17. The guidance of the particle beam over the raster area 17 is
indicated by arrows. In the raster pattern shown in FIG. 6C, the
particle beam passes through the abovementioned raster points in
the form already described above. Because of the movements which
are predetermined by the raster pattern, there are different time
intervals between one raster point and its adjacent raster points,
wherein a time interval is given by the difference between the
respective times at which two adjacent raster points are in each
case scanned. For example, the tenth raster point 28 has the
following adjacent raster points: the second raster point 20, the
ninth raster point 27, the eleventh raster point 29 and the
eighteenth raster point 36. The time interval between the times at
which the second raster point 20 and the tenth raster point 28 are
scanned is different to the time interval between the times at
which the ninth raster point 27 and the tenth raster point 28 are
scanned. The time interval between the times at which the eleventh
raster point (or the eighteenth raster point 36) and the tenth
raster point 28 are scanned is also different to the abovementioned
time intervals. The different time intervals are likewise not
correlated, as a result of which, in this method as well,
disturbing artifacts in an FFT image are only greatly restricted,
or are even no longer perceptible at all.
[0108] All the exemplary embodiments of the method as described
above also allow the particle beam to pass over the raster area 17
more than once. In this case, at least one first image and at least
one second image are produced. The first image and the second image
are then combined using an averaging method or an integration
method to form a final representation. Further embodiments provide
for the particle beam to be passed over the raster area 17 more
than twice, and for each of the images produced in this way to be
combined with one another. This results in particularly good
low-noise images of the object.
[0109] FIG. 17 shows a schematic illustration of a further particle
beam device 100 using which the method according to the system
described herein can be carried out. The particle beam device 100
has two particle beam columns, specifically a first particle beam
column 101 and a second particle beam column 102, which are
arranged on a sample chamber 103. The first particle beam column
101 is in the form of an electron beam column, and is arranged
vertically with respect to the sample chamber 3.
[0110] The first particle beam column 101 has a first beam
generator 104 in the form of an electron source (cathode), and a
system consisting of a first electrode unit 105 and a second
electrode unit 106. The second electrode unit 106 forms one end of
a beam guidance tube (not illustrated). For example, the first beam
generator 104 is in the form of a thermal field emitter. Electrons
which emerge from the first beam generator 104 are accelerated to a
predeterminable potential because of a potential difference between
the first beam generator 104 and the second electrode unit 106, and
form a primary electron beam.
[0111] The primary electron beam first of all passes through a
condenser unit 107 and then through a first objective 108 in the
form of a magnetic lens. The beam guidance tube is passed through
an opening in the first objective 108. The first objective 108 is
provided with pole shoes (not illustrated), in which coils (not
illustrated) are arranged. Furthermore, raster device 120 is
provided, using which the primary electron beam can be deflected
and can be scanned over an object 109 which is arranged in the
sample chamber 103. The object 109 is arranged on an adjustable
object holder (not illustrated). The object holder is designed such
that it can move in three directions (x direction, y direction and
z direction) which are arranged at right angles to one another.
Furthermore, it can preferably rotate about a first rotation axis
and a second rotation axis, with the first rotation axis and the
second rotation axis being arranged at right angles to one
another.
[0112] For imaging, secondary electrons and/or back-scattered
electrons which are created as a result of the interaction of the
primary electron beam with the object 109 are detected by a
detector arrangement in the first particle beam column 101. For
this purpose, a first detector 110 is provided on the object side
along the optical axis OA of the first particle beam column 101,
while a second detector 111 is arranged along the optical axis OA
on the source side (that is to say in the direction of the first
beam generator 104). Furthermore, the first detector 110 and the
second detector 111 are arranged offset with respect to one
another.
[0113] The second particle beam column 102 is in the form of an ion
beam column, and is arranged tilted through an angle of about
50.degree. with respect to the first particle beam column 101. The
second particle beam column 102 has a second beam generator 112 in
the form of an ion beam generator. The second beam generator 112
generates ions, which form an ion beam. By way of example, the ion
beam is formed from noble-gas ions. By way of example, the ion beam
can be formed from argon ions. However, the system described herein
is not restricted to argon ions. In fact, other ion types can also
be used, for example gallium ions, gold ions, silicon ions and/or
helium ions.
[0114] The ions are accelerated to a predeterminable potential
using an extraction electrode 113. The ion beam then passes through
ion optics in the second particle beam column 102, in which case
the ion optics have a condenser lens 114 and an arrangement of
further lenses as a second objective lens 115. The second objective
lens 115 produces a focused ion probe, which strikes the object
109. An adjustable stop 116, a first electrode arrangement 117 and
a second electrode arrangement 118 are arranged above the second
objective lens 115 (that is to say in the direction of the second
beam generator 112), with the first electrode arrangement 117 and
the second electrode arrangement 118 being in the form of raster
electrodes. The ion beam is scanned over the surface of the object
109 using the first electrode arrangement 117 and the second
electrode arrangement 118.
[0115] The second particle beam column 102 has two functions. On
the one hand, it can be used for imaging an area of interest on the
surface of the object 109. Interaction particles are detected by a
fourth detector 123 and/or by the first detector 110 and/or the
second detector 111. On the other hand, however, it is also used
for processing the area of interest on the surface of the object
109.
[0116] Furthermore, a third detector 119 is arranged in the sample
chamber 103. The third detector 119 is used to detect interaction
particles transmitted by the object 109 or scattered by the object
109.
[0117] The raster device 120 is connected to a first control unit
121 and is controlled by the first control unit 121, with the first
control unit 121 having a first processor with an appropriate
program code. The raster device 120 can be used to scan the first
particle beam in the form of the electron beam over the object
109.
[0118] Both the first electrode arrangement 117 and the second
electrode arrangement 118 are connected to a second control unit
122. The second control unit 122 controls the first electrode
arrangement 117 and the second electrode arrangement 118, with the
second control unit 122 having a second processor with a
corresponding program code. The first electrode arrangement 117 and
the second electrode arrangement 118 can be used to scan the ion
beam over the object 109.
[0119] Artifacts in an image of the object 109 can likewise occur
when using the further particle beam device 100. When both the
electrode beam and the ion beam are scanned at the same time, then,
fundamentally, this results in a combined image of two interleaved
images, with one of the images being governed by the electron beam,
and the other of the images being governed by the ion beam. If
periodic control signals are used for guidance of the electron beam
and of the ion beam over the raster area of the object 109, it is
possible for one of the two particle beams (for example the
electron beam) to be guided over the raster area of the object 109
more quickly than the other of the two particle beams (for example
the ion beam). When both particle beams pass through the raster
area, it is possible for the combined image to contain strips since
the one particle beam has already passed completely over the raster
area while the other particle beam is still passing over the raster
area. The abovementioned strips are produced precisely at these
times. These strips can be removed from the combined image by
carrying out the methods described above both on the first particle
beam column 101 and on the second particle beam column 102.
[0120] It should be explicitly noted that the first particle beam
column 101 and the second particle beam column 102 may each be in
the form of an ion beam column.
[0121] Various embodiments discussed herein may be combined with
each other in appropriate combinations in connection with the
system described herein. Additionally, in some instances, the order
of steps in the flowcharts, flow diagrams and/or described flow
processing may be modified, where appropriate. Further, various
aspects of the system described herein may be implemented using
software, hardware, a combination of software and hardware and/or
other computer-implemented modules or devices having the described
features and performing the described functions. Software
implementations of the system described herein may include
executable code that is stored in a computer readable storage
medium and executed by one or more processors. The computer
readable storage medium may include a computer hard drive, ROM,
RAM, flash memory, portable computer storage media such as a
CD-ROM, a DVD-ROM, a flash drive and/or other drive with, for
example, a universal serial bus (USB) interface, and/or any other
appropriate tangible storage medium or computer memory on which
executable code may be stored and executed by a processor. The
system described herein may be used in connection with any
appropriate operating system.
[0122] Other embodiments of the invention will be apparent to those
skilled in the art from a consideration of the specification or
practice of the invention disclosed herein. It is intended that the
specification and examples be considered as exemplary only, with
the true scope and spirit of the invention being indicated by the
following claims.
* * * * *