U.S. patent application number 13/543568 was filed with the patent office on 2013-12-05 for contamination reduction electrode for particle detector.
This patent application is currently assigned to ICT Integrated Circuit Testing Gesellschaft fur Halbleiterpruftechnik GmbH. The applicant listed for this patent is Stefan Lanio. Invention is credited to Stefan Lanio.
Application Number | 20130320228 13/543568 |
Document ID | / |
Family ID | 49669077 |
Filed Date | 2013-12-05 |
United States Patent
Application |
20130320228 |
Kind Code |
A1 |
Lanio; Stefan |
December 5, 2013 |
CONTAMINATION REDUCTION ELECTRODE FOR PARTICLE DETECTOR
Abstract
A charged particle detector arrangement is described. The
detector arrangement includes a detection element and a collector
electrode configured to collect charged particles released from the
detection element upon impact of signal charged particles.
Inventors: |
Lanio; Stefan; (Erding,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lanio; Stefan |
Erding |
|
DE |
|
|
Assignee: |
ICT Integrated Circuit Testing
Gesellschaft fur Halbleiterpruftechnik GmbH
Heimstetten
DE
|
Family ID: |
49669077 |
Appl. No.: |
13/543568 |
Filed: |
July 6, 2012 |
Current U.S.
Class: |
250/397 |
Current CPC
Class: |
H01J 37/244 20130101;
H01J 2237/022 20130101; H01J 37/28 20130101; H01J 2237/2449
20130101 |
Class at
Publication: |
250/397 |
International
Class: |
H01J 37/244 20060101
H01J037/244 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 5, 2012 |
EP |
12175165.5 |
Claims
1. A charged particle detector arrangement, comprising a detection
element and a collector electrode configured to collect charged
particles released from the detection element upon impact of signal
charged particles.
2. The charged particle detector arrangement according to claim 1,
wherein the collector electrode is a plate having an opening for
passing secondary charged particles.
3. The charged particle detector arrangement according to claim 1,
further comprising a voltage supply electrically connected to the
collector electrode for biasing the collector electrode to collect
charged particles.
4. The charged particle detector arrangement according to claim 3,
wherein the voltage supply is further connected to the detection
element.
5. The charged particle detector arrangement according to claim 3,
wherein the collector electrode is positively biased with respect
to the detection element.
6. The charged particle detector arrangement according to claim 5,
wherein the collector electrode is biased with a voltage in the
range of 100-500 Volts.
7. The charged particle detector arrangement according to claim 1,
wherein the collector electrode is arranged in a plane positioned
in direction of the signal charged particles before the plane of
the detection element.
8. The charged particle detector arrangement according to claim 1,
wherein the collector electrode is a ring arranged coaxially with
an optical axis of the detector arrangement.
9. The charged particle detector arrangement according to claim 1,
wherein the collector electrode is arranged in a plane of the
detection element, surrounding the detection element.
10. The charged particle detector arrangement according to claim 1,
wherein charged particles are electrons.
11. A charged particle beam device, comprising a charged particle
detector arrangement comprising a detection element and a collector
electrode configured to collect charged particles released from the
detection element upon impact of signal charged particles.
12. The charged particle beam device according to claim 11, wherein
the collector electrode is a plate having an opening for passing
secondary charged particles.
13. The charged particle beam device according to claim 11, further
comprising a voltage supply electrically connected to the collector
electrode for biasing the collector electrode to collect charged
particles.
14. The charged particle beam device according to claim 13, wherein
the voltage supply is further connected to the detection
element.
15. A method of operating a charged particle detector arrangement,
the method comprising: providing a charged particle detector
arrangement, comprising a detection element and a collector
electrode arranged to collect charged particles released from the
detection element upon impact of signal charged particles; applying
a biasing potential to the collector electrode, wherein the
potential is positive with respect to the detection element.
16. The method according to claim 15, wherein the collector
electrode (30) is positively biased with respect to the detection
element.
17. The method according to claim 16, wherein the collector
electrode is biased with a voltage in the range of 100-500 Volts.
Description
FIELD
[0001] Embodiments of the present invention relate to means for
reduction of contamination of particle detectors. In particular,
they relate to a charged particle detector arrangement with a
contamination reduction electrode. Specifically, embodiments relate
to a charged particle detector arrangement, a charged particle beam
device, comprising a charged particle detector arrangement, and a
method of operating a charged particle detector arrangement.
BACKGROUND
[0002] Charged particle beam apparatuses have many functions in a
plurality of industrial fields, including, but not limited to,
inspection of semiconductor devices during manufacturing, exposure
systems for lithography, detecting devices and testing systems.
Thus, there is a high demand for structuring and inspecting
specimens within the micrometer and nanometer scale.
[0003] Micrometer and nanometer scale process control, inspection
or structuring is often done with charged particle beams, e.g.
electron beams, which are generated and focused in charged particle
beam devices, such as electron microscopes or electron beam pattern
generators. Charged particle beams offer superior spatial
resolution compared to, e.g. photon beams, due to their short
wavelengths.
[0004] The requirements of fast scanning are in particular
important in applications of the manufacturing of semiconductors,
where high throughput is essential. Such applications include
electron beam inspection, defect review and critical dimension
measurements.
[0005] Charged particle beam systems, such as a scanning electron
microscope (SEM) can include detectors, such as scintillation
detectors (e.g. P47 powders, YAG or YAP crystals or the like) or
semiconductor detectors such as pin diodes, to detect charged
particles, e.g. electrons and ions. They are usually arranged
inside a vacuum environment. The vacuum contains residual
contaminants like hydrocarbons outgassing from pumps or plastic
components inside the vacuum chamber. These hydrocarbons adsorb on
the surface of the detector leading to contamination of the
detector.
[0006] Therefore, there is a need for a reduction of a detector
contamination. It is desired to provide a means for reduction of
contamination of a charged particle detector.
SUMMARY
[0007] According to one embodiment, a charged particle detector
arrangement is provided. The detector arrangement includes a
detection element and a collector electrode configured to collect
charged particles released from the detection element upon impact
of signal charged particles.
[0008] According to another embodiment, a charged particle beam
device, including a charged particle detector arrangement is
provided. The detector arrangement includes a detection element and
a collector electrode configured to collect charged particles
released from the detection element upon impact of signal charged
particles.
[0009] According to a further embodiment, a method of operating a
charged particle detector arrangement is provided. The method
includes: providing a charged particle detector arrangement,
comprising a detection element and a collector electrode arranged
to collect charged particles released from the detection element
upon impact of signal charged particles; applying a biasing
potential to the collector electrode, wherein the potential is
positive with respect to the detection element.
[0010] Further advantages, features, aspects and details that can
be combined with the above embodiments are evident from the
dependent claims, the description and the drawings.
[0011] Embodiments are also directed to apparatuses for carrying
out the disclosed methods and including apparatus parts for
performing each described method step. These method steps may be
performed by way of hardware components, a computer programmed by
appropriate software, by any combination of the two or in any other
manner. Furthermore, embodiments are also directed to methods by
which the described apparatus operates. It includes method steps
for carrying out every function of the apparatus or manufacturing
every part of the apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] 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:
[0013] FIG. 1 shows a schematic view of a charged particle detector
arrangement according to an embodiment described herein;
[0014] FIG. 2 shows a schematic view of a charged particle detector
arrangement according to another embodiment described herein;
[0015] FIG. 3 shows a schematic side view of a charged particle
beam device having a charged particle detector arrangement
according to embodiments described herein;
[0016] FIG. 4 shows a schematic side view of a charged particle
beam device according embodiments described herein;
[0017] FIG. 5 shows a block diagram of a method for operating a
charged particle detector arrangement according to embodiments
described herein.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] 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.
[0019] 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. As described herein, reference to secondary
particles can be understood as reference to any secondary and/or
backscattered particles described herein.
[0020] 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.
[0021] A "specimen" as referred to herein, includes, but is not
limited to, semiconductor wafers, semiconductor workpieces, and
other workpieces such as memory disks and the like. Embodiments of
the invention may be applied to any workpiece on which material is
deposited or which are structured. A specimen includes a surface to
be structured or on which layers are deposited, an edge, and
typically a bevel.
[0022] According to an embodiment, a charged particle detector
arrangement is provided. The detector arrangement includes a
detection element and a collector electrode configured to collect
charged particles released from the detection element upon impact
of signal charged particles.
[0023] FIG. 1 shows a schematic view of a charged particle detector
arrangement 10 according to an embodiment. A detection element 20
is arranged on a carrier. A collector electrode 30 is positioned in
the vicinity of the detection element 20. The collector electrode
30 is electrically biased positively with respect to the detection
element 20. The charged particles to be detected impinge from the
left (shown by an arrow B) along an optical axis. Secondary charged
particles B are the signal particles scattered from a specimen to
be inspected upon impact of primary charged particles originating
from a charged particle source.
[0024] When the detector element is hit by signal particles, the
particle energy suffices to crack the hydrocarbon molecules, and a
carbonization layer is created, which continuously grows during
operation of the detector. This carbonization layer leads to signal
loss, spatial and temporal non-uniformities in signal
generation/detection and the reduction of the detector lifetime
resulting in the need to replace the expensive detectors
frequently.
[0025] However, the secondary particles B impinging on the detector
are not the main contributors to the cracking of the molecules,
since their energy is rather high (over 5 keV) which leads to a low
carbonization rate. The main contribution to carbonization stems
from the tertiary particles C which are created upon impact of the
secondary signal particles B. They only have a low energy of a few
eV, but the stopping power of the adsorbed hydrocarbons for low
energy electrons is very high, and, consequently, the carbonization
rate is high.
[0026] Many of the tertiary particles return to the detector
surface, especially if the surface is biased positively with
respect to the surroundings. In this case, most of the tertiary
particles may return and quickly create a contamination layer,
resulting in a dramatic decrease of detector lifetime.
[0027] The purpose of the collector electrode 30, which is an
element with the highest potential in the vicinity of the detection
element 20, is to provide a pull on the charged particles released
on the detection element 20. As a result, the particles contaminate
the collector electrode 30, which can be a very inexpensive and
easy-to-replace sheet metal part, instead of the valuable detection
element 20.
[0028] According to an embodiment, the collector electrode 30 is a
plate having an opening for passing secondary charged particles.
The collector electrode 30 can be a ring arranged coaxially with an
optical axis of the detector arrangement.
[0029] According to an embodiment, the charged particle detector
arrangement 10 further includes a voltage supply (not shown)
electrically connected to the collector electrode 30 for biasing
the collector electrode 30 to collect charged particles,
particularly wherein the voltage supply is further connected to the
detection element 20. The detection arrangement 10 can comprise a
housing 40 which is electrically grounded.
[0030] According to an embodiment, the voltage supply is further
connected to the detection element 20.
[0031] The biasing potential with respect to the detection element
is typically in the range of a few hundred Volts. Its optimum value
depends on the geometry of the collector electrode 30, the geometry
of the surrounding components and their electric potentials and is
best determined experimentally. It should be high enough to collect
many charged particles, but not unnecessarily high in order to
minimize the influence on the secondary charged particles beam,
i.e. the signal particles. Simulations show that at 300 Volts
collector electrode potential only 3% of the tertiary electrons
return to the detection element and 96% of the same reach the
collector electrode, whereas 100% of the tertiary electrons return
to the detection element when the collector electrode is
unbiased.
[0032] According to an embodiment, the collector electrode 30 is
positively biased with respect to the detection element 20. The
collector electrode 30 can be biased with a voltage in the range of
30-500 Volts.
[0033] According to an embodiment, the collector electrode 30 is
arranged to a side of the detection element 20. In this case it is
assumed that related effects, such as beam deflection, astigmatism
etc. can be tolerated.
[0034] According to an embodiment, the collector electrode 30
comprises two or more collection plates. The plates can be round,
square or of any other shape.
[0035] The signal charged particles can be directed along an
optical axis perpendicular to the detection element 20. By this,
the collecting action is symmetrical and the influence on the
secondary particles beam is limited to a very small focusing
effect. The charged particles can be electrons, ions or other
particles.
[0036] According to an embodiment, the collector electrode 30 is
shaped as a ring arranged coaxially with the optical axis of the
detector arrangement in the drift space in front of the detection
element.
[0037] FIG. 2 shows a schematic view of a charged particle detector
arrangement 10 according to another embodiment. A detection element
20 is arranged on a carrier. As opposed to the embodiment of FIG.
1, a collector electrode 30 is arranged in a plane of the detection
element 20, surrounding the detection element 20.
[0038] According to other embodiments, the collector electrode or
the detection element can also have an arbitrary tilt angle with
respect to the optical axis of the incoming particles.
[0039] According to another embodiment, a charged particle beam
device, including a charged particle detector arrangement is
provided. The detector arrangement includes a detection element and
a collector electrode configured to collect charged particles
released from the detection element upon impact of signal charged
particles.
[0040] FIG. 3 shows a schematic side view of a charged particle
beam device having a charged particle detector arrangement
according to embodiments described herein;
[0041] The beam device includes a column, including an emitter 105
and an objective lens 10. A primary electron beam 130 from the
emitter 105 is directed at a specimen 125. Secondary electrons 140
are emitted/scattered from the specimen 125, are then separated
from an optical axis by an angle of several degrees and are further
deflected towards a detector arrangement 220 by means of a sector
440 acting as a beam bending or a deflection angle increasing unit.
The secondary electrons are detected by detection elements 20 of
the detector arrangement 220 to produce a secondary electron
signal.
[0042] The detector arrangement 220 includes detection elements 20
and a collector electrode 30. According to typical embodiments,
collector electrodes 30 can be biased at a potential close to that
of the detection elements 20. The potential can be slightly
positive, for example a few hundred volts over the potential of the
detection elements 20, in order to attract tertiary electrons
released at the detection elements 20. Due to the collector
electrodes 30, contamination of the detection elements 20 due to
tertiary electrons as well as arcing between an aperture plate 201
and the detection elements 20 can be reduced.
[0043] According to embodiments described herein, a secondary
particle optics 200 is provided. As shown in FIG. 3, the particle
optics 200 includes at least an aperture plate 201 having two or
more aperture openings. The aperture plate 201 can be biased to a
deceleration potential. Thereby, the deceleration of the aperture
plate 201 in combination with an acceleration of the detection
elements 20 are configured for a separation and focusing of the
secondary particles, e.g. the secondary electron beam. In light of
the two or more aperture openings, the separation of the secondary
beam on different detection elements can be provided. According to
typical embodiments, the aperture plate 201 has a central aperture
opening 202 and at least two radially outer aperture openings 204.
Typically, four outer aperture openings 204 can be provided.
Thereby, a topgrahpic contrast can be provided.
[0044] According to yet further embodiments, the charged particle
beam device includes voltage supplies 992, 994, and 996. Voltage
supply 992 is connected to the aperture plate 201 for biasing
thereof and thereby providing a deceleration field. According to
typical examples, the deceleration field can correspond to a
decrease of particle energy of about 20 keV to 30 keV. Voltage
supply 994 is connected to detection elements 20 in order to
accelerate the secondary particles towards the detection elements
20. Thereby, also a focusing is provided. The acceleration field
can correspond to an increase of particle energy of about 20 keV to
30 keV. Voltage supply 996 can bias the collector electrodes 30 to
a potential, which is slightly more positive as compared to that of
the detection elements 20 to attract tertiary electrons released at
the detection elements 20. The voltage difference between the
detection elements 20 and the collector electrodes 30 can be e.g.
100 V to 300 V.
[0045] According to yet further embodiments, which can be combined
with other embodiments described herein, particle optics 200 can
include a focus lens 301 and/or one or more deflection assemblies
901/903.
[0046] According to yet further embodiments, which can be combined
with other embodiments described herein, the particle optics 200
can further include one or more deflection assemblies. Thereby, the
deflection assemblies 901 and 903 can be controlled for aligning
the signal beam, e.g. the SE bundle to the aperture plate.
Additionally or alternatively, the deflections assemblies can be
controlled for de-scanning the signal beam. That is a deflection
(de-scan, anti-scan or counter-scan) is provided for compensating a
movement of the signal beam which results from scanning of the
primary beam, which generates the signal beam on impingement on a
specimen.
[0047] According to typical embodiments, for each of the deflection
assemblies 901 and 903, a set of at least 4 deflection plates can
be provide that can be connected to deflection voltages. The
deflection voltages can be synchronized with the image scan of the
primary beam and amplified and/or rotated such that deflection of
the signal beam generated by primary beam scanning cancels the
motion of the signal beam in the sensor plane.
[0048] As shown in FIG. 3, the first deflection assembly 901 can
de-scan the signal beam and align the signal beam to the focus lens
301. The deflection of the first deflection assembly 901 can
introduce a beam tilt with respect to the optical axis of the
signal beam. This beam tilt can be compensated for by the second
deflection assembly 903. The second deflection assembly can further
improve alignment on the aperture plate 201.
[0049] A secondary electron beam 140 passes through an opening 410
in an objective lens 100 and an opening in a plate 520 to enter a
sector 440. Sector 440 has a negatively-charged U-bend 535 and a
positively-charged U-bend 525 serving to bend the
secondary-electron beam 405. Further, a pair of sector side plates
is provided. Secondary electron beam 405 is then aligned as it
passes through an SE alignment quadrupole element 445 and focused
as it passes through an SE focusing lens 301. Secondary electron
beam 405 then passes through openings in grounded plate 455 and in
SE optics 200 to the detector arrangement 220.
[0050] FIG. 4 is a schematic illustration of a wafer inspection
system 900 in accordance with an embodiment of the invention,
employing an electron-optical subsystem. An electron beam column
902 includes an e-beam source 904, magnetic beam separator 906 and
objective lens 908 for applying a primary beam 910 to a wafer 912
carried on an x-y stage 915. Secondary electrons from wafer 912
pass through beam separator 906, sector 914, and focusing and
deflecting elements 200 to detector 220. The signals from detector
220 are supplied to imaging electronics 920.
[0051] Wafer 912 and stage 915 are contained in a vacuum chamber
922 supported on an isolation frame 924. Vacuum pumps 926 maintain
a suitable vacuum in the chamber 922 and column 902 during
operation. Wafer 912 is placed in and removed from chamber 922 by a
wafer handler subsystem 928.
[0052] Wafer inspection system 900 is controlled by a computer
system 930 having a control processor, image processor and image
memory, for example. Computer system 930 is in communication with a
workstation 932 having input/output devices 934 such as a keyboard
and a pointing device or other suitable devices permitting human
interaction, and a display 936. Control processor 930 communicates
via a bus 938 with control circuits such as PE-beam control 940
which regulates the primary-electron beam 910, SE optics control
942 which controls the focusing and deflection elements of column
902 to provide a suitable secondary-electron beam on detector 220,
PE alignment and deflection control 944 which controls the
application of primary beam 910 on wafer 912, vacuum pumps control
946 for controlling vacuum pumps 926, wafer voltage control 948,
stage control 950, and handler control 952. Control processor 930
also receives imaging data via bus 938 from imaging electronics 920
for storage, processing and image analysis.
[0053] FIG. 5 shows a block diagram of a method for operating a
charged particle detector arrangement according to embodiments
described herein. In the first method step 102 the beam is guided
to a charged particle detector arrangement as disclosed in the
embodiments herein. In the next method step 104 a biasing potential
is provided by a power supply to the collector electrode.
[0054] According to some embodiments, a method of operating a
charged particle detector arrangement is provided. The method
includes: providing a charged particle detector arrangement,
comprising a detection element and a collector electrode arranged
to collect charged particles released from the detection element
upon impact of signal charged particles; applying a biasing
potential to the collector electrode, wherein the potential is
positive with respect to the detection element. The method can
further comprise replacing the collector electrode with a new
one.
[0055] In light of the above, embodiments as described herein
provide an arrangement which is capable of a more effective and
accurate alignment as compared to common SEM tools. Thereby, the
complexity of the alignment system is not increased and it might be
possible that a more compact charged particle beam column can be
provided.
[0056] 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.
* * * * *